离子辐照引起的金属/绝缘体界面混合与相变研究

载能离子穿过固体界面引起界面原子迁移使界面原子混合和物质成分变化,从而导致界面发生材料相变。简要介绍了载能离子辐照引起金属/绝缘体界面混合效应及相变现象的主要实验研究进展、低能离子和高能离子辐照引起金属/绝缘体界面现象差异,并对离子辐照引起界面混合及相变的机制进行了初步探讨。

金属/绝缘体的场致发射

本文推导了金属 /绝缘体场致发射电流密度公式 ,并应用于金刚石 /碳薄膜场致发射 ,对其现象获得较好的解释 ,同时指出了提高发射电流密度的因素和相应方法。

栅极几何结构对MIS栅结构常关p-GaN/AlGaN/GaN HEMTs性能的影响

高电子迁移率晶体管(high electron mobility transistors,HEMTs)具有高速开关和极高击穿电场等特性,在功率器件领域应用广泛。为提高HEMT器件性能,通过实验研究了栅极几何结构对具有金属/绝缘体/半导体(MIS)栅极结构的常关型p-GaN/AlGaN/GaN HEMTs性能的影响。栅极介质层采用5 nm厚的原位生长AlN,AlN/p-GaN界面呈现出更明显的能带弯曲和更宽的耗尽区,有利于阈值电压向正向偏移,且其相对较宽的能带错位有助于抑制栅极电流。实验结果表明:与栅极非覆盖区长度为0μm和6μm的MIS栅极相比,非覆盖区长度为3μm的MIS栅极可提高器件综合性能,有效抑制正向栅极电流,将阈值电压提高至3 V,并较好地保持电流密度为46 mA/mm;栅极结构中两侧没有栅极覆盖的区域在导通过程和导通状态下均可引起较大的沟道电阻,且沟道电阻随着非覆盖区长度增加而上升。

不连续Fe_(25)Ni_(75)/SiO_2多层膜的微结构和隧道磁电阻效应

用射频磁控溅射技术制备了[SiO2(t1)/Fe25Ni75(t2)]N多层膜系列(其中t1和t2分别代SiO2层和Fe25Ni75层的厚度,N代表层数).研究发现,对[SiO2(3.3nm)/Fe25Ni75(t2)]10系统,当Fe25Ni75层厚度小于2.4nm时,Fe25Ni75层从连续变为不连续;当Fe25Ni75层不连续时,InR基本上正比于T-1/2,表明导电机制为热激发的隧穿导电;在t2=2.1nm时,隧道磁电阻(TMR)有极大值,为-0.64%.对[SiO2(1.8nm)/Fe25Ni75(1.6nm)]N系统,发现磁电阻先随着层数的增加而增加,然后趋于饱和.

Development of Novel Thin-Film SOI High Voltage MOSFET

Two kinds of thin-film SOI high voltage MOSFETs are developed.One is general structure,the other is novel two-drift-region structure.The gate width is 760μm,and the active area is 8.58×10 -2 mm 2.The experiments show that the breakdown voltages of the two-drift-region and general structures are 26V and 17V,respectively,and the on resistances are 65Ω and 80Ω,respectively.

DCIV技术表征MOS/SOI界面陷阱能级密度分布

基于直流电流电压(DCIV)理论和界面陷阱能级U型对称分布模型,可以获取硅界面陷阱在禁带中的分布,即利用沟道界面陷阱引起的界面复合电流与不同源/漏-体正偏电压(Vpn)的函数关系,求出对应每个Vpn的有效界面陷阱面密度(Neff),通过Neff函数与求出的每个Neff值作最小二乘拟合,将拟合参数代入界面陷阱能级密度(DIT)函数式,作出DIT的本征分布图。分别对部分耗尽的n MOS/SOI和p MOS/SOI器件进行测试,得到了预期的界面复合电流曲线,并给出了器件界面陷阱能级密度的U型分布图。结果表明,两种器件在禁带中央附近的陷阱能级密度量级均为109cm-2·e V-1,而远离禁带中央的陷阱能级密度量级为1011cm-2·e V-1。

Phase Transition Behaviour of VO2 Nanorods

The metal-insulator transition （MIT） of VO2 （M） nanorods was studied. It was found that there were two MITs in the differential scanning calorimetry （DSC） curves of the VO2（M） nanorods, one situated at low temperature from -3 ℃ to 19 ℃ and the other was at high temperature of 65-74℃. The low temperature MIT was always accompanied with VO2（B） nanorods, and the high temperature MIT existed singly only in pure VO2（M） nanorods. The mechanisms of these two MITs were analyzed and discussed.

Formation mechanism and modulation of electromagnetically induced transparency-like transmission in side-coupled structures

Based on Fabry model and finite-different time-domain(FDTD) method, the plasmonic structure composed of a metal-insulator-metal(MIM) bus waveguide and a side-coupled resonator was investigated. It is found that the transmission features can be regulated by the cavity width and coupling distance. Electromagnetically induced transparency(EIT)-like transmission can be excited by adding an identical resonator on the pre-existing structure. Combining the foregoing theoretical analysis with coupled mode theory(CMT), the formation process of the EIT-like transmission was detailedly analyzed. EIT-like transmission can also be excited in plasmonic structure with two detuned resonators. By altering the structure parameters, the transparency window can be purposefully modulated. With the merits of compact structure and simplicity in fabrication, the proposed structures may have a broad prospect of applications in highly integrated optical circuits.

Lifetime of metal rubber isolator with different vibration amplitudes

The lifetime of metal rubber isolator and its characteristics during lifetime experiment were studied. The stepped-up test principle was adopted to study the lifetime of resonant frequency, the breakage form of metal rubber isolator was obtained, and the relation between the energy dissipation, resonant frequency and stiffness was obtained in (available) lifetime of the isolator. Furthermore, the reason for the changes of properties of metal rubber isolator was analyzed with contact model of metal rubber material. The results show that if the resonant amplitude is large, the stiffness of metal rubber isolator will be kept steadily for a long time, its resonant frequency will be stable and the effective working time in the protecting area will be long. The lifetime of metal rubber isolator is more than 1376 h in the experiment. The main failure forms of metal rubber isolator are accumulative wear and breaking of metal wires and spirals. In protecting area the metal rubber isolator can work effectively for a long time, and the effective working time depends on the concrete working condition.

Optical Reskponse of Metal—Dielectric Composite Containing Interfacial Layers

A phenomenological approach to investigate the effect of interfacial layers on the absorption of metal-dielectric composite at elevated temperatures is put forward by making use of a model in which weakly nonlinear spherical metallic particles with linear concentric shells are randomly embedded in a linear host. Corresponding formulae in terms of the interfacial factor are derived in detail by incorporating Taylor expansion and Drude model. We take composite as numerical calculation. It is concluded that such absorption is dependent not only on the temperature, but also on the properties of interfacial layers. Many other interesting phenomena are shown.

Light Emission Characteristics of Metal/Insulator/Metal and Metal/Insulator/Si Tunnel Junctions Mediated by Surface Plasmon-polaritons

The Au/Al2O3/Al metal/insulator/metal junction(MIMJ) and Au/SiO2/Si metal/insulator/Si junction(MISJ) have been constructed successfully. The light emission of these junctions was mediated by surface plasmon-polaritons(SPPs) under surface roughness. The light emission from MISJ was more uniform and stable than that from MIMJ. The light power of MISJ was about 2~3 orders higher than that of MIMJ. The light emission spectrum of MISJ was analyzed especially. In the spectrum, there was one main peak located at the wavelength of 610 nm^640 nm, which was mainly due to the couple of SPP with the surface roughness at the Au/air and Au/SiO2 interfaces. A weak peak located at the shorter wavelength region in the spectrum was also found, which was caused by the direct radiation of doped-Si plasma oscillation.

Influence of Doping on the Mott Metal—Insulator Transition in Infinite Dimensions

We have studied the effect of hole-doping on the established scenerio of the first-order Mott metal-insulator transition (MIT) at half-filling using dynamical mean-field theory and exact diagonalization technique. The Mott insulator state is changed into metallic state immediately as holes are doped into the system. The latter is expected to be Fermi liquid. The previously found unanalytical structure of MIT no longer exists for doping as small as 2 percent. We compare our results with that obtained from Gutzwiller approximation.

Well Dispersed SnO2 Nanoclusters Preparation and Modulation of Metal-Insulator Transition Induced by Ionic Liquid

Tin dioxide (SnO2) has attracted broad interest due to its particular gas-sensor property. Nano- or atom-scale SnO2 material has always been the aim in order to ultimately improve the sensitivity. However, until now, it remains difficult to synthesize SnO2 nanoclusters by using traditional methods. In the present work, we have achieved the preparation of SnO2 nanoclusters by using the cluster beam deposition technique. The obtained nanoclusters were well characterized by high resolution transmission electron microscope HR-TEM. Results indicated the formation of the well-dispersed SnO2 nanoclusters with uniform size distribution (5-7 nm). Furthermore, an obvious metal insulator transition was observed by gating with ionic liquid. Combined with theory calculation, the corresponding mechanism was systematically analyzed from oxygen vacancy induced electron doping.

Josephson Effect in FS/I/N/I/FS Tunnel Junctions

The Bogoliubov de Gennes equation is applied to the study of coherence effects in the ferromagnetic superconductor/insulator/normal metal/insulator/ferromagnetic/superconductor （FS/I/N/I/FS） junction. We calculated the Josephson current in FS/I/N/I/FS as a function of exchange field in ferromagnetic superconductor, temperature, and normal metal thickness. It is found that the Josephson critical current in FS/I/N/I/FS exhibits oscillations as a function of the length of normal metal. The exchange field always suppresses the Josephson critical current Ip for a parallel configuration of the magnetic moments of two ferromagnetic superconductor （FS） electrodes. In the antiparallel configuration, the Josephson critical current IAv at the minimum values of oscillation increases with the exchange field for strong barrier strength and at low temperatures.

Pressure Rise in Electrical Installations due to Internal Arcing in CO2 as Insulating Gas

Internal arcs cause a rapid increase in pressure in electrical installations. The type of insulation gas has influence on pressure development. Typically SF6 is used incompact metal-clad switchgear, however, it has a high global warming potential. Because of this, the replacement of SF6 by alternative gases such as CO2 is under discussion. The pressure developments in a closed vessel filled with air, SF6 and CO2 are measured and compared. During internal arcing in gas-insulated switchgear, overpressure causes a rupture of a burst plate and hot gas escapes into the surrounding room mixing with air. In order to predict the pressure development in electrical installations reliably, the portion of energy causing pressure rise, arc voltage as well as reliable gas data i.e., thermodynamic and transport properties, must be known in a wide range of pressure and temperature. These data are up to now not available for CO2/air mixtures. The thermodynamic properties are directly calculated from the number densities, internal partition functions and enthalpies of formation. The transport coefficients are deduced using the Chapman-Enskog method. Comparing measured and calculated pressure developments in a test arrangement demonstrates the quality of the calculation approach.

表面等离极化激元对电荷输运影响的自洽场理论研究

采用自洽场方法获得体系电荷密度分布 ,根据激子理论分析体系电荷密度矩阵 ,推导出表面等离极化激元(SPP)的频谱分布 ,并在原子轨道函数基上构造电流输运的矩阵等式 ,然后采用SPP频谱规范电流输运矩阵得到电流输运多项式的表达形式 .

Strain-modulation and service behavior of Au-MgO-ZnO ultraviolet photodetector by piezo-phototronic effect

Au-MgO-ZnO （AMZ） ultraviolet （UV） photodetectors were fabricated to enhance their sensitivities by an inserting ultrathin insulating MgO layer. With the insulating layer, the sensitivities of the UV photodetectors were improved via the reduction of the dark current. Furthermore, strain modulation was used to enhance the sensitivities of the AMZ UV photodetectors. The sensitivities of the photodetectors were enhanced by the piezo-phototronic effect. However, there was a limiting value of the applied strains to enhance the sensitivity of the photodetector. When the external strains exceeded the limiting value, the sensitivity decreased because of the tunneling dark current. The external strains loaded on the photodetectors result in the degradation of the photodetectors, and an applied bias can accelerate the process. This work presents a prospective approach to engineer the performance of a UV photodetector. In addition, the study on the service behavior of the photodetectors may offer a strain range and theoretical support for safely using and studying metal-insulator-semiconductor （MIS） UV photodetectors.

A density functional theory study of the tunable structure, magnetism and metal-insulator phase transition in VS2 monolayers induced by in-plane biaxial strain

We report a density functional theory study of a phase transition of a VS2 monolayer that can be tuned by the in-plane biaxial strain. This results in both a metal-insulator transition and a low spin-high spin magnetic transition. At low temperature, the semiconducting H-phase is stable and large strain （〉3%） is required to provoke the transition. On the other hand, at room temperature （300 K）, only a small tensile strain of 2% is needed to induce the phase transition from the semiconducting H-phase to the metallic T-phase together with the magnetic transition from high spin to low spin. The phase diagram dependence on both strain and temperature is also discussed in order to provide a better understanding of the phase stability of VS2 monolayers.

Large unsaturated positive and negative magnetoresistance in Weyl semimetal TaP

After successfully growing single-crystal TaP, we measured its longitudinal resistivity （Pxx） and Hall resistivity （Pyx） at magnetic fields up to 9 T in the temperature range of 2-300 K. At 8 T, the magnetoresistance （MR） reached 3.28 ×10^5% at 2 K, 176% at 300 K. Neither value appeared saturated. We confirmed that TaP is a hole-electron compensated semimetal with a low carrier concentration and high hole mobility ofμh=3.71 × 105 cm2/V s, and found that a magnetic-field-induced metal-insulator transition occurs at room temperature. Remarkably, because a magnetic field （H） was applied in parallel to the electric field （E）, a negative MR due to a chiral anomaly was observed and reached -3000% at 9 T without any sign of saturation, either, which is in contrast to other Weyl semimetals （WSMs）. The analysis of the Shubnikov-de Haas （SdH） oscillations superimposed on the MR revealed that a nontrivial Berry＇s phase with a strong offset of 0.3958, which is the characteristic feature of charge carriers enclosing a Weyl node. These results indicate that TaP is a promising candidate not only for revealing fundamental physics of the WSM state but also for some novel applications.

Intrinsic superconducting transport properties of ultra-thin Fe_(1+y)Te_(0:6)Se_(0:4) microbridges

We investigated the superconducting properties of Fe_(1+y)Te_(0:6)Se_(0:4) single-crystalline microbridges with a width of 4 m and thicknesses ranging from 20.8 to 136.2 nm. The temperature-dependent in-plane resistance of the bridges exhibited a type of metalinsulator transition in the normal state. The critical current density(J_c) of the microbridge with a thickness of 136.2 nm was82.3 kA/cm^2 at 3K and reached 105 kA/cm^2 after extrapolation to T = 0 K. The current versus voltage characteristics of the microbridges showed a Josephson-like behavior with an obvious hysteresis. These results demonstrate the potential application of ultra-thin Fe-based microbridges in superconducting electronic devices such as bolometric detectors.