Light-induced force microscope system and application method thereof

Abstract

The invention provides a light-induced force microscope system and an application method thereof. The system comprises a first laser, an atomic force microscope probe, a photosensitive detector, a first lock-in amplifier, a control box, piezoelectric ceramic, a second lock-in amplifier, a semiconductor laser, a light path system, a sample table, a piezoelectric scanning tube and a host. According to the light-induced force microscope system, the semiconductor laser is used, sine wave modulation is directly carried out on the semiconductor laser through the oscillator in the lock-in amplifier, and the light-induced force microscope system can accurately measure light force information at a needle point-sample position by using a common silicon needle point probe in the atmosphere. By analyzing the light force information, the light-induced force component can be qualitatively identified, and the rigidity, polarizability and other property information of the material can be reflected. According to the invention, accurate measurement of the light force signal on the surface of the two-dimensional material is realized, and a technology which is economical, simple in structure and convenient to operate is provided for identifying components and defects of the two-dimensional material in electronic devices, optoelectronic elements and sensors.

Description

Technical Field

[0001] The present invention belongs to the technical field of two-dimensional material detection systems, and specifically relates to a light-induced force microscope system and an application method thereof. Background Art

[0002] With the rapid development of semiconductor technology, manufacturing processes have reached the 3nm node and are approaching the 1nm physical limit. Further reduction in the size of electronic components has reached a bottleneck. The IEEE International Roadmap for Devices and Systems (IRDS) states that new materials, particularly two-dimensional materials, will be a key cornerstone of next-generation information processing technologies and are expected to serve as channel materials for next-generation field-effect transistors (FETs). Since the first successful isolation of graphene by mechanical exfoliation in 2004, a series of two-dimensional materials, such as transition metal dichalcogenides (TMDs, such as molybdenum disulfide (MoS2)) and hexagonal boron nitride (h-BN), have been successfully synthesized. These materials exhibit high carrier mobility, unique light-matter interactions, remarkable mechanical strength, atomically flat surfaces, ultra-low friction, and excellent thermal conductivity. Compared to single-element materials, vertical or lateral heterojunctions of two-dimensional materials offer enhanced carrier mobility, tunable band gaps, and highly efficient photoelectric responses, showing broad application prospects in fields such as FETs, photodetectors, optoelectronic devices (solar cells), light-emitting diodes, thermoelectric devices, and biosensors.

[0003] In recent years, a lot of research has been carried out on the detection of two-dimensional materials, mainly including three methods: optics, electronics, and mechanics.

[0004] Optical methods: Traditional optical microscopes and white light interferometers have a resolution of about a hundred nanometers due to the Abbe diffraction limit, and can only measure surface morphology, and cannot resolve the components of two-dimensional materials. Scanning near-field optical microscopy (SNOM) can study objects with subwavelength resolution by detecting evanescent waves reflected or transmitted near the sample, overcoming the optical diffraction limit and achieving a spatial resolution of up to 20nm. Tip-enhanced Raman spectroscopy (TERS) combines the chemical selectivity of Raman spectroscopy and can achieve a resolution of 10nm. However, SNOM and TERS have the following main problems: the signal light is interfered by environmental scattering, reducing the signal-to-noise ratio and contrast. The energy coupling efficiency of the nanospot at the probe tip is low, and it is difficult to achieve both high resolution and transmittance.

[0005] Electronic methods include scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HR-TEM). Both can achieve nanometer and subnanometer resolution and distinguish material components. However, the high-energy beam of HR-TEM can cause radiation damage. For subsurface material testing, a focused ion beam (FIB) is required to cut and prepare TEM samples, which can cause irreversible damage to the sample. Furthermore, both methods require testing in a vacuum, which is a limited environment.

[0006] Mechanical methods: mainly include scanning tunneling microscopy (STM) and atomic force microscopy (AFM). The spatial resolution of SPM can reach 0.1nm, which can image atomic structures and defects, but traditional STM requires conductive samples. AFM uses the interaction between the tip and sample atoms to image local structures, including insulating samples, but ordinary AFM can only detect the sample surface and provide information on the sample surface morphology, but cannot provide information on the sample composition. AFM-based infrared spectroscopy technology (AFM-IR) and photothermal induced resonance technology (PTIR) use AFM in conjunction with infrared lasers to identify material types based on the infrared absorption spectrum of the sample. However, the high laser power of this method may cause thermal damage to the material and is mainly used to detect organic compounds with significant thermal expansion coefficients. Traditional photoinduced force microscopy (PiFM) is mainly used to detect materials such as metal nanostructures, polymer films, single-molecule materials, biological samples, quantum dots, etc., and can distinguish the components of the materials. However, AFM-IR, PTIR and PiFM usually use optical parametric oscillator lasers (OPO) or quantum cascade lasers (QCL) as laser sources, equipped with choppers or acousto-optic modulators (AOM) to modulate the laser, and use gold-plated needle tips for detection, which increases the complexity and cost of the system. In addition, due to the use of choppers or acousto-optic modulators (AOM), the laser is not directly modulated by an external trigger of the laser device. At the same time, the AOM will experience phase drift during long scanning processes. Therefore, AFM-IR and PTIR only detect the optical force amplitude and do not measure the corresponding optical force phase signal, while amplitude modulation (AM)-PiFM has shortcomings in accurately capturing the optical force phase signal. Although frequency modulation (FM)-PiFM can achieve higher resolution through precise frequency shift measurement, it needs to be operated under vacuum, with long scanning times and complex operations.

[0007] Therefore, how to provide a new type of photoinduced force microscopy system to achieve accurate measurement of photoforce signals on the surface of two-dimensional materials is a technical problem that needs to be solved urgently. Summary of the Invention

[0008] In order to solve the problems existing in the prior art, the present invention provides a light-induced force microscopy system and an application method thereof, aiming to achieve accurate measurement of the light force signal on the surface of two-dimensional materials.

[0009] To achieve the above object, the present invention provides the following solutions:

[0010] A light-induced force microscope system, comprising: a first laser, an atomic force microscope probe, a photosensitive detector, a first lock-in amplifier, a control box, piezoelectric ceramics, a second lock-in amplifier, a semiconductor laser, an optical path system, a sample stage, a piezoelectric scanning tube, and a host;

[0011] The laser output by the first laser hits the cantilever of the atomic force microscope probe and is reflected to the photosensitive detector; the atomic force microscope probe is used to detect the dynamic force signal between the needle tip and the sample during scanning and convert the force signal into an electrical signal; the photosensitive detector converts the laser into an electrical signal to obtain the normal deflection of the cantilever;

[0012] The second lock-in amplifier demodulates the normal deflection to obtain optical force information; the second lock-in amplifier includes a second oscillator, which simulates and modulates the semiconductor laser with a sine wave, and the semiconductor laser emits a modulated laser according to the modulation signal; the optical path system guides the modulated laser to the needle tip-sample position on the sample stage;

[0013] The first lock-in amplifier demodulates the normal deflection to obtain a first-order amplitude and a first-order phase;

[0014] The control box contains a first oscillator, which inputs a demodulated electrical signal to the piezoelectric ceramic, causing the piezoelectric ceramic to excite the atomic force microscope probe according to the electrical signal; the control box obtains a first feedback signal output by the first lock-in amplifier, and based on the first feedback signal and a preset set value, inputs a z-direction feedback signal to the piezoelectric scanning tube, so that the amplitude of the atomic force microscope probe remains constant, thereby obtaining sample morphology information;

[0015] The host receives the optical force information, the first-order amplitude, the first-order phase and the sample morphology information for data processing.

[0016] Preferably, the optical path system includes: a reflector, a concave lens, a first achromatic lens, a second achromatic lens, a translation stage and a climbing mirror;

[0017] The reflecting mirrors include a first reflecting mirror, a second reflecting mirror, a third reflecting mirror and a fourth reflecting mirror;

[0018] The reflector guides the modulated laser to the needle tip-sample;

[0019] The concave lens and the first achromatic lens form a beam expansion system, and the beam expansion system expands the modulated laser beam;

[0020] The climbing mirror climbs the modulated laser beam after beam expansion;

[0021] The second achromatic lens and the translation stage focus the modulated laser light after climbing up to the needle tip-sample.

[0022] Preferably, the semiconductor laser is a single-wavelength semiconductor laser with a wavelength in the range of ultraviolet, visible light and infrared.

[0023] Preferably, the system further comprises:

[0024] An arbitrary waveform generator is connected after the second lock-in amplifier, and the waveform generator changes the sine wave signal into a square wave signal to perform pulse level modulation on the semiconductor laser.

[0025] Preferably, when the system scans the sample in the tapping mode, the optical force signal demodulation method adopts the heterodyne detection mode.

[0026] Preferably, the modulated laser light emitted by the semiconductor laser is incident from the side or from the bottom of the sample.

[0027] The present invention also provides a two-dimensional material detection method based on a light-induced force microscope system. The method is implemented using the aforementioned light-induced force microscope system, and the method includes:

[0028] S1. Preparation of two-dimensional material samples;

[0029] S2. Setting parameters of the light-induced force microscope system;

[0030] S3, placing the two-dimensional material sample on a sample stage of a light-induced force microscope system with set parameters;

[0031] S4. Start the light-induced force microscope system to distinguish components in the two-dimensional material sample in a tapping mode and detect defects in the two-dimensional material.

[0032] Preferably, the method is also used to detect organic polymers, quantum dots, biological soft tissues, minerals, conductors, semiconductors, and insulator materials other than two-dimensional materials.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] 1. This invention uses a semiconductor laser and utilizes the signal generator in a lock-in amplifier to directly modulate the laser, avoiding the environmental sensitivity and phase drift that can occur during the modulation process with an acousto-optic modulator or chopper. The laser's excitation frequency is directly controlled by the lock-in amplifier, and the phases of the excitation signal and demodulation signal remain synchronized, avoiding the accumulation of phase drift. This significantly improves the phase stability of the entire system and enables a stable and accurate phase of the optical force signal.

[0035] 2. The present invention can achieve high signal-to-noise ratio measurement of photomechanical signals at a laser power of 2 mW. The low excitation power does not damage the sample due to the laser thermal effect.

[0036] 3. The present invention can achieve non-destructive testing in tapping mode;

[0037] 4. The present invention avoids the use of OPO or QCL as a laser source, equips a chopper or AOM for laser modulation, and adopts a silicon needle tip to detect the photoforce signal in the atmosphere, greatly reducing the complexity and cost of the system and simplifying the operation.

[0038] 5. This invention uses side-incident laser light to the probe tip and sample. Compared with traditional side-incident AFM-IR, PTIR and PiFM, it uses a lens to focus the laser instead of an off-axis parabolic mirror, which reduces the cost of the optical system.

[0039] 6. This invention uses side-incident laser light to the probe tip and sample. Compared with bottom-incident AFM-IR, PTIR and PiFM, it does not require an objective lens for focusing, greatly reducing the cost of the optical system.

[0040] 7. The present invention uses side-incident laser to the probe tip and the sample. Compared with bottom-incident AFM-IR, PTIR and PiFM, the substrate used is diversified and does not need to be transparent, which greatly increases the applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the technical solution of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0042] Figure 1 Schematic diagram of the overall design of the light-induced force microscope system according to an embodiment of the present invention;

[0043] Figure 2 Schematic diagram of the optical system design in the laser modulation and focusing module according to an embodiment of the present invention;

[0044] Figure 3 Schematic diagram of the Graphene / MoS2 heterojunction according to an embodiment of the present invention, wherein (a) is a schematic diagram of the morphology; (b) is a schematic diagram of the phase;

[0045] Figure 4 Schematic diagram of the optical force signal scanning the graphene / MoS2 heterojunction in the tapping mode (heterodyne detection) according to an embodiment of the present invention, where (a) is a schematic diagram of the amplitude; (b) is a schematic diagram of the phase;

[0046] Figure 5 Schematic diagram of a single-layer MoS2 produced by CVD according to an embodiment of the present invention, wherein (a) is a schematic diagram of the morphology; (b) is a schematic diagram of the phase;

[0047] Figure 6 Schematic diagram of the photomechanical signal of a single-layer MoS2 produced by scanning CVD in tapping mode (heterodyne detection) according to an embodiment of the present invention, where (a) is an amplitude diagram; (b) is a phase diagram;

[0048] Figure 7 Schematic diagram of mechanically exfoliated graphene according to an embodiment of the present invention, wherein (a) is a schematic diagram of the morphology; (b) is a schematic diagram of the phase;

[0049] Figure 8 Schematic diagram of the optical force signal of scanning Graphene in tapping mode (heterodyne detection) according to an embodiment of the present invention, where (a) is an amplitude diagram and (b) is a phase diagram. DETAILED DESCRIPTION

[0050] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0051] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0052] Example 1

[0053] like Figure 1 As shown, the present invention provides a light-induced force microscope system, comprising: a first laser, an atomic force microscope probe, a photosensitive detector, a first lock-in amplifier, a control box, piezoelectric ceramics, a second lock-in amplifier, a semiconductor laser, an optical path system, a sample stage, a piezoelectric scanning tube, and a host;

[0054] The laser output from the first laser hits the cantilever of the atomic force microscope probe and is reflected to the photodetector. The atomic force microscope probe is used to detect the dynamic force signal between the tip and the sample during scanning and convert the force signal into an electrical signal. The photodetector converts the laser light into an electrical signal to obtain the normal deflection of the cantilever.

[0055] A second lock-in amplifier demodulates the normal deflection to obtain optical force information. The second lock-in amplifier contains a second oscillator, which simulates the modulation of the semiconductor laser with a sine wave. The semiconductor laser emits a modulated laser according to the modulation signal. The optical path system guides the modulated laser to the needle tip-sample position on the sample stage.

[0056] The first lock-in amplifier demodulates the normal deflection to obtain the first-order amplitude and first-order phase;

[0057] The control box contains a first oscillator, which inputs a driving signal to the piezoelectric ceramic, causing the piezoelectric ceramic to drive and excite the atomic force microscope probe. The control box obtains a first feedback signal output by the first lock-in amplifier and, based on the first feedback signal and a preset set value, inputs a z-direction feedback signal to the piezoelectric scanning tube, thereby maintaining a constant amplitude of the atomic force microscope probe and obtaining sample morphology information.

[0058] The host receives the optical force information, first-order amplitude, first-order phase and sample morphology information for data processing.

[0059] Furthermore, the specific implementation process of the present invention is as follows:

[0060] The optical system guides the modulated laser to the needle tip-sample, and simultaneously expands and focuses the beam, reducing the focused spot size by 10 times.

[0061] The second lock-in amplifier is used to 解调 Frequency (f 驱动 With f 调制 The normal deflection of the probe detected by the photosensitive detector is demodulated by mixing and the photoforce phase of the photoforce signal is obtained. The optical force amplitude A2 is the optical force information. At the same time, the second phase-locked amplifier contains a second oscillator, which simulates the modulation of the semiconductor laser with a sine wave, and the modulation frequency is f 调制 .

[0062] The extraction of optical force signal is achieved by deflecting the probe normal, f 驱动 The second lock-in amplifier extracts the normal deflection signal at f 解调 Frequency demodulation is performed to obtain the required optical force phase and optical force amplitude of the optical force signal.

[0063] This invention utilizes the signal generator in a lock-in amplifier to directly modulate the laser, avoiding the environmental sensitivity and phase drift often associated with acousto-optic modulators or choppers. Because the laser's excitation frequency is directly controlled by the lock-in amplifier, the phases of the excitation and demodulation signals remain synchronized, preventing the accumulation of phase drift. This significantly improves the phase stability of the entire system, resulting in a stable and accurate optical force signal phase.

[0064] The semiconductor laser emits modulated laser light according to the modulation signal.

[0065] The atomic force microscope probe is used to detect the dynamic force signal between the probe tip and the sample during the scanning process and convert the force signal into an electrical signal.

[0066] The first laser uses a 650nm laser, the output laser hits the atomic force microscope probe cantilever and is reflected to the photosensitive detector.

[0067] The photosensitive detector converts the changes in the received reflected laser light into electrical signals, thereby obtaining the normal deflection of the probe cantilever.

[0068] The first lock-in amplifier deflects the normal direction according to f 驱动 Demodulate and obtain the first-order phase With the first-order amplitude A1.

[0069] The control box contains a first oscillator, which inputs f to the piezoelectric ceramic 驱动 The electrical signal makes the piezoelectric ceramic follow the f 驱动 The probe is excited. At the same time, the control box obtains the feedback signal output by the first phase-locked amplifier, compares it with the preset set value, and inputs the z-direction feedback signal to the piezoelectric scanning tube, so that the probe amplitude remains constant and the sample morphology information is obtained.

[0070] Furthermore, the set value is preset to 70%, and the probe amplitude is at 70% of the free amplitude. When scanning a sample morphology with a lower height, the probe amplitude increases. For example, when the probe amplitude increases to 72%, the z-direction signal is input to the deflection piezoelectric scanning tube to raise it, so that the tip-sample distance is maintained at 70%, and the Z signal becomes the sample morphology signal; if the sample morphology with a higher height is scanned, the amplitude decreases. For example, when the probe amplitude becomes 68%, the z-direction signal input to the deflection piezoelectric scanning tube causes the scanning tube to be lowered, so that the tip-sample distance is maintained at 70%.

[0071] The piezoelectric scanning tube is responsible for the movement in the xyz direction, where the z direction is closed-loop controlled to keep the probe amplitude constant.

[0072] The sample stage is responsible for placing the sample.

[0073] In the light-induced force microscopy system provided by the present invention, the atomic force microscope probe needs to be 30 nm above the sample, the modulated laser needs to be shot at the needle tip-sample, and other components can be reasonably arranged according to the actual application scenario.

[0074] The present invention simplifies the optical path system. Figure 2 As shown, the optical system includes: a reflector, a concave lens, a first achromatic lens, a second achromatic lens, a translation stage and a climbing mirror;

[0075] The reflectors include a first reflector, a second reflector, a third reflector and a fourth reflector;

[0076] The reflector guides the modulated laser to the needle tip-sample;

[0077] The concave lens and the first achromatic lens form a beam expansion system, which expands the modulated laser beam;

[0078] The climbing mirror climbs the modulated laser beam after beam expansion;

[0079] The second achromatic lens and the translation stage focus the modulated laser light after climbing to the tip-sample.

[0080] Furthermore, the optical path system uses a plano-concave lens with a focal length of -50mm and a first achromatic lens with a focal length of 500mm to form a 10x beam expansion system; then a second achromatic lens with a focal length of 200mm is used to focus the modulated laser after climbing. By adjusting the translation stage, the modulated laser after climbing is focused on the needle tip-sample, and the focused spot size is 14μm.

[0081] The light-induced force microscope was used in tapping mode (f 驱动 =f1, f1 is the first-order natural frequency of the probe), the optical force signal demodulation mode adopts the heterodyne detection mode. In the heterodyne detection mode, the laser modulation frequency is set to f2-f1, f2 is the second-order natural frequency of the probe, and the demodulation frequency is converted to f by the mixer. 驱动 With f 调制 Related, f 解调 =f 调制 +f 驱动 .

[0082] Furthermore, the semiconductor laser used in the present invention is a single-wavelength semiconductor laser with a wavelength in the range of ultraviolet, visible light and infrared.

[0083] In the present invention, an arbitrary waveform generator can be connected after the second lock-in amplifier, and the waveform generator changes the sine wave signal into a square wave signal to perform pulse level modulation on the semiconductor laser.

[0084] In the present invention, when the tapping mode (heterodyne detection) is used, the driving frequency f of the probe is驱动 =f1, laser modulation frequency f 调制 It can also be set to f2+f1, and the demodulation frequency is converted to f by the mixer. 驱动 With f 调制 Related, f 解调 =f 调制 -f 驱动 ;

[0085] In the tapping mode (heterodyne detection), the driving frequency of the probe can be set to f 驱动 =f2, laser modulation frequency f 调制 It can also be set to |f1±f2|, and the demodulation frequency is converted to f by the mixer. 驱动 With f 调制 Related, f 解调 =|f 调制 -f 驱动 |;

[0086] The present invention can replace the atomic force microscope probe with a silicon probe or a gold-plated conductive probe for detecting photoforce signals.

[0087] The first achromatic lens and the second achromatic lens in the optical system of the present invention may also be other optical components with focusing function.

[0088] The modulated laser light emitted by the semiconductor laser of the present invention can be incident from the side or from the bottom of the sample.

[0089] The principle functions of the present invention are as follows:

[0090] 1. The present invention can measure a variety of optical force signals in tapping mode (heterodyne detection). The optically induced force usually includes the photothermal expansion force F th and the light-induced electromagnetic force F ele The photothermal expansion force also includes the light modulation Derjaguin-Muller-Toporov (DMT) force ΔF DMT and light-modulated van der Waals force ΔF vdW The light-induced electromagnetic force includes the light gradient force F grad and light scattering force F scat The optical force signal mainly includes the conservative force, ΔF DMT , ΔF vdW , F grad , non-conservative force, F scat When in tapping mode (heterodyne detection), the detection mainly detects conservative forces that are sensitive to the tip-sample distance. These forces are related to material properties such as polarizability, refractive index, thermal expansion coefficient, etc., which can provide higher contrast.

[0091] 2. When the laser is focused on the tip-sample junction, the light-induced force changes the vibration state of the cantilever. 解调 By frequency-demodulating the optical force signal, the present invention can obtain an optical force phase image in addition to the optical force amplitude. Compared with the optical force amplitude, the optical force phase has higher sensitivity and contrast with the scanned image;

[0092] 3. The present invention can qualitatively evaluate the main components of the light-induced force detected in the scanning area by analyzing the light-force phase of the scanning area. In the tapping mode (heterodyne detection), the light-force signal mainly includes ΔF DMT , ΔF vdW , F grad When affected by ΔF DMT When , the probe's natural frequency shifts to the right and the phase is greater than 0. vdW , F grad Both are attractive forces. When affected by the two, the probe's natural frequency shifts to the left and the phase is less than 0.

[0093] In summary, the present invention provides a novel light-induced force microscope system, which uses a semiconductor laser and does not require a chopper or AOM. The semiconductor laser is directly sinusoidally modulated by the oscillator (signal generator) in the phase-locked amplifier. The light-induced force microscope system can accurately measure the amplitude and phase of the light force signal at the tip-sample under the atmosphere using an ordinary silicon tip probe. By analyzing the amplitude and phase of the light force signal, the light-induced force component can be qualitatively identified, reflecting information about the stiffness, polarizability and other properties of the material. The novel light-induced force microscope system of the present invention can distinguish the components of two-dimensional materials, detect defects, and realize the precise measurement of light force signals on the surface of two-dimensional materials. The present invention provides an economical, simple-structured, and easy-to-operate technology for identifying the components and defects of two-dimensional materials in electronic devices, optoelectronic components, and sensors.

[0094] Example 2

[0095] The present invention also provides a two-dimensional material detection method based on a light-induced force microscope system. The method is implemented using the light-induced force microscope system of the above embodiment, and the method includes:

[0096] S1. Preparation of two-dimensional material samples;

[0097] S2. Setting parameters of the light-induced force microscope system;

[0098] S3, placing the two-dimensional material sample on a sample stage of a light-induced force microscope system with set parameters;

[0099] S4. Start the light-induced force microscope system to distinguish components in the two-dimensional material sample in a tapping mode and detect defects in the two-dimensional material.

[0100] Preferably, the method is also used to detect organic polymers, quantum dots, biological soft tissues, minerals, conductors, semiconductors, and insulator materials other than two-dimensional materials.

[0101] In summary, the present invention can distinguish the components of two-dimensional materials and detect defects, realizing the precise measurement of the photomechanical signals on the surface of two-dimensional materials, and providing an economical, simple-structured, and easy-to-operate technology for identifying the components and defects of two-dimensional materials in electronic devices, optoelectronic components, and sensors.

[0102] Example 3

[0103] Based on the same inventive concept, the present invention provides the following specific application examples according to any of the aforementioned embodiments:

[0104] Instrument settings: The laser power of the light-induced force microscopy system was set to 1.6 mW. In the tapping mode (heterodyne detection), the laser modulation frequency f 调制 =1344.262kHz, demodulation frequency f 解调 =1603.075kHz.

[0105] Sample Preparation: Graphene was transferred onto a substrate (Si(100) wafer with a 300nm thick thermally oxidized SiO2 layer) using polydimethylsiloxane (PDMS) via mechanical exfoliation. For the preparation of the 2D heterojunction (graphene / MoS2), a dry-phase directional transfer method was used. After the MoS2 2D material was prepared on the substrate, the graphene 2D material was exfoliated using PDMS and then directional transferred onto the MoS2 2D material. A single layer of MoS2 was grown using chemical vapor deposition (CVD).

[0106] (1) Figure 3 、 Figure 4 As shown, the graphene / MoS2 heterojunction is subjected to component detection and defect detection.

[0107] The morphology of the graphene / MoS2 heterojunction is shown in Figure 2. Figure 3 As shown in (a), only the height information of the sample can be determined, but the component resolution of the sample cannot be achieved. Similarly, relying on the phase diagram, such as Figure 3 As shown in (b) in the figure, it is also impossible to distinguish the material components of the two.

[0108] Figure 4This is a schematic diagram of the optical force signal scanning the graphene / MoS2 heterojunction in tapping mode (heterodyne detection). The optical force amplitudes of the MoS2 region, graphene region, and SiO2 region in the dotted white box are 2.18μV, 2.01μV, and 1.27μV, and the optical force phases are -100.282°, -107.638°, and -77.160°, respectively.

[0109] When using the tapping mode (heterodyne detection), the optical properties of the material will change due to the type of material and defects, resulting in differences in the optical force amplitude and optical force phase. This is a means of detection based on the physical properties of the material, rather than just characterizing the surface information of the material like the topography and phase diagram. Figure 4 As shown in the figure, the photoforce amplitude map and photoforce phase map can distinguish the graphene area, MoS2 area, and SiO2 substrate; at the same time, they can also identify impurities and wrinkles on the sample surface.

[0110] (2) Figure 5 、 Figure 6 As shown, component detection and defect detection are performed on single-layer MoS2 produced by CVD.

[0111] The morphology of single-layer MoS2 produced by CVD is shown in the figure Figure 5 As shown in (a), only the height information of the sample can be determined, but the contrast is poor and the characterization of the single-layer MoS2 cannot be clearly achieved. Similarly, relying on the phase image, such as Figure 5 As shown in (b), it is also impossible to clearly characterize the single-layer MoS2.

[0112] When using the tapping mode (heterodyne detection), such as Figure 6 As shown in the figure, the optical force amplitude and phase images enable the distinction between CVD-produced single-layer MoS2 and SiO2 substrates, with clear contrast. They also enable the detection of surface impurities. Furthermore, through comprehensive analysis of the optical force amplitude and phase images, surface grain boundaries and wrinkles can be detected.

[0113] (3) Figure 7 、 Figure 8 As shown, the mechanically peeled graphene was subjected to component detection and defect detection.

[0114] The morphology of mechanically exfoliated graphene is shown in Figure 2. Figure 7 As shown in (a), only the height information of the sample can be determined, the contrast is poor, and it is impossible to distinguish whether the surface protrusions are impurities or graphene blocks. Similarly, relying on the phase image, such as Figure 7 As shown in (b), it is also impossible to clearly determine whether the surface protrusions are impurities.

[0115] When using the tapping mode (heterodyne detection), such as Figure 8 As shown in Figure 2, the optical force amplitude map and optical force phase map can distinguish Graphene from SiO2 substrate with obvious contrast. At the same time, the optical force amplitude map and optical force phase map can detect surface impurities (the impurities in the morphology and phase map are Figure 8 In addition, the detection of bubbles on the sample surface was achieved by comprehensive judgment based on the optical force amplitude map and the optical force phase map.

[0116] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A light-induced force microscopy system, characterized in that: The system includes: a first laser, an atomic force microscope probe, a photosensitive detector, a first lock-in amplifier, a control box, piezoelectric ceramics, a second lock-in amplifier, a semiconductor laser, an optical path system, a sample stage, a piezoelectric scanning tube and a host; The laser output by the first laser hits the cantilever of the atomic force microscope probe and is reflected to the photosensitive detector; the atomic force microscope probe is used to detect the dynamic force signal between the needle tip and the sample during scanning and convert the force signal into an electrical signal; the photosensitive detector converts the laser into an electrical signal to obtain the normal deflection of the cantilever; The second lock-in amplifier demodulates the normal deflection to obtain optical force information; the second lock-in amplifier includes a second oscillator, which simulates and modulates the semiconductor laser with a sine wave, and the semiconductor laser emits a modulated laser according to the modulation signal; the optical path system guides the modulated laser to the needle tip-sample position on the sample stage; The first lock-in amplifier demodulates the normal deflection to obtain a first-order amplitude and a first-order phase; The control box contains a first oscillator, which inputs a demodulated electrical signal to the piezoelectric ceramic, causing the piezoelectric ceramic to excite the atomic force microscope probe according to the electrical signal; the control box obtains a first feedback signal output by the first lock-in amplifier, and based on the first feedback signal and a preset set value, inputs a z-direction feedback signal to the piezoelectric scanning tube, so that the amplitude of the atomic force microscope probe remains constant, thereby obtaining sample morphology information; The host receives the optical force information, the first-order amplitude, the first-order phase and the sample morphology information for data processing.

2. The light-induced force microscopy system according to claim 1, characterized in that: The optical path system includes: a reflector, a concave lens, a first achromatic lens, a second achromatic lens, a translation stage and a climbing mirror; The reflecting mirrors include a first reflecting mirror, a second reflecting mirror, a third reflecting mirror and a fourth reflecting mirror; The reflector guides the modulated laser to the needle tip-sample; The concave lens and the first achromatic lens form a beam expansion system, and the beam expansion system expands the modulated laser beam; The climbing mirror climbs the modulated laser beam after beam expansion; The second achromatic lens and the translation stage focus the modulated laser light after climbing up to the needle tip-sample.

3. The light-induced force microscopy system according to claim 1, characterized in that: The semiconductor laser is a single-wavelength semiconductor laser with a wavelength in the range of ultraviolet, visible light and infrared.

4. The light-induced force microscopy system according to claim 1, characterized in that The system further comprises: An arbitrary waveform generator is connected after the second lock-in amplifier, and the waveform generator changes the sine wave signal into a square wave signal to perform pulse level modulation on the semiconductor laser.

5. The light-induced force microscopy system according to claim 1, characterized in that: When the system scans the sample in the tapping mode, the optical force signal demodulation method adopts the heterodyne detection mode.

6. The light-induced force microscopy system according to claim 1, characterized in that The modulated laser light emitted by the semiconductor laser is incident from the side or from the bottom of the sample.

7. A two-dimensional material detection method based on a light-induced force microscope system, the method being implemented using the light-induced force microscope system according to any one of claims 1 to 6, characterized in that: The method comprises: S1. Preparation of two-dimensional material samples; S2. Setting parameters of the light-induced force microscope system; S3, placing the two-dimensional material sample on a sample stage of a light-induced force microscope system with set parameters; S4. Start the light-induced force microscope system to distinguish components in the two-dimensional material sample in a tapping mode and detect defects in the two-dimensional material.

8. The two-dimensional material detection method based on the optically induced force microscopy system according to claim 7, characterized in that: The method can also be used to detect organic polymers, quantum dots, biological soft tissues, minerals, conductors, semiconductors, and insulator materials other than two-dimensional materials.

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