CN111864070B - Two-dimensional material heterojunction and performance analysis method and application thereof - Google Patents
Two-dimensional material heterojunction and performance analysis method and application thereof Download PDFInfo
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Abstract
The invention provides a two-dimensional material heterojunction and a performance analysis method thereof, and application of the heterojunction in semiconductor and photoelectric energy conversion. The two-dimensional material heterojunction includes: a first two-dimensional material comprising a Janus two-dimensional material; a second two-dimensional material comprising a silylene; the first two-dimensional material and the second two-dimensional material are stacked longitudinally. The heterojunction provided by the invention can not only utilize the excellent properties of different materials, but also overcome the defects of a single two-dimensional material, and the band gap of the silylene is opened through the interaction of the Janus two-dimensional material and the silylene, so that the energy spectrum distribution of the two-dimensional material is obviously changed relative to the respective independent properties of two components forming the heterojunction. The performance analysis method of the heterojunction is based on the time-density functional theory and the random phase approximation to carry out electron energy loss spectrum analysis, has simple steps and easy operation, and provides a rapid analysis path and powerful support for heterojunction design based on the purpose of opening the band gap.
Description
Technical Field
The invention relates to a two-dimensional material and a simulation analysis method of material performance, in particular to a heterojunction formed by the two-dimensional material, and a performance analysis method and application thereof.
Background
As device sizes become smaller in the IC industry, conventional silicon-based semiconductors have come closer to the physical limits of the materials themselves. Silicon-based microelectronics technologies are increasingly challenged by short channel effects, quantum tunneling effects, power consumption, etc., and the need to find next-generation semiconductor materials that can replace silicon.
With the discovery of graphene in 2004, a surge of research into two-dimensional materials began to develop. The graphene, the silylene and other materials have excellent physical properties, such as ultrahigh carrier mobility, monoatomic layer thickness, ultrahigh mechanical strength and flexibility, and have good potential application value in the future semiconductor field. However, graphene and silicon alkene have no band gap, so that the graphene and silicon alkene cannot be directly applied to semiconductor electronic devices, and the problem of opening the band gap of the graphene and silicon alkene needs to be solved.
The currently commonly used method for opening the band gap comprises using a series of external conditions such as doping, strain, electric field, heterojunction construction and the like to open the band gap values of graphene and silylene, however, the related art has not yet obtained satisfactory results, and it is difficult to keep the linear electron dispersion and the ultrahigh mobility of graphene, silylene and the like while opening the band gap.
The structure of the silicon alkene is similar to or different from that of the graphene as a two-dimensional material. The silylene has unique electronic properties, and the electronic structure of the silylene can be designed and modified by adsorption, doping and other atomic layer methods. The preparation of silylene and the study of the electronic structure of silylene have become an important point of current research, and the opening of the energy band gap of silylene is also an important point of the study of its electronic properties. However, the prior art has not found a satisfactory solution to the problem of opening the bandgap of the silylene.
Disclosure of Invention
To address at least one of the problems of the prior art to a degree, embodiments in accordance with the first aspect of the present invention provide a two-dimensional material heterojunction comprising: a first two-dimensional material comprising a Janus two-dimensional material; and a second two-dimensional material comprising a silylene, the first two-dimensional material and the second two-dimensional material being stacked longitudinally.
Optionally, the Janus two-dimensional material comprises a three-layer structure, and the elements of the upper layer and the lower layer are respectively different atoms.
Optionally, the Janus two-dimensional material has an intrinsic electric field perpendicular to an interface of the first two-dimensional material and the second two-dimensional material, the intrinsic electric field modulating a silylene energy band structure.
Optionally, the Janus two-dimensional material is a third main group sulfur-containing compound.
Optionally, the Janus two-dimensional material is Ga 2 SSe。
Optionally, in the spatial structure of the two-dimensional material heterojunction, the Ga 2 The S-face of SSe faces the silylene, or the Ga 2 The Se face of SSe faces the silylene.
The heterojunction provided by the invention can not only utilize the excellent properties of different materials, but also overcome the defect of a single two-dimensional material, and brand new and excellent physical properties are generated through the interface coupling of the two-dimensional materials. By the interaction of the Janus two-dimensional material with the silylene, the bandgap of the silylene is opened, so that the energy spectrum distribution of the two-dimensional material is significantly changed with respect to the respective individual properties of the two components constituting it.
According to an embodiment of the second aspect of the present invention there is provided the use of the two-dimensional material heterojunction of the first aspect in semiconductor materials and/or in photovoltaic energy conversion.
Based on the characteristics of the two-dimensional material heterojunction in the first aspect of the invention in two aspects of mechanical physical characteristics and energy band structures, the silylene/Janus material two-dimensional heterojunction with a specific band gap is used for semiconductor materials, can provide a solution idea for breaking through the short channel effect bottleneck of the traditional silicon-based semiconductor, has good mechanical strength, and becomes a choice for next-generation semiconductor materials. In addition, the two-dimensional heterojunction of the silylene/Janus material can also be used for photoelectric energy conversion. The silicon alkene band gap which can be regulated and controlled through heterojunction material selection can be designed for the requirements of photoelectric conversion, for example, according to the matching requirements of the frequency spectrum of a light source and the band gap of materials, a two-dimensional material heterojunction with a specific band gap is designed, and therefore higher photoelectric conversion efficiency is achieved. Meanwhile, compared with the monocrystalline silicon or polycrystalline silicon battery material used on the current photovoltaic panel, the two-dimensional material heterojunction has better mechanical strength and can be used for photovoltaic battery materials with better flexibility and thinner.
In some embodiments, the two-dimensional material heterojunction of the first aspect of the present invention is used in a far-infrared sensor. The photoelectric conversion device is required to have a relatively small band gap due to detection in the far infrared band, but cannot have no band gap, and no suitable material has been found in the art within this specific band gap range. The heterojunction provided by the invention can open the band gap of the silylene, and can control the opening amplitude to meet the requirement of far infrared band detection. The far infrared sensor prepared by the heterojunction can have good photosensitivity and even can carry out the custom band gap design for the two-dimensional material heterojunction according to the wavelength of target photosensitivity and the analysis method provided by the fourth aspect of the invention.
Meanwhile, in order to perform performance analysis on the heterojunction proposed in the first aspect of the present invention, an embodiment of the third aspect of the present invention provides a method for performing analysis calculation on performance of a two-dimensional material heterojunction, which includes:
constructing the two-dimensional material heterojunction by adopting first simulation software, wherein the spatial structure of the heterojunction has a plurality of stacking modes;
adopting second simulation software to perform structural optimization on the heterojunction, and selecting a structure with the lowest energy from different structures of a plurality of stacking modes of the heterojunction as a stable structure of the heterojunction;
according to the stable structure of the heterojunction, calculating an electron energy loss spectrum of the heterojunction based on the time-dependent density functional theory, wherein the electron energy loss spectrum specifically comprises the following steps: performing self-consistent calculation by adopting third simulation software, testing the cutoff energy, and then adjusting parameters to perform non-self-consistent calculation; and calculating an electron energy loss spectrum of the two-dimensional material heterojunction;
and analyzing the performance of the heterojunction according to the electron energy loss spectrum.
Optionally, the first simulation software is at least one of a Material Studio, a VESTA and a crystal maker; the second simulation software is at least one of Quatum-ESPRESSO, VASP; the third simulation software is Quatum-ESPRESSO.
Optionally, in the step of performing structural optimization on the heterojunction, the cutoff energy is selected to be 400-600ev, the k point is 11 x 1, the electron convergence precision is selected to be 1E-5 order of magnitude, and the ion convergence precision is selected to be 1E-2 order of magnitude; in the step of calculating the electron energy loss spectrum of the heterojunction according to the stable structure of the heterojunction, the cutting energy is selected to be more than 70Ry, the self-consistent K point is 6 x 1, and the non-self-consistent K point is 32 x 1.
The method for analyzing and calculating the performance of the two-dimensional material heterojunction is based on the time-density functional theory and the random phase approximation, is simple in steps and easy to operate, can be used for rapidly and accurately analyzing the performance of the two-dimensional material heterojunction, is particularly suitable for observing the energy band distribution change of the heterojunction relative to the independent material forming the heterojunction, and can provide a rapid analysis path and powerful support for heterojunction design based on the purpose of opening the band gap. The method has the characteristics of less time consumption and simple calculation, can be used for researching the electron energy loss of other materials, and can also provide necessary basis for researching the surface properties of the materials. Has obvious advantages and wide application prospect in the aspects of researching the space environment and various physical and chemical properties of electrons in materials.
Drawings
FIG. 1 is Si/Ga 2 Schematic diagrams of different stacking modes of SSe heterojunction;
FIG. 2 is Si/Ga 2 SSe heterojunction and single-component electron energy loss spectrum contrast map;
FIGS. 3A and 3B are Si/Ga 2 Electron energy loss spectrum contrast diagram of SSe heterojunction with or without local field;
FIGS. 4A, 4B, 4C and 4D are Si/Ga respectively 2 SSe heterojunction and its single component momentum-dependent electron energy loss spectrum.
Detailed Description
The present invention will be described in further detail with reference to the following embodiments in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the detailed description is presented by way of example only and is not intended to limit the invention.
Because a single two-dimensional material often cannot meet the requirements of a multifunctional device in practical application, the idea of assembling different two-dimensional materials into a heterostructure has been developed. Two-dimensional material heterojunctions provide an excellent platform for exploring physical properties that are not available for a single two-dimensional material. At present, the academy has some preliminary researches on the construction and performance of the two-dimensional material heterojunction, but no design method and performance analysis method for forming a system are provided. However, the achievement of the two-dimensional material heterojunction is not ideal in terms of constructing the two-dimensional material heterojunction to open the band gap of graphene and silicon alkene.
The idea of the invention is that the two-dimensional material heterojunction is constructed by utilizing the excellent properties of different materials, overcoming the defect of a single two-dimensional material and generating brand new and excellent physical properties through the interface coupling of two-dimensional materials. One of the main purposes of the invention is to construct a heterojunction formed by silylene and other two-dimensional materials so as to solve the problem of opening the gap of silylene.
To this end, the invention provides a two-dimensional material heterojunction comprising: a first two-dimensional material comprising a Janus two-dimensional material; a second two-dimensional material comprising a silylene; the first two-dimensional material and the second two-dimensional material are stacked longitudinally.
The structure of the silylene is different from the planar honeycomb lattice of graphene, and the silylene is due to sp of Si atoms 3 Hybrid with a low-fold honeycomb structure. Pure silicon is not bandgap like graphene, but the curved structure of silicon makes it more flexible than graphene and therefore easier to match the lattice of the substrate. Therefore, the invention jumps out of the related art to prepare the nest of the heterojunction with graphene, and selects the silicon graphene instead of the graphene as one of the raw materials of the heterojunction. By sp of Si atoms 3 The hybridization orbit interacts with the polarity of Janus two-dimensional material to achieve the purpose of opening the silylene band gap.
Janus, used to describe materials, began in 1992 with the use of the nobel prize acquirer de Gennes in prize presentation, was used to describe particles with different compositions or properties on both sides, janus particles resembling amphiphilic molecules, with two different (e.g. hydrophilic/hydrophobic) or even opposite (polar/non-polar, positive/negative etc.) properties on the surface. Janus materials have gained widespread attention in the academy and industry for the last 20 years due to their unique properties, and while much research has been conducted, janus materials have become a common naming scheme for such materials in the academy and industry.
In the present invention, the Janus two-dimensional material refers to a two-dimensional material composed of Janus materials. The band gap of the silylene can be adjusted by the polar action of Janus two-dimensional materials.
In some embodiments, the Janus two-dimensional material can be designed into a three-layer structure, wherein the upper layer element and the lower layer element are respectively different atoms, and the two-dimensional material has a built-in electric field due to the asymmetry of the upper layer element and the lower layer element, and the structure is similar to a sandwich structure. Few heterojunctions in the current material design schemes can open the band gap of silylene under the condition of no external influence. In the invention, the Janus two-dimensional material with polarization characteristics is used as a polarization substrate of the silylene to adjust the performance of the silylene. The bandgap of the silylene can be opened only by the structure of the heterojunction itself without the need to exert an external influence.
The two-dimensional material heterojunction can be prepared by adopting the existing two-dimensional material heterojunction preparation method, for example, a manual fixed-point transfer method is used, and related technical details about the manual fixed-point transfer method can be obtained by referring to related technologies by a person skilled in the art, and are not repeated herein.
Preferably, janus two-dimensional materials with an intrinsic electric field perpendicular to the plane of the two-dimensional material can be selected to achieve better modulation of the energy band structure of the silylene. When the Janus monolayer has an intrinsic electric field perpendicular to the plane of the two-dimensional material, its effect is equivalent to a gate voltage, which can modulate the energy band structure of the silylene. According to the intensity of the intrinsic electric field and the interaction intensity of the Janus two-dimensional material and the silylene, when different Janus two-dimensional materials are used as the components of the heterojunction, the modulation of different intensities of the silylene band gap opening can be realized.
In the selection of practical Janus two-dimensional materials, due to the variety of Janus materials, how to select materials from which the effect is better under certain specific requirements, a design and analysis verification method combining theory and simulation is needed. However, in the related art, no theory or practice exists for the theory analysis of heterojunction or the simulation and analysis of performance.
Based on two aspects of theoretical innovation and experimental innovation, the invention provides a two-dimensional heterojunction of Janus two-dimensional material by adopting a third main group sulfur-containing compound. The third main group sulfur-containing compound may be a compound formed by the third main group element and sulfur element, such as GaS, or a compound formed by the third main group element and sulfur element together with other elements, such as Ga 2 SSe, etc.
For Janus two-dimensional material of sulfide of the third main group, the main component of the valence band is p orbit of outer sulfur element, and silicon atom has sp 3 The hybridized orbitals, and therefore orbital overlapping between the two layers of the heterojunction, readily occurs, creating a strong interaction.
Optionally, in the spatial structure of the two-dimensional material, the Ga 2 The S-face of SSe faces the silylene, or the Ga 2 The Se face of SSe faces the silylene. Thereby obtaining a relatively stable heterojunction structure.
The heterojunction provided by the invention can not only utilize the excellent properties of different materials, but also overcome the defect of a single two-dimensional material, and brand new and excellent physical properties are generated through the interface coupling of the two-dimensional materials. By the interaction of the Janus two-dimensional material with the silylene, the bandgap of the silylene is opened, so that the energy spectrum distribution of the two-dimensional material is significantly changed with respect to the respective individual properties of the two components constituting it. The specific band structure of the two-dimensional material heterojunction of the present invention will be exemplified later in connection with an analytical method.
Embodiments of the second aspect of the present invention provide for the use of the two-dimensional material heterojunction in semiconductor materials and/or in photovoltaic energy conversion based on various physical and chemical properties of the chromene/Janus two-dimensional material heterojunction.
In semiconductor applications, two-dimensional materials have unique advantages over bulk materials in that their atomic-scale thickness structure provides excellent immunity to short channel effects. Therefore, those skilled in the art have always desired to use two-dimensional materials such as graphene or graphene for the fabrication of semiconductor devices, but the zero bandgap problem of graphene and graphene has made attempts at this aspect have been very successful. The two-dimensional heterojunction of the silylene/Janus material with the specific band gap is used for a semiconductor material, can provide a solution idea for breaking through the short channel effect bottleneck of the traditional silicon-based semiconductor, has good mechanical strength, and becomes a choice for next-generation semiconductor materials.
In addition, the silylene-Janus material two-dimensional heterojunction can also be used for photoelectric energy conversion. The silicon alkene band gap which can be regulated and controlled through heterojunction material selection can be designed into a two-dimensional heterojunction with a specific band gap according to the requirements of photoelectric conversion, for example, the matching requirements of the frequency spectrum of a light source and the band gap of materials, so that higher photoelectric conversion efficiency is realized. Meanwhile, compared with the monocrystalline silicon or polycrystalline silicon battery material used on the current photovoltaic panel, the two-dimensional material heterojunction has better mechanical strength and can be used for photovoltaic battery materials with better flexibility and thinner.
In particular, the two-dimensional material heterojunction according to the first aspect of the present invention can be used in a far infrared sensor. The photoelectric conversion device is required to have a relatively small band gap due to detection in the far infrared band, but cannot have a band gap, and no suitable material has been found in the art within this band gap. The heterojunction provided by the invention can open the band gap of the silylene, and can control the opening amplitude to meet the requirement of far infrared band detection. The far infrared sensor prepared by the heterojunction can have good photosensitivity and even can carry out custom band gap design for the two-dimensional material heterojunction according to the wavelength of target photosensitivity and the analysis method provided by the third aspect of the invention.
Further optimization and performance verification of Janus two-dimensional materials forming two-dimensional heterojunction are supported in an experimental or simulation mode in the current technological background. Because the existing theoretical basis, whether theoretical methods such as valence bond theory, molecular orbit theory, van der Waals force analysis and the like are not enough to guide the design of opening the band gap aiming at the target, the expected purpose can be achieved by directly finding out which atoms are combined into which structure molecules in which number is not realized. Thus, there is a need for those skilled in the art to find better Janus two-dimensional material choices and to conduct performance analysis on constituent two-dimensional material heterojunctions with creative thinking to verify whether the energy band characteristics of the heterojunctions meet the requirements. Therefore, a simple, rapid, accurate and efficient performance analysis method is very important for designing and verifying two-dimensional material heterojunction.
To this end, an embodiment of the third aspect of the present invention provides a method for calculating an electron energy loss spectrum of a two-dimensional material heterojunction based on an time-dependent density functional theory, thereby performing an analytical calculation on the performance of the two-dimensional material heterojunction.
Electron Energy Loss Spectroscopy (EELS) is an important characterization means for the research fields of physics, material science, etc. In the electron energy loss spectrum, after an electron beam with known kinetic energy is incident on a material to be measured, part of electron and atom interaction generates inelastic scattering, part of energy is lost, and a path generates random small deflection, and the energy loss is measured and analyzed by an electron energy spectrometer. By studying the energy loss distribution of the inelastic scattered electrons, spatial environmental information of electrons in atoms can be obtained, thereby studying various physical and chemical properties of the sample.
The electron energy loss spectrum is obtained in two ways of experimental measurement and simulation calculation. The experimental mode is time-consuming, laborious and high in cost, and the two-dimensional material heterojunction product itself needs to be prepared, so that the method is more used for finding the optimal product, and the later verification experiment is not suitable for the verification requirement of the design stage. Therefore, the invention selects a simulation calculation mode to obtain the electron energy loss spectrum.
The Time-dependent density functional theory (Time-Dependent Density Functional Theory, TDDFT) is a computationally efficient theoretical method for studying such problems for the material excited state properties and response under external fields. The TDDFT avoids the complex solving process of the Schrodinger equation by introducing the correlation function, so that the high-precision calculation of the time-containing property of a large system is possible.
In the simulation calculation, based on the time-density functional theory simulation and the method of random phase approximation RPA, the electron energy loss spectrum of the material can be obtained through theoretical calculation. TDDFT obtains a macroscopic dielectric function by including a so-called Local Field Effect (LFE) in the calculation of the response function, while the electron energy loss is proportional to the imaginary part of the inverse dielectric function. Because the method can accurately calculate the dielectric function of the material, the electron energy loss spectrum can be accurately obtained. However, this method is relatively complex in steps, and is computationally time consuming and laborious, thus requiring the introduction of random phase approximations, i.e. considering only the extent to which the electrons interact to generate the screening field is required. By combining the TDDFT and the phase approximation PRA methods, electron energy loss spectrums of different materials can be obtained quickly and accurately.
At present, mature simulation software exists in the market, and the specific calculation process of the TDDFT numerical method can be directly realized according to the set thought, so that the method is only described aiming at the whole thought of the set simulation calculation, and details of numerical calculation are not repeated. The simulation calculation of the present invention can be implemented by those skilled in the art through simulation flexibility as exemplified in the examples hereinafter under the guidance of the present invention.
According to the embodiment of the invention, the method for analyzing and calculating the performance of the two-dimensional material heterojunction comprises the following steps S1 to S4:
in step S1, the two-dimensional material heterojunction is constructed by using first simulation software, wherein the spatial structure of the heterojunction has a plurality of stacking modes. In this step, the first simulation software is mainly used for constructing a Material space structure, and may be implemented by using any one of materials Studio, VESTA, crystal maker, and the like.
In step S2, a second simulation software is adopted to perform structural optimization on the heterojunction, and a structure with the lowest energy is selected from different structures of multiple stacking modes of the heterojunction to be used as a stable structure of the heterojunction. In this step, the second simulation software is used to calculate the architecture energy of the structure, and may be implemented using any one of Quatum-ESPRESSO, VASP.
In step S3, according to the stable structure of the heterojunction, an electron energy loss spectrum of the heterojunction is calculated based on the time-dependent density functional theory, and specifically includes: performing self-consistent calculation by adopting third simulation software, testing the cutoff energy, and then adjusting parameters to perform non-self-consistent calculation; and calculating an electron energy loss spectrum of the two-dimensional material heterojunction. In this step, the third simulation software is used to calculate the energy loss spectrum based on the time-dependent density functional theory, which can be implemented using Quatum-esponsso.
The electron energy loss spectrum is calculated according to the following formula:
wherein,,representing the dielectric function>Is the wave vector of the first brillouin zone, ω is frequency.
In step S4, the performance of the heterojunction is analyzed according to the electron energy loss spectrum.
Next, the mixture was treated with silylene and Ga 2 An embodiment of electron energy loss spectrum calculation of a two-dimensional material heterojunction composed of SSe is taken as an example to further explain a method for analyzing and calculating the performance of the two-dimensional material heterojunction. The result of the calculation also illustratesSilylene and Ga 2 Excellent performance of two-dimensional material heterojunction composed of SSe.
First, a Material Studio software is used to build a composition comprising a silylene and Ga 2 Longitudinal heterojunction of SSe (also denoted Si/Ga 2 SSe), there are a number of different stacking schemes, as shown in fig. 1, due to the high symmetry points. Wherein 1AA-I,1AB-M-I,1AB-Y-I,1AA-II,1AB-M-II,1AB-Y-II,2AA-I,2AB-M-I,2AB-X-I,2AA-II,2AB-M-II,2AB-Y-II respectively represent different stacking modes of atoms near the heterojunction interface, and a total of 12 kinds are shown.
In this embodiment, a single layer of the composition having a vertical interface, i.e., a vertically stacked heterojunction, is selected, and the lattice matching is preferably 95% or more in order to ensure structural stability. Due to the silicon alkene and Ga 2 The lattice mismatch rate of SSe is within 6%, and the stacking mode of 1*1 can be selected.
And then, optimizing various structures of the longitudinal heterojunction by adopting VASP software, and further calculating the structure of the lowest point of energy. The most stable of the 12 stacked structures is AB-M-I type (2 AB-M-I or 1 AB-M-I) with lattice parameter ofThe unit cell employs a 1 x 1 unit cell containing 6 atoms.
For Si/Ga 2 In the above calculation method of the SSe heterojunction, optionally, when VSP software is adopted for calculation, the cutoff energy is 500ev, the k point is 11×11×1, and the electron convergence precision is 1E -5 Ion convergence accuracy is 1E -2 . The method is characterized in that the truncated energy and the grid division are tested, a convergent value is taken, and the truncated energy is enough to always change by about 0.001eV, but the process is time-consuming, so that the truncated energy is generally selected to be 400-600eV in the calculation process according to the parameter analysis of a large number of documents and the empirical parameters obtained by calculation for a plurality of times, and the empirical parameters of the grid division are obtained by multiplying the value by the lattice constant in the POSCAR to be 30-40. EDIFF defaults to 10 -4 EDIFFG defaults to EDIFF 10 in order to make the calculationThe result is more accurate, and this embodiment uses more accuracy.
Next, self-consistent calculations were performed using QUANUM ESPRESSO software, and the truncated energies were tested, followed by non-self-consistent calculations. Optionally, the cut-off energy is above 70Ry, the self-consistent K point is 6×6×1, and the non-self-consistent K point is 32×32×1. And finally, calculating an electron energy loss spectrum. When the cutoff energy is more than 70Ry, better precision can be obtained, and meanwhile, the calculation amount is increased along with the increase of the cutoff energy, so that the optimization selection can be performed according to actual conditions by a person skilled in the art.
Referring to FIG. 2, FIG. 2 is a diagram of Si/Ga according to the above embodiment of the present invention 2 SSe heterojunction electron energy loss spectrum calculation result, and constructed Si/Ga 2 SSe heterojunction and single component electron energy loss spectrum control.
Wherein calculations were made for two relatively most stable stacked structures, one being Ga 2 The S-face of SSe is directed towards silylene, denoted (Si/Ga 2 SSe-S), one being Ga 2 The Se-facing side of SSe is facing the silylene and is denoted (Si/Ga 2 SSe-Se). In addition, the silylene, ga 2 Electron energy loss spectra of constituent monolayers of SSe. As can be seen from fig. 2, the electron energy loss spectrum c, d of the heterojunction is significantly altered with respect to the spectral lines a and b of the constituent monolayers. Wherein the low energy plasma peak of the silylene disappears and the substrate Ga is polarized 2 The enhancement of the eigenvalue of SSe, this information indicates that the polarized substrate has a strong interaction with the silylene.
In one embodiment of the invention, the effect of local field effects is also calculated. The electron energy loss spectra of the hetero-junctions with and without localized fields are compared, including both cases Si/Ga2SSe-S and Si/Ga2SSe-Se, as two different examples. As shown in fig. 3A and 3B, the pi plasma peak will decrease and slightly red shift when considering the local field effect. In addition, plasmons including localized field effects result in strong positive dispersion due to non-uniformity of spatial charge distribution in the localized field, and can be explained by short-range coulomb interactions. In particular, since the charge unevenness is remarkable, the local field effect in the vertical direction is stronger, which is a well-known depolarization effect.
In one embodiment of the invention, the electron energy loss spectrum related to momentum is obtained by controlling the QpntsRXd parameter. After the non-self-consistent function is calculated, energy levels and wave functions of different K points are obtained. According to conservation of momentum, the phase difference momentum between different K points is q. The calculation parameter QpntsRXd is used to control the range of q values in the Dyson equation below to handle electron energy loss spectra with different momentums.
Wherein, the related formula is as follows:
wherein χ is G,G' (q, ω) represents the interactive response function of the system,representing a non-interactive response function of the system, +.>The wave vector in the first brillouin zone, ω is the frequency, G' is the inverted lattice vector.
Under the RPA approximation, the full kernel function (K) in the above equation G1 G2 (q, ω) is reduced to a static coulomb nucleus,
wherein χ is G,G' (q, ω) represents the interactive response function of the system.
For a more detailed description of the time-dependent density functional theory and PRA approximation, those skilled in the art will further understand with reference to the prior art documents in the relevant art that the present invention will not be repeated.
The following table shows two according to the inventionThe performance of the dimensional heterojunction is compared with the heterojunction of other materials and silylene in terms of opening the silylene band gap. From the above, the Si/Ga provided by the invention 2 SSe heterojunction, S-plane or Se-plane are two structures facing silylene, which opens the bandgap of silylene to the order of 0.1 electron volts, far higher than the heterojunction made of other silylene.
| Heterojunction structure | Lattice of crystal | E b (eV) |
| Si/BN | 2*2/3*3 | 0.012 1 |
| Si/graphane | 2*2/3*3 | 0.033 1 |
| Si/MoS 2 | 4*4/5*5 | 0.047 1 |
| Si/Ga 2 SSe-S/Se | 1*1/1*1 | 0.1360/0.1682 |
Fig. 4A to 4D show electron energy loss spectra of materials at different momentum transfer q. Wherein FIG. 4A shows silicon, and FIG. 4B shows Ga 2 SSe, FIG. 4C shows Si/Ga2SSe-S, and FIG. 4D shows Si/Ga2SSe-Se. Curves a to g in each figure represent different momentum transfer situations, respectively. It can be seen that the two-dimensional material heterojunction also has a different response with respect to different momentum transfer relative to the material alone.
In general, the peak gradually decreases as the momentum transfer K increases. The most significant effect in the overall graph is the blue shift of the plasma peak. For Ga 2 SSe, the secondary peak around the peak gradually becomes smaller and the peak width gradually increases as K increases. For heterojunction and Janus monolayer Ga 2 SSe, when At this time, another peak which did not exist before, the so-called pi+σ peak around 20eV, appears. Furthermore, plasmons originate from the collective excitation of valence electrons, the dispersion of which is related to the delocalization of these electrons.
Pi and pi+sigma plasmons with higher energy have great scientific significance and are subjected to intensive theoretical and experimental research. The change in electron energy loss spectra before and after heterojunction formation demonstrates a strong interaction between the Si monolayer and the polar two-dimensional substrate, and the intrinsic electric field in the polar two-dimensional substrate has a strong modulating effect on the electron energy loss spectra of the Si monolayer.
In conclusion, by calculation of electron energy loss spectrum, the two-dimensional material Ga of silylene and Janus is verified 2 The bonding properties of SSe-built heterojunctions, which have excellent properties in opening the silylene bandgap.
The method for analyzing the heterojunction performance of the two-dimensional material by calculating the electron energy loss spectrum is based on the time-containing density functional theory and the calculation of the random phase approximation, has the characteristics of simple steps, easy operation, less time consumption and simple calculation, can be used for researching the electron energy loss of the material, and can also provide necessary basis for researching the surface performance of the material. The research method based on the time-density functional theory has great significance for the measurement and research of the electron energy loss spectrum of the material. The method has obvious advantages and wide application prospect in researching the space environment and various physical and chemical properties of electrons in the material.
In addition, the electron energy loss spectrum of the heterojunction obtained by the calculation method has obvious change difference relative to the electron energy loss spectrum of the component single-layer material, and the heterojunction provided by the invention is fully verified to have good effect on opening the silylene band gap and excellent performance.
Although the present disclosure is described above, the scope of protection of the present disclosure is not limited thereto. Various changes and modifications may be made by one skilled in the art without departing from the spirit and scope of the disclosure, and these changes and modifications will fall within the scope of the invention.
Claims (8)
1. A two-dimensional material heterojunction, the heterojunction comprising:
a first two-dimensional material comprising a Janus two-dimensional material; and
a second two-dimensional material comprising a silylene;
the first two-dimensional material and the second two-dimensional material are longitudinally stacked;
the Janus two-dimensional material comprises a three-layer structure, wherein the upper layer element and the lower layer element are respectively different atoms, the Janus two-dimensional material is provided with an intrinsic electric field perpendicular to the interface between the first two-dimensional material and the second two-dimensional material, the intrinsic electric field modulates the silylene energy band structure, and the Janus two-dimensional material is a third main group sulfur-containing compound.
2. The heterojunction according to claim 1 wherein the Janus two-dimensional material is Ga 2 SSe。
3. The heterojunction according to claim 2, wherein in the spatial structure of the two-dimensional material heterojunction, the Ga 2 The S-face of SSe faces the silylene, orThe Ga 2 The Se face of SSe faces the silylene.
4. Use of a two-dimensional material heterojunction according to any of claims 1-3 in semiconductor materials and/or in photovoltaic energy conversion.
5. The use according to claim 4, wherein the two-dimensional material heterojunction is used for a far infrared sensor.
6. A method for analyzing the performance of a two-dimensional material heterojunction as claimed in any one of claims 1 to 3, comprising:
constructing the two-dimensional material heterojunction by adopting first simulation software, wherein the spatial structure of the heterojunction has a plurality of stacking modes;
adopting second simulation software to perform structural optimization on the heterojunction, and selecting a structure with the lowest energy from different structures of a plurality of stacking modes of the heterojunction as a stable structure of the heterojunction;
according to the stable structure of the heterojunction, calculating an electron energy loss spectrum of the heterojunction based on the time-dependent density functional theory, wherein the electron energy loss spectrum specifically comprises the following steps: performing self-consistent calculation by adopting third simulation software, testing the cutoff energy, and then adjusting parameters to perform non-self-consistent calculation; and calculating an electron energy loss spectrum of the two-dimensional material heterojunction; and
and analyzing the performance of the heterojunction according to the electron energy loss spectrum.
7. The method of claim 6, wherein the step of providing the first layer comprises,
the first simulation software is at least one of Material Studio, VESTA and crystal maker;
the second simulation software is at least one of Quatum-ESPRESSO, VASP;
the third simulation software is Quatum-ESPRESSO.
8. The method of claim 7, wherein in the step of optimizing the structure of the heterojunction, the cutoff energy is selected to be 400-600ev, the k point is 11 x 1, and the electron convergence accuracy is selected to be 1E -5 The ion convergence accuracy is selected to be 1E -2 An order of magnitude;
in the step of calculating the electron energy loss spectrum of the heterojunction based on the time-density functional theory according to the stable structure of the heterojunction, the cutoff energy is selected to be more than 70Ry, the self-consistent K point is 6 x 1, and the non-self-consistent K point is 32 x 1.
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