Status and Trends in Advanced SOI Devices and Materials

提供了一种用于安德鲁反射测量样品制备新方法. 该方法采用聚焦粒子束刻蚀和磁控溅射,可以获得可控的、干净的、无应力的纳米接触用于自旋极化探测. 所制备的样品中,磁性和非磁性材料样品的反射谱都表现出复杂的峰和谷结构,这些结构可能源于与界面相关的零偏压反常以及与激发态相关的准离子相互作用. 对另一个Co40Fe40B20合金样品采用简单的钕针尖压针方法进行了对比性测量,反射谱中没有观察到谷结构,但谱结构出现较明显的热扩展,这种热扩展可能来源于界面处的非弹性输运. 所有的反射谱目前还不能由现有的理论给出令人满意的解释. 利用点接触反射方法获得可靠的自旋极化信息还有赖于接触界面特征的进一步分析. 而一个更切合实际的、更完善的理论成为迫切的需要.     

Status and Trends in Advanced SOI Devices and Materials

提供了一种用于安德鲁反射测量样品制备新方法.该方法采用聚焦粒子束刻蚀和磁控溅射,可以获得可控的、干净的、无应力的纳米接触用于自旋极化探测.所制备的样品中,磁性和非磁性材料样品的反射谱都表现出复杂的峰和谷结构,这些结构可能源于与界面相关的零偏压反常以及与激发态相关的准离子相互作用.对另一个Co40Fe40B20合金样品采用简单的钕针尖压针方法进行了对比性测量,反射谱中没有观察到谷结构,但谱结构出现较明显的热扩展,这种热扩展可能来源于界面处的非弹性输运.所有的反射谱目前还不能由现有的理论给出令人满意的解释.利用点接触反射方法获得可靠的自旋极化信息还有赖于接触界面特征的进一步分析.而一个更切合实际的、更完善的理论成为迫切的需要.     

AlGaN /GaN分布布拉格反射镜的设计与表征

设计了反射中心波长为500nm的Al0.3Ga0.7N/GaN和AlN/GaN两种分布布拉格反射镜（DBR）,并采用光学传递矩阵方法对其光谱反射率进行了理论上的模拟.采用金属有机物化学气相淀积（MOCVD）技术在蓝宝石衬底上制备了样品.实际测量的样品反射谱中有明显的反射峰,但峰值波长与理论设计有偏差,峰值反射率也比理论设计值偏低.SEM和AFM测量结果表明：这是由生长层厚与设计的偏差和界面不平整引起的.     

AlGaN /GaN分布布拉格反射镜的设计与表征

设计了反射中心波长为500nm的Al0. 3 Ga0. 7N /GaN和AlN /GaN两种分布布拉格反射 镜(DBR) ,并采用光学传递矩阵方法对其光谱反射率进行了理论上的模拟。采用金属有机物化学气相淀积(MOCVD)技术在蓝宝石衬底上制备了样品。实际测量的样品反射谱中有明显的反射峰,但峰值波长与理论设计有偏差,峰值反射率也比理论设计值偏低。SEM和AFM测量结果表明:这是由生长层厚与设计的偏差和界面不平整引起的。     

纳米La0.67Sr0.33MnO3块体的磁性与电输运特性研究

采用溶胶–凝胶法制备了纳米La0.67Sr0.33MnO3样品,通过XRD、TEM及PPMS(物理性质测量系统)研究了样品的结构、磁性和电输运特性。结果表明,样品为单相菱方钙钛矿结构,平均晶粒大小为61 nm,在10 K到300 K间样品具有铁磁性和绝缘体导电行为,在温度小于60 K时因库仑阻塞效应样品电阻随温度降低急遽增加。纳米晶粒尺寸导致样品具有强的磁电阻效应,其中低场磁电阻效应由晶粒间自旋极化电子隧穿界面引起,高场磁电阻效应由界面磁无序引起。     

纳米La_(0.67)Sr_(0.33)MnO_3块体的磁性与电输运特性研究

采用溶胶–凝胶法制备了纳米La0.67Sr0.33MnO3样品,通过XRD、TEM及PPMS(物理性质测量系统)研究了样品的结构、磁性和电输运特性。结果表明,样品为单相菱方钙钛矿结构,平均晶粒大小为61 nm,在10 K到300 K间样品具有铁磁性和绝缘体导电行为,在温度小于60 K时因库仑阻塞效应样品电阻随温度降低急遽增加。纳米晶粒尺寸导致样品具有强的磁电阻效应,其中低场磁电阻效应由晶粒间自旋极化电子隧穿界面引起,高场磁电阻效应由界面磁无序引起。     

新的电调制反射谱技术及其应用

提出一种微接触电调制反射谱（LCER）测试方法,该方示与无接触电调制反射（CER）谱相比较,可极大降低调制电压。给出了自制的详细样品架结构,测量了InGaAs／GaAs量子阱样品,并与光调制反射谱（PR）相比较,结果证实了此方法的可行性和高光谱灵敏度,表明样品与电极的轻微接触既对测量结果没有明显的影响,又可简化测试条件,降低对测量环境的要求,是研究半导体材料和微结构一种方便而又有效的方法。     

IPC-E掺杂聚合物polysulfone薄膜电光系数的测量

制备了以生色团IPC-E为客体的掺杂型有机聚合物polysulfone薄膜样品,对其进行了接触极化。电光聚合物极化后的电光系数是聚合物波导的重要参数。利用基于简单反射法的聚合物薄膜电光系数测量系统对极化样品进行了测量,得到极化聚合物薄膜的电光系数为37pm/V左右,随后又对误差产生的原因进行了详细的分析。这为进一步研究有机聚合物光波导器件创造了条件。     

自旋电子学研究的最新进展

自旋极化电子的高效注入、自旋霍尔效应和自旋流的产生与探测都是目前自旋电子学中热门研究专题,世界一些著名学术刊物屡见报道。对这些重要内容的理论和实验的最新研究成果进行了介绍。通过自旋极化电子高效注入方法和材料的研究,人们期望研制出新一代自旋电子器件,进而实现应用电子自旋传输、记录和存储信息的目标。近期实验给出,自旋极化电子从铁磁金属注入半导体和金属都获得较高的极化率。各种注入方法中,自旋流直接注入法目前备受关注,因为自旋霍尔效应为自旋流的产生与探测提供了新的途径,即自旋霍尔效应可以产生自旋流,但因无霍尔电压故不容易测量;而逆自旋霍尔效应又将自旋流转化为电流,使得难以测量的自旋流又可以直接用电学方法测量。     

白光干涉法测量光纤布喇格光栅反射谱

为了实现光纤布喇格光栅反射谱的低成本测量,采用白光干涉技术搭建了一套结构简单的反射谱测量装置,利用该装置进行了实验,对所采集的干涉信号进行了数据处理,获得了光纤布喇格光栅的反射谱,光谱分辨率达到3pm,并对所测反射谱的光谱分辨率进行了理论分析.结果表明,利用该装置测得的反射谱具有良好的光谱分辨率,通过增加测量量程可以进一步提高光谱分辨率.     

Information Processing With Pure Spin Currents in Silicon: Spin Injection, Extraction, Manipulation, and Detection

We demonstrate that information can be transmitted and processed with pure spin currents in silicon. Fe/Al₂O₃ tunnel barrier contacts are used to produce significant electron spin polarization in the silicon, generating a spin current which flows outside of the charge current path. The spin orientation of this pure spin current is controlled in one of three ways: 1) by switching the magnetization of the Fe contact; 2) by changing the polarity of the bias on the Fe/Al₂O₃ "injector" contact, which enables the generation of either majority or minority spin populations in the Si, providing a way to electrically manipulate the injected spin orientation without changing the magnetization of the contact itself; and 3) by inducing spin precession through the application of a small perpendicular magnetic field. Spin polarization by electrical extraction is as effective as that achieved by the more common electrical spin injection. The output characteristics of a planar silicon three-terminal device are very similar to those of nonvolatile giant magnetoresistance metal spin-valve structures.     

Modulating magnetic ordering of the zigzag-edge trigonal graphene by functionalizations

A pristine zigzag-edge trigonal graphene (ZTG) is a magnetic semiconductor, thus its spin polarization is extremely low. Here, we report the calculated results on enhancing the spin magnetism of a zigzag-edge trigonal graphene (ZTG) by functionalizations, including the heteroatom doping, edge modifications, and introducing topologic defects. It is found that the ZTG features a good tuning ability for functionalizations to improve its spin polarization. When one boron (B) atom is doped to replace one carbon atom in the B sublattice of graphene, a higher spin polarization can be achieved, and the edge modification by Cu, Co, O or B atom can modulate the magnetic ordering significantly due to the spin-polarized charge transfer between the ZTG and terminations, especially for O and Co terminations. And also, the introduced defect (a vacancy and a Stone–Wales defect) can obviously tune local magnetic structures owing to geometrically structural deformations (variations of bond length and bond angle). For these behaviors, in-depth analyses are performed. Our findings suggest that the desirable functionalized ZTG structures might promise importantly potential applications for developing nano-scale spintronics devices.     

人造目标散射结构的零极化辨识与应用

目标最优极化是雷达极化问题研究的重要理论基础.目标零极化又称共极化零点,是目标最优极化的重要组成部分.通过目标零极化可以推导出目标的其他最优极化状态,其广泛应用于目标极化匹配接收、目标对比增强等领域.文中从目标结构辨识角度首次揭示了零极化理论方法在人造目标散射结构辨识方面具有独特优势,并基于人造目标典型散射结构从理论上推导出典型散射结构的零极化矢量.将复极化比平面的极化表征方法与极化响应特征相结合,提出了零极化三维响应特征图可视化表征方法,揭示了典型散射结构的零极化差异,得到了零极化响应特征矢量.在此基础上提出了一种人造目标散射结构的零极化辨识方法,通过提取极化雷达图像中人造目标的强散射中心,将散射中心的零极化响应特征矢量与典型散射结构进行匹配,从而确定散射中心的散射结构类型,实现人造目标结构辨识.结合车辆和无人机等典型人造目标的电磁计算数据,开展了目标结构辨识对比实验.与Cameron分解方法相比,本文提出的零极化散射结构辨识方法能够准确识别出散射中心的散射结构类型.特别对结构对称型人造目标,本文方法识别结果呈现的对称性更准确,更符合目标实际的散射特性.     

Optical and electrical characterization of (Ga,Mn)N/InGaN multiquantum well light-emitting diodes

(Ga,Mn)/N/InGaN multiquantum well (MQW) diodes were grown by molecular beam epitaxy (MBE). The current-voltage characteristics of the diodes show the presence of a parasitic junction between the (Ga,Mn)N and the n-GaN in the top contact layer due to the low conductivity of the former layer. Both the (Ga,Mn)N/InGaN diodes and control samples without Mn doping show no or very low (up to 10% at the lowest temperatures) optical (spin) polarization at zero field or 5 T, respectively. The observed polarization is shown to correspond to the intrinsic optical polarization of the InGaN MQW, due to population distribution between spin sublevels at low temperature, as separately studied by resonant optical excitation with a photon energy lower than the bandgap of both the GaN and (Ga,Mn)N. This indicates efficient losses in the studied structures of any spin polarization generated by optical spin orientation or electrical spin injection. The observed vanishing spin injection efficiency of the spin light-emitting diode (LED) is tentatively attributed to spin losses during the energy relaxation process to the ground state of the excitons giving rise to the light emission.     

AC-Hall effect in multilayered semiconductors

A new technique is presented which exploits ac-Hall effect in the characterization of layered semiconductor structures. The method involves the use of laser signals by means of optical fibers in the presence of a dc magnetic bias field. Upon incidence the polarization of the optical signal is rotated via a Lorentz force due to the ac-Hall effect. As such, the reflected waves carry informations on the Hall mobility of the charge carriers. The calculations show that ac-Hall reflection coefficient warrants sufficient intensity to be measured. Our theory is complete in the sense that depth profiling has been explicitly incorporated in the formulation     

Spin Filtering through Single‐Wall Carbon Nanotubes Functionalized with Single‐Stranded DNA

High spin polarization materials or spin filters are key components in spintronics, a niche subfield of electronics where carrier spins play a functional role. Carrier transmission through these materials is “spin selective,” that is, these materials are able to discriminate between “up” and “down” spins. Common spin filters include transition metal ferromagnets and their alloys, with typical spin selectivity (or, polarization) of ≈50% or less. Here carrier transport is considered in an archetypical one‐dimensional molecular hybrid in which a single wall carbon nanotube (SWCNT) is wrapped around by single stranded deoxyribonucleic acid (ssDNA). By magnetoresistance measurements it is shown that this system can act as a spin filter with maximum spin polarization approaching ≈74% at low temperatures, significantly larger than transition metals under comparable conditions. Inversion asymmetric helicoidal potential of the charged ssDNA backbone induces a Rashba spin‐orbit interaction in the SWCNT channel and polarizes carrier spins. The results are consistent with recent theoretical work that predicted spin dependent conductance in ssDNA‐SWCNT hybrid. Ability to generate highly spin polarized carriers using molecular functionalization can lead to magnet‐less and contact‐less spintronic devices in the future. This can eliminate the conductivity mismatch problem and open new directions for research in organic spintronics.     

Cr∶Mg_2SiO_4晶体中络离子(CrO_4)~(4-)的自旋极化MS-X_α计算

本文采用自旋极化MS-X_α方法计算了Cr:Mg_2SiO_4晶体中络离子(CrO_4)~(4-)的电子结构,给出了T_d群和C_(3v)群下的单电子能量本征值、本征函数和自旋极化分裂值。用过渡态理论计算了部分光学跃迁和电荷转移跃迁的能量。采用Case-Karplus电荷分配法计算得到自旋-轨道耦合常数ζ_(?)。讨论了配位体的距离对单电子轨道和基态组态的影响,也讨论了对称性变化的影响。     

Cr:Mg2SiO4晶体中络离子(CrO4)4-的自旋极化MS-Xα计算

本文采用自旋极化MS-Xα方法计算了Cr:Mg2SiO4晶体中络离子(CrO4)4-的电子结构,给出了Td群和C(3v)群下的单电子能量本征值、本征函数和自旋极化分裂值。用过渡态理论计算了部分光学跃迁和电荷转移跃迁的能量。采用Case-Karplus电荷分配法计算得到自旋-轨道耦合常数ζ(?)。讨论了配位体的距离对单电子轨道和基态组态的影响,也讨论了对称性变化的影响。     

基于超表面的超宽带线极化转换特性研究

极化转换在太赫兹调制领域具有重要的研究意义和应用价值。传统的极化转换器件存在尺寸大、集成度低、损耗高、带宽窄等诸多不足。该文提出一种对称“山”型超表面共振单元结构,可用于实现反射、透射极化转换器件的设计。其中反射型器件实现了极高极化转换率的宽带线极化转换,透射型器件实现了相对带宽达135.5%的超宽带线极化转换。采用各向异性理论分析了反射型器件产生极化转换的机制,并基于多重干涉理论对共振结构阵列与金属背板构成的类F-P腔进行了计算,计算结果与仿真吻合较好。进一步使用正交线栅类F-P腔与共振结构阵列,构成透射型器件,并深入分析了共振单元结构不同部分对宽带极化转换的贡献,讨论了不同结构形成的极化转换频段间的耦合方式。研究结果为基于固定相位差的超宽带偏振极化转换器件的实现以及超表面类F-P腔应用提供了新的思路。