Textural aspects of electrodeposition processes

Electrodeposition is the most widely used electrochemical surface treatment process for fabrication of functional and decorative coatings. Electrochemical and hydrodynamic parameters of the electrodeposition process and substrdte texture affect the formation of layers of texture and consequently, tbe pbysical and mechanical properties of coating associated with their anisotropy. The uniformity and structure of electroplated metals also strongly depend on the deposition kinetics (charge transfer reaction or mass transport conlrol), which detemlines the conditions of cathode deposit formation and consequently the crystallites orientation. The present work aims to investigate the influence of Cu substrate texture on developing of it in the copper coating electrodeposited under activation control as tbe simple model system for the first stage of thjs study. The texture analysis was performed on the basis of the back-renection pole figures and of ones with a constant information depth, measured by means of X-ray technique. The non-destructive method allowed to analyse the texture for different chosen areas of the deposited layer. The results show the existing texture inhomogenity. The texture of the substrate reveals a strong influence on the texture of the formed Cu layer in its near-interface area. As far as depositing from withdraws from the substrate surface, the texture proceeds to ,3 one component of axis type of (Ill)

Structural and magnetic properties of GaMnAs layers with high Mn content grown by Migration Enhanced Epitaxy on GaAs(100) substrates

We have grown the ferromagnetic semiconductor GaMnAs containing up to 10% Mn by migration enhanced epitaxy at a substrate temperature of 150^oC. The alternate supply of As2 molecules and Ga and Mn atoms made it possible to grow single crystalline GaMnAs layers at very low substrate temperature, at which conventional molecular beam epitaxial growth under excess As supply is not possible due to As condensation. Secondary ion mass spectroscopy and X-ray diffraction measurements confirmed a higher Mn content in the films grown by this method in comparison to the GaMnAs layers grown by low temperature molecular beam epitaxy. The lattice constant of hypothetical zinc-blende structure MnAs is determined to be 5.9 \AA, which deviates somewhat from previously reported values. This deviation is ascribed to growth-condition dependent density of point defects. It is stressed that this effect must be taken into account for any assessment of Mn content from X-ray diffraction data. Magnetization measurements showed an onset of ferromagnetic ordering around 75 K for the GaMnAs layer with 10% Mn. This means that the trend of falling Curie temperatures with increasing Mn concentrations above 5.5% is broken. We tentatively assign this to the variation of the carrier concentration, including contributions from donor and acceptor centers formed by antisite defects and Mn doping, and increased density of magnetically active Mn ions.Comment: No LaTeX source; gzipped postscript text + 3 gzipped postscript figure

Interactions between Casein Kinase Iε (CKIε) and Two Substrates from Disparate Signaling Pathways Reveal Mechanisms for Substrate-Kinase Specificity

Members of the Casein Kinase I (CKI) family of serine/threonine kinases regulate diverse biological pathways. The seven mammalian CKI isoforms contain a highly conserved kinase domain and divergent amino- and carboxy-termini. Although they share a preferred target recognition sequence and have overlapping expression patterns, individual isoforms often have specific substrates. In an effort to determine how substrates recognize differences between CKI isoforms, we have examined the interaction between CKIepsilon and two substrates from different signaling pathways.CKIepsilon, but not CKIalpha, binds to and phosphorylates two proteins: Period, a transcriptional regulator of the circadian rhythms pathway, and Disheveled, an activator of the planar cell polarity pathway. We use GST-pull-down assays data to show that two key residues in CKIalpha's kinase domain prevent Disheveled and Period from binding. We also show that the unique C-terminus of CKIepsilon does not determine Dishevelled's and Period's preference for CKIepsilon nor is it essential for binding, but instead plays an auxillary role in stabilizing the interactions of CKIepsilon with its substrates. We demonstrate that autophosphorylation of CKIepsilon's C-terminal tail prevents substrate binding, and use mass spectrometry and chemical crosslinking to reveal how a phosphorylation-dependent interaction between the C-terminal tail and the kinase domain prevents substrate phosphorylation and binding.The biochemical interactions between CKIepsilon and Disheveled, Period, and its own C-terminus lead to models that explain CKIepsilon's specificity and regulation

The influence of ion implantation by phosphorous on structural changes in porous silicon

Structural changes in the surface layer of technologically treated silicon by ion implantation, chemical etching, and their combined action have been investigated by the X-ray diffractometry methods. The functional and quantitative differences in the thickness dependences of strains, values of maximum strain, level of lattice disturbance and extension of elastic strains nave been revealed after different steps of treatment. The essential modification of photoluminescence spectra was observed in the porous layer after implantation by phosphorus ions in the process of natural aging