WO2018089022A1

WO2018089022A1 - Enhancing optical signals with probe tips optimized for chemical potential and optical characteristics

Info

Publication number: WO2018089022A1
Application number: PCT/US2016/061708
Authority: WO
Inventors: Aaron Lewis; Galina Fish; Rina DEKHTER; Sophia Kokotov; Yossi BAR-DAVID
Original assignee: Aaron Lewis
Priority date: 2016-11-11
Filing date: 2016-11-11
Publication date: 2018-05-17

Abstract

Probes with novel material properties and geometric confined curved tip shapes have been developed as part of cantilevered probes for scanning apertureless near-field microscopy. They produce enhanced resolution for various modalities of combined operation with optical phenomena both linear phenomena such as Raman spectroscopy, absorption, fluorescence etc and non-linear microscopies. This novel probe operates as a sensitive AFM probe with combined capabilities for enhancement of the various modalities noted above. The probes are configured to be optimized for their combined optical properties and their material properties to permit both enhanced fields and quantum state formation with the close approach of the tip to the sample. The local enhancement increases the lateral (X, Y) and axial (Z) resolution of these optical processes without the need for an apertured probe for near-field-field effects thus providing apertureless near-field optical imaging of various modalities.

Description

ENHANCING OPTICAL SIGNALS WITH PROBE TIPS OPTIMIZED FOR CHEMICAL POTENTIAL AND OPTICAL CHARACTERISTICS

BACKGROUND OF THE INVENTION

FIELD OF THE INVENTION

[0001] This invention relates to scanning probe microscopy (SPM); tip enhanced Raman spectroscopy (TERS), apertureless near-field scanning optical microscopy, confocal microscopy, absorption and fluorescence microscopy and other linear and non-linear optical imaging methods.

DESCRIPTION OF THE BACKGROUND ART

[0002] There has been in the past decades a great emphasis on improving the optical resolution of various methods of optical imaging. An example of one such method is Raman microscopy which is a non-destructive spectroscopic technique for chemical materia! characterization and identification widely used in research and industry. This technique is based on the inelastic scattering of the incident laser light by the sample. Frequency shift of the scattered light relative to the incident excitation wavelength gives an individual spectroscopic signature for materials and provides chemical characterization of chemical compounds in terms of their chemical structure, stresses in the material and electronic alterations.

[0003] Optical resolution of the confocal Raman microscope is limited by optical diffraction. Normally lateral resolution of confocal Raman microscopy is 250 nm and axial resolution is >1 .0 um. Due to this limitation characterization of materials on surfaces such as thin films and molecular species is problematic. Application of Raman microscopy for nano-science and nano-technology requires improvement of the lateral and axial resolution.

[0004] In many ways the history of resolution improvement in Raman imaging tracks other methods of optical imaging, in Raman several methods have been suggested to improve lateral Raman resolution and to overcome optical diffraction limit.

[0005] Near-field Raman spectroscopy with an apertured probe: Laser light is delivered through an apertured metal coated tapered optical fiber. The aperture size can be less than 100nm. The laser light coming out from the nanometric aperture excites the Raman signal in the cylindrical volume (diameter and height of this cylinder correspond to the aperture diameter). Thus, the Raman lateral resolution is defined by aperture diameter. [See J.Grausem et al, "Near-field Raman

spectroscopy" Journal of Raman spectroscopy, Volume 30, Issue 9 _^ pages 833- 840, September 1999].

[0006] The main disadvantage of this technique is low optica! transmission throughput of the apertured probe resulting in an extremely weak Raman signal excited. Raman imaging with a near-field aperture probe requires extremely long acquisition times. This drawback makes this technique not practical for Raman characterization.

[0007] Apertureiess near-field Raman spectroscopy or Tip Enhanced Raman

Spectroscopy (TERS): This method uses meta!ized probes and was developed as an integrated SPM/Raman technique for enhancement of the Raman signal at the nanometric size tip. This method when it works results improvement of the Raman resolution. This technique uses metal or metal coated SP probes which are approached to the sample surface. The intensify of the electromagnetic field can be enhanced at the tip end and the Raman signal should be generated mostly near the probe apex. The Raman resolution can be associated with the tip size, excitation wavelength, light polarization and experimental geometry. There are three main optical configurations of TERS: top illumination, side illumination and bottom illumination. Top and side illumination are used for opaque and half transparent samples. Bottom illumination is used for transparent samples. (See Shen and Sun, U.S. Pat, No, 8,643,012 and "Near-field scanning Raman microscopy using

apertureiess probes", J, Raman Spectrosc, 34, 668-676 (2003)). The main drawback is that there are no guiding principles that define how to make such a probe with a high degree of success and lasting performance.

[0008] This most problematic issue of the TERS technique results from that there is no defined understanding of the TERS process and thus the probes are not reproducibly fabricated and there is little to no understanding of a defined way to achieve success, in addition once a signal is received the lifetime of such a signal is short. Thus TERS is far from a developed technique.

[0009] Also most of the metalized TERS probes seem most effective in enhancing the Raman intensity in what has been called gap mode when a noble metal probe in brought in close proximity to a noble metal surface by a feedback mechanism called scanning tunneling microscopy or STM. [See E.Sherement et al Surface-enhanced Raman scattering and gap-mode tip-enhanced Raman scattering investigations of phthalocyanine molecules on gold nanostructured substrates", J. Vac. Sci. Technol.B, Vol.32, No.4, 2014]. Our analysis that led to this patent is that the preference of the application of STM comes from simply the virtue of its ability to achieve ultraciose approach of the tip to the surface. Of course a severe limitation of such an approach is that only samples on conductive substrates can be investigated and even this has less than a high probability of working.

[0010] An alternate approach that has also been considered is to stick a dielectric microsphere at the tip of an AFM probe. Even though this is a challenging task there have been reports that such a dielectric microsphere can focus the exciting laser light into what has been called a photonic nanojet with sub- diffraction limited dimensions. Nano-jet dimensions depend on the excitation wavelength, diameter and refractive index of the microsphere. In addition, to the difficulty noted above the glue which is used for the mounting of the microsphere can leave the contaminations and this can cause Raman artifacts [See.Z.Shen et al. Patent "Near-field Raman spectroscopy" US 20100245816 A1].

[0011] Other ways to place the microspheres on the sample surface in addition to the method mentioned above are:

[0012] Dispersion of the microspheres on the sample surface. This method is not controlled, not reversible and does not allow the mapping. [See Yinzhou Yan et al "Self- assembled dielectric microsphere array enhanced Raman scattering for large-area and ultra- long working distance con focal detection" OPTICS EXPRESS 25854, Vol.23, No.20, Oct.2015].

[0013] Another method is to use optical tweezers to hold the microsphere on the sample surface. This technique can work only in liquid and thus is highly limited and optically not optimal. [See Johnson Kasim et al, "Near-field Raman imaging using optically trapped dielectric microsphere" Optics Express Vol. 18, Issue 11, pp. 7976-7984, 2008].

[0014] A third direction which is related to a microsphere is the idea of using a high index solid immersion lens that also could permit high resolution but has little capability of providing AFM topography. [See E.Ostertag"Extension of solid immersion lens technology to super-resolution Raman microscopy" Nanospectroscopy 2014; 1: 1-11].

SUMMARY OF THE INVENTION

[0016] It is an object of the invention to provide a new geometric confined curved shape integrally produced cantilevered probe with capabilities to get sub-diffraction limited resolution in a variety of optical imaging modalities including Raman imaging, apertureless near field microscopy and confocal microscopy, transmission, fluorescence and other linear imaging methods and even non-linear imaging modalities. The confined curved shape of the probe apex which is an integral part of the probe interacts with sub-diffraction limited area of the sample and enhances the Raman and optical signals in this area underneath of the tip.

[0016] It is an object of the invention to allow for such a cantilevered or straight probe to be integrated with scanning probe microscopy. The probe is constructed to enable one to acquire the sample topography simultaneously with sub-diffraction limited Raman and apertureless near-field imaging methods.

[0017] It is further the intent of this invention to allow such a probe to have a geometry that permits contact with another AFM probe in a multiprobe AFM system.

[0018] It is a further object of this invention to provide a stable, long life time probe with such abilities for enhancement of optical signals enhancement on both conductive and non-conductive samples without the need for conductive substrates or applied voltage and thus to allow a TERS probe to be generally applied.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIG. 1 A-1 C illustrate capillaries and tubes that are used as the basis for the curved defined probes production process in accordance with the present invention. FIG. 1A illustrates a glass hollow capillary; FIG. 1 B illustrates a glass hollow capillary with glass inner filament; and, FIG. 1 C illustrates a glass solid tube.

[0020] FIG. 2 is a schematic diagram of the apparatus for production of tapered structures from glass hollow or solid capillaries or tubes.

[0021] FIG. 3A schematically shows the process of pulling heated tubes and thus decreasing the tube diameter. FIG. 3B shows the resulting separation of the heated tube into first and second hollow tapered pipettes.

[0022] FIG. 4A schematically shows the process of pulling heated tubes and thus decreasing the tube diameter. The pulling is stopped long enough for a laser to heat the pulled cantilever to make it solid. The pulling is resumed as illustrated in FIG. 4B to separate the solid cantilever into two tapered pipettes with a solid cantilever.

[0023] FIGs. 5A and 5B show two straight tapered pipettes with solid and hollow cantilevers, respectively, produced by the pulling procedure.

[0024] FIGs. 6A and 6B illustrate the bending procedure of a tapered straight pipette. FIG. 6A shows a C0₂ laser beam that is focused by a lens on the cantilever of the straight pipette. FIG. 6B shows the resulting bent cantilevered pipette with typical dimensions as indicated. [0025] FIG. 7 is a diagram showing that the exposed tips of the probes do not obscure the optical axis from the top and from the bottom and enable multiprobe operation.

[0026] FIGs. 8A and 8B schematically show tip coating procedures. Tip coating is required for the further production of the curved defined probe. The tip can be coated by a thin layer of gold or silver as shown in FIG. 8A or by nanoparticles as shown in FIG. 8B.

[0027] FIG. 9 illustrates a cantilever probe having a tip coated by a high reflection metal film. The cantilever probe is shown integrally formed with an optical feedback SPM, which requires use of the high reflection metal film for operation.

[0028] FIGs. 10A and 10B illustrate the attachment of a cantilevered pipette probe to the prong of a quartz tuning fork. FIG. 10A shows the attachment of the probe to the tuning fork for normal force feedback operation. FIG. 10B shows the attachment of the probe to the tuning fork for shear force feedback operation.

[0029] FIG. 1 1 illustrates the cantilever probe of FIG. 9 attached to a tuning fork and mounted on a probe holder for further incorporation with a scanning probe microscope.

[0030] FIG. 12 illustrates the process of the curved defined tip production by heating with a focused laser beam.

[0031] FIG. 13 schematically shows the curved defined tip integrated with the cantilever and the dielectric or metallic particle at the end of tip.

[0032] FIG. 14A schematically shows a strained silicon tested sample; while FIG.

14B is a graph showing the Raman spectrum of strained silicon.

[0033] FIG. 15 is a schematic illustration of the curved defined probe alignment with the "hot spot" of the focused laser.

[0034] FIG. 16A illustrates the procedure of curved defined probe characterization in terms of the enhancement wherein measurements are taken both with the curved defined probe tip both in contact with the sSi sample and out of contact with the sample. The Raman spectrum of sSi taken when the curved defined probe is in contact and out of contact is shown in the graph of FIG. 16B.

[0035] FIGs. 17A-17D are graphs illustrating the Raman signal enhancement on four different materials obtained with a curved defined probe constructed in accordance with the present invention. FIG. 17A shows the Raman enhancement of a MoS epilayer. FIG. 17B shows the enhancement of single wall carbon nano-tubes (SWCNT). FIG. 17C shows the enhancement of a graphene layer. FIG. 17D shows the Raman enhancement obtained on a biological sample: single bio molecular.

[0036] FIG. 18 illustrates the setup for simultaneous topographic/tip enhanced Raman measurements using a cantilevered TERS probe.

[0037] FIGs. 19A and 19B show the Raman images obtained on the sSi pattern with a curved defined probe (FIG. 19A) and without a curved defined probe (FIG. 19B). FIG. 19C is a line scan showing the lateral Raman resolution at 40 nm.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0038] As used in this application and in the claims, the singular forms "a", "an" and "the" include the plural forms unless the context clearly dictates otherwise.

Additionally, the term "includes" means "comprises".

[0039] The described probe, apparatus, procedures and methods described herein should be not construed as limiting in any way. Instead, the present disclosure is directed toward all novel and nonobvious features and aspects of various disclosed embodiments, alone and in various combinations and subcombinations with one another. The disclosed probes, methods and apparatus are not limited to any specific aspect or feature or combinations thereof, nor do the disclosed probes, methods and require that any one or more specific advantages be present or problems be solved.

[0040] Although the operations of some of the disclosed methods are described in a particular, sequential order for convenient presentation, it should be understood that this manner of description encompasses rearrangement, unless a particular ordering is required by specific language set forth below. For example, operations described sequentially may in some cases be rearranged or performed concurrently. Moreover, for the sake of simplicity, the attached figures may not show the various ways in which the disclosed probes, methods and apparatus can be used in conjunction with other probes, methods and apparatus. Additionally, the description sometimes uses terms like" produce" and "provide" to describe the disclosed methods. These terms are high- level abstractions of actual operations that are performed. The actual operations that correspond to these terms will vary depending on the particular implementation and are readily discernible by one ordinary skill in art. [0041] The invented novel probes are produced using advanced pulling, forming or lithographic technologies. Such technology can be applied to a variety of materials. Examples are either with hollow glass capillaries or solid glass structures or other materials.

[0042] FIGs. 1 A-1 C illustrate tubes and capillaries that can be pulled in accordance with one emulation of the present invention. In this emulation the pulling parameters can reach small dimensions at the tip and can be integrally connected to the cantilever.

[0043] FIG. 2 shows the steps of the tapering procedure using one fabrication technology based on pulling. In this case a laser based puller is employed although a metal filament based puller machine or other tapering methods can be used.

[0044] In this particular emulation FIG. 2 shows a capillary 2.1 mounted on a laser based puller in holders 2.2 and 2.3. The capillary 2.1 is heated by a C0₂ laser 2.4. The tip size in this and other emulations can have a diameter from 20-500 nm. The fabrication is controlled by forming or pulling parameters that can include temperature, pulling force, cooling, etching etc.

[0045] FIGs. 3A and 3B illustrate the thin cantilever formation based on pulling and heating. For such tip formation the capillary 3.1 in FIG. 3A is heated by a C0₂ laser 3.2 and slightly pulled in order to decrease the diameter from 1 mm to about 50-200 μιη. The length and diameter of the resulting cantilever are controlled by heating and pulling parameters. This structure is pulled to create tapered sharp hollow pipettes 3.3 and 3.4 as illustrated in FIG. 3B.

[0046] FIGs. 4A and 4B illustrate production of a solid cantilevered pipette. Here the structure 4.1 is first heated by laser 4.2 but without pulling to melt a portion of the structure 4.1 and create the solid region 4.3. Then, as illustrated in FIG. 4B, the structure 4.1 is pulled to separate it into two tapered sharp pipettes 4.4 and 4.5, each with a solid cantilever section 4.6 and 4.7, respectively.

[0047] The resulting solid and hollow pipette structures 5.1 and 5.2 shown in FIGs. 5A and 5B, respectively, can be used for AFM without obscuring the optical axis after a controlled, precision bending process which enables the angle of the bend to be varied and the tip to be exposed to the optical axis of a microscope.

[0048] The bending process is illustrated in FIGs. 6A and 6B. As shown in FIG. 6A, a CO₂ laser 6.1 is focused by a lens 6.2 on the cantilever pipette 6.3 far away from the tip 6.4. The process is visually controlled by an optical microscope 6.5. The resulting bent cantilevered probe and its parameters 6.6 are shown in FIG. 6B. Such exposed tip geometries prevent obscuring illumination from the top and also allow for multiprobe operation as illustrated in FIG. 7.

[0049] As part of the production of these enhancing probes the material properties can be adjusted. One of the ways in which to alter the material properties is shown in FIGs. 8A and 8B. Tip coating is required for the further production of the curved defined probe. The tip 8.1 of a curved defined probe 8.2 can be coated by a thin layer or film 8.3 of gold or silver as shown in FIG. 8A. Alternatively, as illustrated in FIG. 8B, the tip 8.1 can have gold or silver nanoparticles 8.4 attached thereto. This procedure can be applied when the starting material already has the correct material properties for the further production of the curved defined probe.

[0050] The novel probe that is evolved from this structure has the characteristics of operating as an AFM probe with ultrasensitive force sensing. As illustrated in FIG. 9, a cantilever probe 9.1 having a tip coated by a high reflection metal film 9.2 can be integrally formed with an optical feedback scanning probe microscope (SPM) 9.3, which requires use of the high reflection metal film for operation.

[0051] This probe can also be integrated with a tuning fork based SPM as shown in FIGs. 10A and 10B, and with all other mechanisms of SPM feedback including such things as attachment to tuning forks. SPM feedback enables the approach of the probe to the studied sample and to maintain it in close proximity to the point of contact with it.

[0052] Extremely soft surfaces can be touched with such soft probes if they are associated with a feedback mechanism in which high Q can be maintained even in liquid such as a tuning fork. To achieve this, two aspects of this invention for such high force constant cantilever probes is that the Q initially associated with the probe is altered as a function of the depth of penetration of the probe into the liquid. This requires methodologies to limit the depth of penetration by for example limiting the extent of liquid and then providing a method of preventing the liquid to change its level.

[0053] In a general sense a description of our invention is based on a basic understanding we have evolved for the TERS process. Although TERS is related to Raman scattering what we have learnt about enhancement of a probe tip of a sample is applicable to all other optical imaging phenomena. Specifically, the material and the tip forming parameters have to be chosen such that the close approach of such a tip to a surface forms an appropriate interaction either chemical, optical or both to result in such an enhanced signal.

[0054] In terms of a chemical interaction one has to sensitively adjust the electronic structure of the probe tip relative to the surface. In essence this is related to the chemical potential difference between the probe tip and the surface which maximizes the electronic interaction. Thus, the electronic states that result have to be able to interact with the laser excitation that is employed in a resonant way. This means that the interactions of the tip and the sample have to be excited by the laser excitation. One form for this to occur is through a resonance Raman effect when this is applied to Raman slatternly. Thus one way to look at TERS is that the effect is dominated by resonance Raman scattering of an incident laser with an electronic interaction induced by the tip.

[0055] Along with this the optical characteristics of the resulting structure have to be appropriately chosen to not deteriorate the enhancing optical effect of the structure. A further requirement is that for a defined time the tip has to be very close to the surface. The distance has to be <3 nm and the closer the better.

[0056] Based on this understanding the probe that has been evolved can be used for all apertureless forms of enhancement of optical phenomena for imaging, sensing and other applications.

[0057] In such probes the probe cantilever can, in a general sense, be opaque or transparent, conical, cylindrical or flat and can be tens to hundreds of microns.

However, a transparent cantilever generally reduces scattering artifacts.

[0058] In addition, the cantilever angle of bending can be varied in the range 0°-

90° depending on the required optical configuration as it is shown in FIG. 6B. This permits either bent probe operation or allows for a straight probe.

[0059] When the probe tip is in the bent configuration the resulting extended tip shaft does not obscure the optical axis. In both configurations multiprobe operation has been demonstrated such that one tip can touch another tip in feedback and without feedback. However bent operation gives better multiprobe characteristics.

These advanced properties of the probe are illustrated in FIG. 7.

[0060] As one specific example of such an implementation of our method for producing a probe of this type, let us for example take a probe that could be made of one of a variety of materials to make it enhance a particular surface. For this either the starting material or after production the probe tip can have a specific material character relative to the surface to generate the electronic interactions noted above. If this is after the production of the tip then the tip can be altered after production with one of a variety of dopants. As a specific example let as consider a curved defined tip integrated with the probe to provide the enhancement of the optical, fluorescence, Raman and other optical linear and non-linear signals. To achieve such a curved tip with these optical and chemical characteristics one method is to produce such a curved tip by laser melting. If the starting material is a dielectric then one can directly bring the tip in contact with a metal, semiconductor or dielectric interface for appropriate doping with heat, chemistry or other means such as implantation. Such a procedure forms the smallest probe tips with the appropriate chemical and optical characteristics. If tips beyond 1 micron are required then direct laser melting is the procedure of choice. Alternately contacting the tip with heat onto an appropriate interface for doping various methods can overlap in their dimensions such that the method with the largest tips could overlap the method with the smallest tips.

[0061] As an example it has been noted above that doping a fused silica tip with gold can give the right tip/surface characteristics to enhance a variety of materials. Examples of materials that we have shown can be enhanced by such a tip are strained silicon, MoS2 etc. Furthermore in such a probe the final probe tip has to be adjusted in form and character not to obscure the enhanced signal and to have an index of refraction through doping or other means to allow for further optimizing and enhancing the signal optically.

[0062] As noted previously a variety of starting materials can be chosen such that the doping step may not be necessary. An example of such a material where post doping for the appropriate surface may not be needed is for example leaded glass or doped silicon.

[0063] From the point of view of how one form of the doping operation is consummated consider as one example a metal coated probe. This probe is mounted on the scanning probe microscope as illustrated in FIGs. 9-1 1 . As an example, FIGs. 10A and 10B illustrate the probe attachment to one form of sensing element for SPM-a quartz tuning fork. In FIG. 10A, a cantilevered pipette probe 10.1 is shown attached to the prong 10.2 of a quartz tuning fork 10.3 for normal force feedback operation. The probe 10.1 is shown attached to the tuning fork 10.3 between 50-1000 μιη from the bend in the probe 10.1 . With normal force geometry, the probe oscillates perpendicular to the sample surface. FIG. 10B shows a variation in which the attachment of the probe 10.1 to the tuning fork 10.3 is for shear force feedback operation. With the tuning fork in shear force geometry, the probe oscillates in parallel to the sample surface. In addition a straight probe could be mounted on the SPM in a shear force geometry, Micro and nano devices with abilities to approach the probe to the sample surface without probe damage can be used.

[0064] FIG. 1 1 Illustrates the probe 1 1 .1 attached to the tuning fork 1 1 .2 and mounted on a probe holder 1 1 .3 for further incorporation with a scanning probe microscope as illustrated next in FIG. 12..

[0065] In the specific example shown in FIG. 12 the scanning probe microscope should have an open optical axis for integration with laser 12.1 focused by optical objective 12.2 on the substrate 12.3 to which the probe tip is brought for the doping operation. The probe is approached to the metal, semiconductor or other substrate 12.3 depending on the type of probe tip alteration needed for maximizing the electromagnetic field interaction.

[0066] The next step in such a tip alteration is that the metal coated tip is aligned in proximity of the focused laser. The focused laser 12.1 heats the metal coated tip interacting with the substrate surface. In this operation the sharp coated apex transforms into the curved defined tip as illustrated in FIG. 13. After that the probe is removed from the scanning probe microscope and the tip can be washed in HCI/ HN03 mixture and alcohol or distilled water. The dimensions of the curved defined tip depend on the laser spot, laser power and tip material.

[0067] Another method for producing such curved defined tips is to use hollow tapered sharp pipettes. Gold nanoparticles are attached to the tip of the pipette either inside or outside as illustrated in FIG. 8B. Other nano particles can depend on the nature of the tip surface electromagnetic interactions desired. However the ease of the operation is aided if the nano particle has high heat conductivity. Nanoparticles with different shapes and dimensions can also be used.

[0068] For the above operation where gold nanoparticles were attached on pulled tips, these tips were modified with gold attaching functional groups. As only one example the pulled tips were dipped in 1 % solution of (3-Mercaptopropyl)

triethoxysilane or (3-Aminopropyl) trimethoxysilane in ethanol for 20 minutes. These functionalized tips were dipped in gold solution for 3 hours. There are of course many methods of particle attachment that can be used to coat the tip of a hollow probe as in this specific case or to coat a solid probe. Such nanoparticle coated probe tips could be used directly or could undergo further processing.

[0069] For further processing if needed such a probe with nanoparticles coating the tip is mounted on the scanning probe microscope integrated with a focused laser beam from above or from the side. The probe is approached to the metal, semiconductor or other substrate depending on the modifications needed based on the sample character. The nanoparticle coated tip is then aligned in the proximity of the focused laser. The laser heats the tip coated by nanoparticles interacting with the substrate surface and as a result the sharp tip is transformed to the curved defined apex 13.1 illustrated in FIG. 13

[0070] The enhancement properties of the curved defined probes can then be tested with an appropriate sample, such as one with semiconductor character. A sample of strained silicon (sSi) on silicon was thus selected as a test sample as illustrated in FIG. 14A. This sample included a 50 nm strained silicon layer 14.1 on a silicon substrate 14.2. Note, that any other stable sample with strong Raman or fluorescence signal can be used as a reference sample. We chose the strained silicon sample because of its strong and well known Raman bands as illustrated in the graph of FIG. 14B and low heat sensitivity.

[0071] The characterization of the probe as produced with the above procedure is done with a scanning probe microscope integrated with Raman microscope in an upright configuration as illustrated in FIG. 15. The probe 15.1 is approached to the sample surface and the curved defined tip 15.2 was aligned in the vicinity of the focused laser spot. The probe was moved in X and Y directions relative to the focused laser spot in order to find the maximum Raman signal (so called "hot spot"). This location of the hot spot depends on the laser polarization, magnification of the optical objective 15.3 and the laser wavelength.

[0072] With reference to FIG. 16A, the Raman spectrum of strained silicon was measured when the probe is in feedback with the sSi surface and located in the "hot spot" as depicted at 16.1 and then when the probe is out of contact as depicted at 16.2. The Raman spectrum of strained Si illustrated in the graph of FIG. 16B shows the strong enhancement of strained silicon Raman band. The enhancement value can be calculated as the difference in the intensity in percent between enhanced and non-enhanced Raman band of sSi at 516 cm^"1. Note that any other theoretical models can be employed for definition of the enfacement factor. [0073] To give an indication of the modifications possible in our procedures consider once again the hollow pipette as the starting material. Unlike the previous procedure the probe is filled both inside and outside at the tip with a high refractive index materials with unique conductivity properties. In this emulation the hollow pipette is filled with a diamond solution. The probe is left to dry overnight. This probe is mounted on the scanning probe microscope and can be approached to the sample surface for further interaction with a chosen substrate to enhance the optical and spectral signals.

[0074] All of the probes mentioned above can be used for enhancement of the optical, fluorescent, Raman and other optical phenomena and thus to get the sub- diffraction lateral and axial optical resolution. FIGs. 17A-17D show four examples of the curved defined probe application for Raman enhancement on different types of materials. FIG. 17A shows the Raman enhancement of a MoS epilayer. FIG. 17B shows the enhancement of single wall carbon nano-tubes (SWCNT). FIG. 17C shows the enhancement of the graphene layer. The Raman peak of graphene at 1350 cm ^"1 which corresponds to the defects is enhanced by the curved defined probe. Furthermore, FIG. 17D shows the Raman enhancement obtained on a biological sample: single bio molecular.

[0075] FIG. 18 illustrates the schematic setup for simultaneous topographic and Raman enhancement measurements with a curved defined probe 18.1 . Curved defined probe 18.1 is approached to the sample surface 18.2 with the SPM microscope combined with a Raman confocal microscope. The tip is aligned in the hot spot of the focused laser beam 18.3. Piezo scanner 18.4 of the scanning probe microscope moves the sample in X, Y and Z directions with nanometric steps.

Topography and Raman enhancement spectrum are collected simultaneously pixel by pixel.

[0076] The Raman map obtained with the curved defined probe 18.1 is shown in FIG. 19A. The sample is a strained silicon (sSi) nanometric pattern. FIG. 19A shows the TERS Raman map at Raman peak of strained silicon 510 cm^"1 This image was obtained when the curved defined probe was in contact with the sample and positioned in the laser "hot spot". Then the curved defined probe was retracted and the same measurements were repeated. FIG. 19B shows the result of this measurement. It is clearly seen that the measurements with the curved defined probe shown in FIG. 19A enable one to resolve the sample nanostructure with Raman lateral resolution 40 nm as illustrated in the graph of FIG. 19C, while the Raman image obtained with the probe out of contact.

[0077] Figures 17-19 demonstrate the unique capabilities of the invented curved probe with defined material properties to get the sub-diffration Raman resolution. Note that this probe can be used not only for enhancement of the Raman signal and improvement of the Raman imaging resolution, but also for any other optical phenomenon including apertureless NSOM, confocal microscopy and fluorescent microscopy.

Claims

1 . A device comprising a probe having a tip which is in ultraclose proximity to a surface <3nm such that the tip's presence exhibits chemical potential differences between the probe and the surface that result in electronic alterations and enhanced Raman and other optical signals from a surface both linear and non-linear with or without online atomic force microscopic feedback.

2. A device as in claim 1 further including electronic alterations that are in resonance with external excitation by an electromagnetic wave induced by the close approach of the tip to the surface.

3. A device as in claim 1 in which the material of the probe tip is chosen to optically enhance the optical signals from the surface.

4. A device as in claim 1 in which the tip is composed of the same material as the rest of the probe and the material can be a dielectric, semiconductor or metal.

5. A device as in claim 1 in which the tip is doped to enhance chemical potential

differences such that the tip material is different from the rest of the probe.

6. A device as in claiml in which Gold or other nanoparticles either of homogenous geometry or mixed geometry are applied to the tip by a number of means including dipping the tip in 1 % solution of (3-Mercaptopropyl) triethoxysilane or (3-Aminopropyl ) trimethoxysilane in ethanol for 20 minutes and then by dipping in a solution of gold nano particles for up to for 3 hours with other chemistries of attachment depending on the tip being formed.

7. A device as in claim 1 where the probe tip is integrally formed with the rest of the probe.

8. A device as in claim 1 in which the starting material to generate the probe is

cylindrical, conical or flat.

9. A device as in claim 1 in which the starting material to generate the probe is a solid or hollow material.

10. A device as in claim 1 in which the probe tip is contiguous and straight with the rest of the probe.

1 1 . A device as in claim 1 in which the probe tip is cantilevered with respect to the rest of the probe.

12. A device as in claim 1 in which the cantilever is cylindrical, conical or flat.

13. A device as in claim 1 in which the cantilever is left uncoated with any other

material.

14. A device as in claim 1 in which the cantilever is coated.

15. A device as in claim 1 in which the tip is bent between 20°-90° relative to the

cantilever such that the optical axis from above is not obscured.

16. A device as in claim 1 in which the tip is exposed such that the tip in atomic force feedback can be in physical contact with one or more other tips in atomic force feedback.

17. A device as in claim 1 in which a curved defined apex is integrated as part of the probe.

18. A device as in claim 1 in which there is a curved defined apex with dimensions from tens to thousands of nanometers.

19. A device as in claim 1 in which the probe is attached to a tuning fork or other similar device so that there is no jump to contact and adhesion ringing in atomic force microscopy feedback and Q factors of 500 and above are maintained even in liquid.

20. A device as in claim 1 in which the probe employs a feedback that permits switching between atomic fork and scanning tunneling microscopy feedback for a conducting probe.

21 . A device based on the fact that a probe of an AFM using tuning fork based feedback changes its Q as the probe tip enters liquid and thus to work in liquid there has to be minimal liquid and thus such liquid which would evaporate needs by passive shielding or active refilling to be kept at constant height.

22. A method to produce a probe tip that in ultraclose proximity to the surface <3nm such that its presence exhibits chemical potential differences between the probe and the surface that result in electronic alterations and enhanced Raman and other optical signals from a surface both linear and non-linear with or without on-line atomic force microscopic feedback.

23. A method as in claim 22, exhibits chemical potential differences between the probe and the surface that result in electronic alterations.

24. A method as in claim 22 to produce a probe tip that exhibits electronic alterations that are in resonance with external excitation by an electromagnetic wave induced by the close approach of the tip to the surface.

25. A method as in claim 22 to produce a probe tip that optically enhances the optical signals from the surface.

26. A method as in claim 22 to produce a probe tip in which the tip is composed of the same material as the rest of the probe and the material can be a dielectric, semiconductor or metal.

27. A method as in claim 22 to produce a probe tip that is doped to enhance chemical potential differences such that the tip material is different from the rest of the probe.

28. A method as in claim 22 to produce a probe tip where the probe tip is integrally formed with the rest of the probe.

29. A method as in claim 22 to produce a probe tip that in which the starting material to generate the probe is cylindrical, conical or flat.

30. A method as in claim 22 to produce a probe tip in which the starting material to generate the probe is a solid or hollow material.

31 . A method as in claim 22 to produce a probe tip in which the probe tip is contiguous and straight with the rest of the probe.

32. A method as in claim 22 to produce a probe tip in which the probe tip is cantilevered with respect to the rest of the probe.

33. A method as in claim 22 to produce a probe tip in which the cantilever is cylindrical, conical or flat.

34. A method as in claim 22 to produce a probe tip in which the cantilever is left

uncoated with any other material.

35. A method as in claim 22 to produce a probe tip in which the cantilever is coated.

36. A method as in claim 22 to produce a probe tip in which the tip is bent between 20°- 90° relative to the cantilever such that the optical axis from above is not obscured.

37. A method as in claim 22 to produce a probe tip in which the tip is exposed such that the tip in atomic force feedback can be in physical contact with one or more other tips in atomic force feedback.

38. A method as in claim 22 to produce a probe tip in which a curved defined apex is integrated as part of the probe.

39. A method as in claim 22 to produce a probe tip in which there is a curved defined apex with dimensions from tens to thousands of nanometers.

40. A method as in claim 22 to produce a probe tip in which the probe is attached to a tuning fork or other similar device so that there is no jump to contact and adhesion ringing in atomic force microscopy feedback and Q factors of 500 and above are maintained even in liquid.

41 . A method as in claim 22 to produce a probe tip in which the probe employs a

feedback that permits switching between atomic fork and scanning tunneling microscopy feedback for a conducting probe.

42. A method as in claim 22 to produce a probe tip in which pulling of hollow or solid glass tube using pulling technology to sharp pipette with tip diameter 20-500 nm.

43. A method as in claim 22 to produce a probe tip in which the probe can be metal, semiconductor or dielectric or some combination.

44. A method as in claim 22 in which chemical etching can be used for sharp pipette production.

45. A method as in claim 22 where a hollow pipette starting material for the probe can have integrated glass filament inside.

46. A method as in claim 22. where the bending operation is with a focused laser beam to produce the cantilevered probe.

47. A method as in claim 22 in which the tip of the device is coated with thin metal coating where the coating can be gold or silver thin film evaporated by electron beam technique or any other evaporation or deposition methods can be employed.

48. A method as in claim 22 in which the tip is coated by nanoparticles with dimensions 5-100 nm attached by adhesion forces or chemical modification or other methods of nanoparticle attachment.

49. A method as in claim 22 in which Gold or other nanoparticles either of homogenous geometry or mixed geometry a number of means including dipping the tip in 1 % solution of (3-Mercaptopropyl) triethoxysilane or (3-Aminopropyl ) trimethoxysilane in ethanol for 20 minutes and then by dipping in a solution of gold nano particles for up to for 3 hours with other chemistries of attachment depending on the tip being formed.

50. A method as in claim 22 in which the probe mounting of the device in a Scanning probe microscope is with a tuning fork for feedback to prevent jump to contact or adhesion ringing.

51 . A method as in claim 22 in which the attachment of the probe can be mounted on the tuning fork by different geometries: so called normal force oscillations (the probe oscillates perpendicular to the sample surface) and shear force oscillations (the probe oscillates parallel to the sample surface) can be realized.

52. A method as in claim 22 in which a probe is appropriately configured for optical feedback without obstruction of the optical axis of the microscope from above.

53. A method as in claim 22 for producing a probe tip for enhancement which includes approaching a probe to the sample with SPM feedback; alignment of the tip to the "hot spot" of a focused laser by tip movement in X,Y direction (or laser movement relative to the tip) heating of the tip by the focused laser spot and thus production of the curved defined apex.

54. A method which is based on the fact that a probe of an AFM using tuning fork based feedback changes its Q as the probe tip enters liquid and thus to work in liquid there has to be minimal liquid and thus such liquid which would evaporate needs by passive shielding or active refilling to be kept at constant height.

55. A method for testing a probe tip that enhances optical phenomena that involves a substrate which consists of a strained silicon grating on top of silicon with line widths and spacings that vary from 20 to 500nm.

56. A method that realizes that the basis of tip enhanced Raman scattering is actually resonance Raman scattering in which the probe tip interaction generate new electronic absorptions in resonance with the exciting laser.

57. A method that realizes that the basis of surface enhanced Raman scattering is actually resonance Raman scattering in which the surface roughness generate particle spacings resulting in new electronic absorptions in resonance with the exciting laser.