Method for modulating the direction of piezoelectric effect of two-dimensional material by argon ion irradiation and application thereof

Abstract

The application discloses a method for modulating the direction of piezoelectric effect of a two-dimensional material based on argon ion irradiation and application thereof. First, two-dimensional materials with different thicknesses are transferred to a substrate; then, the two-dimensional materials are exposed to an argon ion irradiation source, the dose of the argon ion irradiation source is changed, and the direction of piezoelectric effect of the two-dimensional materials is modulated based on the argon ion irradiation technology. The application modulates the direction of piezoelectric effect of the two-dimensional materials through ion irradiation, obtains the relationship between the voltage applied to the two-dimensional materials with different thicknesses on the substrate and the amplitude, and effectively obtains the piezoelectric coefficient of the two-dimensional materials by applying a piezoelectric force microscope technology. The direction of piezoelectric effect of the two-dimensional materials is modulated through ion irradiation, the application of the two-dimensional materials in the field of thin electromechanical coupling devices is promoted, and the direction of piezoelectric effect can be modulated according to actual requirements.

Description

Technical Field

[0001] This invention relates to piezoelectric materials, and more specifically to a method for modulating the direction of the piezoelectric effect in two-dimensional materials based on argon ion irradiation and its application. Background Technology

[0002] The piezoelectric effect, proposed by the Curie brothers in 1880, is defined as the ability of matter to convert mechanical stimuli into electrical signals. The piezoelectric phenomenon in two-dimensional (2D) materials represents a milestone in the further development of low-dimensional structures. Research on the piezoelectric effect using 2D piezoelectric materials as a model system is attracting increasing attention, demonstrating broad application prospects and providing tremendous opportunities for various fields such as electronics, optoelectronics, energy harvesting, sensors, actuators, and biotechnology.

[0003] Two-dimensional piezoelectric materials are becoming increasingly important for several reasons: (1) When the thickness is reduced to the atomic layer, many non-piezoelectric crystals exhibit piezoelectric properties in two-dimensional structures by breaking symmetry; (2) Compared with bulk crystals, two-dimensional materials have better mechanical properties and can withstand larger strains, making them more suitable for flexible and wear-resistant piezoelectric electronic devices; (3) Two-dimensional materials have multifaceted properties and can be assembled layer by layer to form van der Waals heterostructures, which are expected to bring about richer new phenomena and applications based on piezoelectric properties. 2D piezoelectric materials have unique and unprecedented properties that are not found in other forms. For a long time, the focus of piezoelectric material research has been to seek material systems with larger piezoelectric coefficients, but the sign of the piezoelectric coefficient and the direction of the piezoelectric effect have often been neglected. Summary of the Invention

[0004] To improve the performance of two-dimensional piezoelectric materials or endow them with new properties, this invention provides a method and its application for modulating the piezoelectric effect direction of two-dimensional materials based on argon ion irradiation. By transferring the two-dimensional material to a substrate and then subjecting it to argon ion irradiation, not only can the stable modulation of the piezoelectric effect direction be achieved, but the piezoelectric coefficient value can also be effectively improved, thereby enhancing the piezoelectric performance of the obtained two-dimensional material or even endowing it with new properties, which is very beneficial for its application in thin electromechanical coupling devices.

[0005] The technical solution adopted in this invention is as follows:

[0006] A method for modulating the piezoelectric effect orientation of two-dimensional materials based on argon ion irradiation includes the following steps:

[0007] (1) Transfer or grow two-dimensional materials with different thickness gradients onto a substrate and expose the two-dimensional material nanosheets to an argon ion irradiation source;

[0008] (2) Based on piezoelectric microscopy (PFM), the direction of the piezoelectric effect and the piezoelectric coefficient of two-dimensional nanosheets before and after argon ion irradiation under different thickness gradients were characterized.

[0009] Furthermore, the piezoelectric coefficient includes out-of-plane piezoelectric coefficient and in-plane piezoelectric coefficient.

[0010] Furthermore, the two-dimensional material is mechanically peeled into layers before transfer or growth.

[0011] Furthermore, in step (2), the method for characterizing the piezoelectric coefficient includes the following steps:

[0012] 1) Amplitude data of two-dimensional material nanosheets under different AC voltages were obtained by piezoelectric force microscopy (PFM).

[0013] 2) Amplitude data of two-dimensional material nanosheets of different thicknesses were obtained using PFM;

[0014] 3) Determine the piezoelectric coefficient d of the two-dimensional material nanosheet on the substrate based on the data obtained in steps 1) and 2). 33 .

[0015] Using PFM for testing can avoid direct contact between the substrate and the test platform, thus avoiding experimental errors caused by contact between the transition layer or substrate and the test platform.

[0016] Furthermore, in step (2), the method for characterizing the direction of the piezoelectric effect includes the following steps:

[0017] Argon ion irradiation was used to modulate the piezoelectric effect direction of two-dimensional materials. By adjusting the flux rate and flux of ion irradiation, the defect concentration, number of intercalated atoms, and dopant atoms in the two-dimensional materials were controlled, and the changes in the piezoelectric effect direction of the two-dimensional materials before and after irradiation were recorded.

[0018] Ion irradiation can induce displacement effects in two-dimensional nanosheets, thereby causing crystal defects. Meanwhile, piezoelectric and photoelectric effects, as well as piezoresistive effects, also have some influence.

[0019] Furthermore, the argon ion irradiation flux is 0-14 × 10⁻⁶. 13 cm -2 The inventors discovered during their research that the irradiation source is crucial; appropriate doses of low-energy argon ion irradiation can introduce beneficial defects into two-dimensional materials, thereby enhancing their piezoelectric properties.

[0020] Furthermore, the two-dimensional material is any one or more of group II oxides, group II vanadates, metal disulfides, and InP.

[0021] Furthermore, the two-dimensional material is a single-layer or two-layer or more two-dimensional layered material composed of one or more of In2Se3, MoS2, Al2Se3, CdS, Ga2S3, Ga2Se3, Ga2Te3, In2S3, and In2Te3, or a single-layer or two-layer or more two-dimensional layered material composed of one or more of Co, Fe, or Mn-doped In2Se3, Al2S3, Al2Se3, CdS, Ga2S3, Ga2Se3, MoS2, In2S3, and In2Te3.

[0022] Furthermore, the thickness of the two-dimensional material nanosheet is 20-100 nm, and the lateral two-dimensional surface size is larger than the thickness size. <100 nm is considered ultrathin, in which case the substrate clamping effect can play a major role. When the thickness exceeds 100 nm, the substrate clamping effect weakens, and the piezoelectric coefficient tends to a stable value.

[0023] The two-dimensional material obtained by the above method can exhibit good piezoelectric properties when applied to thin electromechanical coupling devices.

[0024] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0025] This invention transfers an ultrathin two-dimensional material onto a substrate and combines this with argon ion irradiation; then, by using PFM to obtain the relationship between the thickness of the two-dimensional material on the substrate, the applied voltage, and the amplitude, it can effectively obtain the piezoelectric coefficient d of the ultrathin two-dimensional material. 33 By controlling the flux rate of argon ion irradiation, the defect concentration, intercalation atom number, and doping atom number in two-dimensional materials, the direction of the piezoelectric effect can be adjusted, thereby improving the piezoelectric properties of two-dimensional materials and even endowing them with new properties. When applied to thin electromechanical coupling devices, it can achieve good technical results. Attached Figure Description

[0026] Figure 1 As the argon ion irradiation flux increases, the vertical piezoelectric constant d... 33 The numerical variation graph;

[0027] Figure 2 The graph shows the numerical variation of LPFM (in-plane piezoelectric response force microscopy) amplitude as the argon ion irradiation dose increases. Detailed Implementation

[0028] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but the present invention is not limited thereto.

[0029] Example 1

[0030] A method for modulating the piezoelectric effect orientation of two-dimensional materials based on argon ion irradiation includes the following steps:

[0031] (1) The selected two-dimensional material is α-In2Se3. As a typical two-dimensional piezoelectric material, α-In2Se3 has outstanding piezoelectric properties when it is ultrathin. At the same time, it is not affected by the thickness of the odd and even layers, and its chemical and physical properties are relatively stable. It has great potential in ultrathin coupling devices.

[0032] (2) Two-dimensional material α-In2Se3 was mechanically exfoliated to obtain two-dimensional material nanosheets with a gradient thickness of 20-100nm, which were then transferred onto a p-Si substrate. The piezoelectric properties of the two-dimensional material were utilized, and its piezoelectric performance was controlled based on the substrate clamping effect at the interface.

[0033] (3) The two-dimensional material nanosheets transferred to the substrate were exposed to an argon ion irradiation source with an irradiation flux of 3.5 × 10⁻⁶. 13 cm -2 7.0×10 13 cm -2 1.05×10 14 cm -2 The piezoelectric properties of two-dimensional nanosheets can be further modulated based on argon ion irradiation.

[0034] The following control methods were used before and after argon ion irradiation:

[0035] 1) Before (or after) argon ion irradiation, PFM was used to obtain the amplitude of two-dimensional material nanosheets as a function of AC voltage.

[0036] 2) Using PFM, determine how the amplitude of two-dimensional material nanosheets changes with thickness;

[0037] 3) Determine the piezoelectric coefficient d of the two-dimensional material nanosheet on the substrate based on the data obtained in steps 1)-2). 33 ;

[0038] Experimental results are as follows Figure 1 As shown, in the initial state, i.e. before irradiation, the relationship between the thickness of α-In₂Se₃ and the piezoelectric coefficient can be divided into three stages in the range of 20-100 nm. When the thickness is 0-20 nm, the piezoelectric coefficient d 33 Increased to 2.07844 pm / V; when the thickness is 20-40 nm, the piezoelectric coefficient d 33 The piezoelectric coefficient d increased from 2.07844 pm / V to 2.9674 pm / V; when the thickness is 40-60 nm, the piezoelectric coefficient d 33 It increased from 2.9674 pm / V to 3.7513 pm / V.

[0039] Subsequently, PFM tests were performed on α-In₂Se₃ with a thickness gradient of 20-100 nm to measure the piezoelectric coefficient d before and after argon ion irradiation. 33 Furthermore, after irradiation, the polarization of the two-dimensional material α-In2Se3 is not controlled.

[0040] The initial irradiation dose was 3.5 × 10⁻⁶. 13 cm -2 For a thickness of 0-20 nm, the piezoelectric coefficient d 33 The piezoelectric coefficient d changes from the initial state of 2.07844 pm / V to -2.97556 pm / V; for a thickness of 20-40 nm, the piezoelectric coefficient d 33 The piezoelectric coefficient d changes from the initial state of 2.9674 pm / V to -3.1171 pm / V; at a thickness of 40-60 nm, the piezoelectric coefficient d 33 The initial value changes from 3.7513 pm / V to -3.75252 pm / V. Within the aforementioned thickness gradient range, d 33 The change in value from positive to negative indicates a change in the direction of the piezoelectric response.

[0041] The second irradiation, i.e., the total irradiation dose, was 7.0 × 10⁻⁶. 13 cm -2 For a thickness of 0-20 nm, the piezoelectric coefficient d 33 The piezoelectric coefficient d changes from the initial state of 2.07844 pm / V to -1.17638 pm / V; at a thickness of 20-40 nm. 33 The piezoelectric coefficient d changes from the initial state of 2.9674 pm / V to -1.92277 pm / V; at a thickness of 40-60 nm, the piezoelectric coefficient d 33 The piezoelectric coefficient changes from an initial 3.7513 pm / V to -1.66367 pm / V. Within the aforementioned thickness gradient range, the piezoelectric coefficient d... 33 The absolute value of the numerical value decreased slightly compared to the first irradiation, which is related to the weak voltage polarization during the piezoelectric microscopy test, but is still mainly regulated by ion irradiation.

[0042] The third irradiation, i.e., the total irradiation dose, was 1.05 × 10⁻⁶. 14 cm -2 For a thickness of 0-20 nm, the piezoelectric coefficient d 33 The piezoelectric coefficient d changes from the initial state of 2.07844 pm / V to -4.12462 pm / V at a thickness of 20-40 nm. 33 The piezoelectric coefficient d changes from the initial state of 2.9674 pm / V to -4.78046 pm / V; at a thickness of 40-60 nm, the piezoelectric coefficient d 33 The piezoelectric coefficient d changes from the initial 3.7513 pm / V to -6.13568 pm / V. Within the above thickness gradient range, the piezoelectric coefficient d... 33The absolute value of the irradiation was significantly larger than that of the first and second irradiations, which is due to the cumulative effect after irradiation.

[0043] In summary, low-energy argon ion irradiation can modulate the piezoelectric effect direction of two-dimensional materials, especially when the two-dimensional materials are ultrathin (20 nm), where ion irradiation significantly modulates their piezoelectric properties. Furthermore, with increasing irradiation dose, the absolute value of the piezoelectric coefficient initially decreases and then increases. This is because the weak polarization caused by the positive voltage applied in the piezoelectric microscope influences the two-dimensional material's radiation resistance. Under a reasonable irradiation dose, the d-axis of the two-dimensional piezoelectric material... 33 The ability of the piezoelectric effect to change direction from positive to negative and maintain the negative direction is stable, reaching 1.05 × 10⁻⁶. 14 cm -2 At that time, the d of ultrathin nanosheets 33 It has changed by 298% compared to its initial state.

[0044] Three or four different points on the sample surface were selected to quantitatively collect the piezoelectric response. This was done to estimate the vertical piezoelectric coefficient d. 33 The vertical deflection of the cantilever in an atomic force microscope is an important parameter. The amplitude of the tip motion (in pm) can be derived by multiplying the calibration of the reverse optical lever sensitivity (InvOLS) by the deflection signal. The calibration constant is obtained from the slope of the force-distance curve.

[0045] In piezoelectric measurements, the electric field between the atomic force microscope tip and the conductive substrate is always non-uniform. Therefore, the effective piezoelectric coefficient (d) can only be obtained from the driving voltage and the slope of the amplitude. eff As shown in the following formula:

[0046] A f =V f ×δ=Q d eff ×U f

[0047] Among them, A f V represents the amplitude (in nm). f U is the vertical deflection signal (in mV), δ is the InvOLS calibration constant (nm / V), and U f d represents the applied AC driving voltage (V), and Q is the quality factor. In the case of weak indentation, the indentation left by the atomic force microscope tip in the sample is smaller than the tip radius (~25 nm), d 33 and d eff The value of d roughly follows the following equation: 33 =2×d eff From this relationship, we can estimate the d of α-In₂Se₃ thin films. 33 Piezoelectric coefficient.

[0048] The results are as follows Figure 2 As shown, the relationship between α-In2Se3 thickness and LPFM amplitude can be divided into three stages in the case of 20-100nm: when the thickness is 0-20nm, the LPFM amplitude increases to 0.754pm; when the thickness is 20-40nm, the LPFM amplitude increases from 0.754pm to 1.14pm; and when the thickness is 40-60nm, the LPFM amplitude increases from 1.14pm to 1.39407pm.

[0049] The initial irradiation dose was 3.5 × 10⁻⁶. 13 cm -2 When the thickness is 0-20nm, the LPFM amplitude changes from the initial state of 0.754pm to -0.252082pm; when the thickness is 20-40nm, the LPFM amplitude changes from the initial state of 1.14pm to -0.293743pm; when the thickness is 40-60nm, the LPFM amplitude changes from the initial state of 1.39407pm to -0.179349pm.

[0050] The second irradiation, i.e., the total irradiation dose, was 7.0 × 10⁻⁶. 13 cm -2 When the thickness is 0-20nm, the LPFM amplitude changes from the initial state of 0.754pm to -0.334061pm; when the thickness is 20-40nm, the LPFM amplitude changes from the initial state of 1.14pm to -0.437804pm; when the thickness is 40-60nm, the LPFM amplitude changes from the initial state of 1.39407pm to -0.523271pm.

[0051] The third irradiation, i.e., the total irradiation dose, was 1.05 × 10⁻⁶. 14 cm -2 When the thickness is 0-20nm, the LPFM amplitude changes from the initial state of 0.754pm to -0.799107pm; when the thickness is 20-40nm, the LPFM amplitude changes from the initial state of 1.14pm to -0.916455pm; when the thickness is 40-60nm, the LPFM amplitude changes from the initial state of 1.39407pm to -1.04142pm.

[0052] In summary, LPFM can accurately measure the in-plane piezoelectric coefficient (d). 11 Due to the strong coupling between the vertically oriented piezoelectric phenomena in curved and suspended α-In₂Se₃ sheets, the in-plane piezoelectric coefficient cannot be precisely determined, but the dependence of the quantitative LPFM amplitude on the sample thickness still exists. Meanwhile, the in-plane piezoelectric coefficient is related to the out-of-plane d... 33 Same, d 11 It is also related to the radiation dose and exhibits a pattern of change in the direction of the piezoelectric effect, d 11 It can be used Figure 2The vertical axis represents the piezoelectric response. It can be seen that, similar to out-of-plane piezoelectric behavior, the in-plane piezoelectric response exhibits an increasing trend and is highly correlated with thickness. This is because the substrate clamping effect weakens as the thickness increases.

Claims

1. A method for modulating the piezoelectric effect direction of two-dimensional materials based on argon ion irradiation, characterized in that, Includes the following steps: (1) Two-dimensional materials α-In2Se3 with different thickness gradients are transferred or grown onto a substrate, and the two-dimensional material nanosheets are exposed to an argon ion irradiation source; (2) Based on piezoelectric microscopy, the direction and piezoelectric coefficient of the piezoelectric effect of two-dimensional nanosheets before and after argon ion irradiation under different thickness gradients are characterized. The method for characterizing the piezoelectric coefficient includes the following steps: 1) Amplitude data of two-dimensional material nanosheets under different AC voltages were obtained using piezoelectric force microscopy. 2) Amplitude data of two-dimensional material nanosheets of different thicknesses were obtained using piezoelectric force microscopy. 3) Determine the piezoelectric coefficient of the two-dimensional nanosheets on the substrate based on the data obtained in steps 1) and 2). d 33 ; The thickness of the two-dimensional material nanosheets was controlled to be 20-60 nm, and the lateral two-dimensional surface dimension was larger than the thickness dimension. Simultaneously, the argon ion irradiation flux was controlled to be 3.5 × 10⁻⁶ nm. 13 cm -2 7.0×10 13 cm -2 1.05×10 14 cm -2 This makes two-dimensional piezoelectric materials d 33 The direction of the piezoelectric effect changes from positive to negative.

2. The method for modulating the piezoelectric effect direction of two-dimensional materials based on argon ion irradiation according to claim 1, characterized in that, The two-dimensional material is mechanically peeled into layers before transfer or growth.

3. The method for modulating the piezoelectric effect direction of two-dimensional materials based on argon ion irradiation according to claim 1, characterized in that, The piezoelectric coefficient includes out-of-plane piezoelectric coefficient and in-plane piezoelectric coefficient.

4. The application of the two-dimensional material obtained by the method according to any one of claims 1 to 3 in thin electromechanical coupling devices.

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