CN117607498A - Scanning probe sensor with three signal channel acquisition functions - Google Patents
Scanning probe sensor with three signal channel acquisition functions Download PDFInfo
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- CN117607498A CN117607498A CN202311535204.0A CN202311535204A CN117607498A CN 117607498 A CN117607498 A CN 117607498A CN 202311535204 A CN202311535204 A CN 202311535204A CN 117607498 A CN117607498 A CN 117607498A
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Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01Q—SCANNING-PROBE TECHNIQUES OR APPARATUS; APPLICATIONS OF SCANNING-PROBE TECHNIQUES, e.g. SCANNING PROBE MICROSCOPY [SPM]
- G01Q60/00—Particular types of SPM [Scanning Probe Microscopy] or microscopes; Essential components thereof
- G01Q60/10—STM [Scanning Tunnelling Microscopy] or apparatus therefor, e.g. STM probes
- G01Q60/16—Probes, their manufacture, or their related instrumentation, e.g. holders
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
- G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
- G01N21/65—Raman scattering
- G01N21/658—Raman scattering enhancement Raman, e.g. surface plasmons
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01Q—SCANNING-PROBE TECHNIQUES OR APPARATUS; APPLICATIONS OF SCANNING-PROBE TECHNIQUES, e.g. SCANNING PROBE MICROSCOPY [SPM]
- G01Q60/00—Particular types of SPM [Scanning Probe Microscopy] or microscopes; Essential components thereof
- G01Q60/24—AFM [Atomic Force Microscopy] or apparatus therefor, e.g. AFM probes
- G01Q60/38—Probes, their manufacture, or their related instrumentation, e.g. holders
- G01Q60/40—Conductive probes
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
- G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
- G01N21/65—Raman scattering
- G01N2021/653—Coherent methods [CARS]
- G01N2021/656—Raman microprobe
Abstract
The invention relates to a scanning probe sensor with three signal channel acquisition functions, and belongs to the field of material analysis and test instruments. The quartz tuning fork comprises a ceramic base, a quartz tuning fork and a probe; the ceramic base is made of insulating materials, and the top surface of one side of the ceramic base is provided with two pole steps which are upwards raised; the quartz tuning fork is provided with an upper arm and a lower arm which are symmetrically equivalent and is fixed on a ceramic base at the two pole steps; the probe of pure silver is fixed at the insulating end of the upper arm, the bottom of the needle bar is connected with a tunneling current wire of pure silver, and the tip of the probe collects weak tunneling current, namely the scanning tunnel microscope function of detecting the surface electrical property of the measured material is realized; the conical tip of the needle point is used for generating a nano-cavity plasmon under the irradiation of laser, so that the needle point enhanced Raman spectrum function of detecting the chemical components on the surface of the measured material is realized; according to the working stability of the atomic force microscope needle point, the atomic force microscope function of detecting the surface structure of the measured material with the mechanical resolution of up to 45pN is realized.
Description
Technical Field
The invention belongs to the field of material analysis and test instruments, and particularly relates to a novel integrated scanning probe sensor which simultaneously realizes surface characterization technologies of three tips of a scanning tunneling microscope STM, an atomic force microscope AFM and a tip enhanced Raman spectrum TERS so as to obtain important information such as electrical properties, topological morphology, chemical components and the like of the surface of a material sample.
Background
Scanning tunneling microscopy (Scanning Tunneling Microscopy, STM), atomic force microscopy (Atomic Force Microscopy, AFM) and Tip-enhanced raman spectroscopy (Tip-Enhanced Raman Spectroscopy, TERS) are three widely used and vital characterization techniques in the field of nanomaterial science.
STM technology was invented by the scientist Gerd Binnig and Heinrich Rohrer in the IBM Zurich laboratory in the last 80 th century based on quantum tunneling effect. They use a sharp metal tip near the surface of the material to be measured, where quantum tunneling of electrons occurs when the distance between them approaches one nanometer. At this time, a certain bias voltage is applied to the material to be tested, so that tunneling current can be formed.
I∝Vρ s (0,E F )e -2Kz (1)
According to formula relation (1) of STM working principle, tunneling current I and needle tip-sample distance z are in e exponential relation, namely every reduction of zI increases by an order of magnitude. It is this tunneling current that is highly sensitive to the distance between the tip and the sample that allows STM to achieve atomic resolution imaging of the material surface. The invention of STM makes human realize observation of molecule and atom for the first time, and opens up a new era of visual measurement and material property control. With such an important breakthrough, two scientists have earned the Nobel physical prize in 1986. However, the working principle of STM limits that the sample to be tested must have good conductivity, and effective performance on semiconductor and insulator materials with larger band gaps cannot be realizedAnd (5) measuring.
To solve this problem, atomic Force Microscopy (AFM) has been developed based on STM. AFM uses an extremely sharp probe to scan the surface of a sample, then measures the resulting minute interaction forces between the probe and the sample, and then computer processes to obtain a topography map of the surface. Unlike STM, AFM tips in dynamic modes of operation typically need to be mounted on an oscillating cantilever. When the cantilever in a stable oscillation state senses the interaction force between the needle point and the sample, the change of the vibration amplitude or frequency can be used as a signal to extract the magnitude of the interaction force. Conventional cantilevers are typically fabricated using silicon materials, also known as silicon cantilevers. A silicon tip is mounted at one end and an external laser system is used to detect the slight deflection of the cantilever under force. Since silicon is a semiconductor, this design makes it difficult to detect tunneling currents, i.e., STM measurements cannot be made simultaneously. The later further developed cantilever based on the quartz tuning fork can utilize the piezoelectric effect of quartz, does not need to introduce an external laser system to detect deflection, and can directly analyze the change of the surface charge of the cantilever. In addition, a conductive needle tip is generally installed at one end of the quartz tuning fork, so that measurement of the STM can be realized while measuring the AFM.
In the field of material characterization, it is an important challenge how to obtain information on the chemical composition of a sample, however, both STM and AFM are not capable of this. Raman spectroscopy, a common spectroscopic analysis technique, has been widely used for the study of the chemical structure of materials. However, the scattering cross section of ordinary raman is very small, usually every 10 6 To 10 10 The generation of only one raman photon per incident photon severely limits chemical structure measurements for micro-molecules as well as single molecules. If a laser is introduced into the nanochamber between the needle tip and the sample, the light will be converted into a nanochamber plasmon generating a very large electric field strength, which will result in an enhanced raman signal, i.e. a tert technique. The advent of tert technology has enabled the analysis of chemical composition of matter on an atomic scale of eating. At present, three technologies of STM, AFM and TERS realize the material tableThe surface is characterized by single bond level resolution (spatial resolution approaching one a meter).
In practical instruments, three scanning microscopy techniques, namely STM, AFM and TERS, need to rely on different scanning probe sensors, and extremely weak current, force and photons are used as detection signals respectively. In contrast to the "blind image", a single technique can only provide partial property information of a material, which can lead to one-sided or even erroneous knowledge of material research, and greatly limits scientific research and engineering application of the material. However, if the measurement by the above three techniques is to be performed, the probe sensor must be switched. To develop measurements of different technologies. The defects are that: 1. from a scientific point of view, this switch is fatal to many targets to be tested that require molecular level size for "in situ" measurements. Since such a mechanical switching is almost impossible to find the same object to be measured again. 2. From a technical point of view, switching between various sensors in ultra-high vacuum and ultra-low temperature environments not only requires complex and accurate operations, but also is extremely prone to cause instability in the state of the surrounding environment, thereby affecting the performance of the next measurement. 3. From an economic standpoint, there are duplicate or similar parts of these probe sensors, so configuring multiple sensors can increase the cost of the associated instrumentation.
In response to this challenge, the global scientific research and industry is actively seeking multiple signal integration measurement technologies and solutions, namely, integrating the three probe sensors. Three two-by-two integration schemes have been reported internationally, namely, the combination of STM and AFM (STM+AFM), the combination of STM and TERS (STM+TERS), and the combination of AFM and TERS (AFM+TERS), respectively. The method comprises the following steps: (1) A method for achieving integrated measurement of stm+afm by designing a cantilever with piezoelectric properties as a sensor is described in US patent 20120131704 A1. They then used tungsten tips without plasmonic activity here and were not able to make tert measurements. (2) In Nature 2013,498,82 paper, the integrated measurement method of sub-nanoscale stm+ters is realized by adjusting and controlling the nano-cavity plasmon mode between the silver needle tip and the sample to match with molecular vibration resonance. However, this method is based on STM tip, without integrating qPlus force sensor, and thus AFM measurement cannot be achieved. (3) In the APL Photonics 4,021301 (2019) article, an integrated measurement method of afm+ters based on qPlus force sensors is reported. Here, they use a conventional silicon cantilever to realize AFM measurement, and cannot realize the function of STM.
However, to date, the integration scheme of three measurement techniques of STM+AFM+TERS has not been reported internationally. The main technical challenge is that STM requires a sensor with excellent conductivity, AFM requires a sensor with excellent mechanical stiffness, and TERS requires a sensor with plasmon response. Meeting these stringent requirements at the same time is extremely difficult in integrated technology, which also why the development of stm+afm+ters integrated scanning probe sensors has not been achieved internationally.
Disclosure of Invention
In order to realize the acquisition functions of three signal channels of a Scanning Tunneling Microscope (STM), an Atomic Force Microscope (AFM) and a Tip Enhanced Raman Spectrum (TERS), and complete the global measurement of electronic states, atomic forces and chemical components on the surface of a material, the invention provides a scanning probe sensor with the acquisition functions of three signal channels.
A scanning probe sensor with three signal channel acquisition functions comprises a ceramic base, a quartz tuning fork and a probe;
the ceramic base is made of insulating materials, is in a flat plate shape formed by an isosceles triangle and a rectangle, and is divided into two parts which are symmetrical and equal by taking the height of the isosceles triangle as a central line;
the top surface of the ceramic base at one side of the central line is provided with two upward-protruding steps, the step at one side corresponding to the tip of the isosceles triangle is a first step 12, and the other side connected with the first step is a second step 13; the first step 12 is lower than the second step 13, and the same side surface of the two steps adjacent to the other side of the center line is a positioning surface 14;
the quartz tuning fork is provided with two completely symmetrical and equivalent cantilevers, namely an upper arm and a lower arm, the rear part of the lower arm is fixed on the positioning surface 14 and the top surface of the ceramic base through insulating heat conducting glue, the opening end of the quartz tuning fork extends to the outside of the tip of the isosceles triangle of the ceramic base, the upper arm of the quartz tuning fork is in a cantilever shape, and the upper arm is positioned above the first step 12;
the cantilever end part of the upper arm is an insulating end 25, and the rear part of the upper arm is provided with an upper electrode 23; the rear part of the lower arm is provided with a lower electrode 24;
the probe 3 is fixed on the insulating end 25 of the upper arm through conductive silver colloid; the material of the probe 3 is pure silver, and the probe 3 consists of a needle bar 31 and a needle tip 32; the bottom of the needle bar 31 is connected with a tunneling current wire 4, the tunneling current wire 4 is made of pure silver, and the needle tip 32 of the probe 3 collects weak tunneling current, namely, a Scanning Tunneling Microscope (STM) function of detecting the surface electrical property of the measured material is realized;
needle tip 32 is a conical tip for generating a nano-cavity plasmon under irradiation of laser light; the Fourier transform component of the surface roughness of the conical tip in the wave vector space can enable the wave vector matching condition along the interface to be realized, and finally, effective coupling of surface plasmons (SPPs) and an external radiation field is realized, so that the needle Tip Enhanced Raman Spectrum (TERS) function of detecting the surface chemical components of the measured material is realized;
noise formulas (3) and (4) in Atomic Force Microscope (AFM) dynamic mode measurement are as follows:
due to thermal noise δk ts thermal And oscillation noise δk ts thermal Is inversely proportional to the quality factor Q of the quartz tuning fork, so that an Atomic Force Microscope (AFM) function of detecting the surface structure of the measured material with a mechanical resolution of up to 45pN is realized.
The further defined technical scheme is as follows:
the ceramic base is made of 99 alumina insulating material, has a hardness of 1500HV, a thermal conductivity of 25w/m.k and a thickness of not less than 0.5mm.
The area of the two pole steps protruding upwards is smaller than half of the area of the ceramic base; the height c of the first step 12 is 0.25mm, the height error is less than 0.05mm, the area of the first step 12 is less than half of the area of the two-pole steps, the distance g between the positioning surface of the first step 12 and the central line of the ceramic base is 0.05mm, and the distance error is less than 0.05mm; the height d of the second step 13 is 0.6mm and the height error is less than 0.1mm.
The intrinsic resonance frequency of the quartz tuning fork is 32.768kHz, and the rigidity coefficient is 1800N/m.
The gold film on the upper arm end surface of the quartz tuning fork is removed or insulated from the rest of the tuning fork by an insulating paste to obtain an insulating end 25.
The probe 3 is made of pure silver, the length k of the probe is smaller than 0.5mm, the diameter of the needle bar 31 is 25-50 mu m, the needle tip 32 is a conical tip with the curvature radius smaller than 100nm, and the surface roughness of the needle tip 32 is smaller than 0.01mm.
The purity of the pure silver is more than 99.999 percent.
The insulating heat-conducting glue is heat-conducting epoxy resin glue.
The conductive silver adhesive is solid silver filled epoxy resin adhesive.
The diameter of the tunneling current wire 4 is one half of the diameter of the needle shaft of the probe 3.
The beneficial technical effects of the invention are as follows:
1. the invention realizes the integrated acquisition of three signals of a Scanning Tunneling Microscope (STM), an Atomic Force Microscope (AFM) and a Tip Enhanced Raman Spectrum (TERS) in a scanning probe microscope, and realizes the simultaneous precise measurement of the electronic state, the mechanical state and the vibration state of the surface of a material. The invention integrates the functions of three devices into one device, greatly expands the breadth and width of technical application and provides global measurement technology for material physical property analysis.
2. The invention adopts 50-micron high-purity metal silver wire as the material for manufacturing the needle point, and utilizes 25-micron high-purity silver wire as a lead to collect weak tunneling current collected by the needle point, thereby realizing detection of the surface electrical property of a material sample, namely measurement by a Scanning Tunneling Microscope (STM). Under the same parameters, the high-purity silver material selected here has the best conductivity in the metal. So that the longitudinal resolution of STM measurement can reach 0.01 nanometer.
3. The E158 quartz tuning fork material adopted by the invention has a rigidity coefficient of 1800N/m. According to the criterion formula (2) of the working stability of an Atomic Force Microscope (AFM) needle tip, the needle tip can stably vibrate with the amplitude smaller than 100 picometers when the material with the high rigidity coefficient is used as a cantilever, and an excellent AFM measurement effect is provided. In addition, the unique connection mode of the quartz tuning fork and the ceramic base ensures that the quartz tuning fork has a quality factor Q value as high as 45000, see FIG. 7. Also because of such high Q value and system stability, AFM measurement has achieved mechanical resolution up to 45 piconewtons, see fig. 12, successfully effecting imaging of the internal framework structure of the organic molecule pentacene, see fig. 11.
4. One end of the 50 micron silver wire was etched using electrochemical etching to have a conical tip with a radius of curvature typically less than 100 nanometers, see fig. 9. The needle point ensures that near free electrons in silver metal generate collective oscillation under the action of an alternating electric field of incident electromagnetic waves, namely, surface plasmons are formed. Highly localized nano-cavity plasmons excited by such tip designs greatly enhance photon absorption and raman scattering processes of individual molecules therein, thereby enabling measurement of single molecule TERS, see fig. 13.
Drawings
FIG. 1 is an overall block diagram of the present invention;
FIG. 2 is a schematic structural view of a ceramic base;
FIG. 3 is a top view of FIG. 2;
FIG. 4 is a schematic diagram of a quartz tuning fork;
FIG. 5 is a schematic structural view of a probe;
FIG. 6 is a schematic diagram of the operation of a scanning probe sensor of the present invention for a scanning probe microscope system;
FIG. 7 is a graph of the measurement of the integrated sensor quality factor Q at liquid helium temperature and ultra-high vacuum;
FIG. 8 is a scanning transmission electron microscope image of a high purity silver needle tip after chemical etching;
fig. 9 is an enlarged view of the broken line rectangle in fig. 8.
FIG. 10 is a graph showing the results of STM imaging of a plurality of pentacene molecules by a scanning probe sensor of the present invention;
FIG. 11 is a graph showing the results of AFM imaging of individual pentacene molecules using a scanning probe sensor of the present invention;
FIG. 12 is a graph of the mechanical resolution measurements of a scanning probe sensor according to the present invention;
FIG. 13 is a graph showing the results of TERS measurements performed on individual pentacene molecules by a scanning probe sensor of the present invention.
Sequence numbers in fig. 1-6: the device comprises a ceramic base 1, a first step 12, a second step 13, a positioning surface 14, a quartz tuning fork 2, an upper arm 21, a lower arm 22, an upper electrode 23, a lower electrode 24, an insulating end 25, a probe 3, a tunneling current wire 4, a needle rod 31, a needle tip 32, a scanning probe sensor 5, a vacuum cavity 6, a scanning tube 7, a measured material 8, a prism 9, an optical window 10 and an optical detection device 11.
Detailed Description
The invention is further described by way of examples with reference to the accompanying drawings.
Referring to fig. 1, a scanning probe sensor with three signal channel acquisition functions includes a ceramic base 1, a quartz tuning fork 2, and a probe 3.
Referring to fig. 2, the ceramic base 1 is formed in a flat plate shape consisting of an isosceles triangle and a rectangle, and is divided into two parts which are symmetrically equal by taking the height of the isosceles triangle as a center line. The ceramic base 1 is made of 99 alumina insulating material, has a hardness of 1500HV, a thermal conductivity of 25w/m.k, and a rectangular shape in the ceramic base 1 has a length a of 2.5mm, a width e of 1.7mm, and a thickness b of not less than 0.5mm.
Referring to fig. 2, the top surface of the ceramic base 1 at one side of the center line is provided with two pole steps protruding upwards, and the area of the two pole steps is smaller than half of the area of the ceramic base. The step on one side corresponding to the tip of the isosceles triangle is a first step 12, and the other side connected with the isosceles triangle is a second step 13. The first step 12 is lower than the second step 13, and the same side surface of the two-pole steps adjacent to the other side of the center line is a positioning surface 14.
Referring to fig. 2 and 3, the height c of the first step 12 is 0.25mm, the height error is less than 0.05mm, the area of the first step 12 is less than half of the area of the two pole steps, the distance g between the positioning surface of the first step 12 and the center line of the ceramic base is 0.05mm, and the distance error is less than 0.05mm. The height d of the second step 13 is 0.6mm, the height error is less than 0.1mm, the length i of the second step 13 is 0.71mm, and the width f is 0.70mm.
Referring to fig. 4, the quartz tuning fork has two completely symmetrical and equivalent cantilevers, an upper arm 21 and a lower arm 22, the four outer sides of which are respectively plated with a specific gold film wire as a conductive electrode at the time of shipment. The rear part of the lower arm is fixed on the positioning surface 14 and the top surface of the ceramic base by a heat conducting epoxy resin glue and baked at 150 ℃ for one hour, so that the lower arm 22 is ensured to be firmly fixed on the ceramic base 1, and no extra noise is generated when the sensor works. The open end of the quartz tuning fork extends to the outside of the tip of the isosceles triangle of the ceramic base, so that the upper arm of the quartz tuning fork is cantilevered and is located above the first step 12.
The quartz tuning fork was an E158 quartz tuning fork manufactured by Microcrystal AG, switzerland, having an intrinsic resonance frequency of 32.768kHz and a stiffness coefficient of 1800N/m.
The gold film on the upper arm end surface of the quartz tuning fork is removed to insulate the other parts of the tuning fork and to obtain an insulated end 25.
An upper electrode 23 is mounted on the rear of the upper arm, and a lower electrode 24 is mounted on the rear of the lower arm.
The stability criteria for Atomic Force Microscopy (AFM) in dynamic mode are:
in the above formula (2), k is the rigidity coefficient of an Atomic Force Microscope (AFM) cantilever, a is the amplitude of the cantilever when vibrating, and V and z are the potential energy and the distance between the tip of the Atomic Force Microscope (AFM) and the sample to be measured, respectively. Therefore, according to the formula (2), the high rigidity coefficient k value of the quartz tuning fork 3 ensures that the cantilever can stably vibrate with relatively small amplitude, and is beneficial to increasing the contribution of short-range forces such as bubble repulsive force and the like in Atomic Force Microscope (AFM) imaging, so that atomic-level resolution is realized.
Referring to fig. 5, the probe 3 is fixed to the insulating end 25 of the upper arm by a solid silver filled epoxy glue. The probe 3 is composed of a needle bar 31 and a needle tip 32. The material of the probe 3 is pure silver with purity of more than 99.999%, the length k of the pure silver is less than 0.5mm, the diameter of the needle bar 31 is 50 μm, the needle tip 32 forms a conical tip with curvature radius of less than 100nm through chemical corrosion, and the surface roughness of the needle tip 32 is less than 0.01mm, see fig. 8 and 9.
The bottom of the needle bar 31 is connected with a tunneling current wire 4, the tunneling current wire 4 is made of pure silver, and the diameter of the tunneling current wire 4 is 25 μm. The collection of weak tunneling current by the needle tip 32 of the probe 3 realizes a Scanning Tunneling Microscope (STM) function of detecting the electrical property of the surface of the measured material.
Needle tip 32 is a conical tip for generating a nano-cavity plasmon under irradiation of laser light; referring to fig. 8, a conical tip is obtained by a chemical etching method. Referring to fig. 9, the radius of curvature of the tip was measured to be 69.37nm. The wavevector values of surface plasmons (Surface Plasmon Polaritons, SPPs) are higher at each frequency than the free-light wavevector at the same frequency, whereas at the interface, the wavevector values of SPPs cannot match the wavevector values of free photons. When the interface is flat, the wave vector matching condition cannot be satisfied, which results in that the SPPs cannot be coupled with free photons outside the interface, and cannot excite or emit photons. In order to achieve the interaction between SPPs and free photons, a special structure is required to satisfy the wave-vector matching condition to excite the surface plasmon. The method has the advantages that tiny surface roughness is introduced on the very close smooth metal surface of the tip of the probe through a chemical corrosion method, fourier transform components of the surface roughness in a wave vector space can enable wave vector matching conditions along an interface to be realized, and finally effective coupling of SPPs and an external radiation field is realized, so that the working principle of Tip Enhanced Raman Spectrum (TERS) is met, and the function of Tip Enhanced Raman Spectrum (TERS) for detecting chemical components on the surface of a detected material is realized.
Referring to fig. 7, the quality factor Q of the probe sensor was measured, and the result was as high as 45000. Noise formulas (3) and (4) in Atomic Force Microscope (AFM) dynamic mode measurement are as follows:
due to thermal noise δk ts thermal And oscillation noise δk ts thermal Is inversely proportional to the quality factor Q of the quartz tuning fork, so that an Atomic Force Microscope (AFM) function of detecting the surface structure of the measured material with a mechanical resolution of up to 45pN is realized.
Referring to fig. 6, when the scanning probe sensor with the collection function of three signal channels of the present invention is used for detection, it is assembled in the vacuum chamber 6 of the 1400 type scanning probe microscope system manufactured by Unisoku corporation of japan, the lower electrode 24 is connected to the ground wire, and the upper electrode 23 is connected to the Atomic Force Microscope (AFM) channel of the scanning probe microscope system for collecting the piezoelectric charges generated when the upper arm 21 is forced to vibrate.
The measured material 8 is single pentacene molecules adsorbed on the surface of Ag (110) monocrystal, and is arranged right above the scanning probe sensor 5 in the vacuum cavity 6 and keeps a distance of approximately one nanometer from the tip of the probe 3.
When the surface electrical property of the measured material 8 is detected, the probe 3 needs to be kept at zero potential, and at the moment, a certain bias voltage is applied to the measured material, so that tunneling current can be formed between the needle point and the surface of the material. By using the tunneling current as a signal, the probe is further moved to scan the surface of the measured material 8, and an STM image of the surface can be obtained; referring to fig. 10, the measured material 8 is biased with 0.1V, and tunneling current is formed between the needle tip 3 and the Ag (110) single crystal surface. The tunneling current is set to be a specific value of 200pA by using a constant current mode, when the needle tip 3 scans above pentacene molecules, the tunneling current is larger than the set value of 200pA due to the existence of electron states of the molecules, and at the moment, the probe 3 is far away from the surface of the sample so as to keep the tunneling current constant. By using the height variation of the probe in the direction perpendicular to the surface of the material, the morphology of single benzene-free molecules can be imaged, and the morphology of eight pentacene molecules presenting a spindle shape can be seen.
When detecting the atomic force of the material 8 to be measured, the scanning tube 7 is applied with the tuning fork resonance frequency f 0 A uniform alternating voltage, at which the scanning tube 7 will have a frequency f 0 And (5) vibrating. Because the scanning tube 7 is rigidly connected with the probe sensor 5, the quartz tuning fork 2 can generate forced vibration with the vibration frequency f 0 . When the probe 3 senses the force from the measured material 8, the vibration frequency of the quartz tuning fork 2 is f 0 Will move and become f 0 + - Δf; this shift in frequency Δf is used as a signal for AFM imaging. Referring to fig. 11, the tip of probe 3 was modified with CO molecules, and AFM imaging of a single pentacene molecular skeleton structure was achieved in a constant height mode, in which five benzene rings were clearly visible. Referring to FIG. 12, a mechanical resolution of about 45pN can be obtained by performing a force spectrum on the C-C chemical bond of the molecule.
When the chemical components of the measured material are detected, p-polarized laser with 532nm wavelength is focused between the probe 3 and the measured material 8 in a grazing incidence mode, and then the nano-cavity plasmon is excited. The light absorption and raman scattering processes of the individual pentacene molecules therein are greatly enhanced. The scattered raman photons are converted into far-field photon signals by the antenna of the probe 3. These far-field raman photons are collected by the prism 9 and finally enter the optical detection means 11 through the optical window 10; referring to fig. 13, the raman spectra collected on individual pentacene molecules, the arrow indicates the raman peak associated with a particular molecular vibration.
Claims (10)
1. A scanning probe sensor with three signal channel acquisition functions, which is characterized in that: the quartz tuning fork comprises a ceramic base, a quartz tuning fork and a probe;
the ceramic base is made of insulating materials, is in a flat plate shape formed by an isosceles triangle and a rectangle, and is divided into two parts which are symmetrical and equal by taking the height of the isosceles triangle as a central line;
the top surface of the ceramic base at one side of the central line is provided with two pole steps which are raised upwards, the step at one side corresponding to the tip of the isosceles triangle is a first step (12), and the other side connected with the first step is a second step (13); the first step (12) is lower than the second step (13), and the same side surface of two steps adjacent to the other side of the center line is a positioning surface (14);
the quartz tuning fork is provided with two completely symmetrical and equivalent cantilevers, namely an upper arm and a lower arm, the rear part of the lower arm is fixed on a positioning surface (14) and the top surface of the ceramic base through insulating heat conducting glue, the opening end of the quartz tuning fork extends to the outside of the tip of an isosceles triangle of the ceramic base, so that the upper arm of the quartz tuning fork is cantilever-shaped, and the upper arm is positioned above the first step (12);
the cantilever end part of the upper arm is an insulating end (25), and the rear part of the upper arm is provided with an upper electrode (23); a lower electrode (24) is arranged at the rear part of the lower arm;
the probe (3) is fixed on the insulating end (25) of the upper arm through conductive silver colloid; the material of the probe (3) is pure silver, and the probe (3) consists of a needle bar (31) and a needle tip (32); the bottom of the needle bar (31) is connected with a tunneling current wire (4), the tunneling current wire (4) is made of pure silver, and the needle point (32) of the probe (3) collects weak tunneling current, namely, the function of a Scanning Tunnel Microscope (STM) for detecting the surface electrical property of the tested material is realized;
the needle point (32) is a conical tip which is used for generating a nano-cavity plasmon under the irradiation of laser; the Fourier transform component of the surface roughness of the conical tip in the wave vector space can enable the wave vector matching condition along the interface to be realized, and finally, effective coupling of surface plasmons (SPPs) and an external radiation field is realized, so that the needle Tip Enhanced Raman Spectrum (TERS) function of detecting the surface chemical components of the measured material is realized;
noise formulas (3) and (4) in Atomic Force Microscope (AFM) dynamic mode measurement are as follows:
due to thermal noise δk tsthermal And oscillation noise δk tsthermal Is inversely proportional to the quality factor Q of the quartz tuning fork, so that an Atomic Force Microscope (AFM) function of detecting the surface structure of the measured material with a mechanical resolution of up to 45pN is realized.
2. A scanning probe sensor with three signal path acquisition functions according to claim 1, characterized in that: the ceramic base is made of 99 alumina insulating material, has a hardness of 1500HV, a thermal conductivity of 25w/m.k and a thickness of not less than 0.5mm.
3. A scanning probe sensor with three signal path acquisition functions according to claim 1, characterized in that: the area of the two pole steps protruding upwards is smaller than half of the area of the ceramic base; the height c of the first step (12) is 0.25mm, the height error is less than 0.05mm, the area of the first step (12) is less than half of the area of the two-pole steps, the distance g between the positioning surface of the first step (12) and the central line of the ceramic base is 0.05mm, and the distance error is less than 0.05mm; the height d of the second step (13) is 0.6mm, and the height error is less than 0.1mm.
4. A scanning probe sensor with three signal path acquisition functions according to claim 1, characterized in that: the intrinsic resonance frequency of the quartz tuning fork is 32.768kHz, and the rigidity coefficient is 1800N/m.
5. A scanning probe sensor with three signal path acquisition functions according to claim 1, characterized in that: the gold film on the upper arm end surface of the quartz tuning fork is removed or insulated from the other parts of the tuning fork by insulating glue to obtain an insulated end (25).
6. A scanning probe sensor with three signal path acquisition functions according to claim 1, characterized in that: the probe (3) is made of pure silver, the length k of the probe is smaller than 0.5mm, the diameter of the needle rod (31) is 25-50 mu m, the needle point (32) is a conical tip with the curvature radius smaller than 100nm, and the surface roughness of the needle point (32) is smaller than 0.01mm.
7. A scanning probe sensor with three signal path acquisition functions according to claim 1, characterized in that: the purity of the pure silver is more than 99.999 percent.
8. A scanning probe sensor with three signal path acquisition functions according to claim 1, characterized in that: the insulating heat-conducting glue is heat-conducting epoxy resin glue.
9. A scanning probe sensor with three signal path acquisition functions according to claim 1, characterized in that: the conductive silver adhesive is solid silver filled epoxy resin adhesive.
10. A scanning probe sensor with three signal path acquisition functions according to claim 1, characterized in that: the diameter of the tunneling current wire (4) is one half of the diameter of the needle rod of the probe (3).
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