冷拔碳素钢丝的纤维组织及其亚结构

用光学显微镜、透射和扫描电镜观察、分析冷拔碳素钢丝的纤维组织及其亚结构的形貌和特点,指出它对钢丝力学性能及断裂行为的影响,对金属制品生产者和用户加深对材料的认识有重要的理论和实际意义     

锥形图形衬底上氮化镓薄膜生长和表征

GaN films are grown on cone-shaped patterned sapphire substrates(CPSSs)by metal-organic chemical vapor deposition,and the influence of the temperature during the middle stage of GaN growth on the threading dislocation(TD)density of GaN is investigated.High-resolution X-ray diffraction(XRD)and cathodeluminescence(CL)wereusedtocharacterizetheGaNfilms.TheXRDresultsshowedthattheedge-typedislocation density of GaN grown on CPSS is remarkably reduced compared to that of GaN grown on conventional sapphire substrates(CSSs).Furthermore,whenthegrowthtemperatureinthemiddlestageofGaNgrownonCPSSdecreases,the full width at half maximum of the asymmetry(102)plane of GaN is reduced.This reduction is attributed to the enhancement of vertical growth in the middle stage with a more triangular-like shape and the bending of TDs.The CL intensity spatial mapping results also showed the superior optical properties of GaN grown on CPSS to those of GaN on CSS,and that the density of dark spots of GaN grown on CPSS induced by nonradiative recombination is reduced when the growth temperature in the middle stage decreases.     

Plastic deformation kinetics of electrodeposited Cu foil at low and intermediate homologous temperatures

The plastic deformation kinetics of electrodeposited (EP) Cu foil (grain size d=0.6 μm) were determined at 296–448 K and compared with those for vapor-deposited (VP) foil (d=0.5 μm) tested at 77–473 K. The apparent activation volume v=kT ∂ ln for both materials exhibited a minimum at ∼350 K, and at this temperature, there occurred a marked increase in the temperature dependence of the flow stress σ. The rate-controlling mechanism in both materials at T<373 K appears to be grain boundary shear induced by dislocation pileups at the grain boundaries. The results at T=373–473 K suggest that the dislocation pileups are relieved or prevented and that either cross slip or intersection of dislocations is rate controlling with stronger support for the latter. The determination of the rate-controlling mechanism at the higher temperatures is complicated by possible changes in defect structure due to thermal annealing, and therefore, the operative mechanism corresponds to a structure that may differ from the initial, as-deposited condition.     

LED用非极性GaN外延膜的制备技术进展

GaN是实现白光LED的关键材料。GaN外延膜通常沿极性c轴生长,基于极性GaN的LED有源层量子阱中由于强内建电场的存在而导致器件发光效率降低,而沿非极性面生长的GaN外延膜可以改善或消除极化效应导致的辐射复合效率降低和发光波长蓝移等问题。文章总结了非极性GaN外延膜的制备技术及研究进展,包括平面外延技术和横向外延过生长技术,指出开发非极性GaN自支撑衬底、发展非极性GaN的横向外延生长技术是制备低位错密度非极性GaN的研究方向。     

Si衬底GaN基多量子阱外延材料的TEM研究

本文采用高分辨透射电子显微技术对在Si衬底生长的GaN基多量子阱外延材料的位错特征、外延层与衬底的晶体取向关系及界面的结晶形态等微观结构进行了分析和研究.结果表明:Si衬底生长的GaN与衬底有一定的取向关系;材料在MQW附近的穿透位错密度达108 cm-2量级,且多数为刃型位错;样品A的多量子阱下方可见平行于界面方向的...     

30CrMnSiA绝热剪切带显微观察与分析

采用分离式霍普金森装置对30CrMnSiA的片式帽型试样进行动态剪切,利用光学显微、扫描电镜、透射电镜、显微硬度等金相分析方法对材料绝热剪切带的微观结构演化过程进行分析。研究发现,随着加载应变率的增大,剪切带发生由形变带到转变带的变化趋势,转变带呈"白亮"色,带内由尺寸约为50 nm的低位错、等轴晶粒组成,这是典型的再结晶晶粒特征。转变带形成过程可分为剪切变形、晶粒细化、晶粒断裂旋转、动态再结晶4个阶段。     

A modified vertical Bridgman method for growth of high-quality Cd<Subscript>1−x</Subscript>Zn<Subscript>x</Subscript>Te crystals

In order to deal with the phenomena of Cd evaporation from the raw materials and the heterogeneity caused by the larger-than-unity segregation coefficient of Zn in CdTe during the conventional vertical Bridgman method (VBM) growth of Cd1-xZnxTe (CZT), two modifications—Cd compensation and accelerated crucible rotation technique (ACRT)—are simultaneously adopted to the VBM. By a combination of VBM with the two modifications, several CZT ingots with the dimensions of ∼60×150 mm² are grown. Structural, optical, and electrical characterization of the as-grown CZT crystals reveals that the application of Cd compensation and ACRT is of obvious efficiency in improving concentration homogeneity, reducing defect density, raising crystal quality and, therefore, upgrading the optoelectronic properties of CZT crystals. Nuclear spectra measurements of detectors fabricated from the as-grown crystals also indicate that both modifications can upgrade the detecting performance of CZT.     

Characterization of HgCdTe Diodes on Si Substrates Using Temperature-Dependent Current-Voltage Measurements and Deep Level Transient Spectroscopy

Reverse current in diodes can be dominated by generation processes, depending exponentially on temperature according to the rate-limiting step in the generation process. In this report, the current-voltage-temperature (IVT) relationship is analyzed for several midwave infrared and long-wave infrared (MWIR x = 0.295, LWIR x = 0.233) Hg_1−x Cd _x Te (MCT) diodes. The energy varied from diode to diode. At high reverse biases, the energy tends toward the band gap energy. Close to zero bias, the energy ranged from 0.06 to 0.1 eV. Deep level transient spectroscopy (DLTS) showed a broad peak centered at 55–80 K for the MWIR MCT. Comparison of the DLTS spectrum to a simulation based on the energy and capture cross section from a rate window analysis shows that the peak is a band of traps. The capacitance transient amplitude increased as the filling pulse increased from 1 μs to 0.1 s, consistent with capture at a dislocation. A shift to lower temperatures for the peak was also observed when the diodes are cooled under forward bias. The shift is reversible, indicating that the traps consist at least partially of a bistable defect.     

On the influence of light on dislocation motion in compound semiconductors

The influence of light on dislocation motion and the associated flow stress is examined for CdS and (Hg_0.3Cd_0.7)Te semiconductors. For CdS, a large increase in flow stress is observed for slip on the basal planes during irradiation. In contrast, (Hg_0.3Cd_0.7)Te exhibits a smaller photoplastic effect with a time delay. Results of experiments on the effect of light, slip direction, strain rate, and temperature are presented with emphasis on CdS. Possible mechanisms of photoplasticity, along with methods of exploiting the photoplastic effect to reduce dislocation densities in semiconductor devices, are also discussed.     

The isolation and nucleation of misfit dislocations in strained epitaxial layers grown on patterned,ion-damaged GaAs

As shown previously, the misfit dislocation density of strained epitaxial III–V layers can be significantly reduced by isolating sections (via patterned etching) of a GaAs substrate before epitaxial growth. A disadvantage of this technique is that the wafer surface is no longer planar, which can complicate subsequent device fabrication. As an alternative, we have investigated growth of 350 nm of In_0.5Ga{0.95}As by molecular beam epitaxy at two temperatures on substrates which were patterned and selectively damaged by Xe ion implantation (300 keV, 10¹⁵ cm²). Selectively etched substrates were prepared as reference samples as well. The propagation of the misfit dislocations was stopped by the ion-implanted regions of the low growth temperature (400° C) material, but the damaged portions also acted as copious nucleation sources. The resulting dislocation structure was highly anisotropic, with dislocation lines occurring in virtually only one direction. At the higher growth temperature (500° C) the defect density fell, but the ion damaged sections no longer blocked dislocation glide. Images from cathodoluminescence and transmission electron microscopy show thatthe low growth temperature material has a dislocation density of 70,000 cm^-1 in the 110 direction and less than 10,000 cm^-1 in the 110 direction. Ion channeling and x-ray diffraction show that strain is relieved in only one direction. The strain relief is consistent with the relief derived from TEM dislocation counts and Burgers vector determination. However, even this high dislocation count is not sufficient to reach the expected equilibrium strain. Reasons for the anisotropy are discussed.