CN116223927A - Method for distinguishing two-dimensional Bi2O2Se surface polarity by circularly polarized light current - Google Patents
Method for distinguishing two-dimensional Bi2O2Se surface polarity by circularly polarized light current Download PDFInfo
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Abstract
The invention relates to a circularly polarized light current distinguishing two-dimensional Bi 2 O 2 Method for testing the polarity of Se surface by testing Bi 2 O 2 The variation trend of the circularly polarized light current of the Se nano sheet along with the grid voltage of the ionic liquid can simply distinguish two-dimensional Bi 2 O 2 Se surface polarity; if the circularly polarized light current increases linearly with the increase of the gate voltage, it is explained that Bi 2 O 2 The initial surface polarity of Se is Bi atom cut-off, and the initial surface is positively charged; if the amplitude of the circularly polarized light current is reduced to 0 along with the grid voltage, and then the circularly polarized light current is continuously and reversely increased after the sign is reversed, the Bi is indicated 2 O 2 The initial surface polarity of Se is the Se atom cutoff, and the initial surface is negatively charged. The method is accurate in measurement, simple and easy to operate, does not damage the surface of the sample, and is widely applicable to materials with polarity and spin orbit coupling on the surface.
Description
Technical Field
The invention relates to the field of spintronics, in particular to a circularly polarized light current distinguishing two-dimensional Bi 2 O 2 A method for polarity of Se surface.
Background
Bi 2 O 2 Se is used as a layered two-dimensional material with high mobility, has proper band gap, super-large light response rate and super-fast response speed, and has excellent development potential in the field of photoelectric devices. And, it shows super high water oxygen stability, has very big advantage in practical application. In addition, bi was found by low temperature magnetic transport measurement 2 O 2 The strong spin-orbit coupling effect exists in Se, which is found as Bi 2 O 2 Se lays a foundation for research in the fields of spintronics and spin-optic devices.
Bi 2 O 2 Se is a typical layered oxidized chalcogenide. The crystal structure of which is compensated by cations (Bi 2 O 2 ) n 2n+ And anions (Se) n 2n- Alternate stacking composition, maintaining the layered structure with weak electrostatic interactions. In two dimensions Bi 2 O 2 In the growth process of Se, the development mode is that the Se grows layer by layer, so that the surface of the outermost layer is cut off by a positively charged Bi layer or a negatively charged Se layer, which is Bi 2 O 2 The Se surface incorporates different surface polarities. Opposite surface polarity causes surface energy bands in different directions to bend, different forms of Rashba type surface states are introduced between band gaps, and the Rashba spin-orbit coupling coefficients are opposite, so that Bi with two surface cut-off types 2 O 2 Se has a different surface electron band structure and the circularly polarized light current produced by Se is opposite in direction. Due to Bi 2 O 2 In the surface growth process of Se, the cut-off type is random, and the cut-off type of Se surface is judged to be a difficult point, and Bi is treated 2 O 2 Se presents challenges in the study of spintronics.
Disclosure of Invention
The invention aims to provide a circularly polarized light current distinguishing two-dimensional Bi 2 O 2 The Se surface polarity method is accurate in measurement, simple and feasible, and wide in application range.
In order to achieve the above purpose, the invention adopts the following technical scheme:circularly polarized light current distinguishing two-dimensional Bi 2 O 2 A method of Se surface polarity comprising the steps of:
step S1: growth of Bi by chemical vapor deposition on substrates in a tube furnace 2 O 2 Se nanoplatelets;
step S2: manufacturing a contact electrode on the nano-sheet by ultraviolet lithography and thermal evaporation technology, and manufacturing a gate electrode at a position with a set distance from the nano-sheet;
step S3: arranging an annular support on a substrate so as to form a groove on the surface of the nano sheet, wherein the groove covers the whole nano sheet and part of gate electrode, adding ionic liquid into the groove, covering a cover glass for packaging, and forming a test structure; the ionic liquid covers the whole nano-sheet surface and is contacted with the gate electrode, and the gate electrode applies gate voltage to the nano-sheet surface through the ionic liquid;
step S4: setting up an experimental light path: the laser source emits laser and sequentially passes through the chopper, the optical attenuation sheet, the polarizer and the quarter wave plate; polarized light is focused through a lens and irradiates on the nano sheet of the test structure to form light spots; aligning the positions of the light spots through the micro-distance camera to enable the micro-distance camera to completely cover the nano-sheets;
step S5: inputting photocurrent collected by the contact electrode into a pre-amplifier, inputting the photocurrent into a lock-in amplifier by the pre-amplifier, and inputting a signal of the lock-in amplifier into a data acquisition card and acquiring the signal by a computer; applying a gate voltage through an electrometer, the electrometer being grounded in common with the preamplifier;
step S6: bi test at room temperature 2 O 2 Photocurrent in Se nano sheet changes angle along with quarter wave plate
Extracting the C value of circularly polarized light current;
step S7: applying a grid voltage of 0 to-2V, repeating the step S6 every time the grid voltage is increased by a set value, recording the extracted C value, and observing the change trend of the C along with the grid voltage; if the C value increases linearly with the increase of the gate voltage, it is explained that Bi 2 O 2 The initial surface polarity of Se isThe Bi atoms are blocked, and the initial surface of the Bi atoms is positively charged; if the C value is reduced to 0 along with the gate voltage, and is increased reversely after the sign is reversed, the Bi is indicated 2 O 2 The initial surface polarity of Se is the Se atom cutoff, and the initial surface is negatively charged.
Further, in the step S1, bi 2 O 2 The Se nano sheet has a medium single crystal structure and has a thickness of 5-50 nanometers.
Further, in the step S3, the ring-shaped support is a polycarbonate support, the polycarbonate support and the substrate are sealed by epoxy resin, and the polycarbonate support and the cover glass are also sealed by epoxy resin, so that the whole test structure is sealed.
Further, in the step S4, the laser light source uses a diode pumped solid state laser with a wavelength of 1064nm.
Further, in the step S4, the laser power is 100mW, the diameter of the light spot is smaller than 100 μm, the laser is incident from the x-z plane, the incident angle is 30 °, and the photocurrent is measured in the x direction; the polarization direction of the polarizer was 45 deg. from the horizontal, and the frequency of the chopper was set to 229Hz.
Further, in the step S5, the reference frequency of the lock-in amplifier is 229Hz, which is consistent with the chopper.
Further, in the step S6, bi is measured at room temperature 2 O 2 Photocurrent in Se nano sheet changes angle along with quarter wave plate
Extracting circularly polarized light current through the following unique image formula;
wherein ,
representing the circularly polarized current HDPC induced component; />
Item and->
Photocurrent components derived from the linearly polarized photovoltaic effect and the linearly polarized photovoltaic dragging effect; j (J) 0 Representing a photocurrent component independent of polarization, induced by a linearly polarized photovoltaic effect, a photon drag effect, a thermoelectric effect, a photovoltaic effect, and a dander effect; and obtaining circularly polarized light current C through fitting.
Further, in the step S7, the ionic liquid grid is used for applying the grid voltage instead of the solid dielectric layer.
Compared with the prior art, the invention has the following beneficial effects: provides a circularly polarized light current-differentiated two-dimensional Bi 2 O 2 Method for testing the polarity of Se surface by testing Bi 2 O 2 The variation trend of the circularly polarized light current of the Se nano sheet along with the grid voltage of the ionic liquid can simply distinguish two-dimensional Bi 2 O 2 Se surface polarity and no damage to the sample surface. The invention has accurate measurement result, is simple and easy to operate, has low cost, and is widely applicable to materials with polar surfaces and spin orbit coupling.
Drawings
FIG. 1 shows Bi in the embodiment of the present invention 2 O 2 Schematic diagram of experimental apparatus for Se nano sheet growth.
FIG. 2 is a schematic diagram of a test structure in an embodiment of the invention.
FIG. 3 is a schematic diagram of a circularly polarized light circuit and a testing system according to an embodiment of the invention.
FIG. 4 is a graph of photocurrent versus quarter wave plate rotation angle and a fitted polarization dependent photocurrent component in an embodiment of the present invention.
Fig. 5 is a graph showing the variation of the amplitude of the circularly polarized light current with the grid voltage of the ionic liquid according to the embodiment of the present invention, where the inset shows the situation that the surface of the ionic liquid grid has curvature and the polarity of the surface charge accumulation layer.
Detailed Description
The invention will be further described with reference to the accompanying drawings and examples.
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present application. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments in accordance with the present application. As used herein, the singular is also intended to include the plural unless the context clearly indicates otherwise, and furthermore, it is to be understood that the terms "comprises" and/or "comprising" when used in this specification are taken to specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof.
The embodiment provides a circularly polarized light current distinguishing two-dimensional Bi 2 O 2 A method of Se surface polarity comprising the steps of:
step S1: growth of Bi by chemical vapor deposition on substrates in a tube furnace 2 O 2 Se nanoplatelets.
wherein ,Bi2 O 2 The Se nano sheet has a single crystal structure and the thickness is between 5 and 50 nanometers.
In this example, the substrate used for growth was a high quality, high flatness mica substrate having a specification of 1.5X2 cm; the mica top surface was peeled off by mechanical peeling prior to use to give a freshly cleaved clean surface. The evaporation source used is Bi with the purity of 99.999 percent 2 Se 3 Powder and 99.999% Bi 2 O 3 Powder, 0.02g and 0.04g were weighed separately and placed at both ends of a quartz boat 10cm long. The mica substrate was also placed in a furnace, and its schematic placement is shown in fig. 1. Wherein Bi is 2 O 3 Is positioned at the very center of the heating temperature zone of the tube furnace, bi 2 Se 3 The powder was 8cm upstream of the center position, the left edge of the mica substrate was 10.5cm downstream of the center position, bi 2 O 2 The growth sites of Se nanoplates appear in11cm to 11.5cm downstream of the heart zone as shown in FIG. 1.
Before raising the temperature of the furnace area, the tube furnace needs to be subjected to a gas washing operation to remove redundant oxygen in the growing environment. The specific operation is to pump the tube to vacuum (0.5 Pa), then fill high purity argon to standard atmospheric pressure, repeat this step 3-5 times. Argon is used as a growth carrier gas, and the gas flow rate is controlled to be 200sccm; the pressure in the furnace is kept at 450-500 torr by controlling the fine tuning valve. Subsequently, setting a heating parameter, and firstly setting the temperature to be increased to 680 ℃ from the room temperature at a heating rate of 25 ℃/min; thereafter, the temperature was maintained at 680℃for twenty minutes. And taking out the grown sample after the furnace temperature is reduced to room temperature.
The grown sample was approximately 100 μm in size and 25nm thick.
Step S2: and manufacturing a contact electrode on the nano-sheet by ultraviolet lithography and thermal evaporation technology, and manufacturing a gate electrode at a position which is 1mm away from the nano-sheet.
In this embodiment, the ultraviolet lithography process and the electrode manufacturing method are as follows: firstly, spin-coating negative photoresist on the surface of a sample, wherein spin-coating parameters are 5000r/min and 150s; then, pre-baking for 120s at the temperature of 85 ℃; then, aligning the positions of the nano-sheets and the mask under a microscope, and performing accurate exposure, wherein the exposure time is 9.8s; subsequently, post-baking for 120s at 110 ℃; developing the exposed sample for 60s; and finally, cleaning the sample by deionized water to remove the residual developing solution on the surface.
After photolithography, 100nm of gold was evaporated on the sample surface by thermal evaporation technique, and the gas pressure in the chamber during evaporation was maintained at 10 -5 Pa. Finally, the sample is soaked in special photoresist removing solution to remove photoresist, the nano-sheet and the electrode pattern are exposed, and then the photoresist removing solution is cleaned by deionized water. The channel width of the device was 20 μm, and a gate electrode 1mm away from the sample was fabricated in the vicinity of the contact electrode. After the gold electrode is manufactured, the electrode is led out through silver paste and silver wires, and the silver paste is solidified by thermal annealing for 120min under the vacuum condition of 120 ℃ to enhance contact.
Step S3: arranging an annular support on a substrate so as to form a groove on the surface of the nano sheet, wherein the groove covers the whole nano sheet and part of the gate electrode; the grooves are filled with ionic liquid and covered with a cover glass for packaging, so that a test structure is formed, as shown in fig. 2. The ionic liquid covers the whole nano-sheet surface and is contacted with the gate electrode, and the gate electrode applies gate voltage to the nano-sheet surface through the ionic liquid. The manufacturing process ensures that the entire test structure is sealed.
In this embodiment, the annular support is a polycarbonate support, the polycarbonate support is sealed with the substrate by epoxy resin, and the polycarbonate support is also sealed with the cover glass by epoxy resin, so as to realize the sealing of the whole test structure.
Step S4: setting up an experimental light path: the laser light source emits laser, which sequentially passes through the chopper, the optical attenuation sheet, the gram taylor prism (polarizer) and the quarter wave plate. The quarter wave plate rotates to change the polarization of light, so that the polarization of light is periodically changed from linear polarized light to left-handed polarized light to linear polarized light to right-handed polarized light. Polarized light is focused by a lens and irradiates on the nano-sheet of the test structure to form a light spot. The micro-camera is aligned to the spot position to enable the light spot to completely cover and irradiate Bi 2 O 2 Se nanoplatelets, as shown in fig. 3.
In this embodiment, the laser light source uses a diode pumped solid state laser with a wavelength of 1064nm. The laser power is 100mW, the diameter of a light spot is smaller than 100 mu m, the laser is incident from an x-z plane, the incident angle is 30 degrees, and the photocurrent is measured in the x direction; the polarization direction of the polarizer was 45 deg. from the horizontal, and the frequency of the chopper was set to 229Hz. The magnification of the macro camera is 1000.
Step S5: inputting photocurrent collected by the contact electrode into a pre-amplifier, inputting the photocurrent into a lock-in amplifier by the pre-amplifier, and inputting a signal of the lock-in amplifier into a data acquisition card and acquiring the signal by a computer; the gate voltage is applied by an electrometer, which is common to the preamplifier.
In this embodiment, the reference frequency of the lock-in amplifier is 229Hz, consistent with the chopper.
Step S6: bi test at room temperature 2 O 2 Photocurrent in Se nanoplatelets is quarter-dependentOne-wave plate corner
And extracting the circularly polarized light current C value.
In this example, bi was measured at room temperature 2 O 2 Photocurrent in Se nano sheet changes angle along with quarter wave plate
The circularly polarized light current is extracted by the following unique formula as shown in fig. 4.
wherein ,
representing the circularly polarized current (HDPC) induced component; />
Item and->
Photocurrent components derived from the linearly polarized photovoltaic effect and the linearly polarized photovoltaic dragging effect; j (J) 0 Representing a photocurrent component irrelevant to polarization, and inducing the photocurrent component by a linearly polarized photovoltaic effect, a photon drag effect, a thermoelectric effect, a photovoltaic effect, a danmultiple effect and the like; and obtaining circularly polarized light current C through fitting.
Step S7: applying a grid voltage of 0 to-2V, repeating the step S6 every time the grid voltage is increased by 0.2V, recording the extracted C value, and observing the change trend of the C along with the grid voltage; if the C value increases linearly with the increase of the gate voltage, it is explained that Bi 2 O 2 The initial surface polarity of Se is Bi atom cut-off, and the initial surface is positively charged; if the C value is reduced to 0 along with the gate voltage, and is increased reversely after the sign is reversed, the Bi is indicated 2 O 2 The initial surface polarity of Se is Se atom cut-off, and the initial surface thereofNegatively charged.
In this embodiment, the ionic liquid gate is used to apply the gate voltage instead of the solid dielectric layer.
Circularly polarized light current determination Bi 2 O 2 The principle of initial surface polarity of Se is as follows: first, bi 2 O 2 Se has surface polarity, different energy band structures of different polarity surfaces, and has opposite Rashba spin orbit coupling coefficients, and the generated circular polarized light current has opposite photocurrent directions under the same irradiation condition. Secondly, the ionic liquid grid can effectively regulate the density and the surface energy band bending of electrons on the surface of a sample, and at the interface of the ionic liquid and the semiconductor, the ionic liquid grid can be regarded as a nanoscale gap capacitor with huge capacitance, which can convert Bi into 2 O 2 The charge on the Se surface builds up to a high density that is not attainable with conventional solid gate dielectrics. Further, the ionic liquid gate can influence Rashba spin-splitting of electrons on the surface of the sample, so that the Rashba spin-splitting can be used for Bi 2 O 2 The circularly polarized light current generated by Se surface state is effectively regulated.
When a negative voltage is applied to the grid, cations in the ionic liquid move to the grid and are contained in Bi 2 O 2 Forming a positively charged charge accumulation layer on the Se surface, resulting in Bi 2 O 2 The surface energy band of Se is curved upward. If Bi is 2 O 2 The initial surface polarity of Se is positive (Bi cut-off surface), the intrinsic band bending is consistent with the influence of the grid, and the grid voltage can enhance Rashba spin splitting of surface electrons, namely the circular polarized light current is enhanced. If Bi is 2 O 2 The initial surface polarity of Se is negative (Se cut-off surface), and the surface electric field and the surface energy band bending caused by the ionic liquid grid are offset with the intrinsic energy band bending, so that the circularly polarized light current is reduced. When the influence of the surface electric field is larger than the influence of the intrinsic energy band bending, the Rashba spin orbit coupling coefficient is overturned, and the circularly polarized light current is in the opposite sign; further increasing the surface electric field, the circularly polarized light current increases with the enhancement of the Rashba spin-splitting caused by the electric field.
In this embodiment, as shown in fig. 5, the circularly polarized light current decreases for negative grid voltage, and increases continuously after the sign is turned over, which means that the initial polarity of the surface of the sample is negative, and the Se atomic layer is cut off, and the intrinsic surface energy band bends downwards. The inset shows the ionic liquid grid with surface curvature and polarity of the surface charge accumulation layer.
In conclusion, the invention provides a simple and easy-to-operate method, which distinguishes two-dimensional Bi by judging the variation trend of the amplitude of circularly polarized light current along with the ion liquid grid 2 O 2 Initial surface polarity and intrinsic band bending of Se material. Moreover, the method has the advantages of being generally applicable to spin-orbit coupling materials with surface polarity and being a nondestructive detection method.
It will be appreciated by those skilled in the art that embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flowchart illustrations and/or block diagrams, and combinations of flows and/or blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the invention in any way, and any person skilled in the art may make modifications or alterations to the disclosed technical content to the equivalent embodiments. However, any simple modification, equivalent variation and variation of the above embodiments according to the technical substance of the present invention still fall within the protection scope of the technical solution of the present invention.
Claims (8)
1. Circularly polarized light current distinguishing two-dimensional Bi 2 O 2 A method of Se surface polarity comprising the steps of:
step S1: growth of Bi by chemical vapor deposition on substrates in a tube furnace 2 O 2 Se nanoplatelets;
step S2: manufacturing a contact electrode on the nano-sheet by ultraviolet lithography and thermal evaporation technology, and manufacturing a gate electrode at a position with a set distance from the nano-sheet;
step S3: arranging an annular support on a substrate so as to form a groove on the surface of the nano sheet, wherein the groove covers the whole nano sheet and part of gate electrode, adding ionic liquid into the groove, covering a cover glass for packaging, and forming a test structure; the ionic liquid covers the whole nano-sheet surface and is contacted with the gate electrode, and the gate electrode applies gate voltage to the nano-sheet surface through the ionic liquid;
step S4: setting up an experimental light path: the laser source emits laser and sequentially passes through the chopper, the optical attenuation sheet, the polarizer and the quarter wave plate; polarized light is focused through a lens and irradiates on the nano sheet of the test structure to form light spots; aligning the positions of the light spots through the micro-distance camera to enable the micro-distance camera to completely cover the nano-sheets;
step S5: inputting photocurrent collected by the contact electrode into a pre-amplifier, inputting the photocurrent into a lock-in amplifier by the pre-amplifier, and inputting a signal of the lock-in amplifier into a data acquisition card and acquiring the signal by a computer; applying a gate voltage through an electrometer, the electrometer being grounded in common with the preamplifier;
step S6: bi test at room temperature 2 O 2 Photocurrent in Se nano sheet changes angle along with quarter wave plate
Extracting the C value of circularly polarized light current;
step S7: applying a grid voltage of 0 to-2V, repeating the step S6 every time the grid voltage is increased by a set value, recording the extracted C value, and observing the change trend of the C along with the grid voltage; if the C value increases linearly with the increase of the gate voltage, it is explained that Bi 2 O 2 The initial surface polarity of Se is Bi atom cut-off, and the initial surface is positively charged; if the C value is reduced to 0 along with the gate voltage, and is increased reversely after the sign is reversed, the Bi is indicated 2 O 2 The initial surface polarity of Se is the Se atom cutoff, and the initial surface is negatively charged.
2. A circularly polarized light current distinguishing two-dimensional Bi according to claim 1 2 O 2 A method for polarity of Se surface, characterized in that in the step S1, bi is contained in the mixture 2 O 2 The Se nano sheet has a single crystal structure and the thickness is between 5 and 50 nanometers.
3. A circularly polarized light current distinguishing two-dimensional Bi according to claim 1 2 O 2 A method for polarity of Se surface is characterized in that in the step S3, the annular support is a polycarbonate support, and theThe polycarbonate support and the substrate are sealed through epoxy resin, and the polycarbonate support and the cover glass are also packaged through the epoxy resin, so that the sealing of the whole test structure is realized.
4. A circularly polarized light current distinguishing two-dimensional Bi according to claim 1 2 O 2 The method for Se surface polarity is characterized in that in the step S4, a diode pump solid laser is adopted as a laser source, and the wavelength of the laser source is 1064nm.
5. A circularly polarized light current distinguishing two-dimensional Bi according to claim 1 2 O 2 The Se surface polarity method is characterized in that in the step S4, the laser power is 100mW, the diameter of a light spot is smaller than 100 mu m, the laser is incident from an x-z plane, the incident angle is 30 degrees, and the photocurrent is measured in the x direction; the polarization direction of the polarizer was 45 deg. from the horizontal, and the frequency of the chopper was set to 229Hz.
6. A circularly polarized light current distinguishing two-dimensional Bi according to claim 1 2 O 2 The method of Se surface polarity is characterized in that in the step S5, the reference frequency of the lock-in amplifier is 229Hz, which is consistent with the chopper.
7. A circularly polarized light current distinguishing two-dimensional Bi according to claim 1 2 O 2 A method for measuring the polarity of Se surface, characterized in that Bi is measured at room temperature in the step S6 2 O 2 Photocurrent in Se nano sheet changes angle along with quarter wave plate
Extracting circularly polarized light current through the following unique image formula;
wherein ,
representing the circularly polarized current HDPC induced component; />
Item and->
Photocurrent components derived from the linearly polarized photovoltaic effect and the linearly polarized photovoltaic dragging effect; j (J) 0 Representing a photocurrent component independent of polarization, induced by a linearly polarized photovoltaic effect, a photon drag effect, a thermoelectric effect, a photovoltaic effect, and a dander effect; and obtaining circularly polarized light current C through fitting.
8. A circularly polarized light current distinguishing two-dimensional Bi according to claim 1 2 O 2 A method for Se surface polarity, wherein in the step S7, the ionic liquid grid is used for applying the grid voltage instead of the solid dielectric layer.
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