Impact of substrate material and annealing conditions on the microstructure and chemistry of yttria-stabilized-zirconia thin films

Si-diffusion from Si-based substrates into yttria-stabilized-zirconia (YSZ) thin films and its impact on their microstructure and chemistry is investigated. YSZ thin films used in electrochemical applications based on micro-electrochemical systems (MEMS) are deposited via spray pyrolysis onto silicon-based and silicon-free substrates, i.e. Si_xN_y-coated Si wafer, SiO₂ single crystals and Al₂O₃, sapphire. The samples are annealed at 600 °C and 1000 °C for 20 h in air. Transmission electron microscopy (TEM) showed that the Si_xN_y-coated Si wafer is oxidized to SiO_z at the interface to the YSZ thin film at temperatures as low as 600 °C. On all YSZ thin films, silica is detected by X-ray photoelectron spectroscopy (XPS). A particular large Si concentration of up to 11 at% is detected at the surface of the YSZ thin films when deposited on silicon-based substrates after annealing at 1000 °C. Their grain boundary mobility is reduced 2.5 times due to the incorporation of SiO₂. YSZ films on Si-based substrates annealed at 600 °C show a grain size gradient from the interface to the surface of 3 nm to 10 nm. For these films, the silicon content is about 1.5 at% at the thin film's surface.     

Preliminary characterization of a nuclear factor interacting with the silencer element at the 3'-side of the chicken alpha-globin gene domain

A silencer element has been identified previously on the 3'-side of the chicken alpha-globin genes placed next to the major enhancer in this domain (Recillas Targa et al., unpublished). Deletion fragments of this negative element show the requirement of the entire DNA segment for maximum silencing activity. Additionally, the sub-fragments including the previously defined SF1 (Silencer Factor 1) sequence seem to play an important role on the negative action of this silencer. Preliminary characterization of the nuclear factor interacting with the SF1 sequence was carried out. Methylation interference experiments show the contact points and, by electrophoretic retardation analysis with SF1 and SF1-mutated oligonucleotides, the critical role of these contacts points on the formation of the DNA-protein complex could be demonstrated. These results provide a basis for further experiments on the characterization and understanding of the mechanisms of action of the coupled positive and negative regulatory elements.     

New opportunities for processing the OSI-7 layer protocols using parallel processing (transputers)

The attractiveness of the OSI-7 layer model is closely dependent upon a highly ambitious intent to promote a series of quasi-universal standards to coordinate the communication between heterogeneous applications, whatever the distributed architectures might be. However, a major criticism of the OSI-model is the performance and the handling of the presentation layer. This paper deals with the evaluation of parallel processing techniques operating at the upper levels of the OSI-model using transputers in a parallel co-processor. It is shown that the performance problem is highly dependent on the structure of the protocol stack and its implementation. With the object-oriented modularization of the protocol stack, an architecture of a possible co-processor using transputers is considered and its performance is considered adequate. An ideal configuration is briefly presented. A final performance appraisal of the parallelism effect is discussed with some insight into the future.     

Temperature dependent study of carbon-doped InP/InGaAs HBT's

We report on a temperature dependent study of the dc and the microwave performance of carbon-doped InP/In_0.53Ga_0.47 As heterojunction bipolar transistors (HBT's). The turn on voltage increased 114% and the dc current gain decreased 25% as the temperature was reduced from 300 K to 33 K. Under high-current injection, there was a 29% increase in the current gain cutoff frequency of these devices as the temperature was lowered from 300 K to 77 K. By investigating the operation of HBT's at cryogenic temperatures, increased understanding of the mechanisms of carrier transport in these devices can be obtained, and this may lead to improvements in device performance     

Preparation of the Bi8Sb32Te60 solid solution by mechanical alloying

Bi₂Te₃, Sb₂Te₃ and Bi₈Sb₃₂Te₆₀ thermoelectric materials have been prepared by mechanical alloying using a high energy planetary ball mill. The alloy formation was followed by X-ray diffraction (XRD), the morphology by scanning electron microscopy (SEM) and the composition by electron microprobe. The samples of Bi₈Sb₃₂Te₆₀ were prepared in a reasonable milling time (less than 8 h) by mechanical alloying of binary alloys (Bi₂Te₃ and Sb₂Te₃). The single phase Bi₈Sb₃₂Te₆₀ solid solution obtained presents convenient stoichiometry and good homogeneity in composition. This revised version was published online in November 2006 with corrections to the Cover Date.     

Pulsed laser deposition of Bi2Te3 thin films

A feasibility study of thin stoichiometric Bi₂Te₃ films by pulsed laser deposition (PLD) was performed, the difficulty arising from the differences of vapour pressure between Te and Bi. The films were elaborated using a pulsed Nd:YAG laser under various experimental conditions and were characterized by electron microsprobe, scanning electron microscopy, X-ray diffraction and secondary ion mass spectroscopy analyses. Congruent transfer of stoichiometry occurs from the target to the substrate on several cm² and a good crystallinity can be achieved, even on glass substrates at room temperature, by combining convenient target to substrate facing and distance, respectively. Depletion in Te observed in some films may result from a laser beam-plume interaction that was put forward during elaboration of films on large scale substrates.     

Mechanical and structural characteristics of commercially pure grade 2 Ti welds and solder joints

This study aimed at determining whether data previously gathered for a laser welds and IR brazings using a Au–Pd alloy were applicable to titanium joints. As to its resistance under fatigue loading, Au–Pd alloy had shown a poor response to pre-ceramic laser welding and post-ceramic brazing. The present study was designed to assess the mechanical resistance, the microstructure and the elemental diffusion of laser welded, electric arch welded and brazed joints using commercially pure titanium as substrate metal.Mechanical resistance was determined by determining the joints' ultimate tensile strength and their resistance to fatigue loading. Elemental diffusion to and from the joints was assessed using microprobe tracings. Optical micrographs of the joints were also obtained and evaluated.Under monotonic tensile stress, three groups emerged: (1) the GTAW and the native (i.e. as received) substrate, (2) the annealed substrate and the laser welds and (3) the brazed joints. Under fatigue stress, the order was: first the native and annealed substrate, second the brazings and laser welds, third the GTAW joints. No Au-filler brazing withstood the applied fatigue loading. The micrographs showed various patterns, an absence of HAZ cracking and several occurrences of Widmanstätten structures. Elemental diffusion to and from the Ti substrate was substantial in the Ti filler brazings and virtually nil in the Au-based brazings.Under fatigue stress application, the titanium-based brazings as well as the laser- and electric arc welds performed equally well if not better than a previously tested AuPd alloy. There was a definite increase in grain size with increased heat application. However, no feature of the microstructures observed or the elemental analysis could be correlated with the specimen's resistance to fatigue stress application. © 2001 Kluwer Academic Publishers