BRPI1107185B1 - hollow device with undimensional end for near-field microscopy and optical spectroscopy - Google Patents

Abstract

LEAKED DEVICE WITH UNIDIMENSIONAL END FOR MICROSCOPY AND OPTICAL FIELD SPECTROSCOPY NEARBY. The treated material (Figure 1) is described by a hollow device that contains at least one one-dimensional element (4) at its ends (3); for near-field microscopy and optical spectroscopy. This device is applied, preferably, in equipment and techniques of microscopy and spectroscopy, both by probe scanning. The proposed device (Figure 1) has adequate dimensions for coupling with the electric field of light that propagates in the direction preferably normal to the surface to be analyzed. The treated material (Figure 1) is robust during the surface analysis process, being able to analyze structures with dimensions smaller than lOnm with high resolution.

Description

The treated material (Figure 1) is described by a hollow device that contains at least one one-dimensional element (4) at its ends (3); for near-field microscopy and optical spectroscopy. This device is applied, preferably, in equipment and techniques of microscopy and spectroscopy, both by probe scanning. The proposed device (Figure 1) presents suitable dimensions for coupling with the electric field of light that preferably propagates in the normal direction to the surface to be analyzed. The treated material (Figure 1) is robust during the surface analysis process, being able to analyze structures with dimensions less than 10 nm with high resolution.

In the early 1980s, Probe Scanning Microscopy (from English, Scanning Probe Microscopyou SPM) surprised the world with the first atomic resolution images of the surface of a silicon crystal. Since then, the SPM technique has been used widely, producing images from 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 main 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 worldwide (Neves, B.R.A. et AL .. Cerâmica, vol.44, n.290, 1998).

The acronym SPM represents 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 or atomic force microscopy; EFM (electrical force microscopy or electric force microscopy; MFM (magnetic force microscopy or magnetic force microscopy; STM (scanning tunneling microscopy or scanning tunneling microscopy); SNOM (scanning near-field optical microscopy. Several of these techniques can offer, in addition to microscopy information, spectroscopic information, being named by changing M to S in the acronym (example: STS instead of STM). to provide information that is quite different from each other, such as morphology, electrical conductivity, hardness and magnetic and optical properties, all techniques in the SPM family are based on the same operating principle. Every microscope that operates SPM techniques has at least one mechanical probe with the specific property required for technique (electrical, magnetic, optical property, etc.), a piezo positioner electric device capable of moving the probe with subnanometric precision, monitoring mechanism of the probe interaction, preliminary positioning system of the probe on the sample, system (s) for measuring the effect of the specific technique used, and a computer that controls the entire system (Neves , BRA et AL .. Ceramics. vol.44, n.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, E.H. 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 microscopy and optical spectroscopy with spatial resolution higher than that given by the diffraction limit of light. In one of its possible conceptions, this probe is formed by a very thin optical fiber that carries visible light to the sample surface. 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. Cerâmica, 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 the light, due to the effect of diffraction. However, at the opening of the probe there is a very intense “near field”, which can be used for microscopy and spectroscopy with the use of the SPM technique, which is responsible for bringing the probe close to the surface enough (in the order of 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 in the order of 10 nm, which is well below the resolution of an atomic force or tunneling microscope. However, it brings the advantages of the SPM hybrid with microscopy and optical spectroscopy, which are diverse. Among the main parameters that may be of interest for the investigation of a structure on the nanoscale, in addition to shape and size, are its chemical composition, molecular structure, as well as its dynamic and electronic properties, widely measured by several optical properties of materials.

The record resolution of 12nm was obtained not with the use of an optical fiber as a probe, but with the resonance effect of the propagating light with the plasmons of a metallic probe (Hartschuh et al., Phys. Rev. Lett.90, 2003) . As an example, the system can use the usual confocal configuration of an inverted optical microscope, but the light being condensed in a small region of 12nm due to the resonance with the plasma of a metallic probe of nanometric dimension placed in the region to be studied by a system of SPM. This effect allows effective measurements of low intensity signals, such as Raman scattering on the nanoscale, being called in this case TERS (Tip Enhanced Raman Spectroscopy, see Chem. Phys. Lett. 335, 369374, (2001)), in analogy to the known SERS (Surface Enhanced Raman Spectroscopy, see Chem. Phys. Lett. 126, 163, (1974)), which uses metallic particles dispersed on a surface to increase the Raman signal of molecules. The difference is that, in the TERS configuration, the position of this metallic particle is controlled by an SPM type system. Spectroscopic images with nanometric resolution can be generated, and the observation of Raman scattering and light emission located in nanometric regions has been obtained using this technique (Maciel et al. Nature Materials 7, 878 (2008)). Raman spectroscopy has wide application in the pharmaceutical, chemical and oil industries, with TERS having great potential for generating technological advances in these and other branches of activity.

The SNOM principle is relatively simple. The sample to be characterized is scanned by an optical fiber or by a metal probe, which has an opening of the order of ten or tens of nanometers in diameter at its end. Visible light passes through the fiber, which will interact or interact 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 metallic film, thus taking advantage of the advantages of the two technologies described above. In all cases, the intensity of the optical signal detected at each point of the probe scan constitutes a set of data that will reproduce an image of the sample surface, with spatial resolution determined by the size of the probe tip (currently limited to 10nm, see 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. For this reason, the probe is trapped in a system capable of detecting the interaction of the probe with the surface, so that the probe approaches that surface enough 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 device similar to a tuning fork, with a well-defined vibration frequency (K. Karrai and RD Grober, Appl. Phys. Lett.66, 1842-1844, (1995)). When the probe, attached to this device, approaches the surface to be analyzed, the probe-surface interaction alters the frequency of the tuning fork, and this variation is detected by the system electronics. There are also other methods of measuring the probe-surface interaction, such as by the reflection of a laser on the top of the probe, more common in AFM systems (Neves, B.R.A. et AL .. Cerâmica, vol.44, n.290, 1998). Finally, with SNOM, optical images of a sample are obtained which, for the purposes of data analysis, can be compared with topographic images, for example, acquired simultaneously by the atomic force method (LG Cancado, A. Hartschuh and L. Novotny , J. Raman Spectrosc. 40, 1420-1426 (2009)). However, there are several limitations to the efficiency of an SNOM with regard to the efficiency of the optical signal, both in the use of fiber optics (metallized or not), as well as metallic probes.

In the case of the operation of near-field optical microscopy using a fiber-optic probe, one of the biggest limitations is the amount of light sent and / or collected that passes through this probe. The transmitted power decays exponentially with the reduction of the fiber diameter. For this reason, an accuracy of 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 a 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 metallic tip of nanometric dimensions is approached by the SPM system, condensing the electric field of light around it. In this technique, the resolution reaches the order of 10 nm. This resolution is limited by the manufacturing technology of the metal probes, which will hardly evolve to values below 10 nm due to the metallurgical properties of the material used for its manufacture.

Improving the resolution of the 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 the SNOM with a metal probe. In fact, it is noted that a large part of the articles published in the field of near-field optical microscopy is 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. Sei. 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, an effect 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 metallic probe with the light is not very efficient is that, as in any antenna, the electric field of polarization of the light must be in the direction of the axis of the dipole, ideally in the antenna.

However, in the case of near-field microscopy and spectroscopy with the ends of the “zerodimensional” probes, the nano-antenna axis is perpendicular to the surface. Thus, to illuminate the surface, one has to use a light propagation direction that, consequently, will have its normal polarized electric field to the surface, that is, perpendicular to the antenna axis. For the implementation of this geometry, the so-called “donut mode”, which generates a propagating light with radial polarization, 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 surface of the objective focus, that is, parallel to the axis of the nanoantenna.

In all the processes used in probe scanning microscopy and spectroscopy, a probe probe is used that scans a surface obtaining topography, electrical, magnetic, elastic, optical and other information. To obtain the best possible spatial resolution in this process of collecting information from the surface or from objects on it (for example, adsorbed molecules), this probe should have the tip that comes in contact with the sample as small as possible, ideally a point , representing, for the surface, a material of “zero” dimension. Ideally, this point or “zerodimensional” probe is effectively a single atom at the end of the probe as a whole, thus generating images with subatomic resolution, common in probe scanning tunneling microscopy (STM) experiments.

Then, a hollow device is proposed (Figure 1), comprised of a probe where the region of surface-probe interaction is “one-dimensional”. In this case, you have a one-dimensional element that sweeps a surface, instead of a point. The probe is defined as “having a one-dimensional end”, considering that the end that approaches the surface has one of its dimensions being as small as possible, and the other, as elongated as necessary (Figure 1). This determines the importance of proposing a "Hollow device with one-dimensional end (Figure 1) for microscopy and near-field optical spectroscopy".

If, on the one hand, the one-dimensional system loses spatial resolution along one of its dimensions (Figure 1), when compared to a tip, on the other hand, two important aspects are gained when applied in microscopy and optical spectroscopy by probe scanning: ( 1) the coupling with the excitation light is increased, thus increasing the efficiency of the optical effect; (2) mechanical strength is gained so that the spatial resolution in the other dimension (Figure 1) can be reduced below the current technological limit of 10 nm.

Several patent applications describe microscopes in detail for carrying out SNOM, as verified in document JP2011122896A, entitled “Near-field optical microscope”, and in document US6194711B1, entitled “Scanning near-field optical microscope”.

Other documents specifically focus on the properties of the SNOM probe, addressing its operation and, in some cases, its manufacture. This can be seen in documents US4917462, entitled “Near field scanning optical microscopy”; US4604520, entitled “Optical nearfield 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, entitled “Spm cantilever and manufacturing method thereof’; W02009 / 085184A1, entitled “Protected metallic tip or metallized scanning probe microscopy tip for optical applications”). In the patent US005831743A, entitled “Optical probes”, for example, a new probe design with a double angle is proposed. However, the objective is the measurement of light fully reflected in the interface, differently from what was proposed in the present invention.

There are also several documents that claim the use of one-dimensional materials for applications such as SPM probes, as verified in documents 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 unidimensional material is arranged perpendicular to the surface under study, so that the interaction with the surface is made with its end, essentially “zerodimensional”, as usual in the state of the art.

It can be seen, then, that no document describes or claims a hollow device with one-dimensional end (Figure 1) for near-field microscopy and optical spectroscopy, as proposed in this invention.

In all cases described in the literature, the deficiency lies in the development of effective, robust probes, with spatial resolution below tens of nanometers. The requirements are mechanical stiffness, optical efficiency and spatial resolution, combined. The system must be rigid so that it can also serve as a probe for atomic force microscopy, and must present a coupling with the electromagnetic field of the incident light, generating an increase in the local field nearby. This increase must be located in a region of space that, currently, using metallic probes or metallized optical fibers, is in the range of tens of nanometers.

The treated material (Figure 1), in turn, can solve the above deficiencies, since the one-dimensional element at the end of the probe may have an electrical dipole with direction (x in Figure 2) and dimensions suitable for coupling with the field propagating light in the normal direction to the surface (z, Figure 2). The unidimensioanl element at the end of the probe can have a dimension less than 10nm in the reduced dimension (y in Figure 2), also improving the resolution in the NSOM process.

DESCRIPTION OF THE FIGURES

Figure 1 illustrates the one-dimensional hollow device that has a substantially cylindrical body (1), so that it has an extension represented by two faceted regions (2) substantially pyramidal and separated from each other by a hollow region (5); where at the ends (3) of the same, at least one one-dimensional element (4) is coupled.

Figure 2 illustrates the device (Figure 1) coupled to a tuning fork or tuning fork (7), close to a substantially flat surface (6), to be analyzed.

Figure 3 illustrates the bottom view of the device (Figure 1), where the one-dimensional element (4) has a reduced dimension (8) and an elongated dimension (9).

DETAILED DESCRIPTION OF THE INVENTION

The treated material (Figure 1) comprises a one-dimensional cast device for microscopy and near-field optical spectroscopy, which has a substantially cylindrical body (1), so that it has an extension represented by two faceted regions (2) substantially pyramidal and separated each other by a hollow region (5); where at the ends (3) of the same, at least one one-dimensional element (4) is coupled.

The substantially cylindrical body (1), as well as its extensions (2), consists preferably of Si, W, Au, Ag or Cu, or combined with each other.

The one-dimensional element (4) is a system that has an elongated dimension (x-axis in Figure 1) and two reduced dimensions (y and z in Figure 1). It is represented, preferably by a carbon nanotube or a bundle of carbon nanotubes, or by a nanowire or nano-stick, both from Au, Ag or Cu.

This device (Figure 1) is used, preferably, in microscopy and spectroscopy equipment and techniques, both by probe scanning. The proposed device (Figure 1) has adequate dimensions for coupling with the electric field of light, which preferably propagates in the normal direction to the surface to be analyzed.

The treated material (Figure 1) can be coupled to a surface-probe interaction sensing system, preferably a tuning fork or tunning fork (7 in Figure 2), which will be coupled to an SNOM system.

The present invention (Figure 1) can make different angles with the surface (6 in Figure 2), by rotating the one-dimensional element along the xz, xy or yz planes. In fact, another important aspect that can be modulated is the angle that the probe's one-dimensional element makes with the surface. This angle allows modulating the coupling of the light with the probe and recovering the zerodimensional precision of the scan. The probe-surface angle can also be obtained in several ways: the one-dimensional element is fixed to the probe with an angle; the probe as a whole is fixed to the probe-surface sensing system with an angle; the probe can be fixed in line with the sensing system, and it has an angle in relation to the surface, and others. Anyway, they are non-limiting descriptions. The important thing is the angle between the one-dimensional end of the probe and the surface.

The hollow device with a one-dimensional element for microscopy and near-field optical spectroscopy (Figure 1) is characterized by understanding means of evaluating the topography and optical properties of a surface.

The treated matter can be better understood through the following non-limiting example.

Example Manufacturing process of the cast device with coupled one-dimensional element.

A Si crystal (wafer, generally used in the semiconductor industry) was broken manually in order to present a pointed region. Then, this pointed region was attacked by an ion beam (FIB), in order to generate an end with the structure of pyramidal rods (Figure 1). After the construction of the rod system, transition metal nanoparticles (Fe or Ni or Cu or combination of these) were deposited in the system by evaporation, followed by the growth of carbon nanotubes by the chemical vapor deposition (CVD) method. The alignment of nanotubes grown connecting the two rods was obtained with the presence of an electric field of appropriate direction within the CVD system. After this process, the device was produced (Figure 1), which was then fixed to a 5 “tunning fork” with epoxy resin, to perform SNOM measurements.

AFM and NSOM images were obtained with resolutions compatible with the material dimensions.

Claims (4)

1. Hollow device with one-dimensional end for near-field microscopy and optical spectroscopy, characterized by comprising a cylindrical body (1), composed of Si, W, Au, Ag or Cu, or combined with each other, so that it has an extension represented by two faceted regions (2) pyramidal and separated from each other by a hollow region (5); where at the ends (3) of them there is coupled at least a one-dimensional element (4), a carbon nanotube or a bundle of carbon nanotubes, or a nanowire or a nanobond, composed of Au, Ag or Cu; and be coupled to a system for sensing the probe-surface interaction, for example a tuning fork or tunning fork, (7), which can (4) rotate along the xz, xy and yz planes in relation to the flat (6) surface. 2. Hollow device with one-dimensional element for near-field microscopy and optical spectroscopy, according to claim 1, characterized by the dimensions of the one-dimensional element (4) that can vary from 1 angstrom to 50 nm in its reduced dimension (8), and from 1 nm to 500 nm in its elongated dimension (9). 3. Hollow device with one-dimensional element for near-field microscopy and optical spectroscopy, according to claims 1 to 2, characterized in that it can be used in near-field microscopy and optical spectroscopy and SNOM. 4. Hollow device with one-dimensional element for near-field microscopy and optical spectroscopy, according to claims 1 to 3, characterized by comprising means of assessing the topography and optical properties of a surface.

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