Low-vibration near-field imaging system

Abstract

The invention discloses a low-vibration near-field imaging system, and belongs to the technical field of near-field imaging, the system comprises a first support frame, a working spring, a second support frame and a shifter, the upper end of the second support frame is hung on the first support frame through the working spring, the second support frame is provided with a tray, and the tray is connected with a probe module for detecting a sample. The staggered design of the natural vibration frequency of the working spring and the vibration frequency of the cold table is combined with the composite vibration reduction structure of the double supporting frames, an efficient heat conduction path is constructed in cooperation with the heat conduction copper strip, and the vibration amplitude is reduced from the hundred nanometers to the micron level to the nanometer level; according to the imaging system, the reliability of the superconductive Josephson probe microscope during detection of a nano structure and surface waves is improved, the nano-scale high resolution of the superconductive Josephson probe is fully exerted, and the problem of vibration interference of a refrigerator in low-temperature microscopic imaging is successfully solved.

Description

Technical Field

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

[0002] In recent years, with the rapid development of the electronics field in information science, electronic devices have achieved a high degree of integration. Among them, the development of near-field detection is particularly important.

[0003] Near-field imaging refers to imaging in a region where the distance is within the wavelength or sub-wavelength range. The superconducting Josephson probe in the superconducting Josephson probe microscope system has an intrinsic frequency in the microwave band. At present, microwave-band detection imaging of the superconducting Josephson probe has been carried out and good results have been obtained. Moreover, it has high sensitivity in the terahertz band, indicating its application potential in the microwave and terahertz bands. At the same time, it is also hoped that it can be applied in visible light, infrared and other bands.

[0004] However, the samples in the visible light band are relatively small both in terms of their own structural dimensions and the electromagnetic field waveforms they generate. Therefore, although samples with relatively large sizes for detection can be prepared and imaged to verify the response and application potential of the superconducting Josephson probe for the visible light band, since the cold stage is directly connected to the superconducting Josephson probe microscope system by bolts, the superconducting Josephson probe microscope system has relatively large vibrations (in the range of hundreds of nanometers to micrometers), making it impossible to obtain the desired results when detecting the waveforms (nanometer level) generated by small-sized visible light samples, thus limiting its spatial resolution. Summary of the Invention

[0005] Aiming at 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 damping of the probe and the sample platform.

[0006] Technical Solution: 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 the sample to be detected. The upper end of the second support frame is suspended on the first support frame through the working spring. A tray is provided on the second support frame, and a probe module for detecting the sample is connected to the tray.

[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. The second support frame further 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 chassis through a plurality of first heat conduction belts, and the first top plate is connected to the second top plate through a plurality of second heat conduction 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. 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, both the first heat conduction belt and the second heat conduction belt are made of heat-conducting copper belts.

[0013] Preferably, the vibration frequency of the cold stage is f 0 , and the natural vibration frequency of the working spring during hanging is f, and the f is greater than or less than f 0 .

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

[0015] 1. The system adopts a multi-stage suspension vibration damping structure, including a first support frame rigidly connected to the cold stage, a second support frame suspended by a working spring, a nano-displacer, and a probe module. Through the misalignment design of the natural vibration frequency of the working spring and the vibration frequency of the cold stage (the natural vibration frequency of the working spring and the vibration frequency of the refrigerator are not allowed to be equal), combined with the composite vibration damping structure of the double support frames, and cooperating with the heat-conducting copper belt to construct an efficient heat conduction path, the vibration amplitude is reduced from hundreds of nanometers to micrometers to the unit nanometer level;

[0016] 2. The system includes: 1) A four-spring suspension system is constructed using 304 stainless steel tension springs to achieve three-dimensional vibration isolation; 2) Gradient heat conduction from the cold stage to the probe is realized through the heat-conducting copper belt, taking into account both thermal stability and mechanical decoupling; Through experiments, it is verified that the system improves the reliability of the superconducting Josephson probe microscope when detecting nanostructures and surface waves, fully exerts the high resolution at the nanometer level of the superconducting Josephson probe, and successfully solves the problem of vibration interference of the refrigerator in cryogenic microscopy imaging. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0018] Figure 2 It is a schematic structural diagram of the second support frame, working spring and displacer in the embodiment;

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

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

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

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

[0023] Figure 7 It is a physical rendering of the imaging system in the embodiment. Specific embodiments

[0024] The present invention will be further clarified below in conjunction with specific embodiments. The embodiments are implemented on the premise of the technical solution of the present invention. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention.

[0025] As Figure 1 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 an overall rectangular frame. 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 with corresponding sizes. The side length of the first chassis 11 is 55 mm and the thickness is 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 bolted to both the first chassis 11 and the first top plate 13. The first chassis 11 is bolted to the cold stage 9. The cold stage 9 uses a cylindrical cold stage of an 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 during use. Heat is transferred between the cold stage 9 and the entire imaging system to reduce the temperature of the entire imaging system.

[0026] As Figure 1 and Figure 2As shown, the second support frame 2 is also a rectangular frame as a whole. 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 corresponding in size. 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 bolted to both the tray 21 and the second top plate 23. In this embodiment, the overall materials of the first support frame 1 and the second support frame 2 are oxygen-free copper, or can also be materials such as brass and beryllium copper, which play a good role in support and heat conduction.

[0027] As Figure 1 and Figure 5 shown, four working springs 3 are provided. 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 both ends of the spring middle section 33. When pulled by the first hook 31 or the second hook 32, 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. Thus, the upper end of the second support frame 2 is suspended on the first support frame 1 through the working springs 3, and the second support frame 2 as a whole is located inside the first support frame 1. In this embodiment, the material of the working springs 3 is selected as 304 stainless steel (phosphor bronze can also be selected. The phosphor bronze spring has no magnetism and will not affect the subsequent detection of magnetic samples, improving the accuracy of experimental results). The working springs 3 are bolted to the first top plate 13 and the second top plate 23. Grooves corresponding to the hooks at both ends are provided at the positions of the first top plate 13 and the second top plate 23 corresponding to the working springs 3. A threaded hole is opened at the center of one side of the groove. First through holes 231 are provided at the positions corresponding to the threaded holes on the sides of the first top plate 13 and the second top plate 23. The first through holes 231 on the side and the threaded hole on the other side of the groove are concentric. When fixing the working springs 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 bring the screw into the groove through the first through hole 231. After the screw passes through the first through hole 231, it passes through the first hook 31 or the second hook 32 of the working spring 3, and then the screw is connected to the threaded hole on the side of the groove to complete the connection of the working spring 3 to the first top plate 13 or the second top plate 23.

[0028] As Figure 1As shown, the displacer 4 is connected to the lower end face of the second top plate 23 of the second support frame 2. 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 back and forth. The displacer is controlled by a program and achieves minute movement through friction, enabling the probe to scan and image the entire sample fixed on the displacer. The displacer 4 adopts an existing nanoscale displacer, such as an attocube displacer or a multi-field technology displacer. In this embodiment, the displacer 4 selected is a displacer of attocube company, including a coarse adjustment displacer (positioner) and a fine adjustment displacer (scanner). The coarse adjustment displacer (positioner) has three displacement stages, with models ANPz51, ANPx51, and ANPy51, to achieve coarse adjustment displacement in the Z-axis (up and down), X-axis (left and right), and Y-axis (back and forth). The typical single-step displacement step size is: at room temperature of 300K, 50nm; at low temperature of 4K, 10nm. The fine adjustment displacer (scanner) selects a scanning stage, with models ANSz50 and ANSxy50. ANSz50 achieves fine adjustment displacement in the Z-axis (up and down), and ANSxy50 achieves fine adjustment displacement in the XY-axis (left and right and back and forth). The scanning accuracy of the fine adjustment displacer is better than 1nm.

[0029] As Figure 1 , Figure 3 and Figure 4As shown, the probe module 5 is connected to the middle position of the upper end face of the tray 21. 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 component 53. The support block 51 has two support surfaces, namely a first support surface and a second support surface. The first support surface is inclined, and the angle between the first support surface and the horizontal plane is α, where 30° ≤ α ≤ 90°. The probe cartridge 521 equipped with the probe 52 is connected to the first support surface of the support block 51. The probe cartridge 521 is a metal structure for isolating external electromagnetic interference and is adhered to the first support surface using GE vanish cryogenic glue. The second support surface intersects with the first support surface, and the detection component 53 is arranged on the second support 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 support surface of the support block 51. The tuning fork 531 is located below the probe 52 and contacts the tip of the probe 52. The tuning fork 531 has two fork arms, and one side of the probe 52 near the tip contacts the top of one fork arm. The tuning fork 531 of the detection component 53 can sense the interaction force between the tip of the probe 52 and the sample surface in real time through the change of its own vibration frequency or amplitude, so as to convert the mechanical signal into a measurable electrical signal through the piezoelectric ceramic plate 532. The probe 52 is a superconducting Josephson probe with nanoscale resolution. The tip part has a 50-nm superconducting Josephson microbridge structure, which can realize high-resolution near-field imaging. The probe cartridge 521 can adjust the position where it is fixed with GE vanish cryogenic glue according to the needs of the sample 8 to be detected. Using the existing probe module includes a tuning fork-piezoelectric ceramic sensing system to achieve real-time monitoring of nanoscale vibration.

[0030] As Figure 1 , Figure 2 and Figure 5As shown in the figure, the tray 21 is connected to the first chassis 11 through four first heat conduction belts 61. The four first heat conduction belts 61 are respectively connected to the four side edges of the tray 21. Pressing belts are respectively connected to the corresponding positions of the tray 21 and the first chassis 11 through bolts. Both ends of the pressing belt are connected to the tray 21 or the first chassis 11 through bolts. The middle section of the pressing belt presses on the first heat conduction belt 61. The two ends of the first heat conduction belt 61 are respectively pressed on the tray 21 and the first chassis 11 through the pressing belt. The first top plate 13 is connected to the second top plate 23 through four second heat conduction belts 62. One end of the second heat conduction belt 62 is pressed on the lower surface of the first top plate 13 through a pressing belt, and the other end is pressed on the lower surface of the second top plate 23 through a pressing belt (the second heat conduction belt 62 conducts heat through another path, through the cold table 9 - the first chassis 11 - the first support rod 12 - the first top plate 13 - the second heat conduction belt 62 - the second top plate 23 - the second support rod 22 - the tray 21 - the probe module 5, heat transfer, increasing a certain heat conduction effect). Both the first heat conduction belt 61 and the second heat conduction belt 62 are made of heat-conducting copper strips, in the shape of rectangular strips, and the thickness of the heat-conducting copper strip is 0.2 mm. The first chassis 11 is in direct contact with the cold table 9. The cold table 9 is a part of the refrigerator, and its temperature is the lowest. The temperature is directly conducted to the first chassis 11 through the cold table 9. The temperature of the first chassis 11 is the lowest in the imaging system. The core module for detection is the probe module 5. The temperature of the probe 52 needs to reach a certain low temperature to work. Therefore, connecting the tray 21 and the first chassis 11 through the first heat conduction belt 61 shortens the heat conduction path, and better enables the temperature of the probe 52 to be reduced to the lowest.

[0031] In this embodiment, the vibration frequency f of the refrigerator 0 is about 2 Hz (the vibration frequency of the cold table 9). In this embodiment, when the imaging system is in use, it is installed in an existing refrigerator, and a thermal shielding cover is put on the outside. The imaging system and the thermal shielding cover are integrally located in the refrigerator. The maximum elongation of the spring is preset according to the size of the internal space of the refrigerator (try to reserve the maximum without changing the external thermal shielding cover to ensure that the imaging system can be installed in the current refrigerator). Research professional literature to query the shear modulus G of 304 stainless steel (query phosphor bronze if phosphor bronze is selected) at normal temperature and low temperature. The number of turns of the working spring 3 is n, the wire diameter is d, and the diameter is D;

[0032] Then, through calculation (calculated by matlab programming), the coefficient formula:

[0033]

[0034] In the formula, n is the number of turns 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 spring constant of the working spring 3;

[0035] Obtain the spring constant of the working spring 3, and then through the formula:

[0036]

[0037] In the formula, 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 are as Figure 4 shown. Then calculate the mass of the load (this load includes the weights of the second support frame 2, the displacer 4, the sample 8 and the probe module 5) connected by the working spring 3 , calculate the gravity it receives, and then divide it equally to obtain the load that each working spring 3 needs to carry , and finally through the helical spring - mass system formula:

[0039]

[0040] In the formula, k is the stiffness coefficient 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 vibration frequency of the working spring 3.

[0041] Calculate the natural vibration frequency f of the working spring 3 when it is mounted to avoid resonance with the refrigerator. In this embodiment, through calculation, the natural vibration frequency of the working spring 3 when it is mounted can be obtained as 14.792 Hz, which is much greater than the vibration frequency of the refrigerator 2 Hz. Therefore, resonance with the refrigerator can be avoided, and it can play a role in reducing vibration during the superconducting Josephson probe imaging process, improving its spatial resolution in a larger range, so as to achieve higher-precision atomic force, electromagnetic field, and thermal imaging, and better expand its application in cryogenic detection.

[0042] The vibration damping effect of the imaging system is proved as follows. By means of an atomic force microscope, the vibration of the probe module 5 is measured atomically at low temperature. After the cold stage 9 works to reduce the temperature by turning on the refrigerator at low temperature, the probe 52 contacts the tuning fork 531. By moving the displacer 4, the sample and the probe 52 are brought as close as possible until the vibration brought by the refrigerator is atomically force-feedbacked, and then the vibration spectrum of the probe module 5 at low temperature can be obtained through spectrum analysis. The calibration signal is given by the displacer, and the displacer vibrates 5 nm at 27 Hz to infer the vibration in other places, such as Figure 5 shown, and through data processing by matlab, the average vibration can be obtained as 3.35 nm, and the imaging system reduces the vibration brought by the cold stage 9 to the unit nanometer level (in the case of no damping system, when the refrigerator is turned on, the vibration amplitude of the refrigerator is large at low temperature, exceeding the atomic force range).

[0043] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope 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) via the working spring (3), the second support frame (2) is provided with a tray (21), and the tray (21) is connected to a probe module (5) for detecting the sample.

2. The low-vibration near-field imaging system according to claim 1, characterized in that: 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, characterized in that: 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 2, characterized in that: The probe module (5) comprises a support block (51), a probe (52) connected to the support block (51), and a detection component (53) connected to the support block (51); the detection component (53) comprises 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).

5. The low-vibration near-field imaging system according to claim 4, characterized in that: The probe (52) is a superconducting Josephson probe, and the tuning fork (531) is in contact with the probe (52).

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

7. The low-vibration near-field imaging system according to claim 1, characterized in that: The vibration frequency of the cold stage (9) is f0, and the natural vibration frequency of the working spring (3) when mounted is f, and f is greater than or less than f0.

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