A low-vibration near-field imaging system

Abstract

The present invention discloses a low-vibration near-field imaging system, belonging to the field of near-field imaging technology. The system includes a first support frame, a working spring, a second support frame, and a displacer. The upper end of the second support frame is suspended from the first support frame by the working spring. The second support frame is provided with a tray, and the tray is connected to a probe module for detecting samples. The present invention combines a composite vibration reduction structure of two support frames with a design that staggers the natural frequency of the working spring and the vibration frequency of the cold stage, and uses a thermally conductive copper strip to construct an efficient heat conduction path, thereby reducing the vibration amplitude from hundreds of nanometers to micrometers to nanometers. The imaging system improves the reliability of superconducting Josephson probe microscopes in detecting nanostructures and surface waves, fully utilizing the nanometer-level high resolution of superconducting Josephson probes, and successfully solves the problem of refrigerator vibration interference in low-temperature microscopic imaging.

Description

Technical Field

[0001] The present invention belongs to the technical field of near-field imaging, and in particular relates to a low-vibration near-field imaging system. Background Art

[0002] In recent years, with the rapid development of electronics in information science, electronic devices have achieved high integration, among which the development of near-field detection is quite important.

[0003] Near-field imaging refers to imaging at wavelength or subwavelength distances. The superconducting Josephson probes in superconducting Josephson probe microscope systems have an eigenfrequency in the microwave band. Microwave imaging with superconducting Josephson probes has been successfully performed, with excellent results. Furthermore, they exhibit high sensitivity in the terahertz band, demonstrating their potential for application in both microwave and terahertz bands. Applications in the visible and infrared bands are also anticipated.

[0004] However, samples in the visible light band are relatively small, both in terms of their inherent structural dimensions and the electromagnetic field waveforms they generate. Therefore, while relatively large samples can be prepared for detection, and imaging of these samples has verified the responsiveness and potential of superconducting Josephson probes in the visible light band, the direct bolted connection between the cold stage and the superconducting Josephson probe microscope system results in significant vibrations (hundreds of nanometers to micrometers). This prevents the microscope from achieving the desired results when detecting the waveforms (nanometer level) generated by tiny visible light samples, limiting its spatial resolution. Summary of the Invention

[0005] In view of the above problems existing in the prior art, the technical problem to be solved by the present invention is to provide a low-vibration near-field imaging system to achieve vibration reduction of the probe and the sample platform.

[0006] Technical solution: In order to solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0007] A low-vibration near-field imaging system includes a first support frame connected to a cold stage, a working spring connected to the first support frame, a second support frame connected to the working spring, and a displacer connected to the second support frame and used to connect to a sample to be detected. The upper end of the second support frame is suspended on the first support frame by the working spring. The second support frame is provided with a tray, and the tray is connected to a probe module for detecting the sample.

[0008] Preferably, the first support frame includes a first chassis, a first support rod connected to the first chassis, and a first top plate connected to the first support rod, and the second support frame also includes a second support rod connected to the tray and a second top plate connected to the second support rod.

[0009] Preferably, the tray is connected to the first bottom plate via a plurality of first thermal conductive belts, and the first top plate is connected to the second top plate via a plurality of second thermal conductive belts.

[0010] Preferably, the probe module includes a support block, a probe connected to the support block, and a detection component connected to the support block, and the detection component includes a tuning fork, a piezoelectric ceramic plate connected to the tuning fork, and a sapphire substrate connected to the piezoelectric ceramic plate.

[0011] Preferably, the probe is a superconducting Josephson probe, and the tuning fork is in contact with the probe.

[0012] Preferably, the first thermal conductive belt and the second thermal conductive belt are both made of thermal conductive copper belt.

[0013] Preferably, the vibration frequency of the cold stage is f0, the natural frequency of the working spring when mounted is f, and f is greater than or less than f0.

[0014] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0015] 1. The system uses a multi-stage suspension vibration reduction structure, consisting of a first support frame rigidly connected to the cold table, a second support frame suspended by a working spring, a nanometer displacer, and a probe module. By staggering the natural frequency of the working spring and the vibration frequency of the cold table (the natural frequency of the working spring and the vibration frequency of the refrigerator are not allowed to be equal), combined with a composite vibration reduction architecture of the double support frames, and using thermal conductive copper tape to create an efficient heat conduction path, the vibration amplitude can be reduced from hundreds of nanometers to micrometers to single nanometers.

[0016] 2. The system includes: 1) a four-spring suspension system constructed using 304 stainless steel tension springs to achieve three-dimensional vibration isolation; 2) thermal conductivity from the cold plate to the probe is achieved through thermally conductive copper tape, achieving both thermal stability and mechanical decoupling. Experimental verification shows that this system improves the reliability of superconducting Josephson probe microscopes in detecting nanostructures and surface waves, fully utilizing the nanometer-level high resolution of superconducting Josephson probes, and successfully solves the problem of refrigerator vibration interference in low-temperature microscopy. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 1 is a schematic structural diagram of an imaging system according to an embodiment of the present invention;

[0018] Figure 22. It is a schematic structural diagram of the second support frame, the working spring and the displacer in the embodiment;

[0019] Figure 3 is a schematic diagram of the three-dimensional structure of the imaging system in the embodiment;

[0020] Figure 4 2 is a schematic diagram of the structure of the probe module in the embodiment;

[0021] Figure 5 2. It is a schematic diagram of the working spring structure in the embodiment;

[0022] Figure 6 is the test result of the vibration spectrum in the embodiment;

[0023] Figure 7 This is a physical rendering of the imaging system in the embodiment. DETAILED DESCRIPTION

[0024] The present invention will be further illustrated below with reference to specific examples. The examples are implemented based on the technical solutions of the present invention. It should be understood that these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0025] like Figure 1 As shown, a low-vibration near-field imaging system includes a first support frame 1, a second support frame 2, a working spring 3, a displacer 4 and a probe module 5. The first support frame 1 is a rectangular frame as a whole. The first support frame 1 includes a first chassis 11, four first support rods 12 and a first top plate 13. The first chassis 11 and the first top plate 13 are rectangular plates of corresponding sizes. The first chassis 11 has a side length of 55 mm and a thickness of 4 mm. The four first support rods 12 are connected between the first chassis 11 and the first top plate 13. The four first support rods 12 are connected to the first chassis 11 and the first top plate 13 by bolts. The first chassis 11 is connected to the cold stage 9 by bolts. The cold stage 9 adopts the cylindrical cold stage of the existing Montana refrigerator with an outer radius of 15.88 mm and an inner radius of 9.27 mm. The cold stage 9 is fixed in the refrigerator by screws. The entire imaging system is also placed in the refrigerator when in use. Heat is transferred between the cold stage 9 and the entire imaging system to reduce the temperature of the entire imaging system.

[0026] like Figure 1 and Figure 2As shown, the second support frame 2 is also a rectangular frame. The overall volume of the second support frame 2 is smaller than that of the first support frame 1. The second support frame 2 includes a tray 21, four second support rods 22, and a second top plate 23. The tray 21 and the second top plate 23 are rectangular plates of corresponding sizes. The four second support rods 22 are connected between the tray 21 and the second top plate 23. The four second support rods 22 are connected to the tray 21 and the second top plate 23 by bolts. In this embodiment, the first support frame 1 and the second support frame 2 are made of oxygen-free copper, but can also be made of brass, beryllium copper, or other materials, to provide good support and thermal conductivity.

[0027] like Figure 1 and Figure 5 As shown, four working springs 3 are provided, and the four working springs 3 are symmetrically arranged vertically. The working springs 3 are tension springs, including a spring middle section 33, a first hook 31, and a second hook 32. The first hook 31 and the second hook 32 are respectively connected to the ends of the spring middle section 33. When the first hook 31 or the second hook 32 is pulled, the spring middle section 33 is stretched. The first hook 31 at the upper end of the working spring 3 is connected to the first top plate 13, and the second hook 32 at the lower end is connected to the second top plate 23. As a result, the upper end of the second support frame 2 is suspended from the first support frame 1 via the working springs 3, and the second support frame 2 is entirely located within the first support frame 1. In this embodiment, the working springs 3 are made of 304 stainless steel (phosphor bronze can also be used. Phosphor bronze springs are non-magnetic and will not affect the subsequent detection of magnetic samples, thereby improving the accuracy of experimental results). The working spring 3 is connected to the first top plate 13 and the second top plate 23 by bolts. The first top plate 13 and the second top plate 23 are provided with grooves corresponding to the hooks at both ends at the corresponding positions of the working spring 3. A threaded hole is provided in the center of one side of the groove. The first through hole 231 is provided on the side of the first top plate 13 and the second top plate 23 at the corresponding positions of the threaded hole. The first through hole 231 on the side is concentric with the threaded hole on the other side of the groove. When fixing the working spring 3, first place the first hook 31 of the spring in the groove of the first top plate 13, and the second hook 32 in the groove of the second top plate 23. Use a screwdriver to insert the screw from the first through hole 231 into the groove. The screw passes through the first through hole 231 and then through the first hook 31 or the second hook 32 of the working spring 3. Then the screw is connected to the threaded hole on the side of the groove, completing the connection between the working spring 3 and the first top plate 13 or the second top plate 23.

[0028] like Figure 1As shown, the displacer 4 is connected to the lower end surface of the second top plate 23 of the second support frame 2, and the sample 8 to be detected is connected to the lower end of the displacer 4. The displacer 4 is used to drive the sample 8 to be detected to move up and down, left and right, and forward and backward. The displacer is controlled by a program and realizes small movements through friction, so that the probe can scan and image the entire sample fixed on the displacer. The displacer 4 uses an existing nanometer-level displacer, such as an attocube displacer or a multi-field technology displacer. In this embodiment, the displacer 4 uses a displacer from attocube, including a coarse adjustment positioner and a fine adjustment scanner. The coarse adjustment positioner has three displacement stages, model ANPz51, ANPx51, and ANPy51, which achieve coarse adjustment displacement along the Z axis (up and down), X axis (left and right), and Y axis (forward and backward). The typical single-step displacement step size is: 50nm at room temperature of 300K and 10nm at low temperature of 4K. The fine adjustment displacer (scanner) uses scanning stages, model ANSz50 and ANSxy50. The ANSz50 achieves fine adjustment displacement along the Z axis (up and down), and the ANSxy50 achieves fine adjustment displacement along the XY axis (left and right and forward and backward). The scanning accuracy of the fine adjustment displacer is better than 1nm.

[0029] like Figure 1 、 Figure 3 and Figure 4As shown, the probe module 5 is connected to the middle position of the upper end surface of the tray 21, and the probe module 5 is used to detect the sample 8. The probe module 5 includes a support block 51, a probe 52 and a detection assembly 53. The support block 51 has two support surfaces, a first support surface and a second support surface. The first support surface is tilted, and the angle between the first support surface and the horizontal plane is α, 30°≤α≤90°. The probe box 521 equipped with the probe 52 is connected to the first support surface of the support block 51. The probe box 521 is a metal structure used to isolate external electromagnetic interference and uses GE Vanish low-temperature adhesive is adhered to the first supporting surface, the second supporting surface intersects with the first supporting surface, the detection component 53 is arranged on the second supporting surface, the detection component 53 includes a tuning fork 531, a piezoelectric ceramic plate 532 and a sapphire substrate 533, the tuning fork 531 is 5.5 mm long, 1.6 mm thick, and has a groove depth of 4.5 mm, the tuning fork 531 is connected to the piezoelectric ceramic plate 532, the piezoelectric ceramic plate 532 is connected to the sapphire substrate 533, and the sapphire substrate 533 is connected to the second supporting surface of the support block 51, the tuning fork 531 is located below the probe 52 and contacts the needle tip of the probe 52, 31 has two prongs. The side of the probe 52 near the needle tip contacts the top of one prong. The tuning fork 531 of the detection component 53 senses the interaction force between the tip of the probe 52 and the sample surface in real time through changes in its own vibration frequency or amplitude, thereby converting the mechanical signal into a measurable electrical signal through the piezoelectric ceramic plate 532. Probe 52 is a superconducting Josephson probe with nanometer-level resolution. The tip of the probe has a 50nm superconducting Josephson microbridge structure, which enables high-resolution near-field imaging. The probe box 521 can be adjusted according to the needs of the sample 8 to be detected. The probe box is fixed to its position with GE Vanish low-temperature glue. The existing probe module includes a tuning fork-piezoelectric ceramic sensing system to achieve real-time monitoring of nanometer-level vibration.

[0030] like Figure 1 、 Figure 2 and Figure 5As shown, the tray 21 is connected to the first chassis 11 through four first conductive belts 61, and the four first conductive belts 61 are respectively connected to the four sides of the tray 21. The positions corresponding to the first conductive belts 61 on the tray 21 and the first chassis 11 are respectively connected with pressing belts by bolts. The two ends of the pressing belts are connected to the tray 21 or the first chassis 11 by bolts. The middle section of the pressing belt is pressed on the first conductive belt 61, and the two ends of the first conductive belt 61 are respectively pressed on the tray 21 and the first chassis 11 by the pressing belt. The first top plate 13 is connected to the second top plate 23 through four second conductive belts 62, and the second One end of the heat-conducting tape 62 is pressed against the underside of the first top plate 13 by a pressure tape, and the other end is pressed against the underside of the second top plate 23 by a pressure tape. (The second heat-conducting tape 62 conducts heat through a separate path: from the cold plate 9 to the first base plate 11, the first support rod 12, the first top plate 13, the second heat-conducting tape 62, the second top plate 23, the second support rod 22, the tray 21, and finally the probe module 5, thereby enhancing thermal conductivity.) Both the first and second heat-conducting tapes 61 and 62 are made of rectangular, 0.2mm thick copper tape. The first base plate 11 directly contacts the cold plate 9, which is part of the refrigerator and has the lowest temperature. The temperature is directly transferred to the first base plate 11 through the cold plate 9. The first base plate 11 has the lowest temperature in the imaging system. The core detection module is the probe module 5, and the probe 52 must reach a certain low temperature for operation. Therefore, connecting the tray 21 and the first base plate 11 with the first heat-conducting tape 61 shortens the heat conduction path, effectively minimizing the temperature of the probe 52.

[0031] In this embodiment, the vibration frequency f0 of the refrigerator is approximately 2 Hz (the vibration frequency of the cold stage 9). The imaging system of this embodiment is installed in an existing refrigerator, with a heat shield covering the outside. The imaging system and the heat shield are located entirely within the refrigerator. The maximum elongation of the spring is preset based on the internal dimensions of the refrigerator (maximum elongation is reserved as much as possible without changing the external heat shield to ensure that the imaging system can be installed in the existing refrigerator). Professional literature is researched to determine the shear modulus G of 304 stainless steel (if phosphor copper is used, then phosphor copper should be consulted) at room and low temperatures. The number of turns of the working spring 3 is n, the wire diameter is d, and the diameter is D.

[0032] Then calculate (using Matlab programming) the coefficient formula:

[0033]

[0034] Where n is the number of coils of the working spring 3, d is the wire diameter of the working spring 3, D is the diameter of the working spring 3, G is the shear modulus of the material of the working spring 3, and k is the stiffness coefficient of the working spring 3;

[0035] Get the stiffness coefficient of the working spring 3, and then use the formula:

[0036]

[0037] Where, d is the wire diameter of the working spring 3, H is the total length of the working spring 3, is the density of the material of the working spring 3, and m is the mass of the working spring 3;

[0038] Calculate the mass of the working spring 3 and the various dimensional parameters of the working spring 3 as follows: Figure 4 Then calculate the mass of the load connected to the working spring 3 (this load includes the weight of the second support frame 2, the displacement device 4, the sample 8 and the probe module 5) , calculate the gravity it is subjected to, and then divide it equally to obtain the load that each working spring 3 needs to carry , and finally through the coil spring-mass system formula:

[0039]

[0040] Where, k is the spring constant of the working spring 3, m is the mass of the working spring 3, is the load that each working spring 3 needs to carry, β is the fundamental frequency correction coefficient, in this embodiment β=1 / 3, and f is the natural frequency of the working spring 3.

[0041] The natural frequency f of the working spring 3 when mounted is calculated to avoid resonance with the refrigerator. In this embodiment, the natural frequency f of the working spring 3 when mounted is calculated to be 14.792 Hz, which is much larger than the vibration frequency of the refrigerator of 2 Hz. Therefore, resonance with the refrigerator can be avoided, and vibration during imaging of the superconducting Josephson probe can be reduced, thereby improving its spatial resolution to a greater extent, so as to achieve higher-precision imaging of atomic forces, electromagnetic fields, and heat, and better expand its application in low-temperature detection.

[0042] The vibration reduction effect of the imaging system is proved. By using an atomic force microscope, the vibration of the probe module 5 is measured by atomic force at low temperature. By turning on the refrigerator at low temperature and working the cold stage 9 to reduce the temperature, the probe 52 is in contact with the tuning fork 531. The sample and the probe 52 are moved as close as possible by moving the displacement device 4 until the vibration caused by the refrigerator is fed back by atomic force. The vibration spectrum of the probe module 5 at low temperature can be obtained by spectrum analysis. The calibration signal is given by the displacement device. The displacement device vibrates 5nm at 27Hz and is used to infer the vibration of other places, such as Figure 5 As shown in the figure, and through data processing with Matlab, it can be obtained that the average vibration is 3.35nm. The imaging system reduces the vibration caused by the cold stage 9 to the unit nanometer level (in the absence of a shock absorption system, when the refrigerator is turned on at low temperatures, the vibration amplitude of the refrigerator is large, exceeding the range of atomic force).

[0043] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A low-vibration near-field imaging system, characterized in that: The invention comprises a first support frame (1) connected to a cold stage (9), a working spring (3) connected to the first support frame (1), a second support frame (2) connected to the working spring (3), and a displacer (4) connected to the second support frame (2) and used for connecting to a sample to be detected, wherein the upper end of the second support frame (2) is suspended on the first support frame (1) through the working spring (3), the second support frame (2) is provided with a tray (21), the tray (21) is connected to a probe module (5) for detecting a sample, and the probe module (5) comprises a support block (51), a probe connected to the support block (51), and a probe (52) and a detection component (53) connected to the support block (51), the detection component (53) comprising a tuning fork (531), a piezoelectric ceramic plate (532) connected to the tuning fork (531), and a sapphire substrate (533) connected to the piezoelectric ceramic plate (532), the probe (52) being a superconducting Josephson probe, the tuning fork (531) being in contact with the probe (52), the tuning fork (531) sensing the interaction force between the tip of the probe (52) and the sample surface in real time through changes in its own vibration frequency or amplitude, thereby converting the mechanical signal into an electrical signal through the piezoelectric ceramic plate (532); The vibration of the probe module (5) is measured by atomic force. After the cold stage (9) is in operation, the sample and the probe (52) are moved closer by the displacement device (4) until the vibration caused by the cold stage (9) is fed back by atomic force. Then, a spectrum analysis is performed to obtain the vibration spectrum of the probe module (5).

2. The low-vibration near-field imaging system according to claim 1, wherein: The first support frame (1) comprises a first bottom plate (11), a first support rod (12) connected to the first bottom plate (11), and a first top plate (13) connected to the first support rod (12); the second support frame (2) further comprises a second support rod (22) connected to the tray (21), and a second top plate (23) connected to the second support rod (22).

3. The low-vibration near-field imaging system according to claim 2, wherein: The tray (21) is connected to the first bottom plate (11) via a plurality of first heat-conducting belts (61), and the first top plate (13) is connected to the second top plate (23) via a plurality of second heat-conducting belts (62).

4. The low-vibration near-field imaging system according to claim 3, wherein: The first heat-conducting belt (61) and the second heat-conducting belt (62) are both made of heat-conducting copper belts.

5. The low-vibration near-field imaging system according to claim 1, wherein: The vibration frequency of the cold stage (9) is f 0, the natural frequency of the working spring (3) when mounted is f , f Greater than or less than f 0.

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