Method for regulating interfacial friction of van der waals heterojunction, in-situ measurement system and method

Abstract

The application provides a method for regulating van der Waals heterojunction interlayer friction, an in-situ measurement system and a method, and belongs to the technical field of light-controlled interlayer friction. The method comprises the following steps: controlling excitation light beams to be irradiated to a two-dimensional van der Waals heterojunction sliding interface; wherein the sliding interface is formed by the contact between a first two-dimensional semiconductor material layer and a second two-dimensional semiconductor material layer, and the photon energy of the excitation light beams matches the band edge electron transition energy of the first two-dimensional semiconductor material layer, so as to induce the cross-layer transfer of photo-generated electrons; the irradiation state of the excitation light beams is controlled to be changed to change the cross-layer transfer strength of the photo-generated electrons, so as to regulate the interlayer friction of the sliding interface when relative sliding occurs. The application can realize the reversible regulation and control of the interlayer friction of the two-dimensional van der Waals heterojunction through a non-contact mode and by using a clear physical mechanism.

Description

Technical Field

[0001] This invention relates to the field of optically controlled interlayer friction technology, and in particular to a method for controlling interlayer friction in van der Waals heterostructures, an in-situ measurement system and method. Background Technology

[0002] Two-dimensional van der Waals heterojunctions are formed by stacking different two-dimensional semiconductor materials through weak van der Waals forces. They have atomically flat interfaces and tunable band arrangements, and have important applications in nanotribology, micro-nano electromechanical systems and solid lubrication.

[0003] Existing methods for controlling interlayer friction mainly rely on external conditions such as mechanical load, scanning speed, interface contamination, humidity, or electric field. These methods are usually slow to control, have poor spatial selectivity, and are prone to introducing irreversible structural changes, making it difficult to achieve rapid, local, reversible, and continuous control of van der Waals interface friction. Summary of the Invention

[0004] This invention provides a method for controlling interlayer friction in van der Waals heterostructures, an in-situ measurement system and method, which can achieve reversible control of interlayer friction in two-dimensional van der Waals heterostructures through non-contact means and by utilizing a clear physical mechanism.

[0005] In a first aspect, the present invention provides a method for controlling interlayer friction in van der Waals heterostructures, comprising: An excitation beam is directed onto the sliding interface of a two-dimensional van der Waals heterojunction; wherein the sliding interface is formed by the contact between a first two-dimensional semiconductor material layer and a second two-dimensional semiconductor material layer, and the photon energy of the excitation beam is matched with the band-edge electron transition energy of the first two-dimensional semiconductor material layer to induce photogenerated electrons to undergo interlayer transfer. The irradiation state of the excitation beam is controlled to change the intensity of translayer transfer of photogenerated electrons, thereby adjusting the interlayer friction force of the slip interface when relative slip occurs.

[0006] In some embodiments, controlling the change in the irradiation state of the excitation beam to adjust the interlayer frictional force of the sliding interface during relative slippage includes: The incident light power of the excitation beam is continuously adjusted to continuously adjust the magnitude of the interlayer friction force; The excitation beam is controlled to be turned on and off in order to achieve reversible switching of the interlayer friction response.

[0007] In some embodiments, both the first two-dimensional semiconductor material layer and the second two-dimensional semiconductor material layer are transition metal chalcogenide monolayer materials; the wavelength of the excitation beam is configured as a resonant excitation wavelength to maximize the translayer transfer intensity of photogenerated electrons while excluding photothermal effects.

[0008] Secondly, the present invention also provides an in-situ measurement system for controlling interlayer friction in van der Waals heterostructures, comprising: The first friction pair assembly is mounted on the probe tip of an atomic force microscope, and the probe tip is fixed with a first two-dimensional semiconductor material layer; The second friction pair component has a second two-dimensional semiconductor material layer fixed on its surface; wherein the first two-dimensional semiconductor material layer and the second two-dimensional semiconductor material layer are in contact to form a two-dimensional van der Waals heterojunction sliding interface; A photoexcitation control component for irradiating the sliding interface with an excitation beam of adjustable power and wavelength; A spot alignment component is used to monitor and adjust the transmission optical path of the excitation beam so that the spot of the excitation beam coincides spatially with the scanning area of ​​the probe on the second friction pair component; A data processing component, which is communicatively connected to the atomic force microscope, is used to obtain the interlayer friction force of the sliding interface when relative slippage occurs, based on the lateral force signals of the sliding interface during forward and reverse scanning in the probe scanning process.

[0009] In some embodiments, both the first friction pair assembly and the second friction pair assembly include a dielectric support layer. The second friction pair assembly sequentially includes a rigid substrate, the dielectric support layer, and a second two-dimensional semiconductor material layer. The probe tip is fixed with the dielectric support layer by a van der Waals transfer process, and the first two-dimensional semiconductor material layer is attached to the dielectric support layer at the probe tip.

[0010] In some embodiments, it also includes: The transient absorption spectroscopy testing component, coupled to the photoexcitation control component, is used to emit a femtosecond-level first beam for excitation and a second beam for monitoring to the slip interface, and to obtain in situ the lifetime and spatial diffusion coefficient of the interlayer electron-hole pairs of the slip interface under photoexcitation.

[0011] Thirdly, the present invention also provides an in-situ measurement method for controlling interlayer friction in van der Waals heterostructures, executed by the in-situ measurement system for controlling interlayer friction in two-dimensional van der Waals heterostructures as described in the second aspect, the in-situ measurement method comprising: The photoexcitation control component is controlled to shut off the excitation beam and drive the probe of the atomic force microscope to scan and obtain the initial interlayer friction force; The photoexcitation control component is controlled to turn on the excitation beam and adjust the wavelength of the excitation beam to match the resonant wavelength of the band-edge transition energy, thereby driving the probe of the atomic force microscope to scan and obtain the interlayer frictional force under the resonant excitation state. The change in interlayer friction induced by the excitation beam is obtained based on the interlayer friction under the resonant excitation state and the initial interlayer friction.

[0012] In some embodiments, after obtaining the interlayer frictional force in the resonant excitation state, the method further includes: The photoexcitation control component is controlled to switch the excitation beam to a non-resonant wavelength with insufficient energy to effectively excite band-edge electron transitions, and the interlayer friction force in the non-resonant state is obtained. If the interlayer friction force in the non-resonant state does not change significantly compared to the initial interlayer friction force, it is established that the change in the interlayer friction force originates from interlayer charge transfer.

[0013] In some embodiments, it also includes: The photoexcitation control component is controlled to cycle on and off the excitation beam, and the interlayer friction force under different illumination conditions is obtained to verify the reversibility of the interlayer friction force regulation process.

[0014] Fourthly, the present invention also provides a light-controlled micro / nano tribological device, comprising: A movable friction assembly includes a stator assembly and a mover assembly disposed opposite to each other. The stator assembly includes a first two-dimensional semiconductor material layer, and the mover assembly includes a second two-dimensional semiconductor material layer. The first two-dimensional semiconductor material layer and the second two-dimensional semiconductor material layer are arranged opposite to each other and in contact to form a two-dimensional van der Waals heterojunction sliding interface having a second type of band arrangement. An external drive component is used to drive the mover assembly to slide relative to the stator assembly; The photoexcitation control component is used to irradiate the sliding interface with an excitation beam and induce interlayer charge transfer by adjusting the irradiation state of the excitation beam, thereby adjusting the interlayer friction force of the movable friction component in real time during operation in a non-contact manner.

[0015] In some embodiments, the photoexcitation control component is configured to emit a periodically modulated pulsed excitation beam toward the sliding interface; wherein the modulation frequency of the pulsed excitation beam is configured to be coupled to the mechanical stick-slip vibration frequency of the movable friction component during operation, so as to suppress unstable stick-slip during the sliding process of the moving component by dynamically adjusting the interlayer friction force of the sliding interface.

[0016] In some embodiments, the light-controlled micro / nano tribological device is a two-dimensional material photo-induced solid lubrication structure or a microelectromechanical system with adjustable interface energy dissipation.

[0017] This invention achieves non-contact optical control of interlayer friction in two-dimensional heterostructures. Compared with traditional methods that rely on mechanical loads, scanning speeds, or changes in surface chemistry, this invention can alter interlayer friction simply by adjusting the incident light beam, without requiring changes to the mechanical structure or external environment. It offers advantages such as being non-contact, localized, and easily integrated. Furthermore, since the generation and recombination of photogenerated electrons are very rapid and reversible, this invention provides a physical basis for achieving rapid and reversible friction control. Moreover, by explicitly limiting the photon energy of the excitation beam to match the transition energy of band-edge electrons, it ensures that the control effect primarily originates from photoinduced electronic processes rather than photothermal effects, providing a basis for subsequent precise control. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced one by one below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0019] Figure 1 This is a schematic flowchart of a method for controlling interlayer friction in a van der Waals heterostructure provided in an embodiment of the present invention; Figure 2 This is a schematic diagram illustrating the working mechanism of a method for controlling interlayer friction in a two-dimensional van der Waals heterostructure provided in an embodiment of the present invention; Figure 3 This is a schematic diagram illustrating the variation of interlayer friction force in a two-dimensional van der Waals heterostructure with normal load, provided by an embodiment of the present invention. Figure 4 This is a schematic diagram illustrating the variation of interlayer friction force in a two-dimensional van der Waals heterostructure with normal load under different external scanning rates, provided by an embodiment of the present invention. Figure 5 This is a schematic diagram of the in-situ optical properties of a two-dimensional van der Waals heterojunction slip interface provided in an embodiment of the present invention; Figure 6 This is a schematic diagram of the structure of an in-situ measurement system for controlling interlayer friction of van der Waals heterostructures provided in an embodiment of the present invention; Figure 7 This is a schematic diagram of the real-time imaging field of a microscope for a spot alignment component in an in-situ measurement system provided by an embodiment of the present invention; Figure 8 This is a basic characterization diagram of a second friction pair component and a dielectric support layer provided in an embodiment of the present invention; Figure 9 This is a basic characterization diagram of a first friction pair component and a dielectric support layer provided in an embodiment of the present invention; Figure 10This is a schematic diagram of the lateral distribution obtained by a transient absorption spectroscopy testing component provided in an embodiment of the present invention; Figure 11 This is a schematic diagram of two-dimensional spatial diffusion of interlayer electron-hole pairs provided in an embodiment of the present invention; Figure 12 This is a schematic diagram of the two-dimensional spatial diffusion coefficient of interlayer electron-hole pairs provided in an embodiment of the present invention; Figure 13 This is a schematic flowchart of an in-situ measurement method for controlling interlayer friction in van der Waals heterostructures provided in an embodiment of the present invention. Figure 14 This is a schematic diagram illustrating the stability and reversibility test of interlayer friction response provided in an embodiment of the present invention; Figure 15 This is a schematic diagram comparing interlayer friction response in an in-situ measurement method provided by an embodiment of the present invention; Figure 16 This is a schematic diagram of the lifetime evolution of interlayer electron-hole pairs provided in an embodiment of the present invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0021] Two-dimensional van der Waals materials and their heterostructures possess atomically flat surfaces, weak interlayer van der Waals coupling, and tunable bandgap arrangements, providing an ideal platform for studying interfacial friction, interlayer slip, energy dissipation, and photoelectric coupling behavior. In two-dimensional material systems such as graphene, hexagonal boron nitride, and transition metal chalcogenides, interlayer friction not only determines the mechanical stability during material stacking, peeling, transfer, and slippage, but also directly affects the interfacial reliability in nanodevices, micro / nano-electromechanical structures, flexible devices, and low-dimensional solid lubrication systems.

[0022] Existing techniques for controlling and measuring interlayer friction in two-dimensional materials suffer from the following shortcomings: First, traditional friction control methods lack rapid, reversible, and localized adjustment capabilities. Traditional interlayer friction control primarily relies on external conditions such as mechanical load, scanning speed, interface contamination, humidity, strain, rotation angle, surface roughness, or electric field. However, these methods are typically slow in speed and have poor spatial selectivity, often making it difficult to achieve rapid switching, continuous adjustment, and reversible cycling within the same sample region. Furthermore, some methods can cause permanent changes in interface structure, adsorption state, or slip trajectory, easily introducing irreversible structural changes. Second, existing photo-induced friction experiments struggle to distinguish between photothermal effects and real interface electronic effects. Ordinary continuous illumination may simultaneously introduce multiple effects such as thermal expansion, localized temperature rise, carrier generation, and surface adsorption changes, making it difficult to determine whether frictional changes originate from interlayer charge transfer itself. Therefore, it is necessary to combine wavelength selection, control experiments, and ultrafast dynamic characterization to confirm the dominant role of photo-induced charge transfer in interlayer friction.

[0023] Third, there is a lack of experimental systems that directly link picosecond-level charge transfer dynamics with nanoscale tribological responses. Interlayer charge transfer typically occurs on the femtosecond to picosecond scale, while atomic force microscopy (AFM) tribological tests usually record mechanical responses on the millisecond to second scale. Existing technologies lack a cross-scale experimental platform capable of simultaneously verifying photogenerated charge transfer, interlayer electron-hole pair diffusion, and changes in tribological response. Fourth, conventional AFM tribological tests cannot actively control the interface electronic structure. Traditional AFM lateral force tests mainly reflect the tribological behavior under a given interface state. They typically only allow for changes in mechanical boundary conditions through external loads or scanning speeds, making it difficult to adjust the interface charge distribution, interlayer coupling strength, and potential energy surface morphology in real time during the test. Fifth, interface tribological control lacks clearly quantifiable input variables. In existing methods, tribological control often relies on environmental or structural factors that cannot be precisely controlled. This invention, by adjusting the incident light power, wavelength, and spot position, makes the photogenerated carrier density a controllable input and establishes a correspondence between it and changes in tribological force. Therefore, there is an urgent need for a non-contact, reversible, continuous, localized interlayer friction control method with a clear physical mechanism in two-dimensional van der Waals heterostructures, which can simultaneously obtain photoinduced charge transfer dynamics and frictional response under in-situ conditions.

[0024] To address the aforementioned technical challenges, the applicant discovered interlayer charge transfer in two-dimensional semiconductor heterostructures, providing a novel physical approach for controlling interfacial friction. Two-dimensional van der Waals heterostructures with type II band arrangement can form interlayer electron-hole pairs at the interface under specific photoexcitation conditions. This process alters the charge distribution, local electric field, interlayer coupling strength, and potential energy surface fluctuations at the interface, thereby changing energy dissipation and frictional resistance during interlayer slip. Therefore, combining photoexcited charge transfer with in-situ interlayer friction measurement holds promise for achieving a non-contact, rapid, reversible, and continuously adjustable method for controlling interlayer friction in two-dimensional heterostructures.

[0025] Therefore, this invention relates to the fields of two-dimensional materials, nanotribology, photoelectric modulation, and in-situ atomic force microscopy testing technology. Specifically, it relates to a method and in-situ measurement system for controllingly modulating interlayer friction by inducing interlayer charge transfer in a two-dimensional semiconductor heterojunction using photoexcitation and adjusting the interface electronic structure and energy dissipation. By exciting the two-dimensional semiconductor heterojunction with light of a specific wavelength, photogenerated carriers are generated in one of the semiconductor layers, leading to interlayer charge transfer and the formation of interlayer electron-hole pairs. This alters the interface charge distribution, interlayer attraction, and slip potential surface fluctuations, ultimately achieving controllable adjustment of interlayer friction. For example, an in-situ measurement platform coupling a femtosecond photoexcitation system and an atomic force microscope (AFM) tribological testing system was constructed based on a tungsten diselenide / tungsten disulfide van der Waals heterojunction. Interlayer charge transfer from tungsten diselenide to tungsten disulfide was induced by 740nm resonant light excitation, and the interlayer friction response was recorded in real time using an AFM, establishing a control path for photoexcitation, charge transfer, interface interaction reconstruction, and enhanced interlayer friction.

[0026] In summary, the embodiments of this invention address the following problems existing in the control of interlayer friction in two-dimensional materials: existing control methods struggle to achieve non-contact, reversible, and continuous adjustment of interlayer friction; existing light-induced friction experiments struggle to eliminate photothermal effects and background absorption interference; existing atomic force microscopy (AFM) friction tests struggle to actively adjust the electronic structure and energy dissipation channels of the van der Waals interface; and there is a lack of in-situ measurement methods that directly correlate light-induced interlayer charge transfer, changes in interface electronic structure, and interlayer friction response. The embodiments of this invention construct a two-dimensional semiconductor van der Waals heterojunction with a second-type band arrangement, utilize resonant light excitation to induce interlayer charge transfer, and simultaneously record the interlayer friction response during AFM friction testing. By changing the excitation light power, wavelength, incident position, normal load, and scan rate, a quantitative correspondence between the intensity of photogenerated charge transfer and the interlayer friction force is established.

[0027] Figure 1 This is a schematic flowchart illustrating a method for controlling interlayer friction in van der Waals heterojunctions according to an embodiment of the present invention. The method for controlling interlayer friction in van der Waals heterojunctions can be executed by a controller, such as a microcontroller. Figure 1 As shown, the method for controlling interlayer friction in van der Waals heterostructures includes the following steps: S101. Control the irradiation of the excitation beam onto the sliding interface of the two-dimensional van der Waals heterojunction; wherein, the sliding interface is formed by the contact between the first two-dimensional semiconductor material layer and the second two-dimensional semiconductor material layer, and the photon energy of the excitation beam matches the band-edge electron transition energy of the first two-dimensional semiconductor material layer to induce photogenerated electrons to undergo interlayer transfer.

[0028] S102. Controlling the irradiation state of the excitation beam to change the intensity of translayer transfer of photogenerated electrons, thereby adjusting the interlayer friction force when relative slip occurs at the slip interface.

[0029] Specifically, a two-dimensional van der Waals heterojunction refers to a heterostructure formed by stacking two or more two-dimensional materials through weak van der Waals forces, such as a layered structure with a specific band arrangement formed by the contact of a first two-dimensional semiconductor material layer and a second two-dimensional semiconductor material layer. A slip interface refers to a physical interface where the first two-dimensional semiconductor material layer and the second two-dimensional semiconductor material layer are in direct contact and can slide relatively parallel under external force. An excitation beam refers to incident light with a specific wavelength used to irradiate the slip interface to excite electron transitions within the material. The band-edge electron transition energy refers to the minimum energy required for an electron in a semiconductor material to transition from the top of its valence band to the bottom of its conduction band. When the photon energy equals this value, the material's light absorption efficiency is highest, effectively generating photogenerated electron-hole pairs. Photogenerated electrons refer to electrons that, after absorbing photon energy, are excited from the valence band to the conduction band, allowing them to move freely within the crystal lattice. Interlayer transfer refers to the physical process by which photogenerated electrons generated in the first two-dimensional semiconductor material layer spontaneously move from their own layer to the adjacent second two-dimensional semiconductor material layer due to a specific band arrangement between the two layers, such as a type II band arrangement.

[0030] The core of this control method lies in using photoexcitation-induced interlayer charge transfer to alter the physical state of the van der Waals interface, thereby controlling the frictional force. First, a two-dimensional van der Waals heterojunction is constructed, formed by the direct contact of a first two-dimensional semiconductor layer and a second two-dimensional semiconductor layer; its slip interface is the region where subsequent friction occurs. An excitation beam is selected, and its photon energy is precisely set to match the band-edge electron transition energy of the first two-dimensional semiconductor layer. When this excitation beam irradiates the slip interface, valence band electrons in the first two-dimensional semiconductor layer absorb the photon energy and transition to the conduction band, thus generating photogenerated electron-hole pairs within the layer.

[0031] Due to the band structure characteristics of heterojunctions, such as type II band structures, where the conduction band bottom of one layer is lower than that of the other, photogenerated electrons in the first layer's conduction band tend to move to lower energy positions in the second layer's conduction band, resulting in interlayer transfer. This process alters the original charge distribution in the two layers; the second layer gains additional negative charge, while the first layer loses electrons and acquires an equivalent positive charge. This change in interface charge distribution generates a localized electric field perpendicular to the interface, enhancing the electrostatic attraction between the first and second layers, leading to a shorter effective interlayer distance and increased fluctuations in the slip potential energy surface. Therefore, when driving relative slip at the slip interface, a larger potential barrier needs to be overcome, macroscopically manifested as an increase in interlayer friction. By controlling the irradiation state of the excitation beam, such as turning it on, off, or changing its intensity, the intensity of interlayer transfer of photogenerated electrons can be altered, thereby continuously and reversibly adjusting the interlayer friction at the slip interface.

[0032] Therefore, this invention achieves non-contact optical control of interlayer friction in two-dimensional heterostructures. Compared with traditional methods that rely on mechanical loads, scanning speeds, or changes in surface chemistry, this invention can alter interlayer friction simply by adjusting the incident beam, without requiring changes to the mechanical structure or external environment. It offers advantages such as being non-contact, localized, and easily integrated. Furthermore, since the generation and recombination of photogenerated electrons are very rapid and reversible, this invention provides a physical basis for achieving rapid and reversible friction control. Moreover, by explicitly limiting the photon energy of the excitation beam to match the transition energy of band-edge electrons, it ensures that the control effect primarily originates from photoinduced electronic processes rather than photothermal effects, providing a basis for subsequent precise control.

[0033] Figure 2 This is a schematic diagram illustrating the working mechanism of a method for controlling interlayer friction in a two-dimensional van der Waals heterostructure provided in an embodiment of the present invention. Figure 2 As shown, from left to right, the diagram illustrates the smooth slippage when the excitation beam is turned off, the interlayer state response after laser intervention, and the process of charge transfer forming interlayer electron-hole pairs. The interlayer state response after laser intervention corresponds to the excitation beam with photon energy matched by the photoexcitation control component, inducing interlayer transfer from the first two-dimensional semiconductor material layer to the second material layer. Thus, the control method forms a complete closed loop of changing the irradiation state, inducing interlayer transfer, and adjusting the frictional force, which is the fundamental mechanism for the operation of photo-controlled micro / nano triboelectric devices.

[0034] In one embodiment, controlling the change of the irradiation state of the excitation beam to adjust the interlayer friction force when the sliding interface undergoes relative slip includes: continuously adjusting the incident light power of the excitation beam to continuously adjust the magnitude of the interlayer friction force; and controlling the excitation beam to turn on and off to achieve reversible switching of the interlayer friction force response.

[0035] Specifically, incident light power refers to the energy flux carried by the excitation beam illuminating the slip interface, measured in microwatts or milliwatts. Adjusting the incident light power can be achieved by using a neutral density filter or adjusting the laser output power. Continuous adjustment means that within a certain power range, the incident light power can be increased or decreased steplessly and gradually. Reversible switching means that after the excitation beam is turned off, the interlayer frictional force can return to a level essentially the same as or acceptable to its initial level before being turned on, and this process of turning on, increasing, turning off, and returning can be repeated multiple times.

[0036] By continuously adjusting the incident light power of the excitation beam, the number of photons absorbed by the first two-dimensional semiconductor material layer per unit time can be changed. The number of photons absorbed directly determines the generation rate and concentration of photogenerated electrons, thus affecting the number of electrons transferred from the first layer to the second layer. The more electrons transferred across layers, the greater the degree of interface charge separation, resulting in a stronger local electric field and interlayer electrostatic attraction. This enhanced attraction leads to increased fluctuations in the slip potential energy surface, causing the interlayer friction to continuously increase with increasing incident light power. Therefore, the magnitude of the friction is continuously and precisely controlled by a quantifiable external physical quantity, namely, light power. Furthermore, by controlling the opening and closing of the excitation beam, the occurrence and cessation of the photogenerated electron transfer process across layers can be controlled. When the light beam is turned on, the aforementioned charge transfer and interfacial force enhancement processes occur, and the frictional force increases. When the light beam is turned off, the generation of photogenerated electrons stops, and the electrons that were previously transferred across layers return to their original state through recombination and other pathways. The interfacial charge distribution returns to equilibrium, and the interlayer attraction and potential energy surface also return to the state without light. The frictional force then falls back to the initial baseline value. This process does not involve permanent structural changes or wear of the material, so reversible switching of the frictional response can be achieved.

[0037] Therefore, this invention establishes a quantitative relationship between photogenerated charge transfer intensity and friction by continuously adjusting the incident light power of the excitation beam, thereby continuously adjusting the magnitude of interlayer friction. This achieves continuous adjustability of interlayer friction, and precise control of the friction magnitude can be realized simply by adjusting the light power knob. This provides a possibility for applications requiring dynamic adjustment of friction, such as variable dampers. Simultaneously, by controlling the photoexcitation control component to cyclically turn the excitation beam on and off, the interlayer friction under different illumination conditions is obtained. This verifies that the friction increases when the light is on and returns to its initial level when it is off, thus demonstrating and utilizing the reversibility of the control process. This avoids irreversible damage caused by interface wear or structural changes in traditional methods, making the control method reusable and highly reliable. This is crucial for devices that require frequent switching of friction states, such as photocontrolled switches.

[0038] Figure 3This is a schematic diagram illustrating the variation of interlayer friction force in a two-dimensional van der Waals heterostructure with normal load, provided by an embodiment of the present invention. Figure 3 As shown, the distance represents the physical sliding space coordinates or scanning displacement of the probe on the sample surface, the friction force represents the interlayer friction force, and the load represents the externally applied normal load. From left to right, the diagrams show the original interlayer friction force observation under continuous adjustment, the original interlayer friction force curve under continuous adjustment, and the curve of interlayer friction force changing with normal load. The slope of the friction force baseline, which increases linearly with the increase of load, represents the friction coefficient, proving that the probe sliding process conforms to the basic tribological laws.

[0039] Figure 4 This is a schematic diagram illustrating the variation of interlayer frictional force in a two-dimensional van der Waals heterostructure with normal load under different external scanning rates, as provided in an embodiment of the present invention. Figure 4 As shown, the frictional force exhibits a stepwise pattern under different scanning speeds of the external driving components, indicating that the mechanical behavior of the interface remains stable and measurable even when the moving component slides at different speeds.

[0040] In one embodiment, both the first two-dimensional semiconductor material layer and the second two-dimensional semiconductor material layer are transition metal chalcogenide monolayer materials; the wavelength of the excitation beam is configured as a resonant excitation wavelength to maximize the translayer transfer intensity of photogenerated electrons while excluding photothermal effects.

[0041] Specifically, transition metal chalcogenides refer to layered materials with the chemical formula MX2, where M represents a transition metal element, such as tungsten (W) and molybdenum (Mo), and X represents a chalcogen element, such as sulfur (S) and selenium (Se). Examples of transition metal chalcogenides include tungsten disulfide, tungsten diselenide, and molybdenum disulfide. Monolayer materials refer to two-dimensional materials composed of a single layer of atoms or molecules, with a thickness only at the atomic scale. The resonant excitation wavelength refers to the excitation wavelength whose photon energy is precisely equal to the band-edge electron transition energy of the first two-dimensional semiconductor material layer. Under irradiation at this wavelength, the material achieves the highest photon absorption efficiency, enabling the most efficient generation of photogenerated electron-hole pairs.

[0042] Transition metal chalcogenide monolayers were chosen as the first and second two-dimensional semiconductor layers because these materials possess advantages such as direct band gaps, strong photomatter interactions, and ease of forming high-quality van der Waals heterostructures. Their monolayer morphology ensures a clear band structure and pure interlayer coupling. Furthermore, configuring the excitation beam wavelength to the resonant excitation wavelength is crucial for maximizing the efficiency of photogenerated electron transfer across layers and eliminating interference. When using the resonant excitation wavelength, the photon energy precisely meets the energy required for electrons to transition from the valence band to the conduction band in the first two-dimensional semiconductor layer. Therefore, the vast majority of photon energy is used to generate photogenerated electron-hole pairs, rather than being converted into lattice vibrations (i.e., heat). This ensures that changes in interlayer friction primarily originate from alterations in the interface electronic structure and electrostatic forces caused by photogenerated electron transfer across layers, rather than from thermal expansion, softening, or changes in the adsorption layer caused by photothermal effects. By maximizing the intensity of photogenerated electron transfer across layers, significant friction modulation effects can be achieved at lower incident light power, reducing potential thermal damage to the sample.

[0043] Therefore, this invention employs a transition metal chalcogenide monolayer material, ensuring a clear type II band arrangement and high crystal quality in the heterojunction, laying the foundation for efficient interlayer charge transfer. Simultaneously, by using the resonant excitation wavelength, the interference of photothermal effects is eliminated from a physical mechanism perspective, making the experimental conclusions more reliable. The root cause of the triboelectric response is clearly pointed to electronic processes, and energy utilization efficiency is maximized, achieving the maximum charge transfer intensity and triboelectric modulation amplitude with minimal light input. This is crucial for low-power, light-controlled micro / nano devices.

[0044] Figure 5 This is a schematic diagram illustrating the in-situ optical properties of a two-dimensional van der Waals heterojunction slip interface provided in an embodiment of the present invention. Figure 5 As shown, energy represents luminescence energy, and from left to right, they represent the optical surface corresponding to the heterojunction formed by the contact between the first and second two-dimensional semiconductor material layers, the Raman spectrum corresponding to the heterojunction, and the photoluminescence spectrum corresponding to the heterojunction. For example, the first two-dimensional semiconductor material layer is a monolayer of tungsten diselenide, and the second two-dimensional semiconductor material layer is a monolayer of tungsten disulfide. The two layers contact to form a two-dimensional van der Waals heterojunction sliding interface with a type II bandgap arrangement. Under an excitation beam matching the band-edge electron transition energy, such as 740 nm irradiation, electrons in the first two-dimensional semiconductor material layer can undergo interlayer transfer to the second two-dimensional semiconductor material layer. Figure 5 It can be seen that after the first two-dimensional semiconductor material layer and the second two-dimensional semiconductor material layer form a heterojunction, they still retain their respective characteristic optical peak positions. That is, after the materials come into contact, their inherent band-edge electron transition energy characteristics are not destroyed, ensuring that the excitation beam of a specific wavelength can accurately induce cross-layer transfer.

[0045] This invention also provides an in-situ measurement system for controlling interlayer friction in van der Waals heterostructures. Figure 6 This is a schematic diagram of the structure of an in-situ measurement system for controlling interlayer friction in van der Waals heterostructures, provided in an embodiment of the present invention. Figure 6 As shown, the in-situ measurement system for controlling interlayer friction in van der Waals heterostructures includes: a first friction pair component 100, a second friction pair component 200, a photoexcitation control component 300, a spot alignment component, and a data processing component. The first friction pair component 100 is mounted on the end of the probe 400 of an atomic force microscope, and a first two-dimensional semiconductor material layer 500 is fixed to the end of the probe 400. A second two-dimensional semiconductor material layer 600 is fixed to the surface of the second friction pair component 200. The first two-dimensional semiconductor material layer 500 and the second two-dimensional semiconductor material layer 600 are connected... The probe 400 forms a two-dimensional van der Waals heterojunction sliding interface; the photoexcitation control component 300 is used to irradiate the sliding interface with an excitation beam of adjustable power and wavelength; the spot alignment component is used to monitor and adjust the transmission optical path of the excitation beam so that the spot of the excitation beam and the scanning area of ​​the probe 400 on the second friction pair component 200 are spatially overlapped; the data processing component is communicatively connected to the atomic force microscope and is used to obtain the interlayer friction force of the sliding interface when relative sliding occurs based on the lateral force signal of the sliding interface during forward and reverse scanning during the scanning process of the probe 400.

[0046] Specifically, an in-situ measurement system refers to an integrated device capable of real-time, synchronous observation and measurement of a sample while it is in its original state or undergoing a physicochemical process, such as photoexcitation. The first friction pair assembly 100 refers to the moving component constituting the friction pair, integrated into the end of the probe 400 of an atomic force microscope. Its core function is to provide an upper friction portion that contacts and slides relative to the mating surface, and a first two-dimensional semiconductor material layer 500 is fixed on it. The second friction pair assembly 200 refers to the stationary or base component constituting the friction pair, with a second two-dimensional semiconductor material layer 600 fixed on its surface for contacting and forming a sliding interface with the first two-dimensional semiconductor material layer 500 on the first friction pair assembly 100. The beam alignment assembly refers to a system including components such as an optical lens, a mirror, and a charge-coupled device (CCD) camera, used to monitor the position of the excitation beam on the sample surface in real time, and capable of changing the beam direction through a mechanical adjustment mechanism to ensure that the beam spot accurately covers the target area. The data processing component refers to the computer and its supporting software that are connected to the atomic force microscope controller. It is able to receive and process the electrical signals output by the atomic force microscope, especially the lateral force signals obtained from the forward and reverse scans, and extract the pure friction force values ​​through differential algorithms.

[0047] The first friction pair assembly 100 fixes the first two-dimensional semiconductor material layer 500 to the end of the atomic force microscope probe 400, making it a movable upper friction element. The second friction pair assembly 200 fixes the second two-dimensional semiconductor material layer 600 to its surface, serving as a stationary lower friction element. When the two components come into contact, they form the two-dimensional van der Waals heterojunction sliding interface to be studied. The photoexcitation control assembly 300 generates and emits an excitation beam with adjustable power and wavelength, such as... Figure 6 A medium blue light beam is used to induce interlayer charge transfer at the slip interface. The beam alignment component acts as a sight, displaying the position of the beam spot and the atomic force microscope probe 400 in real time through optical imaging. By adjusting the optical path, it ensures that the beam spot of the excitation beam precisely coincides with the tip of the probe 400, i.e., the actual contact area of ​​the first and second two-dimensional semiconductor material layers 600, ensuring that the photoexcitation acts on the actual friction contact area. When the atomic force microscope drives the probe 400, i.e., the first friction pair component 100, to scan the surface of the second friction pair component 200, the slip interface undergoes relative slippage. During this process, the probe 400 is subjected to a lateral force opposite to the slippage direction, i.e., friction. The data processing component is communicatively connected to the atomic force microscope, receiving the electrical signals generated by the lateral force sensor during forward and reverse scanning of the probe 400. Since other lateral interference forces are opposite in direction during forward and reverse scanning, while the friction force is always opposite to the direction of motion, the interference can be effectively eliminated and the pure interlayer friction force value can be extracted by calculating the difference between the two.

[0048] Therefore, this invention creatively couples the photoexcitation system and the atomic force microscope friction testing system into an in-situ measurement platform, achieving simultaneous friction control and measurement. It allows for real-time monitoring of dynamic changes in frictional force during photoexcitation, providing a direct means to study the photo-mechanical coupling mechanism. Simultaneously, the spot alignment component ensures spatial overlap between the photoexcitation position and the friction contact area, a prerequisite for obtaining effective and repeatable control effects, avoiding inaccurate experimental results due to excitation position misalignment. Furthermore, the data processing component performs differential processing on the forward and reverse lateral force signals, obtaining high signal-to-noise ratio frictional force data, enabling the precise capture and quantification of even minute photoinduced frictional changes.

[0049] Figure 7 This is a schematic diagram of the real-time imaging field of a microscope for a spot alignment component in an in-situ measurement system provided by an embodiment of the present invention. Figure 7 As shown, from left to right, the image shows the probe and sliding interface observed by the spot alignment component without an ultrafast excitation beam, and the bright spot of the excitation beam being precisely adjusted to below the probe tip when there is an ultrafast excitation beam. Thus, the spot alignment component is used to monitor and adjust the transmission optical path so that the spot and the probe scanning area coincide in space.

[0050] In one embodiment, such as Figure 6 As shown, both the first friction pair assembly 100 and the second friction pair assembly 200 include a dielectric support layer. The second friction pair assembly 200 includes a rigid substrate, a dielectric support layer, and a second two-dimensional semiconductor material layer 600 in sequence. The probe 400 end is fixed with a dielectric support layer by a van der Waals transfer process. The first two-dimensional semiconductor material layer 500 is attached to the dielectric support layer at the end of the probe 400.

[0051] Specifically, the dielectric support layer refers to a two-dimensional material with insulating properties, used to support and carry the first two-dimensional semiconductor material layer 500 and the second two-dimensional semiconductor material layer 600. It is preferably hexagonal boron nitride due to its atomically flat surface, minimal charge traps, and excellent chemical stability. The rigid substrate refers to a robust and non-deformable substrate, such as a silicon wafer with a silicon oxide layer on its surface, used to provide mechanical support for the entire lower friction pair. The van der Waals transfer process refers to a non-destructive dry transfer technique that utilizes the weak van der Waals forces between the two-dimensional material layers, using a polymer film as the transfer medium, to pick up and release the two-dimensional material from its growth substrate onto a target substrate.

[0052] For the second friction pair component 200, a sandwich structure of a rigid substrate, a dielectric support layer, and a second two-dimensional semiconductor material layer 600 is adopted. The rigid substrate provides mechanical stability for the entire component. The dielectric support layer, such as hexagonal boron nitride, is placed between the rigid substrate and the second two-dimensional semiconductor material layer 600. Its function is to isolate the charge traps, roughness, and chemical contamination that may exist on the surface of the rigid substrate, and to provide an atomically flat and electrically clean support environment for the second two-dimensional semiconductor material layer 600, thereby ensuring that the intrinsic properties of the second two-dimensional semiconductor material layer 600 are preserved, and that the slip interface is uniform and has few defects. For the first friction pair assembly 100, instead of simply attaching the first two-dimensional semiconductor material layer 500 directly to the atomic force microscope probe 400, a dielectric support layer, such as hexagonal boron nitride, is first fixed to the end of the probe 400 using a van der Waals transfer process. Then, the first two-dimensional semiconductor material layer 500 is attached to this dielectric support layer. The dielectric support layer acts as a buffer and adhesion layer, using van der Waals forces rather than chemical adhesives to fix the first two-dimensional semiconductor material layer 500, avoiding adhesive contamination and mechanical damage. Furthermore, the dielectric support layer ensures that the contact surface of the upper friction pair is also atomically flat, resulting in a flat-to-flat ideal van der Waals interface that is ultimately formed.

[0053] Therefore, by introducing a dielectric support layer such as hexagonal boron nitride into the two friction pairs, this embodiment of the invention minimizes the interference of substrate roughness and charge traps on friction testing, ensuring that the measured friction force data truly reflects the intrinsic frictional behavior between the two-dimensional material layers. Simultaneously, the use of van der Waals transfer technology avoids contamination from traditional photoresists or adhesives, ensuring the chemical purity of the first two-dimensional semiconductor material layer 500 and the slip interface, significantly improving the success rate of the experiment and the repeatability of the data.

[0054] For example, the sample can also be characterized in advance, such as by using optical microscopy, atomic force microscopy, Raman spectroscopy and photoluminescence spectroscopy, to confirm the number of layers, surface flatness, crystal quality and optical characteristics of the first two-dimensional semiconductor material layer 500, the second two-dimensional semiconductor material layer 600 and their heterojunction, to ensure that there are stable van der Waals contacts. Figure 8 This is a basic characterization diagram of a second friction pair assembly and a dielectric support layer provided in an embodiment of the present invention. Figure 8 As shown, the distance represents the physical sliding spatial coordinates or scanning displacement of the probe on the sample surface. From top to bottom, the images represent: optical observation images of the second friction pair component and dielectric support layer obtained using optical microscopy; surface morphology of the second friction pair component and dielectric support layer obtained using atomic force microscopy; height variation curve of the second friction pair component and dielectric support layer; Raman spectrum of the second friction pair component and dielectric support layer; and photoluminescence spectrum of the second friction pair component and dielectric support layer. Figure 8 It is known that the thickness of the second two-dimensional semiconductor material layer is about 0.83 nm, confirming that it is a single layer with atomically flat surface. The spectral characteristics further confirm that the material has no lattice defects, thus proving that the fabrication quality of the second friction pair component in the measurement system has reached the extremely high flatness required by the experiment, providing a hardware basis for forming an ideal van der Waals heterojunction sliding interface.

[0055] Figure 9 This is a basic characterization diagram of a first friction pair component and a dielectric support layer provided in an embodiment of the present invention. Figure 9 As shown, from top to bottom, the diagrams depict the optical observations of the first friction pair component and the dielectric support layer obtained using an optical microscope, the surface morphology of the first friction pair component obtained using an atomic force microscope, the surface morphology of the dielectric support layer obtained using an atomic force microscope, the height variation curve of the dielectric support layer, the height variation curve of the first friction pair component, the Raman spectrum of the first friction pair component and the dielectric support layer, and the photoluminescence spectrum of the first friction pair component and the dielectric support layer. Figure 9It is known that the thickness of the first two-dimensional semiconductor material layer is about 0.74 nm, confirming that it is a single layer with an atomically flat surface. The spectral characteristics further confirm the excellent luminescence properties and crystal quality of the material, thus proving that after the dielectric support layer and the first two-dimensional semiconductor material layer are transferred to the probe end by the van der Waals transfer process, the material still maintains its single-layer characteristics and is not damaged by the process.

[0056] In one embodiment, such as Figure 6 As shown, the in-situ measurement system for controlling interlayer friction in van der Waals heterostructures also includes a transient absorption spectroscopy testing component 700, coupled to the photoexcitation control component 300, for emitting a femtosecond-level first excitation beam toward the slip interface, as can be seen from... Figure 6 The blue beam in the image, and the second beam used for monitoring, can be found in [reference]. Figure 6 The red beam in the image was understood, and the lifetime and spatial diffusion coefficient of interlayer electron-hole pairs at the slip interface under photoexcitation were obtained in situ.

[0057] Specifically, the transient absorption spectroscopy testing component 700 refers to an ultrafast optical measurement system based on pump-probe technology, used to study changes in the excited-state absorption characteristics of materials within an extremely short time after photoexcitation, such as femtoseconds to nanoseconds. The first beam, i.e., the pump beam, in transient absorption spectroscopy testing refers to a high-intensity femtosecond pulsed laser beam used to excite the sample and initiate the physical process under study, such as electron transitions. The second beam, i.e., the probe beam, refers to another femtosecond pulsed laser beam with a weaker intensity and a time delay precisely relative to the pump beam. It is used to detect the optical properties of the sample excited by the pump beam at a specific delay time point, such as changes in absorptivity. Interlayer electron-hole pairs refer to composite particles formed when, under photoexcitation, electrons transfer across layers from the first two-dimensional semiconductor material layer 500 to the second two-dimensional semiconductor material layer 600, and are bound together with holes remaining in the first layer by Coulomb attraction.

[0058] The transient absorption spectroscopy testing component 700 is coupled to the photoexcitation control component 300, sharing a portion of the optical path or being synchronously triggered. Its operating principle is based on pump-probe technology. First, a femtosecond-level first beam illuminates the slip interface, its wavelength set to the resonant excitation wavelength to induce electron transitions and interlayer transfers in the first two-dimensional semiconductor material layer 500. Subsequently, a femtosecond-level second beam, with a precise time delay, illuminates the same region. The wavelength of the probe light is selected to match a certain electron transition energy in the second two-dimensional semiconductor material layer 600, i.e., the electron receiving layer. Without pump light excitation, the absorption of the probe light is constant. When the pump light excites and causes electrons to transfer to the second layer, the electron population in the second layer changes, and its absorption capacity for the probe light changes accordingly. By precisely changing the arrival time difference between the first and second beams and measuring the change in probe light absorption at each delay time point, the entire interlayer charge transfer and recombination process can be constructed. By analyzing these kinetic data, key physical parameters can be extracted, such as the lifetime of interlayer electron-hole pairs, i.e. how long they exist before recombination, and their spatial diffusion coefficient in the interface plane direction, i.e. how fast they diffuse.

[0059] Therefore, this invention directly correlates the ultrafast charge transfer dynamics occurring on the femtosecond to picosecond scale with the macroscopic frictional response occurring on the millisecond to second scale. Within the same system, both the passage of electrons and the increase in frictional force can be observed, providing direct evidence that charge transfer leads to increased friction. By obtaining the lifetime and diffusion coefficient of interlayer electron-hole pairs, the behavior of photogenerated charges at the interface can be quantitatively evaluated, thereby gaining a deeper understanding of how they alter interlayer coupling and energy dissipation. This component can be used to verify whether this method is also applicable to other material systems, i.e., by observing the presence of long-lived transient absorption signals to determine whether effective interlayer charge transfer occurs.

[0060] Figure 10 This is a schematic diagram of the lateral distribution obtained by a transient absorption spectroscopy testing component provided in an embodiment of the present invention. For example... Figure 10As shown, the transient absorption spectrum represents the lateral distribution of interlayer electron-hole pairs at different times. The meaning of distance differs from that in the previous embodiment. The distance in the transient absorption spectrum represents the radial diffusion offset of photogenerated electron-hole pairs relative to the laser excitation center point. The 0 point represents the absolute center point of the first beam hitting the material. Positive and negative values ​​represent the relative distance that electrons diffuse outward to the surrounding plane within a picosecond time. Normalization represents the normalized transient absorption signal. The color depth represents the delay time. The central peak represents the concentration of interlayer electron-hole pairs under the action of the first or second beam. As the delay time increases, the central peak decreases and widens to both sides. Thus, the microscopic physical process of interlayer transfer of photogenerated electrons can be directly observed using the first and second beams.

[0061] Figure 11 This is a schematic diagram of two-dimensional spatial diffusion of interlayer electron-hole pairs provided in an embodiment of the present invention. Figure 11 As shown, the distance represents the diffusion distance, i.e., the distance an electron travels from the center of the light spot. Normalization represents the transient absorption signal intensity; the stronger the signal, the higher the concentration of interlayer electron-hole pairs at that location. The top-left appendix shows that over time, the peaks representing concentration gradually become shorter, indicating electron-hole recombination and dissipation, while the base of the peaks widens. The top-right appendix arranges these curves vertically in a staggered manner and marks the outward expansion trajectory of the half-width at half-maximum (HWHM) with two dashed lines, visually demonstrating that the charge cloud is expanding outward. The bottom appendix shows a top-down view of two-dimensional spatial coordinates, with color gradations from black to bright yellow representing signal intensity, i.e., charge concentration, providing a visual effect like ripples spreading across water. At 0 ps, ​​the light spot is extremely small and bright; at 900 ps, ​​the spot area significantly expands, but the brightness becomes dimmer. Figure 11 This demonstrates that the translayer electrons induced by the photoexcitation control component are not static, but possess macroscopic spatial diffusion capabilities within the slip interface.

[0062] Figure 12 This is a schematic diagram of the two-dimensional spatial diffusion coefficient of interlayer electron-hole pairs provided in an embodiment of the present invention. Figure 12 As shown in the attached chart, the left side represents the planar signal at 1000 ps, ​​where the signal is extremely weak and appears as background noise, indicating that charge recombination is essentially complete. The right side represents the change in diffusion area on the vertical axis, with the blue dots representing the change from... Figure 11 The real experimental data extracted from the Gaussian fitting, the red line is the linear fitting of these scattered points, this linear relationship fits the two-dimensional diffusion formula, the slope of the line corresponds to the diffusion coefficient, and it is established that the change response of interlayer friction force originates from interlayer charge transfer and diffusion.

[0063] This invention also provides an in-situ measurement method for controlling interlayer friction in van der Waals heterostructures, which is executed by the in-situ measurement system for controlling interlayer friction in two-dimensional van der Waals heterostructures as described in the above embodiments. Figure 13 This is a schematic flowchart of an in-situ measurement method for controlling interlayer friction in van der Waals heterostructures, provided by an embodiment of the present invention. Figure 13 As shown, the in-situ measurement method includes the following steps: S201. The photoexcitation control component shuts off the excitation beam and drives the probe of the atomic force microscope to scan and obtain the initial interlayer friction force.

[0064] S202. The photoexcitation control component turns on the excitation beam and adjusts the wavelength of the excitation beam to match the resonant wavelength of the band-edge transition energy, driving the probe of the atomic force microscope to scan and obtain the interlayer frictional force in the resonant excitation state.

[0065] S203. Based on the interlayer friction force under resonant excitation state and the initial interlayer friction force, obtain the change in interlayer friction force induced by the excitation beam.

[0066] Specifically, the initial interlayer friction force refers to the value of the interlayer friction force when relative slippage occurs at the sliding interface under conditions of no photoexcitation, serving as the baseline for subsequent comparisons. The interlayer friction force under resonant excitation refers to the value of the interlayer friction force when relative slippage occurs at the sliding interface under conditions where the excitation beam is turned on and its wavelength is set to the resonant excitation wavelength, i.e., the photon energy matches the electron transition energy at the band edge of the first two-dimensional semiconductor material layer. The change in interlayer friction force refers to the difference between the interlayer friction force under resonant excitation and the initial interlayer friction force; it quantifies the net effect of the photoinduced interlayer charge transfer process on the interlayer friction force.

[0067] The core of this method is to compare the difference in frictional force between illuminated and dark states. First, a baseline is established by controlling the photoexcitation control component to shut off the excitation beam, ensuring no photogenerated electrons are generated or interlayer transfer occurs. Under this condition, the probe of an atomic force microscope is driven to scan, causing relative slippage between the first and second two-dimensional semiconductor material layers. The interlayer frictional force acquired by the data processing component at this point is the initial interlayer frictional force, representing the intrinsic frictional state of the system without external light intervention. Next, a photoexcitation variable is introduced: the photoexcitation control component is controlled to turn on the excitation beam and precisely adjust its wavelength to the resonant excitation wavelength. At this point, interlayer transfer of photogenerated electrons occurs at the slip interface, altering the interface electronic structure and interlayer coupling. Under the same mechanical scanning conditions (e.g., equal load and speed), the probe is driven to scan again, acquiring the interlayer frictional force at this point, i.e., the interlayer frictional force under resonant excitation. Finally, quantitative analysis is performed: the difference between the two is calculated by the data processing component, representing the change in interlayer frictional force. This change directly reflects the net modulatory effect of the interlayer charge transfer process induced by resonant photoexcitation on the frictional behavior of the slip interface. For example, the data processing component synchronously acquires the interlayer frictional force. In the absence of light, it drives the atomic force microscope probe to scan, and the data processing component acquires the initial interlayer frictional force based on the lateral force signals from the forward and reverse scans. Then, it controls the activation of the excitation beam to acquire the interlayer frictional force under resonant excitation, and obtains the change in interlayer frictional force induced by the excitation beam based on the difference between the two.

[0068] Therefore, by comparing the frictional force in the light-off and light-on states, this embodiment of the invention can clearly attribute the frictional change to the electronic effect brought about by photoexcitation, eliminating the influence of other uncertain factors. The key performance indicator of the change in interlayer frictional force is defined and calculated, enabling objective comparison of the control effects under different light powers and different material systems, providing a quantitative basis for method optimization and application.

[0069] In one embodiment, after obtaining the interlayer frictional force in the resonant excitation state, the method further includes: controlling the photoexcitation control component to switch the excitation beam to a non-resonant wavelength with insufficient energy to effectively excite band-edge electron transitions, and obtaining the interlayer frictional force in the non-resonant state; if the interlayer frictional force in the non-resonant state does not change significantly compared to the initial interlayer frictional force, it is established that the change in interlayer frictional force originates from interlayer charge transfer.

[0070] Specifically, the non-resonant wavelength refers to the excitation wavelength whose photon energy does not match the band-edge electron transition energy of the first two-dimensional semiconductor material layer. When irradiated with a non-resonant wavelength, the material's absorption efficiency for photons is extremely low, primarily used to generate thermal effects rather than photogenerated charge carriers. "No significant change" means the difference between the interlayer frictional force in the non-resonant state and the initial interlayer frictional force is within the experimental error range. A crucial control experimental step was introduced to rigorously eliminate the interference of non-electronic effects on frictional modulation. After completing the resonant excitation measurement, the photoexcitation control component was switched to a non-resonant wavelength while keeping other conditions, such as incident light power, sample, and scanning parameters, unchanged. Because the photon energy of the non-resonant wavelength is insufficient to effectively excite band-edge electron transitions, a significant concentration of photogenerated electrons is not generated in the first two-dimensional semiconductor material layer, thus failing to induce effective interlayer charge transfer. However, the non-resonant wavelength light is still partially absorbed by the sample and converted into heat, potentially causing localized thermal expansion or temperature rise. Under these conditions, the same frictional test was performed to obtain the interlayer frictional force in the non-resonant state. If the frictional force does not change significantly compared to the initial interlayer frictional force, it means that non-electronic factors such as photothermal effects and photoinduced adsorption changes have little influence on the interlayer frictional force and can be ignored. Based on this, combined with the significant frictional force changes observed under resonant excitation, the observed interlayer frictional force change response is fundamentally caused by the interlayer transfer of photogenerated electrons, rather than other accompanying effects.

[0071] Therefore, this embodiment of the invention eliminates the possibility of a photothermal effect, which is the biggest point of contention in existing photo-induced friction experiments. By setting up a non-resonant wavelength control, it can be strongly demonstrated that the frictional change is not caused by the material being heated, but rather originates from a purely electronic process. This control experiment provides irrefutable experimental evidence for photoexcitation, interlayer charge transfer, and enhanced interlayer friction.

[0072] In one embodiment, the in-situ measurement method for controlling interlayer friction in van der Waals heterostructures further includes: controlling the photoexcitation control component to cyclically turn the excitation beam on and off, and obtaining the interlayer friction under different illumination conditions to verify the reversibility of the interlayer friction control process.

[0073] Specifically, cyclic on / off refers to repeatedly performing the sequence of operations of turning on the excitation beam, holding it for a period of time, turning off the excitation beam, and holding it for a period of time multiple times. The reversible interlayer friction can switch back and forth repeatedly between two different conditions, such as light on and light off, and can return to the same or highly consistent state as before after each switch, without showing drift or permanent change.

[0074] After completing the aforementioned initial friction force, resonant excitation, and non-resonant control measurements, a dynamic, periodic excitation was further applied to the system. Specifically, the photoexcitation control component was controlled to cyclically turn the excitation beam on and off at certain time intervals. During the cycle, the change in interlayer friction force over time was recorded synchronously and continuously. If this control mechanism is based on a reversible physical process, such as the generation and recombination of photogenerated electrons, then ideally, each time the beam is turned on, the friction force should rise rapidly and stabilize at the level of the resonant excitation state; each time the beam is turned off, the friction force should fall rapidly and recover to the initial interlayer friction force level. By observing the friction force response curve after multiple cycles, it can be determined whether there is attenuation, drift, or unrecoverable phenomena. If, after tens or even hundreds of cycles, the friction force values ​​in the on and off states remain stable without any obvious trend of change, such as the friction force not returning to the baseline after the light is turned off, or the friction force decreasing with each subsequent turn after the light is turned on, then it proves that the interlayer friction force control process is highly reversible.

[0075] Therefore, this invention demonstrates non-destructive manipulation. The existence of reversibility strongly suggests that the photoexcitation and charge transfer processes do not cause wear, structural damage, or permanent chemical changes to the atomically smooth van der Waals interface, which is crucial for the long-lifetime operation of micro / nano devices. Reversible cycle testing shows that this manipulation method is not a one-time effect but can be used repeatedly and reliably, which is essential for engineering applications that require frequent switching of frictional states, such as optically controlled clutches or switches.

[0076] Figure 14 This is a schematic diagram illustrating the stability and reversibility test of interlayer friction response provided in an embodiment of the present invention. Figure 14 As shown, the horizontal axis represents the number of scans, and the vertical axis represents the interlayer friction. During the 6000-second, thousands of back-and-forth scans, the friction signal remained fluctuating on a horizontal baseline without any sharp increase or decrease due to wear. This verified the reversibility of the control process, ruled out the possibility that the probe would damage the material and cause additional friction, and established that the subsequent light-controlled changes were a non-destructive physical response.

[0077] Figure 15 This is a schematic diagram comparing interlayer friction response in an in-situ measurement method provided by an embodiment of the present invention. Figure 15As shown, the color gradients in the upper left appendix represent the physical undulations of the sample. The uniform color indicates that the sample surface is atomically smooth. The color gradients in the upper middle and right appendixes represent the magnitude of the original lateral torque experienced by the probe. The obvious horizontal zebra stripes appear in the graphs, indicating that the operator manually turned the excitation beam on and off repeatedly during the probe's downward scanning process; the alternation of light and dark directly corresponds to the beam's on and off states. The horizontal axis of the lower appendix represents the physical distance scanned by the atomic force microscope probe. The lower left appendix shows the raw signal from a unidirectional scan, which is very coarse and includes sample tilt errors. The lower right appendix shows the pure interlaminar frictional force data extracted by the data processing component by subtracting the reverse scan signal from the forward scan signal. The blue curve exhibits a stepped shape; when in the light-on region, the average frictional force suddenly increases by 8 nN, and then immediately drops back to the original baseline after entering the light-off region. Therefore, corresponding to the cyclic opening and closing of the excitation beam and the extraction of frictional force changes, 8nN is the interlayer frictional force change created by the excitation beam, confirming the non-contact, reversible, and instantaneous response characteristics of photosensitive friction.

[0078] This invention also provides a light-controlled micro / nano tribological device, including a movable tribological component, an external driving component, and a photoexcitation control component. The movable tribological component includes a stator component and a mover component arranged opposite to each other. The stator component includes a first two-dimensional semiconductor material layer, and the mover component includes a second two-dimensional semiconductor material layer. The first two-dimensional semiconductor material layer and the second two-dimensional semiconductor material layer are arranged opposite to each other and in contact to form a two-dimensional van der Waals heterojunction sliding interface with a second type of band arrangement. The external driving component is used to drive the mover component to slide relative to the stator component. The photoexcitation control component is used to irradiate the sliding interface with an excitation beam and induce interlayer charge transfer by adjusting the irradiation state of the excitation beam, thereby adjusting the interlayer friction force of the movable tribological component in real time during operation in a non-contact manner.

[0079] Specifically, light-controlled micro / nano tribological devices refer to functional devices with dimensions on the micrometer or nanometer scale that actively adjust the frictional force between their internal relatively moving parts using light as an external control signal. Movable tribological components refer to the mechanical parts of the device responsible for generating relative motion, consisting of a stator and a mover. External driving components refer to external devices or mechanisms that provide driving force for the mover assembly, such as electrostatic comb actuators, piezoelectric ceramic actuators, and electromagnetic actuators. Type II bandgap arrangement refers to a situation at the interface of a heterojunction composed of two different semiconductors where the conduction band bottom and valence band top of one semiconductor are lower than the corresponding bands of the other semiconductor. This arrangement facilitates the separation of photogenerated electrons and holes into the materials on either side.

[0080] The stator assembly of the movable friction component comprises a first two-dimensional semiconductor material layer, and the mover assembly comprises a second two-dimensional semiconductor material layer. These two components are arranged opposite each other and in contact, forming a two-dimensional van der Waals heterojunction sliding interface with a second-type band arrangement. This band arrangement is the physical basis for achieving photoinduced interlayer charge transfer. Driven by an external driving component, the mover assembly slides relative to the stator assembly. At this time, interlayer frictional force that hinders movement is generated at the sliding interface. To actively regulate this frictional force, the device integrates a photoexcitation control component that can irradiate an excitation beam onto the sliding interface. When it is necessary to change the frictional force, the irradiation state of the excitation beam is adjusted, such as turning it on, off, or changing its power, to induce photogenerated electrons in the first or second two-dimensional semiconductor material layer, which then undergo interlayer transfer driven by the second-type band arrangement. As mentioned above, this interlayer charge transfer changes the charge distribution at the interface, enhances interlayer electrostatic attraction, and reconstructs the potential energy surface, thereby changing the interlayer frictional force experienced by the movable friction component during operation in real time without contact.

[0081] Therefore, in this embodiment of the invention, the photoexcitation control component and the movable component do not have physical contact, avoiding frictional interference or dielectric breakdown problems that may arise from traditional mechanical or electric field control methods. The frictional force can be dynamically adjusted during device operation. Since light can be focused to the micrometer or even nanometer scale and has an extremely fast response speed, this device can theoretically achieve frictional force control with extremely high spatial selectivity and temporal response speed. Compared to complex electrical control structures, this device uses an optical window for control, making it structurally easier to integrate and package.

[0082] In one embodiment, the photoexcitation control component is configured to emit a periodically modulated pulsed excitation beam toward the sliding interface; wherein the modulation frequency of the pulsed excitation beam is configured to be coupled with the mechanical stick-slip vibration frequency of the movable friction component during operation, so as to suppress unstable stick-slip during the sliding process of the moving component by dynamically adjusting the interlayer friction force of the sliding interface.

[0083] Specifically, a periodically modulated pulsed excitation beam refers to an excitation beam that is not continuous and stable, but rather repeatedly turns on and off at fixed time intervals, forming a pulse sequence. The modulation frequency is the number of pulses per second. The mechanical stick-slip vibration frequency refers to the discontinuous, self-excited vibration phenomenon of the moving component during micro-nano sliding, caused by the alternating action of static and dynamic friction, involving sticking, sliding, re-sticking, and re-slipping. Coupling refers to setting the modulation frequency of the optical pulse to be the same as or an integer multiple of the system's inherent mechanical stick-slip vibration frequency, allowing the optical control force to resonate or anti-resonate with the system's mechanical vibration, thereby controlling the amplitude of the vibration.

[0084] During the operation of the aforementioned devices, due to the nonlinearity of interfacial friction, the moving component often exhibits unstable stick-slip motion, which is extremely detrimental to positioning accuracy and service life. This invention utilizes the rapid response characteristics of optical modulation to actively intervene in this process. Specifically, the optical excitation control component is configured to emit periodically modulated pulsed excitation beams. Since the generation of photoelectrons and the interlayer charge transfer process occur on an ultrafast timescale of femtoseconds to picoseconds, the frictional response can follow the on / off state of the optical pulses in real time. Therefore, by adjusting the modulation frequency of the pulsed excitation beam, the interlayer friction of the sliding interface can be made to oscillate rapidly between high and low values ​​at a set frequency. The most crucial step is to precisely configure this modulation frequency to couple, for example, to be equal to, the mechanical stick-slip vibration frequency of the movable friction component during operation. When the system begins to experience stick-slip vibration, the period of change in the magnitude of the optically controlled friction force remains synchronized with the system's vibration period. By finely adjusting the duty cycle or phase of the light pulse, friction can be reduced at the moment the system is about to stick, to help it start up, or friction can be increased at the moment it is about to slip and provide damping. This friction modulation can effectively suppress the amplitude of stick-slip vibration, or even completely eliminate the stick-slip phenomenon, making the movement of the mover assembly smoother and more stable.

[0085] Therefore, this invention, by coupling the optical pulse modulation frequency with the inherent vibration frequency of the mechanical system, achieves closed-loop active control of the motion state of the moving component, greatly improving the smoothness of motion and the accuracy of position control during micro-nano sliding. It elevates the control from simple average friction force to dynamic waveform control, enabling the device not only to adjust resistance but also for active vibration reduction and motion stability control.

[0086] Figure 16 This is a schematic diagram illustrating the lifetime evolution of interlayer electron-hole pairs provided in an embodiment of the present invention. Figure 16 As shown, the left side is a 3D surface map, with the XY plane representing the spatial coordinates. The Z-axis and color simultaneously represent the intensity of the transient absorption signal, visually demonstrating how a mountain of charges transforms from a high-concentration accumulation to a low, gentle slope within 1000 ps, ​​corresponding to the dynamic three-dimensional process of recombination dissipation and outward diffusion. The right side is a 3D waterfall slice image, with the vertical axis representing the delay time. This is equivalent to stacking the two-dimensional plane images at each moment in chronological order. The two orange dashed conical outlines clearly delineate the physical boundary of the charge's influence range expanding outward over time. Thus, Figure 16 It has been proven that the generation, diffusion, and recombination lifetime of photogenerated electrons are all completed within the picosecond range. Because of its extremely fast response speed, it can emit periodically modulated pulsed excitation beams, causing friction to oscillate at extremely high frequencies, thereby achieving active dynamic suppression of stick-slip instability in mechanical systems.

[0087] In one embodiment, the light-controlled micro / nano tribological device is a two-dimensional material photo-induced solid lubrication structure or a microelectromechanical system with adjustable interface energy dissipation.

[0088] Specifically, two-dimensional material photo-induced solid lubrication structures refer to structures or coatings that utilize two-dimensional materials as solid lubricants and actively adjust their lubrication effect through light illumination, i.e., reducing or increasing friction. Microelectromechanical systems (MEMS) with adjustable interfacial energy dissipation refer to a class of MEMS whose core function or performance is directly related to the ability of its internal interfaces to dissipate mechanical energy during relative motion, and this energy dissipation capability can be actively adjusted through external light signals. Examples include variable dampers, controllable adhesive surfaces, and energy absorption structures.

[0089] Optically controlled micro / nano friction devices, as two-dimensional material photo-induced solid lubrication structures, are designed as a lubricating coating or interface in such applications. In the absence of light, the two-dimensional material heterojunction interface provides a basic lubrication effect. When the system requires greater resistance or needs to stop movement, a specific wavelength excitation beam can be activated to induce interlayer charge transfer, instantaneously increasing interlayer friction, thereby shutting off the lubrication effect or providing braking functionality. Alternatively, optically controlled micro / nano friction devices can function as microelectromechanical systems (MEMS) with adjustable interfacial energy dissipation. Many MEMS, such as micro-relays, micromirrors, and microresonators, are highly sensitive to the dynamic response and reliability of interfacial energy dissipation, i.e., friction and damping. By integrating the optically controlled micro / nano friction devices of this invention, the energy dissipation rate at these interfaces can be adjusted in real time.

[0090] Therefore, this invention provides a new solution for intelligent lubrication. The photo-induced solid lubrication structure can achieve on-demand lubrication, that is, provide lubrication when low friction is required and release lubrication when high friction or stopping is required. This is very useful for the positioning and locking of precision machinery. It also provides adjustable damping functionality for microelectromechanical systems (MEMS). By adjusting the interface energy dissipation, the quality factor and response speed of the MEMS can be dynamically changed, enabling a single device to adapt to multiple operating modes, greatly improving the system's functional integration and flexibility.

[0091] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for controlling interlayer friction in van der Waals heterostructures, characterized in that, include: An excitation beam is directed onto the sliding interface of a two-dimensional van der Waals heterojunction; wherein the sliding interface is formed by the contact between a first two-dimensional semiconductor material layer and a second two-dimensional semiconductor material layer, and the photon energy of the excitation beam is matched with the band-edge electron transition energy of the first two-dimensional semiconductor material layer to induce photogenerated electrons to undergo interlayer transfer. The irradiation state of the excitation beam is controlled to change the intensity of translayer transfer of photogenerated electrons, thereby adjusting the interlayer friction force of the slip interface when relative slip occurs.

2. The method for controlling interlayer friction in van der Waals heterostructures according to claim 1, characterized in that, Controlling the irradiation state of the excitation beam to adjust the interlayer friction force of the sliding interface during relative slippage includes: The incident light power of the excitation beam is continuously adjusted to continuously adjust the magnitude of the interlayer friction force; The excitation beam is controlled to be turned on and off in order to achieve reversible switching of the interlayer friction response.

3. The method for controlling interlayer friction in van der Waals heterostructures according to claim 1 or 2, characterized in that, Both the first two-dimensional semiconductor material layer and the second two-dimensional semiconductor material layer are transition metal chalcogenide monolayer materials; the wavelength of the excitation beam is configured as a resonant excitation wavelength to maximize the translayer transfer intensity of photogenerated electrons while eliminating photothermal effects.

4. An in-situ measurement system for controlling interlayer friction in van der Waals heterostructures, characterized in that, include: The first friction pair assembly is mounted on the probe tip of an atomic force microscope, and the probe tip is fixed with a first two-dimensional semiconductor material layer; The second friction pair component has a second two-dimensional semiconductor material layer fixed on its surface; wherein the first two-dimensional semiconductor material layer and the second two-dimensional semiconductor material layer are in contact to form a two-dimensional van der Waals heterojunction sliding interface; A photoexcitation control component for irradiating the sliding interface with an excitation beam of adjustable power and wavelength; A spot alignment component is used to monitor and adjust the transmission optical path of the excitation beam so that the spot of the excitation beam coincides spatially with the scanning area of ​​the probe on the second friction pair component; A data processing component, which is communicatively connected to the atomic force microscope, is used to obtain the interlayer friction force of the sliding interface when relative slippage occurs, based on the lateral force signals of the sliding interface during forward and reverse scanning in the probe scanning process.

5. The in-situ measurement system for controlling interlayer friction in van der Waals heterostructures according to claim 4, characterized in that, Both the first friction pair assembly and the second friction pair assembly include a dielectric support layer. The second friction pair assembly sequentially includes a rigid substrate, the dielectric support layer, and a second two-dimensional semiconductor material layer. The probe tip is fixed with the dielectric support layer by a van der Waals transfer process. The first two-dimensional semiconductor material layer is attached to the dielectric support layer at the probe tip.

6. The in-situ measurement system for controlling interlayer friction in van der Waals heterostructures according to claim 4 or 5, characterized in that, Also includes: The transient absorption spectroscopy testing component, coupled to the photoexcitation control component, is used to emit a femtosecond-level first beam for excitation and a second beam for monitoring to the slip interface, and to obtain in situ the lifetime and spatial diffusion coefficient of the interlayer electron-hole pairs of the slip interface under photoexcitation.

7. An in-situ measurement method for controlling interlayer friction in van der Waals heterostructures, characterized in that, Performed by the in-situ measurement system for controlling interlayer friction in two-dimensional van der Waals heterostructures as described in any one of claims 4-6, the in-situ measurement method comprising: The photoexcitation control component is controlled to shut off the excitation beam and drive the probe of the atomic force microscope to scan and obtain the initial interlayer friction force; The photoexcitation control component is controlled to turn on the excitation beam and adjust the wavelength of the excitation beam to match the resonant wavelength of the band-edge transition energy, thereby driving the probe of the atomic force microscope to scan and obtain the interlayer frictional force under the resonant excitation state. The change in interlayer friction induced by the excitation beam is obtained based on the interlayer friction under the resonant excitation state and the initial interlayer friction.

8. The in-situ measurement method for controlling interlayer friction in van der Waals heterostructures according to claim 7, characterized in that, After obtaining the interlayer frictional force in the resonant excited state, the method further includes: The photoexcitation control component is controlled to switch the excitation beam to a non-resonant wavelength with insufficient energy to effectively excite band-edge electron transitions, and the interlayer friction force in the non-resonant state is obtained. If the interlayer friction force in the non-resonant state does not change significantly compared to the initial interlayer friction force, it is established that the change in the interlayer friction force originates from interlayer charge transfer.

9. The in-situ measurement method for controlling interlayer friction in van der Waals heterostructures according to claim 7 or 8, characterized in that, Also includes: The photoexcitation control component is controlled to cycle on and off the excitation beam, and the interlayer friction force under different illumination conditions is obtained to verify the reversibility of the interlayer friction force regulation process.

10. A light-controlled micro / nano tribological device, characterized in that, include: A movable friction assembly includes a stator assembly and a mover assembly disposed opposite to each other. The stator assembly includes a first two-dimensional semiconductor material layer, and the mover assembly includes a second two-dimensional semiconductor material layer. The first two-dimensional semiconductor material layer and the second two-dimensional semiconductor material layer are arranged opposite to each other and in contact to form a two-dimensional van der Waals heterojunction sliding interface having a second type of band arrangement. An external drive component is used to drive the mover assembly to slide relative to the stator assembly; The photoexcitation control component is used to irradiate the sliding interface with an excitation beam and induce interlayer charge transfer by adjusting the irradiation state of the excitation beam, thereby adjusting the interlayer friction force of the movable friction component in real time during operation in a non-contact manner.

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