Understanding silica-supported metal catalysts: Pd/silica as a case study

Supported metal catalysts, particularly noble metals supported on SiO₂, have attracted considerable attention due to the importance of the silica–metal interface in heterogeneous catalysis and in electronic device fabrication. Several important issues, e.g., the stability of the metal–oxide interface at working temperatures and pressures, are not well-understood. In this review, the present status of our understanding of the metal–silica interface is reviewed. Recent results of model studies in our laboratories on Pd/SiO₂/Mo(1 1 2) using LEED, AES and STM are reported. In this work, epitaxial, ultrathin, well-ordered SiO₂ films were grown on a Mo(1 1 2) substrate to circumvent complications that frequently arise from the silica–silicon interface present in silica thin films grown on silicon.     

An anti-plane crack perpendicular to the weak/micro-discontinuous interface in a bi-FGM structure with exponential and linear non-homogeneities

Treated was an anti-plane crack perpendicular to the interface of an exponential-type FGM strip bonded to another linear-type FGM substrate with infinite thickness. Through Fourier integral transform, the problem was reduced as a Cauchy singular integral equation, which was further solved numerically by the Lobatto–Chebyshev collocation method. Based on the numerical solution, the effects of the geometrical and physical parameters on the stress intensity factor (SIF) were analyzed and the following conclusions were obtained: (a) A notable discrepancy between the interface-perpendicular crack and the interfacial one is that, to reduce the weak-discontinuity of interface or to make the interface micro-discontinuous will not necessarily decrease the SIF of the former, but will surely decrease that of the latter. (b) When a crack tip is situated very near to the interface (or free surface), its SIF will be high and totally dominated by the interface (or free surface). (c) To increase the stiffness of the FGM on one side of the interface is beneficial to preventing the crack on the other side from growing toward the interface. Besides, some practical suggestions were further given for material design in the field of composites.     

Design of sustainable V-based hydrogen separation membranes based on grain boundary segregation

Inter-diffusion between vanadium and palladium coating layers in vanadium-based hydrogen separation membranes is investigated by using a computational approach based on first-principles calculations and semi-empirical atomistic simulations, paying attention to the surface stability and the prevention of the degradation of hydrogen permeability. It is found that the governing mechanism of the inter-diffusion is the grain boundary diffusion, and therefore a diffusion barrier based on the grain boundary segregation of impurities can be an efficient way to inhibit the inter-diffusion that causes the degradation. An interesting aspect in previous experimental works that showed a good resistance to the inter-diffusion by an addition of a trace amount of yttrium is discussed from the view point of the grain boundary segregation. An experiment that proves the validity of the present alloy design scheme (inhibition of inter-diffusion using grain boundary segregation) is carried out, and a process to maximize the sustainability of the membrane is also proposed.     

S and Te inter-diffusion in CdTe/CdS hetero junction

Effects of post formation thermal annealing of the CdTe–CdS device on the inter-diffusion of S and Te at the junction in a substrate configuration device have been studied by Auger electron spectroscopy. While the migration of S and Te atoms increases with annealing temperature, the extent of S diffusion is always higher than the diffusion of Te atoms. Inter-diffusion of S and Te causes the formation of CdTe_1-xS_x ternary compound at the CdTe–CdS interface.     

P3HT based solution-processed pseudo bi-layer organic solar cell with enhanced performance

We present a solution-processed pseudo bi-layer organic solar cell with poly(3-hexyl thiophene) (P3HT) as donor and indene-C₆₀ bisadduct (ICBA) as acceptor. The devices were fabricated by sequential processing of the active components followed by a thermal annealing treatment. An efficiency of 5.9% was achieved under AM 1.5G irradiation (1000 W/m²). The obtained efficiency is attributed to an enhanced nanomorphology that arises from the inter-diffusion of the ICBA molecules into a layer of pre-organised polymer (P3HT) and also due to the subsequent crystallisation of the ICBA molecules. These processes facilitate efficient charge generation and extraction. Time of flight-secondary ion mass spectroscopy (TOF-SIMS) depth profiling was carried out for different thermal annealing treatments of these pseudo bi-layer devices, which reveals full inter-diffusion of ICBA into the polymer P3HT. Photo-CELIV (charge extraction by linearly increasing voltage) studies elucidates that the thermal annealing imparts crystallinity to the fullerene phase which results in the improvement of charge carrier mobility.     

一种基于Ag-Sn等温凝固的圆片键合技术

研究了用Ag-Sn作为键合中间层的圆片健合。相对于成熟的Au-Sn键合系统(典型键合温度是280℃),该系统可以提供更低成本、更高键合后分离(De-Bonding)温度的圆片级键合方案。使用直径为100mm硅片,盖板硅片上溅射多层金属Ti/Ni/Sn/Au,利用Lift-off工艺来形成图形。基板硅片上溅射Ti/Ni/Au/Ag。硅片制备好后,将盖板和基板叠放在一起送入键合机进行键合。键合过程在N2气氛中进行,键合过程中不需要使用助焊剂。研究了不同键合参数,如键合压力、温度等对键合结果的影响。剪切强度测试表明样品的剪切强度平均在55.17MPa。TMA测试表明键合后分离温度可以控制在500℃左右。He泄漏测试证明封接的气密性极好。     

Microstructural changes of aluminized Alloy 617 during high-temperature aging

In this study, aluminized Alloy 617 was prepared by Al-pack cementation of high temperature high Al activity process. The microstructure evolution and microstructural changes of aluminide coating were investigated after Al-pack cementation and high-temperature aging. The aluminide coating was composed of Ni-aluminide layers, such as δ-Ni₂Al₃, β-NiAl, Cr₂Al, Al_3 + xMo_1 − x, and inter-diffusion zone by pack cementation. After high-temperature aging, the aluminide coating was transformed from the δ-Ni₂Al₃ to the β-NiAl because of outward Ni diffusion from substrate. The Cr₂Al and the Al_3 + xMo_1 − x were dissolved during aging. On the other hand, the α-(Cr, Mo) particles were precipitated during aging due to the low solubility of alloying elements in the β-NiAl. The β-NiAl newly formed by the outward Ni diffusion during aging and resulted in the formation of the inter-diffusion zone. The inter-diffusion zone consisted of β-NiAl, Ni₃(Al, Ti), Cr-rich M₂₃C₆ carbide, and sigma phases.     

Microstructural evolution of CoCrAlY bond coat on Ni-based superalloy DZ 125 at 1050 °C

CoCrAlY alloy has been widely used as metallic protective coatings or the bond coats in thermal barrier coatings (TBCs) to protect the underlying superalloy from oxidation and hot-corrosion. In this paper, the TBC consisting of yttria stabilized zirconia (7YSZ) ceramic top coat and CoCrAlY bond coat was deposited onto directionally solidified nickel based superalloy DZ 125 by electron beam physical vapor deposition (EB-PVD). The microstructural evolution of the bond coat on this superalloy was investigated after thermal exposure for 100 h at 1050 °C. Due to a significant inward diffusion of Al, Co and Cr from the coating and outward diffusion of Ni, Hf, W and Ti from the substrate, the phase transformation from the Co-based Al-rich β-CoAl phase to the Al-deficient γ-CoNi solid solution phase occurred in the bond coat. Simultaneously, a large amount of Ni-based β-NiCoAl phase was present in the bond coat. In addition, the particles containing substrate strengthening elements Hf and/or W are abundant in the thermally grown oxides (TGO) and within the bond coat. The mechanism for the microstructural evolution is discussed.     

Preparation and oxidation behavior of NiCrAlYSi coating on a cobalt-base superalloy K40S

Arc ion plating had been employed on a cobalt-base superalloy K40S to deposit a NiCrAlYSi coating to improve its oxidation resistance at 1323-1423 K in air. The K40S superalloy had poor oxidation resistance because a non-protective and easy spalling surface oxides scale mixed of Cr₂O₃ and CoCr₂O₄ was formed on its surface. After coated with NiCrAlYSi coating, a dense and protective α-Al₂O₃ scale was formed on the coating and excellently improved its oxidation resistance. Inter-diffusion obviously occurred between the coating and the substrate K40S superalloy in oxidation process, which resulted from Co atoms in K40S outwards diffused. A richen Cr and W carbides inter-diffusion layer was formed, which could acted as a diffusion barrier that barred Al atoms in coating inwards diffusion. Though the NiCrAlYSi changed into NiCoCrAlYSi during oxidation process, it still possessed a good oxidation resistance and had a considerable long-term life.     

Bulk heterojunction formation with induced concentration gradient from a bilayer structure of P3HT:CdSe/ZnS quantum dots using inter-diffusion process for developing high efficiency solar cell

Bulk heterojunction (BHJ) solar cells consisting of poly(3-hexylthiophene) (P3HT) as donor and cadmium selenide/zinc sulphide (CdSe/ZnS) core shell quantum dots (QDs) as acceptor have been developed. Starting from the bilayer of P3HT/QD structure a BHJ is induced using the process of thermal inter-diffusion. The absorption measurements on the bilayer structure show that the absorption coefficient increases and the absorption spectrum becomes broader in the annealed device. Also, the photoluminescence of the annealed device is found to decrease by an order of magnitude showing a significant transfer of electrons to the QDs. With this approach and under broadband white light with an irradiance of 8.19 mW/cm², we have been able to achieve a power conversion efficiency of 5.1% and fill factor 0.45 for this solar cell.