Functionalized atomic force microscope probe and preparation method thereof

Abstract

The invention discloses a functionalized atomic force microscope (AFM) probe, which comprises a probe main body made of a silicon-based material, the probe main body comprises a substrate, a cantilever and a needle tip, the cantilever extends outwards from the front end of the substrate, and the needle tip is located at the tail end of the free end of the cantilever; the surface of the probe main body is covered with a metal layer and a first insulating layer in sequence, and the tail end of the needle tip is provided with a metal tip exposed outside the first insulating layer and electrically connected with the metal layer; the metal layer on the surface of the tail end of the substrate is exposed out of the first insulating layer and forms a conductive contact area, and the conductive contact area is electrically connected with the wire and covered with a second insulating layer. The invention also discloses a preparation method of the composition. The functionalized AFM probe can simultaneously meet the requirements of three instruments, namely an electrochemical AFM (EC-AFM), an EC-TERS and an SECM, can simultaneously realize high-spatial-resolution characterization of surface morphology, chemical composition and electrochemical activity of a sample by utilizing a single probe, and has the capability of comprehensively characterizing a complex electro-catalysis interface.

Description

Technical Field

[0001] The invention belongs to the technical field of electrochemical and analytical chemistry research, and specifically relates to a functionalized atomic force microscope probe for an instrument combining electrochemical tip enhanced Raman spectroscopy and scanning electrochemical microscope and a preparation method thereof. Background Art

[0002] As people's demand for clean energy continues to increase, electrocatalysis has received widespread attention in recent years. It is worth noting that the nanoscale or even atomic-scale active sites on electrocatalysts contribute to the vast majority of electrocatalytic activity. Therefore, accurately characterizing the structure and properties of the active sites of electrocatalysts and the electrocatalytic reaction process occurring at the active sites at the nanoscale is conducive to a deep understanding of the microscopic mechanism of the electrocatalytic process, and then to the construction of a clear structure-activity relationship.

[0003] However, the size of the active sites is small, the coverage of surface species is low, and the structure, properties and reaction activity of the active sites will change dynamically with potential and time. Therefore, in order to achieve accurate characterization of the active sites of electrocatalysts, it is necessary to develop electrochemical in situ characterization methods with both high sensitivity and high spatial resolution to obtain interrelated structural information, chemical fingerprint information and electrochemical activity information. In recent years, in situ characterization technology has been booming. However, it is difficult for a single characterization technology to fully characterize the behavior of active sites. The development of combined technologies to simultaneously obtain multimodal information is the general trend of electrochemical research. Among them, the electrochemical tip enhanced Raman spectroscopy (hereinafter referred to as EC-TERS) technology that combines electrochemical scanning probe microscopy and surface enhanced Raman spectroscopy can simultaneously obtain structural information and chemical information with nanometer-level spatial resolution, and has received widespread attention in recent years. If it is further combined with scanning electrochemical microscopy (hereinafter referred to as SECM) technology, it is expected to further obtain electrochemical activity information with nanometer-level resolution under electrochemical in situ conditions and establish a clear structure-activity relationship. Existing probes are difficult to meet the needs of multi-function, which limits the realization of the combined use of EC-TERS and SECM technologies. Summary of the invention

[0004] The object of the present invention is to provide a functionalized atomic force microscope (AFM) probe for an EC-TERS-SECM instrument, which can simultaneously realize nano-resolution surface morphology analysis, chemical fingerprint information analysis and electrochemical activity information analysis under electrochemical in-situ conditions.

[0005] In order to achieve the above purpose, the technical solution of the present invention is:

[0006] A functional atomic force microscope probe comprises a probe body made of silicon-based material, wherein the probe body comprises a substrate, a cantilever and a needle tip, wherein the cantilever extends outward from the front end of the substrate, and the needle tip is located at the end of the free end of the cantilever; the surface of the probe body is sequentially covered with a metal layer and a first insulating layer, wherein the end of the needle tip has a metal tip exposed outside the first insulating layer and electrically connected to the metal layer; the metal layer at the rear end of the substrate is exposed outside the first insulating layer and forms a conductive contact area, wherein the conductive contact area is electrically connected to a wire; and a second insulating layer is also provided on the surface of the substrate, wherein the second insulating layer covers the conductive contact area.

[0007] The silicon-based material is silicon, silicon nitride or other silicon-based material.

[0008] The first insulating layer may be an inorganic insulating layer or an organic insulating layer. Preferably, the first insulating layer is an inorganic insulating layer with a thickness of 1nm-2μm. The material of the inorganic insulating layer includes silicon oxide, silicon nitride, aluminum oxide or a laminated structure thereof. The organic insulating layer may be polyimide, poly(p-dichlorotoluene), epoxy resin, etc. These materials all have excellent electrical insulation properties, as well as good thermal stability and chemical stability, and can effectively meet the probe insulation requirements.

[0009] Optionally, the metal layer includes a conductive metal capable of generating plasmon enhancement, and has a thickness of 1 nm-1 μm; the metal tip is formed by the metal layer or by a conductive metal capable of generating plasmon enhancement.

[0010] Optionally, the conductive metal capable of generating plasmon enhancement includes gold, silver, copper, a laminate containing gold, silver, copper, or an alloy containing gold, silver, copper. Optionally, in order to improve the bonding ability between the metal layer and the silicon-based material, the metal layer can be a laminate of an adhesion layer and a conductive metal capable of generating plasmon enhancement. The adhesion layer is, for example, metal Cr, etc.; laminates with other functional metals can also be applied to the metal layer.

[0011] Optionally, the length of the metal tip is 1 nm-10 μm.

[0012] Optionally, the needle tip is arranged to face one side, and the conductive contact area is arranged on the substrate surface on the same side as the metal tip.

[0013] Optionally, a second insulating layer is further provided on the surface of the substrate, and the second insulating layer covers the conductive contact area; the second insulating layer is an organic insulating layer. The organic insulating material is epoxy resin, ultraviolet glue, hot melt adhesive and other materials. The organic insulating layer covers the probe substrate, including the conductive contact area and part of the wire.

[0014] A method for preparing the above-mentioned functionalized atomic force microscope probe comprises:

[0015] Step 1, providing a probe body, and depositing a metal layer on the surface of the probe body;

[0016] Step 2, forming a first insulating layer on the surface of the metal layer;

[0017] Step 3, removing the first insulating layer at the end of the needle tip and forming a metal tip;

[0018] In step 2 or after step 2, the metal layer at the rear end of the substrate is exposed outside the first insulating layer to form a conductive contact area;

[0019] Step 4, electrically connecting the wire to the conductive contact area;

[0020] Step 5: forming a second insulating layer on the surface of the substrate.

[0021] Optionally, step 3 includes: covering the surface of the first insulating layer with a sacrificial layer; circularly removing the sacrificial layer at the end of the needle tip by a focused ion beam to form an etching window; removing the first insulating layer exposed in the etching window by inductively coupled plasma etching to form a metal tip through the exposed metal layer; and removing the sacrificial layer.

[0022] The sacrificial layer is made of a material having different corrosion characteristics from the first insulating layer and the metal layer.

[0023] Optionally, step 3 includes: cutting off part of the end of the needle tip by a focused ion beam, the cutting length being enough to expose the surface of the metal layer; and depositing metal at the end of the needle tip to form a metal tip electrically connected to the metal layer.

[0024] The beneficial effects of the present invention are:

[0025] The functionalized atomic force microscope probe combines three functions: morphology imaging, Raman signal enhancement and electrochemical current detection. It can perform nano-resolution imaging of the morphology structure, molecular chemical fingerprint and electrochemical activity of the same area under electrochemical in situ conditions. It can simultaneously meet the needs of three instruments: electrochemical AFM (EC-AFM), electrochemical tip-enhanced Raman spectroscopy (EC-TERS) and scanning electrochemical microscopy (SECM). It can use a single probe to simultaneously achieve high spatial resolution characterization of the sample surface morphology, chemical composition and electrochemical activity, and has the ability to comprehensively characterize complex electrocatalytic interfaces.

[0026] Other features and advantages of the present invention will be set forth in the following description, and in part will be apparent from the description, or may be learned by practicing the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a schematic diagram of the structure of the functionalized atomic force microscope probe of Example 1;

[0028] Figure 2 Schematic diagram of the preparation process of the functionalized atomic force microscope probe of Example 1;

[0029] Figure 3 A scanning electron microscope image (SEM) of a partial structure of the functionalized atomic force microscope probe of Example 1;

[0030] Figure 4 This is a schematic diagram of the structure of the functionalized atomic force microscope probe of Example 2;

[0031] Figure 5 Schematic diagram of the preparation process of the functionalized atomic force microscope probe of Example 2;

[0032] Figure 6 A scanning electron microscope image (SEM) of a partial structure of the functionalized atomic force microscope probe of Example 2;

[0033] Figure 7 The TERS signal spectra of the functionalized atomic force microscope probes of Example 1(a) and Example 2(b) are shown. DETAILED DESCRIPTION

[0034] The present invention is further explained below in conjunction with the accompanying drawings and specific embodiments. The various drawings of the present invention are only for illustration to make it easier to understand the present invention, and the specific proportions can be adjusted according to design requirements. The upper and lower relationships of the relative elements and the definitions of the front / back in the figures described in the text should be understood by those skilled in the art to refer to the relative positions of the components, so they can all be flipped to present the same components, which should all fall within the scope disclosed in this specification.

[0035] Example 1

[0036] refer to Figure 1 The functionalized atomic force microscope probe of Example 1 includes a probe body 1 of silicon-based material, the probe body 1 includes a substrate 11, a cantilever 12 and a needle tip 13, the cantilever 12 extends outward from the front end of the substrate 11, and the needle tip 13 is located at the end of the free end of the cantilever 12. The surface of the probe body 1 is sequentially covered with a metal layer 2 and a first insulating layer 3, wherein the end of the needle tip 13 has a metal tip 21 formed by a metal layer exposed outside the first insulating layer 3. The metal layer 2 at the tail end of the substrate 11 is exposed outside the first insulating layer 3 and forms a conductive contact area 22, and the conductive contact area 22 is electrically connected to the wire 4. A second insulating layer 5 is also provided on the outside of the substrate 11, and the second insulating layer 5 covers the first insulating layer 3, the exposed metal layer 2 and part of the wire 4 on the surface of the substrate 11.

[0037] The probe substrate 11 and cantilever 12 are plate-like structures with upper and lower surfaces, and the needle tip 13 is similar to a triangular pyramid structure. The needle tip 13 is tilted upward, and the angle between it and the surface of the cantilever 12 is 30 degrees; the metal layer 2 is located on the upper and lower surfaces of the probe, wherein the conductive contact area 22 is located on the substrate surface on the same side as the tilt direction of the needle tip 13, that is, located on the upper surface of the tail end of the substrate 11, and is electrically connected to a wire 4 through a conductive silver glue 6, which is used to derive the current signal detected at the end of the needle tip 13.

[0038] The metal layer 2 material includes metals such as gold, silver, and copper, which provide both Raman enhancement activity and electrochemical current detection capability. Metals such as gold, silver, and copper are common electrode materials, and metals such as gold, silver, and copper can produce strong surface plasmon resonance in the visible light region, and are suitable as materials for TERS needle tips. The thickness of the metal layer 2 is less than 1 μm. The length of the needle tip end that is not covered by the first insulating layer 3 is 10 nm to 10 μm, and the exposed needle tip metal tip 21 provides Raman signal enhancement and acts as a microelectrode to detect electrochemical current.

[0039] The first insulating layer 3 can be made of inorganic materials (such as silicon oxide, silicon nitride, aluminum oxide, etc.) or organic polymer materials (such as polyimide, polyparadichlorotoluene, epoxy resin, etc.), with a thickness of less than 2 μm, covering the entire probe except the tip end and the conductive contact area to achieve complete insulation. The second insulating layer 5 is made of organic materials, such as epoxy resin, ultraviolet glue, hot melt glue, etc. The second insulating layer 5 additionally insulates the substrate part of the probe so that the probe substrate part does not generate additional current interference.

[0040] The following example specifically illustrates the method for preparing the functionalized atomic force microscope probe. Figure 2 .

[0041] (1) A silicon AFM probe is selected as the probe body 1, and a metal layer 2 is formed on the surface of the probe body. Specifically, 5 nm Cr and 75 nm Au are evaporated on the back side of the probe body by electron beam evaporation as a reflective layer to enhance the reflection of the AFM probe cantilever to the feedback laser; 5 nm Cr and 75 nm Au are evaporated on the front side of the probe body to provide conductivity and TERS enhancement capability.

[0042] (2) The gold-plated AFM probe is placed on a fixed fixture, and a 50 nm silicon oxide layer and a 150 nm silicon nitride layer are grown on the surface of the AFM probe by inductively coupled plasma enhanced deposition, and the growth is repeated three times to form an inorganic material stack as the first insulating layer 3. The fixture can partially cover the tail end of the probe body so that the first insulating layer 3 is not deposited on this surface area, and the exposed metal layer 2 surface can be used as the conductive contact area 22. In other embodiments, the insulating material can also be deposited as a whole, and the first insulating layer 3 is subsequently opened to form a conductive contact area.

[0043] (3) A 50 nm thick Cr layer 7 is deposited on the surface of the AFM probe covered with the first insulating layer 3 by electron beam evaporation to form a metal sacrificial layer, which serves as a sacrificial layer for subsequent etching.

[0044] (4) A portion of the end of the AFM probe (about 400 nm in length) is removed by focused ion beam, including the Cr layer 7 and part of the first insulating layer 3. The Cr layer 7 of about 1 μm at the end of the needle tip is annularly removed to provide an etching window a.

[0045] (5) The first insulating layer 3 exposed by the etching window a is etched by inductively coupled plasma etching using CF4 gas for 5 minutes, so that the metal layer 2 is exposed to form a metal tip 21; after the etching is completed, the probe is cleaned by oxygen plasma in the cavity to remove organic impurities remaining on the surface of the needle tip.

[0046] (6) The probe was immersed in a 3% cerium ammonium nitrate solution for about 20 minutes to remove the remaining Cr layer 7 on the surface of the AFM probe. After immersion, the probe was rinsed with deionized water and dried with nitrogen gas.

[0047] (7) Use conductive silver glue 6 to connect the thin wire 4 to the conductive contact area 22 at the end of the probe, and leave it at room temperature for 24 hours to allow the conductive silver glue 6 to completely cure.

[0048] (8) Epoxy resin is evenly coated on the entire substrate and the conductive contact area of ​​the probe, and the epoxy resin is left at room temperature for 24 hours to be completely cured to form a second insulating layer 5 .

[0049] The SEM image of the prepared functionalized atomic force microscope probe tip is shown in Figure 3 As shown, the exposed metal layer at the end forms a metal tip 21 , and the rest is covered by the first insulating layer 3 .

[0050] Example 2

[0051] refer to Figure 4 The functionalized atomic force microscope probe of Example 2 includes a probe body 1 of silicon-based material, the probe body 1 includes a substrate 11, a cantilever 12 and a needle tip 13, the cantilever 12 extends outward from the front end of the substrate 11, and the needle tip 13 is located at the end of the free end of the cantilever 12. The surface of the probe body 1 is sequentially covered with a metal layer 2 and a first insulating layer 3, wherein the end of the needle tip 13 has a metal tip 8 exposed outside the first insulating layer 3, and the metal tip 8 is electrically connected to the metal layer 2. The metal layer 2 at the tail end of the substrate 11 is exposed outside the first insulating layer 3 and forms a conductive contact area 22, and the conductive contact area 22 is electrically connected to the wire 4. A second insulating layer 5 is also provided on the outside of the substrate 11, and the second insulating layer 5 covers the first insulating layer 3, the exposed metal layer 2 and part of the wire 4 on the surface of the substrate 11.

[0052] The difference between this embodiment and embodiment 1 is that the metal tip 8 is not formed by the metal layer 2, but is formed separately, and its material is a conductive metal that can generate plasmon enhancement, including gold, silver, copper and other metals, and its length is 10nm to 10μm, which can achieve similar technical effects. Other settings refer to embodiment 1.

[0053] The following example specifically illustrates the method for preparing the functionalized atomic force microscope probe. Figure 5 .

[0054] (1) A silicon AFM probe is selected as the probe body 1, and a metal layer 2 is formed on the surface of the probe body 1. Specifically, 5 nm Cr and 75 nm Au are evaporated on the back of the probe by electron beam evaporation as a reflective layer to enhance the reflection of the AFM probe cantilever to the feedback laser; 5 nm Cr and 75 nm Au are evaporated on the front of the probe to provide conductivity.

[0055] (2) Place the gold-plated AFM probe on a fixed fixture (partially shield the gold-plated area as a conductive contact area), grow a 50nm silicon oxide layer and a 150nm silicon nitride layer on the surface of the AFM probe by inductively coupled plasma enhanced deposition, and repeat the growth three times to form an inorganic material stack as the first insulating layer 3. The fixture can partially shield the tail end of the probe body so that the first insulating layer 3 is not deposited on this surface area, and the exposed metal layer 2 surface can be used as the conductive contact area 22. In other embodiments, the insulating material can also be deposited as a whole, and the first insulating layer 3 is subsequently opened to form a conductive contact area. .

[0056] (3) The end of the AFM tip (about 1 μm in length) is removed by focused ion beam, including part of the first insulating layer 3 and the metal layer 2, and a small portion of the gold-plated area is exposed on the removed surface.

[0057] (4) The obtained probe is immersed in a gold potassium cyanide solution, and a pulse voltage is provided on the probe to deposit gold at the end of the needle tip as a metal tip 8, and the metal tip 8 is electrically connected to the metal layer 2 exposed on the cut surface. The length of the metal tip 8 is about 1 nm-10 μm.

[0058] (5) Connect the thin wire 4 to the conductive contact area 22 at the end of the probe with conductive silver glue 6, and leave it at room temperature for 24 hours to allow the conductive silver glue 6 to completely solidify.

[0059] (6) The epoxy resin is evenly coated on the entire substrate and the conductive contact area of ​​the probe, and the epoxy resin is left at room temperature for 24 hours to completely cure to form a second insulating layer 5 .

[0060] The SEM image of the prepared functionalized atomic force microscope probe tip is shown in Figure 6As shown, metal is deposited at the end to form a metal tip 8 , and the rest is covered by the first insulating layer 3 .

[0061] The functionalized AFM probes obtained in Example 1 and Example 2 were used to detect the TERS signals of 4-PBT molecules adsorbed on the Au(111) surface to characterize the TERS activity of the needle tip.

[0062] (1) Au(111) was immersed in 160 μM 4-PBT ethanol solution for 5 min, then rinsed with a large amount of ethanol and dried with nitrogen gas.

[0063] (2) Figure 7 (a) and (b) are the TESR signals of Example 1 and Example 2, respectively. Curve 1 is the TERS spectrum of 4-PBT molecules on the surface of gold single crystal (111) in the needle-in state, in which significant characteristic peaks such as 1591cm-1, 1280cm-1 and 1179cm-1 appear. Curve 2 is the TERS spectrum of the needle tip in the withdrawn state, and no characteristic peaks of 4-PBT molecules are detected. The above experimental results prove that the prepared functionalized AFM needle tip has obvious TERS enhancement activity.

[0064] As a comparative example, commercial AFM probe materials are usually silicon or silicon nitride, which can only achieve morphology imaging, but cannot provide Raman signal enhancement and electrochemical current detection functions. The SECM probe is a microelectrode that is partially sealed in a glass tube. It is difficult to achieve morphology imaging and does not have Raman signal enhancement activity. The AFM-TERS probe can achieve morphology imaging and Raman signal enhancement, but it is difficult to achieve SECM function as a microelectrode; the AFM-SECM probe can achieve morphology imaging and SECM imaging, but does not have Raman signal enhancement capability. The functionalized atomic force microscope probe of the present invention simultaneously has the three functions of nano-resolution morphology imaging, million-fold Raman signal enhancement, and picoampere current detection, and can realize the combined use of EC-TERS and SECM technologies.

[0065] The above embodiments are only used to further illustrate a functionalized atomic force microscope probe and a preparation method thereof of the present invention, but the present invention is not limited to the embodiments. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention fall within the protection scope of the technical solution of the present invention.

Claims

1. A functionalized atomic force microscope probe, characterized in that: A probe body comprising a silicon-based material, the probe body comprising a substrate, a cantilever and a needle tip, the cantilever extending outward from the front end of the substrate, the needle tip being located at the end of the free end of the cantilever; the surface of the probe body is sequentially covered with a metal layer and a first insulating layer, wherein the end of the needle tip has a metal tip exposed outside the first insulating layer and electrically connected to the metal layer; The metal layer on the rear end surface of the substrate is exposed outside the first insulating layer and forms a conductive contact area, which is electrically connected to the wire; a second insulating layer is also provided on the surface of the substrate, which covers the conductive contact area.

2. The functionalized atomic force microscope probe according to claim 1, characterized in that: The first insulating layer is an inorganic insulating layer with a thickness of 1 nm-2 μm.

3. The functionalized atomic force microscope probe according to claim 1, characterized in that: The metal layer includes a conductive metal capable of generating plasmon enhancement; the metal tip is formed by the metal layer or by a conductive metal capable of generating plasmon enhancement.

4. The functionalized atomic force microscope probe according to claim 3, characterized in that: The conductive metal capable of generating plasmon enhancement includes gold, silver, copper, a stack containing gold, silver, copper, or an alloy containing gold, silver, copper.

5. The functionalized atomic force microscope probe according to claim 1, characterized in that: The thickness of the metal layer is 1 nm-1 μm.

6. The functionalized atomic force microscope probe according to claim 1, characterized in that: The length of the metal tip is 1 nm-10 μm.

7. The functionalized atomic force microscope probe according to claim 1, characterized in that: The second insulating layer is an organic insulating layer.

8. A method for preparing a functionalized atomic force microscope probe according to any one of claims 1 to 7, characterized in that: include: Step 1, providing a probe body, and depositing a metal layer on the surface of the probe body; Step 2, forming a first insulating layer on the surface of the metal layer; Step 3, removing the first insulating layer at the end of the needle tip and forming a metal tip; In step 2 or after step 2, the metal layer at the rear end of the substrate is exposed outside the first insulating layer to form a conductive contact area; Step 4, electrically connecting the wire to the conductive contact area; Step 5: forming a second insulating layer on the surface of the substrate.

9. The method for preparing a functionalized atomic force microscope probe according to claim 8, characterized in that: Step 3 includes: Covering the surface of the first insulating layer with a sacrificial layer; The sacrificial layer at the end of the needle tip is circularly removed by a focused ion beam to form an etching window; Using inductively coupled plasma etching to remove the first insulating layer exposed by the etching window, so that the exposed metal layer forms a metal tip; The sacrificial layer is removed.

10. The method for preparing a functionalized atomic force microscope probe according to claim 8, characterized in that: Step 3 includes: Cutting off part of the end of the needle tip by using a focused ion beam, until the length of the cutting is enough to expose the surface of the metal layer; Metal is deposited at the end of the needle tip to form a metal tip electrically connected to the metal layer.

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