Electronic control skyrmion motion method based on chiral nematic liquid crystal

Abstract

The invention provides an electronic control skyrmion movement method based on chiral nematic liquid crystal, which belongs to the field of optics, and comprises the following steps of: spin-coating an orientation layer on a glass plate plated with an electrode coating, and performing unidirectional orientation; secondly, preparing two glass plates which are placed in the same orientation direction into a liquid crystal box, and injecting chiral nematic liquid crystals into the liquid crystal box; a square wave electric field is applied to the electrode coating on the glass plate to generate the skyrmion, the motion direction of the skyrmion is changed by changing the bias voltage of the square wave electric field, and the motion speed of the skyrmion is changed by changing the bias voltage or the electric field frequency of the square wave electric field. According to the invention, motion in any direction and trajectory control of the skyrmion can be realized in a two-dimensional plane.

Description

Technical Field

[0001] The present invention belongs to the field of optics, and specifically relates to an electro-controlled skyrmion motion method based on chiral nematic liquid crystal. Background Art

[0002] Topologically protected skyrmions exhibit particle-like dynamical behaviors under an alternating electric field. The dynamical behaviors of these topological solitons play a key role in information transmission, storage, and computing. Skyrmions in a parallel-aligned liquid crystal cell exhibit more complex dynamical behaviors, such as turning, collision, and collective motion. However, it still faces challenges to achieve arbitrary motion direction control of skyrmions in a two-dimensional plane. On the one hand, for non-polar liquid crystals, the rotation direction of the director is independent of the direction of the applied electric field. Therefore, introducing spatial polarity is required to change the two-dimensional motion direction of skyrmions in a non-polar system. On the other hand, previous studies have only broken the topological structure symmetry of skyrmions in one dimension. To extend the motion control of skyrmions from one-dimensional linear motion to two-dimensional planar motion, the symmetry of its two-dimensional topological structure must be broken. Summary of the Invention

[0003] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide an electro-controlled skyrmion motion method based on chiral nematic liquid crystal, which can solve the limitation in the prior art that only the topological structure symmetry of skyrmions in one dimension can be changed, so as to achieve omnidirectional motion of skyrmions in a two-dimensional plane.

[0004] The present invention discloses an electro-controlled skyrmion motion method based on chiral nematic liquid crystal, and the method is as follows:

[0005] After a glass plate coated with an electrode coating is spin-coated with an alignment layer, unidirectional alignment is performed; then, two glass plates with the same alignment direction are prepared into a liquid crystal cell and injected with chiral nematic liquid crystal;

[0006] A square-wave electric field is applied to the electrode coating on the glass plate to generate skyrmions. The parameters of the square-wave electric field include a bias voltage, an electric field frequency, and an effective voltage; the motion direction of skyrmions is changed by changing the bias voltage of the square-wave electric field, and the motion speed of skyrmions is changed by changing the bias voltage or the electric field frequency of the square-wave electric field.

[0007] Further, the bias voltage of the square-wave electric field is represented by U b and ranges from -11V to 11V; the electric field frequency is 0 - 100Hz; the effective voltage value is 0 - 10V.

[0008] Further, the method for changing the motion direction of skyrmions by changing the bias voltage is:

[0009] When U b is set to 0V, the motion direction of skyrmions is downward motion;

[0010] When U b varies from 0 V to 11 V, the movement direction of the skyrmion rotates counterclockwise as U b increases, and becomes moving to the right when U b is 5 V, and becomes moving upward when U b is 11 V;

[0011] When U b varies from 0 V to -11 V, the movement direction of the skyrmion rotates clockwise as U b decreases, and becomes moving to the left when U b is -7.5 V, and becomes moving upward when U b is -11 V.

[0012] Furthermore, the method for changing the movement speed of the skyrmion by changing the bias voltage of the square-wave electric field is as follows:

[0013] Keeping the electric field frequency unchanged, the movement speed of the skyrmion is the maximum when the bias voltage is 0 V, and decreases as the absolute value of the bias voltage increases.

[0014] Furthermore, the method for changing the movement speed of the skyrmion by changing the electric field frequency of the square-wave electric field is as follows:

[0015] Keeping the bias voltage unchanged, for the movement speed of the skyrmion, as the electric field frequency increases, the movement speed of the skyrmion gradually decreases.

[0016] Furthermore, the preparation method of the chiral nematic liquid crystal is as follows: Dissolve the nematic liquid crystal and the chiral dopant in dichloromethane respectively and mix them together, perform ultrasonic treatment on the obtained solution in an ultrasonic cleaner, and heat and evaporate the dichloromethane solvent on a constant-temperature hot stage to obtain the chiral nematic liquid crystal.

[0017] Furthermore, when preparing the liquid crystal cell, stagger two glass plates and separate them with a curing glue in the middle to form the liquid crystal cell; the staggering distance between the two glass plates is 3 - 4 mm.

[0018] Furthermore, the electrode coating is an indium tin oxide coating; the alignment layer is a polyimide layer; the thickness of the liquid crystal cell is 6 - 7 μm; the curing glue is an ultraviolet curable glue doped with 6 μm silicon nanoparticles.

[0019] Furthermore, when applying a square-wave electric field to the electrode coating on the glass plate, the operation is carried out on a constant-temperature hot stage at 34 °C.

[0020] Beneficial effects:

[0021] 1) The method for electrically controlling skyrmion motion based on chiral nematic liquid crystals according to the present invention can achieve adjustable arbitrary motion directions of skyrmions in large-scale and small-scale ranges according to the range of the electric field and the alignment layer, and has prominent features such as easy fabrication, low cost, and simple structure. Compared with the existing methods, the method of the present invention can achieve the regulation of skyrmions in any direction within a two-dimensional plane without a complex electric field, and has the characteristics of large range and fast response speed regulation.

[0022] 2) The method of the present invention has advantages such as simplicity, high flexibility, and low price, and can achieve precise control of the trajectories of topological defects, providing new ideas for applications in the fields of information storage and nanorobots. Brief Description of the Drawings

[0023] Figure 1 It is a schematic flowchart of a method for electrically controlling skyrmion motion based on chiral nematic liquid crystals in an embodiment of the present invention;

[0024] Figure 2 It is a polarized light micrograph of the directional motion of skyrmions under different bias voltages;

[0025] Figure 3 It is the relationship between the bias voltage and the motion direction of skyrmions in Example 1; among them, (a) is the motion trajectory diagram of skyrmions in 8 representative directions under different bias voltages, and (b) is the relationship diagram between different bias voltages and the motion direction of skyrmions at 20 Hz;

[0026] Figure 4 It is the relationship between the bias voltage and frequency and the motion speed of skyrmions in Example 1; among them, (a) is the relationship between different bias voltages and the magnitude of the motion speed of skyrmions at 20 Hz, and (b) is the relationship between different frequencies and the motion speed of skyrmions under a 10 V voltage;

[0027] Figure 5 It is a sectional view and a color gradient trajectory diagram of skyrmions moving along the preset path "NJUPT" by changing the bias voltage in Example 2. Detailed Embodiment

[0028] The technical solution of the present invention will be described in detail below through examples and drawings, but the protection scope of the present invention is not limited to the described examples.

[0029] Example 1

[0030] The present invention provides a method for electrically controlling skyrmion motion in chiral nematic liquid crystals. The flowchart of the method of the present invention is as Figure 1 shown, and includes the following steps:

[0031] S1. Prepare chiral nematic liquid crystals;

[0032] The liquid crystal phase used is chiral nematic phase, the orientation mode is friction orientation, the dual-frequency nematic liquid crystal used is DP002-026 (purchased from Jiangsu Hecheng Display Technology Co., Ltd.), and the chiral dopant is S811 (purchased from Nanjing Leyao Technology Co., Ltd.). The mass fractions of DP002-026 and S811 are 97wt% and 3wt%, respectively, the working temperature of the ultrasonic cleaning machine is 34°C, and the hot stage temperature for evaporating the dichloromethane solvent is 108°C.

[0033] The specific operation is as follows: the nematic liquid crystal and the chiral dopant are dissolved in dichloromethane respectively and mixed together, the resulting solution is thoroughly ultrasonicated in an ultrasonic cleaning machine for 20 minutes, and the dichloromethane solvent is heated on a constant temperature hot plate to evaporate.

[0034] S2, making a liquid crystal box; the steps of making a liquid crystal box are:

[0035] S2.1. Prepare glass plates. Spin-coat the orientation layer on two glass plates coated with electrode coatings. After vacuum drying, perform unidirectional orientation treatment. The orientation method is friction orientation.

[0036] In this embodiment, the electrode coating is a transparent electrode coating, specifically an indium tin oxide coating. The resistivity of these electrodes is between 10 and 50 Ω / sq. The alignment layer includes polyimide PI-2555 (purchased from Nanjing Ningcui Optical Technology Co., Ltd.).

[0037] The specific operation is as follows: spin-coat polyimide on a glass plate (20 mm long × 20 mm wide × 1.1 mm high) coated with a transparent indium tin oxide (ITO) coating, dry it in a vacuum drying oven at 120°C for 5 minutes, heat it to 220°C and dry it for 20 minutes before taking it out; lay the glass plate spin-coated with a parallel orientation layer flat on an orientation table and use an orientation cloth for unidirectional orientation.

[0038] S2.2, stagger the two glass plates and separate them with curing glue to form a liquid crystal box;

[0039] Specifically, the two glass plates are combined into a liquid crystal box. The two glass plates are oriented in the same direction and are staggered by 3 to 4 mm to the left and right to facilitate the exposure of the ITO coating for applying an electric field. The upper and lower parts are separated by ultraviolet light-curing glue doped with 6-micron silicon nanoparticles to control the box thickness (6 to 7 μm). The thickness of the liquid crystal box finally formed in this embodiment is 6.7 μm.

[0040] The specific operation is as follows: stagger the two glass plates by 3 to 4 mm; add UV curing glue doped with 6 μm silicon nanoparticles to the opposite sides of the two glass plates (the side coated with the orientation layer); and irradiate with a 365nm UV light source to cure the glue.

[0041] S3. Use capillary action on a thermostatic hot stage to pour the chiral nematic liquid crystal into the liquid crystal cell;

[0042] The specific operation is as follows: Heat the chiral nematic liquid crystal on a thermostatic hot stage to a transparent state. The temperature of the thermostatic hot stage is 120 °C. When the hot stage is heated to 120 °C, the liquidity of the liquid crystal is relatively large, making it easy to enter the liquid crystal cell and form a uniform liquid crystal layer. Then, use a glass capillary to suck up the liquid crystal and pour the liquid crystal into the liquid crystal cell from the side on the thermostatic hot stage by capillary action to form a uniform liquid crystal layer.

[0043] S4. Apply an electric field to the electrode coatings on both sides of the liquid crystal cell on a thermostatic hot stage to generate skyrmions, regulate the movement speed and direction of the skyrmions by changing the bias voltage, and acquire and record the data of the movement speed and direction of the generated skyrmions. The specific operation method is as follows:

[0044] Use a signal generator to generate a square wave voltage; use a signal amplifier to amplify the voltage signal and then apply an electric field to the electrode coating of the liquid crystal cell. The signal generator is selected as RIGOL DG4162; the voltage amplifier is selected as Aigtek ATA - 2041. For the generated square wave electric field, its electric field frequency is 0 - 2000 Hz, the effective voltage is 0 - 10 V, and the bias voltage is - 11 - 11 V.

[0045] After adjusting to the preset voltage and frequency, by fixing the effective voltage and the electric field frequency and only changing the bias voltage, regulate the movement direction of the skyrmions; changing the magnitude of the bias voltage can destroy the symmetry of the two - dimensional topological structure of the skyrmions, resulting in skyrmions being pushed in different directions and making the skyrmions move in all directions. Fix the effective voltage and the bias voltage and only change the electric field frequency to regulate the movement speed of the skyrmions.

[0046] During the regulation process, use a high - speed camera to record the trajectories of the skyrmions and analyze to obtain the speed and movement direction of the skyrmions.

[0047] Specific operations of S4:

[0048] 1) Place the liquid crystal cell on a thermostatic hot stage at 34 °C and wait for 5 min for the temperature to stabilize. Apply a square wave electric field on both sides. When the effective voltage = 10 V and the bias voltage = 0 V, the background becomes completely black under a polarized light microscope. At this time, the skyrmions move downward, and set this direction as the initial direction. △

[0049] 2) Keep the effective voltage = 10V, set the electric field frequency to 20Hz, adjust the bias voltage from -11 to 11V, adjust and record the skyrmion motion video at every 1V interval, and use matlab (MATrix LABoratory, a high-level technical computing language and interactive environment for numerical calculation and data visualization) and Imagej (an open-source image processing and analysis software) to analyze the influence of different bias voltages on the skyrmion motion direction. The results are as Figure 2 and Figure 3 shown.

[0050] Figure 2 Figure is the polarized light micrograph of the directional movement of skyrmions in 8 representative directions under different bias voltages in Example 1. It can be seen from the figure that the skyrmion motion directions are different under different bias voltages; Figure 3 Figure Figure 3 is the schematic diagram and relationship diagram of different bias voltages and skyrmion motion directions. From Figure 3 it can be seen that the skyrmion motion directions are different under different bias voltages, and the skyrmions can be regulated to any motion angle under the corresponding bias voltages.

[0051] Figure 2 In Figure 3 and b U represents the bias voltage, and v represents the skyrmion motion direction.

[0052] Figure 3 In

[0053] Figure 3 (a), Δχ represents the displacement distance of the skyrmion relative to the initial position at different times. b In b (b), a represents the angle between the skyrmion motion direction and the skyrmion motion direction when U

[0054] From Figure 2 and Figure 3 it can be known that when U b is set to 0V, the skyrmion motion direction is downward;

[0055] When U b changes from 0V to 11V, the skyrmion motion direction rotates counterclockwise as U b increases, becomes rightward when Ub is 5V, and becomes upward when Ub is 11V;

[0056] When U b changes from 0V to -11V, the skyrmion motion direction rotates clockwise as U b decreases, becomes leftward when U b is -7.5V, and becomes downward when U bWhen it is -11V, it moves upward.

[0057] 3) Keep the effective voltage = 10V, the electric field frequency is 20Hz, adjust the bias voltage from –11 to 11V, and obtain the relationship between the skyrmion motion speed and the bias voltage. The results are as Figure 4 shown in (a) below.

[0058] From Figure 4 It can be seen from (a) that the skyrmion speed reaches the maximum when the bias voltage is 0V, and decreases as the absolute value of the bias voltage increases.

[0059] 4) Keep the effective voltage = 10V, the bias voltage is 0V, adjust the electric field frequency from 10Hz to 2000Hz, and obtain the relationship between the skyrmion motion speed and the electric field frequency. The results are as Figure 4 shown in (b) below

[0060] From Figure 4 It can be seen from (b) that as the electric field frequency f increases, the skyrmion motion speed gradually decreases, and the decreasing trend is obvious in the range of 10Hz to -100Hz; after exceeding 1000Hz, because the response time of the nematic director is on the order of dozens of milliseconds and cannot effectively respond to the kHz-level frequency field, the decreasing trend of the speed slows down.

[0061] Therefore, by jointly adjusting the bias voltage and frequency, the motion speed of the skyrmion can be effectively controlled.

[0062] Example 2

[0063] A method for electrically controlling skyrmion motion in a cholesteric liquid crystal, comprising the following steps:

[0064] Prepare the cholesteric liquid crystal and the liquid crystal cell according to the methods of S1-S3 in Example 1, and pour the cholesteric liquid crystal into the liquid crystal cell.

[0065] Use a signal generator to generate a square wave voltage; use a signal amplifier to amplify the voltage signal and apply an electric field to the electrode coating of the liquid crystal cell; the signal generator is selected as RIGOL DG4162; the voltage amplifier is selected as Aigtek ATA-2041. Place the liquid crystal cell on a constant temperature hot stage at 34°C and wait for 5 min for the temperature to stabilize. Apply a square wave electric field on both sides, with the effective voltage U rms = 10V and the bias voltage U bias = 0V. The background becomes completely black under a polarizing microscope. At this time, the skyrmion moves downward, which is set as the initial direction.

[0066] The signal generated by a signal generator is controlled by a Labview (graphical programming environment) program to achieve program control of the movement direction of skyrmions. This method can achieve the generation of complex trajectories, such as forming the letters "NJUPT", as Figure 5 shown.

[0067] Figure 5 Figs. to Figure 5 are sectional views and color gradient trajectory diagrams of the complex trajectory movement of skyrmions regulated by controlling the signal generator through a program in Example 2.

[0068] Figure 5 (a) in Fig. Figure 5 is a sectional view of the positions of skyrmions at different times, Figure 5 (b) in Fig. is the movement trajectory diagram of skyrmions.

[0069] The polarized light microscope light passes through a polarizer, a liquid crystal cell, and an analyzer in sequence and then enters the camera to obtain a polarized light micrograph. The shape and position information of skyrmions in the polarized light micrographs at different times are superimposed to obtain a sectional view of the positions of skyrmions at different times, that is, Figure 5 (a) in Fig. Figure 5 , where the transmission axis of the analyzer is perpendicular to the transmission axis of the polarizer. The coordinate position information of skyrmions at different times is obtained through ImageJ, and the position information is plotted by Matlab and given a gradient effect according to time to obtain a color gradient trajectory diagram, that is, Figure 5 (b) in Fig. .

[0070] The method for electrically controlling skyrmion movement based on chiral nematic liquid crystals in the present invention can achieve adjustable movement directions of skyrmions in any direction in a large-scale range and a small-scale range according to the range of the electric field and the alignment layer, and has prominent characteristics such as easy fabrication, low cost, and simple structure; compared with the existing methods, the method of the present invention can achieve the regulation of skyrmions in any direction in a two-dimensional plane, without a complex electric field, and has the characteristics of large-range and fast-response regulation.

[0071] The method of the present invention has the advantages of simplicity, high flexibility, and low price, etc., and can achieve precise control of the trajectories of topological defects, providing new ideas for applications in the fields of information storage and nanorobots.

[0072] As described above, although the present invention has been shown and described with reference to specific preferred embodiments, it should not be construed as a limitation to the present invention itself. Various changes can be made to it in form and detail without departing from the spirit and scope of the present invention.

Claims

1. An electro-controlled skyrmion motion method based on chiral nematic liquid crystal, characterized in that After a glass plate coated with an electrode coating is spin-coated with an alignment layer, unidirectional alignment is performed; then, two glass plates with the same alignment are placed together to prepare a liquid crystal cell and injected with chiral nematic liquid crystal. A square-wave electric field is applied to the electrode coating on the glass plate to generate skyrmions. The parameters of the square-wave electric field include a bias voltage, an electric field frequency, and an effective voltage; the motion direction of the skyrmions is changed by changing the bias voltage of the square-wave electric field, and the motion speed of the skyrmions is changed by changing the bias voltage or the electric field frequency of the square-wave electric field.

2. The exercise method according to claim 1, wherein The bias voltage of the square-wave electric field is represented by U b and ranges from -11V to 11V; the electric field frequency is 0 to 100Hz; the effective value of the voltage is 0 to 10V.

3. The exercise method according to claim 1, wherein, The method of changing the motion direction of the skyrmions by changing the bias voltage is: Set U b to 0 V, the moving direction of the skyrmion is downward; When U b varies from 0 V to 11 V, the movement direction of the skyrmion rotates counterclockwise as U b increases, and changes to moving right when U b is 5 V, and changes to moving upward when U b is 11 V; When U b varies from 0 V to -11 V, the movement direction of the skyrmion rotates clockwise as U b decreases. When U b is -7.5 V, it changes to move left, and when U b is -11 V, it changes to move upward.

4. The exercise method according to claim 1, wherein, The method of changing the motion speed of the skyrmions by changing the bias voltage of the square-wave electric field is: Keeping the electric field frequency unchanged, the motion speed of the skyrmions is the maximum when the bias voltage is 0V, and decreases with the increase of the absolute value of the bias voltage.

5. The exercise method according to claim 1, wherein The method of changing the motion speed of the skyrmions by changing the electric field frequency of the square-wave electric field is: Keeping the bias voltage unchanged, the motion speed of the skyrmions gradually decreases as the electric field frequency increases.

6. The exercise method according to claim 1, characterized in that, The preparation method of the chiral nematic liquid crystal is as follows: the nematic liquid crystal and the chiral dopant are respectively dissolved in dichloromethane and mixed together, and the obtained solution is ultrasonically treated in an ultrasonic cleaner, and the dichloromethane solvent is evaporated by heating on a constant-temperature hot stage.

7. The exercise method according to claim 1, wherein When preparing the liquid crystal cell, the two glass plates are staggered and separated by a curing glue in the middle to form the liquid crystal cell.

8. The exercise method according to claim 7, characterized in that, The electrode coating is an indium tin oxide coating; the alignment layer is a polyimide layer; the thickness of the liquid crystal cell is 6-7 μm; the curing glue is an ultraviolet-curable glue doped with 6 μm silicon nanoparticles.

9. The exercise method according to claim 1, characterized in that, When applying a square-wave electric field to the electrode coating on the glass plate, the operation is carried out on a constant-temperature hot stage at 34°C.

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