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High-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) images of electron-transparent samples show dominant atomic number (Z-) contrast with a high lateral resolution. HAADF STEM at low electron energies <30 keV is applied in this work for quantitative composition analyses of InGaAs quantum wells. To determine the local composition, normalized experimental image intensities are compared with results of Monte Carlo simulations. For verification of the technique, InGaAs/GaAs quantum-well structures with known In concentration are used. Transmission electron microscopy samples with known thickness are prepared by the focused-ion-beam technique. The method can be extended to other material systems and is particularly promising for the analysis of materials that are sensitive toward knock-on damage.
Frictional behavior and interfacial adhesion of differently textured pyrolytic carbon layers on Si substrate were investigated by indentation and scratch testing. A large amount of elastic recovery and a low coefficient of friction (μ = 0.05 to 0.09) were observed. Elastic/plastic and frictional behaviors of the coatings are strongly influenced by the microstructure of the pyrolytic carbon films, especially by the texture. The critical load at which the first abrupt increase in the normal displacement occurs was used to characterize interfacial adhesive strength. A pyrolytic carbon film deposited at higher residence time from a gas mixture containing 3% oxygen exhibited higher critical loads than film deposited at lower residence time without oxygen. The results can be understood if one assumes that the gas phase composition during deposition significantly influences the bonding strength at the interface. Failure mechanisms are discussed for both types of films.