CN111811939A - High-precision nano-mechanics detection system in ultralow temperature environment - Google Patents

High-precision nano-mechanics detection system in ultralow temperature environment Download PDF

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CN111811939A
CN111811939A CN202010714529.5A CN202010714529A CN111811939A CN 111811939 A CN111811939 A CN 111811939A CN 202010714529 A CN202010714529 A CN 202010714529A CN 111811939 A CN111811939 A CN 111811939A
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laser
unit
temperature
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CN111811939B (en
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司乐致
邵志峰
张司琪
丹尼尔·恰可夫
沈轶
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Shanghai Jiaotong University
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    • G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
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Abstract

The invention discloses a high-precision nano-mechanical detection system in an ultralow temperature environment, which comprises a low-temperature system unit, a high-precision nano-mechanical detection unit and a control unit, wherein the low-temperature system unit is used for providing a stable normal-pressure non-vacuum low-temperature clean environment; the shell is arranged in an upper space enclosed by the tank body and the liquid level of the low-temperature liquid; the probe is fixed in the shell and provided with a micro cantilever; the optical detection unit comprises a laser light path unit and a laser detection unit; the processing unit is used for converting the electric signal into the deflection quantity of the micro-cantilever; and the feedback and execution unit comprises a piezoelectric ceramic tube which is used for adjusting the relative displacement between the sample and the probe. The system is kept at low temperature, and the cold trap effect is utilized to reduce the pollutants in the measurement space, so that stable ultralow-temperature high-precision mechanical measurement is performed on the material or single molecule, and the temperature application range of nano mechanical measurement is expanded.

Description

High-precision nano-mechanics detection system in ultralow temperature environment
Technical Field
The invention relates to the technical field of nano-mechanical detection, in particular to a high-precision nano-mechanical detection system in an ultralow temperature environment.
Background
The nano-mechanics detection technology is a technical means for measuring the mechanical properties of a sample in a nano-scale manner, and the conventional method is to stretch or compress the sample at a constant speed or under a constant acting force by using a micro-nano probe to measure the relationship between the mechanical information of the material or the force between molecules and the displacement information. The research on the nanometer mechanical property of the sample aims to better improve the macroscopic property, the connection between the micromechanics and the macroscopic mechanical property is not obvious, and the mechanical quantities such as hardness, modulus and the like are not equal under the macroscopic and the microscopic conditions, so the development of the nanometer mechanical detection technology can better establish a mechanical system of the material from the macroscopic to the microscopic conditions and has greater effect on understanding the modulus, the hardness, the toughness, the creep deformation and the like of the material.
At present, nano mechanical detection mainly focuses on measuring samples in a normal temperature range, and partial materials in the fields of aviation, aerospace and the like need to work for a long time at a low temperature (for example, work at a temperature of minus 196 ℃ of a precooling pipeline of an aircraft engine), so that the state of the materials at the working temperature can be reflected better by researching the materials in a low-temperature environment, and the mechanical properties such as the bearing capacity, the strength, the stress and the like of the materials can be measured more reliably. At present, most research means of low-temperature material mechanics are limited to be above minus 100 ℃, an active local temperature control method is adopted, the temperature stability is poor, the measurement precision is insufficient, and development of a material mechanics detection means capable of carrying out ultralow-temperature high-precision is urgently needed.
Therefore, there is still no high-precision nanomechanical detection system in the ultra-low temperature environment that can achieve high-precision measurement in the ultra-low temperature environment in the art.
Disclosure of Invention
The invention aims to provide a high-precision nano-mechanical detection system in an ultralow temperature environment, wherein a detection system main body is suspended in a closed Dewar tank filled with a certain volume of low-temperature liquid (liquid nitrogen and the like) and runs in low-temperature gas, and the detection system applies a compression or stretching acting force to a low-temperature material sample by utilizing a micro-cantilever; the deflection amount of the micro-cantilever is detected through an optical lever system, the relative displacement between the sample substrate and the micro-cantilever substrate is obtained, and further the deformation amount of the sample after the sample is subjected to the action of external force is obtained, so that the mechanical properties of the sample such as elasticity, interaction force and the like in a low-temperature environment are obtained. The high-precision nano-mechanics detection system under the ultralow temperature environment has unique advantages for the mechanical properties of materials and the research of single-molecule nano-mechanics at low temperature.
The invention provides a high-precision nano-mechanical detection system in an ultralow temperature environment, which comprises a low-temperature system unit, a probe, an optical detection unit, a processing unit, a feedback and execution unit and a shell, wherein the low-temperature system unit is connected with the probe; the low-temperature system unit is used for providing a stable normal-pressure non-vacuum low-temperature clean environment and comprises a tank body, and low-temperature liquid is contained in the tank body; the shell is arranged in an upper space enclosed by the tank body and the liquid level of the low-temperature liquid; the probe is fixed in the shell and is provided with a micro-cantilever; the optical detection unit comprises a laser light path unit and a laser detection unit, and is also fixed in the shell; the laser light path unit includes: a laser for emitting laser light; the laser collimator is used for fixing the laser, carrying out position focusing on the laser emitted by the laser, and irradiating the laser to the needle point of the micro-cantilever by adjusting the laser collimator in a use state; the laser detection unit comprises a photoelectric detector, and the photoelectric detector is used for receiving the laser signal reflected by the micro-cantilever and converting the laser signal into an electric signal; the processing unit is used for converting the electric signal into the deflection quantity of the micro-cantilever; the feedback and execution unit comprises a piezoelectric ceramic tube, and the piezoelectric ceramic tube is used for adjusting the relative displacement between the sample and the probe.
In another preferred example, the tank body is a dewar tank.
In another preferred example, the liquid level height of the low-temperature liquid does not exceed 1/2 of the height of the tank body; preferably, 1/3; more preferably 1/4.
In another preferred example, the distance between the bottom surface of the shell and the liquid level is 10-100 cm; preferably, 20-90 cm; more preferably, 30-70 cm.
In another preferred example, the tank includes a pressure relief valve for controlling the pressure inside the tank. This pressure can suppress the boiling of the cryogenic liquid and the resulting vibrational disturbances.
In another preferred example, the pressure relief valve is a manual pressure relief valve and/or an automatic pressure relief valve.
In another preferred example, the tank body comprises a pressure gauge, and the pressure gauge is used for displaying the pressure in the tank body.
In another preferred example, the low-temperature system unit comprises an insulating layer, and the insulating layer is used for insulating the tank body.
In another preferred example, the heat-insulating layer comprises a vacuum heat-insulating layer and/or a baffle system; the vacuum heat insulation layer is used for reducing heat transfer between the tank body and the external environment; the separator system is used to block thermal cycling.
In another preferred example, the vacuum heat insulation layer surrounds the side surface of the tank body, and the partition plate system covers the upper surface of the tank body.
In another preferred example, the vacuum insulation layer surrounds the whole tank body, and the partition plate system surrounds the outer side of the vacuum insulation layer.
In another preferred example, the tank body comprises a viewing window through which an operator can observe to assist in adjusting the laser, placing and fixing the experimental sample and the probe, inserting the needle, filling the cryogenic liquid and the like.
In another preferred example, the laser is a laser diode.
In another preferred embodiment, a long laser light path is used to increase the amplification of the optical lever to increase the detection sensitivity.
In another preferred example, the focusing lens is a line focusing lens.
In another preferred example, the two-quadrant photodiode includes an a chamber (a-cell) and a B chamber (a-cell), the a chamber and the B chamber are configured to receive a focused laser signal and convert the laser signal into two current signals, i.e., an a current signal and a B current signal, and output the current signals to the outside, where the magnitude of the current difference output by the photodetector A, B is related to the position of the probe microcantilever reflecting the laser light to the detector, and the deflection amount of the probe microcantilever is obtained in real time by detecting the variation of the current difference.
In another preferred example, the housing is used for fixing the laser optical path unit, the laser detection unit, the gear box unit and the probe, is a main body part of the system, and can block interference of potential gas circulation on the laser signal and the micro-cantilever.
In another preferred embodiment, the system can perform mechanical measurement at a certain position of a specified sample, and can also perform multi-point matrix mechanical measurement on the surface of the sample.
In another preferred example, the laser optical path unit includes a laser driver, and the laser driver is configured to emit a driving signal to adjust the power of the laser.
In another preferred example, the radio frequency modulation circuit is used for sending out a high-frequency radio frequency signal to adjust the laser oscillation mode.
In another preferred example, the piezo ceramic tube adjusts relative displacement between the sample and the probe in one dimension (e.g., Z direction).
In another preferred example, the control precision of the piezoelectric ceramic tube is 0.01 nm.
In another preferred example, the cryogenic liquid is liquid nitrogen, and the temperature of the liquid nitrogen is 77-100K.
In another preferred example, the cryogenic liquid is liquid helium, the temperature of which is 4.2K and above.
In another preferred example, the low-temperature liquid is liquid oxygen, and the temperature of the liquid oxygen is 90K or above.
In another preferred example, the laser detection unit includes a focusing lens, and the photodetector is disposed behind the focusing lens, and the photodetector can receive a laser signal reflected by the probe micro-cantilever after being focused by the focusing lens.
In another preferred example, the photodetector is a two-quadrant photodiode.
In another preferred example, the processing unit is a signal amplifying and processing circuit unit, the signal amplifying and processing circuit unit includes a pre-amplifying circuit unit and a signal post-processing unit, and the pre-amplifying circuit unit 4 converts a current signal into a voltage signal and outputs the voltage signal to a post-stage circuit; and the signal post-processing unit is used for reprocessing the voltage signal.
In another preferred example, the system comprises a hanger unit, the upper end of the hanger unit is fixedly connected with the top of the tank body, and the lower end of the hanger unit is fixedly connected with the shell and used for hanging the shell.
In another preferred example, the hanger unit includes a separate lever for adjusting the laser light path unit and the laser detector system.
In another preferred example, the hanger unit includes a frame in which the housing is provided, the frame providing a shielding space for the housing to reduce external electromagnetic interference.
In another preferred embodiment, the system comprises a magnetic damped suspension unit connected between the hanger unit and the housing for suspending the housing and damping vibrations by permanent magnet damping.
In another preferred example, the magnetic damping suspension unit comprises a spring suspension system and a permanent magnet damping system.
In another preferred embodiment, the spring suspension system comprises 2-10 (preferably 3-8; more preferably 4-6) springs connected to the upper part of the housing for suspending the housing and thereby reducing the effect of environmental vibrations.
In another preferred embodiment, the springs have the same elastic coefficient.
In another preferred embodiment, the permanent magnet damping system is a permanent magnet on the housing, which interacts with the surrounding metal plate to provide a shock absorbing effect.
In another preferred embodiment, a sample and probe transfer unit for transporting the sample and probe into the housing.
In another preferred example, the sample and probe transfer unit comprises a sample operation box, a sample transfer chain and a mechanical manipulator, wherein the sample operation box is a clean space for sample preparation; the sample transfer chain transfers samples to the tank body; the mechanical manipulator fixes the sample and the probe at a proper position, and the sample and the probe can be conveyed to a room temperature operation box after the experiment is finished.
In another preferred embodiment, the system comprises a probe approaching system for controlling the approaching/approaching of the probe microcantilever to/from the sample surface.
In another preferred embodiment, the probe approaching system is also referred to as a "stepper motor gear box variable speed needle inserting system", and the probe approaching system includes a stepper motor and a gear box, and the stepper motor drives the gear box to operate, so as to control the probe approaching/approaching to/from the sample surface.
In another preferred example, the gear box decelerates the rotational movement of the stepping motor and converts it into a linear movement by a fine adjustment screw to control the distance between the probe and the sample.
In another preferred example, the stepping motor is a low-temperature stepping motor, and the low-temperature stepping motor can work at ultra-low temperature.
In another preferred example, the system further comprises a control unit for controlling the mechanical operation and the mechanical detection of the system.
It is to be understood that within the scope of the present invention, the above-described features of the present invention and those specifically described below (e.g., in the examples) may be combined with each other to form new or preferred embodiments. Not to be reiterated herein, but to the extent of space.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a schematic view of a nanomechanical detection system in one embodiment of the present invention;
FIG. 2 is a functional diagram of a nanomechanical detection system in one embodiment of the present invention;
FIG. 3 is a schematic diagram of a nanomechanical detection system operating under compression and a force-compression depth graph in one embodiment of the present invention;
FIG. 4 is a schematic diagram and force-stretch length graph of the nanomechanical detection system operating in a constant velocity mode of stretching in one embodiment of the present invention;
FIG. 5 is a schematic diagram and a graph of stretch length versus time for a nanomechanical detection system operating in a constant force mode of stretching in one embodiment of the present invention;
FIG. 6 is an optical lever diagram of a nanomechanical detection system in an embodiment of the present invention;
FIG. 7 is a radio frequency interference circuit diagram of a nanomechanical detection system in one embodiment of the present invention;
FIG. 8 is a schematic diagram of the operation of the nanomechanical detection system in one embodiment of the present invention.
In the drawings, each symbol is as follows:
1-a cryogenic system unit;
2-laser light path unit;
3-a laser detector unit;
4-a leading signal amplifying circuit unit;
5-a signal post-processing circuit unit;
6-a shell;
7-magnetic damping suspension unit;
8-a hanger system unit;
9-sample and probe transfer unit;
10-probe approach system;
11-a feedback and execution unit;
12-a control unit;
13-a control box;
14-a laser driver;
15-radio frequency modulation circuit;
16-a display screen;
17-a sample;
18-a laser;
19-laser collimator;
20-a probe;
21-a microcantilever;
22-line focusing lens;
23-a photodetector;
24-a piezoelectric ceramic tube;
25-a substrate;
26-a bias device;
27-a laser detector;
28-Voltage controlled Oscillator.
Detailed Description
The inventor of the invention develops a high-precision nano-mechanical detection system under an ultralow temperature environment for the first time through extensive and intensive research and a large number of screens, compared with the prior art, the invention breaks the limitation of the temperature measurement range of the nano-mechanical detection technology in the prior art, and improves the stability and the measurement precision of temperature control, specifically, the detection system main body of the invention is suspended in a closed Dewar tank filled with a certain volume of low-temperature liquid (liquid nitrogen and the like), runs in low-temperature gas, and applies compression or tensile acting force to a low-temperature material sample by using a probe tip, or connects a single sample molecule (pair) between the probe tip and the substrate surface, and applies compression or tensile acting force to the single sample molecule (pair) by using a probe micro-cantilever; the deflection amount of the probe micro-cantilever is detected through an optical lever system, the relative displacement between the sample substrate and the probe base is obtained, and further the deformation amount of the sample after the sample is subjected to the action of external force is obtained, so that the mechanical property and the interaction of a low-temperature material or a single sample molecule (pair) in a low-temperature environment are obtained. The operating temperature of the force spectrum detection system is controlled by adjusting the distance between the detection system and the liquid level of the cryogenic liquid (77-100K when the cryogenic liquid is liquid nitrogen), and the passive temperature stability of the detection system is realized by sealing a large amount of cryogenic liquid in the dewar tank; the dewar tank restrains the boiling of the low-temperature liquid and the vibration interference caused by the boiling by properly and actively pressurizing (0.01-0.03 MPa); a large amount of low-temperature liquid also plays a role of a cold trap (pollutants are easier to condense on the surface with lower temperature, and the temperature is slightly higher than that of the low-temperature liquid because the detection system is arranged on the low-temperature liquid), so that the pollution of a detection space is effectively reduced; the detection system reduces the thermal noise of the micro-cantilever and the electronic noise of a pre-amplification circuit through a low-temperature working environment, increases the optical lever to improve the detection sensitivity, adopts a magnetic damping suspension vibration isolation design, eliminates laser mode hopping noise by superposing a high-frequency (300MHz) radio-frequency signal on a laser signal, pressurizes and inhibits the boiling of low-temperature liquid and other measures to jointly ensure the capability of the measuring probe, namely the system finally converts the deflection information of the micro-cantilever into the accuracy of force value information, namely the measuring accuracy; therefore, the high-precision nano-mechanical detection system under the ultralow-temperature high-precision ultralow-temperature environment has unique advantages on the mechanical properties of materials at low temperature and the research on monomolecular nano-mechanical; the present invention has been completed based on this finding.
The system can perform mechanical detection and analysis on the low-temperature material at ultralow temperature (the low-temperature liquid is liquid nitrogen, 77K-100K).
The low-temperature system unit is used for providing a low-temperature stable environment for the detection system, and the heat transfer and heat circulation processes are reduced through the design of the vacuum heat insulation layer and the partition plate, so that the heat loss is reduced, the stable temperature gradient is maintained, and the stable mechanical measurement can be carried out at low temperature; the boiling of the low-temperature liquid and the vibration interference caused by the boiling are inhibited by active pressurization (0.01-0.03 MPa); controlling the detection temperature by controlling the distance between the cryogenic liquid and the detection system; the laser adjustment, the fixing of the experimental sample and the probe, the needle insertion and the filling process of the low-temperature liquid are assisted through a surface window.
The nanometer mechanics detection technology is to apply force and measure displacement by using a micrometer-sized micro-cantilever, and the micro-cantilever is influenced by self thermal disturbance due to small size, so that the resolution of the displacement and the force is limited. In general, to make an approximation, the microcantilever is considered to be attached to a linear spring with a stiffness α, which is either the spring constant of the cantilever or the stiffness of the molecule to which the probe is attached. The spatial resolution of the system is finally determined by the thermal noise of the micro-cantilever, and according to the fundamental principle of quantum mechanics, the minimum unit of the energy of thermal vibration is KBT/2, wherein KBIs boltzmann constant (1.3807 × 10)-23J/K), T is the absolute temperature, therefore
Figure BDA0002595331080000081
z is the magnitude of the positional noise, KBAccording to hooke's law (F ═ α x), the corresponding mechanical resolution is:
Figure BDA0002595331080000082
the data α is 0.06, T is 77K (-196 ℃), and F is 8 pN.
The noise can be reduced by filtering, and the above formula can be converted into the following formula according to the power spectrum lorentz conversion formula:
Figure BDA0002595331080000083
β is hydrodynamic drag (β ═ 6 π η r, η is the viscosity coefficient, r is the probe tip perturbation radius), and B is the bandwidth. Therefore, the temperature can be reduced from the above formula, and the mechanical resolution can be improved by reducing the bandwidth. The experiment was carried out in a low temperature gas (e.g. nitrogen), η ═ 3.12 μ Pa · S, r ═ 100 μm, B ═ 4kHz, T ═ 77K, KB＝1.3807×10-23J/K. F ═ 1pN can be obtained. The above is the theory of the mechanical resolution of the systemPhysical limits.
F at room temperature (298K) is 2pN, which is 2 times the physical limit of low temperature, and it is known that the resolution of the system can be greatly improved at low temperature.
The main advantages of the invention include:
the high-precision nano mechanical detection system under the ultralow-temperature high-precision ultralow-temperature environment, which is built by the invention, can detect different mechanical properties of various materials at low temperature, such as: strength, hardness and rigidity of composite materials, metal materials, and the like; elasticity, maintained length, intramolecular interaction, intermolecular interaction and the like of a single biological or chemical molecule, and provides a brand-new technical method for the research of material mechanics and biochemistry at low temperature.
(a) The detection process is carried out in a non-vacuum low-temperature Dewar flask, and the mechanical detection can be carried out on the material at a specific low temperature by adjusting the distance between the detection system and the liquid level of the low-temperature liquid to control the operating temperature of a force spectrum detection system (77-100K when the low-temperature liquid is liquid nitrogen); the passive temperature stability of the detection system is realized through a large amount of low-temperature liquid in the closed Dewar flask; the low-temperature liquid boiling and the vibration interference caused by the low-temperature liquid boiling are inhibited by proper active pressurization (0.01-0.03 MPa); a large amount of low-temperature liquid also plays a role of a cold trap (pollutants are easier to condense on the surface with lower temperature, and the temperature is slightly higher than that of the low-temperature liquid because a detection system is arranged on the low-temperature liquid), so that the pollution of a detection space is effectively reduced, and the mechanical resolution is improved;
(b) the detection system is carried out at ultralow temperature, the thermal disturbance of the probe is low, and the overall signal-to-noise ratio and stability of the system are greatly improved, so that the acting force of the probe on the sample and the deformation of the sample can be more finely controlled and detected;
(c) the closed space of the Dewar tank body greatly reduces the interference of external electric noise and the like, and reduces the mechanical vibration interference by special mechanical mechanism design (magnetic damping suspension unit);
(d) the detection frequency is far lower than the resonance frequency of the cantilever, so that the cantilever cannot be influenced, and the mechanical consistency and the influence of air damping are ensured;
(e) the radio frequency interference circuit can effectively modulate a laser signal, reduce mode hopping noise of the laser and directly reduce the influence of the noise of the laser on the background noise of a system;
(f) the detection system can automatically insert the needle at low temperature, so that the needle point of the probe is greatly protected, and the pollution and damage of the needle point are avoided;
(g) the low-temperature detection system has low background thermal noise and the mechanical resolution of 1-10 pN; preferably, 1-5 pN; more preferably, 1.1 pN.
The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Furthermore, the drawings are schematic and, thus, the apparatus and devices of the present invention are not limited by the size or scale of the schematic.
It is to be noted that in the claims and the description of the present patent, relational terms such as first and second, and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, the use of the verb "comprise a" to define an element does not exclude the presence of another, same element in a process, method, article, or apparatus that comprises the element.
Examples
The high-precision nano mechanical detection system in the ultra-low temperature environment of the present embodiment is shown in fig. 1, and performs high-resolution stable mechanical analysis on materials and single molecules at low temperature. The system can perform mechanical measurement at a certain position of a designated sample, and can also perform multi-point matrix mechanical measurement on the surface of the sample.
The high accuracy nanometer mechanics detecting system under the ultra-low temperature environment in this embodiment includes: the system comprises a low temperature system unit 1, an optical detection unit, a shell 6, a probe 20, a processing unit, a mechanical auxiliary unit, a feedback and execution unit 11 and a control unit 12.
The cryogenic system unit 1 is used for providing a stable normal-pressure non-vacuum low-temperature clean environment and comprises a tank body, a vacuum thermal insulation layer, a partition plate system and an observation window.
The low-temperature liquid is filled in the Dewar tank, and a stable low-temperature environment is provided for the work of a detection system which is hung at a certain height from the liquid level of the low-temperature liquid. The tank body is used for storing cryogenic liquid, the operating temperature of the force spectrum detection system is controlled by adjusting the distance between the detection system and the liquid level of the cryogenic liquid (77-100K when the cryogenic liquid is liquid nitrogen), passive temperature stability of the detection system can be realized due to a large amount of cryogenic liquid in the closed Dewar tank, and a large amount of liquid nitrogen also plays a role in cold traps (pollutants are easier to condense on the surface of lower temperature, the temperature is slightly higher than that of the cryogenic liquid because the detection system is arranged on the cryogenic liquid), so that the detection space pollution is effectively reduced.
The tank body is provided with a manual pressure relief valve, an automatic pressure relief valve, a pressure gauge and the like for controlling the internal pressure of the tank body, and the boiling of the low-temperature liquid and the vibration interference caused by the boiling can be inhibited through appropriate active pressurization (0.01-0.03 MPa). The vacuum heat insulation layer is an interlayer between the tank body and the external environment and is used for reducing the heat transfer process and reducing the temperature fluctuation, and the active carbon in the vacuum heat insulation layer can further improve the vacuum environment. The baffle system can obstruct thermal circulation, reduce heat loss and maintain stable temperature gradient. The observation window is the only window for the experimenter to observe the internal detection system and is used for assisting in adjusting laser, placing and fixing an experimental sample and a probe, inserting a needle and filling low-temperature liquid.
The optical detection system comprises a laser light path unit 2 and a laser detector unit 3, wherein the laser light path unit 2 focuses and irradiates laser on a micro-cantilever 21 of a probe 20 by adjusting the position of a laser 18 to generate a laser reflection signal; the laser detection unit performs photoelectric conversion on the reflected laser signal and converts the reflected optical position signal into a current signal.
The laser light path unit 2 includes a laser driver 14, a radio frequency modulation circuit 15, a laser collimator 19, and a laser 18 (laser diode) thereof. The laser light path unit 2 needs to be debugged at room temperature. The laser diode is used to emit laser light. The laser driver 14 can emit a driving signal to adjust the power of the laser diode in the constant power operation mode, so that the laser diode can normally operate at a low temperature. A high-frequency (300MHz) rf signal of the rf modulation circuit 15 is superimposed on the laser driving signal, so that the laser oscillation mode is changed from a single mode to a multi-mode. The laser collimator 19 is used for fixing the laser diode and focusing the position of the laser emitted by the laser diode, the position of the laser is adjusted through a nut mechanical structure to control the laser irradiation direction and position, the laser is irradiated on the micro-cantilever 21 of the probe 20, and the long optical path is used for improving the amplification factor of the optical lever so as to improve the detection sensitivity.
The laser detection unit comprises a line focusing lens 22 and a photodetector 23 (two-quadrant photodiode). The line focus lens 22 receives and focuses the laser signal reflected by the micro-cantilever 21 of the probe 20. The photodetectors 23(a-cell and B-cell) can receive the focused laser signal, convert the laser signal into two paths of current signals a and B, and output the current signals. The magnitude of the current difference A, B output by the photodetector 23 is related to the position of the micro-cantilever 21 reflecting the laser to the detector, and the deflection of the micro-cantilever 21 of the probe 20 is obtained in real time by detecting the variation of the current difference.
The laser wavelength emitted by the photodiode is matched with the wavelength received by the laser detector 27, and the photodiode is placed in low-temperature liquid for luminescence test before subsequent installation. The laser collimator 19 is required to focus the laser at the tip of the micro-cantilever 21 of the probe 20, and the reflection effect is optimal.
The radio frequency modulation circuit 15(RF) in the present embodiment effectively reduces system noise by modulating the laser drive source as shown in fig. 7. In fig. 7, a 300MHz rf signal generated by the vco 28 is superimposed on the dc laser driving signal generated by the laser driver 14 through the biaser 26, and the biaser 26 outputs a superimposed dc and ac signal for driving the laser to operate and reducing laser noise.
The processing unit is a signal amplifying and processing circuit unit, which includes a pre-signal amplifying circuit unit 4 and a signal post-processing circuit unit 5 (it should be noted that the signal amplifying and processing circuit unit can be implemented by the prior art). The front signal amplifying circuit unit 4 adopts a mutual resistance amplifying circuit design, converts A, B two paths of current signals into voltage signals and outputs the voltage signals to a rear-stage circuit, and designs a specific bandwidth and an amplification factor according to the signal processing requirement; the signal post-processing unit can perform operations such as operational amplification, differential amplification, normalization and the like on A, B voltage signals input by the front stage, display the sum of the voltage signals A and B and the normalized difference in real time through the display screen 16, and readjust the positions of the laser 18 and the photoelectric detector 23 according to the value displayed by the display screen 16 (i.e., adjust the laser signal and assist in adjusting the position of the laser on the micro-cantilever 21 of the probe 20) so that the sum of the two voltage signals is the maximum and the difference of the two voltage signals is the minimum. The display value is used for obtaining a stable reflection signal, and the feedback control is carried out on the piezoelectric ceramic tube 24 in cooperation with external control, and meanwhile, the display value is connected with an external feedback system to control the force spectrum measurement of the detection system. The signal post-processing circuit unit 5 selects 2 low-noise conventional operational amplifiers to perform addition and subtraction operations of voltage signals respectively, a low-noise divider performs normalization processing on the signals, and a stable and symmetrical instrument amplifier and an external feedback control system cooperatively control the mechanical measurement process of the detection system.
The operational amplifier in the mutual resistance amplifying circuit can normally operate at a low temperature of 77K, the gain (amplification factor) of the circuit is selected, meanwhile, the feedback resistor is selected according to the bandwidth requirement, a preceding-stage current signal is converted into a voltage signal, the plate manufacturing selection position is arranged close to the output end of the laser detector 27, the output circuit path is shortened, and the interference of the environment on a weak current signal is reduced.
The chip, the resistor and the capacitor in the pre-amplifying circuit are all selected to be low in noise, and normal operation at low temperature can be guaranteed.
The pre-amplification circuit chip selection mainly considers two parameters of low bias current and high common mode rejection ratio.
The signal post-processing unit comprises the operation of the difference of two paths of voltage signals and the division of the difference and the two paths of voltage signals, the larger the sum of the signals is known according to a noise transfer function, the smaller the total noise is, so the signal intensity needs to be improved, and meanwhile, the background noise of the operational amplifier is as small as possible.
The signal post-processing unit is provided with an instrument amplifying circuit part which needs to ensure circuit symmetry, and the selected resistance values are required to ensure the same symmetrical arrangement, so that the circuit processing error is reduced.
The shell 6 is used as a main body supporting structure of the detection system, is used for fixing and positioning other system units (such as the laser light path unit 2, the laser detection unit, the gear box unit and the probe 20), does not generate relative movement, provides mechanical precision, and can simultaneously obstruct interference of potential gas circulation to laser signals and the micro-cantilever 21.
The piezoelectric ceramic tube 24 in the feedback and execution unit 11 receives an external system voltage signal to perform one-dimensional (Z-direction) microscopic motion to realize the relative displacement change between the sample 17 and the probe 20, and the Z-direction control precision of the piezoelectric ceramic tube 24 is 0.01 nm. The piezoelectric ceramic tube 24 is made of piezoelectric ceramic material, has sufficient sensitivity at low temperature, and the magnetic part for fixing the sample 17 is arranged on the piezoelectric ceramic tube 24, so that the requirement of microscopic motion in a one-dimensional direction (Z direction) can be met.
The control unit 12 controls the mechanical operation and the mechanical detection of the detection system, for example, performs feedback control on the low-temperature detection system, and performs detection and analysis calculation on the mechanical properties of the material or the single molecule, so as to obtain the deflection amount of the micro-cantilever 21 of the probe 20 and the change in the relative distance between the probe 20 and the sample 17, and thus perform model construction and analysis on the obtained mechanical information (it should be noted that, the control unit 12 also performs reprocessing on the offset parameter of the micro-cantilever 21, and it can also be implemented by the prior art).
The control unit 12 includes a control box 13, and the control box 13 can control the related operations of the detection system and send feedback signals back to the computer in real time to control the needle point to reciprocate in the vertical direction relative to the sample 17.
The mechanical analysis software (for example: Nanoscope) in the computer records the change of the bending degree of the micro-cantilever 21 in the process of approaching the needle tip to the sample 17 and approaching and stretching the low-temperature material or sample molecules (pair) from the sample 17, then converts the change into the change curve of the acting force applied to the sample 17 (the magnitude of the force F is equal to the product of the needle tip elastic constant k and the distance variable x, and F is k.x) along with the Z-direction stretching distance of the piezoelectric ceramic tube 24, namely the force-distance (the bending degree of the micro-cantilever 21) curve in the mechanical measurement process, and then combines the deflection amount of the micro-cantilever 21 of the probe 20 to obtain the deformation amount of the sample 17 under different external forces, and combines the mechanical model analysis to obtain the mechanical characteristics (strength, hardness and rigidity) of the low-temperature material (composite material, metal material and the like) or the elastic elasticity of single sample molecule, Maintaining mechanical properties and interaction parameters such as length, pulling force, etc.
The mechanical assistance units include a magnetic damping suspension unit 7, a gantry system unit 8, a sample and probe transfer unit 9 and a probe approach system 10. The magnetic damping suspension unit 7 is used to suspend the housing 6 and damp vibrations by permanent magnet damping, i.e. to remove vibration disturbances caused by mechanical coupling. The detection system hanger unit is used to secure and suspend the detection system body portion (e.g., housing 6) in the cryogenic dewar system. The sample and probe transfer unit is a mechanical device used to transport the sample and scanning probe 20 to the detection system body in the cryogenic dewar. The probe approaching system 10 is a stepping motor gear box variable speed needle inserting system, and the stepping motor is controlled by signals to drive a gear box gear to rotate, so that the probe 20 is controlled to approach/approach the surface of the sample 17.
The magnetic damping suspension system comprises a spring suspension system and a permanent magnet damping system. The spring suspension system comprises 4 springs with appropriate spring constant for suspending the housing 6 to reduce vertical mechanical vibrations. 4 permanent magnets are arranged on the shell 6, and form a magnetic damping group together with iron materials on the hanger system, so that mechanical vibration in the horizontal direction is reduced. The permanent magnet damping system is a permanent magnet on the housing 6 that interacts with the surrounding metal plates to provide a shock absorbing effect.
The detection system hanger unit is a structural metal frame for hanging the detection system main body, the detection system is hung in the Dewar flask, a separated operating lever is arranged on the detection system hanger unit and used for carrying out adaptive adjustment on the laser light path unit 2 and the laser detector system which are arranged in the Dewar flask, so that the laser position is adjusted in a long distance, the laser irradiation on the needle point part of the probe 20 is ensured, the position of the laser detector 27 can be adjusted through the separated operating lever, the laser signals are fully absorbed and the sizes of two paths of output current signals are adjusted, the sizes of the two paths of signals are generally the same, and the follow-up needle inserting operation is facilitated. The hanger unit also comprises a shell, and the shell provides a shielding space for the detection system main body, so that the hanger unit is kept in a closed state in the mechanical measurement process, and external electromagnetic interference is reduced or even shielded, so that the interference of thermal noise to the mechanical measurement process is reduced.
The sample and probe transfer unit 9 includes a sample manipulation box, a sample transfer chain, and a manipulator. The sample handling box is a clean space where sample 17 preparation is performed. The transfer chain may transfer the test sample 17 into the cryogenic dewar. The manipulator holds the test sample 17 and the probe 20 in place. When the device is used, a sample 17 prepared in a sample operation box and a probe holder provided with a probe 20 are transferred to a specific position in a Dewar tank through a chain, the sample 17 and the probe 20 are fixed at proper positions by using a remote manipulator, and after an experiment is finished, the sample 17 and the probe 20 are transferred to a room temperature operation box. In another preferred example, the system is controlled by an external feedback regulating system to realize the needle inserting action. In another preferred embodiment, the system can perform automatic needle insertion, effectively protect the tip of the probe 20, and ensure the true accuracy of the intermolecular force.
The probe approximation system 10 includes a cryogenic stepper motor and a gear box. The low-temperature stepping motor can work at ultralow temperature and is used for driving the gear box to operate. The gear box can reduce the speed of the rotation of the stepping motor and convert the rotation into linear motion through a fine adjustment screw, and the distance between the probe 20 and the experimental sample 17 is controlled. During the use, through the gear train motion of specific gear ratio in the low temperature step motor drive gear box and then adjust the distance between probe 20 and experimental sample 17, step motor drive signal receives the control of external feedback governing system to realize the action of inserting the needle, avoids probe 20 pollution and damage that the firing pin caused. The low-temperature stepping motor is specially designed for wiring and is matched with an external control system. The change gear box of the needle inserting unit of the change gear box of the stepping motor compresses the volume of the gear box on the premise of ensuring the length of a single-step needle inserting, reduces the number of gears, and avoids the phenomenon that the coaxiality error is enlarged due to low-temperature deformation, and the driving moment of the motor is influenced or even blocked.
FIG. 2 shows a schematic diagram of the operation of the nanomechanical detection system of FIG. 1 with a laser diode lasing. The laser driver (not shown) can send out a driving signal to adjust the power of the laser diode in the constant power operation mode, so that the laser diode can normally operate at low temperature. A high-frequency (300MHz) rf signal of the rf modulation circuit 15 is superimposed on the laser driving signal, so that the laser oscillation mode is changed from a single mode to a multi-mode. The laser collimator 19 is used for fixing the laser diode and focusing the position of the laser emitted by the laser diode, the position of the laser is adjusted through a nut mechanical structure to control the laser irradiation direction and position, the laser is irradiated on the needle point of a micro-cantilever 21 arranged on a probe 20 (the probe 20 is fixed on the shell 6), and the long optical path is used for improving the amplification factor of the optical lever so as to improve the detection sensitivity. The laser detection unit includes a line focusing lens 22 and a photodetector 23 (two-quadrant photodiode), and the line focusing lens 22 may receive and focus a laser signal reflected by the micro-cantilever 21 of the probe 20. The photodetectors 23(a-cell and B-cell) can receive the focused laser signal, convert the laser signal into two paths of current signals a and B, and output the current signals. The magnitude of the current difference A, B output by the photodetector 23 is related to the position of the micro-cantilever 21 reflecting the laser to the detector, and the deflection of the micro-cantilever 21 of the probe 20 is obtained in real time by detecting the variation of the current difference. The sample 17 is mounted on a substrate 25, and the substrate 25 is fixed on the piezoelectric ceramic tube 24. Controlling the control voltage of the piezo-ceramic tube 24 adjusts the relative displacement between the tip of the probe 20 and the sample 17 in one dimension (e.g., the Z-direction) (the probe 20 is stationary). The control accuracy of the piezoelectric ceramic tube 24 was 0.01 nm.
The probe tip of the probe 20 applies a compression or tension force to the low-temperature sample, or a single sample molecule (pair) is connected between the probe tip of the probe 20 and the surface of the substrate 25, the micro-cantilever 21 of the probe 20 applies a compression or tension force to the single sample molecule (pair), the deflection amount of the micro-cantilever 21 of the probe 20 is detected through an optical lever system, the relative displacement between the sample substrate 25 and the probe 20 is obtained, and then the deformation amount of the sample molecule (pair) after the sample molecule (pair) is subjected to the external force action is obtained, so that the intramolecular or intermolecular mechanical properties and interaction of the sample molecule (pair) in the low-temperature environment are obtained.
The system has two force modes, a compression mode (as shown in fig. 3) and a tension mode (as shown in fig. 4-5).
The compression mode is that the tip of the probe 20 is used for pressing materials or single molecules in the mechanical measurement process; the stretching mode is to stretch the material or single molecule by using the micro-cantilever 21 of the probe 20 in the mechanical measurement process.
The two stretching modes are constant speed mode (as shown in fig. 4) and constant force mode (as shown in fig. 5).
The constant velocity mode is a main usage mode, in which the movement velocity of the micro-cantilever 21 is kept constant during the mechanical measurement process, in the constant velocity stretching mode, the piezoelectric ceramic tube 24 is controlled to be away from the probe 20 at a constant velocity, the force value loaded on the molecule is recorded along with the change of the stretching distance, when the distance between the probe 20 and the substrate 25 is gradually increased, the force applied on the molecule bridged between the probe 20 and the substrate is increased until the breaking (unfolding of the protein or breaking of chemical bonds) occurs, at this time, a peak value appears on the force-stretching curve, and the force value rises again rapidly each time until the next breaking occurs, so as to form a sawtooth-shaped multi-peak signal.
In the constant force mode, namely, under the condition that the stress magnitude of the probe 20 is kept unchanged, namely, the cantilever deflection amount of the probe 20 is kept unchanged, the deformation time of the sample 17 is recorded so as to research the problems of the service life of chemical bonds and intermolecular action and the like. When the unfolding or chemical bond breaking occurs, the stretching distance-time curve has a step rising characteristic to form a stair-shaped signal.
The laser light path unit 2 is a signal source of the system, controls constant power laser emitted by a laser diode through a laser driver 14 and a radio frequency modulation circuit 15, uses a collimating lens to focus the laser in position, adjusts the laser irradiation position through an adjusting mechanical knob to ensure that short-range linear laser can vertically irradiate the back of a micro-cantilever 21 of the probe 20 and reflect to form an optical lever, and the outside can properly adjust the laser power range through the laser driver 14 to meet the experimental requirements.
Fig. 6 shows an optical lever schematic diagram, in this embodiment, the optical lever magnification is 1240 times, and is derived as follows: when the micro-cantilever 21 of the probe 20 is bent, assuming that there is a θ angle shift, the length of the probe 20 is equal to 100um, the bending amount R is equal to T × θ (the bending amount of the cantilever is much smaller than the cantilever length), the direction of the laser emitted by the laser diode is fixed, and since the laser reflected by the cantilever bent cantilever is shifted from N to K at the laser detector 27, the size is S, α is equal to 2 θ (the distance M between the cantilever reflection position and the laser detector 27 is much larger than the cantilever length), and S is equal to M × α. When the cantilever is bent R, the laser position detected by the laser detector 27 changes to S, the micro-length magnification of the optical lever
Figure BDA0002595331080000161
Figure BDA0002595331080000162
In this embodiment, the optical lever M is 62mm, and the optical lever pseudo-magnification Q is 1240.
The larger housing 6 ensures that the optical lever arm is long enough to improve the sensitivity of the system.
Two parameters are needed in the mechanical measurement process: the instrument sensitivity S (nm/V) is the ratio of the bending deformation distance D (nm) of the micro-cantilever to the voltage value U (V) corresponding to the recorded laser deflection degree, and can be obtained by measuring the slope of a blank substrate mechanical stretching curve, and the micro-cantilever elastic coefficient k (pN/nm) can be obtained by thermal disturbance energy spectrum fitting. Formula for calculating force value F: f (pN) × u (V) × S (nm/V) × k (pN/nm).
The construction is completed based on the system, and the measured value of the force value resolution of the whole system is as follows: noise root mean square measurement: u1374 μ V, system measurement sensitivity S0.000013 nm/μ V, reduced force detection sensitivity: f is 1.1pN (k is 0.06N/m), is close to the physical limit of mechanical resolution, and meets the requirements of system design and application.
In the high-precision nano mechanical detection system in the ultra-low temperature environment in the embodiment, the mechanical detection part is suspended in a closed dewar tank filled with a certain volume of low-temperature liquid (liquid nitrogen and the like), and the deformation quantity of the micro-cantilever 21 after contacting with the sample 17 is detected by an optical lever method to reflect the mechanical property of the surface of the sample 17. The mechanical detection part runs in low-temperature gas, controls the temperature of the sample 17 during mechanical detection (77-100K when the low-temperature liquid is liquid nitrogen) by adjusting the distance between the mechanical detection part and the liquid level of the low-temperature liquid, and realizes passive temperature stabilization of the detection system by sealing a large amount of low-temperature liquid in the Dewar tank; the dewar tank restrains the boiling of the low-temperature liquid and the vibration interference caused by the boiling by properly and actively pressurizing (0.01-0.03 MPa); through the cold trap effect (substance particles are easier to agglomerate on the surface with lower temperature), pollutants in the environment are adsorbed on the surface of the low-temperature liquid with the lowest temperature in the system, so that the pollution of a detection space is effectively reduced. The detection system reduces the thermal noise of the micro-cantilever 21 and the electronic noise of a pre-amplification circuit through a low-temperature working environment, improves the detection sensitivity by lengthening the optical lever, improves the mechanical measurement precision of the system through the measures of magnetic damping suspension vibration isolation design, eliminating laser mode hopping noise by superposing a high-frequency (300MHz) radio frequency signal on a laser signal, suppressing low-temperature liquid boiling by pressurization and the like, and enables the mechanical measurement precision of the whole system to reach 1.1 pN.
The application of the high-precision nanomechanical detection system in the ultra-low temperature environment in the present embodiment to single-molecule mechanical analysis should include the following steps, as shown in fig. 8.
8-1: the outer vacuum layer of the low-temperature dewar system is vacuumized by using a vacuum machine with a molecular pump, the vacuum layer of the inner container of the dewar and the external environment is constructed, the heat transfer process is isolated, the heat dissipation of the system is reduced as much as possible, and the stability of the temperature of the system is maintained. The vacuum pumping is more difficult to perform as the vacuum degree is increased, so that the time is needed to performSlowly extracting gas absorbed by the activated carbon inside the vacuum chamber for a long time to gradually reach the rated vacuum degree of 5 multiplied by 10-6torr。
8-2: low-temperature liquid (liquid nitrogen is taken as an example in the embodiment) is filled into the Dewar tank through a specific pipeline, the nitrogen is required to be heated when the liquid nitrogen is filled in the Dewar tank in the early stage, a heating belt is used for heating the filling pipe, the gas entering the Dewar tank is ensured to be above 0 ℃, the purpose is to discharge the gas such as water vapor and the like in the Dewar tank and simultaneously prevent the water vapor from being desublimated, and the freezing and the blocking of a system gear box, a knob screw and a stepping motor are avoided. After nitrogen is slowly filled and heated for a period of time, the heating belt is removed, and conventional filling of liquid nitrogen is carried out, wherein the speed is slow in the filling process, so that on one hand, the window glass is prevented from being cracked in the process of too fast cooling due to the fact that the thermal expansion coefficient of the window glass is different from that of peripheral alloy; and on the other hand, the system gear box and the knob are prevented from being blocked due to shrinkage in the cooling process. The filling period of the liquid nitrogen is longer, the temperature is reduced by about 40 ℃ every day, the liquid nitrogen is liquefied in a Dewar flask after the temperature is reduced to-196 ℃, the height of a filling layer is controlled, the liquid nitrogen is prevented from being boiled and splashed onto a window and a detection system to cause damage, and the temperature stability is ensured.
8-3: preparing a sample, selecting a mica sheet with a flat surface as a substrate 25, controlling the concentration of the sample (if the sample is a molecule, most molecules are dispersed in a solution in the form of single molecules, most signals are single-molecule signals, and the efficiency of capturing the single molecules by the probe 20 is influenced by too low concentration.) fixing the sample on the substrate 25 by using a physical adsorption method and the like, and preserving the sample before experiment (the preservation condition depends on the property of the sample per se.
8-4: the prepared sample is transferred to a sealed, clean nitrogen filled process chamber for further preparation and the functionalized probe 20 (specially modified or otherwise treated) is mounted on the probe holder.
8-5: the prepared sample and probe holder are transferred from the handling box to the inside of the dewar via a chain transfer system, and are fixed to the piezoelectric ceramic tube 24 and the housing 6, respectively, by a robot.
8-6: the power is supplied to a pre-amplification circuit, a post-processing operation circuit, a computer and a control box system, an external laser driver 14 is turned on, the laser intensity is adjusted under a constant power mode, the laser is subjected to optical noise reduction processing by matching with a radio frequency interference circuit, the horizontal position of the laser is adjusted by using a separated operating lever on a detection system hanger, the voltage indication displayed by the post-processing operation circuit is matched, the laser irradiates on the needle point part of the probe 20, and the position of a laser detector 27 is adjusted by using the separated operating lever, so that the two paths of signals of the laser detector 27 have the same size.
8-7: and (3) outputting a control signal by using a computer to drive the low-temperature stepping motor to move, matching with the piezoelectric ceramic tube 24 to enable the sample to slowly approach the probe 20, and determining whether the sample approaches the distance required by the design by judging the signal reflected by the probe 20 by using a computer feedback control system until the preset parameter is met.
8-8: mechanical measurement operation is carried out by utilizing computer software, the voltage in the Z direction of the piezoelectric ceramic tube 24 is controlled to carry out repeated pulling action in the Z direction (based on the physical adsorption effect between a needle point and a sample) by adjusting the parameters of a feedback system, a large number of stretching curves (force curves) with specificity (characteristics such as a sudden change peak, a sawtooth peak or a platform) are randomly obtained, the force curves are subjected to work such as model simulation (FJC, WLC and other models) and comparison, and then force spectrum analysis (physical quantities such as molecular chain elasticity, intermolecular interaction strength and the like) is carried out by utilizing software.
The embodiment provides a high accuracy nanometer mechanics detecting system under ultra-low temperature environment, through setting up ultra-low temperature mechanics detecting system and carrying out the power spectrum to material or unimolecule under the low temperature and obtaining and the analysis, come stable control system temperature through the low temperature system, utilize the cold trap effect, reduce and measure the space pollutant, and then carry out stable ultra-low temperature high accuracy mechanics measurement to material or unimolecule, the temperature range of application of nanometer mechanics measurement has been expanded, provide the measuring means for the research of low temperature material mechanical properties and unimolecule mechanics effect.
All documents referred to herein are incorporated by reference into this application as if each were individually incorporated by reference. Furthermore, it should be understood that various changes and modifications of the present invention can be made by those skilled in the art after reading the above teachings of the present invention, and these equivalents also fall within the scope of the present invention as defined by the appended claims.

Claims (10)

1. A high-precision nano-mechanics detection system in an ultralow temperature environment is characterized by comprising a low-temperature system unit, a probe, an optical detection unit, a processing unit, a feedback and execution unit and a shell;
the low-temperature system unit is used for providing a stable normal-pressure non-vacuum low-temperature clean environment and comprises a tank body, and low-temperature liquid is contained in the tank body;
the shell is arranged in an upper space enclosed by the tank body and the liquid level of the low-temperature liquid;
the probe is fixed in the shell and is provided with a micro-cantilever;
the optical detection unit comprises a laser light path unit and a laser detection unit, and is also fixed in the shell;
the laser light path unit includes:
a laser for emitting laser light; and
the laser collimator is used for fixing the laser, carrying out position focusing on the laser emitted by the laser, and irradiating the laser to the needle point of the micro-cantilever by adjusting the laser collimator in a use state;
the laser detection unit comprises a photoelectric detector, and the photoelectric detector is used for receiving the laser signal reflected by the micro-cantilever and converting the laser signal into an electric signal;
the processing unit is used for converting the electric signal into the deflection quantity of the micro-cantilever;
the feedback and execution unit comprises a piezoelectric ceramic tube, and the piezoelectric ceramic tube is used for adjusting the relative displacement between the sample and the probe.
2. The nanomechanical detection system of claim 1, wherein the cryogenic liquid is liquid nitrogen, and the temperature of the liquid nitrogen is 77-100K.
3. The nanomechanical detection system of claim 1, wherein the laser detection unit comprises a focusing lens, wherein the photodetector is disposed behind the focusing lens, and wherein the photodetector receives a laser signal reflected by the probe microcantilever after being focused by the focusing lens.
4. The nanomechanical detection system of claim 1, wherein the photodetector is a two-quadrant photodiode.
5. The nanomechanical detection system of claim 1, wherein the processing unit is a signal amplifying and processing circuit unit, the signal amplifying and processing circuit unit comprises a pre-amplifying circuit unit and a signal post-processing unit, and the pre-amplifying circuit unit 4 converts a current signal into a voltage signal and outputs the voltage signal to a post-stage circuit; and the signal post-processing unit is used for reprocessing the voltage signal.
6. The nanomechanical detection system of claim 1, wherein the system includes a hanger unit, an upper end of the hanger unit is fixedly connected to a top of the tank, and a lower end of the hanger unit is fixedly connected to the housing for suspending the housing.
7. The nanomechanical detection system of claim 6, wherein the system includes a magnetic damped suspension unit connected between the hanger unit and the housing for suspending the housing and damping vibrations through permanent magnet damping.
8. The nanomechanical detection system of claim 1, wherein a sample and probe transfer unit is used to transport a sample and a probe into the housing.
9. The nanomechanical detection system of claim 1, wherein the system comprises a probe proximity system configured to control the approach/approach of the probe microcantilever to/from a sample surface.
10. The nanomechanical detection system of claim 1, further comprising a control unit configured to control mechanical operation and mechanical probing of the system.
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