掺钕钇铝石榴石晶体中存在的几种主要缺陷以及对晶体激光特性的影响

掺钕钇铝石榴石晶体(简称YAG:Nd)因具有良好的物理化学性能,高的激光效率和激光破坏阈值、且无需电荷补偿而能掺入三价稀土和过渡元素激活或敏化离子等优点,直到现在仍然作为各种晶体激光器(连续、重复频率、脉冲、倍频、可调谐激光器)的最佳工作物质。有关YAG:Nd晶体制备及性能测试方面的文献国外在1965—1970年间发表较多,以后则报导得很少。但不论在国内外,到目前为止,由于YAG:Nd晶体制备上的困难,在晶体的质量方面还存在着很多问题。

一种LEC-GaAs单晶位锗密度检测和参考面制定的方法

本文从分析LEC-GaAs单晶中wug位错的分布规律出发,结合实验观察,提出了LEC-GaAs单晶{111}和{100}面位错密度检测方法,包括样品制备,位错显示剂和显示条件、测量条件以及取点部位等。 考虑到GaAs单晶的极性对器件工艺的影响,本文提出了一种由位错蚀坑的形状确定极性,在单晶锭上作两个参考面的方法,以保证衬片方位的一致性。

NaI(Tl)晶体的制备

本文叙述了用晶种提引法制备NaI(Tl)晶体的过程。指出了影响晶体能量分辨率的各种因素,卽結晶条件、激活剂含量以及密封包装等。現已能制成直径30毫米、高20毫米的晶体,其最好的能量分辨率好于8%(对Cs^(137)661千电子伏γ射綫而言)。

水平法生长GaAs晶体中位错的产生及其排除机构

本文讨论水平法生长的GaAs晶体中产生位错的原因,以及位错排除的机构。提出“小晶面控制成核”的机构解释位错的分布特征和选择有利晶向生长利用小晶面效应抑制位错增生的方法。 水平晶体生长中由于应力引入位错的因素有:(1)沾润,(2)不均匀热场和(3)大的沉淀物。其中沾润是主要的。产生“生长”位错的因素有:(1)籽晶中位错的延伸,(2)小晶面效应,(3)组分过冷和(4)异质成核。这些因素除小晶面效应外都是可以控制的。 晶体中位错密度沿轴向分布的规律说明位错有增生和排除两种过程。凹界面和籽晶取向对位错增生有重要影响,而小晶面的位置又起关键作用。用〈110〉晶带的〈311〉等方向生长可以利用小晶面效应控制成核过程,抑制位错的增生。通过“位错沿其轴向传播”的排除机构,可以保证生长成无位错的GaAs晶体。

V形槽的腐蚀及其应用

本文简要地回顾了腐蚀V形槽的几种方法。并以联氨(N_2H_4)腐蚀V形槽工艺为主,结合半导体硅的结构报告了腐蚀方法,及达到最佳化的条件。并指出了此工艺的应用。

Band Structure of Three-dimensional Phononic Crystals

By using the plane-wave-expansion method, the band structure of three-dimension phononic crystals was calculated, in which the cuboid scatterers were arranged in a host with a face-centered-cubic （FCC） structure.The influences of a few factors such as the component materials, the filling fraction of scatterers and the ratio （RHL） of the scatterer＇s height to its length on the band-gaps of phononic crystals were investigated.It is found that in the three-dimension solid phononic crystals with FCC structure, the optimum case to obtain band-gaps is to embed high-velocity and high-density scatterers in a low-velocity and low-density host. The maximum value of band-gap can be obtained when the filling fraction is in the middle value. It is also found that the symmetry of the scatterers strongly influences the band-gaps. For RHL＞1, the width of the band-gap decreases as RHL increases. On the contrary, the width of the band-gap increases with the increase of RHL when RHL is smaller than 1.

First-principles thermodynamics of metal-oxide surfaces andinterfaces:A case study review

An important step for achieving the knowledge-based design freedom on nano-and interfacial materials is attained by elucidating the related surface and interface thermodynamics from the first principles so as to allow engineering the microstructures for desired properties through smartly designing fabrication processing parameters.This is demonstrated for SnO2 nano-particle surfaces and also a technologically important Ag-SnO2 interface fabricated by in-situ internal oxidation.Based on defect thermodynamics,we first modeled and calculated the equilibrium surface and interface structures,and as well corresponding properties,as a function of the ambient temperature and oxygen partial pressure.A series of first principles energetics calculations were then performed to construct the equilibrium surface and interface phase diagrams,to describe the environment dependence of the microstructures and properties of the surfaces and interfaces during fabrication and service conditions.The use and potential application of these phase diagrams as a process design tool were suggested and discussed.

Fabrication of Bottom-Gate and Top-Gate Transparent ZnO Thin Film Transistors

Transparent zinc oxide thin film transistors （ZnO-TFTs） with bottom-gate and top-gate structures were constructed on 50mm silica glass substrates. The ZnO films were deposited by RF magnetron sputtering and SiO2 films served as the gate insulator layer. We found that the ZnO-TFTs with bottom-gate structure have better electrical performance than those with top-gate structure. The bottom-gate ZnO-TFTs operate as an n-channel enhancement mode, which have clear pinch off and saturation characteristics. The field effect mobility, threshold voltage, and the current on/off ratio were determined to be 18.4cm^2/（V ·s）, - 0. 5V and 10^4 , respectively. Meanwhile, the top-gate ZnO-TFTs exhibit n-chan- nel depletion mode operation and no saturation characteristics were detected. The electrical difference of the devices may be due to the different character of the interface between the channel and insulator layers. The two transistors types have high transparency in the visible light region.

Intermetallics and phase relations of Mg-Zn-Ce alloys at 400 ℃

The crystal structures,compositions and phase relations of the intermetallics of Mg-Zn-Ce system in the Mg-rich corner at 400 ℃ were identified through equilibrium alloy method.For Mg-Zn-Ce system,there is a linear ternary compound（T phase）,whose chemical formula is（Mg1-xZnx）11Ce.The range of Zn content in T phase is from 9.6% to 43.6%（molar fraction）.The crystal structure of T phase is C-centered orthorhombic lattice with lattice parameters of a=0.96-1.029 nm,b=1.115-1.204 nm,c=0.940-1.015 nm.And the lattice parameters of T phase are decreasing a little with increasing Zn content.According to the results of composition and crystal structure,the maximal solubility of Zn in Mg12Ce is about 7.8%（molar fraction）,and the chemical formula of the solid solution can be identified as（Mg1-xZnx）12Ce.The isothermal section of Mg-Zn-Ce system in Mg-rich corner at 400 ℃ was constructed.

Static Induction Devices with Planar Type Buried Gate

Based on the surface-gate and buried-gate structures,a novel buried-gate structure called the planar type buried-gate (PTBG) structure for static induction devices (SIDs) is proposed.An approach to realize a buried-gate type static induction transistor by conventional planar process technology is presented.Using this structure,it is successfully avoided the second epitaxy with a high degree of difficulty and the complicated mesa process in conventional buried gate.The experimental results demonstrate that this structure is desirable for application in power SIDs.Its advantages are high breakdown voltage and blocking gain.

Effect of surface roughness on plasticity of Zr_(52.5)Cu_(17.9)Ni_(14.6)Al_(10)Ti_5 bulk metallic glass

Zr52.5Cu17.9Ni14.6Al10Ti5 bulk metallic glass （BMG） rods were abraded to different surface roughnesses using different types of waterproof abrasive papers and sometimes polishing pastes, and the compressive deformation behavior was examined. The results show that the yield strength of the BMG is hardly affected while the compressive plasticity increases from 2.3% to 4.5% with decreasing the surface roughness. Observation of the fractured samples under a scanning electron microscope indicates that the rise in plasticity is accompanied with an increase in shear band density. The results suggest that it is necessary to reduce the surface roughness of BMGs for achieving a large plasticity.

A New Poly-Si TFTs DC Model for Device Characterization and Circuit Simulation

A new physical current-voltage model for polysilicon thin-film transistors （poly-Si TFTs） is presented. Taking the V-shaped exponential distribution of trap states density into consideration,explicit calculation of surface potential is derived using the Lambert W function, which greatly improves computational efficiency and is critical in circuit simulation. Based on the exponential density of trap states and the calculated surface potential, the drain current characteristics of the subthreshold and the strong inversion region are predicted. A complete and unique drain current expression, including kink effect, is deduced. The model and the experimental data agree well over a wide range of channel lengths and operational regions.

Probe the Effects of Surface Adsorbates on ZnO Nanowire Conductivity using Dielectric Force Microscopy

Characterization of electric properties of nanomaterials usually involves fabricating field effect transistors （FET） and deriving materials properties from device performances. However, the quality of electrode contacts in FET devices heavily influences the device performance, which makes it difficult to obtain the intrinsic electric properties of nanomaterials. Dielectric force microscopy （DFM）, a contactless method developed recently, can detect the low-frequency dielectric responses of nanomaterials without electric contact, which avoids the influence of electric contact and can be used to study the intrinsic conductivity of nanomaterials. Here we study the influences of surface adsorbates on the conductivity of ZnO nanowires （NWs） by using FET and DFM methods. The conductivity of ZnO NW is much larger in N2 atmosphere than that in ambient environment as measured by FET device, which is further proven by DFM measurement that the ZnO NW exhibits larger dielectric response in N2 environment, and the influence of electrode contacts on measurement can be ruled out. Based on these results, it can be concluded that the adsorbates on ZnO NW surface highly influence the conductivity of ZnO NW rather than the electrode contact. This work also verifies the capability of DFM in measuring electric properties of nanomaterials.

'The Theory of Field-Effect Transistors XII.The Bipolar Drift and Diffusion Currents(1-2-MOS-Gates on Thin-Thick Pure-Impure Base)

The previous report （XI） gave the electrochemical-potential theory of the Bipolar Field-Effect Transistors. This report （XII） gives the drift-diffusion theory. Both treat 1-gate and 2-gate, pure-base and impure-base, and thin and thick base. Both utilize the surface and bulk potentials as the parametric variables to couple the voltage and current equations. In the present drift-diffusion theory, the very many current terms are identified by their mobility multiplier for the components of drift current,and the diffusivity multiplier for the components of the diffusion current. Complete analytical driftdiffusion equations are presented to give the DC current-voltage characteristics of four common MOS transistor structures. The drift current consists of four terms： 1-D （One-Dimensional） bulk charge drift term, 1-D carrier space-charge drift term,l-D Ex^2 （transverse electric field） drift term,2-D drift term. The diffusion current consists of three terms： 1-D bulk charge diffusion term,l-D carrier space-charge diffusion term,and 2-D diffusion term. The 1-D Ex^2 drift term was missed by all the existing transistor theories, and contributes significantly, as much as 25 % of the total current when the base layer is nearly pure. The 2-D terms come from longitudinal gradient of the longitudinal electric field,which scales as the square of the Debye to Channel length ratio, at 25nm channel length with nearly pure base, （LD/L）^2 = 10^6 but with impurity concentration of 10^18cm^-3 , （LD/L）^2 = 10^-2 .

Effects of different characteristic surfaces at initial stage of frost growth

The effects of surface energy on phase change of water vapor at initial stage of frost growth were studied to find an effective method of restraining frost growth.The mechanism of restraining frost growth by low energy surface(bigger contact angle) was analyzed based on crystal growth theory.Then,the phase change of water vapor and the process of frost growth on the copper and wax energy surfaces were observed using microscope.The results indicate that it is difficult for wax surface(low energy surface),on which there are still water droplets at 100 s,to form critical embryo,so frost growth can be restrained in a way.Water formation,droplet growth,ice formation and dendritic ice growth processes happen on both surfaces,ordinally.But the ice beads,with larger average diameter and sparse distribution on the wax surface,form later(at about 300 s) than that on the copper surface,and the dendritic ice also appears later.All of these support that ice crystal formation and dendritic crystal growth at initial stage of frost growth can be retarded on the low energy surface.

Multipartite Entanglement of a Tetrahedron Lattice

Three-dimensional Heisenberg model in the form of a tetrahedron lattice is investigated. The concurrence and multipartite entanglement are calculated through 2-concurrence C and 4-concurrence C4. The concurrence C and multipartite entanglement G4 depend on different coupling strengths Ji and are decreased when the temperature T is increased. For a symmetric tetrahedron lattice, the concurrence C is symmetric about J1 when J~ is negative while the multipartite entanglement G4 is symmetric about J1 when J2 〈 2. For a regular tetrahedron lattice, the concurrence G of ground state is 1/3 for ferromagnetic case while G = 0 for antiferromagnetic ca.se. However, there is no multipartitc entanglement since C4=0 in a regular tetrahedron lattice. The external magnetic field 13 can increase the maximum value of the concurrence GB and induce two or three peaks in Cn. There is a peak in the multipartite entanglement G4 B when G4B is varied as a function of the temperature T. This peak is mainly induced by the magnetic field B.

Design for SOP AMOLED display panel

A novel full color SOP（system on panel） AMOLED display based on the MIUC polycrystalline silicon TFT technique, and a new control circuit for the panel, which can deal with both VGA and DVI input signals have been developed. To realize gray-scale a sub-frame technique has been designed and im- plemented by FPGA device, in which an 120 module has been inserted. Through actual circuit, the whole design has been proven and the advantages of the SOP AMOLED display panel have been confirmed.

Relationship between solid/liquid interface and crystal orientation for pure magnesium solidified in fashion of cellular crystal

The relationship between the solid/liquid interface and the crystal orientation for pure magnesium,which grows in fashion of cellular crystal in unidirectional solidification,was investigated.The results show that the energy of the solid/liquid interface is the lowest during cellular crystal growth of pure magnesium;and the solid/liquid interface is covered by the basal face{0001}and by the crystal face made up of three atoms located at the orientation{0001}0100and two atoms located at the inner of magnesium crystal cell.The strongest bond is formed in the direction of 61.9°viating from the growth direction,and the second strong bond is formed in the directions of 8.5°d 47.7°espectively,deviating from the growth direction.The angle between the basal face{0001} and the growth direction is 61.9°he theoretical analysis results are basically consistent with the experimental results from SUSUMU et al.

Lithium storage performance of {010}-faceted and [111]-faceted anatase TiO2 nanocrystals

As a popular anode material for lithium-ion batteries,anatase TiO2 nanoparticles with exposed{001}facets usually exhibit exceptional lithium storage performance owing to more accessible sites and fast migration of lithium ions along the good crystalline channels.However,there are few researches on the lithium storage capability of TiO2 nanocrystals with other high-energy facets owing to lack of effective synthesis method for controlling crystal facets.Herein,anatase TiO2 nanocrystals with exposed{010}-and[111]-facets are successfully prepared by using the delaminated tetratitanate nanoribbons as precursors.The electrochemical properties of these TiO2 nanocrystals with high-energy surfaces and the comparison with commercial TiO2 nanoparticles(P25)are studied.It is found that the cycle and rate performance of TiO2 nanocrystals is highly improved by reducing the particle size of nanocrystals.Moreover,TiO2 nanocrystals with exposed{010}-and[111]-facets exhibit better lithium storage capacities in comparison with P25 without a specific facet though P25 has smaller particle size than these TiO2 nanocrystals,indicating that the exposed facets of TiO2 nanocrystals have an important impact on their lithium storage capacity.Therefore,the synthesis design of high-performance TiO2 materials applied in the next-generation secondary batteries should both consider the particle size and the exposed facets of nanocrystals.

Device Characteristics Comparison Between GaAs Single and Double Delta-Doped Pseudomorphic High Electron Mobility Transistors

The Al 0.24Ga 0.76As/In 0.22Ga 0.78As single delta-doped PHEMT (SH-PHEMT) and double delta-doped PHEMT (DH-PHEMT) are fabricated and investigated.Based on the employment of double heterojunction,double delta doped design,the DH-PHEMT can enhance the carrier confinement,increase the electron gas density,and improve the electron gas distribution,which is beneficial to the device performance.A high device linearity,high transconductance over a large gate voltage swing,high current drivability are found in DH-PHEMT.These improvements suggest that DH-PHEMT is more suitable for high linearity applications in microwave power device.