Modeling of complex interfaces: Gadolinium‐doped ceria in contact with yttria‐stabilized zirconia

Gadolinium‐doped ceria (GDC) and yttria‐stabilized zirconia (YSZ) are well‐known electrolyte materials in solid oxide fuel cells (SOFCs). Although they can be used independently, it is common to find them in combination in SOFCs, where they are used as protective layers against the formation of secondary phases or electron conduction blockers. Despite their different optimum operating temperatures, it appears that oxygen conduction is not affected by their interface. However, the intrinsic mechanisms of oxygen diffusion at these interfaces still remain unclear. One of the main difficulties when modeling the contact between different materials, or indeed different particles of the same material, is caused by the structural complexity of these systems. If we wish to evaluate the properties of the materials, we first need to obtain a model that includes the main features of the GDC/YSZ interface, such as large‐scale defects or cation interdiffusion in the contiguous phase. Since the generation of such a mixed system is complicated, we show here how the “amorphization and recrystallization” strategy can help us to obtain realistic systems. In this, the first of our papers on the structure and properties of layered GDC/YSZ materials, we discuss the structural features of the grain boundary between GDC and YSZ obtained by molecular dynamics simulations.     

外延生长的Gd掺杂CeO2薄膜内位错的透射电子显微学表征

利用脉冲激光沉积（ pulsed laser depositon, PLD）方法在YSZ（ Y2 O3 stabilised zirconia）单晶衬底上外延生长了Gd掺杂的CeO2薄膜（gadolinium doped CeO2,GDC）。利用透射电子显微镜（TEM）对GDC／YSZ界面以及GDC薄膜内部的位错结构进行了表征。实验发现,界面处存在周期性分布的失配位错,界面失配主要通过失配位错释放。 GDC薄膜内部存在两种不同的位错,其中一种为纯刃型位错,另外一种为混合型位错。     

Chemical Vapor Deposition of Silicon Carbide Epitaxial Films and Their Defect Characterization

A chemical vapor deposition (CVD) system was designed and fabricated in our laboratory and SiC homo-epitaxial layers were grown in the CVD process using silicon tetrachloride and propane precursors with hydrogen as a carrier gas. The temperature field was generated using numerical modeling. Gas flow rates, temperature field, and the gradients are found to influence the growth rates of the epitaxial layers. Growth rates were found to increase as the temperature increased at high carrier gas flow rate, while at lower carrier gas flow rate, growth rates were observed to decrease as the temperature increased. Based on the equilibrium model, “thermodynamically controlled growth” accounts for the growth rate reduction. The grown epitaxial layers were characterized using various techniques. Reduction in the threading screw dislocation (SD) density in the epilayers was observed. Suitable models were developed for explaining the reduction in the SD density as well as the conversion of basal plane dislocations (BPDs) into threading edge dislocations (TEDs).     

Can misfit dislocations be located above the interface of InAs/GaAs (001) epitaxial quantum dots?

ABSTRACT: InAs/GaAs(001) quantum dots grown by droplet epitaxy were investigated using electron microscopy. Misfit dislocations in relaxed InAs/GaAs(001) islands were found to be located approximately 2 nm above the crystalline sample surface, which provides an impression that the misfit dislocations did not form at the island/substrate interface. However, detailed microscopy data analysis indicates that the observation is in fact an artefact caused by the surface oxidation of the material that resulted in substrate surface moving down about 2 nm. As such, caution is needed in explaining the observed interfacial structure.     

基于Cr-O-C钝化层改变多晶Cu表面能和表层位错的脱模力与脱模精度

Cr-O-C钝化层可以提高精密电铸脱模精度,但Cr-O-C钝化层对基底表面的钝化规律和对表层的影响尚未清楚。利用分子动力学方法,在多晶Cu表面沉积离散的Cr、O和C原子,获得不同比例和数量的Cr-O-C钝化层。计算结果表明,不同比例的Cr、O和C原子均可以大幅降低多晶Cu的表面能;随着原子数量的增加,多晶Cu的表面能呈下降趋势;Cr-O-C钝化层增加了多晶Cu表层的位错密度;新增加的位错以Shockley位错为主;在一定沉积原子数量内,位错密度有极值。在多晶Cu表面电沉积不同密度的Cr、O和C原子,通过接触角测试验证了Cr-O-C钝化层降低多晶Cu表面能的结论。电沉积脱模强度和脱模表面粗糙度结果显示,随着沉积原子数的增加,脱模强度和脱模表面粗糙度均降低。研究结果可为利用离散Cr-O-C界面辅助精密电铸脱模提供一种解释。     

低温等径角挤压制备1050铝合金在磁退火后的均匀延伸率和屈服下降现象

采用低温等径角挤压（cryoECAP）制备了超细晶（UFG）1050铝合金。采用拉伸试验、透射电子显微镜和电子背散射衍射等方法,研究了UFG 1050铝合金在90~210 ℃、无磁场和12 T强磁场下退火4 h后的拉伸行为和显微组织。1050铝合金经cryoECAP退火后,晶粒尺寸为0.70~1.28 μm,极限抗拉伸强度与屈服强度之比小于1.24,均匀延伸率小于2.3%。随着退火温度从90 ℃上升到210 ℃,屈服下降现象变得明显,这是因为在拉伸变形过程中,为了维持所施加的应变速率,可动位错有所减少。均匀延伸率从1.55%下降到0.55%,位错密度从5.6×10¹⁴ m^-2下降到4.2×10¹³ m^-2,大角度晶界含量从63.8%增加到70.8%,使得位错湮灭速率提升,从而导致了应变硬化能力的降低。在90~210 ℃的强磁场退火条件下,低含量的大角度晶界（61.7%~66.2%）可以提供一个较慢的位错湮灭速率,从而导致较高的均匀延伸率（0.64%~1.60%）和更慢的屈服点后的流变应力下降。     

Effects of mechanical deformation: Exoemission

An introduction to some of the physical effects (e.g. exoemission, acoustic emission and mechanoluminescence) associated with the mechanical deformation of solids is presented. Greater emphasis has been given to exoelectron emissions. Experimental information and plausible mechanisms for exoemission have been described briefly. In particular, exoelectron emission from metals and oxide-coated metals has been discussed at some length, with the hope of generating a common interest among physicists and metallurgists.     

Compositional nonuniformities and strain relaxation at misoriented InxGa(1−x)As/GaAs interfaces

Compositional nonuniforimities and misfit dislocations are observed near misoriented In_0.2Ga_0.8As/GaAs interfaces. The compositional nonuniformities results from In interdiffusion at the interface over a distance of 3 nm and formation of InAs platelet precipitates. The misfit dislocations are of pure edge and 60° types. The core of pure edge misfit dislocations generally consists of two 60° dislocations separated by approximately 2.5 nm. One of these 60° dislocations is usually split into partials and decorated by platelets of InAs. The interface and surface morphologies are strongly influenced by the substrate tilt away from exact [001] crystallographic orientation.     

Energy-filtering TEM and electron energy-loss spectroscopy of double structure tabular microcrystals of silver halide emulsions

Composite Ag(Br,I) tabular microcrystals of photographic emulsions were studied by the combination of energy-filtering electron microscopy (EFTEM) and electron energy-loss spectroscopy (EELS) in conjunction with energy-dispersive X-ray (EDX) microanalysis. The contrast tuning under the energy-filtering in the low-loss region was used to observe more clearly edge and random dislocations, {11⁻1} stacking faults in the grain shells parallel to {11⁻2} edges and bend and edge contours. Electron spectroscopic diffraction patterns revealed numerous extra reflections at commensurate positions in between the Bragg reflections and diffuse honeycomb contours; these were assigned to the number of defects in the shell region parallel to the grain edges and polyhedral clusters of interstitial silver cations, respectively. Inner-shell excitation bands of silver halide were detected and confirmed by EDX analyses, i.e. the Ag N_2,3 edge at 62 eV (probably overlapped with the weak I N_4,5 edge at 52 eV and the Br M_4,5 edge at 70 eV), the I M_4,5 edge at about 620 eV, and the Br L_2,3 edge at about 1550 eV energy losses. Energy-loss near-edge structure of the Ag M_4,5 edge at about 367 eV energy losses and low-loss fine structure arisen as a result of interband transitions and excitons, possibly superimposed with many electron effects, have been revealed. The crystal thickness was determined by a modified EELS log-ratio technique in satisfactory agreement with measurements on grain replicas.