Layered van der Waals heterostructures composed of two or more distinct two-dimensional materials exhibit remarkable physical properties, offering great potential for the design of novel architectures in high-performance optoelectronic devices. In this work, we systematically investigate the geometric configuration and optoelectronic properties of the heterojunction formed by a monolayer of Boron Arsenide (BAs) and a monolayer of Tin Disulfide (SnS2) using first-principles calculations based on density functional theory (DFT). The results demonstrate that the vertically stacked BAs/SnS2 heterostructure is structurally stable in its ground state, with a band gap of 0.88 eV and a type-II band alignment. Notably, both biaxial strain and an external electric field can significantly modulate the band gap and band structure of the system. Under biaxial compressive strain ranging from-10 % to-4 %, the band gap increases monotonically. However, when the strain is further relaxed to the range of-4 % to 10 %, the band gap begins to decrease. In the case of an applied electric field varying from-0.5 to 0.5 V/& Aring;, the band gap initially increases linearly with the field strength, and the rate of increase slows down as the electric field approaches 0.3 V/& Aring;. Both biaxial strain and electric field are capable of inducing a transition between type-II and type-I band alignments. Moreover, the BAs/SnS2 heterostructure exhibits a theoretical photovoltaic conversion efficiency of approximately 26 % under normal conditions. With appropriate strain and electric field modulation, this efficiency can be enhanced to as high as 34 %. These findings highlight the promising potential of the BAs/SnS2 heterostructure for applications in photovoltaics and optoelectronics.

In recent years, two-dimensional (2D) materials have attracted considerable attention due to their outstanding optical and electronic properties, and they have shown great potential applications in next-generation solar cells and other optoelectronic devices. In this work, density functional theory (DFT) is used to systematically study the electronic and optoelectronic properties of the heterojunction formed by 2D BAs and I-AsP monolayers, as well as the response of this heterojunction under biaxial strain and electric field. The calculation results show that in the ground state, the four vertically stacked BAs/I-AsP heterostructures all have stable geometric structures, and their band gaps range from 0.63 to 0.86 eV. Compared with their constituent monolayers, these heterostructures have the increased optical absorption coefficients (the absorption coefficient in the x-direction reaches 10(6) cm(-1)), and they can effectively separate the photogenerated electron-hole pairs. Of the four structures, the A1 structure exhibits the smallest interlayer spacing, the smallest binding energy, and the highest stability. It has a type-I band alignment and a structure of a direct-band-gap semiconductor with band gaps of 0.86 eV (PBE) and 1.26 eV (HSE06), which can be used in the field of light-emitting diodes. The band gap and band type of the heterostructure can be effectively changed by applying biaxial strain and electric field. Under the application of biaxial tensile or compressive strain in a range of -10% to 8%, the band gap increases accordingly. When the tensile strain is greater than 8%, the band gap starts to decrease. When the biaxial strain epsilon <= -3% and epsilon > 8%, the heterojunction transitions from a type-I band alignment to a type-II band alignment. Under tensile strain, the absorption spectrum undergoes a red shift, while compressive strain leads to a blue shift of the absorption spectrum. Similarly, the externally applied electric field linearly affects the band gap of the BAs/I-AsP heterojunction in a range from -0.5 to 0.5 V/& Aring;, and the band gap decreases as the electric field increases. When a positive electric field with E >= 0.2 V/& Aring; is applied, the band alignment of the heterojunction can also transition from type-I to type-II. The BAs/I-AsP heterojunction has strong absorption properties in the ultraviolet and visible light ranges. Based on the Scharber model, the theoretical power conversion efficiency (PCE) eta of the BAs/I-AsP heterojunction is found to be greater than 13%, which is higher than those of 2D heterojunction materials such as Cs3Sb2I9/InSe (eta = 3.3%), SiPGaS/As (eta = 7.3%) and SnSe/SnS (eta = 9.1%). This further expands the application scope of the BAs/I-AsP heterojunction, making it expected to play an important role in the field of photodetectors and solar cells.

Layered heterostructure is the best candidate for photovoltaic materials because of its significant advantages in electronic and optoelectronic properties. It is well known that the efficiency of a photovoltaic device is mainly determined by the bandgap and band alignment at the interface. By using density functional theory, we have designed ten two-layer or three-layer heterostructures by combining blue photosphorene (BP) with either pure or doped SnS2. Such a combination leads to a van der Waals (vdW) interaction in a two-dimensional plane. Structural stability of these heterostructures has been studied on the basis of the features of their electron configurations and light-interaction capabilities. It turns out that the heterojunctions are all indirect semiconductor materials featured by narrow bandgaps in the range of 0.60-1.22 eV. Compared with the monolayers BP and SnS2, the heterostructures have much smaller bandgaps, which enables to more effectively harvest solar energy in a wide spectral range. All heterojunctions are featured by the type-II band arrangement, which favors to separate the photoexcited electron and hole pairs and increase their mobility. In particular, the BP/doped SnS2 heterojunctions exhibit high photoelectric conversion efficiencies up to 29.1%. These encouraging outcomes show great potential of the vdW heterostructures in the field of solar photovoltaic applications.

Using the first principle method based on density functional theory (DFT), we systematically studied the possibility of arsenic doped single-layer blue phosphorene (AsP) as anode material for Li, Mg, Ca, and Al ion batteries. The calculation of formation energy against temperature shows good thermal and dynamic stability of monolayer AsP, which can provide inherent advantages for electron transmission in materials. Meanwhile, the calculation indicates that AsP can provide excellent mobility for adsorbed atoms. The diffusion barriers of Li, Mg, Ca, and Al on the upper and lower surfaces of AsP are 0.18/0.16 eV, 0.10/0.17 eV, 0.45/0.43 eV, and 0.17/0.18 eV, respectively. These properties indicate that AsP can increase the charging/discharging rate without metal aggregation. The specific capacities of Mg, Ca, and Al can reach over 505.7 mAhg(-1), greater than the values of corresponding graphite or some other 2D materials. In addition, AsP has a lower open circuit voltage, and the charge transferred from metal atoms to AsP enhances its conductivity, which is beneficial to the anode material.

Here, we investigate the possibility of bilayer phosphorene as an anode material for aluminum-ion batteries using first-principles calculations. The characteristics of negative electrode materials are desirable with small volume expansion, large capacity and high mobility. We calculated the adsorption energies, optimal adsorption sites, diffusion barriers, theoretical capacities, open circuit voltages (OCVs), and structural stability of aluminum (Al) on the surface and interlayers of bilayer phosphorene. The intercalation of Al did not significantly change the volume of the bilayer phosphorene. The diffusion barrier of Al on the surface along the zigzag direction is 0.13 eV, while the diffusion barrier along the armchair direction is 0.49 eV. When Al is intercalated into the phosphorene interlayer, the diffusion barriers along the armchair and zigzag directions are 0.77 eV and 0.47 eV, respectively. It can be seen that the diffusion of Al between layers is also relatively easy. And with the increase of Al intercalation concentration, the theoretical capacity of bilayer phosphorene can reach 1047 mAhg(-1). These results demonstrate that bilayer phosphorene is a potential candidate as anode material for aluminum-ion batteries.

The lithium adsorption energies, electronic structures, and properties for single‐walled blue phosphorus nanotubes (SWBPNTs) doped with B, C, N, and Si upon Li intercalation on the inside and outside surfaces are investigated using density functional methods. It is found that the dopants of B, C, N, and Si have negative formation energies. The structure and properties of the SWBPNT will undergo certain changes after doping. Due to the interaction of dopant atoms and P atoms, the bandgap of the nanotubes doped with B and N will be reduced, and the nanotubes doped with C and Si have defects (dopant) state in the forbidden band. For the dopant atoms in SWBPNT, B and Si lose electrons, while C and N gain electrons. Compared with pristine SWBPNT, when Li is adsorbed internal to the tube, the lithium adsorption energies in the doped SWBPNT have a larger negative value, especially for C and Si doping. Consequently, our work suggests that the B‐, C‐, N‐, and Si‐doped SWBPNT have the capability to enhance the Li adsorption capacity.

Moiré pattern in twisted multilayers (tMLs) induces many emergent phenomena by subtle variation of atomic registry to modulate quasiparticles and their interactions, such as superconductivity, moiré excitons, and moiré phonons. The periodic superlattice potential introduced by moiré pattern also underlies patterned interlayer coupling at the interface of tMLs. Although this arising patterned interfacial coupling is much weaker than in-plane atomic interactions, it is crucial in moiré systems, as captured by the renormalized interlayer phonons in twisted bilayer transitional metal dichalcogenides. Here, we determine the quantitative relationship between the lattice dynamics of intralayer out-of-plane optical (ZO) phonons and patterned interfacial coupling in multilayer graphene moiré superlattices (MLG-MS) by the proposed perturbation model, which is previously challenging for MLGs due to their out-of-phase displacements of adjacent atoms in one atomic plane. We unveil that patterned interfacial coupling introduces profound modulations on Davydov components of nonfolded ZO phonon that are localized within the AB-stacked constituents, while the coupling results in layer-extended vibrations with symmetry of moiré pattern for moiré ZO phonons. Our work brings further degrees of freedom to engineer moiré physics according to the modulations imprinted on the phonon frequency and wavefunction.

基于密度泛函理论的第一性原理计算,本文首次研究了过渡金属卤代磷酸酯MBiP2X6(M=Cu,Ag;X=S,Se)三维晶体和二维晶体的声子色谱和拉曼散射谱.以反铁电晶体AgBiP2Se6为例,根据声子谱的计算结果,验证了低温反铁电相是动力学稳定的.结合声子总态密度可以得到:声子谱光学支的低频部分主要来源于阳离子M+和Bi3+的刚性平移振动,光学支相对高频部分来源于[P2Se6]基团的内振动.此外,对MBiP2X6的声子振动模进行了归属和识别,分析其拉曼活性模的振动频率对厚度的依赖关系.研究表明:随晶体结构层数的增加,A1g(或A)模的振动频率稳定在203 cm-1,Eg(或E)模的振动频率在430 cm-1附近红移8 cm-1左右.在低频(≤100 cm-1)下,刚性拉曼振动模较为显著,这与发生顺电-铁电相变时阳离子M+和Bi3+的相对平移有着密切的关系.

Based on first principles calculations, the possibility of zigzag single-walled blue phosphorene nanotube (SWBPNT) as anode materials for high-performance lithium-ion batteries is studied. We calculate the adsorption, diffusion properties and cell voltages of lithium intercalation on the inside and outside of SWBPNT and compare them with those in carbon nanotube (CNT) and single-walled Si nanotube (SWSiNT). The results show that the inside of SWBPNT is a fast diffusion channel of lithium compared with the outside of SWBPNT. By calculating the structure parameters, adsorption energy and charge transfer, we study the adsorption of multiple lithium atoms in SWBPNT. The results show that lithium is easier to diffuse and adsorb inside the tubes, which will help to improve the lithium storage capacity of the system. Therefore, SWBPNT has great potential as anode materials for Li-ion batteries.

For ion batteries, the choice of electrode materials is very important. Over the years, it has attracted more and more attention. In this study, we propose a new anode material for the Li-ion batteries which is silicon-doped (Si-doped) blue phosphorene (BP). Using the first-principles calculation method, we study the geometry, adsorption energy, diffusion barrier, mechanical strength, specific capacity and charge transfer of lithium adsorbed on a single-layer Si-doped BP surface. The results show that the diffusion of Li in the armchair and zigzag directions on Si0.125P0.875 is 1.04 and 0.55 eV, while the diffusion in the armchair and zigzag directions on Si0.25P0.75 is 1.00 and 0.64 eV. Similarly, the theoretical specific capacities of the two Si-doped BP are 875 mAhg(-1) (Si0.125P0.875) and 886 mAhg(-1) (Si0.25P0.75), which are greater than the pure single-layer BP anode in a Li-ion battery. In addition, during the insertion or diffusion of Li, the structural integrity of Si-doped BP can be well maintained. Therefore, it can be concluded that Si-doped BP is an excellent candidate material for Li-ion battery anodes.

三维铁电体材料以其众多优良的性质在许多电子行业内起着无可替代的作用,如制作铁电存储器、高能电容器等等.但随着纳米技术的日趋成熟,磁电材料逐渐受到悬空键和量子隧穿效应等负面因素的影响.因而,二维铁电材料逐渐进入科研人员的视野,它有望克服上述难题.本文利用第一性原理密度泛函理论模拟,关注了一种典型的层状金属硫磷酸盐——CuCrP2S6晶体,揭示了自发极化的原理,同时探究了能带、态密度和光学等物理性质.结果 显示其是一种能保持铁电极化状态的二维半导体材料.

We investigate the exchange integrals and magnetic anisotropy change in Sc substituted barium hexaferrite BaFe12-xScxO19 (x = 0, 0.5, 1, 1.5, 2) by density functional theory (DFT) calculations. The general gradient approximation (GGA) with on-site coulomb repulsion U (GGA + U) method was used to improve the description of the strongly correlated 3d electrons of Fe. Our calculations reveal that Sc3+ preferentially replace Fe3+ at the 4f(2) and 2b sites successively. The total energies of 9 spin configurations are calculated to obtain 8 inter-sublattice exchange integrals for different values of x. Comparison of the exchange integrals between BaFe12O19 (BFO) and BaFe12-xScxO19 (x = 0.5, 1, 1.5, 2) (BFSO) shows that substituting Sc for Fe influences most interactions involving the 4f(2) sites. The f(1)-f(2) and f(2)-k interactions decreases as substitution increases, while the b-f(2) interaction fluctuates significantly as x changes. Magnetic anisotropy change of Sc substituted M-type barium hexaferrite (Ba-M hexaferrite) has been studied by using the force theorem method. The results show that Sc3+ in its preferred 4f(2) and 2b sites contribute to the decrease of the uniaxial magnetic crystal anisotropy. The magnetic anisotropy of BFSO transforms from uniaxial to planar with transition point in the range of 1 < x < 1.5.

针对不同形式振动的叠加问题,课上在理论推导后用自制LabVIEW仿真实验对振动的叠加现象进行演示,从而加深学生对波形叠加问题的理解.

For silicon carbide (SiC) processed by ion-implantation, dedicated test structure fabrication or destructive sample processing on test wafers are usually required to obtain depth profiles of electrical characteristics such as carrier concentration. In this study, a rapid and non-destructive approach for depth profiling is presented that uses confocal Raman microscopy. As an example, a 4H–SiC substrate with an epitaxial layer of several micrometers thick and top layer in nanoscale that was modified by ion-implantation was characterized. From the Raman depth profiling, longitudinal optical (LO) mode from the epitaxial layer and longitudinal optical phonon-plasmon coupled (LOPC) mode from the substrate layer can be sensitively distinguished at the interface. The position profile of the LOPC peak intensity in the depth direction was found to be effective in estimating the thickness of the epitaxial layer. For three kinds of epitaxial layer with thicknesses of 5.3 μm, 6 μm, and 7.5 μm, the average deviations of the Raman depth analysis were −1.7 μm, −1.2 μm, and −1.4 μm, respectively. Moreover, when moving the focal plane from the heavily doped sample (~1018 cm−3) to the epitaxial layer (~1016 cm−3), the LOPC peak showed a blue shift. The twice travel of the photon (excitation and collection) through the ion-implanted layer with doping concentrations higher than 1 × 1018 cm−3 led to a difference in the LOPC peak position for samples with the same epitaxial layer and substrate layer. Furthermore, the influences of the setup in terms of pinhole size and numerical aperture of objective lens on the depth profiling results were studied. Different from other research on Raman depth profiling, the 50× long working distance objective lens (50L× lens) was found more suitable than the 100× lens for the depth analysis 4H–SiC with a multi-layer structure.

本文采用基于第一性原理的密度泛函理论(DFT)和密度泛函微扰理论(DFPT)方法,计算了ZnCo3(OH)6Cl2和ZnNi3(OH)6Cl2两种六角结构晶体的结构,声子谱和模式密度,进而分析和比较了对称性,频率以及热力学性质.通过理论计算得到的声子谱没有虚频,可知该结构可以稳定存在;声子模式密度结果显示了不同种类原子的贡献大小.确定了拉曼活性振动模式的对称性和频率,并与量子自旋液体材料Z nC u3(O H)6 C l2进行了比较,结果显示它们的主要拉曼峰位置比较接近.最后,计算和分析得到的热力学性质符合物理规律.

In this work, 4H SiC samples with a multilayer structure (shallow implanted layer in a lowly doped n-type epitaxial layer grown on a highly doped thick substrate) were investigated by Raman scattering. First, Raman depth profiling was performed to identify characteristic peaks for the different layers. Then, Raman scattering was used to characterize the carrier concentration of the samples. In contrast to the conventional Raman scattering measuring method of the Longitudinal Optical Plasmon Coupled (LOPC) mode, which is only suitable to characterize carrier concentrations in the range from 2 × 1016 to 5 × 1018 cm−3, in this work, Raman scattering, which is based on exciting photons with an energy above the band gap of 4H-SiC, was used. The proposed method was evaluated and approved for different Al-implanted samples. It was found that with increasing laser power the Al-implanted layers lead to a consistent redshift of the LOPC Raman peak compared to the peak of the non-implanted layer, which might be explained by a consistent change in effective photo-generated carrier concentration. Besides, it could be demonstrated that the lower concentration limit of the conventional approach can be extended to a value of 5 × 1015 cm−3 with the approach presented here.

In the present work, a novel anode candidate – sulfur‐doped phosphorene – for the Na‐ion batteries and K‐ion batteries has been proposed. The doped geometry, Na/K adsorption energy, average open‐circuit voltage, specific capacity, Na/K diffusion barriers, and charge transfer on sulfur‐doped phosphorene sheets are investigated through the way of adopting ab initio periodic quantum chemical method. The results demonstrate that, toward the directions of armchair and zigzag, the energy barriers of Na/K diffusion on the doped monolayer are 0.81/0.68 and 0.14/0.08 eV, respectively. In addition, the theoretical specific storage capacity of sulfur‐doped phosphorene in Na‐ion batteries is 431 mAh g−1, which is larger than for other commercial anode materials. Besides, the Na/K insertion/diffusion in sulfur‐doped phosphorene well preserves its structural integrity. Owing to its good stability, high capacity, excellent electrical conductivity and high Na/K mobility, sulfur‐doped phosphorene will have immense application prospects as anode material for Na‐ion batteries, K‐ion batteries and other novel electronic devices.

We combine rectangular nanopits of different lengths and find that strong localized field regularly transfers from one pit to another as incident wavelength increases. This phenomenon is due to the ability of rectangular pits to tune resonant wavelength by varying the structural parameters. The relation between pit structure parameters and resonant wavelength is explained by the waveguide theory. Furthermore, the coupling between two adjacent pits and its influence on electric field distribution and resonant wavelength are investigated. The red-shifts of resonant wavelength caused by coupling are explained by Bethe's cavity coupling theory.

文章利用超声光栅先测量不同温度下纯净水中的声速,测量结果与之前文献报道相一致.随后,在室温条件下分别对不同浓度的白砂糖溶液在超声光栅中形成的光谱进行测量,并详细研究声速与溶液浓度的关系.室温下又分别测量雪碧和冰糖雪梨中的声速,利用声速与糖溶液浓度的关系,得到两种饮料中的糖含量分别为14.6％和11.0％,与饮料瓶身标注的11％和9.2％相差很小,而差别主要来源于饮料中的其他微量物质.为精确比较,文章还测量两种浓度分别为11％和9.2％的糖溶液中声速随温度的变化关系,同时测量两种饮料中的声速随温度的变化关系.实验证明利用超声光栅衍射测量物质溶液浓度的实用性和可靠性.