Laser fabrication method for tensile strain engineering of 2D materials

Abstract

The present invention discloses a laser manufacturing method for two-dimensional material tensile strain engineering, comprising the following steps: firstly, depositing a metal film on a substrate, then transferring the two-dimensional material on the metal film, using laser direct scanning to convert the metal film into nanoparticles, and finally using a pulsed laser to shock the metal nanoparticles for processing, so that the two-dimensional material covered on the nanoparticles produces local strain. The method of the present invention can avoid the material rupture and secondary defects caused by the transfer of the two-dimensional material to a substrate with a large surface roughness; selecting a laser with a suitable wavelength and power to scan the metal film can controllably adjust its morphology without damaging the two-dimensional material; through further laser shock processing, the two-dimensional material can produce local strain, thereby changing the energy band structure of the two-dimensional material, greatly improving the electrical properties of the two-dimensional material such as carrier mobility, and can be applied to electronic devices such as high-performance field effect transistors.

Description

Technical Field

[0001] The present invention relates to the technical field of strain engineering of two-dimensional semiconductor materials, and in particular to a laser manufacturing method for tensile strain engineering of two-dimensional materials. Background Art

[0002] Moore's Law, on which the traditional silicon-based integrated circuit industry relies, is increasingly approaching its physical limits, causing concerns from industry and academia about the future development of the integrated circuit industry. Against this background, two-dimensional electronic materials such as graphene, MoS2, and WSe2 stand out with their unique atomic-level thickness and excellent gate control capabilities. They are seen as one of the backup materials that are expected to replace silicon-based materials, and have great application potential in the fields of transistors, photodetectors, and memory. Theoretical and experimental results show that mechanical strain strongly perturbs the band structure of 2D materials, so that their electronic and photonic properties can be effectively adjusted through mechanical deformation. In fact, this principle, called strain engineering, is now commonly used to manufacture traditional semiconductor devices.

[0003] The methods currently used to produce strain in two-dimensional materials are mainly divided into two categories: in-plane mode and out-of-plane mode. The in-plane mode involves using the lattice mismatch between the substrate and the two-dimensional material or the difference in thermal expansion coefficient to cause strain in the two-dimensional material during the growth of the two-dimensional material. The out-of-plane mode includes compressing or pre-stretching the substrate to cause wrinkles in the two-dimensional material, bending the two-dimensional material on an elastic substrate, or transferring the two-dimensional material on a patterned substrate and then achieving the strain of the two-dimensional material through nanoimprinting. These methods have their own limitations. For example, the substrate used to cause strain in the two-dimensional material using lattice mismatch is not suitable for the preparation of electronic devices, and the use of patterned substrates often involves expensive and time-consuming processes such as electron beam lithography and cannot be mass-produced. Therefore, it is of great significance to develop a method for controllable strain of two-dimensional materials that is simple to operate and suitable for large-scale manufacturing. Summary of the invention

[0004] The purpose of the present invention is to provide a laser manufacturing method for tensile strain engineering of two-dimensional materials. Through laser shock, the two-dimensional material in contact with metal nanoparticles undergoes local deformation, the energy band structure of the two-dimensional material is adjusted, and the electrical properties of the two-dimensional material are improved and applied to two-dimensional material electronic devices.

[0005] The solution adopted by the present invention to achieve the purpose is: a laser manufacturing method for tensile strain engineering of two-dimensional materials, characterized in that it includes the following steps:

[0006] (1) depositing a metal film on a substrate;

[0007] (2) Transferring a single layer or a few layers of two-dimensional semiconductor materials onto a metal film;

[0008] (3) directly irradiating a metal film covered with a two-dimensional material with a laser to form metal nanoparticles;

[0009] (4) Using pulsed laser shock to process the metal nanoparticles after laser scanning, so as to cause local strain in the two-dimensional material covering the nanoparticles.

[0010] As a preferred embodiment, in step (1), the substrate comprises Si / SiO2, Si, quartz, or sapphire.

[0011] Furthermore, in step (1), the deposited metal film includes Au, Ag, Al, Ti, Cu, and the film thickness is 1-20 nm.

[0012] Furthermore, in the step (1), the method of depositing the metal film is one of magnetron sputtering, atomic layer deposition, chemical vapor deposition, pulsed laser deposition, and electron beam evaporation.

[0013] Furthermore, in step (3), the laser types used include continuous lasers, nanosecond pulse lasers, picosecond pulse lasers, and femtosecond pulse lasers, the laser power is greater than 15 W, the irradiation time is less than 1 min, and the sample is placed at the laser focus or 1-5 cm away from the focus.

[0014] Furthermore, in step (4), the method of using pulsed laser shock is specifically as follows:

[0015] The surface of the two-dimensional material is sequentially covered with an absorption layer and a light-transmitting layer, and the light-transmitting layer is vertically irradiated with a pulsed laser; the laser used for the pulsed laser shock includes a nanosecond laser, a picosecond laser and a femtosecond laser; the laser wavelength includes 1064nm, 532nm, 355nm and 266nm, the frequency is 1Hz or above, and the laser power density is greater than 10 -3 GW / cm 2 , the irradiation time is less than 1min.

[0016] Furthermore, in step (4), the method of using pulsed laser shock is specifically as follows:

[0017] The surface of the two-dimensional material is sequentially covered with an absorption layer and a light-transmitting layer, and the light-transmitting layer is vertically irradiated with a pulsed laser; the laser used for the pulsed laser shock includes a nanosecond laser, a picosecond laser and a femtosecond laser; the laser wavelength includes 1064nm, 532nm, 355nm and 266nm, the frequency is 1Hz or above, and the laser power density is greater than 10 -3 GW / cm 2 , the irradiation time is less than 1min.

[0018] Furthermore, in step (4), in order to prevent the absorption layer from being broken due to excessive laser shock intensity, thereby causing contamination of the two-dimensional material, a liquid that does not dissolve the two-dimensional material and metal particles, such as deionized water or anhydrous ethanol, is added between the absorption layer and the two-dimensional material.

[0019] The present invention has the following advantages and beneficial effects:

[0020] The laser manufacturing method of the two-dimensional material tensile strain engineering of the present invention deposits a metal film on the surface of the substrate by physical or chemical deposition methods, and then transfers a single layer or multiple layers of two-dimensional materials by dry or wet transfer methods, and uses a laser of a suitable wavelength to scan the metal film covering the two-dimensional material, so that the metal film changes its morphology under the action of light and heat to form nanoparticles with different degrees of roughness. In order to cause local strain in the two-dimensional material, a high-speed shock wave generated by irradiating the absorption layer with a pulsed laser acts on the transferred two-dimensional material to cause a strain of 5%. The method of the present invention can avoid the material rupture and secondary defects caused by the transfer of the two-dimensional material to a substrate with a large surface roughness. Selecting a laser of suitable wavelength and power to scan the metal film can controllably adjust its morphology without damaging the two-dimensional material. Through further laser shock treatment, the two-dimensional material can produce local strain, thereby changing the band structure of the two-dimensional material, greatly improving the electrical properties of the two-dimensional material such as carrier mobility, and the strained two-dimensional material can be applied to electronic devices such as high-performance field effect transistors. Compared with the prior art, it has the following obvious substantial characteristics and significant advantages:

[0021] Transferring a single or multi-layer thin film of two-dimensional material directly onto a continuous and flat metal film can avoid damage to the two-dimensional material and the generation of secondary defects; selecting a laser with a suitable wavelength (the selection of laser wavelength depends on the optical band gap of the two-dimensional material) to irradiate the sample surface can change the morphology of the metal film under the action of light and heat without affecting the two-dimensional material, and the morphology can be controlled by controlling the laser power and the type of laser; the laser shock method can generate a pressure of up to GPa on a very small area and nanosecond time scale, which can cause local strain in the two-dimensional material on the metal nanoparticles, greatly improving the electrical properties of the two-dimensional material such as carrier mobility. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1-Figure 5 This is a schematic diagram of the process of the laser manufacturing method of the two-dimensional material tensile strain engineering of the present invention:

[0023] Figure 1 is a schematic diagram of a substrate on which a metal film is deposited;

[0024] Figure 2 Schematic diagram of a metal film / substrate with two-dimensional materials transferred;

[0025] Figure 3 Schematic diagram of the formation of metal particles from a metal film after pulsed laser irradiation;

[0026] Figure 4 Schematic diagram of the transfer of two-dimensional materials / metal nanoparticles / substrate by pulsed laser shock processing;

[0027] Figure 5 Schematic diagram of the two-dimensional material after strain is generated;

[0028] Among them: 1. SiO2 / Si substrate, 2. metal film, 3. metal nanoparticles, 4. two-dimensional material, 5. absorption layer, 6. light-transmitting layer, 7. deformed two-dimensional material.

[0029] Figure 6 SEM image of Ag film grown by magnetron sputtering;

[0030] Figure 7 This is the SEM image of the Ag film after laser irradiation;

[0031] Figure 8 This is the SEM image of the Ag film covering MoS2 after laser irradiation.

[0032] Fig. 9 PL spectra of MoS2 before and after laser irradiation. DETAILED DESCRIPTION

[0033] For a better understanding of the present invention, the following examples are provided to further illustrate the present invention, but the present invention is not limited to the following examples.

[0034] The transfer, deposition method, substrate and base film involved in the present invention are all prior art and do not belong to the innovation of the present invention. They are only used for application. The transfer includes but is not limited to dry transfer or wet transfer. The deposition method includes but is not limited to atomic layer deposition, chemical vapor deposition, magnetron sputtering, electron beam deposition, pulsed laser deposition, physical vapor deposition, etc.

[0035] Example 1

[0036] The laser manufacturing method of the two-dimensional material tensile strain engineering of the present invention comprises the following specific steps:

[0037] (1) The SiO2 / Si substrate 1 was repeatedly cleaned in acetone, alcohol, and deionized water and dried with nitrogen gas;

[0038] (2) Using physical vapor deposition, a 2 nm thick Ag film 2 is deposited on the surface of the SiO2 / Si substrate 1. Figure 1 As shown;

[0039] (3) using a spin coater to evenly spin-coat the PMMA solution on the MoS2 grown on the SiO2 / Si substrate, and drying in a vacuum environment at 100°C;

[0040] (4) Soak the cured SiO2 / Si with PMMA in a 2 mol / L potassium hydroxide solution for 1-2 hours, and the PMMA film will naturally separate from the substrate;

[0041] (5) Use SiO2 / Si substrate 1 deposited with Ag film 2 to pick up the PMMA film from bottom to top. After drying naturally, use a heating plate at 80°C to heat the SiO2 / Si substrate 1 with MoS2 / PMMA. After etching away the residual PMMA by soaking in acetone, the transfer of MoS24 is completed. Figure 3 As shown;

[0042] (6) The MoS2 / Ag / SiO2 / Si sample was fixed 5 cm away from the light outlet of the nanosecond pulse laser, the laser wavelength was adjusted to 1064 nm, the laser power supply voltage was 700 V, and the irradiation time was 1 s. After the pulse laser irradiation, the Ag film 2 was transformed into Ag nanoparticles 3;

[0043] (6) 1-2 drops of deionized water are added to the MoS2 of the MoS2 / Ag nanoparticle / SiO2 / Si sample, and an aluminum foil absorption layer 5 and a light-transmitting layer 6 coated with graphite with a thickness of 10 μm are placed on the sample; a pulsed laser emitted by a Nd-YAG laser with a pulse width of 10 ns and a wavelength of 1064 nm is used to vertically irradiate the light-transmitting layer, and the laser power supply voltage is adjusted to 620 V, and the irradiation time is 1 s. After the impact, the MoS2 is deformed to obtain strained MoS27, such as Figure 4 and Figure 5 As shown;

[0044] (7) The microscopic morphology of the samples before and after laser treatment was measured by field emission scanning electron microscopy. Figure 6-8 shown. Figure 6 This is an Ag film grown by magnetron sputtering. It can be seen that the grown film is a continuous film with a smooth surface and no obvious defects. Figure 7 This is the microscopic morphology of the Ag film after laser irradiation. Under the light and heat of the laser, the grains of the Ag film shrink and turn into Ag nanoparticles. Figure 8 This is a microscopic image of the Ag film covering MoS2 after laser irradiation. Under the action of the laser, the Ag film still forms nanoparticles, and the MoS2 is not damaged. In the area marked by the white box, it can be seen that the nanoparticles support the single layer of MoS2 to form local strain. The photoluminescence spectrum of MoS2 before and after laser treatment was tested by the Raman test system under 532 nm laser excitation, as shown in Figure 2. Fig. 9As shown in Figure 2, after laser treatment, the characteristic peak of the photoluminescence spectrum of MoS2 moves toward the long wavelength direction, that is, red shift. This indicates that the band structure of MoS2 has changed. Comparison with the literature proves that the change in the band structure is caused by the local strain of MoS2.

[0045] The above is only a preferred embodiment of the present invention, which certainly cannot be used to limit the scope of rights of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and changes can be made without departing from the principle of the present invention, and these improvements and changes are also regarded as the protection scope of the present invention.

Claims

1. A laser manufacturing method for tensile strain engineering of two-dimensional materials, characterized by: The following steps are involved: (1) depositing a metal film on a substrate; the substrate includes Si / SiO2, Si, quartz, and sapphire; the deposited metal film includes Au, Ag, Al, Ti, and Cu, and the film thickness is 1-20 nm; the method of depositing the metal film is one of magnetron sputtering, atomic layer deposition, chemical vapor deposition, pulsed laser deposition, and electron beam evaporation; (2) Transferring a single layer or a few layers of two-dimensional semiconductor materials onto a metal film; (3) directly irradiating a metal film covered with a two-dimensional material with a laser to form metal nanoparticles; the types of lasers used include continuous lasers, nanosecond pulse lasers, picosecond pulse lasers, and femtosecond pulse lasers, with a laser power greater than 15 W and an irradiation time less than 1 min. The sample is placed at the laser focus or 1-5 cm away from the focus; (4) Using pulsed laser shock to process the metal nanoparticles after laser scanning, so that the two-dimensional material covered on the nanoparticles produces local strain; the method of using pulsed laser shock is specifically as follows: The surface of the two-dimensional material is sequentially covered with an absorption layer and a light-transmitting layer, and the light-transmitting layer is vertically irradiated with a pulsed laser; the laser used for the pulsed laser shock includes a nanosecond laser, a picosecond laser and a femtosecond laser; the laser wavelength includes 1064nm, 532nm, 355nm and 266nm, the frequency is 1Hz or above, and the laser power density is greater than 10 -3 GW / cm 2 , irradiation time is less than 1min; In order to prevent the absorption layer from being broken due to excessive laser shock intensity, thereby causing contamination of the two-dimensional material, a liquid that does not dissolve the two-dimensional material and metal particles is added between the absorption layer and the two-dimensional material.

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