WO2006015105A2

WO2006015105A2 - Nanowire photonic circuits, components thereof, and related methods

Info

Publication number: WO2006015105A2
Application number: PCT/US2005/026759
Authority: WO
Inventors: Charles M. Lieber; Andrew B. Greytak; Carl J. Barrelet
Original assignee: President And Fellows Of Harvard College
Priority date: 2004-07-28
Filing date: 2005-07-28
Publication date: 2006-02-09
Also published as: WO2006015105A3

Abstract

The present invention generally relates to energy transmission in materials, specifically, electromagnetic (e.g., photonic) pathways and circuits, including various components for use in such pathways and circuits, for example, nanoscale wires such as semiconductor nanowires. One aspect of the invention is the propagation of energy in the form of electromagnetic radiation in a material such as a nanoscale wire (20) at or near the band edge (i.e., at or near the band gap wavelength), of the material, as defined below, optionally along with energy propagation at one or more different energy levels. Such propagation allows for a variety of new arrangements and methods, including diodes and other devices, transmission of electromagnetic radiation around tight corners with low loss, coupling between materials, electric field-generated generation of amplitude-varying electromagnetic radiation, and other features.

Description

NANOWIRE PHOTONIC CIRCUITS. COMPONENTS THEREOF, AND

RELATED METHODS

FEDERALLY SPONSORED RESEARCH Various aspects of the present invention were sponsored by the Air Force Office of Scientific Research, Grant No. F49620-03-1-0063, and the Office of Naval Research, Grant No. NOOO 14-01-1 -0651. The Government may have certain rights.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Patent Application Serial No. 60/592,058, filed July 28, 2004, entitled "Nanowire Photonic Circuits, Components Thereof, And Related Methods," by Barrelet, et al., incorporated herein by reference.

FIELD OF INVENTION

The present invention generally relates to photonic circuits, including various components for use in photonic circuits, for example, nanoscale wires. BACKGROUND

There has been much recent interest in the use of integrated photonics as a way to overcome the limitations of speed and power dissipation being faced in silicon-based electronics. Recent advancements include photonic crystals and plasmon waveguides. For example, certain defects in photonic crystals may enable light to be guided through sharp bends, although the length scale of these structures is on the order of the wavelength of light (typically in the hundreds of nanometers). Light has been also transported in nanoscale plasmon waveguides fabricated from metal nanoparticles, but these have been shown to have substantial losses. Thus, new systems and methods are needed in integrated photonics. SUMMARY OF THE INVENTION

The present invention generally relates to photonic circuits, including various components for use in photonic circuits, for example, nanoscale wires such as semiconductor nanowires. The subject matter of the present invention involves, in some cases, interrelated products, alternative solutions to a particular problem, and/or a plurality of different uses of one or more systems and/or articles.

One aspect of the invention provides systems and methods for guiding and manipulating light on sub-wavelength scales using active nanoscale wire waveguides and devices. For example,, in some embodiments, certain semiconductor nanoscale wire structures of the invention may propagate light with only moderate losses, even through sharp or acute angle bends, or between crossed nanoscale wires. In some cases, the energy being transmitted may be at and/or greater than the band gap energy wavelength of the nanoscale wire structures. Another set of embodiments of the invention provides for nanoscale wire heterostructures able to function as optical diodes, and in some cases, efficient injection into and/or modulation of light through the nanoscale wire waveguides. For example, certain nanoscale wires may be positioned in an electric field, for example, between two electrodes, such that, when the electric field is varied, the nanoscale wire produces light that varies in response to the variations in the electric field. In yet another set of embodiments, integrated nanoscale photonic systems may be produced using various nanoscale wire components, as described herein, that can be assembled into integrated structures.

Another aspect of the invention provides a method of detecting a result of light propagation within and/or emission from a first location of a nanoscale wire when light is established within a second location of the nanoscale wire. The light propagating within and/or emitted from the first location of the nanoscale wire may have an intensity of at least about 10% of the intensity of the light established within the second location. In some cases, the nanoscale wire includes a non-straight portion between the first location and the second location. The non-straight portion may have cross-sections defined along its length and centers of the cross-sections that define a curve, and the curve may have a radius of curvature that, at a point of maximum value, is less than 10 times the maximum diameter of the nanoscale wire at that point.

Yet another aspect of the invention provides a method of detecting a result of light propagation within and/or emission from a first location of a first nanoscale wire when light is established within a second location of a second nanoscale wire. The first nanoscale wire and the second nanoscale wire may be positioned such that light established within the second location of the second nanoscale wire is able to be transmitted through at least portions of the first and second nanoscale wires to the first location of the first nanoscale wire. In some cases, the light propagating within and/or emitted from the first location of the first nanoscale wire has an intensity of at least about 10% of the intensity of the light established within the second location of the second nanoscale wire. One aspect of the invention provides a method of transmitting light through a first material and a second material. The light may include light having a particular wavelength that is able to pass from the first material into the second material at a first intensity, but is not able to pass from the second material into the first material at an intensity greater than about 50% of the first intensity.

Still another aspect of the invention provides an apparatus. In one set of embodiments, the apparatus includes a photonic circuit comprising a nanoscale wire having a non-straight portion having a radius of curvature that, at its maximum value at a specific point, is less than 10 times the maximum diameter of the nanoscale wire at that specific point. In yet another set of embodiments, the apparatus includes a photonic circuit comprising an optical diode comprising a nanoscale wire. The invention, in still another set of embodiments, includes an apparatus comprising an optical memory unit comprising an optical diode comprising a nanoscale wire.

In another aspect of the invention, a method is provided that includes an act of applying an electric field to a light-emitting material and varying the electric field such that light emitted by the light-emitting material directly varies in amplitude in response to the variation in the electric field.

An aspect of the invention provides an article comprising an electric field generator. In one set of embodiments, the invention also includes a light-emitting material, where the electric field generator and the light-emitting material are constructed and arranged such that When a time-varying voltage of less than about 100 V_RMS is applied to the electric field generator, the electric field generator produces a time-varying electric field that causes the light-emitting material to emit light that varies in response to variations in the electric field. In another set of embodiments, the invention also includes a nanoscale wire, where the nanoscale wire and the electric field generator are constructed and arranged such that when the electric field generator produces a time- varying electric field, the nanoscale wire emits light that varies in response to variations in the electric field. In yet another set of embodiments, the invention also includes a light-emitting material, where the light-emitting material and the electric field generator are constructed and arranged such that when the electric field generator produces a time- varying electric field, the light-emitting material emits light that varies in response to variations in the electric field, wherein the light-emitting material is free of a crystalline substrate. The invention, in another aspect, provides a method of detecting a result of non¬ coherent light propagation within and/or emission from a first location of a semiconducting nanoscale wire when energy is applied to a second location of the nanoscale wire. In still another aspect, the method includes an act of detecting a result of light propagation within and/or emission from a first location of a semiconducting nanoscale wire when light is applied to a second location of the nanoscale wire at a substantially non-straight angle with respect to a longitudinal axis of the nanoscale wire.

In yet another aspect, the method includes an act of detecting a result of light propagation within and/or emission from a first location of a first nanoscale wire when light is established within a second location of a second nanoscale wire. The light, in some cases, is transmitted between the second nanoscale wire and the first nanoscale wire via a light-coupling region defined between the first nanoscale wire and the second nanoscale wire. In one embodiment, the light-coupling region has a maximum dimension of less than about 1 mm and is able to couple at least about 10% of light established within the second nanoscale wire to the first nanoscale wire

In another aspect, the present invention is directed to a method of making one or more of the embodiments described herein, including various components for use in photonic circuits, for example, nanoscale wires. In yet another aspect, the present invention is directed to a method of using one or more of the embodiments described herein, including various components for use in photonic circuits. In still another aspect, the present invention is directed to a method of promoting one or more of the embodiments described herein, including various components for use in photonic circuits.

Other advantages and novel features of the present invention will become ^' apparent from the following detailed description of various non-limiting embodiments of the invention when considered in conjunction with the accompanying figures. In cases where the present specification and a document incorporated by reference include conflicting and/or inconsistent disclosure, the present specification shall control. If two or more applications incorporated by reference include conflicting and/or inconsistent disclosure with respect to each other, then the later-filed application shall control.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying figures, which are schematic and are not intended to be drawn to scale. In the figures, each identical or nearly identical component illustrated is typically represented by a single numeral. For the purposes of clarity, not every component is labeled in every figure, nor is every component of each embodiment of the invention shown where illustration is not necessary to allow those of ordinary skill in the art to understand the invention. In the figures:

Figs. IA- IJ illustrate various nanoscale waveguides, and characterization data of the nanoscale waveguides, according to one set of embodiments of the invention;

Figs. 2A-2D illustrate various nanowire waveguide structures of certain embodiments of the invention; Kgs. 3A-3D illustrate certain optical diodes of an embodiment of the invention;

Figs. 4A-4F illustrate the electrical modulation of light, according to certain embodiments of the invention;

Figs. 5 A-5D illustrate an optical memory device, according to one embodiment of the invention; Fig. 6 illustrates a light-coupling region, according to another embodiment of the invention

Figs. 7A-7D illustrate various nanowire waveguides, in another embodiment of the invention;

Figs. 8A-8E illustrate various nanowire waveguide schemes, in other embodiments of the invention; and

Figs. 9A-9D illustrate various electro-optic modulator devices, in still another embodiment of the invention.

DETAILED DESCRIPTION

The present invention generally relates to energy transmission in materials, specifically, electromagnetic (e.g. photonic) pathways and circuits, including various components for use in such pathways and circuits. One aspect of the invention is the propagation of energy in the form of electromagnetic radiation in a material such as a nanoscale wire at or near the band edge (i.e., at or near the band gap wavelength), of the material, as defined below, optionally along with energy propagation at one or more different energy levels. Such propagation allows for a variety of new arrangements and methods, including diodes and other devices, transmission of electromagnetic radiation around tight corners with low loss, coupling between materials, electric field-generated generation of amplitude- varying electromagnetic radiation, and other features. The invention makes use of the propagation of energy through a material, and/or energy propagation from a first material to a second, adjacent material that has the same or a lower band gap as the first material. Thus, for example, in a nanoscale wire, photons incident on one end of the nanoscale wire may propagate to the other end of the nanoscale wire as energy, then be emitted from the second end of the nanoscale wire as light, and/or detected, for example, directly or indirectly (i.e., a result of the light transmission, such as a change in a memory state or a reaction, may be detected). In such fashion, certain materials of the invention may be used as waveguides, and such waveguides may be bent or angled in some cases, with zero or low loss in light transmission around the bent or angled regions. The light may be applied to the materials of the invention from any suitable source, including another nanoscale wire. In some cases, the material may also include a heterojunction between a first material and a second material, where each material has different band gaps. Such materials may allow the propagation of light energy from the first material to the second material, but prevent or inhibit the propagation of light energy from the second material to the first material.

In one set of embodiments, the emission of light energy from the material may be controlled through the use of an electric field applied to the material. Other aspects of the present invention relate to components and systems of components having some of the above characteristics, as well techniques of making and using such components and systems.

The invention is described in the context of the introduction into, induction within, propagation within, and emission of energy, or electromagnetic radiation, or light, in association with materials. Wherever "energy," "electromagnetic radiation," or "light," is used in this context, it is to be understood that these terms can represent any form of energy introduced into, propagated within, and/or emitted from such material. For example, in one embodiment, light is directed at a nanoscale wire, travels within the wire, and is emitted from the wire. It is to be understood that, although "light" may be used in describing this traversal of energy from an energy source to the wire and from the wire as emitted light, different forms of energy may pass through this pathway at different locations. For example, non-visible, ultraviolet electromagnetic radiation ("UV light") might be directed at the wire. At the wire, this energy might be converted to a pathway of successive atomic-scale absorption and emission of energy at the band edge of the material at an energy level ("band edge") equal to or less than that of the UV light, and optionally converted to lower energy within the wire at a material and/or doping junction in the wire. At some point, this energy may be emitted from the wire in the form of electromagnetic radiation of wavelength corresponding to the energy of the band edge, which may be visible light, or may be outside of the visible spectrum. Embodiments

Various aspects of the invention relate to the transmission of light energy through certain materials, i.e., where light (photons) incident on a first location of the material and/or passing within a first location may be transmitted to or otherwise established within a second location of the material, and emitted from the second location of the material as light (i.e., photons) or otherwise brought to use at the second location. The light propagated within and/or emitted from the second location may be detected in some fashion, for example, directly or indirectly (i.e., a result of the transmission of light may be detected or determined). For example, light established within the second location may be a time-varying signal that may be decoded, the light may be used to affect a function of an photonic circuit and determining the result of the function (e.g., as further discussed below), the light may be used to affect and/or analyze a chemical, biological, and/or biochemical reaction using that light, and determining the reaction (qualitatively and/or quantitatively), etc. Some light energy may also be emitted at other portions of the material between the first location and the second location. For instance, in a nanoscale wire, photons incident on one end (or other location) of the nanoscale wire may propagate to the other end (or another location) of the nanoscale wire, and from there, be emitted as light or otherwise detected. Electromagnetic radiation that is propagated within materials in accordance with the invention typically is at a wavelength or within a wavelength range comparable' to (e.g., within an order of magnitude) or smaller than the length scale of a cross-sectional dimension of the material, i.e., at a sub- wavelength length scale. Thus, for instance, a subwavelength waveguide may be a nanoscale wire having a diameter at any point and/or on average along a section of its length or entire length of less than about 200 nm, but be able to propagate light having wavelengths greater than 200 nm in vacuum. However, it should be noted that the electromagnetic radiation propagating within the material can have, in certain cases, a wavelength that is larger than the cross-sectional diameter of the material. Thus, for example, a nanoscale wire having a diameter of about 100 nm may be able to transmit light having a wavelength of about 400 nm in vacuum, about 500 nm, etc. In some embodiments of the invention, the light to be transmitted may be visible light (e.g., having a wavelength of about 380 nm to about 780 ran), ultraviolet light (e.g., having a wavelength of about 1 or 10 nm to about 700 nm), or infra-red light (e.g., having a wavelength of about 100 micrometers to about 400 nm). Without wishing to be bound by any theory, it is believed that the transmission of light energy through certain materials in accordance with the invention can occur through an absorption/emission mechanism, where the light energy propagates through the material by being continually absorbed and emitted by atoms within the material. Under such a mechanism, modes of light energy having near band edge energies can be transmitted through the material, and such transmission typically occurs from atoms having a first band gap to other atoms having a band gap that is the same as, or lower than, the first band gap. Thus, under such a mechanism, the material is not necessarily transparent, as is required in fiber optic systems and similar systems where photons themselves are directly propagated through the material. Also, in contrast with the present invention, optically-pumped lasers, while also energized using light energy, can only emit coherent light at specific wavelength, regardless of the wavelength of the incident light; such lasers produce light using a mechanism involving population inversion (i.e., where a majority of the atoms are stimulated, using the incident light energy, into an excited state), rather than an absorption/emission mechanism. In one set of embodiments of the invention, light having energy substantially equal to and/or above the band gap may be transmitted through the material or otherwise established within the material using the above-described absorption/emission mechanism and be emitted from the material, while light having energy substantially less than the band gap may not be easily absorbed by the material, and thus, cannot be readily transmitted through the material using an absorption/emission mechanism. The band gap of the material may be selected such that the material is able to transmit light having a wavelength below a predetermined threshold wavelength (corresponding to higher energies). This enables devices of the invention including diodes and the like. Examples of potentially suitable semiconductors and/or dopants are further described herein. It should be noted that such materials do not emit light only in specific wavelengths (i.e., as in a laser), but are able to emit a broad distribution of wavelengths above the threshold wavelength. - Ci -

As mentioned, various aspects of the invention make new uses of a class of waveguides, i.e., materials able to transmit at least a portion of light incident on or otherwise coupled into a first location of a material to a second location of the material. Light may then be emitted from the second location or otherwise used, e.g. directed to a second waveguide via coupling as discussed more fully below. The first location and/or the second location of the waveguide may be, for example, ends of the waveguides, and/or certain locations or regions along the length of the waveguide. The light that is incident ("injected") on the first location of the waveguide may be at any angle in relation to the longitudinal axis of the waveguide (the axis along which the light propagates), and the transmission of the light energy to the second location is generally not limited by the angle of incidence of light at the first location. Thus, for example, light may be incident on the first location at an angle of about 0° (i.e., a straight angle), about 5°, about 10°, about 30°, about 45°, about 60°, about 90° (i.e., perpendicular), about 135°, about 150°, about 175°, or any other suitable angle or angles (e.g., if more than one light source is used). The incident light can be coupled into the waveguide without splicing apparatus or other apparatus that would be required, in traditional optical waveguides, to introduce light from a non-linear direction into the axis of a waveguide. The present invention also does not require intermediate emissive dopants between the incident light and the light introduced into the waveguide, as may be the case in prior art arrangements in which incident light may excite a dopant in a "pump cladding" layer, and the dopant emits light of a lower wavelength that is introduced into the waveguide and travels as classical optical guided light in the waveguide.

In some cases, the waveguide is able to transmit substantially all of the light that is incident and effectively coupled into on the first location to the second location (for example, using the above-described absorption/emission mechanism); however, in other cases, due to inefficiencies, a portion of light is lost, e.g., due to scattering, absorption, impurities within the rnaterial, emission from other locations within the material, etc. Thus, in some embodiments, the waveguide is able to emit light at the second location that has an intensity that is at least about 10% of the intensity of the light incident on the first location, and in some cases, the light emitted from the second location may have an intensity that is at least about 20%, at least about 30%, at least about 40%, at least about 50%, at least about 60%, at least about 70%, at least about 80%, at least about 90%, or at least about 95% of the light incident on the first location, including situations where the first and second locations are separated by a bend as described herein. At such bends, it is believed that there may be light propagation within the waveguide, occurring via classical optical principles, that may experience high loss at the bend, while other light at or near the band edge of the material propagates around the bend with low loss. In some cases, the material may be at least partially surrounded with a cladding material to reduce such losses (e.g., emission from the sides of the waveguide). In one embodiment, the cladding material is air. In other embodiments, however, the cladding material may be any material having a band gap higher than the waveguide material.

The waveguide may have any shape or dimension. For example, in one set of embodiments, the waveguide comprises a nanoscale wire. In one embodiment, the nanoscale wire is not straight, i.e., at least a portion of the nanoscale wire may be angled, bent, curved, branched, etc., and able to propagate light around the bent, curved, etc. region with no loss or low loss. Accordingly, in one set of embodiments applicable to all embodiments herein, all numerical loss characteristics are applicable to light at or near the band edge of the material. If the nanoscale wire is curved or angled, it may be curved or angled at any bend angle (e.g., at about 5°, about 10°, about 30°, about 45°, about 60°, about 90°, about 135°, about 150°, about 175°, etc.) and/or at any radius of curvature (which can be defined by a mathematical curve connecting the centers of cross-sections defined along the nanoscale wire). The nanoscale wire may have any number of bends, curves, angles, branches, etc. In some cases, the nanoscale wire may be bent or angled in such a fashion that the maximum radius of curvature is less than about 10 times the maximum diameter of the nanoscale wire at that specific point, and in some cases, the radius of curvature is less than about 7 times, less than about 5 times, less than about 3 times Or less than about 2 times the maximum diameter of the nanoscale wire at the point of the maximum radius of curvature. In other cases, the radius of curvature may be less than the maximum diameter of the nanoscale wire at that point. In still other cases, the radius of curvature may be less than the wavelength of the light to be transmitted through or otherwise established within the waveguide. The maximum radius of curvature for circularly curved nanoscale wires may be constant in some cases (i.e., everywhere along the curve may be mathematically considered to be a point of maximum radius of curvature); in other cases (i.e., for non-circularly curved nanoscale wires), the radius of curvature may be a mathematical function, which may have one or more maxima. It should be noted that the maximum radius of curvature can be essentially zero in some cases, e.g., in a perfectly bent nanoscale wire (i.e., the radius of curvature mathematically tends to 0).

In some embodiments, more than one waveguide or nanoscale wire may be used. Thus, for example, at least a portion of the light emitted from a second location of a first waveguide may be incident on a first location of a second waveguide, and be transmitted to or otherwise established within a second location of the second waveguide to be emitted or otherwise used (and, in some cases, may then be transmitted to or otherwise established within a third waveguide, etc.). Each of the waveguides may independently have any shape, depending on the specific application, e.g., straight or non-straight (angled, bent, curved, branched, etc.). The waveguides do not necessarily have to be aligned in any particular fashion in order for light transmission to occur, but need only be positioned such that at least a portion of the light emitted from the first waveguide is able to strike the second waveguide, etc. Thus, in the case of nanoscale wire waveguides, the waveguides may be positioned such that the waveguides are collinear or non-collinear with each other. As a non-limiting example, two nanoscale wires may be positioned such that the wires are collinear or non-collinear. For example, the two nanoscale wires may be positioned at an angle, or crossed with respect to each other, etc.

In some embodiments of the invention, light may be created at the junction of the two nanoscale wires and then used for various purposes, and light thus created can be light "incident upon" one or both of these wires in accordance with the discussion above. For example, as in the case of a light-emitting diode defined at one or more points of contact between contacting n-type and p-type semiconducting components (which can be used as a light source for any embodiments herein as well), one nanoscale wire may be n-type and the other nanoscale wire may be p-type, for example, and placed in proximity with each other (e.g. crossed in close proximity or in contact) for generation of light. Light created at the point of contact may then be propagated through either or both wires as waveguide(s) and used for purposes described herein.

In some cases, light may be transferred between a first waveguide and a second waveguide through a "light-coupling region," i.e., a spatial region, defined between the waveguides (which do not necessarily have to be in physical contact), in which at least about 10% of the light energy in the first waveguide is transferred to the second waveguide, and in some cases at least about 20%, at least about 30%, at least about 40%, at least about 50%, at least about 60%, at least about 70%, at least about 80%, at least about 90%, or at least about 95% of the light energy is transferred from the first waveguide to the second waveguide. Thus, as an example, at least a portion of the light incident on a first waveguide may be transmitted through the first waveguide, through a light-coupling region, to a second waveguide to be emitted from the second waveguide (or to be transmitted to a third waveguide, to another photonic component, etc.). A non- limiting example of a light-coupling region is illustrated in Fig. 6, where a light coupling region 65 is defined between nanowires 61 and 62, and at least a portion of light 66 incident on nanowire 61 (at a substantially non-straight angle) is emitted by nanowire 62 as emitted light 67. Possibly because of the absorption/emission mechanism previously discussed, such light-coupling regions according to this embodiment of the invention may be relatively small, in comparison with previously reported light-coupling regions. In some cases, the light-coupling region may have a maximum dimension of less than 1 mm; and in other cases, the region may have maximum dimensions of less than about 700 micrometers, less than about 500 micrometers, less than about 300 micrometers, less than about 100 micrometers, less than about 70 micrometers, less than about 50 micrometers, less than about 30 micrometers, less than about 10 micrometers, less than about 7 micrometers, less than about 5 micrometers, less than about 3 micrometers, less than about 1 micrometer, less than about 700 nm, less than about 500 nm, less than about 300 nm, less than about 100 nm, less than about 70 nm, or less than about 50 nm, less than about 30 nm, or less than about 10 nm in some cases.

As previously discussed, it is believed that the transmission of light energy in accordance with propagation devices and techniques of the invention may occur between atoms having a first band gap to other atoms having a band gap that is the same or lower than the first band gap. Thus, another aspect of the invention is directed to a first material and a second material, positioned adjacent the first material, having a band gap that is substantially the same as or lower than the band gap of the first material. The interface or heterojunction between the two materials may be sharp or even atomically- abrupt, or the interface or heterojunction may be a gradual transition in some cases. In some instances, one or both of the materials may independently be an alloy or a mixture. As particular non-limiting examples, the first material may include CdS and the second material may include CdSe, which has a lower band gap than CdS; the first material may be CdSχSei_-x (x ranging between 0 and 1) and the second material may be CdS_ySe_1-y (y ranging between 0 and 1); the first material may be Al₂Ga_1-2As (z ranging between 0 and 1) and the second material may be CdS_xSei_-x (x ranging between 0 and 1) or vice versa, etc. An another example, the waveguide can be a nanoscale wire including any of a variety of different heterojunctions, for example, those described in U.S. Patent Application Serial No. 10/196,337, filed July 16, 2002, entitled "Nanoscale Wires and Related Devices," by Lieber, et al, published as U.S. Patent Application Publication No. 2003/0089899 on May 15, 2003, incorporated herein by reference in its entirely. Such heterojunctions find utility, in accordance with the invention, for a variety of devices and techniques. In one set of embodiments, such materials may be used as an optical diode. As used herein, an "optical diode" is a device in which light, or at least a portion of light having certain wavelengths, is preferentially transmitted in one direction (i.e., from a first material to a second material) relative to the other direction (i.e., from the second material to the first material). In some cases, light (which may be of a particular wavelength) may be preferentially transmitted in a first direction, relative to a second direction, such that the intensity of light transmission in the second direction is less than about 75% of the intensity of light transmission in the first direction, and in some cases, the intensity of light transmission in the second direction may be less than about 50%, less than about 40%, less than about 30%, less than about 20%, less than about 10%, or less than about 5% or less of the intensity of light transmission in the first direction, i.e., the light is inhibited from being transmitted or otherwise established in the second direction, relative to the first direction. All of these comparative transmission percentages are based on light of equivalent amplitude and frequency incident on the material in the first and second directions. In one embodiment, substantially no light can be transmitted or otherwise established in the second direction. In other cases, the device may have a rectification ratio or "on/off ratio (i.e., the ratio of light intensities between the first and second directions) of at least about 2, at least about 3, at least about 5, at least about 10, or at least about 15. Typically, to determine intensity, the light passing through a material is measured from a distance of at least the smaller minimum dimension of the first and second materials.

A waveguide including an optical diode typically has asymmetry and directionality. Such devices can be used, for example, in one-way communication (e.g., by passing light energy encoding information through the optical diode), in single directional lasing (e.g., within ring lasers, ring cavities, etc., to ensure that the lasing can be performed in one direction), to reduce or eliminate parasitic reflection in certain communication modalities (parasitic reflection is a situation in which an optical communication, intended for a receiver, is partially reflected back to the sender), or in certain eavesdropping techniques (e.g., where an eavesdropper can eavesdrop on an optical communication without being detected).

Certain optical diodes of the invention can also be used in computers and computer architecture, e.g., for storing and addressing memory. Thus, one embodiment of the invention provides a computer having photonic memory, for example, including optical diodes. In some cases, light propagated within and/or emitted from a waveguide may be used within the computer, and such detection may be direct or indirect, for example, the light may be transmitted to another photonic circuit, used to alter a state of a memory element, etc. A non-limiting example is photonic circuit 50 in Fig. 5, where memory elements are represented by switches 51, 52, 53, 54, each of which can independently be in two states, on (closed) or off (open). Elements within the photonic circuit may be connected using waveguides (for example, waveguide 55), for example, waveguides such as those previously described. Each row of the array is a "word," accessible by Word Line 0 (element 60 in Fig. 5A) and Word Line 1 (element 61), and the number of bits in each word is equal to the number of columns in the array, accessible by Bit Line 0 (element^"62) and Bit Line 1 (element 63). Depending on the positions of the switches, outputs of the circuit may be read through Output Line 0 (element 64) and Output Line 1 (element 65). In Fig. 5A, the four switches 51, 52, 53, 54 in the photonic circuit, representing memory, are each in an open or "off state. A word of data can be read in this example photonic circuit (Fig. 5B) by applying a "high" ("HI") signal to one of the word lines (in this case, Word Line 0). According to the states of the switches, the "high" signal is either passed or not passed into the bit lines, allowing the word to be read in output lines 64, 65 by determining if each output line independently has a "low" ("LO") signal or a "high" ("HI") signal. If each memory element was a switch, errors can arise due to signals making "loops" through elements on other word lines, as shown in Fig. 5C. This is possible because the signal can run "backwards" through a memory element (in this figure, bit 0 of word 1, switch 51). An optical diode, placed in series with each switch may prevent such "backwards" signaling, as is shown in Fig. 5D. The optical diode ensures that only a single path can connect a given word line to a given bit line; thus, the optical diode enables the use of optical memory devices comprising memory elements in arrays. It should be understood that this example is byway of illustration only, and any number of switches, bits, words, waveguides, etc., may be added to the photonic circuit as needed for a particular application, without departing from the scope of the invention.

Another device provided by certain aspects of the invention is an "electro-optic modulator," i.e., a device in which the light produced by a material emitting the light can be altered or affected ("modulated") in some fashion by applying an electric field to at least a portion of the material. In some cases, by varying the applied electric field in some fashion (e.g., in intensity, phase, wavelength, etc.), the light emitted by the material may vary in response (e.g., in amplitude, phase, wavelength, polarization, etc.). The emission response of the material may be proportional to (e.g., linearly, or as another predictable function of) variations in the electric field, or, in some cases, the emission response may not be proportional to variations in the electric field, but may vary in a fashion indicative of the variations in the electric field. Certain electro-optic modulators of the invention may also produce an asymmetric response, i.e., where increasing the electric field strength reduces the emitted light intensity and decreasing the electric field strength increases the emitted light intensity. In some cases, if the electric field encodes a time-varying signal (I.e., representing communication, information, a datastream, etc.), the light emitted by the material may vary in a fashion that encodes the time-varying signal. It should be noted that "time-varying," as used herein, does not include the inherent oscillating electric field properties of the electric field. Thus, the electro-optic modulator can be used in such cases to convert electrically-encoded information to optically-encoded information. In one set of embodiments, the electro-optic modulator includes an electric field generator and a light-emitting material, such as a waveguide or a nanoscale wire, previously discussed above. More than one light-emitting material may be present in some instances. In some cases, the electro-optic modulator can be constructed and arranged without the use of an additional substrate material, such as a crystalline substrate. As a non-limiting example, in Fig. 4A, an electro-optic modulator 45 includes electrodes 43 and 44, and a light-emitting material 42 (in this case, a nanowire), but electro-optic modulator 45 does not contain an additional substrate material. The electric field generator is any device or system able to produce an electric field. Techniques for producing electric fields are known to those of ordinary skill in the art. For example, in one embodiment, an electric field is produced by applying a voltage across a pair of electrodes, for example, as in a capacitor. One such example is illustrated in Fig. 4A, which includes upper electrode 43 and lower electrode 44. The electric field generator can be used to produce a time-varying electric field, in some cases, by varying the voltage supplied to the generator. In some cases, one or more of the electrodes may be a substantially planar electrode, i.e., an electrode including a pair of opposing surfaces (two major surfaces) that are substantially larger in area than the other surfaces of the electrode, that are substantially planer, and that are substantially parallel to each other. In other cases, one or more of the electrodes may be non-planar overall, but include a major surface that is substantially larger in area than the average of the areas of other surfaces, and that is substantially planar. "Surface", in this context, means a substantially planar portion of the overall electrode. The major surface, in any arrangement, may have any shape, for example, rectangular, square, circular, triangular, hexagonal, etc. In some embodiments, if the electrodes are each substantially planar, the electrodes may be positioned in parallel (e.g., such that the two major surfaces of the two electrodes face each other), and optionally, the light-emitting material may be positioned between the two electrodes. However, in other embodiments, the electrodes need not be positioned in parallel. For example, the electrodes may be positioned at an angle with respect to each other, or the electrodes may be positioned "end-on," (i.e., in substantially the same imaginary plane) optionally with the light-emitting material or waveguide positioned between the electrodes, e.g., as is shown in Fig. 8B.

In certain embodiments, the electric field generator within the electro-optic modulator may be constructed and arranged to generate an electric field, able to modulate light emission, such that when a time- varying voltage of less than about 100 V_RMS, less than about 30 V_RMS, or less than 10 V_RMS is applied to the electric field generator, the electric field generator produces a time-varying electric field. "V_RMS" refers to the root-mean-square voltage, and is given its ordinary meaning as used in the art, le., V_rm ≡^ή

The light-emitting material may be any material able to produce light that is altered in some fashion upon applying an electric field to the material. Non-limiting examples of such materials include those previously described, for example, nanoscale wires. In certain preferred embodiments, the material is a semiconductor nanowire. As an example, a nanoscale wire may be positioned between two electrodes of an electric field generator to produce an electro-optic modulator. In some cases, an electro-optic modulator of the invention is able to produce light where the amplitude of the light emitted by the nanoscale wire (or other light-emitting material) directly varies with variations in the electric field, i.e., no further devices or elements are required to produce light where its amplitude modulates in response to modulations in the electric field. The light, in certain preferred embodiments, is light having an energy substantially equal to the band gap energy, i.e., light at or near the band gap wavelength.

Another aspect of the invention generally relates to a photonic circuit including one or more of the above-described components, for example, waveguides, light- coupling systems, optical diodes, memory arrays, electro-optic modulators, or the like. As used herein, a "photonic circuit" is a circuit in which energy, which can encode information, is transmitted and manipulated primarily within the circuit through the use of light energy (e.g., photons) rather than through the use of electrons, i.e., as in a standard electronic circuit. Larger photonic circuits may be assembled from some or all of these components, as well as other photonic and/or electronic components, e.g., nanoscale lasers, such as those described in U.S. Patent Application Serial No. 10/734,086, filed December 11, 2003, entitled "Nanowire Coherent Optical

Components," by Lieber, et ah, incorporated herein by reference. Other non-limiting examples of electronic components that may be included in the photonic circuit include switches, diodes, light-emitting diodes, tunnel diodes, Schottky diodes, bipolar junction transistors, field effect transistors, inverters, complimentary inverters, optical sensors, analyte sensors, memory devices or arrays (including dynamic and/or static), lasers, logic gates (e.g., AND, OR, NOT, NAND, NOR, XOR, etc.), amplifiers, transformers, signal processors, etc.

Examples of compositions potentially useful in the above-described nanoscale wires and other materials of the invention include semiconductors and dopants. The specific semiconductors and dopants, and/or concentrations thereof, may be chosen to give different band gap energies, and/or chosen to allow certain wavelengths to be transmitted. The following are non-comprehensive examples of materials that may be used as semiconductors and/or dopants. The material may be an elemental semiconductor, for example, silicon, germanium, tin, selenium, tellurium, boron, diamond, or phosphorous. The material may also be a solid solution of various elemental semiconductors. Non-limiting examples include a mixture of boron and carbon, a mixture of boron and P(BP₆), a mixture of boron and silicon, a mixture of silicon and carbon, a mixture of silicon and germanium, a mixture of silicon and tin, or a mixture of germanium and tin.

In some embodiments, the material may include mixtures of Group IV elements, for example, a mixture of silicon and carbon, or a mixture of silicon and germanium. In other embodiments, the material may include a mixture of a Group III and a Group V element, for example, BN, BP, BAs, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN, InP, InAs, or InSb. Mixtures of these may also be used, for example, a mixture of BN/BP/BAs, or BN/A1P. In other embodiments, the materials may include alloys of Group III and Group V elements. For example, the alloys may include a mixture of AlGaN, GaPAs, InPAs, GaInN, AlGaInN, GaInAsP, or the like. In other embodiments, the materials may also include a mixture of Group II and Group VI semiconductors. For example, a semiconductor may include ZnO, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe, HgTe, BeS, BeSe, BeTe, MgS, MgSe, or the like. Alloys or mixtures of these are also be possible, for example, (ZnCd)Se, or Zn(SSe), or the like. Additionally, alloys of different groups of semiconductors may also be possible, for example, a combination of a Group II-Group VI and a Group Ill-Group V semiconductor, for example,

(GaAs)_x(ZnS)_1-X. Other examples include combinations of Group IV and Group VI elements, such as GeS, GeSe, GeTe, SnS, SnSe, SnTe, PbO, PbS, PbSe, or PbTe. Other semiconductor mixtures may include a combination of a Group I and a Group VII, such as CuF, CuCl, CuBr, CuI, AgF, AgCl, AgBr, AgI, or the like. Other materials may include different mixtures of these elements, such as BeSiN₂, CaCN₂, ZnGeP₂, CdSnAs₂, ZnSnSb₂, CuGeP₃, CuSi₂P₃, Si₃N₄, Ge₃N₄, Al₂O₃, (Al,Ga,In)₂(S,Se,Te)₃, Al₂CO, (Cu,Ag)(Al,Ga,In,Tl,Fe)(S,Se,Te)₂ and the like.

For Group IV dopant materials, a p-type dopant may be selected from Group III, and an n-type dopant may be selected from Group V, for example. For silicon semiconductor materials, a p-type dopant may be selected from the group consisting of B, Al and In, and an n-type dopant may be selected from the group consisting of P, As and Sb. For Group Ill-Group V semiconductor materials, a p-type dopant may be selected from Group II, including Mg, Zn, Cd and Hg, or Group IV, including C and Si. An n-type dopant may be selected from the group consisting of Si, Ge, Sn, S, Se, and Te. It will be understood that the invention is not limited to these dopants, but may include other elements, alloys, or materials as well.

As used herein, the term "Group," with reference to the Periodic Table, is given its usual definition as understood by one of ordinary skill in the art. For instance, the Group II elements include Mg and Ca, as well as the Group II transition elements, such as Zn, Cd, and Hg. Similarly, the Group III elements include B, Al, Ga, In, and Tl; the Group rV elements include C, Si, Ge, Sn, and Pb; the Group V elements include N, P, As, Sb, and Bi; and the Group VI elements include O, S, Se, Te, and Po. Combinations involving more than one element from each Group are also possible. For example, a Group II- VI material may include at least one element from Group II and at least one element from Group VI, for example, ZnS, ZnSe, ZnSSe, ZnCdS, CdS, or CdSe. Similarly, a Group III- V material may include at least one element from Group III and at least one element from Group V, for example GaAs, GaP, GaAsP, InAs, InP, AlGaAs, or InAsP. Other dopants may also be included with these materials and combinations thereof, for example, transition metals such as Fe, Co, Te, Au, and the like. As used herein, transition metal groups of the periodic table, when referred to in isolation (i.e., without referring to the main group elements), are indicated with a "B." The transition metals elements include the Group EB elements (Cu, Ag, Au), the Group HB elements (Zn, Cd, Hg), the Group IIIB elements (Sc, Y, lanthanides, actinides), the Group IVB elements (Ti, Zr, Hf), the Group VB elements (V, Nb, Ta), the Group VIB elements (Cr, Mo, W), the Group VIIB elements (Mn, Tc, Re), and the Group VIIIB elements (Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt).

Controlled doping of nanoscale wires can be carried out to form, e.g., n-type or p- type semiconductors. One set of embodiments involves use of at least one semiconductor, controllably-doped with a dopant (e.g., boron, aluminum, phosphorous, arsenic, etc.) selected according to whether an n-type or p-type semiconductor is desired. A bulk-doped semiconductor may include various combinations of materials, including other semiconductors and dopants. For instance, the nanoscopic wire may be a semiconductor that is doped with an appropriate dopant to create an n-type or p-type semiconductor, as desired. As one example, silicon may be doped with boron, aluminum, phosphorous, or arsenic. In various embodiments, this invention involves controlled doping of semiconductors selected from among indium phosphide, gallium arsenide, gallium nitride, cadmium selenide. Dopants including, but not limited to, zinc, cadmium, or magnesium can be used to form p-type semiconductors in this set of embodiments, and dopants including, but not limited to, tellurium, sulfur, selenium, or germanium can be used as dopants to form n-type semiconductors from these materials. These materials may define direct band gap semiconductor materials and these and doped silicon are well known to those of ordinary skill in the art. The present invention contemplates use of any doped silicon or direct band gap semiconductor materials for a variety of uses.

Other examples of compositions potentially useful in nanoscale wires and other materials of the invention, and methods of their fabrication and assembly, include those described in U.S. Patent Application Serial No. 09/935,776, filed August 22, 2001, entitled "Doped Elongated Semiconductors, Growing Such Semiconductors, Devices Including Such Semiconductors, and Fabricating Such Devices," by Lieber, et al, published as U.S. Patent Application Publication No. 20020130311 on September 19, 2002; and U.S. Patent Application Serial No. 10/196,337, filed July 16, 2002, entitled "Nanoscale Wires and Related Devices," by Lieber, et ah, published as U.S. Patent Application Publication No. 2003/0089899 on May 15, 2003, each incorporated herein by reference. Definitions The following definitions will aid in the understanding of the invention. Certain devices of the invention may include wires or other components of scale commensurate with nanometer-scale wires, which includes nanotubes and nanowires. In some embodiments, however, the invention comprises articles that may be greater than nanometer size (e. g., micrometer-sized). As used herein, "nanoscopic-scale," "nanoscopic," "nanometer-scale," "nanoscale," the "nano-" prefix (for example, as in "nanostructured"), and the like generally refers to elements or articles having widths or diameters of less than about 1 micrometer, and less than about 100 nm in some cases. In all embodiments, specified widths can be a smallest width (i.e. a width as specified where, at that location, the article can have a larger width in a different dimension), or a largest width (i.e. where, at that location, the article has a width that is no wider than as specified, but can have a length that is greater).

A "width" of an article, as used herein, is the distance of a straight line from a point on a perimeter of the article, through the center of the article, to another point on the perimeter of the article. As used herein, a "width" or a "cross-sectional dimension" at a point along a longitudinal axis of an article is the distance along a straight line that passes through the center of a cross-section of the article at that point and connects two points on the perimeter of the cross-section. The "cross-section" at a point along the longitudinal axis of an article is a plane at that point that crosses the article and is orthogonal to the longitudinal axis of the article. The "longitudinal axis" of an article is the axis along the largest dimension of the article. Similarly, a "longitudinal section" of an article is a portion of the article along the longitudinal axis of the article that can have any length greater than zero and less than or equal to the length of the article. Additionally, the "length" of an elongated article is a distance along the longitudinal axis from end to end of the article.

As used herein, a "wire" generally refers to any material having a conductivity of or of similar magnitude to any semiconductor or any metal, and in some embodiments may be used to connect two electronic components such that they are in electronic communication with each other. For example, the terms "electrically conductive," a "conductor," or an "electrical conductor" when used with reference to a "conducting" wire or a nanoscale wire, refers to the ability of that wire to pass charge. Typically, an electrically conductive nanoscale wire will have a resistivity comparable to that of metal or semiconductor materials, and in some cases, the electrically conductive nanoscale wire may have lower resistivities, for example, resistivities of less than about 100 microOhm cm (μΩ cm). In some cases, the electrically conductive nanoscale wire will have a resistivity lower than about 10^'3 ohm meters, lower than about 10^"4 ohm meters, or lower than about 10^"6 ohm meters or 10^"7 ohm meters.

A "semiconductor," as used herein, is given its ordinary meaning in the art, i.e., an element having semiconductive or semi-metallic properties (i.e., between metallic and non -metallic properties). An example of a semiconductor is silicon. Other non-limiting examples include gallium, germanium, diamond (carbon), tin, selenium, tellurium, boron, or phosphorous.

A "nanoscale wire" (also known herein as a "nanoscopic-scale wire" or "nanoscopic wire") generally is a wire, that at any point along its length, has at least one cross-sectional dimension and, in some embodiments, two orthogonal cross-sectional dimensions less than 1 micrometer, less than about 500 nm, less than about 200 nm, less than about 150 nm, less than about 100 nm, less than about 70, less than about 50 nm, less than about 20 nm, less than about 10 nm, or less than about 5 nm. In certain instances, the nanoscale wire has a minimum dimension that is at least about 10 nm, at least about 20 nm, at least about 40 nm, or at least about 60 nm. In some cases, the nanoscale wire is electrically conductive. Where nanoscale wires are described having, for example, a core and an outer region, the above dimensions generally relate to those of the core. The cross-section of a nanoscopic wire may be of any arbitrary shape, including, but not limited to, circular, square, rectangular, annular, polygonal, or elliptical, and may be a regular or an irregular shape. The nanoscale wire may be solid or hollow. A non-limiting list of examples of materials from which nanoscale wires of the invention can be made appears further below. Other conductive or semiconducting elements that may not be molecular wires, but are of various small nanoscopic-scale dimensions, can also be used in some instances, e.g. inorganic structures such as main group and metal atom-based wire-like silicon, transition metal-containing wires, gallium arsenide, gallium nitride, indium phosphide, germanium, cadmium selenide, etc. A wide variety of these and other nanoscale wires can be grown on and/or applied to surfaces in patterns useful for electronic devices in a manner similar to techniques described herein involving the specific nanoscale wires used as examples, without undue experimentation. The nanoscale wires, in some cases, may be formed having dimensions of at least about 1 micrometer, at least about 3 micrometers, at least about 5 micrometers, or at least about 10 micrometers or about 20 micrometers in length, and can be less than about 100 nm, less than about 80 nm, less than about 60 nm, less than about 40 nm, less than about 20 nm, less than about 10 nm, or less than about 5 nm in thickness (height and width). The nanoscale wires may have an aspect ratio (length to thickness) of greater than about 2:1, greater than about 3:1, greater than about 4:1, greater than about 5:1, greater than about 10:1, greater than about 25 : 1 , greater than about 50:1, greater than about 75:1, greater than about 100:1, greater than about 150:1, greater than about 250:1, greater than about 500:1, greater than about 750:1, or greater than about 1000:1 or more in some cases. As used herein, an "elongated" article (e.g., a nanoscale wire) is an article for which, at any point along the longitudinal axis of the article, the ratio of the length of the article to the largest width at that point is greater than 2:1.

A "nanowire" (e. g. comprising silicon and/or another semiconductor material) is a nanoscopic wire that is typically a solid wire, and may be elongated in some cases. Preferably, a nanowire (which is abbreviated herein as "NW") is an elongated semiconductor, i.e., a nanoscale semiconductor. A "non-nanotube nanowire" is any nanowire that is not a nanotube. In one set of embodiments of the invention, a non- nanotube nanowire having an unmodified surface (not including an auxiliary reaction entity not inherent in the nanotube in the environment in which it is positioned) is used in any arrangement of the invention described herein in which a nanowire or nanotube can be used.

As used herein, a "nanotube" (e.g. a carbon nanotube) is a nanoscopic wire, at least a portion of which is hollow, or that has a hollowed-out core, including those nanotubes known to those of ordinary skill in the art. "Nanotube" is abbreviated herein as "NT." Nanotubes are used as one example of small wires for use in the invention and, in certain embodiments, devices of the invention include wires of scale commensurate with nanotubes.

As used herein, a "cylindrical" article is an article having an exterior shaped like a cylinder, but does not define or reflect any properties regarding the interior of the article. In other words, a cylindrical article may have a solid interior, may have a hollowed-out interior, etc. Generally, a cross-section of a cylindrical article appears to be circular or approximately circular, but other cross-sectional shapes are also possible, such as a hexagonal shape. The croδs-section may have any arbitrary shape, including, but not limited to, square, rectangular, or elliptical. Regular and irregular shapes are also included.

As used herein, an "array" of articles (e.g., nanoscopic wires) comprises a plurality of the articles, for example, a series of aligned nanoscale wires, which may or may not be in contact with each other. As used herein, a "crossed array" or a "crossbar array" is an array where at least one of the articles contacts either another of the articles or a signal node (e.g., an electrode).

The following applications are incorporated herein by reference: U.S. Patent Application Serial No. 09/935,776, filed August 22, 2001, entitled "Doped Elongated Semiconductors, Growing Such Semiconductors, Devices Including Such Semiconductors, and Fabricating Such Devices," by Lieber, et ah, published as U.S. Patent Application Publication No. 20020130311 on September 19, 2002; U.S. Patent Application Serial No. 10/020,004, filed December 11, 2001, entitled "Nanosensors," by Lieber, et al\ U.S. Patent Application Serial No. 10/152,490, filed May 20, 2002, entitled "Nanoscale Wires and Related Devices," by Lieber, et ah; U.S. Patent Application Serial No. 10/196,337, filed July 16, 2002, entitled "Nanoscale Wires and Related Devices," by Lieber, et al, published as U.S. Patent Application Publication No. 2003/0089899 on May 15, 2003; U.S. Provisional Patent Application Serial No. 60/397,121, filed July 19, 2002, entitled "Nanowire Coherent Optical Components," by Lieber, et al ; U.S. Patent Application Serial No. 10/624, 135, filed July 21 , 2003, entitled "Nanowire Coherent Optical Components," by Lieber, et al; U.S. Patent Application Serial No. 10/734,086, filed December 11, 2003, entitled "Nanowire Coherent Optical Components," by Lieber, et al ; U.S. Provisional Patent Application Serial No. 60/524,301, ■ filed November 20, 2003, entitled "Nanoscale Arrays and Related Devices," by Whang, et al ; U.S. Provisional Patent Application Serial No. 60/579,996, filed June 15, 2004, entitled "Nanosensors," by Lieber, et al. ; International Patent Application No. PCT/US01/26298, filed August 22, 2001, entitled "Doped Elongated Semiconductors, Growing Such Semiconductors, Devices Including Such Semiconductors, and Fabricating Such Devices," by Lieber, et al, published as International Patent Application Publication No. WO 02/17362 on February 28, 2002; International Patent Application No. PCT/USOl/48230, filed December 11, 2001, entitled "Nanosensors," by Lieber, et al, published as International Patent Application Publication No. WO 02/4870 Ion June 20, 2002; International Patent Application No. PCT/US02/16133, filed May 20, 2002, entitled "Nanoscale Wires and Related Devices," by Lieber, et al, published as International Patent Application Publication No. WO

03/005450 on January 16, 2003; International Patent Application No. PCT/US03/22061, filed July 16, 2003, entitled "Nanoscale Wires and Related Devices," by Lieber, et al, published as International Patent Application Publication No. WO 2004/038767 on May 6, 2004; International Patent Application No. PCT/US03/11078, filed July 21, 2003, entitled "Nanowire Coherent Optical Components," by Lieber, et al and U.S.

Provisional Patent Application Serial No. 60/592,058, filed July 28, 2004, entitled "Nanowire Photonic Circuits, Components Thereof, And Related Methods," by Barrelet, et al.

The following examples are intended to illustrate certain embodiments of the present invention, but do not exemplify the full scope of the invention.

EXAMPLE 1

In this example, losses through straight and sharply bent sub-wavelength diameter CdS active nanowire waveguide structures were characterized using scanning optical microscopy ("SOM")- These experiments were performed with nanowire guides operating in a sub-wavelength or nanophotonic regime, with approximately 200 nm diameter nanowires and about a 515 nm wavelength light, and were not optimized in any manner. CdS nanowires were synthesized using gold nanoclusters (Ted Pella, Inc.,

Redding, CA) as catalysts, and either a single-source molecular precursor (cadmium diethyldithiocarbamate, Lorad Chemical Co., St. Petersburg, FL) or laser ablation of a solid CdS target as a reactant source. Bent nanowires were prepared by raising the growth temperature by 40 ⁰C above the optimal value for purely axial growth. Modulation of the temperature or pressure during growth yielded abrupt bends along the nanowire axis in a controlled manner.

The nanowires were then dispersed in ethanol and deposited on Si wafer substrates with a 600 nm thermal oxide. Photoluminescence (PL) images were obtained using a far-field epifiuorescence microscope equipped with a liquid-nitrogen-cooled charge coupled device i^'CCD") camera. Laser excitation (488 nm) was focused through the objective (NA = 0.7) to a diffraction-limited spot on the sample surface, providing a typical excitation power density of about 1000 kW/cm². SOM images were recorded by determining the intensity at the nanowire end from a series of PL images, which were obtained by scanning the sample beneath the laser spot. The resolution in these experiments, about 1 micrometer, was determined by the x-y sample scanning stage. Spatial maps of the intensity of light emitted from the end of a nanowire (Fig. IA) were recorded as a function of the position of a diffraction-limited laser spot that is higher in energy than the band gap of CdS. In Fig. IA, a scheme for SOM is illustrated, showing a focused laser spot 10, produced by laser 11, scanned over the sample surface 15 (indicated by track 12) while one end of a nanowire 20 is determined or analyzed for light emission, using a detector 18. The intensity at the end of the nanowire indicated by the detector is then plotted as a function of laser position to generate SOM images, as can be seen in Fig. IB.

A sample SOM image recorded from a nearly straight, 50 micrometer long CdS nanowire (Fig. 1C) exhibited little intensity variation as a function of detector-laser excitation source separation along the wire, indicative of a good waveguide. On the left of the image, the monitored end of the nanowire is indicated symbolically with a detector symbol 21. Lighter shades in the image correspond to greater end intensity. The scale bar represents 10 micrometers.

A plot of intensity versus position quantitatively confirmed this observation. This plot, shown in Fig. ID, quantitatively illustrated the dependence of the end intensity on the distance between the laser spot and the end of the nanowire for a path that follows the nanowire, and demonstrated that there was no detectable loss in this nanowire. These data thus illustrate that the waveguiding of light is very efficient in a straight nanowire structure of the invention.

Other experiments in this example were generally directed to the characterization of the waveguiding of light through sharp bends in CdS nanowire structures. An SOM image recorded from a CdS nanowire with a bend formed by a change in axial growth direction (Fig. IF) showed that the optical loss was small across this sharp bend. Fig. IE shows a scanning electron micrograph ("SEM") of the nanowire structure (in both Figs. IE and IF, the scale bars each represent 10 micrometers). The bend angle, which is defined relative to the deviation from propagation along a straight path, was 59 ° ± 1°. The radius of curvature for such abrupt bends is not easy to measure and is close to zero. The radius of the nanowire, approximately 100 nm, is an upper bound and highlights the sub-wavelength nature of these waveguides and bends.

Analysis of the intensity versus position along the nanowire (Fig. IG) showed that the loss through this abrupt bend is 1 dB to 2 dB, after accounting for loss in the straight portion of the nanowire in a manner similar to previous studies of photonic crystals. The intensity profile along the nanowire was used to quantify the loss in these waveguides. The loss between two points reported in decibels is given by 10 x log (I_\IIi), where J₁ and /₂ correspond to the end intensity recorded with the laser at the two different positions along the waveguide. In this manner, the loss due to a bend or junction was estimated by comparing the loss observed in two segments of equal length along the waveguide: one along a straight section and the other containing the bend or junction.

Fig. IG illustrates the intensity profile along the path indicated in the SOM image, with the location of the bend (designated by the white arrow) set as the origin. The losses observed in the straight sections of this and other nanowires (data not shown) were believed to be due to surface roughness, which can be easily minimized as shown by the nearly loss-free transmission in Figs. 1C and ID. In addition, SOM characterization of an approximately 55 -micrometer long nanowire containing two abrupt 46 ° + 1° bends separated by about 6 micrometers in a "Z" structure (Fig. II) demonstrated that it was possible to guide light through multiple sub-wavelength bends with only a moderate loss. Fig. IH shows an SEM of the same structure as Fig. II. The scale bar in both images represents 10 micrometers. The inset in Fig. IH shows a magnified view of one of the bends, where the scale bar indicates 200 nm. The intensity vs. position data for this nanowire, shown in Fig. IJ, demonstrated that there was an about 0.5 dB to 1 dB loss per abrupt bend in this structure, after accounting for loss in the straight portion of the nanowire. The intensity profile was measured along the path indicated in the SOM map. Arrows 1 and 2 designate the locations of the two intrawire bends.

EXAMPLE 2

In this example, nanowires were assembled into crossed and more complex structures useful in photonic elements and devices, such as logic gates. This example, also demonstrates that the nanowires of the invention may function as a structural motif that can be used for guiding light around sharp and even acute turns. The nanowires were fabricated using techniques similar to those discussed in Example 1.

Fig. 2A illustrates an SOM image and an optical micrograph (inset) of two CdS nanowires assembled in a crossed geometry. In both images, the scale bar represents 10 micrometers. The CdS nanowires are crossed at an angle of 43 + 1 °. This figure thus demonstrates that light was guided through the sharp bend defined by the cross. The intensity versus position data for this arrangement is shown in Fig. 2B. This figure shows that the loss per unit length including the cross was comparable to losses per unit length in the straight segments of these two nanowires, and thus the loss associated with the cross itself was about 1 dB. In this figure, the intensity profile was measured along the path indicated in Fig. 2A, with the junction (marked by the white arrow in Fig. 2A) set as the origin.

In another set of experiments, a related structural motif involving a bend defined by an end-to-end assembly of CdS nanowires was characterized. This arrangement can be seen in Fig.2C in an SOM image and an optical micrograph (inset). In both images, the scale bar represents 10 micrometers. These data show that the nanowire assembly exhibited good transmission through the acute angle defined by this assembly. Quantitative analysis of intensity versus position (Fig.2D) further showed that there was no abrupt increase in loss associated with guiding light through this acute angle structure, and that the loss associated with the end-to-end junction was about 1 dB. In this figure, the intensity profile was measured along the path marked in Fig. 2C, with the junction of the nanowires (marked by the white arrow in Fig. 2C) set as the origin. The above measurements demonstrate that light can be guided or coupled efficiently through sub-wavelength turns defined by junctions between two nanowires. Given the observed substantial transfer of energy observed for interaction lengths on the order of 100 nm or a fraction of the wavelength of light in junctions defined by crossed and end-to-end nanowire structures, band gap absorption of the evanescent field and subsequent radiative recombination within the second nanowire waveguide may be operating as the transfer mechanism.

EXAMPLE 3

The mechanism discussed in Example 2 may imply that junctions between nanowires having different band gaps could enable structures that selectively transmit optical signals in certain directions. In this example, transmission of light through a CdS and cadmium selenide (CdSe) axial nanowire heterostructures (Fig. 3A) with band gaps of 2.5 and 1.7 eV, respectively, were characterized.

Fig. 3 A is a schematic diagram of a single nanowire axial heterojunction between CdS and CdSe portions of the nanowire. Laser 30 was used to locally excite either the CdS or the CdSe portion of the nanowire, and the light output was recorded at points 31 and 32. Figs. 3B and 3C are photoluminescence images of a representative axial heterostructure. Excitation of the CdS region of the heterostructures (Fig. 3B) yielded light from the CdS and CdSe ends of the nanowire, with energy characteristic of the respective band gaps; that is, green light 35 and red light 36. In contrast, excitation of the CdSe portion of the heterostructure (Fig. 3C) yielded light 36 with an energy characteristic of CdSe only from the CdSe end of the heterostructure; no light was observed from the CdS end. Thus, the nanowire behaves as an optical diode, as illustrated schematically with diode 37 in Fig. 3A. Similar results were also recorded in studies of five different CdS-CdSe axial heterostructures (data not shown), thus demonstrating that optical rectification was a robust effect. A summary of these results, shown in Fig. 3D, showed the observed optical diode logic truth table.

These experiments of optical rectification in nanowire heterostructures have several important implications. First, these results provide direct support for the coupling mechanism for light propagation of absorption and emission. Light guided in the CdS portion of the heterostructures has sufficient energy to excite the smaller band gap CdSe, which results in subsequent emission and transmission of light characteristic of CdSe band gap; however, excitation of CdSe cannot yield band gap excitation of CdS and light is not observed at this end of the heterostructures. Second, quantitative measurements show that a rectification ratio of 5 was achieved, and higher ratios may be achieved in optimized systems. These results were wholly unexpected, as a simple estimate using the well-known Fresnel's equation for an infinite planar interface between CdS and CdSe did not predict any significant rectification. Lastly, these results suggest that optical diodes in general may be assembled from different band gap nanowires, for example, in a crossed geometry. For example, other experiments using crossed CdS and zinc sulfide (ZnS) nanowire structures (data not shown) showed that light was rectified across the ZnS-CdS interface consistent with an excitation-emission type process.

EXAMPLE 4 In this example, the combination of active nanowire waveguides with electrical inputs was investigated to demonstrate integration of additional functionality. In one set of experiments, light transmission through a nanowire waveguide subjected to a time varying electric field applied via a parallel plate capacitor structure (Fig. 4A) was characterized. Fig. 4 A is a schematic diagram of a nanowire electro-optic modulator 45. A continuous wave ("CW") laser source 40 was used to inject light into a nanowire waveguide 42, and a variable electric field applied across nanowire 42 using a parallel- plate capacitor geometry modulated the end intensity. The capacitor included an upper electrode 43 and a lower electrode 44. The devices were fabricated on a heavily-doped Si substrate, which served as lower electrode 44, with a thermal oxide layer. The nanowire was deposited on the oxide, covered with a crosslinked polymethylmethacrylate) ("PMMA") layer, and then a gold upper electrode 43 was patterned by electron-beam lithography ("EBL"). An example of such a device is illustrated in the SEM image of Fig. 4E, Where the scale bar represents 5 micrometers. Increasing the applied voltage V (Figs. 4B and 4C) yielded a significant and reversible decrease in the output intensity at the end of the nanowire. Figs. 4B and 4C show the intensity modulation at the emission end of the nanowire when 0 V (Fig. 4B) and 20 V (Fig. 4C) were applied to the capacitor. Quantitatively, voltage-dependent measurements (Fig. 4D) showed a linear decrease up to 20 V; although deviations from linearity were observed at larger voltages an attenuation of -3 dB is achieved at 60 V. In Fig. 4D, the corresponding electric field (calculated from the electrode separation) is shown on the top axis.

Further studies of devices made with smaller (150 nni vs. 700 nm) electrode separations further confirm that the percentage modulation scales with the electric field, not capacitor voltage (data not shown). Comparison of these electro-optic modulator to recently reported Si-based and InGaAs waveguide modulators showed that the unoptimized nanowire device performance of the present invention was substantially better than many conventional integrated structures, and at least comparable to others. For example, the nanowires discussed above produced attenuations of 1 dB/10 micrometers, in contrast to silicon (0.015 dB/10 micrometers) or InGaAs (2.3 dB/10 micrometers), where all are measured with 10 V modulation voltage. This work also suggests that nanowire electro-optic modulators can be combined with other nanowire photonic components, such as those described herein. In another set of experiments, integrated electrical injection of light into nanowire waveguides from crossed p-type and «-type materials was investigated. Images were recorded from forward biased p-n diodes fabricated using n-CdS nanowires with diameters of approximately 80 nm. These images (Fig. 4F) demonstrate that, while some light is emitted at the cross point, most of the light is emitted from the CdS nanowire end. These data also show that the crossed nanowire p-n diode structure can couple light efficiently into the guided modes of the nanowire.

EXAMPLE 5

This example describes electric field modulation of excitonic lasing in CdS nanowires. In addition, experiments conducted below threshold on nanowire electro- optic modulator (EOM) devices of varied geometry support an absorption-based mechanism for modulation. Finally, these aspects of the observed behavior were reproduced in GaN, demonstrating the generality of this effect and emphasizing the potential for assembling integrated optical systems that function over a variety of wavelengths. Cadmium sulfide nanowires were grown catalytically using gold nanocluster- directed pulsed laser deposition (PLD) or metal-organic chemical vapor deposition (MOCVD). Gallium nitride nanowires were grown by MOCVD using a nickel catalyst. For both materials, transmission electron microscopy (TEM) studies revealed a typical diameter of about 100 nni, lengths > 10 microns, and a wurtzite crystal structure with the c axis orthogonal to nanowires growth axis.

The nanowire EOM devices (shown schematically in Fig. 7A) are constructed and studied in a manner similar to that described herein. A parallel-plate capacitor structure was used in Fig. 7A to apply an electric field to a portion of the nanowire. Fig. 7A indicates the excitation site, region of field modulation, and observed nanowire end. The Ti-coated Si substrate and a Ti stripe defined by electron-beam lithography served as the capacitor plates, from which the nanowire was isolated by SiO₂ dielectric layers. The degenerately doped Si substrates were coated with a 50 nm layer of Ti, followed by the first of two SiO₂ layers deposited by plasma-enhanced chemical vapor deposition. Then, CdS or GaN nanowires were drop-cast from ethanol suspension and located with respect to a pre-defined marker pattern. Following deposition of a second SiO₂ layer, the top Ti electrode was defined by aligned electron-beam lithography, evaporation, and liftoff. Fig. 7D is a superimposed photoluminescence image (recorded below laser threshold) and white-light optical micrograph of a representative nanowire EOM-laser device. Numerals 1 and 2 in Fig. 7D indicate excitation site and observed nanowire end, respectively. The scale bar is 5 microns.

Excitation with an above-bandgap laser beam of constant intensity was used to launch band-edge fluorescence light into the waveguide. The excitation laser was focused to a diffraction-limited spot approximately 5 microns distant from the top electrode. Thus, the excited region experienced a minimal applied field. The intensity and spectrum of light emitted from the output of the nanowire waveguide were then recorded while a time-varying voltage signal was applied to the electrodes. The CdS nanowires were excited at about 405 nm with a frequency-doubled Ti: sapphire laser. The GaN nanowires were excited at 266 nm using the fourth harmonics of fiber-coupled, diode pumped Q-switched Nd:YVO₄ laser. A far-field epifluorescence microscope was used to focus the laser excitation (typical excitation power density of about 100 kW/cm²) and to record images and spectra of nanowire end emission. The resolution of the spectrometer was about 0.2 nm. The intensity modulation values reported below represent averages obtained from about 50 on/off cycles at 0.5 FIz.

Measurements, of field modulation of CdS nanowire lasing were conducted at 4.2 K in order to take advantage of the lower lasing threshold at low temperature. For this experiment, the onset of lasing associated with the exciton line near 489 nm (2.53 eV) was characterized by the enhancement of end vs. body emission, as well as the emergence of a narrow line with superlinear power dependence. Fig. 7B is an emission spectra of a CdS nanowire laser showing effect of 30 V signal, showing the modulation of the output spectrum of a representative CdS EOM-laser with L = 6 microns, ttop^ ftot= 50 nm. Fig. 7B. Fig. 7C shows modulation versus applied voltage at the two indicated wavelengths for the EOM-laser emission spectrum shown in Fig. 7B. The error bars reflect the standard deviation of the responses to 50 pulses at 0.5 Hz. The device was operated just above threshold in order to allow comparison between the response of the exciton lasing line and the free electron-bound hole (FEBH) feature at about 514 nm, which showed a linear power dependence. Significantly, the 489 nm exciton lasing line was modulated by up to 40% at 45V with no measurable chirp, and was modulated more than twice as strongly as the FEBH feature. Thus, this experiment shows electric field- modulated nanowire lasing.

EXAMPLE 6 In this example, two device geometries (Fig. 8) were used to help identify a scaling relationship which describes the EOM behavior: the parallel-plate capacitor scheme described in Example 5 (Figs. 8A and 8C), and an alternate geometry in which the top electrodes are fabricated alongside the nanowire on a heavily-doped Si substrate with a thermal oxide (Fig. 8B and 8D). Employing this alternate geometry helped to distinguish the electric-field response from any other possible stimulus such as electrostatic pressure or charge transfer processes. To facilitate comparison between devices, the modulators were studied at room temperature and at low excitation power, conditions under which optical gain was not present and the end emission spectrum consisted of a single peak at about 515 nm, corresponding to band-edge recombination. Modulation that depended linearly on the voltage difference between the capacitor plates was observed. The modulation was asymmetric about V= O. Both senses are observed, but predominantly V>0 was associated with a decrease in intensity. The modulation did not depend on the ground referencing of the applied voltage, and no modulation was observed if the same voltage was applied to both plates (which varied the potential, but not the field). Fig. 8E presents the length-normalized modulation

1) for several representative devices plotted versus the applied field, as calculated using a finite element analysis model which considered the dielectric constants of SiO₂ and CdS. In this figure, "PP" illustrates representative parallel-plate (PP) devices and "FF" illustrates representative fringe-field (FF) devices. With reference to Fig. 8A-8D for the corresponding dimensions, PP: nanowire "A," Z = IO microns, ttop = 100 nm, t_bot - 600 nm; nanowire "B," L = 4 microns, t_top - 100 nm, t_bot ⁼ 220 nm; nanowire "C," L = 8 microns, t_top = 100 nm, tbot ⁼ 50 nm; nanowire "D," 1 = 4 μm, t_top ^~ 160 nm, t_bot = 160 nm. FF: L = 12 microns, t = 600 nm, d - 2 microns. Note that a positive field corresponds to V< 0.

The results support linear scaling of the modulation electric field and with the length L of the nanowire segment to which the field is applied.

EXAMPLE 7 This example illustrates that electro-optic modulator devices made using GaN nanowires displayed behavior similar to that observed in CdS. Modulation at room temperature of a GaN nanowire laser is shown in Fig. 9A. The laser spectrum was characterized by multimode emission with a peak at 373 nm; as in the case of CdS intensity modulation is accomplished without a change in the peak position. Fig. 9A is an emission spectrum above lasing threshold, with and without bias applied. Fig. 9C was recorded below threshold: top, superimposed PL and white-light image of device. The scale bar is 10 microns. Fig. 9D is a plot of end emission spectra at three different bias values.

The linear, asymmetric response of end emission intensity to the applied voltage is shown in Pig. 9B, recorded below threshold at much lower excitation power. Fig. 9B is a plot of modulation of intensity vs. voltage, below threshold. The top and bottom dielectric thicknesses for this device were 100 nm and 50 nm, respectively. Modulation above 20% was achieved over 4 microns at 45 V. Gallium nitride is a semiconductor of great industrial interest. Other studies of GaN nanowires have demonstrated that the reach of nanowire photonics may extend into the ultraviolet regime. The results in this example show the generality of electric-field modulation in wide-bandgap nanowire waveguides and lasers, and suggest that integrated, nanowire-based optical and electrooptical devices operating over the whole visible and UV spectrum may be enabled using CdS, GaN, and related II- VI and Ill-nitride semiconductor alloy materials. Intensity modulation in semiconductor electro-optic modulators may be generally achieved either by modulation of the absorption coefficient at the signal wavelength, or by modulation of the refractive index n, which imparts a phase or polarization change that can be converted to a change in intensity by a phase- or polarization-selective element. However, a substantial change in n may be required to achieve a phase shift of π/2 (pi/2) within a typical electrode width of 5 microns. For the case of 515 nm light in CdS, a change on the order of An ~ 0.025 may be required. This is roughly 25 times larger than the maximum index change expected for the applied field values, as calculated from the linear, and non-linear electro-optic coefficients of CdS, suggesting that absorption, rather ^"than refractive effects, may be the origin of modulation.

Absorption-based EOMs (also called electroabsorption modulators, EAMs) utilizing the quantum-confined Stark effect (QCSE) in III-V quantum wells can be used to modulate laser-diode output for telecommunications applications. In such devices, quantum confinement may alter the traditional Franz-Keldysh effect, enhancing sub- bandgap absorption within a limited wavelength range. Although significant quantum confinement of carriers in CdS or GaN may not be expected for the nanowire diameters used in this example, deviation from the Franz-Keldysh effect may still be expected due to Coulomb interactions, potentially owing to the significant exciton binding energies in these materials (28 meV and 25 meV in CdS and GaN, respectively). Electric field- modulated absorption has been previously studied in both CdS and GaN thin films. At 4.2 K, the strongest modulation in CdS thin films was associated with the /i exciton absorption line at 2.53 eV, which is about the same energy as the emission peak of the CdS nanowire EOM-lasef . While the Franz-Keldysh effect and related electroabsorption phenomena were intrinsically independent of field polarity, an asymmetric response was frequently observed in semiconductors having internal electric fields, e.g., in semiconductor heterostructures such as those used for QCSE modulators. In the CdS and GaN nanowires studied here, a possible origin of an internal field is differing surface charge on opposite sides of the nanowire. Such a charge difference could arise because the c axis of the uniaxial wurtzite crystal is oriented orthogonally to the growth axis of the nanowirej such that opposite sides of the wire have differing atomic structure: internal fields > 250 kV/cm have been reported in wurtzite CdSe nanocrystals. A difference in surface charge density of 3x10¹² cm^"2 across a 100 nm diameter CdS nanowire would produce a field of 500 kV/cm, which is larger than any external field applied in this example.

Thus, these results show that electric fields are capable of modulating band-edge light in semiconductor nanowire active waveguides, and can modulate the output of nanowire lasers without introducing chirp. An electroabsorption model can be used to rationalize the linear absorption close to the band edge. A number of opportunities exist for future study. For example, electroabsorption measurements on nanowire waveguides incorporating core-shell heterostructures would both be a valuable probe of the electronic structure of such materials, and may lead to enhanced modulation depth due to quantum confinement. It may also be possible to take advantage of the extreme confinement of optical-frequency fields in plasmon waveguides to effect all-optical modulation in nanowires at low power. In combination with other nanoscale optical components, nanowire EOM lasers, and waveguides may open new possibilities for multiplexed optical sensing, storage, or information processing.

While several embodiments of the present invention have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the functions and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the present invention. More generally, those skilled^' in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the teachings of the present invention is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, the invention may be practiced otherwise than as specifically described and claimed. The present invention is directed to each individual feature, system, article, material, kit, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and/or methods, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the scope of the present invention.

All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and/or ordinary meanings of the defined terms. The indefinite articles "a" and "an," as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean "at least one."

The phrase "and/or," as used herein in the specification and in the claims, should be understood to mean "either or both" of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Multiple elements listed with "and/or" should be construed in the same fashion, i.e., "one or more" of the elements so conjoined. Other elements may optionally be present other than the elements specifically identified by the "and/or" clause, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, a reference to "A and/or B", when used in conjunction with open-ended language such as "comprising" can refer, in one embodiment, to A only (optionally including elements other than B); in another embodiment, to B only (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.

As used herein' in the specification and in the claims, "or" should be understood to have the same meaning as "and/or" as defined above. For example, when separating items in a list, "or" or "and/or" shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as "only one of or "exactly one of," or, when used in the claims, "consisting of," will refer to the inclusion of exactly one element of a number or list of elements. In general, the term "or" as used herein shall only be interpreted as indicating exclusive alternatives (i.e. "one or the other but not both") when preceded by terms of exclusivity, such as "either," "one of," "only one of," or "exactly one of." "Consisting essentially of, when used in the claims, shall have its ordinary meaning as used in the field of patent law.

As used herein in the specification and in the claims, the phrase "at least one," in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase "at least one" refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, "at least one of A and B" (or, equivalently, "at least one of A or B," or, equivalently "at least one of A and/or B") can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc. It should also be understood that, unless clearly indicated to the contrary, in any methods claimed herein that include more than one step or act, the order of the steps or acts of the method is not necessarily limited to the order in which the steps or acts of the method are recited.

In the claims, as well as in the specification above, all transitional phrases such as "comprising," "including," "carrying," "having," "containing," "involving," "holding," and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases "consisting of and "consisting essentially of shall be closed or semi-closed transitional phrases, respectively, as set forth in the United States Patent Office Manual of Patent Examining Procedures, Section 2111.03. What is claimed is:

Claims

1. A method, comprising: detecting a result of light propagation within and/or emission from a first location of a nanoscale wire when light is established within a second location of the nanoscale wire, wherein the light propagating within and/or emitted from the first location of the nanoscale wire has an intensity of at least about 10% of the intensity of the light established within the second location, and wherein the nanoscale wire comprises a non-straight portion between the first location and the second location, the non-straight portion having cross- sections defined along its length and centers of the cross-sections that define a curve, the curve having a radius of curvature that, at a point of maximum value, is less than 10 times the maximum diameter of the nanoscale wire at that point.

2. The method of claim 1 , wherein the nanoscale wire comprises material having a band gap, and the light is of an energy at or near the band gap.

3. The method of claim 1, wherein detecting the result comprises decoding a time- varying signal.

4. The method of claim 1, wherein detecting the result comprises using the light to affect a function of an photonic circuit and determining the result of the function.

5. The method of claim 1, wherein detecting the result comprises affecting and/or analyzing a chemical, biological, and/or biochemical reaction using the light, and determining the reaction.

6. The method of claim 1, wherein the nanoscale wire comprises a semiconductor.

7. The method of claim 1, wherein the nanoscale wire is a nanowire.

8. The method of claim 1, wherein the light established within the second location comprises visible light.

9. The method of claim 1, wherein the light propagating within and/or emitted from the first location of the nanoscale wire has an intensity of at least about 30% of the intensity of the light established within the second location

10. The method of claim 1, wherein the light propagating within and/or emitted from the first location of the nanoscale wire has an intensity of at least about 50% of the intensity of the light established within the second location

11. The method of claim 1 , wherein the light propagating within and/or emitted from the first location of the nanoscale wire has an intensity at least about 70% of the intensity of the light established within the second location.

12. The method of claim 1, wherein the light propagating within and/or emitted from the first location of the nanoscale wire has an intensity at least about 80% of the intensity of the light established within the second location.

13. The method of claim 1, wherein the light propagating within and/or emitted from the first location of the nanoscale wire has an intensity at least about 90% of the intensity of the light established within the second location.

14. The method of claim 1, wherein the light propagating within and/or emitted from the first location of the nanoscale wire has an energy substantially equal to the band gap of the nanoscale wire at the first location.

15. The method of claim 1, wherein the nanoscale wire, at the point of maximum value of radius of curvature, has a maximum diameter that is less than about 500 nm.

16. The method of claim 1, wherein the nanoscale wire, at the point of maximum value of radius of curvature, has a maximum diameter that is less than about 200 nm.

17. The method of claim 1 , wherein the nanoscale wire, at the point of maximum value of radius of curvature, has a maximum diameter that is less than about 100 nm.

18. The method of claim 1 , wherein the nanoscale wire, at the point of maximum value of radius of curvature, has a maximum diameter that is less than about 40 nm.

19. The method of claim 1, wherein the nanoscale wire, at the point of maximum value of radius of curvature, has a maximum diameter that is less than about 10 nm.

20. The method of claim 1, wherein the first location is an end of the nanoscale wire.

21. A method, comprising: detecting a result of light propagation within and/or emission from a first location of a first nanoscale wire when light is established within a second location of a second nanoscale wire, the first nanoscale wire and the second nanoscale wire being positioned such that light established within the second location of the second nanoscale wire is able to be transmitted through at least portions of the first and second nanoscale wires to the first location of the first nanoscale wire, wherein the light propagating within and/or emitted from the first location of the first nanoscale wire has an intensity of at least about 10% of the intensity of the light established within the second location of the second nanoscale wire.

22. The method of claim 21, wherein the first nanoscale wire comprises material having a band gap, and the light is of an energy at or near the band gap.

23. The method of claim 21 , wherein detecting the result comprises decoding a time- varying signal.

24. The method of claim 21, wherein detecting the result comprises using the light to affect a function of an photonic circuit and determining the result of the function.

25. The method of claim 21 , wherein detecting the result comprises affecting and/or analyzing a chemical, biological, and/or biochemical reaction using the light, and determining the reaction.

26. The method of claim 21, wherein the first nanoscale wire comprises a semiconductor.

27. The method of claim 21, wherein the second nanoscale wire comprises a semiconductor.

28. The method of claim 21, wherein the first nanoscale wire is a nanowire.

29. The method of claim 21, wherein the second nanoscale wire is a nanowire.

30. The method of claim 21, wherein the light established within the second location of the second nanoscale wire comprises visible light.

31. The method of claim 21 , wherein the light propagating within and/or emitted from the first location of the first nanoscale wire has an intensity at least about

30% of the intensity of the light established within the second location of the second nanoscale wire.

32. The method of claim 21, wherein the light propagating within and/or emitted from the first location of the first nanoscale wire has an intensity at least about

50% of the intensity of the light established within the second location of the second nanoscale wire.

33. The method of claim 21 , wherein the light propagating within and/or emitted from the first location of the first nanoscale wire has an intensity at least about 70% of the intensity of the light established within the second location of the second nanoscale wire.

34. The method of claim 21, wherein the light propagating within and/or emitted from the first location of the first nanoscale wire has an intensity at least about 80% of the intensity of the light established within the second location of the second nanoscale wire.

35. The method of claim 21, wherein the light propagating within and/or emitted from the first location of the first nanoscale wire has an intensity at least about 90% of the intensity of the light established within the second location of the second nanoscale wire.

36. The method of claim 21, wherein the light propagating within and/or emitted from the first location of the first nanoscale wire has an energy substantially equal to the band gap of the nanoscale wire at the first location.

37. The method of claim 21, wherein the first nanoscale wire and the second nanoscale wire are in physical contact.

38. The method of claim 21, wherein the first nanoscale wire has maximum diameter of less than about 500 nm.

39. The method of claim 21, wherein the first nanoscale wire has maximum diameter of less than about 200 nm.

40. The method of claim 21, wherein the first nanoscale wire has maximum diameter of less than about 100 nm.

41. The method of claim 21 , wherein the first nanoscale wire has a minimum diameter of greater than about 10 nm.

42. The method of claim 21, wherein the first nanoscale wire has a minimum diameter of greater than about 40 nm.

43. The method of claim 21, wherein the first location of the first nanoscale wire is an end of the first nanoscale wire.

44. The method of claim 21, wherein each of the first nanoscale wire and the second nanoscale wire has cross-sections defined along each respective nanoscale wire and centers of the cross-sections that define curves, such that the respective curves are not collinear and such that each of the respective curves is not linear.

45. An apparatus, comprising: a photonic circuit comprising a nanoscale wire having a non-straight portion having a radius of curvature that, at its maximum value at a specific point, is less than 10 times the maximum diameter of the nanoscale wire at that specific point.

46. The apparatus of claim 45, wherein the nanoscale wire is a nanowire.

47. An apparatus, comprising: a photonic circuit comprising an optical diode comprising a nanoscale wire.

48. The apparatus of claim 47, wherein the nanoscale wire is a nanowire.

49. An apparatus, comprising: an optical memory unit comprising an optical diode comprising a nanoscale wire.

50. The apparatus of claim 49, wherein the nanoscale wire is a nanowire.

51. A method, comprising: transmitting light through a first material and a second material, the light including light having a particular wavelength that is able to pass from the first material into the second material at a first intensity, but is not able to pass from the second material into the first material at an intensity greater than about 50% of the first intensity.

52. The method of claim 51, wherein the light is able to pass from the first material into the second material through a distance that is equal to a maximum dimension of the first and second materials at a first intensity, but is not able to pass from the second material into the first material through a distance that is equal to a maximum dimension of the first and second materials at an intensity greater than about 50% of the first intensity.

53. The method of claim 51, wherein the second material has a band gap, and the light of the particular wavelength has an energy at or near the band gap.

54. The method of claim 51 , wherein the first material has a maximum dimension of less than about 10 mm.

55. The method of claim 51, wherein the first material has a maximum dimension of less than about 1 mm.

56. The method of claim 51, wherein the first material has a maximum dimension of less than about 100 micrometers.

57. The method of claim 51, wherein the first material has a maximum dimension of less than about 10 micrometers.

58. The method of claim 51 , wherein the first material has a maximum dimension of less than about 1 micrometer.

59. The method of claim 51, wherein the first material has a maximum dimension of less than about 100 nm.

60. The method of claim 51, wherein the second material has a maximum dimension of less than about 10 mm.

61. The method of claim 51 , wherein the light at the particular wavelength is visible light.

62. The method of claim 51 , wherein the light at the particular wavelength is not able to pass from the second material into the first material at an intensity greater than about 30% of the first intensity.

63. The method of claim 51 , wherein the light at the particular wavelength is not able to pass from the second material into the first material at an intensity greater than about 20% of the first intensity.

64. The method of claim 51, wherein the light at the particular wavelength is not able to pass from the second material into the first material at an intensity greater than about 10% of the first intensity.

65. The method of claim 51 , wherein substantially none of the light at the particular wavelength is able to pass from the second material into the first material.

66. The method of claim 51 , wherein the first material and the second material together comprise a nanoscale wire.

67. The method of claim 51, wherein the first material and the second material together comprise a nanowire.

68. The method of claim 51, wherein the first material comprises a first nanoscale wire and the second material comprises a second nanoscale wire.

69. The method of claim 51, wherein an interface between the first material and the second material is atomically abrupt.

70. The method of claim 51 , wherein the light at the particular wavelength has an energy substantially equal to the band gap of the first material.

71. The method of claim 51, wherein the first material comprises a semiconductor.

72. The method of claim 51 , wherein the second material comprises a semiconductor.

73. A method, comprising: applying an electric field to a light-emitting material and varying the electric field such that light emitted by the light-emitting material directly varies in amplitude in response to the variation in the electric field.

74. The method of claim 73, wherein the electric field encodes a time-varying signal.

75. The method of claim 74, wherein the light emitted by the light-emitting material encodes the time-varying signal encoded by the electric field.

76. The method of claim 73, wherein the light-emitting material comprises a nanoscale wire.

77. The method of claim 76, wherein the nanoscale wire comprises a semiconductor.

78. The method of claim 73, wherein the light-emitting material comprises a nanowire.

79. The method of claim 73, wherein the electric field is varied by varying its intensity.

80. The method of claim 73, wherein the electric field is produced by an electric field generator, and the electric field is varied by varying a voltage supplied to the electric field generator.

81. The method of claim 80, wherein the electric field generator comprises a capacitor.

82. The method of claim 80, wherein the electric field is produced using two substantially planar electrodes.

83. An article, comprising: an electric field generator and a light-emitting material, constructed and arranged such that when a time-varying voltage of less than about 100 V_RMS is applied to the electric field generator, the electric field generator produces a time- varying electric field that causes the light-emitting material to emit light that varies in response to variations in the electric field.

84. The article of claim 83, wherein the light-emitting material comprises a nanoscale wire.

85. The article of claim 83, wherein the light-emitting material comprises a nanowire.

86. The article of claim 83, wherein the light-emitting material comprises a semiconductor.

87. The article of claim 83, wherein the electric field generator comprises a capacitor.

88. The article of claim 83, wherein the electric field generator comprises two substantially planar electrodes.

89. The article of claim 88, each of the two electrodes having a major surface, wherein the two major surfaces of the two electrodes face each other.

90. The article of claim 88, each of the two electrodes having a major surface, wherein the two major surfaces of the two electrodes do not face each other.

91. The article of claim 83, wherein the electric field generator produces a time- varying electric field that causes the light-emitting material to emit light that varies in response to variations in the electric field when a time-varying voltage of less than about 30 V_RMS is applied to the electric field generator.

92. The article of claim 83, wherein the electric field generator produces a time- varying electric field that causes the light-emitting material to emit light that varies in response to variations in the electric field when a time-varying voltage of less than about 10 V_RMS is applied to the electric field generator.

93. An article, comprising: a nanoscale wire and an electric field generator, constructed and arranged such that when the electric field generator produces a time-varying electric field, the nanoscale wire emits light that varies in response to variations in the electric field.

94. The article of claim 93, wherein the nanoscale wire comprises a semiconductor.

95. The article of claim 93, wherein the electric field generator comprises a capacitor.

96. The article of claim 93, wherein the electric field generator comprises two substantially planar electrodes.

97. The article of claim 96, each of the two electrodes having a major surface, wherein the two major surfaces of the two electrodes face each other.

98. The article of claim 96, each of the two electrodes having a major surface, wherein the two major surfaces of the two electrodes do not face each other.

99. The article of claim 93, wherein the nanoscale wire is a nanowire.

100. An article, comprising: a light-emitting material and an electric field generator, constructed and arranged such that when the electric field generator produces a time-varying electric field, the light-emitting material emits light that varies in response to variations in the electric field, wherein the light-emitting material is free of a crystalline substrate.

101. The article of claim 100, wherein the light-emitting material comprises a nanoscale wire.

102. The article of claim 101, wherein the nanoscale wire comprises a semiconductor.

103. The article of claim 100, wherein the electric field generator comprises a capacitor.

104. The article of claim 100, wherein the electric field generator comprises two substantially planar electrodes.

105. The article of claim 104, each of the two electrodes having a major surface, wherein the two major surfaces of the two electrodes face each other.

106. The article of claim 104, each of the two electrodes having a major surface, wherein the two major surfaces of the two electrodes do not face each other.

107. The article of claim 100, wherein the light-emitting material comprises a nanowire.

108. A method, comprising: detecting a result of non-coherent light propagation within and/or emission from a first location of a semiconducting nanoscale wire when energy is applied to a second location of the nanoscale wire.

109. The method of claim 108, wherein the nanoscale wire comprises material having a band gap, and the non-coherent light is of an energy at or near the band gap.

110. The method of claim 108, wherein detecting the result comprises decoding a time-varying signal.

111. The method of claim 108, wherein detecting the result comprises using the light to affect a function of an photonic circuit and determining the result of the function.

112. The method of claim 108, wherein detecting the result comprises affecting and/or analyzing a chemical, biological, and/or biochemical reaction using the light, and determining the reaction.

113. The method of claim 108, wherein the energy comprises light.

114. The method of claim 113, wherein the light is directly injected into the nanoscale wire.

115. The method of claim 108, wherein the energy comprises visible light.

116. The method of claim 108, wherein the energy comprises electrical energy.

117. The method of claim 108, wherein the nanoscale wire is non-straight.

118. The method of claim 108, wherein the nanoscale wire is ananowire.

119. The method of claim 108, wherein the light propagating within and/or emitted from the first location of the nanoscale wire has an intensity of at least about 10% of the intensity of the light applied to the second location.

120. The method of claim 108, wherein the light propagating within and/or emitted from the first location of the nanoscale wire has an intensity of at least about 30% of the intensity of the light applied to the second location.

121. The method of claim 108, wherein the light propagating within and/or emitted from the first location of the nanoscale wire has an intensity of at least about 50% of the intensity of the light applied to the second location.

122. The method of claim 108, wherein the light propagating within and/or emitted from the first location of the nanoscale wire has an intensity at least about 70% of the intensity of the light applied to the second location.

123. The method of claim 108, wherein the light propagating within and/or emitted from the first location of the nanoscale wire has an intensity at least about 80% of the intensity of the light applied to the second location.

124. The method of claim 108, wherein the light propagating within and/or emitted from the first location of the nanoscale wire has an intensity at least about 90% of the intensity of the light applied to the second location.

125. The method of claim 108, wherein the light propagating within and/or emitted from the first location of the nanoscale wire has an energy substantially equal to the band gap of the nanoscale wire applied to the first location.

126. The method of claim 108, wherein the first nanoscale wire has maximum diameter of less than about 500 nm.

127. The method of claim 108, wherein the first nanoscale wire has maximum diameter of less than about 200 nm.

128. The method of claim 108, wherein the first nanoscale wire has maximum diameter of less than about 100 nm.

129. The method of claim 108, wherein the first nanoscale wire has a minimum diameter of greater than about 10 nm.

130. The method of claim 108, wherein the first nanoscale wire has a minimum diameter of greater than about 40 nm.

131. The method of claim 108, wherein the first location is an end of the nanoscale wire.

132. The method of claim 108, wherein the energy is applied to the second location of the nanoscale wire using a second nanoscale wire.

133. The method of claim 132, wherein the second nanoscale wire physically contacts the nanoscale wire.

134. The method of claim 133, wherein, when a voltage is applied to the second nanoscale wire, light is created at a point of contact between the nanoscale wire and the second nanoscale wire.

135. The method of claim 132, wherein the nanoscale wire and the second nanoscale wire together define a light-coupling region therebetween.

136. A method, comprising: detecting a result of light propagation within and/or emission from a first location of a semiconducting nanoscale wire when light is applied to a second location of the nanoscale wire at a substantially non-straight angle with respect to a longitudinal axis of the nanoscale wire.

137. The method of claim 136, wherein the nanoscale wire comprises material having a band gap, and the light is of an energy at or near the band gap.

138. The method of claim 136, wherein detecting the result comprises decoding a time-varying signal.

139. The method of claim 136, wherein detecting the result comprises using the light to affect a function of an photonic circuit and determining the result of the function.

140. The method of claim 136, wherein detecting the result comprises affecting and/or analyzing a chemical, biological, and/or biochemical reaction using the light, and determining the reaction.

141. The method of claim 136, wherein the nanoscale wire is non-straight.

142. The method of claim 136, wherein the nanoscale wire is a nanowire.

143. The method of claim 136, wherein the light propagating within and/or emitted from the first location of the nanoscale wire has an intensity of at least about 10% of the intensity of the light applied to the second location.

144. The method of claim 136, wherein the light propagating within and/or emitted from the first location of the nanoscale wire has an intensity of at least about 30% of the intensity of the light applied to the second location.

145. The method of claim 136, wherein the light propagating within and/or emitted from the first location of the nanoscale wire has an intensity of at least about 50% of the intensity of the light applied to the second location.

146. The method of claim 136, wherein the light propagating within and/or emitted from the first location of the nanoscale wire has an intensity at least about 70% of the intensity of the light applied to the second location.

147. The method of claim 136, wherein the light propagating within and/or emitted from the first location of the nanoscale wire has an intensity at least about 80% of the intensity of the light applied to the second location.

148. The method of claim 136, wherein the light propagating within and/or emitted from the first location of the nanoscale wire has an intensity at least about 90% of the intensity of the light applied to the second location.

149. The method of claim 136, wherein the light propagating within and/or emitted from the first location of the nanoscale wire has an energy substantially equal to the band gap of the nanoscale wire at the first location.

150. The method of claim 136, wherein the first nanoscale wire has maximum diameter of less than about 500 nm.

151. The method of claim 136, wherein the first nanoscale wire has maximum diameter of less than about 200 nm.

152. The method of claim 136, wherein the first nanoscale wire has maximum diameter of less than about 100 nm.

153. The method of claim 136, wherein the first nanoscale wire has a minimum diameter of greater than about 10 nm.

154. The method of claim 136, wherein the first nanoscale wire has a minimum diameter of greater than about 40 nm.

155. The method of claim 136, wherein the first location is an end of the nanoscale wire.

156. The method of claim 136, wherein the light applied to the second location is injected into the nanoscale wire.

157. The method of claim 136, wherein the light is applied to the second location of the nanoscale wire using a second nanoscale wire.

158. The method of claim 157, wherein the second nanoscale wire physically contacts the nanoscale wire.

159. The method of claim 158, wherein, when a voltage is applied to the second nanoscale wire, light is created at a point of contact between the nanoscale wire and the second nanoscale wire.

160. The method of claim 157, wherein the nanoscale wire and the second nanoscale wire together define a light-coupling region therebetween.

161. A method, comprising: detecting a result of light propagation within and/or emission from a first location of a first nanoscale wire when light is established within a second location of a second nanoscale wire, wherein the light is transmitted between the second nanoscale wire and the first nanoscale wire via a light-coupling region defined between the first nanoscale wire and the second nanoscale wire, the light- coupling region having a maximum dimension of less than about 1 mm and being able to couple at least about 10% of light established within the second nanoscale wire to the first nanoscale wire.

162. The method of claim 161, wherein the first nanoscale wire comprises material having a band gap, and the light is of an energy at or near the band gap.

163. The method of claim 161, wherein detecting the result comprises decoding a time-varying signal.

164. The method of claim 161, wherein detecting the result comprises using the light to.

165. The method of claim 161, wherein detecting the result comprises affecting and/or analyzing a chemical, biological, and/or biochemical reaction using the light, and determining the reaction.

166. The method of claim 161, wherein the light-coupling region able to couple at least about 30% of light established within the second nanoscale wire to the first nanoscale wire.

167. The method of claim 161, wherein the light-coupling region able to couple at least about 50% of light established within the second nanoscale wire to the first nanoscale wire.

168. The method of claim 161, wherein the light-coupling region able to couple at least about 70% of light established within the second nanoscale wire to the first nanoscale wire.

169. The method of claim 161, wherein the light-coupling region able to couple at least about 80% of light established within the second nanoscale wire to the first nanoscale wire.

170. The method of claim 161, wherein the light-coupling region able to couple at least about 90% of light established within the second nanoscale wire to the first nanoscale wire.

171. The method of claim 161, wherein the light-coupling region has a maximum dimension of less than about 100 micrometers.

172. The method of claim 161, wherein the light-coupling region has a maximum dimension of less than about 10 micrometers.

173. The method of claim 161, wherein the light-coupling region has a maximum dimension of less than about 1 micrometers.

174. The method of claim 161, wherein the light-coupling region has a maximum dimension of less than about 100 nm.

175. The method of claim 161, wherein the first nanoscale wire comprises a semiconductor.

176. The method of claim 161, wherein the second nanoscale wire comprises a semiconductor.

177. The method of claim 161, wherein the first nanoscale wire is a nanowire.

178. The method of claim 161, wherein the second nanoscale wire is a nanowire.

179. The method of claim 161, wherein the light established within the second location of the second nanoscale wire comprises visible light.

180. The method of claim 161, wherein the light established within the second location of the second nanoscale wire comprises visible light.

181. The method of claim 161, wherein the light propagating within and/or emitted from the first location of the first nanoscale wire has an energy substantially equal to the band gap of the nanoscale wire at the first location.

182. The method of claim 161, wherein the first nanoscale wire has maximum diameter of less than about 500 nm.

183. The method of claim 161, wherein the first nanoscale wire has maximum diameter of less than about 200 nm.

184. The method of claim 161, wherein the first nanoscale wire has maximum diameter of less than about 100 nm.

185. The method of claim 161, wherein the first nanoscale wire has a minimum diameter of greater than about 10 nm.

186. The method of claim 161, wherein the first nanoscale wire has a minimum diameter of greater than about 40 run.

187. The method of claim 161, wherein the first location of the first nanoscale wire is an end of the first nanoscale wire.