Chiral spin polarization circular polarization electric device, preparation and application

Abstract

The invention relates to a chiral spin-polarized circularly polarized photoelectric device, preparation and application, and belongs to the technical field of photoelectric devices. Specifically, chiral molecules are introduced to the surface of a semiconductor, and spin polarization induced by a chiral structure is utilized to achieve the purpose of recognizing the light polarization state. Chiral molecules generate a Rashba-like spin orbit coupling effect on the surface through spin exchange interaction, so that symmetric breaking is caused, and a circularly polarized light current effect is generated under an external illumination condition. Molecules with different chiral (-L / -D) structures also have different response effects on polarized light. The chiral spin-polarized optoelectronic device disclosed by the invention has a remarkable circularly polarized light detection effect, the experimental operation is simple and easy to implement, the device preparation cost is low, and the application of a chiral structure in a spin optoelectronic device can be greatly expanded.

Description

Technical field:

[0001] The invention belongs to the field of optoelectronic device preparation technology and relates to a preparation method and application of a chiral spin-polarized circularly polarized optoelectronic device. Background technology:

[0002] Chirality, as a symmetry-breaking property, provides unlimited possibilities for exploring new physics and new mechanisms of materials. The helical spatial structure of chiral molecules and electrons can produce spin polarization of electrons through spin-orbit coupling. This effect is called "chirality-induced spin selectivity", which allows chiral molecules to inject spin into materials in a clean, efficient and low-power manner without the assistance of an external field. Circularly polarized photocurrent is a common scheme for studying spin-orbit coupling. Its characteristic is that it uses the interaction between photons and electrons to generate periodically changing photocurrents, and the experimental device is easy to operate, so it can be used to study and explore new optoelectronic devices. The combination of chirality-induced spin selectivity and circularly polarized photocurrent is expected to prepare new chiral-spin electro-photonic devices, which can be used for circularly polarized light detection and is of great significance to the practical application of spin electronics.

[0003] At present, chiral optoelectronic devices are mostly realized by adding chiral intercalation layers to perovskites or constructing plasmons on metal surfaces. Their preparation process is relatively complicated, sensitive to environmental changes, and relatively poor in stability. There are many defects in actual large-scale production applications. At present, the technology of realizing large-area chiral optoelectronic device preparation through simple and convenient solutions while taking into account good circularly polarized light detection function still needs to be explored. Summary of the invention:

[0004] To achieve the above objectives, the present invention aims to provide a circularly polarized optoelectronic device based on chiral spin polarization and a preparation method and application thereof.

[0005] The invention discloses a chiral spin-polarized circularly polarized photoelectric device, which utilizes the spin polarization effect induced by self-assembled chiral molecules AHPA-L / -D to modify the surface of a semiconductor to generate symmetry breaking, and comprises a substrate, a semiconductor layer, a metal layer, and a chiral molecule layer stacked in sequence from bottom to top.

[0006] Further, the substrate and the semiconductor layer correspond to commercial p-type doped single crystal Si grown on a SiO2 substrate. The thickness of the semiconductor layer used can be 100-500 μm, specifically 100 μm, 200 μm, 400 μm, 500 μm, etc.

[0007] Furthermore, the material of the metal layer is selected from at least one of Au and Al, and the thickness can be 1 to 5 nm, specifically 1 to 2 nm, 2 to 4 nm, 5 nm, etc.

[0008] Further, the material of the chiral molecular monolayer is selected from at least one of chiral polypeptides AHPA-L or AHPA-D, and the thickness of the grown chiral molecular monolayer is about 3 nm. Taking AHPA-L as an example, the -SH of the cysteine ​​at the end of the chiral molecule forms a thiol bond with the surface of the metal layer Au / Al and is fixed on the metal layer, and the other end of the chiral molecule is suspended; the angle between the chiral molecule and the normal direction of the substrate is 20-70°, such as about 50°.

[0009] In the preparation method of the present invention, commercial semiconductor single crystals are used as semiconductor layers, a metal layer is formed by magnetron sputtering, a chiral molecular monolayer is formed by self-assembly, and the layers are sequentially prepared and stacked to obtain a chiral spin-polarized circularly polarized optoelectronic device. The preparation scheme is simple, the process cost is low, the effect is significant, and it is expected to be promoted and used in the future.

[0010] In a second aspect, the present invention provides a detailed method for preparing the above-mentioned optoelectronic device, comprising the following steps:

[0011] (1) The semiconductor layer (commercial p-type doped single-crystalline Si grown on SiO2, crystal plane (100), resistivity 1-20Ω·cm) was mechanically cut into 5 mm × 5 mm squares.

[0012] (2) Growing the metal layer on the semiconductor layer by magnetron sputtering.

[0013] The specific steps include:

[0014] (a) The sample in step (1) was ultrasonically cleaned with deionized water and ethanol in sequence, each time for 5 to 10 minutes, and finally dried with a nitrogen gun;

[0015] (b) The oxide layer on the surface is removed by ion beam etching. The argon ion etching time is 2 to 5 minutes and the beam current is 60-200 mA. After etching, the sample is stored in a vacuum bag.

[0016] (c) The coating chamber of the ultra-high vacuum magnetron sputtering system was evacuated to below 20 Pa using a mechanical pump, and then the molecular pump was turned on to evacuate to 10 -5 Place the sample in step (b) on the sample holder and place it in the sample chamber. First, turn on the mechanical pump to evacuate the sample chamber to below 20 Pa, then turn on the molecular pump to evacuate to 10 -3 Below Pa;

[0017] (d) opening the gate valve between the coating chamber and the sample chamber, and sending the sample holder with the substrate in step (b) into the coating chamber through the lateral servo;

[0018] (e) Inert gas is filled into the coating chamber to reach the ignition pressure, and a DC power supply is used to perform pre-sputtering 1. After completion, the inert gas flow rate is reduced, and the pressure in the coating chamber is reduced to the working pressure, and a DC power supply is used to perform pre-sputtering 2; the inert gas includes argon and / or nitrogen; the power of the DC power supply is 180-220W; the working pressure of the pre-sputtering 1 is 1.3-2.0Pa, and the time is 30-60s; the working pressure of the pre-sputtering 2 is 0.3-0.5Pa, and the time is 30-60s;

[0019] (f) After completion, the target baffle is opened to start formal sputtering. The sputtering is stopped after the sputtering time is reached, and the sample holder is taken out to obtain the grown metal layer.

[0020] (3) growing a self-assembled chiral molecular monolayer on the metal layer by a Czochralski method;

[0021] The specific preparation method comprises the following steps:

[0022] (a) Dissolve the chiral molecule in EtOH to prepare a chiral molecule solution, preferably with a concentration of 1 mmol / L -1 ;

[0023] (b) placing the sample of step (2) upright in a chiral molecule solution, and then sealing and standing at room temperature, for example, using polytetrafluoroethylene sealing tape to seal and standing at room temperature; allowing the chiral molecules to assemble on the metal layer, and assembling for 24-48 hours, for example, when a self-assembled molecular monolayer is formed on the Au surface, let it stand for 24 hours, and when a self-assembled molecular monolayer is formed on the Al surface, let it stand for 48 hours.

[0024] (c) After the self-assembly is completed, the sample is taken out and the surface is washed with EtOH multiple times to remove the molecules that have not formed self-assembly; after the sample preparation is completed, it is placed in a vacuum sealed bag and stored at -18°C.

[0025] (4) Use a pressure welding machine to lead out electrodes from the surface of step (3). The electrode material is Al wire and the electrode spacing is 3 mm.

[0026] In a third aspect, the present invention provides a method for detecting circularly polarized light using the chiral spin-polarized circularly polarized light device.

[0027] The principle of a chiral optoelectronic device provided by the present invention is that molecules of a specific chirality will make it easier for electrons of a certain spin to pass through, while electrons of another spin will have difficulty passing through. When chiral molecules grow on the metal surface by self-assembly, they will induce symmetry breaking at the semiconductor interface through spin exchange interaction and spin selection, and produce Rashba spin splitting, so that the semiconductor that does not have symmetry breaking itself will produce circularly polarized photocurrent. When external circularly polarized light irradiates the sample surface, a circularly polarized photocurrent effect is generated, and molecules of opposite chirality will produce opposite types of circularly polarized photocurrent.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] 1. The method for preparing chiral optoelectronic devices provided by the present invention is simple and easy, low-cost, and achieves high-quality, high-stability, large-area controllable preparation of devices that can be directly used in room temperature air environment, which is conducive to future promotion and application.

[0030] 2. The solution provided by the present invention for circularly polarized light detection using chiral optoelectronic devices has significant effects and high sensitivity. Description of the drawings:

[0031] Figure 1 It is a schematic diagram of the preparation process of the chiral optoelectronic device of the present invention.

[0032] Figure 2 This is a test optical path diagram of the chiral optoelectronic device of the present invention.

[0033] Figure 3 This is a graph showing the relationship between the circularly polarized photocurrent of the AHPA-L chiral optoelectronic device used in the present invention and the polarization state of the incident light.

[0034] Figure 4 This is a graph showing the relationship between the circularly polarized photocurrent of the AHPA-D chiral optoelectronic device used in the present invention and the polarization state of the incident light.

[0035] Figure 5 for Figure 5 It is a schematic diagram of the optical transition selection rule involved in the present invention, wherein +1 / 2, -1 / 2, +3 / 2, -3 / 2 represent the electron angular momentum quantum numbers of light holes and heavy holes. Specific implementation method:

[0036] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0037] It should be noted that, unless otherwise specified, the technical terms or scientific terms used in the present invention should have the common meanings understood by those skilled in the art to which the present invention belongs.

[0038] The experimental methods in the following examples are conventional methods unless otherwise specified. The experimental materials used in the following examples are purchased from conventional biochemical reagent companies unless otherwise specified.

[0039] This embodiment provides a solution for realizing circularly polarized photocurrent detection using chiral optoelectronic devices, and realizes efficient recognition of left / right polarized light by applying chiral molecule modification to ordinary semiconductors.

[0040] In this embodiment, the semiconductor layer used is commercial p-type doped single crystal Si grown on SiO2, with a crystal plane (100), a resistivity of 1-20Ω·cm, and a size of 5mm×5mm. The metal layer Au used is grown on the semiconductor layer by magnetron sputtering technology, with a thickness of 5nm. The chiral molecules used are chiral peptides AHPA-L or AHPA-D, which have significant spin polarization effects. The device electrode spacing in the experiment is 3mm. The complete sample preparation process is as follows: Figure 1 shown.

[0041] In this embodiment, the wavelength of the near-infrared excitation light used is 800 nm, the laser repetition frequency is 80 MHz, and the pulse width is 150 fs.

[0042] In this embodiment, the power of the near-infrared excitation light is continuously adjustable between 1 and 50 mW, the power stability is that the power fluctuation does not exceed 0.15% within 2 hours, the spot size of the excitation light irradiated on the sample is a circular spot with a diameter of 2 mm, and the spot intensity satisfies the Gaussian distribution of TEM 00 mold.

[0043] In this embodiment, the chopping frequency of the optical chopper used is 10-4000 Hz and is continuously adjustable.

[0044] In this embodiment, other optical elements used include an aperture, a polarizer, a quarter wave plate, and a reflector.

[0045] In this embodiment, the electrical testing equipment used includes a current preamplifier and a lock-in amplifier.

[0046] In this embodiment, other devices used include an electric rotating table, a motor, an adapter plate, a probe, and a wire.

[0047] Specifically, the specific implementation process of this embodiment is given below:

[0048] In this embodiment, after completing the device preparation according to the above device preparation process, Figure 2In the test optical path shown, the incident light with an optical power of 5mW has a spot diameter of about 2mm after passing through the aperture. After passing through the polarizer, it reaches the λ / 4 wave plate fixed on the electric rotating stage. As the wave plate rotates continuously in the range of 0°-360°, linear polarization, left-handed circular polarization, linear polarization, and right-handed circular polarization are periodically generated. In actual operation, the step length of the electric rotating stage is set to 5°. After the above changes, the excitation light is irradiated on the sample with an incident angle of 30°. The experimental test environment temperature is room temperature, and the test and control program is written by LabVIEW software.

[0049] In this embodiment, in order to avoid the measured photocurrent signal from being affected by other signals and noise, the phase-sensitive detection technology is used to process the photocurrent signal, that is, the chopper is set to a reference frequency, and the frequency is applied to the photocurrent signal, and then the signal of the frequency is detected by a phase-locked amplifier to achieve the test of weak signals. In the experiment, the reference frequency of the chopper is set to 2350Hz and is connected to the phase-locked amplifier. The photocurrent generated by the light spot irradiating the sample enters the current preamplifier through a wire, and the current signal is converted into a voltage signal and amplified. The amplified voltage signal is further input into the phase-locked amplifier for photocurrent extraction and read out by the computer. At the same time, the computer will collect the rotation angle of the rotating table to obtain the photocurrent size at each wave plate angle.

[0050] The photocurrent variation curves under different polarization states were drawn using Origin software, where the fitting formula is:

[0051]

[0052] In the above formula, is the angle between the quarter-wave plate and the polarizer. J on the left represents the total photocurrent density, and The term represents the circularly polarized photocurrent generated by circularly polarized light excitation, and The term represents the linearly polarized photocurrent effect and the non-polarized photon pulling effect caused by linearly polarized light excitation. j0 comes from the thermoelectric effect, photovoltaic effect, Dember effect, etc. caused by the temperature gradient, and is the background current. is the attenuation term.

[0053] When AHPA-L is used as a chiral monolayer to prepare a device, the device photocurrent change curve is as follows: Figure 3 As shown in the figure, the solid line is the fitting curve of the total photocurrent, and the dotted line is the fitting curve of the circular polarization photocurrent term. It can be seen that the fitting effect is good. Figure 3It can be seen that when the incident angle is 30° and the wavelength of the incident light is 800nm, the circularly polarized photocurrent generated by the AHPA-L chiral optoelectronic device is about 154pA / mW, and it has a larger photocurrent response to right-handed circularly polarized light, which can be reflected in the circularly polarized photocurrent term. The C value normalized by the background current j0 is -0.01878.

[0054] Under the same test environment, the circularly polarized photocurrent generated by the AHPA-D chiral optoelectronic device is about 174pA / mW, but unlike the AHPA-L device, the AHPA-D device has a larger photocurrent response to left-handed circularly polarized light, and the C value normalized by the background current j0 is +0.01415. Both have a higher response to a certain specific circularly polarized light and have opposite circularly polarized photocurrent parameters C. The above results show that the chiral optoelectronic device prepared in this embodiment not only exhibits a high sensitivity recognition ability for polarized light, but also can be prepared on a large scale, and the scheme is simple and feasible.

[0055] The reason why this method can be used to detect circularly polarized light is that chiral molecules can introduce symmetry breaking and spin-orbit coupling to semiconductors through interface effects, allowing semiconductors to exhibit characteristic responses to circularly polarized light. Molecules of different chirality introduce different symmetry breaking, which ultimately leads to opposite circularly polarized photocurrent C values. When chiral molecules approach the surface of a material, the molecules will produce a short-term charge polarization under the action of dispersion forces. Such charge polarization is manifested as spin polarization in chiral molecules, resulting in an asymmetric spin distribution of surface electrons in momentum space. When the molecular layer thickness is When the interface effect is of the order of magnitude (i.e., within a few spirals near the interface layer of the chiral molecule), the interface effect is dominated by spin exchange interaction. When electrons flow through the interface between the chiral molecule and the electrode, the orbital polarization effect and orbital filtering effect of the chiral molecule and the electrode jointly produce spin polarization effect and spin filtering effect, and introduce symmetry breaking. The interface effect between the chiral molecule and the electrode layer will affect the band symmetry of Si near the interface, forming a symmetry breaking. The closer to the interface of the chiral molecule / electrode layer, the stronger the interface effect.

[0056] Due to the existence of symmetry breaking, when external polarized light irradiates the sample, it will cause circularly polarized photocurrent effect. Electrons are fermions with spin of ±1 / 2, photons are bosons with spin of ±1, and the photon spin-electron spin interaction satisfies the selection rule of optical transition, such as Figure 5As shown. When the incident photon energy is greater than or equal to the semiconductor bandgap width, the valence band electrons will absorb the photon energy and transition to the conduction band. The conduction band and light holes are in the ±1 / 2 spin state, and the heavy holes are in the ±3 / 2 spin state. When the incident photon is left-handed circularly polarized light (σ+) with spin +1, the light hole -1 / 2 state can transition to the +1 / 2 state of the conduction band and the heavy hole -3 / 2 state can transition to the -1 / 2 state of the conduction band; when the incident photon is right-handed circularly polarized light (σ-) with spin -1, the light hole +1 / 2 state can transition to the 1 / 2 state of the conduction band and the heavy hole +3 / 2 state can transition to the +1 / 2 state of the conduction band. On this basis, the photocurrent and the circularly polarized photocurrent term are finally generated.

Claims

1. A chiral spin-polarized circularly polarized optoelectronic device, characterized in that: The spin polarization effect induced by the self-assembled chiral molecules AHPA-L / -D is used to modify the semiconductor surface to produce symmetry breaking.

2. A chiral spin-polarized circularly polarized optoelectronic device according to claim 1, characterized in that: It includes a substrate, a semiconductor layer, a metal layer, and a chiral molecule layer stacked in sequence from bottom to top.

3. A chiral spin-polarized circularly polarized optoelectronic device according to claim 2, characterized in that: The substrate and the semiconductor layer correspond to commercial low-doped single crystal p-Si grown on a SiO2 substrate. The thickness of the semiconductor layer used can be 100 to 500 μm.

4. A chiral spin-polarized circularly polarized optoelectronic device according to claim 2, characterized in that: The material of the metal layer is selected from at least one of Au and Al, and the thickness is 1 to 5 nm.

5. A chiral spin-polarized circularly polarized optoelectronic device according to claim 2, characterized in that: The material of the chiral molecular monolayer is selected from at least one of chiral polypeptides AHPA-L or AHPA-D.

6. A chiral spin-polarized circularly polarized optoelectronic device according to claim 2, characterized in that: The -SH of the cysteine ​​at the terminal of the chiral molecule forms a thiol bond with the surface of the metal layer and is fixed on the metal layer, and the other end of the chiral molecule is suspended; the angle between the chiral molecule and the normal direction of the substrate is 20-70 degrees.

7. A method for preparing a chiral spin-polarized circularly polarized optoelectronic device according to any one of claims 1 to 6, characterized in that: A commercial semiconductor single crystal is used as a semiconductor layer, a metal layer is formed by a magnetron sputtering method, a chiral molecular monolayer is formed by a self-assembly method, and the layers are sequentially prepared and stacked to obtain a chiral spin-polarized circularly polarized photoelectric device; the steps include: (1) Mechanically cutting the semiconductor layer, i.e., commercial p-type doped single crystal Si grown on SiO2, with a (100) plane and a resistivity of 1-20 Ω·cm; (2) growing the metal layer on the semiconductor layer by magnetron sputtering; (3) growing a self-assembled chiral molecular monolayer on the metal layer by a Czochralski method; (4) Use a pressure welding machine to lead out electrodes from the surface of step (3). The electrode material is Al wire and the electrode spacing is 3 mm.

8. The method according to claim 7, characterized in that Step (2) specifically includes the following steps: (a) The sample in step (1) was ultrasonically cleaned with deionized water and ethanol in sequence, each time for 5 to 10 minutes, and finally dried with a nitrogen gun; (b) The oxide layer on the surface is removed by ion beam etching. The argon ion etching time is 2 to 5 minutes and the beam current is 60-200 mA. After etching, the sample is stored in a vacuum bag. (c) The coating chamber of the ultra-high vacuum magnetron sputtering system was evacuated to below 20 Pa using a mechanical pump, and then the molecular pump was turned on to evacuate to 10 -5 Place the sample in step (b) on the sample holder and place it in the sample chamber. First, turn on the mechanical pump to evacuate the sample chamber to below 20 Pa, then turn on the molecular pump to evacuate to 10 -3 Below Pa; (d) opening the gate valve between the coating chamber and the sample chamber, and sending the sample holder with the substrate in step (b) into the coating chamber through the lateral servo; (e) Inert gas is filled into the coating chamber to reach the ignition pressure, and a DC power supply is used to perform pre-sputtering 1. After completion, the inert gas flow rate is reduced, and the pressure in the coating chamber is reduced to the working pressure, and a DC power supply is used to perform pre-sputtering 2; the inert gas includes argon and / or nitrogen; the power of the DC power supply is 180-220W; the working pressure of the pre-sputtering 1 is 1.3-2.0Pa, and the time is 30-60s; the working pressure of the pre-sputtering 2 is 0.3-0.5Pa, and the time is 30-60s; (f) After completion, the target baffle is opened to start formal sputtering, and the sputtering is stopped after the sputtering time is reached. The sample holder is taken out to obtain the grown metal layer; The specific preparation method of step (3) comprises the following steps: (a) Dissolve the chiral molecule in EtOH to prepare a chiral molecule solution, preferably with a concentration of 1 mmol / L -1 ; (b) placing the sample of step (2) upright in a chiral molecule solution, and then sealing and standing at room temperature, for example, using polytetrafluoroethylene sealing tape to seal and standing at room temperature; allowing the chiral molecules to assemble on the metal layer, and assembling for 24-48 hours, for example, when a self-assembled molecular monolayer is formed on the Au surface, let it stand for 24 hours, and when a self-assembled molecular monolayer is formed on the Al surface, let it stand for 48 hours. (c) After the self-assembly is completed, the sample is taken out and the surface is washed with EtOH multiple times to remove the molecules that have not formed self-assembly; after the sample preparation is completed, it is placed in a vacuum sealed bag and stored at -18°C.

9. Use of a chiral spin-polarized circularly polarized optoelectronic device as claimed in any one of claims 1 to 6 for detecting circularly polarized light.

10. According to the application of claim 9, molecules with specific chirality will make it easier for electrons of a certain spin to pass through, while electrons of another spin will find it difficult to pass through; when the chiral molecules grow on the metal surface by self-assembly, they will induce symmetry breaking at the semiconductor interface through spin exchange interaction and spin selection, and produce Rashba spin splitting, so that the semiconductor that does not have symmetry breaking itself will produce circularly polarized photocurrent, and when external circularly polarized light irradiates the sample surface, a circularly polarized photocurrent effect will be generated, and molecules of opposite chirality will produce opposite types of circularly polarized photocurrent.

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