Current-induced domain-wall switching in a ferromagnetic semiconductor structure

Magnetic information storage relies on external magnetic fields to encode logical bits through magnetization reversal. But because the magnetic fields needed to operate ultradense storage devices are too high to generate, magnetization reversal by electrical currents is attracting much interest as a promising alternative encoding method. Indeed, spin-polarized currents can reverse the magnetization direction of nanometre-sized metallic structures through torque; however, the high current densities of 10(7)-10(8) A cm(-2) that are at present required exceed the threshold values tolerated by the metal interconnects of integrated circuits. Encoding magnetic information in metallic systems has also been achieved by manipulating the domain walls at the boundary between regions with different magnetization directions, but the approach again requires high current densities of about 10(7) A cm(-2). Here we demonstrate that, in a ferromagnetic semiconductor structure, magnetization reversal through domain-wall switching can be induced in the absence of a magnetic field using current pulses with densities below 10(5) A cm(-2). The slow switching speed and low ferromagnetic transition temperature of our current system are impractical. But provided these problems can be addressed, magnetic reversal through electric pulses with reduced current densities could provide a route to magnetic information storage applications.     

Modulation response performances of a Fabry-Perot semiconductor laser subjected to light injection from another Fabry-Perot semiconductor laser

The modulation response characteristics of a Fabry-Perot semiconductor laser （slave FP-LD） subjected to light injection from another Fabry-Perot semiconductor laser （master FP-LD） have been investigated theoretically. The results show that the modulation response performances of the slave FP-LD depend on the light injection strength, the central mode frequency detuning △f and the mode spacing difference between the slave FP-LD and the master FP-LD. With the increase of the light injection strength from the master FP-LD, the 3 dB modulation bandwidth of the slave FP-LD will be enhanced; however, if the injection strength is increased to certain degree, the front side of the relaxation oscillation peak will be reduced to below 3 dB, which results in the rapid decrease of the 3 dB modulation bandwidth. With the increase of △f, for a relatively small injection strength level, the 3 dB modulation bandwidth will behave a monotonous enlargement until the slave FP-LD operates in a period-one state （P1）. For a relatively strong optical injection level, the slave FP-LD has a broad injection-locked frequency detuning area. Within the injection-locked area, with the increase of frequency detuning △f, the 3dB modulation bandwidth increases at first and then decreases after experiencing a maximum value. For given light injection strength and frequency detuning, the 3 dB modulation bandwidth of the slave FP-LD has two maximums and behaves a symmetrical distribution with the change of △λ By choosing reasonable parameters, the 3 dB modulation bandwidth can be significantly improved. For the parameter values selected in this paper, the 3 dB modulation bandwidth can increase 5.5 times compared with the case of free running.     

Nanomechanics of individual amyloid fibrils using atomic force microscopy

Compression elasticity of glucagon amyloid fibrils in the transverse direction was investigated by a nanoindentation approach based on atomic force microscopy (AFM).With force-volume mapping, we obtained the correlations between radially applied force and compression of amyloid fibrils, from which the radial compressive elasticity can be deduced.The estimated elastic modulus at three typical locations of fibrils varied from (0.72±0.80) GPa to (1.26±0.62) GPa under small external forces, imply-ing the struct...     

Earth-abundant photovoltaic semiconductor NaSbS_2 in the rocksalt-derived structure:A first-principles study

NaSbS_2 was recently proposed as a novel photovoltaic semiconductor with earth-abundant component elements,but its fundamental material properties have not been well studied.The systematical first-principles calculations for its electronic,optical and defect properties were carried out in the present study,and the results show that:i)NaSbS_2 in the rocksalt-derived structure has a quasi-direct band gap and thus may have long minority carrier lifetime;ii) its absorption coefficients are as high as 10~4～10~5 cm~(-1) for the visible light and almost isotropic despite that the structure is distorted relative to the high-symmetry rocksalt structure;iii) the effective masses of the electron and hole carriers are anisotropic with much larger values along the z direction than in the x-y plane,and hence the orientational control of thin films should be important for enhancing the photovoltaic performance;iv) the valence and conduction band edges of NaSbS_2 are close to those of CuGaSe_2) so the n-CdS/pCuGaSe_2 device structure can be inherited to form the n-CdS/p-NaSbS_2 solar cells;v) the acceptor defects (Na_(Sb)antisites and Na vacancies) have very high concentration,making the synthesized NaSbS_2 always be p-type;vi)the S-rich condition can suppress the formation of deep-level donor defects (S vacancies and Sb_(Na) antisites) and therefore should be adopted for fabricating high-efficiency NaSbS_2 solar cells.     

一类半导体器件模拟的Galerkin-MMOCAA方法

用MMOCAA格式（调整对流的特征线修正方法）处理半导体器件模拟的对流占优扩散问题,通过对对流项进行调整,仅增加少童计算量,使该问题既保持了全局质量守恒性质,又具有MMOC格式（特征线修正技术）的所有优点．进行了理论分析,得到了最优阶L^2模误差估计结果．     

某新型半导体显示产业钢厂房备料区抗震性能分析

以某新型半导体显示产业钢结构厂房备料区为工程背景,建立了厂房钢框架-支撑结构的非线性有限元模型,分别对多遇地震和罕遇地震下的结构抗震性能进行了分析。结果表明,结构整体指标均满足设计规范要求,第3层和第6层的层间位移角较大;罕遇地震下构件损伤主要集中在支撑,而结构底层角柱和中部楼层的边跨梁有轻微损伤;钢支撑能够有效提高结构刚度,减小梁柱的损伤。     

Cr掺杂浓度对ZnO基稀磁半导体生长结构的影响

采用射频磁控溅射设备在本征抛光Si(100)衬底上沉积Cr掺杂ZnO薄膜,分析不同掺杂浓度对薄膜的生长结构的影响.分别用XRD、SEM和XRF来表征薄膜的晶相结构、表观形貌和掺杂浓度.实验结果表明,掺杂浓度为2.10%的Zn1-xCrxO薄膜,出现了更好C轴取向性,衍射峰半高宽较窄,样品表面平滑致密,晶粒较大为3.555 nm.     

路面结构动力响应分析

根据结构动力分析理论，建立有限元模型，研究确定了模拟路面瞬态响应的求解策略，通过数值计算，对FWD荷载和车轮荷载作用下的层状体系路面结构响应的一般规律进行分析，得到一些有益的结论。     

带加强层的某框架-核心筒结构地震响应分析

为研究加强层对某大厦抗震性能的影响,文章利用有限元分析程序MSC.Marc分别建立某大厦3种不同方案的有限元模型,对模型进行模态分析和弹性时程计算,并对比分析3种不同方案有限元模型的自振特性、水平地震作用下的位移和内力响应。分析结果表明,就该框架-核心筒结构而言,提高加强层处核心筒和外框架柱的抗震构造措施,带2处加强层的结构方案能较好地控制水平地震作用下结构的侧移。     

Maxwell阻尼耗能隔震结构平稳响应分析

为分析设置Maxwell耗能阻尼器的隔震结构的减震效果,对Maxwell阻尼耗能隔震结构平稳响应分析问题进行了系统研究。首先建立Maxwell阻尼耗能隔震结构运动方程;然后将上部结构按第一振型展开,再将结构运动方程转化为一阶状态方程组,用复模态法获得了结构在平稳白噪声地震激励作用下,隔震层相对于地面位移、速度响应方差和上部结构相对于隔震层位移、速度响应方差以及阻尼器响应方差精确解析解,并通过一算例验证了设置Maxwell耗能阻尼器的隔震结构的减震效果更好。     

二维V型AlP半导体及其可调直接带隙

一种新型单分子层V型结构磷化铝(V-AlP)二维半导体材料被理论预测,且通过第一性原理计算,它的稳定性和电学性质也得到详细考察.在外加应力和电场作用下,其电子结构被有效地调控.计算结果表明它有很好的稳定性,且具有宽的直接带隙(2.6 eV).在双轴应力下,其带隙可以在(1～2.6 eV)范围内调控.在外加张力的作用下,...     

大平台多塔楼结构的隔震减震控制

结合某实际工程,将隔震技术应用到大平台多塔楼结构中,形成大平台多塔楼新型隔震体系.为了进一步提高该新型隔震体系的抗震性能,在隔震层设置了液体粘滞阻尼器,探讨了这种大平台多塔楼结构隔震减震控制的效果.本文建立了大平台多塔楼新型隔震减震体系的运动方程,考虑了隔震支座的非线性,并基于广义Newm ark积分法编写了整个非线性隔震减震体系的仿真分析计算程序.仿真分析结果表明,这种新型隔震体系可以同时减小上部住宅结构与下部平台的地震反应,为提高大平台多塔楼结构的抗震安全性提供了一条崭新的途径.在隔震层附设粘滞阻尼器可进一步减小隔震结构下部平台的地震反应与隔震层的非线性反应,提高这种新型隔震体系的抗震安全性.两种粘滞阻尼器的对比还表明非线性粘滞阻尼器比线性粘滞阻尼器理论上更合理,且更为有效.     

Spin-orbit qubit in a semiconductor nanowire

Motion of electrons can influence their spins through a fundamental effect called spin-orbit interaction. This interaction provides a way to control spins electrically and thus lies at the foundation of spintronics. Even at the level of single electrons, the spin-orbit interaction has proven promising for coherent spin rotations. Here we implement a spin-orbit quantum bit (qubit) in an indium arsenide nanowire, where the spin-orbit interaction is so strong that spin and motion can no longer be separated. In this regime, we realize fast qubit rotations and universal single-qubit control using only electric fields; the qubits are hosted in single-electron quantum dots that are individually addressable. We enhance coherence by dynamically decoupling the qubits from the environment. Nanowires offer various advantages for quantum computing: they can serve as one-dimensional templates for scalable qubit registers, and it is possible to vary the material even during wire growth. Such flexibility can be used to design wires with suppressed decoherence and to push semiconductor qubit fidelities towards error correction levels. Furthermore, electrical dots can be integrated with optical dots in p-n junction nanowires. The coherence times achieved here are sufficient for the conversion of an electronic qubit into a photon, which can serve as a flying qubit for long-distance quantum communication.     

Study of experimental electronic structure of bidimensional semiconductor red bronze K0.33MoO3

X ray photoemission spectra measurements were carried out to elucidate the valence band picture and bonding characters of the two dimensional semiconductor red bronze K_0.33MoO₃. The valence band spectrum is similar to that of measurement of UPS, and in agreement with the molecular orbital model presented by Travaglini. Asymmetric and broadening line shape of O-1s means the presence of several inequivalent bonds of oxygen. Mo-3d core-level spectrum reveals that there are two kinds of valence states of molybdenum (Mo⁺⁵, Mo⁺⁶), and that its average valence state is +5.42. Shi Jing: born in March, 1956, Ph. D. Current research interest is in low dimensional condensed state physics Supported by the National Natural Science Foundation of China     

平转耦联隔震结构简化体系的时程反应分析

在平转耦联隔震结构简化体系的基础上,对地震作用下的反应进行了数值时程计算,并对各有关动力参数对地震反应的影响进行了分析研究,结果表明：在上部结构偏心不大的情况下,隔震层偏心距的变化对上部结构的位移和转角的影响不明显,通过合理地调整隔震层的偏心距,结构的底部扭矩可以明显降低。     

CdZnTe个人剂量计能响特性的Monte Carlo模拟

为了获得合适的CdZnTe(CZT)个人剂量计的剂量-能量响应补偿方案,利用Monte Carlo程序MCNP4C对CZT、CZT加各种补偿物质和CZT在不同电子学下阀的剂量-能量响应特性进行了模拟计算。通过模拟得到了2种CZT个人剂量计剂量补偿方案:在CZT(5mm×5mm×5mm)前加15mm Pb(带有阶梯孔)和2mm Pb(带有孔面积为Pb截面面积3%的孔,并分高、低能两能量道计数)。为今后的CZT个人剂量计设计提供了理论依据。     

Organolead halide perovskites: a family of promising semiconductor materials for solar cells

Great attention has recently been drawn to developing cost-effective, high efficiency solar cells to meet the ever increasing demand for clean energy. We have most recently witnessed a breakthrough and a rapid development in solid state, hybrid solar cells using or- ganolead halide perovskites as light harvesters. These semiconductors can not only serve as sensitizer in solid state sensitized solar cells with efficiency up to unprece- dented 15 %, but also function as both light absorber and hole conductor （or electron conductor） at the same time to display power conversion efficiency above 10 %. In this review, we will introduce their operation mechanism, structure, and especially the development of the organolead halide perovskite based solar cells. Based on the achieve- ments that have been made to date, solid state photovoltaic device with superior performance than the present one is highly expected.     

Generation of ultraviolet entangled photons in a semiconductor

Entanglement is one of the key features of quantum information and communications technology. The method that has been used most frequently to generate highly entangled pairs of photons is parametric down-conversion. Short-wavelength entangled photons are desirable for generating further entanglement between three or four photons, but it is difficult to use parametric down-conversion to generate suitably energetic entangled photon pairs. One method that is expected to be applicable for the generation of such photons is resonant hyper-parametric scattering (RHPS): a pair of entangled photons is generated in a semiconductor via an electronically resonant third-order nonlinear optical process. Semiconductor-based sources of entangled photons would also be advantageous for practical quantum technologies, but attempts to generate entangled photons in semiconductors have not yet been successful. Here we report experimental evidence for the generation of ultraviolet entangled photon pairs by means of biexciton resonant RHPS in a single crystal of the semiconductor CuCl. We anticipate that our results will open the way to the generation of entangled photons by current injection, analogous to current-driven single photon sources.