WO2016004261A1 - Batch processed plasmonic tips with large field enhancement - Google Patents

Abstract

A method for batch fabricating solid metal nanocone tips with well-defined dielectric base material uses a mask layer on a substrate to form at least one inverted pyramid pit below each hole of the mask layer. Metal is then deposited through each hole of the mask layer to form a metal nanocone at a bottom tip of each inverted pyramid pit. A polymer pedestal is then formed that is at least partly within each inverted pyramid pit and attached to the metal nanocone at the bottom tip of that inverted pyramid pit.

Description

BATCH PROCESSED PLASMONIC TIPS WITH LARGE FIELD

ENHANCEMENT

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is entitled to the benefit of provisional U.S. Patent Application Serial Number 62/019,565, filed July 1, 2014, which is incorporated herein by reference.

BACKGROUND

[0002] There is much interest to break the diffraction limit, i.e., obtain resolution beyond the limit calculated by Abbe, associated with light microscopy. One way to achieve such resolution is by an approach commonly referred to as tip- enhanced near-field microscopy (TENOM). Many variant techniques in TENOM, and especially in a technique known as tip-enhanced Raman spectroscopy (TERS), the electric field enhancement at the apex of the tip determines the spatial resolution and the sensitivity of the measurements. TERS instruments are based on either scanning tunneling microscope (STM) or atomic force microscope (AFM) to bring a tip close to the sample surface in a controllable manner. With AFM, the preferred sensor in TERS setup is a tuning fork onto which an etched metal tip is manually glued. The principle of tuning fork-based AFM is reviewed in this publication. (1) The condition of the etched tips varies randomly at the scale of nanometers and leads to unpredictable TERS results, which has prevented a wide-spread adoption of TERS despite its scientific significance. In order to enhance the tips' reliability, some resort to nano- sculpturing where focused ion beam (FIB) is used to shape the ends of either a batch processed tip or etched tip; this is performed individually, which is both time- consuming and costly.

[0003] Recently a batch processed tip based on a technique called template- stripping has shown some promising results (see references 2, 3). In this technique, a gold film is deposited into a Si/SiO mold in the shape of a pyramidal pit fashioned via anisotropic etching of silicon. Since the gold adheres poorly to the SiO layer, a fine wire with glue is attached to the gold layer in order to "strip" the pyramidal- shaped gold shell off of the mold. In order to use it with a tuning fork, the wire has to be glued onto the tuning fork either before or after the gold stripping. The use of silicon pits created via anisotropic etching as a mold for forming microtools that can be extracted has been around since early 1970s (see reference 4). While the template- stripped tips showed reasonably high enhancement factor, it suffers from the following limitations: (a) the gold pyramidal shell has to be large enough to glue a wire onto (the referenced paper uses a tungsten wire with 15 micron diameter), which makes the structure too large for best field-enhancement at the usable wavelengths (roughly 300 nm to 900 nm); (b) while multiple tips can be batch fabricated, the gluing step is performed one at a time and is tricky and unreliable; and (c) the space between the wire and the gold shell which the glue is occupying is ill-defined since it will be very difficult to apply the glue in a controllable and repeatable manner (variability of the interface will affect the enhancement factor of the tip since metal/dielectric interface plays an important role).

[0004] A solid gold nanocone has been looked at as a candidate tip with excellent field enhancement (see references 5, 6, 7). Given the size of the nanocones (ranging in height from about 10 to 200 nm), these are typically post-fabricated individually at the tips of AFM cantilevers or etched metal structures. SUMMARY

[0005] A method for batch fabricating solid metal nanocone tips with well- defined dielectric base material uses a mask layer on a substrate to form at least one inverted pyramid pit below each hole of the mask layer. Metal is then deposited through each hole of the mask layer to form a metal nanocone at a bottom tip of each inverted pyramid pit. A polymer pedestal is then formed that is at least partly within each inverted pyramid pit and attached to the metal nanocone at the bottom tip of that inverted pyramid pit.

[0006] Other aspects and advantages of embodiments of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrated by way of example of the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figs. 1A-1H show a schematic representation of the processing steps required to batch fabricate nanocones in accordance with an embodiment of the invention.

[0008] Figs. 2A-2C show a schematic representation for attaching the nanocones to a wafer full of tuning forks in accordance with an embodiment of the invention.

[0009] Figs. 3 A and 3B show a schematic of a metal/polymer hybrid nanocone attached onto the core of an optical fiber in accordance with an embodiment of the invention.

[0010] Figs. 4A and 4B show the results of finite element analysis (FEA) modeling of the proposed structure highlighting the large field enhancement at the apex of the gold nanocone.

[0011] Fig. 5 is a flow diagram of a method for batch fabricating solid metal nanocone tips with well-defined dielectric base material in accordance with an embodiment of the invention.

[0012] Throughout the description, similar reference numbers may be used to identify similar elements. DETAILED DESCRIPTION

[0013] It will be readily understood that the components of the embodiments as generally described herein and illustrated in the appended figures could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of various embodiments, as represented in the figures, is not intended to limit the scope of the present disclosure, but is merely representative of various embodiments. While the various aspects of the embodiments are presented in drawings, the drawings are not necessarily drawn to scale unless specifically indicated.

[0014] The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by this detailed description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.

[0015] Reference throughout this specification to features, advantages, or similar language does not imply that all of the features and advantages that may be realized with the present invention should be or are in any single embodiment of the invention. Rather, language referring to the features and advantages is understood to mean that a specific feature, advantage, or characteristic described in connection with an embodiment is included in at least one embodiment of the present invention. Thus, discussions of the features and advantages, and similar language, throughout this specification may, but do not necessarily, refer to the same embodiment.

[0016] Furthermore, the described features, advantages, and characteristics of the invention may be combined in any suitable manner in one or more embodiments. One skilled in the relevant art will recognize, in light of the description herein, that the invention can be practiced without one or more of the specific features or advantages of a particular embodiment. In other instances, additional features and advantages may be recognized in certain embodiments that may not be present in all embodiments of the invention.

[0017] Reference throughout this specification to "one embodiment," "an embodiment," or similar language means that a particular feature, structure, or characteristic described in connection with the indicated embodiment is included in at least one embodiment of the present invention. Thus, the phrases "in one

embodiment," "in an embodiment," and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

[0018] A method is provided for batch fabricating solid metal nanocone tips with well-defined dielectric base material, which serves as the anchoring pedestal for mounting (referred to herein as "metal-polymer hybrid structures"). The height of the base can be controlled relatively easily up to large values such as 100 microns. In the method, a solid nanocone is fabricated at the apex region of a pyramidal mold by depositing gold (or other metal such as silver or aluminum) through an evaporation mask. The pyramidal pit is then filled in by a suitable polymer, for example, via spin coating after the removal of the evaporation mask. For the right polymer, the metal nanocone should then transfer to the polymer imprint. The polymer then can be patterned via standard photolithography to the right pedestal shape for optimal attachment to tuning forks (or other sensors). By locating the pyramidal molds with the same physical layout as the wafer of fabricated tuning forks, the entire wafer of the tuning forks can be attached to the nanocone tips at the same time. By using the polymer material with the right optical property, the nanocone tip can be attached to an optical fiber to provide effective light delivery/collection performance as well. Once the polymer pedestal is attached to a sensor (for example, tuning fork or optical fiber), the polymer imprint can be peeled off the mold; the metal nanocone, having been transferred onto the polymer, should come out of the mold cleanly to be used as the plasmonic light source.

[0019] The metal-polymer hybrid structures, which are batch fabricated using the method, have a metal component that has a well-defined plasmonic resonance and polymer component that allows precise and simple attachment to other relevant structures such as a tuning-fork or the core of an optical fiber. In some embodiments, silicon wafer is etched to create a mold into which metal will be evaporated through a mask, followed by spin coating of polymer, in order to create the metal-polymer hybrid structure.

[0020] Figs. 1A-1H schematically describe the procedures involved in fabricating the metal-polymer hybrid structure. While the process is described for a single structure, one or two-dimensional array of such structure can be fabricated at the same time by the standard semiconductor processing techniques. Referring to Fig. 1A, (100) crystalline silicon wafer (10) is covered with a silicon nitride layer (20) whose thickness ranges, for example, between 100 to 200 nm. In one embodiment, both side of the Si substrate (100) is covered by 100 nm Si3N4 using plasma- enhanced chemical vapor deposition (PECVD). Si3N4 mask may be preferable to Si02 due to better chemical resistance to the wet etching. However, in other embodiments, the layer (20) may be composed of other masking material, such as Si02. A hole (30) is then made in the silicon nitride layer via standard lithography, which involves resist deposition, resist development and etching of the silicon nitride. In some embodiments, the hole (30) should be a circle or circular in shape with the diameter on the order of, for example, 100 to 300 nm or a square or rectangular in shape with the side length on the order of, for example, 100 to 300 nm. Given the small size of the feature, the hole may be defined by e-beam lithography, which may involve, for example, an e-beam resist spin coating procedure using positive or negative resist depending on the mask, i.e., the layer (20). In an embodiment, the resist deposition process involves standard e-beam procedure using sub-μ precision stage, which allows for a reasonably short exposure time. In a first alternative embodiment, the resist deposition process involves high resolution sub-μ

photolithography, which may be necessary to obtain a small aperture size. In a second alterative embodiment, nanoimprint with subsequent Reactive Ion Etching (RIE) bottom resist removal can be used as an alternative. After the resist deposition process, the resist development process is executed. In an embodiment, Si3N4 Reactive Ion Etching (RIE) through the resist mask is performed, which may be an Oxygenless process using CHF3 plasma for selectivity. This resist development process results in vertical profile, aperture size equal to mask and good rate control. In addition, subsequent resist 02 plasma ashing may be integrated into the same vacuum process. In an alternative embodiment, wet HF etching through the resist is performed, followed by wet stripping of resist using solvent. Alternative to wet stripping, plasma ashing may instead be used. The wet HF etching may produce less rough opening when compared to RIE. However, the wet HF etching is very time dependent with respect to the diameter of opening, and thus, provides weak control.

[0021] Once the hole (30) in the silicon nitride layer (20) is made, the silicon underneath the hole is etched via an isotropic etchant such as HNA (hydrofluoric, nitric, acetic) acid mixture, which will yield a structure shown in Fig. IB. The feature (40) formed by the isotropic wet etching will be a half sphere nominally. The etch depth (the nominal radius of the half sphere) should be between 1 to 50 microns and controllable by the etch time. Once the desired etch depth is reached (based on etch time using a calibration curve generated separately), it should be thoroughly rinsed to clean the HNA, after which point, the silicon underneath the hole is now etched via anisotropic etchant such as KOH; KOH attacks silicon preferentially in the <100> plane to produce a characteristic anisotropic V-etch resulting in the structure shown in Fig. 1C. The feature (50) formed by the anisotropic etch will be an inverted pyramid pit underneath the hole in the silicon nitride. The anisotropic etch will produce the feature (50) to have the indicated angular properties in Fig. 1C. Alternatively, the anisotropic etching may be performed using tetramethyl ammonium hydroxide (TMAH). In some embodiments, it may be possible to use the anisotropic etching process alone without isotropic etching to achieve the same final result. Fig. ID shows a scanning electron microscope (SEM) micrograph of a cut-away of such a feature (without the silicon nitride cover). The physical size of the feature (50) will be determined by the size of the feature (40); the depth of the pyramidal pit (50) will be roughly equal to the diameter of the feature (40). After the part is cleaned, gold (70) (or other desired metal for the tip point) is evaporated onto the structure to result in what is shown in Fig. IE. In some embodiments, tip point material is deposited by Physical Vapor Deposition (PVD) using thermal heating evaporation, e-beam evaporation, or laser ablation. Deposited layer cross-section repeats V-shape of the groove. Directionality is crucial here in order to fill the very bottom portion of the pit. Some of the gold (60) will conform to the shape of the pyramidal pit, as shown in Fig. IE, and its height (or thickness) will determine the plasmon resonance of the pyramidal nanocone. The typical thickness that will be practical and useful will be between 100 to 300 nm. If a sharper feature at the apex of the metal nanocone is desired (i.e., the angle at the apex is less than 70.6 degrees in Fig. 1C), the structure in Fig. 1C can be exposed to thermal oxidation, which will "sharpen" the apex region due to the restricted growth of the oxide near the apex. A subsequent metal deposition will create a nanocone with sharper feature at the apex.

[0022] If the nanocone is formed by PVD, the resulting structure can typically exhibit residual island or very thin film deposited outside the zone of interest geometrically delimited by the mask aperture. This is due to several factors including distance between suspended mask and the extremity of the deepening in Si substrate (desired tip height), substrate temperature (atom diffusion), mask size (atomic scattering), size of the source of material and the source to the substrate distance. For certain applications, the presence of such additional metal scatterers are annoying as they provide a background light contribution not related to the tip apex to the far- field signal. The presence of the metal scatterers can be reduced by decreasing the sample temperature, reducing the size of the source, increasing slightly the mask aperture size, reducing tip height, increasing the source to the substrate distance and finally by removing chemically or physically the unwanted deposition using the fact that the thickness of this film is much smaller than the thickness of the tip point itself. For example, Ion Beam Etching can be used for physical sputtering of unwanted layer or chemical etching using specific etch agents.

[0023] Once the desired metal nanocone is deposited through the nitride hole, the nitride mask layer (20) can be removed, for example, by a hydrofluoric acid liftoff bath, resulting in the structure shown in Fig. IF. In an embodiment in which the layer (20) is Si3N4, one of the possibilities is to use H3P04 to reduce adhesion of Au to Si3N4 surface without lifting off the tip point (60), followed by RIE selective removal of Si3N4. In an alternative embodiment, wet HF etching can be used to remove Si3N4 instead of the lift off process.

[0024] At this point, in some embodiments, a suitable polymer (80) such as Polydimethylsiloxane (PDMS), Poly(methyl methacrylate) (PMMA), or

OrmoStamp® material, can be spin coated onto the wafer, resulting in the structure shown in Fig. 1G. The thickness (86) of the polymer can be controlled via the spin speed and the viscosity of the polymer used and should range from 5 to 200 microns. The bond between the metal nanocone and the polymer should be stronger than the bond between the metal nanocone and silicon oxide surface (the silicon mold will have a native silicon oxide layer), which is known to have poor adhesion. Thus, the metal nanocone should "transfer" from the silicon mold onto the polymer. The polymer can be patterned via photolithography to a pedestal shape that best accommodates gluing the metal/polymer hybrid structure to a sensor of choice (for example, tuning fork or optical fiber), as shown in Fig. 1H. This patterning process may involve depositing a method mask layer and subsequently performing RIE. In an alternative embodiment, lithography can be used in which the resist will form the tip body. In some embodiments, multiple layers of polymer may be used to form the pedestal of the metal/polymer hybrid structure.

[0025] For tuning forks, the lateral dimension (84) of the pedestal should not be too much greater than the top dimension of the pyramid (no more than 2X) in order prevent obstruction of illumination. The pedestal can be rectangular or circular depending on the need.

[0026] Referring to Fig. 1G, if a stronger bond between the metal nanocone and the polymer is desired, the surface of the gold can be chemically treated to bring about such bonding. Reference 8 gives an example of a surface chemical treatment that would provide a strong bond between the gold nanocone and PDMS. Similar treatment can be used for different polymer materials.

[0027] Once the structure shown in Fig. 1H is formed, the entire metal/polymer hybrid structure, including the nanocone, can be detached from the silicon substrate and used on another structure, such as a turning fork or an optical fiber, as described below. The detaching process may simply involve attaching the metal/polymer hybrid structure to another structure and peeling off the metal/polymer hybrid structure from the silicon substrate. In an alternative process, the silicon substrate may be etched away, leaving only the metal/polymer hybrid structure.

[0028] Fig. 2A schematically shows how an array (90) of tuning forks fabricated on a quartz wafer can be aligned and glued with the metal/polymer hybrid nanocones that are fabricated with the same physical spacing between the nanocones. Once the nanocones are glued onto the tuning forks, the metal/polymer elements can be carefully detached from the silicon mold to yield the tuning forks with

metal/polymer hybrid nanocones attached to them (Fig. 2B). Fig. 2C is a 3D rendition of one metal/polymer hybrid nanocone that is attached to each tuning fork. The removal of polymer elements from a silicon mold is a process that is quite reliable and has successfully yielded millions of tips from a single silicon wafer (see reference 9 and references contained in it, for example). Depending on the need, the metal/polymer nanocone can be also removed one at a time.

[0029] For use with an optical fiber (see Figs. 3 A and 3B), the pedestal can be made into a shape of a cylinder with a diameter that is slightly larger (roughly 50%) than the core diameter of the fiber (roughly 5 to 8 microns for single mode fibers and larger for multi-mode fiber). The height of the pedestal (defined by the thickness (86) of the polymer) should be on the order of the core diameter. The dimensions of the pedestal can be changed while keeping this ratio of about 1.5: 1 between the diameter and the height of the pedestal; this ratio allows the pedestal to effectively couple to the fiber core (95) within the typical numerical aperture of 0.2 for the single mode fiber. The top square pattern of the pyramidal structure (50) should be targeted to fit within the pedestal. The metal/polymer hybrid nanocone can be attached to the fiber core with optical epoxy or via mechanical connector by integrating it into a standard fiber connector. In a similar manner, the pedestal can be designed in such a manner to couple effectively to waveguide structures (98) for effective coupling of light into and out of the plasmonically active metal nanocones (see Fig. 3B); a coupling of multiple tips to multiple waveguides would provide well for multiplexed sensor applications, for example, in conjunction with micro-fabricated multi-channel flow cells. For sensor applications, the gold nanocones can be chemically treated to selectively bind biomarkers for interrogating its optical characteristics. Alternatively, the

metal/polymer hybrid nanocones can be used as the field enhancement element as in the more traditional tip-enhanced Raman spectroscopy (TERS) setup.

[0030] Figs. 4A and 4B show the finite element analysis (FEA) modeling result of the proposed metal/polymer nanocone. Fig. 4A shows the expected near-field when light of 600 nm is incident on the nanocone; note that the region immediately above the apex of the nanocone has the strongest electric field strength, about 15 times greater than the incident field strength at a distance 1 nm away from the apex. Fig. 4B shows that for the nanocone height of 150nm, there is a maximum

enhancement of about 17 at around 700 nm wavelength. This value can be compared to an enhancement calculated for the larger gold pyramidal shell described in reference 2; in reference 2, an enhancement factor for backward radiation (fraction of power radiated in a backward direction with and without a tip) was calculated to be about 15. Since the power is field squared, at least according to the modeling results, the nanocone is in fact enhancing the field by about 440% more (or power by 1900%) when compared to the pyramidal shell. This result is consistent with prior results since it is known that a resonant metal with an interface with a dielectric will generate a much stronger field enhancement compared to a semi-infinite metal structure (see reference 4, for example). [0031] At wavelengths away from the resonant wavelength for a given nanocone, there is a chance that the region where the metal, polymer, and air come together may provide a modest field enhancement, which could produce extraneous optical signal (for example, Raman scattering) from the polymer. This background signal should be weaker compared to the signal from the sample since the

enhancement at the apex is much stronger. However, when examining samples with smaller Raman scattering cross-section, this background signal could still interfere with the sample measurement. In such cases, the background signal can be calibrated out of the sample signal by first acquiring the optical signal without the sample and then subtracting the result as a background from the actual sample signal. The other option is to create a gentler transition between the metal nanocone and the polymer. For example, a thin layer (e.g., 10 - 50 nm) of aluminum, silver, or tungsten can be deposited on top of the gold before the polymer is spin coated. This type of interface layer should define a less well-defined interface between gold and polymer, resulting in lowered field-enhancement at the gold and polymer interface.

[0032] The use of the polymer as the base of the nanocone structure provides numerous advantages including: (1) a well define interface with the metal nanocone for maximum field enhancement; (2) efficient optical coupling when interfaced with light delivery material such as optical fiber or waveguide; and (3) flexible shaping of the polymer pedestal for easy attachment to sensing element such as tuning fork or fiber core.

[0033] A method for batch fabricating solid metal nanocone tips with well- defined dielectric base material in accordance with an embodiment of the invention is now described with reference to the process flow diagram of Fig. 5. At block 502, a substrate with a mask layer is provided. In an embodiment, the substrate is a silicon substrate and the mask layer is a Si3N4 or Si02 layer. At block 504, a hole is created in the mask layer. The hole may be circular or rectangular in shape. At block 506, the substrate is anisotropically etched through the hole in the mask layer so that an inverted pyramid pit is formed below the hole. At block 508, metal is deposited through the hole into the inverted pyramid pit to form a metal nanocone at a bottom tip of the inverted pyramid pit. At block 510, after the metal nanocone is formed, the mask layer is removed from the substrate. At block 512, a polymer pedestal is formed that is at least partly within the inverted pyramid pit and attached to the metal nanocone at the bottom tip of the inverted pyramid pit.

[0034] Although the operations of the method(s) herein are shown and described in a particular order, the order of the operations of each method may be altered so that certain operations may be performed in an inverse order or so that certain operations may be performed, at least in part, concurrently with other operations. In another embodiment, instructions or sub-operations of distinct operations may be implemented in an intermittent and/or alternating manner.

[0035] It should also be noted that at least some of the operations for the methods may be implemented using software instructions stored on a computer useable storage medium for execution by a computer. As an example, an embodiment of a computer program product includes a computer useable storage medium to store a computer readable program that, when executed on a computer, causes the computer to perform operations, as described herein.

[0036] Furthermore, embodiments of at least portions of the invention can take the form of a computer program product accessible from a computer-usable or computer-readable medium providing program code for use by or in connection with a computer or any instruction execution system. For the purposes of this description, a computer-usable or computer readable medium can be any apparatus that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device.

[0037] The computer-useable or computer-readable medium can be an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system (or apparatus or device), or a propagation medium. Examples of a computer-readable medium include a semiconductor or solid state memory, magnetic tape, a removable computer diskette, a random access memory (RAM), a read-only memory (ROM), a rigid magnetic disc, and an optical disc. Current examples of optical discs include a compact disc with read only memory (CD-ROM), a compact disc with read/write (CD-R/W), a digital video disc (DVD), and a Blu-ray disc.

[0038] In the above description, specific details of various embodiments are provided. However, some embodiments may be practiced with less than all of these specific details. In other instances, certain methods, procedures, components, structures, and/or functions are described in no more detail than to enable the various embodiments of the invention, for the sake of brevity and clarity.

[0039] Although specific embodiments of the invention have been described and illustrated, the invention is not to be limited to the specific forms or arrangements of parts so described and illustrated. The scope of the invention is to be defined by the claims appended hereto and their equivalents.

References

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[0041] 2. "Highly Reproducible Near-Field Optical Imaging with Sub-20-nm Resolution Based on Template-Stripped Gold Pyramids", Timothy W. Johnson, Zachary J. Lapin, Ryan Beams, Nathan C. Lindquist, Sergio G. Rodrigo, Lukas Novotny, and Sang-Hyun Oh, ACS Nano, 6, 9168 (2012)

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Schwartzberg, P. James Schuck, Stefano Cabrini, and Dieter P. Kern, ACS Nano, 5, 2570 (2011)

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[0048] 9. "Materials for the Preparation of Polymer Pen Lithography Tip Arrays and a Comparison of Their Printing Properties", Xiao Zhong, Nevette A. Bailey, Kevin B. Schesing, Shudan Bian, Luis M. Campos, Adam B. Braunschweig, Journal of Polymer Science, Part A: Polymer Chemistry, 51, 1533 (2013)

Claims

WHAT IS CLAIMED IS:

1. A method for batch fabricating solid metal nanocone tips with well-defined dielectric base material, the method comprising:

providing a substrate with a mask layer;

creating a hole in the mask layer;

anisotropically etching the substrate through the hole in the mask layer so that an inverted pyramid pit is formed below the hole;

depositing metal through the hole into the inverted pyramid pit to form a metal nanocone at a bottom tip of the inverted pyramid pit; and

after forming the metal nanocone, removing the mask layer from the substrate; and

forming a polymer pedestal that is at least partly within the inverted pyramid pit and attached to the metal nanocone at the bottom tip of the inverted pyramid pit.

2. The method of claim 1, wherein the depositing of metal includes depositing gold or silver through the hole into the inverted pyramid pit to form the metal nanocone at the bottom tip of the inverted pyramid pit.

3. The method of claim 2, wherein the substrate is a silicon substrate.

4. The method of claim 3, wherein the forming of the polymer pedestal includes forming the polymer pedestal using polymer material selected from a group consisting of Polydimethylsiloxane (PDMS), Poly(methyl methacrylate) (PMMA), or

OrmoStamp® material.

5. The method of claim 1, further comprising removing chemically or physically unwanted deposition of the metal that form residual island or very thin film outside a zone of interest geometrically delimited by the hole.

6. A method for batch fabricating solid metal nanocone tips with well-defined dielectric base material, the method comprising:

providing a substrate with a mask layer;

creating multiple holes in the mask layer;

anisotropically etching the substrate through the holes in the mask layer so that inverted pyramid pits are formed below the holes;

depositing metal through the holes into the inverted pyramid pits to form a metal nanocone at a bottom tip of each of the inverted pyramid pits; and

after forming the metal nanocone, removing the mask layer from the substrate; and

forming a polymer pedestal for each metal nanocone that is at least partly within the inverted pyramid pit associated with that metal nanocone and attached to that metal nanocone at the bottom tip of the associated inverted pyramid pit.

7. The method of claim 6, wherein the depositing of metal includes depositing gold or silver through the holes into the inverted pyramid pits to form the metal nanocone at the bottom tip of each of the inverted pyramid pits.

8. The method of claim 7, wherein the substrate is a silicon substrate.

9. The method of claim 8, wherein the forming of the polymer pedestal includes forming the polymer pedestal using polymer material selected from a group consisting of Polydimethylsiloxane (PDMS), Poly(methyl methacrylate) (PMMA), or

OrmoStamp® material.

10. The method of claim 6, further comprising removing chemically or physically unwanted deposition of the metal that form residual island or very thin film outside zones of interest geometrically delimited by the holes.

11. The method of claim 6, wherein the forming of the polymer pedestal for each metal nanocone includes spin coating polymer material over the substrate and into the inverted pyramid pits and patterning the polymer material to form individual and separate polymer pedestals.