Cr掺杂ZnO纳米线的电子结构和磁性

采用自旋极化密度泛函理论系统研究了Cr掺杂ZnO纳米线的电学、磁学以及光学属性.计算结果显示,Cr原子沿[0001]方向替代ZnO纳米线中的Zn原子时体系一般呈现铁磁耦合,沿[1010]和[0110]方向替代Zn原子时体系呈现反铁磁耦合,且磁性耦合状态在费米能级附近出现了明显的自旋劈裂现象,发生了强烈的Cr 3d和O 2p杂化效应.自旋态密度计算结果显示,磁矩主要来源于Cr原子未成对3d态电子的贡献,磁矩的大小与Cr原子的电子排布有关.光学性质计算结果显示,Cr掺杂ZnO纳米线在远紫外和近紫外都具有明显的吸收峰,吸收峰发生了明显的红移.这些结果都表明Cr掺杂ZnO纳米线也许是一种很有前途的稀磁半导体材料. 关键词： ZnO 纳米线 第一性原理 磁性     

Ni 掺杂ZnO纳米线的电子结构与磁性

采用自旋极化密度泛函理论系统研究了Ni掺杂ZnO纳米线的电子结构、磁学和光学性质.磁学性质计算结果显示六种Ni掺杂ZnO纳米线的磁性耦合体系出现了铁磁(FM)、反铁磁(AFM)和顺磁(PM)二种不同的耦合状态.能量计算结果表明Ni原子在纳米线外表面沿[0001]方向替代Zn原子时能量最低,体系的AFM耦合相对稳定,AFM体系表现出金属性.态密度计算结果显示FM耦合在费米能级附近出现了明显的自旋极化现象,发生了强烈的Ni 3d和O 2p杂化效应,掺杂产生的磁矩主要来源于Ni 3d未成对轨道电子和部分O 2p轨道电子的贡献,FM耦合表现出半金属性.另外,光学性质计算结果显示Ni掺杂ZnO纳米线的远紫外吸收峰发生了红移现象,而380 nm附近的近紫外吸收峰发生了明显的蓝移现象,在整个紫外区都表现出了优异的发光性能.以上结果表明Ni掺杂ZnO纳米线是一种很有前途的磁光电子材料.     

Steady-state and transient electronic transport properties of β-(AlxGa1-x)2O3/Ga2O3 heterostructures: An ensemble Monte Carlo simulation

The steady-state and transient electron transport properties of $\beta $-(Al$_{x}$Ga$_{1-x}$)$_{2}$O$_{3}$/Ga$_{2}$O$_{3}$ heterostructures were investigated by Monte Carlo simulation with the classic three-valley model. In particular, the electronic band structures were acquired by first-principles calculations, which could provide precise parameters for calculating the transport properties of the two-dimensional electron gas (2DEG), and the quantization effect was considered in the $\varGamma $ valley with the five lowest subbands. Wave functions and energy eigenvalues were obtained by iteration of the Schrödinger-Poisson equations to calculate the 2DEG scattering rates with five main scattering mechanisms considered. The simulated low-field electron mobilities agree well with the experimental results, thus confirming the effectiveness of our models. The results show that the room temperature electron mobility of the $\beta $-(Al$_{0.188}$Ga$_{0.812}$)$_{2}$O$_{3}$/Ga$_{2}$O$_{3}$ heterostructure at 10 kV$ \cdot$cm$^{-1}$ is approximately 153.669 cm$^{2}\cdot$V$^{-1}\cdot$s$^{-1}$, and polar optical phonon scattering would have a significant impact on the mobility properties at this time. The region of negative differential mobility, overshoot of the transient electron velocity and negative diffusion coefficients are also observed when the electric field increases to the corresponding threshold value or even exceeds it. This work offers significant parameters for the $\beta$-(Al$_{x}$Ga$_{1-x}$)$_{2}$O$_{3}$/Ga$_{2}$O$_{3}$ heterostructure that may benefit the design of high-performance $\beta$-(Al$_{x}$Ga$_{1-x}$)$_{2}$O$_{3}$/Ga$_{2}$O$_{3}$ heterostructure-based devices.     

Ferromagnetism of V-doped ZnO nanowires

The geometry structures,electronic structures,and magnetic properties of Zn46V2O48 nanowires are studied by density functional theory(DFT) calculations.We find that the ferromagnetic(FM) coupling is more stable for six configurations of Zn46V2O48 nanowires,and is mediated by neighboring O as evidenced from the strong hybridization of V 3d and O 2p states,exhibiting strong spin polarization.The spin polarization is found to be 100% in the Zn46V2O48 nanowires,which confirms that it is a half-metallic ferromagnet and very suitable for the injection of the spin carriers,which shows that Zn46V2O48 nanowire is one of the ideal materials to realize spin electronic devices.At the same time,the magnetic coupling mechanisms of Zn46V2O48 nanowires are analyzed with V 3d and O 2p orbitals and their magnetic moments mainly come from the contributions of the unpaired electrons of V 3d orbitals.The above results provide a theoretical basis for the preparation of 3d transition metal-doped ZnO nanowire materials.     

PbxSr1-xTiO3的电子结构

在广义梯度近似下, 采用基于密度泛函理论框架下的超软赝势平面波和虚拟晶体近似方法, 计算了不同Pb/Sr摩尔比的PbxSr1-xTiO3(PST)固溶体的精细结构, 确定了A位离子在铁电相的平衡构型. 利用虚拟晶体近似方法分别计算了摩尔比x为0.6、0.7的PbxSr1-xTiO3精细结构. 结果表明, 在钛酸锶铅固溶体中, 随着Pb的摩尔比增大, 晶胞体积膨胀, c/a值增大. 当0.6相似文献   

硒化镉单晶体的研究进展

总结了CdSe单晶体的多种生长方法,包括温度梯度熔体法,移动区熔法,助熔剂法和气相提拉法等,其中气相提拉法能有效提高CdSe单晶体的晶体纯度及光学质量.介绍了CdSe晶体用于红外非线性光学器件以及室温核辐射探测器件的研究进展,并对CdSe晶体制作中红外偏振测量用波片进行了展望.     

纳米金刚石的变温场发射

研究了温度变化对沉积在钛基底上的纳米金刚石的场发射特性的影响,发现纳米金刚石场发射电流随温度和电场的升高而增大,场发射特性偏离了传统的Fowler-Nordheim理论,场发射电流的稳定性基本没有变化.分析了场发射电流增大的机理,表明是由于纳米金刚石的尺度效应以及外电场下金刚石产生了大量的热载流子共同作用的结果.研究还表明基底钛在温度升高到一定程度后,在外加电场下会有较大的电流产生,对场发射造成较大的影响,表明基底钛具有一定的温度敏感性和电压敏感性. 关键词： 场发射 纳米金刚石 尺度效应 热载流子     

First-principles study of La and Sb-doping effects onelectronic structure and optical properties of SrTiO3

The effects of La and Sb doping on the electronic structure and optical properties of SrTiO 3 are investigated by first-principles calculation of the plane wave ultra-soft pseudo-potential based on density functional theory. The calculated results reveal that corner-shared TiO 6 octahedra dominate the main electronic properties of SrTiO 3 , and its structural stability can be improved by La doping. The La 3+ ion fully acts as an electron donor in Sr 0.875 La 0.125 TiO 3 and the Fermi level shifts into the conduction bands (CBs) after La doping. As for SrSb 0.125 Ti 0.875 O 3 , there is a distortion near the bottom of the CBs for SrSb 0.125 Ti 0.875 O 3 after Sb doping and an incipient localization of some of the doped electrons trapped in the Ti site, making it impossible to describe the evolution of the density of states (DOS) within the rigid band model. At the same time, the DOSs of the two electron-doped systems shift towards low energies and the optical band gaps are broadened by about 0.4 and 0.6 eV for Sr0.875La0.125TiO3 and SrSb0.125Ti0.875O3 , respectively. Moreover, the transmittance of SrSb0.125Ti0.875O3 is as high as 95% in most of the visible region, which is higher than that of Sr0.875La0.125TiO3 (85%). The wide band gap, the small transition probability and the weak absorption due to the low partial density of states (PDOS) of impurity in the Fermi level result in the significant optical transparency of SrSb0.125 Ti0.875 O3 .     

纳米金刚石的变温场发射

研究了温度变化对沉积在钛基底上的纳米金刚石的场发射特性的影响,发现纳米金刚石场发射电流随温度和电场的升高而增大,场发射特性偏离了传统的Fowler-Nordheim理论,场发射电流的稳定性基本没有变化.分析了场发射电流增大的机理,表明是由于纳米金刚石的尺度效应以及外电场下金刚石产生了大量的热载流子共同作用的结果.研究还表明基底钛在温度升高到一定程度后,在外加电场下会有较大的电流产生,对场发射造成较大的影响,表明基底钛具有一定的温度敏感性和电压敏感性.     

Growth and characterization of InAsSb alloys by metalorganic chemical vapour deposition

Low pressure metalorganic chemical vapour deposition (LP-MOCVD) growth and characteristics of InAsSb on (100) GaSb substrates are investigated. Mirror-like surfaces with a minimum lattice mismatch are obtained. The samples are studied by photoluminescence spectra, and the output is 3.17μm in wavelength. The surface of InAsSb epilayer shows that its morphological feature is dependent on buffer layer. With an InAs buffer layer used, the best surface is obtained. The InAsSb film shows to be of n-type conduction with an electron concentration of 8.52×10¹⁶cm^-3.