A field-effect transistor installation in H-waveguide amplifiers

This article touches upon the problem of practical tealization of microwave low-noise transistor amplifiers. A problem of the amplifier oscillating outside of operating frequency range is considered. A way of microwave chip transistor installation for elimination of this effect is investigated

Iron oxide overlayers on Au/SiO2/Si(1 0 0): Promoting effect of Au on the catalytic activity of iron oxide in CO oxidation

Iron oxide layers of 5–10 nm thickness were deposited by pulsed laser techniques (PLD) onto either Au films or nano-sized Au particles supported by SiO2/Si(1 0 0). Samples were characterized by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF SIMS) before and after measurements of the CO oxidation activity. Comparison was made with reference samples either free of iron oxide and/or free of Au particles/films. The initial activity of iron oxide/Au nano-particles/ SiO2/Si(1 0 0) turned out to be the highest followed by the sample containing a sandwiched Au film. While some reaction-induced changes in the chemical composition of the iron oxide overlayer (‘‘FeOx’’, which can be regarded as a mixture of Fe2O3, FeO and FeOOH according to the XPS analysis of the Fe 2p and O 1s core levels) were seen, no Au segregation at the surface was detected by TOF SIMS. The XPS Au 4f spectra indicated, however, that Au atoms might be injected and trapped in this layer. The catalytic activity of the FeOx/Au/SiO2/Si(1 0 0) samples must be attributed to active sites located on the iron oxide overlayer promoted by gold underneath. Since Au nano-particles and Au films caused promotion we infer that an electronic effect is in operation due to the occurrence of an FeOx/Au interface in both cases. Since the promotion is stronger for Au nano-particles the hypothesis of a particle size dependent electronic effect may be advanced. For thicker FeOx of about 40–80 nm no promotion by Au was found.info:eu-repo/semantics/publishe

High-temperature oxidation of CrN/AlN multilayer coatings §

Abstract Experiments are reported on sputter depth profiling of CrN/AlN multilayer abrasive coatings by secondary ion mass spectrometry (SIMS) coupled with sample current measurements (SCM). The coatings were deposited by a closed-field unbalanced magnetron sputtering. It is shown that after oxidation tests, performed in air at 900 8C for 2 h and at 1100 8C for 4 h, the layered structure begins to degrade but is not destroyed completely. Oxidation at 1100 8C for 20 h causes total destruction of the coatings that can be attributed to a fast diffusion of oxygen, nickel, manganese and other elements along defect paths (grain boundaries, dislocations, etc.) in the coating. There are practically no nitrides in the near-surface layer after such a treatment and all the metallic components are in the oxidized form as follows from the data obtained by X-ray photoelectron spectroscopy (XPS). According to XPS and mass-resolved ion scattering spectrometry (MARISS), the surface content of Al in the heat-treated coatings has decreased in comparison with the as-received sample and that of Cr increased. Both XPS and MARISS data exhibit real increase in superficial concentration of the substrate materials (Mn and Ni) that is controversial if using SIMS alone. SCM turned out to be an informative depth profiling method complementary to more expensive and complicated SIMS, being particularly useful for structures with different secondary electron emission properties of the layers. SCM with predetermined SIMS calibration allows a routine characterization of coatings and other multilayer structures, particularly, in situations where the expenses of analysis can be justified. www.elsevier.com/locate/apsus