A method of adjusting a gap distance in a metal tunnel junction

Abstract

The application discloses a method for adjusting gap distance in a metal tunnel junction, and belongs to the field of nanometer or atomic scale devices. The method uses a laser irradiation I-V scanning method to control the gap distance in the metal tunnel junction with high precision. The application can adjust the tunnel gap distance in a relatively large range, and can effectively control the electrical performance of the tunnel junction. The laser irradiation method is mild to the tunnel junction sample, and the adjustment process is damage-free, and belongs to a nondestructive method. Through cooperation of a probe station, a support, an optical path, focusing and other peripheral support systems, the tunnel junction sample prepared on a substrate of different materials can be adjusted, and the application range is wide.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of nanometer or atomic scale devices, and is a method for controllably adjusting the gap distance in a metal tunnel junction. BACKGROUND

[0002] A tunnel junction is usually composed of a pair of tunnel electrodes, and the tunnel gap between the tunnel electrodes is usually vacuum or air, forming a tunnel barrier. When a bias voltage is applied, the energy level position of the pair of tunnel electrodes on both sides is changed, and the electrons on one side of the tunnel electrode can reach the other side via quantum tunneling effect, thereby forming a tunneling current. The tunnel junction can be used in various nanometer or atomic scale devices (such as electronic, optoelectronic, nanoelectromechanical, quantum devices, etc.).

[0003] The size of the tunneling current is extremely sensitive to the distance of the tunnel gap. Generally speaking, the tunneling current is negatively correlated with the tunnel gap distance, and the larger the tunnel gap distance, the smaller the tunneling current, and the two are exponentially related. If the tunnel gap distance changes by several nanometers or even several angstroms, the tunneling current can change by more than several orders of magnitude. The relationship between the tunneling current and the tunnel gap can be described by the Simmons formula:

[0004]

[0005] where m is the effective mass of the electron, φ is the metal work function, s is the tunnel gap distance, q is the electron charge, h is the Planck constant, and V is the voltage.

[0006] Due to the extremely sensitive effect of the tunnel gap on the tunneling current, the tunneling current in the tunnel junction structure is concentrated in the lateral dimension of one or a few atoms near the tip of the tunnel electrode. Changing the position of one or a few key atoms near the tip of the tunnel electrode will change the tunnel gap distance, thereby greatly affecting the current size of the tunnel junction. By controlling the gap distance between the electrode pair in the metal tunnel junction, the electrical and other properties of the tunnel junction can be effectively regulated, and new nanometer or atomic scale devices with physical size much smaller than traditional microelectronic devices can be prepared, and further, new integrated circuit chips with ultra-high integration density can be realized. The most critical issue is how to control the gap distance in the metal tunnel junction. Finding means and methods to regulate the atomic gap distance in the tunnel junction has very important value.

[0007] At present, the commonly used method for controlling the gap distance in the metal tunnel junction is an electrical method, mainly through current-voltage scanning (I-V scanning) method, voltage pulse method, etc. Although these methods can change the distance of the tunnel gap, it is difficult to accurately control the distance of the tunnel gap in a larger distance range, especially when the distance of the tunnel gap is very small, the current on the tunnel junction can rise to tens of microamperes, the joule heat power density is greatly increased, and it is difficult to regulate and control the atomic position in the tunnel junction by using the existing electrical method, and even the tunnel junction may be damaged, so that the gap distance cannot be accurately controlled. SUMMARY

[0008] The purpose of the present application is to provide a method for adjusting the gap distance between the electrode pairs in the metal tunnel junction.

[0009] The technical scheme provided by the present application is as follows:

[0010] A method for adjusting the gap distance in the metal tunnel junction, characterized by comprising a semiconductor parameter analyzer and a matching probe station for I-V scanning of the tunnel junction; a laser and a matching support, optical system and zoom device for laser irradiation of the tunnel junction; and a light power meter for measuring the power density of the laser spot, the adjusting method comprising:

[0011] (1) preparing a metal nanobelt or nanowire: through photolithography-stripping technology or focused ion beam (FIB) deposition method, etc.

[0012] (2) further processing the metal nanobelt or nanowire into a metal tunnel junction through electromigration, extension under strong electric field, controllable mechanical cleavage method, direct etching method, etc., the tunnel gap distance of which is in nanometer or atomic scale, the scale range being 50nm-0.1nm; placing the tunnel junction sample to be adjusted on the surface of the probe station;

[0013] (3) performing a preliminary I-V scanning on the original tunnel junction to determine the initial distance of the tunnel junction;

[0014] (4) focusing the laser beam spot to the surface of the tunnel junction by using the laser optical system and focusing system: selecting a laser beam spot of appropriate size, so that the beam spot irradiated to the surface of the tunnel junction has a certain power density, the power density range being 1mW / mm 2 ~200mW / mm 2 .

[0015] (5) under the condition of laser irradiation, the laser wavelength being 800nm to 400nm, simultaneously performing I-V scanning on the tunnel junction, fitting the distance change of the tunnel gap through the I-V curve and Simmons formula; controlling the gap distance in the tunnel junction with the precision of a single atom under continuous laser irradiation.

[0016] The material of the tunneling junction is metal, including but not limited to gold, silver, palladium, platinum, aluminum, tantalum, indium, etc. The laser wavelength used ranges from 800 nm to 400 nm, i.e. including the near-infrared band, the entire visible light band, and the near-ultraviolet band. The laser power density ranges from 1 mW / mm 2 to 200 mW / mm 2 . The regulation range of atoms in the tunneling junction can make the tunneling gap distance almost continuously adjustable between 30 nm and 0.1 nm, and can also realize the connection of a single-atom bridge between the electrodes of the tunneling junction. The maximum voltage of the I-V scan ranges from 10 mV to 100 mV.

[0017] Principles of the present application:

[0018] Through photolithography-stripping process or FIB deposition, etc., metal nanobands can be prepared on a substrate. Through electromigration, extension under a strong electric field, controllable mechanical cleavage, direct etching, etc., the metal nanobands can be further processed into metal tunneling junctions with nanometer / atomic scale tunneling gaps. Then, by using specific wavelength and power laser irradiation combined with specific current-voltage scanning, the atomic migration process on the surface of the tunneling junction can be accurately controlled, so that the atoms gradually move towards the tip of the tunneling junction. By selecting appropriate parameters, the electrodes can be gradually elongated with nanometer or even sub-nanometer precision, so as to more accurately control the gap distance in the metal tunneling junction.

[0019] The laser can affect the atomic migration process on the surface of the tunneling junction. At least the following three possibilities exist from the physical level: one is that the laser can heat the atoms on the surface of the tunneling junction, so that they obtain higher kinetic energy and are more likely to overcome the migration barrier; two is that the laser of a specific wavelength can excite surface plasmons on the surface of the tunneling junction, and the plasmons can further increase the energy of the metal atoms; three is that the electric field component of the light field actually has a Coulomb force effect on the atoms. For specific metals, the effect of the laser on the atomic migration on the surface of the tunneling junction can include one or several of them.

[0020] By selecting the wavelength of the laser and controlling the power density of the laser, the following two effects can be achieved at the same time:

[0021] (1) A part of atoms that are not easy to migrate can be excited by the laser and can migrate under the action of a certain current and electric field;

[0022] (2) The number of excited atoms is controlled so that only one atom can migrate on average within the time of one I-V scan.

[0023] When the single laser irradiation stops, at very low voltage, if only the current-voltage scanning (but no laser irradiation) is used, the atomic migration cannot continue, and the atoms stay at the position after the previous migration. If the laser irradiation and the current-voltage scanning are simultaneously used, the atoms can continue to migrate. By selecting the number of times of the I-V scanning under the laser irradiation, the gap distance in the metal tunneling junction is controlled. The current in the tunneling junction read during the I-V scanning can be used to determine the distance of the tunneling gap; further, by calculation, the process of the gradual change of the gap distance in the metal tunneling junction can be observed. In this way, the process can be stopped when the tunneling gap distance reaches the required value. It is emphasized that the metal atoms can also migrate without the laser irradiation if the voltage is increased to 1V-10V. However, at this time, the current of the tunneling junction can reach 1μA or more, and a very high Joule heat power is generated. This makes it difficult to control the method of using high voltage but no laser irradiation to control the tunneling gap distance, and even the tunneling junction can be damaged. In the present method, the voltage used is typically only 25mV, and the highest is not more than 100mV, which is 1 / 40-1 / 10 of the voltage without laser irradiation, so the change of the tunneling gap distance can be stably controlled.

[0024] The advantages of the present application are as follows:

[0025] The I-V scanning method of the laser irradiation can control the gap distance in the metal tunneling junction with high precision. The present method can adjust the tunneling gap distance in a relatively large range, and can effectively control the electrical properties of the tunneling junction. The laser irradiation method is mild to the tunneling junction sample, and the adjustment process is not damaged, which is a non-destructive method. Through the cooperation of the probe table, the support, the light path, and the focusing peripheral support system, the tunneling junction sample prepared on different material substrates can be adjusted, and the application range is wide. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 . Schematic diagram of the metal tunneling junction;

[0027] Figure 2 . Schematic diagram of the device for precisely controlling the atomic position in the tunneling junction;

[0028] Figure 3 . Scanning electron microscope photograph of the metal nanobelt in Example 1;

[0029] Figure 4 . Electron microscope photograph of the tunneling junction in Example 1;

[0030] Figure 5 . Result graph of the I-V scanning of Example 1; wherein: line 1 is the tunneling junction current of the I-V scanning without laser irradiation; lines 2-5 are the tunneling junction currents obtained by the I-V scanning under the laser irradiation, which gradually increases with the increase of the scanning times;

[0031] Figure 6 In Example 1, the conductance and the tunneling gap distance of the tunneling junction vary with the scan. The hollow circle point is the change of the conductance; the hollow square is the change of the distance;

[0032] Figure 7 The effect diagram of Example 2; wherein: the hollow triangle point line is the tunneling junction current of the initial I-V scan without laser irradiation; the hollow circle point line is the tunneling junction current obtained by the I-V scan with laser irradiation, which gradually increases with the increase of the scan number;

[0033] Figure 8 In Example 2, the conductance and the tunneling gap distance of the tunneling junction vary with the scan. The hollow circle point is the change of the conductance; the hollow square is the change of the distance;

[0034] Wherein: 1—semiconductor analyzer; 2—substrate; 3—tunneling junction; 4—electrode plate; 5—probe station system; 6—support and focusing system; 7—laser. DETAILED DESCRIPTION

[0035] The implementation process of the present application is described in detail below with reference to the accompanying drawings of the present application.

[0036] Preparation of metal nanobelt

[0037] A tunneling junction device is prepared on a substrate. The substrate can be silicon dioxide, glass, plastic, mica, etc., and the material of the tunneling junction sample is metal, including but not limited to gold, silver, palladium, platinum, aluminum, tantalum, indium, etc.

[0038] The preparation process is divided into two steps. The first step is to prepare a metal nanobelt with a narrow neck structure on the substrate (such as Figure 1 ). This step can be completed by using a mask patterning and then a metal deposition-stripping process; or by directly patterning the metal layer without using a mask. If a mask patterning process is used, the patterning method includes but is not limited to ultraviolet lithography, electron beam lithography, imprinting or pattern transfer process, etc.; and the preparation method of the metal layer includes but is not limited to electron beam evaporation deposition, thermal evaporation deposition, magnetron sputtering, electroplating, atomic layer deposition, epitaxial growth, etc. If the metal layer is directly patterned without using a mask, methods such as gallium ion focused ion beam (FIB) etching, helium ion etching, plasma etching, etc. can be used to directly etch metal nanobelt patterns on the metal layer; or methods such as gold ion focused ion beam, self-assembly, etc. can be used for local deposition or growth on the substrate to directly obtain metal nanobelt structures. The neck width of the metal nanobelt can be from 1 nm to 1000 nm, and the thickness can be from 5 nm to 1000 nm.

[0039] Obtain a tunneling junction sample

[0040] Tunnel junctions are prepared by various methods, with nanometer or atomic scale tunnel gap (such as Figure 1 ).

[0041] The electrical method can use electromigration melting method, or stretching method under strong electric field. When using electromigration method, 0-5V voltage is applied to the tunnel junction, generating 0.5-5mA current. The applied voltage can be triangular wave, square wave or I-V scanning. Under the action of joule heat, current force and electric field, metal atoms migrate violently, the neck of the metal nanobelt is first melted, forming a nanometer or atomic scale gap, and a tunnel junction can be obtained. The stretching method under strong electric field should have a larger gap in the preparation of metal nanobelt. A 10-100V voltage is applied to both ends of the metal nanobelt, which can make the metal atoms migrate to the electrode tip under the action of strong electric field, so as to reduce the gap distance and obtain a tunnel junction.

[0042] When using mechanical stretching method, the metal nanobelt should be prepared on a substrate with certain ductility, or as a suspended structure. The clamps are used to clamp both sides of the metal nanobelt, and high-precision control devices (such as piezoelectric ceramics, precision stepping motor, etc.) are used to make the clamps move slowly to both sides until the neck of the metal nanobelt suddenly breaks, and then stop, so as to obtain a tunnel junction.

[0043] When using direct etching method, local etching methods such as focused ion beam bombardment and helium ion beam etching can be used, or hard mask combined with plasma etching method can be used to etch a nanometer or atomic scale tunnel gap in the neck of the metal nanobelt, so as to directly obtain a tunnel junction.

[0044] Electrical connection

[0045] Place the tunnel junction sample to be adjusted on the surface of the probe station (such as Figure 2 ). For the substrate and the sample, only need to ensure that they remain stable under the used laser power, without decomposition or deformation. The probe station can use commercial probe station system, or self-built probe station system. The positive and negative electrodes of the tunnel junction can be connected to a pair of electrode plates on the substrate, so that a pair of probes can be in contact with them. The probes are connected to the ports of the semiconductor parameter analyzer through wires, and good electrical connection is ensured. The semiconductor parameter analyzer can use commercial instruments or self-designed scientific instruments, but good voltage and current accuracy should be ensured, the voltage output and measurement accuracy should be not less than 1mV, the maximum voltage should be not less than 10V, the current measurement accuracy should be not less than 1nA, and the maximum current should be not less than 1mA.

[0046] Laser system adjustment

[0047] The laser system can employ ordinary commercial laser systems, femtosecond laser systems, self-designed and constructed gas lasers, semiconductor lasers, or other lasers. The wavelength range used can be 400nm to 800nm, and the power range is generally 1–200mW. It is essential to ensure that the power, wavelength, and other properties of the laser beam remain stable and consistent during use. The support and optical path system can utilize tripods, iron stands, optical platforms and supporting equipment, or other support and optical path devices. It is only necessary to ensure that the laser beam can irradiate the substrate surface and that the laser spot can accurately irradiate the tunnel junction position requiring adjustment. Figure 2 The optical power meter measures the laser power at this point and adjusts the focusing system to change the spot area, so that the laser power density reaches the required range. The optical power meter can be a commercially available or custom-designed optical power measurement device, ensuring that its measured power and wavelength ranges cover the parameter range of the laser used.

[0048] Adjusting the distance between tunnels and junctions

[0049] After laser adjustment, the laser is turned off, and an IV scan is performed to obtain the initial current curve. The initial tunneling distance can be calculated using the Simmons formula as a reference. The laser is then turned on and irradiated onto the sample. Under laser irradiation, an IV scan of the tunnel junction is performed using a semiconductor analyzer. The scan starts at 0V and progresses to a maximum scan voltage of 10mV–10V, with a scan speed range of 0.1mV / s–1V / s. During the scan, the IV curve is approximately a straight line, allowing the calculation of the tunneling gap distance. As the number of scans increases, the slope of the IV curve gradually increases, indicating that the tunneling gap gradually decreases, with each decrease approximating the diameter of a single atom. When the tunneling gap decreases to the desired value, the scan is stopped, and the tunneling gap will remain at this distance, thus completing the adjustment of the atomic positions on the surface of the tunnel junction.

[0050] It's important to note that the tunneling distance in the Simmons formula is the distance between the edges of the electron clouds of two atoms, not the distance between the two atomic nuclei. The distance between the two nuclei is equal to the sum of the tunneling gap and the atomic diameter. Therefore, the calculated tunneling distance can be smaller than the diameter of a gold atom (approximately 0.29 nm). Theoretically, when an atomic bridge appears, the tunneling gap should be zero, and the distance between the nuclei should be equal to the atomic diameter. However, in actual devices, due to factors such as stress causing bond length changes and parasitic resistance, the tunneling gap value calculated by the Simmons formula may be extremely small but not zero, which is reasonable. In this case, the formation of a single atomic bridge can be determined based on the device's conductivity. When the tunneling junction conductivity is higher than the quantum conductivity, a single atomic bridge can be considered to have appeared.

[0051] Example 1

[0052] Fabrication of metal nanoribbons

[0053] Tunnel junction devices were fabricated on a silicon dioxide substrate. The material of the tunnel junction was gold. The fabrication process was divided into two steps. The first step was to fabricate gold nanoribbons with a narrow neck structure on the substrate (as shown in Figure 3 ). This step was completed using a mask patterning and then an electron beam metal deposition-stripping process. The neck width of the gold nanoribbons was 100 nm and the thickness was 10 nm.

[0054] Obtaining a tunnel junction sample

[0055] The tunnel junction was subjected to an electromigration melting method by applying a voltage of 0-2 V to generate a current of 1.3 mA. The voltage was applied in a -V scanning manner. The obtained tunnel junction had a tunnel gap of less than 10 nm (as shown in Figure 4

[0056] Electrical connection

[0057] The tunnel junction sample to be adjusted was placed on the surface of a probe station. The probe station was an MPI TS150 type probe station. The positive and negative electrodes of the tunnel junction were led out as a pair of electrode plates on the substrate, so that a pair of probes were in contact with them. The probes were connected to the ports of a semiconductor parameter analyzer through wires, and good electrical connection was ensured. The semiconductor parameter analyzer was a KeySight B1500A type semiconductor analyzer.

[0058] Adjusting the laser system

[0059] The laser system used a common commercial laser system, and the wavelength range used was 480 nm, and the power was 200 mW. The support and optical system can use a tripod to ensure that the laser beam can irradiate the substrate surface, and the laser spot can be accurately irradiated at the tunnel junction position. A THORLABS PM100D optical power meter was used to measure the total power of the laser beam, which was 200 mW. The tuning knob on the laser was turned to adjust the size of the spot area. The measured spot area was about 19.23 mm 2 , and the calculated laser power density at the center of the spot was about 10.4 mW / mm 2 , which was within the allowed power range

[0060] Controlling atomic position operation

[0061] In this embodiment, the atomic position operation was adjusted for a total of 11 times of I-V scanning, of which the first time was the initial scanning, and the rest were adjustment scans under laser irradiation. In order to make the image clear, the initial I-V curve and the typical I-V curves of the 5 times of laser irradiation were selected, a total of 6 curves, as shown in Figure 5 After the laser adjustment was completed, the laser was first turned off to obtain the initial current of the tunnel junction, as shown in​Figure 5 The middle curve 1 (hollow triangle) shows the tunneling conductance of about 2.5 μS. According to the Simmons formula, the tunneling distance can be calculated to be about 2.8 nm. Then the laser is turned on and irradiated on the sample. Under the condition of laser irradiation, the I-V scan of the tunneling junction is performed using the semiconductor analyzer. The scan starts from 0 V to a maximum scan voltage of 25 mV, and the scan speed is 2 mV / s. The I-V curve is recorded after 10 continuous scans, and typical 4 times are shown as Figure 5 The middle curves 2-6 (hollow circles) show the tunneling conductance of about 2.5 μS. According to the Simmons formula, the tunneling distance can be calculated to be about 2.8 nm. Then the laser is turned on and irradiated on the sample. Under the condition of laser irradiation, the I-V scan of the tunneling junction is performed using the semiconductor analyzer. The scan starts from 0 V to a maximum scan voltage of 25 mV, and the scan speed is 2 mV / s. The I-V curve is recorded after 10 continuous scans, and typical 4 times are shown as Figure 6 The calculated conductance and tunneling distance corresponding to the five curves are shown. It can be seen that the tunneling distance corresponding to curve 2 is 2.6 nm, curve 3 is 2.3 nm, curve 4 is 2.0 nm, curve 5 is 1.7 nm, and curve 6 is 1.2 nm. Stop scanning, and the tunneling gap will remain the last tunneling distance of 1.2 nm, i.e. the operation of adjusting the distance of the tunneling junction is completed.

[0062] Example 2

[0063] Preparation of metal nanobelt

[0064] A tunneling junction device is prepared on a silicon dioxide substrate. The material of the tunneling junction is gold. The preparation process is divided into two steps. In the first step, a gold nanobelt with a narrow neck structure is prepared on the substrate Figure 1 ). This step uses mask patterning, and then is completed by electron beam metal deposition-peeling process. The neck width of the metal nanobelt is from 100 nm, and the thickness can be from 10 nm.

[0065] Obtaining a tunneling junction sample

[0066] The tunneling junction is subjected to a voltage of 0-2 V by using the electromigration fusing method to generate a current of 1.3 mA. The voltage is applied in the form of -V scan.

[0067] Electrical connection

[0068] The tunneling junction sample to be adjusted is placed on the surface of the probe station. The probe station is MPI TS150 type probe station. The positive and negative electrodes of the tunneling junction are connected to a pair of electrode plates on the substrate, so that a pair of probes are in contact with them. The probes are connected to the ports of the semiconductor parameter analyzer through wires, and good electrical connection is ensured. The semiconductor parameter analyzer is KeySight B1500A type semiconductor analyzer.

[0069] Adjusting the laser system

[0070] The laser system uses a standard commercial laser system with a wavelength range of 532nm and a power of 60mW. A tripod is used for the support and optical path system to ensure the laser beam can illuminate the substrate surface and the laser spot can be precisely positioned at the tunnel junction. Using a THORLABS PM100D optical power meter, the total laser beam power was measured to be 200mW. The adjustment knob on the laser was rotated to adjust the spot size. The measured spot area was approximately 4.2mm². 2 The calculated laser power density at the center of the laser spot is approximately 14.3 mW / mm². 2 Within the permissible power range

[0071] Atom position manipulation

[0072] In this embodiment, the atomic position adjustment operation involved 11 IV scans, with the first scan being the initial scan and the rest being adjustment scans under laser irradiation conditions. For image clarity, the initial IV curve and four typical IV curves under laser irradiation were selected, totaling five curves, as shown below. Figure 7 As shown. After completing laser tuning, first turn off the laser to obtain the initial current of the tunnel junction, as shown. Figure 7 Curve 1 (hollow triangle) is shown. The initial gap was calculated to be 0.39 nm using the Simmons formula. The laser was then turned on and irradiated onto the sample. Under laser irradiation, an IV scan of the tunnel junction was performed using a semiconductor analyzer. The scan started at 0 V and progressed to a maximum scan voltage of 25 mV, with a scan speed of 2 mV / s. During the scan, the IV curve approximates a straight line, from which the tunnel gap distance can be calculated. Eight consecutive scans were performed, and the IV curves were recorded. Four typical IV curves are shown below. Figure 7 Curves 2 to 5 are shown. According to the Simmons formula, the tunnel spacing variation of the tunnel junction is calculated. Curve 2 is 0.25 nm, curve 3 is 0.19 nm, curve 4 is 0.11 nm, and curve 5 is 0.08 nm.

[0073] It should be noted that the tunneling distance in Simmons' formula is the distance between the edges of the electron clouds of two atoms, not the distance between the two atomic nuclei. The distance between the two atomic nuclei is equal to the sum of the tunneling gap and the atomic diameter. Therefore, the calculated tunneling distance can be smaller than the diameter of a gold atom (approximately 0.29 nm). For example, Figure 7The tunneling distance calculated by curve 5 is 0.08 nm, so the distance between the electron clouds of the two atoms at the tip of the tunneling junction is 0.08 nm, and the distance between the nuclei of the two atoms is 0.37 nm. In theory, when the atomic bridge appears, the tunneling distance should be 0, and the distance between the nuclei should be equal to the atomic diameter. However, in the actual device, due to the stress that may cause the bond length to change, and various factors such as parasitic resistance, the tunneling distance calculated by the Simmons formula may be very small but not 0. In this embodiment, the tunneling distance calculated by curve 5 is close to 0.08 nm, which is already much smaller than the diameter of a gold atom, which is reasonable. At this time, the formation of a single-atom bridge can be judged according to the size of the device conductance. When the conductance of the tunneling junction is higher than the quantum conductance, it can be considered that a single-atom bridge has appeared.

[0074] Figure 8 The variation of the tunneling distance of the tunneling junction in this embodiment and the corresponding conductance are shown. The channel conductance is initially about 20 μS, and at the end of the scan, the tunneling junction conductance reaches 80 μS, which is slightly higher than the quantum conductance (77.5 μS). This indicates that a single-atom bridge structure has appeared in the tunneling junction.

[0075] The above-described embodiments are not intended to limit the present application, and any person skilled in the art can make various modifications and changes without departing from the spirit and scope of the present application, and the protection scope of the present application is defined by the scope of the claims.

Claims

1. A method of adjusting a gap distance in a metal tunneling junction, comprising: The apparatus includes a semiconductor parameter analyzer and a matching probe station for I-V scanning of the tunnel junction, a laser light path and a focusing system for laser irradiation of the tunnel junction, and a power meter for measuring the power density of the laser spot. The adjusting method comprises: 1) preparing a metal nanobelt or nanowire; 2) processing the metal nanobelt or nanowire into a metal tunnel junction by electromigration, elongation under a strong electric field, controllable mechanical cleavage, or direct etching, and placing the tunnel junction sample to be adjusted on the surface of the probe station; 3) performing a preliminary I-V scan on the original tunnel junction to determine the initial gap distance of the tunnel junction; 4) focusing a laser beam spot on the surface of the tunnel junction by using the laser light path and the focusing system, so that the beam spot irradiated on the surface of the tunnel junction has a certain power density; 5) simultaneously performing I-V scanning on the tunnel junction under laser irradiation, fitting the distance change of the tunnel gap by I-V curve and Simmons formula, and controlling the gap distance in the tunnel junction at the precision of a single atom under continuous laser irradiation.

2. The method of claim 1, wherein the gap distance in the metal tunneling junction is adjusted by, The metal nanobelt or nanowire in step 1) is prepared by photolithography-stripping technology or focused ion beam (FIB) deposition method.

3. The method of claim 1, wherein the gap distance in the metal tunneling junction is adjusted by, The metal material of the tunnel junction is gold, silver, palladium, platinum, aluminum, tantalum, or indium.

4. The method of claim 1, wherein the gap distance in the metal tunneling junction is adjusted by, The gap distance of the metal tunnel junction prepared in step 2) is in the nanometer or atomic scale, and the scale range is 50 nm to 0.1 nm.

5. The method of claim 1, wherein the gap distance in the metal tunneling junction is adjusted by, The maximum voltage of I-V scanning in step 3) or 5) is from 10 mV to 100 mV.

6. The method of claim 1, wherein the gap distance in the metal tunneling junction is adjusted by, Power density range in step 4): 1 mW / mm 2 ~ 200 mW / mm 2 .

7. The method of claim 1, wherein the gap distance in the metal tunneling junction is adjusted by, Laser beam spot size range in step 4): 1 mm 2 ~ 100 mm 2 .

8. The method of claim 1, wherein the gap distance in the metal tunneling junction is adjusted by, The laser wavelength in step 5) is from 800 nm to 400 nm.

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