WO2013097018A1

WO2013097018A1 - Fiber-optic device with one-dimensional element for near-field optical spectroscopy and microscopy

Info

Publication number: WO2013097018A1
Application number: PCT/BR2012/000557
Authority: WO
Inventors: Ado JÓRIO DE VASCONCELLOS
Original assignee: Universidade Federal De Minas Gerais - Ufmg
Priority date: 2011-12-29
Filing date: 2012-12-27
Publication date: 2013-07-04
Also published as: BRPI1105972A2; BRPI1105972B1

Abstract

The subject matter (figure 1) is a fiber-optic device (1) with at least one one-dimensional element (3) at the extremity (2) of (1) for near-field optical spectroscopy and microscopy. This device comprises a probe that may be used, preferably, in scanning-probe microscopy and spectroscopy techniques and equipment. The device (figure 1) is suitably dimensioned to carry the light propagated along the fiber to a surface to be analyzed, condensing the light at the fiber output by coupling the light with the one-dimensional element. The subject matter (figure 1) is sufficiently robust for the surface analysis process, and is able to provide high-resolution analysis of structures having dimensions of less than 10 nm.

Description

"UNI-DIMENSIONAL FIBER OPTICAL DEVICE FOR MICROSCOPY AND FIELD OPTICAL SPECTROSCOPY

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The treated matter (Figure 1) is described by a fiber optic device (1) with at least one one-dimensional element (3) at the end (2) of (1); for near field optical microscopy and spectroscopy. This device comprises a probe and may preferably be applied to microscopy and spectroscopy equipment and techniques, both by probe scanning. The device (Figure 1) has adequate dimensions to carry the light propagating through the fiber to a surface to be analyzed, but condensing the light at the fiber outlet by coupling the light with the one-dimensional element. The treated matter (Figure 1) presents robustness during the surface analysis process, being able to analyze with high resolution structures smaller than 10 nm.

In the early 1980s, Probe Scanning Microscopy

Scanning Probe Microscopy (SPM) surprised the world with the first atomic resolution images of the surface of a silicon crystal. Since then, the SPM technique has been widely used, producing images of atoms to nanometric structures on the surface of various materials. In precision manufacturing industries related to technologies such as microelectronics, solar energy, medical devices, automotive, aerospace and others, probe scanning microscopes allow users to monitor their products throughout the manufacturing process to improve productivity, reduce costs and improve product quality. The primary market for probe scanning microscopes is in the semiconductor and electronics sector, where they are routinely used for product inspection and fault analysis. They are also widely used in universities, research centers, and scientific centers around the world (Neves, B.R.A. et AL .. Ceramics, vol.44, n.290, 1998).

SPM stands for a family of techniques that differ from each other by the type of probe-material interaction that is monitored in the process. Some examples are: AFM (atomic force microscopy); EFM {electrical force microscopy; Magnetic force microscopy (MFM); scanning tunneling microscopy (STM); scanning near-field optical microscopy (SNOM) .Many of these techniques can offer, in addition to information from microscopy, spectroscopic information, being named by replacing M with S (for example: STS instead of STM), although they provide very different information such as morphology, electrical conductivity, hardness, and magnetic and optical properties. SPM family techniques are based on the same principle of operation.All microscope operating SPM techniques have at least one mechanical probe with the specific property required for the technique (electrical, magnetic, optical, etc.), a piezoelectric positioner able to move the probe with subnanometric precision, probe-ammonia monitoring mechanism oyster, preliminary probe positioning system on the sample, specific technique effect measurement system (s) used, and a computer that controls the entire system (Neves, BRA et AL .. Ceramics. vol.44, no. 290, 1998).

Microscopy and near field optical spectroscopy (SNOM, SNOM or NFOM) are a hybrid of probe scanning microscopy with optical microscopy and spectroscopy (Synge, EH Phil. Mag. V.6, p.356, 1928). The probe, in this case, is the agent responsible for locating the optical signal primarily in a nanometric region, thus generating optical microscopy and spectroscopy with higher spatial resolution than given by the diffraction limit of light. In one of its possible designs, this probe is formed of a very thin optical fiber that carries visible light to the surface of the sample. As the excited area is of the order of the opening of the optical fiber, with the current technology it is possible to study the optical properties of materials with spatial resolution of the order of 50 nm (Neves et al. Ceramics, vol.44, n.290, 1998 ). The term "near field" comes from the fact that the electromagnetic field does not propagate through holes smaller than the length of light due to the diffraction effect. However, at the opening of the probe there is a very close "field" intense, which can be used for microscopy and spectroscopy using the SPM technique, which is responsible for bringing the probe close enough to the surface (around 1 nm) so that the near field can be felt by the surface.

Near field optical microscopy (SNOM) improves the spatial resolution of conventional optics, this improvement depending on the size of the probe used in the process. With current technology, the SNOM technique can achieve a spatial resolution of the order of 10 nm, which is well below the resolution of a tunnel or atomic force microscope. However, it brings the advantages of the SPM hybrid with optical microscopy and spectroscopy, which are diverse. Among the main parameters that may be of interest for the investigation of a nanoscale structure, in addition to shape and size, are its chemical composition, molecular structure as well as its dynamic and electronic properties, largely measured by various optical properties of the nanoscale. materials.

Record resolution of 12nm was achieved not with the use of an optical fiber as a probe, but with the resonant effect of propagating light with the plasmon of a metal probe (Hartschuh et al., Phys. Rev. Lett. 90, 2003). . As an example, the system may use the usual confocal configuration of an inverted optical microscope, but the light being condensed in a small 12nm region due to the plasma resonance of a nanometer-sized metal probe placed in the region to be studied by a system. from SPM. This effect enables effective measurements of low intensity signals, such as the Raman scattering on the nanometer scale, being called in this case TERS (T / p Enhanced Raman Spectroscopy, Chem. Phys. Lett. 335, 369-374, (2001)). analogy to the known SERS {Suriac Enhanced Raman Spectroscopy, see Chem. Phys. Lett. 126, 163, (1974)), which uses metal particles dispersed on a surface to increase the Raman signal of molecules. The difference is that in the TERS configuration the position of this metal particle is controlled by an SPM type system. Nanoscopic spectroscopic images can be generated, and observation of Raman scattering and light emission located in nanometric regions have been obtained using this technique (Maciel et al. Nature Materials 7, 878 (2008)). Raman spectroscopy has wide application in the pharmaceutical, chemical and petroleum industries, with TERS having great potential to generate technological advances in these and other fields of activity.

The SNOM principle is relatively simple. The sample to be characterized is scanned by an optical fiber or a metal probe having an opening of the order of ten or tens of nanometers in diameter at its end. Through the fiber passes visible light, which will interact or interacted with the sample, going from it to a detector. With the metal probe, the propagating light is condensed in a nanometric region by the resonance effect with the metal surface plasmons. Another possibility is to cover an optical fiber with a metal film, thus taking advantage of the two technologies described above. In all cases, the optical signal strength detected at each point of the probe scan constitutes a data set that will reproduce an image of the sample surface, with spatial resolution determined by the probe end size currently limited to 10nm (N. Anderson, A. Hartschuh and L. Novotny, J. Am. Chem. Soc. 127, 2533 (2005)).

The limitation imposed by the near field effect is that the distance between the probe and the sample has to be a few nanometers. Therefore, the probe is trapped in a system capable of detecting the interaction of the probe with the surface so that the probe is close enough to that surface so that van der Waals interactions can be detected. An example of a system capable of sensing this interaction is the so-called 'tunning forK' ((5), Figure 2), which is a tuning fork-like device with well-defined vibration frequency (K. Karrai and RD Grober, Appl. Lett. 66, 1842-1844 (1995)) When the probe attached to this device approaches the surface to be analyzed, the probe-surface interaction alters the pitch vibration frequency, and this variation is There are also other methods of measuring probe-surface interaction, such as the reflection of a laser at the top of the probe, most common in AFM systems (Neves, BRA et al .. Ceramics, vol.44, n Finally, with the SNOM optical images are obtained from a sample which, for the purpose of data analysis, can be compared with topographic images, eg acquired simultaneously by the atomic force method (LG Cançado, A. Hartschuh and L. Novotny, J. Raman Spectrosc. 40, 1420-1426 (2009)).

There are, however, several limitations to the efficiency of an SNOM with respect to optical signal efficiency, both in the use of fiber optics (metallized or not) and metal probes.

In the case of near field optical microscopy operating using a fiber optic probe, one of the major limiters is the amount of light sent and / or collected that passes through this probe. The transmitted power decreases exponentially with the reduction in fiber diameter. For this reason, an accuracy of about 50 to 100 nm is usually generated. In addition to the problem of low resolution, the use of this type of probe is limited to the study of intense signals, such as photoluminescence. It is, however, unsuitable for the study of weaker signals, such as Raman spectroscopy, where the signal is on the order of a thousand times lower than luminescence signals, making Raman spectroscopy coupled with nanometric spatial resolution unviable.

In the case of the operation of near field microscopy using a metal probe, the material under study is illuminated by an optical microscope. A nanometer-sized metal tip is approached from the sample by the SPM system, condensing the electric field of light around itself. In this technique, the resolution is in the order of 10 nm. This resolution is limited by the manufacturing technology of the metal probes, which will hardly evolve below 10 nm due to the metallurgical properties of the material used for their manufacture.

Improving the resolution of metal probes is not the only or the worst challenge: in all scanning probe microscopy the quality of the results is strongly related to the quality of the probe used. This fact has been the major limitation for the large-scale use of SNOM with metal probe. In fact, it is noted that most of the articles published in the field of near-field optical microscopy are related to the production and characterization of scanning devices / probes (P. Lambelet et al., Applied Optics 37 (31), 7289-7292 (1998); B. Ren, G. Picardi and B. Pettinger, Rev. Sci. Instrum. 75, 837 (2004); P. Bharadwaj, B. Deutsch and Lukas Novotny, Adv. Opt. Photon. 1, 438-483 (2009)). What aggravates the probe quality problem for SNOM is that the coupling of these probes with the propagating light, which is responsible for the condensation of the field around the probe, is not simple, depending on the quality of the probe and the light-probe geometry. One of the reasons that the coupling of the metal probe with light is inefficient is that, as with any antenna, the electric field of light polarization must be in the direction of the dipole axis, ideally when leaving the antenna.

However, in the case of near field microscopy and spectroscopy with the ends of the "zero-dimensional" probes, the nanoanthene axis is perpendicular to the surface. Thus, to illuminate the surface one has to use a direction of light propagation which, consequently, will have its polarized electric field normal to the surface, that is, perpendicular to the axis of the antenna. For the implementation of this geometry, the so-called "doughnut mode", which generates a radially polarized propagating light, has been used (Quabis, S. et al. App. Phys. B: Laser and Optics, v.81, n.5 , p.597-600, 2005). This light, when focused by the microscope objective, generates a polarization component perpendicular to the focus surface of the lens, ie parallel to the nanoanthene axis.

In all processes used in probe scanning microscopy and spectroscopy, a probe is used that scans a surface for topography, electrical, magnetic, elastic, optical, and other information. For the best possible spatial resolution in this process of collecting surface information or objects on it (eg adsorbed molecules), this probe should have the end that contacts the sample as small as possible, ideally a point , representing, for the surface, a "zero" dimension material. Ideally, this point or "zero-dimensional" probe is effectively a single atom at the end of the probe as a whole, thus generating resolution images. subatomic, common in probe scan tuneing microscopy (STM) experiments.

Therefore, a fiber optic device / probe with at least one one-dimensional element is proposed, where the surface-probe interaction region via near field is substantially "one-dimensional". In this case, we have the field near a one-dimensional element that scans a surface, rather than the field near the entire end of the optical fiber. This determines the importance of proposing a "One-Dimensional Element Fiber Optic Device (Figure 1) for near field optical microscopy and spectroscopy".

By utilizing one-dimensional element resolution, the system solves the largest limiter of the state of the art, which is to obtain nanometer-order resolutions using a thinly tuned optical fiber, 100 nm in diameter or more. If on the one hand the one-dimensional system loses spatial resolution along one of its dimensions (Figure 1), when compared to one end, mechanical strength and spatial resolution on the other dimension are gained (Figure 1), which can be reduced below current technological limit of 10 nm.

Several patent applications describe in detail microscopes for performing SNOM, as found in JP2011122896A, entitled "Near-field optical microscope", and US6194711 B1, entitled "Scanning near-field optical microscope".

Other documents focus specifically on the properties of the SNOM probe, addressing its operation and, in some cases, its manufacture. This can be seen in US4917462 entitled "Near field scanning optical microscopy"; US4604520, entitled "Optical near-field scanning microscope"; US20100032719A1, entitled "Probes for scanning probe microscopy"; US007735147B2 entitled "Probe system comprising an electric-field-aligned probe tip and method"; US20030094035A1 entitled "Carbon nanotube probe tip grown on a small probe"; US2004168527A1, entitled "Coated nanotube surface signal probe"; US20050083826A1 entitled "Optical fiber probe using an electrical potential difference and an optical recorder using the same "; US20080000293A1, titled" Spm cantilever and manufacturing method thereof; WO2009 / 085184A1, entitled "Protected metallic tip or metallized scanning probe microscopy tip for optical applications"). In US005831743A entitled Optical probes, for example, a new dual-angle probe design is proposed. However, the objective is to measure light fully reflected at the interface, unlike that proposed in the present invention.

There are also several documents claiming the use of one-dimensional materials for applications such as SPM probes, as found in US007735147B2 entitled "Probe system comprising an electric-field-aligned probe tip and method for fabricating the same"; US20030094035A1 entitled "Carbon nanotube probe tip grown on a small probe"; US2004168527A1 entitled "Coated nanotube surface signal probe"; and US20080000293A1, entitled "SPM Cantilever and Manufacturing Method Thereof". However, the documents deal with the device where the one-dimensional material is arranged perpendicular to the surface under study, so that the interaction with the surface is made with its essentially "zero-dimensional" end.

It is then found that no document describing or claiming a fiber optic device coupled to a one-dimensional element for near field optical microscopy and spectroscopy, as proposed in this invention.

In all cases described in the literature, the deficiency is in the development of effective, robust probes with spatial resolution of less than tens of nanometers. The requirements are mechanical rigidity, optical efficiency and spatial resolution all together. The system must be rigid to serve also as a probe for atomic force microscopy, and must be coupled with the electromagnetic field of the incident light, generating an increase of the local near field. This increase should be located in a region of space that currently, using metal probes or metalized optical fibers, is in the range of tens of nanometers. The treated matter (Figure 1), in turn, can solve the aforementioned deficiencies, since it has adequate dimensions for robust scanning, and the coupling of the one-dimensional element with the electric light field propagating through the fiber ensures near field resolution. in one dimension.

DESCRIPTION OF THE FIGURES

Figure 1 illustrates the device formed by an optical fiber (1) and a one-dimensional element (3) located at the end (2) of (1).

Figure 2 illustrates the device (Figure 1) coupled to a probe-surface interaction sensing system, or a tunning fork (5). It is important to note that the optical fiber (1) can be as long as necessary, with only the end (1) shown in the figure attached to the tunning fork (5).

DETAILED DESCRIPTION OF THE INVENTION The treated material (Figure 1) comprises a device formed by an optical fiber (1) and a one-dimensional element (3), which is coupled to the end (2) of the fiber (1).

The one-dimensional element (3) is preferably a carbon nanotube or a bundle of carbon nanotubes, an Au or Ag or Cu nanowire or an Au or Ag or Cu nanobastane.

This device (Figure 1) is preferably used in microscopy and spectroscopy equipment and techniques, both by probe scanning. The proposed device (Figure 1) has adequate dimensions for the propagation of light by the probe (compatible with light wavelength) and the coupling of the electric field of light propagating by the optical fiber with the one-dimensional element ensures the system a high resolution of near field in one dimension (typically but not limiting values from 1 to 20 nanometers).

The treated matter (Figure 1) can be coupled to a probe-surface interaction sensing system, preferably a tuning fork or tunning fork, which will preferably be coupled to a SNOM system.

Optical fibers can be fabricated using the method proposed by Puygranier (Puygranier, BAF; Dawson, P .; v.85, p.235 (2000)) and one-dimensional element deposition can be performed by chemical method. or by nano-manipulation

The subject matter can be better understood by the following non-limiting example.

Example - Process of manufacturing the carbon nanotube fiber optic device.

The cylinder indicated by (1) in Figure 1 represents the end of an optical fiber, tuned to 300 nm in diameter. In the final part (2) it contained a one-dimensional metallic material (3) that came into contact with the surface and effectively served as a field probe near the light propagating through the fiber. The resolution of the near field effect was given by the diameter of the one-dimensional material, a single-walled carbon nanotube, 0.8 nm in diameter. The near field of light from the optical fiber was condensed around the one-dimensional system from 300 nm to 1 nm in terms of resolution; either for near field optical microscopy or near field optical spectroscopy, considering a device scan along the dimension perpendicular to the carbon nanotube axis.

The carbon nanotube deposition process at the end of the optical fiber consisted of the commercial acquisition of an aqueous solution of isolated carbon nanotubes, selected by chirality. Nanotubes of the type (6,5) with optical transition energy compatible with a photon of wavelength (λ) equal to 568 nm were chosen. Another type of nanotube can also be selected as long as its optical excitation is well known or determined. Drops of the isolated nanotube solution were deposited on the tip of the optical fiber, and the fiber was attached to a spinning system, so that the deposition occurred through the so-called spin coating process. This process generated a homogeneous dispersion of material in the probe surface. At each 5-drop deposition, the fiber was removed and the Raman spectrum from the region where the nanotube was deposited was measured. The optical fiber was then fixed to a probe-surface interaction sensing system, preferably a tuning fork or tuning fork, and then a laser beam of SNOM via optical fiber was used as excitation means for SNOM. same wavelength (λ = 568 nm). AFM images were obtained with approximately 300nm resolution, while SNOM images were obtained with approximately 1nm resolution.

Claims

1. One-dimensional fiber optic device for near-field optical microscopy and spectroscopy, characterized in that it comprises a cylindrical optical fiber body (1) with a one-dimensional system (3) coupled to its end (2), preferably composed of a nanotube carbon or a beam of carbon nanotubes, or by an Au, Ag or Cu nanowire or nanobastane.

Unidimensional element optical fiber device for near field optical microscopy and spectroscopy according to claim 1, characterized in that the fiber diameter dimensions varying from λ / 10 to λ, where λ is the wavelength of light in the process. SNOM, usually ranging from 200nm to 1 micron; and dimension of the one-dimensional element (3) typically from 0.8 nm to 20 nm in diameter.

Massive one-dimensional end device for near field optical microscopy and spectroscopy according to claims 1 and 2, characterized in that it can be used in near field optical microscopy and spectroscopy; preferably SNOM.

Massive one-dimensional end device for near field optical microscopy and spectroscopy according to any of claims 1 to 3, characterized in that it comprises means of assessing the topography and optical properties of a surface.