Fundamental processes in Si/Si and Ge/Si epitaxy studied by scanning tunneling microscopy during growth

Experimental results on the epitaxy of Si and Ge on Si(0 0 1) and Si(1 1 1) surfaces, which are obtained by scanning tunneling microscopy (STM) imaging during growth, are reviewed. Techniques for simultaneous epitaxial growth and STM measurements at high temperature are described. The ability to access the evolution of the growth morphology during growth down to the atomic level enables the study of the influence of surface reconstruction on the growth. The relatively complete characterization of the growth process facilitates comparison to theoretical models and allows the identification of fundamental growth processes. For instance, the observed transition between different growth modes can be explained by specific growth processes included in a model. The influence of strain on the growth morphology is reviewed for the case of heteroepitaxial growth of Ge on Si. With the method of combining STM imaging and epitaxial growth, the transition from two-dimensional to three-dimensional growth as well as the evolution of size and shape of three-dimensional islands can be studied.     

Investigation of InAs—InSb solid solution heteroepitaxial layers and structures

The results of investigations concerning the peculiarities of obtaining InAs—InAs_1−xSb_x heterostructure and of its properties revealed that the quality of epitaxial layers as well as photoelectric and electroluminescent device structure characteristics are to a great extent determined by a disagreement magnitude of heterostructure materials. — To decrease the magnitude of disagreement at the layer-substrate boundary and to achieve the composition with x > 0.1 at some distance the method of layer-by-layer growth (ANDREWS et al.) and the obtaining a graded heterojunction with optimization of component distribution along epilayer thickness seems to be promising.     

Deactivation of Cu-Exchanged Automotive-Emission NH3-SCR Catalysts Elucidated with Nanoscale Resolution Using Scanning Transmission X-ray Microscopy

To gain insight into the underlying mechanisms of catalyst durability for the selective catalytic reduction (SCR) of NO_x with an ammonia reductant, we employed scanning transmission X-ray microscopy (STXM) to study Cu-exchanged zeolites with the CHA and MFI framework structures before and after simulated 135 000-mile aging. X-ray absorption near-edge structure (XANES) measurements were performed at the Al K- and Cu L-edges. The local environment of framework Al, the oxidation state of Cu, and geometric changes were analyzed, showing a multi-factor-induced catalytic deactivation. In Cu-exchanged MFI, a transformation of Cu^II to Cu^I and Cu_xO_y was observed. We also found a spatial correlation between extra-framework Al and deactivated Cu species near the surface of the zeolite as well as a weak positive correlation between the amount of Cu^I and tri-coordinated Al. By inspecting both Al and Cu in fresh and aged Cu-exchanged zeolites, we conclude that the importance of the preservation of isolated Cu^II sites trumps that of Brønsted acid sites for NH₃-SCR activity.     

Design, synthesis and evaluation of new RDP inhibitors

Aminophosphinic acid derivatives were synthesized as potential inhibitors of renal dipeptidase, an enzyme overexpressed in benign and malignant colon tumors. Several compounds showed potent enzyme-inhibitory activity.     

Restarted GMRES preconditioned by deflation

This paper presents a new preconditioning technique for the restarted GMRES algorithm. It is based on an invariant subspace approximation which is updated at each cycle. Numerical examples show that this deflation technique gives a more robust scheme than the restarted algorithm, at a low cost of operations and memory.