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Reflection high energy electron diffraction (RHEED) and high resolution transmission electron microscopy (HREM) are used to study Cu films grown on hydrogen-terminated Si(100) and Si(111) substrates by molecular beam epitaxy. Cu(100) grows epitaxialy on hydrogen-terminated Si(100) substrates. Epitaxial Cu crystallites have discrete orientational variants. The epitaxial growth of Cu on Si(100) is promoted by the lattice match promoted about by interfacial Cu silicide region.

We investigated the behavior of Raman modes for AlN thin films fabricated with plasma source molecular beam epitaxy method having high levels of oxygen contamination. Oxygen atoms occupy different lattice sites depending on their at. % value and, thus, strongly influence spectral features of certain Raman modes. We studied the variations in the width of nonpolar E2low and E2high modes which represent mainly the vibrations of Al sublattice and N atoms, respectively, in the AlN lattice. When oxygen occupies a N site, it affects the width of the E2high mode, and at the same time, the charge neutrality constraint creates an Al vacancy and, thus, simultaneously affects the width of the E2low mode. We found that for our films whose oxygen concentration vary from 1 to 10 at. %, the width of both the E2high and E2low modes varies linearly with the oxygen contamination levels suggesting that even at such high levels of oxygen contamination, oxygen atoms still prefer to occupy the N site. This is contrary to previous studies of single crystal AlN. The oxygen contamination in our films was determined by x-ray photoemission spectroscopy measurements. [ABSTRACT FROM AUTHOR]

Structural, magnetization, and Raman spectroscopic investigations have been carried out on spin coated Zn1-xCoxO (0≤x≤0.1) films. We investigated the broadening of the E2low mode for different values of x in both air and vacuum annealed films, and found a direct correlation of Co ions incorporation at the Zn sites with ferromagnetic order. The magnitudes of the magnetic moment are directly related to the size of the disorder correlation radius. However, for x∼5% where the magnetic moment becomes negligible, the broadening of the E2low Raman mode also becomes negligible, suggesting rejection of the Co ions from the Zn sites. For a given x, Co ions are incorporated at the Zn sites with the same concentration in both the air and vacuum annealed films but the magnetic moment values are much smaller for the air annealed samples. This behavior is directly related to the presence of oxygen vacancies. We also discuss the effects of air and vacuum annealing on the linewidth of E2high and A1 (LO) modes. At higher doping levels, e.g., x>5%, the air annealed films showed a strong phase separation tendency toward Co3O4 as shown by both Raman and high resolution electron microscopy. [ABSTRACT FROM AUTHOR]

The electrical response characteristics of Pd/AlN/6H-SiC and Pd/AlN/3C-SiC devices to hydrogen gas have been investigated. An AlN film, with a thickness of 100 nm, was deposited simultaneously on 6H-SiC(0001) and 3C-SiC(001) substrates. The structural, morphological, and microstructural characterizations of these devices were carried out using x-ray diffraction, atomic force microscopy, and transmission electron microscopy techniques. In both the cases, the AlN film showed a highly textured c axis growth with a wurtzite crystal structure. However, the surface roughness of the AlN film on 3C–SiC was larger by a factor of three compared to that deposited on 6H–SiC, with an associated increase in the value of dielectric constant of AlN. Theoretical analysis of the electrical characteristics suggests that, in addition to the physical properties of the semiconducting layer, the dielectric constant of AlN layer directly influences the electrical response of the device to hydrogen. The Pd/AlN/3C-SiC device showed a consistently reduced electrical response to hydrogen compared to the Pd/AlN/6H-SiC device. [ABSTRACT FROM AUTHOR]

We investigate the temperature dependence of Hall mobility μ and carrier density Ne for thin InN films grown by molecular-beam epitaxy and plasma source molecular-beam epitaxy over three orders-of-magnitude difference in their carrier density: for the low-density film Ne=5.8×1017/cm3 and for the high-density film Ne=3.2×1020/cm3. In both the films, for temperature up to 300 K, a large temperature-independent concentration of carriers is observed. For higher temperatures, however, carrier density increases with temperature. The characteristic behavior of the mobility for the low-density film is different from that of the high-density film, particularly for temperatures less than 300 K. The low-density film shows a peak behavior in the mobility around 250 K in contrast to the temperature-independent mobility observed for the high-density film for T<300 K. We investigate theoretically the concentrations of donor, acceptor, and threading dislocations for both the films and also discussed various electron-scattering mechanisms which contribute to the mobility in these films. [ABSTRACT FROM AUTHOR]

The effect of plasmon and LO-phonon damping on the optical measurements of InN films is discussed. Phonon and plasmon damping dramatically modifies the spectral features of the optical spectra and destabilizes the coupled modes of the system. Phonon damping affects the optical properties in a qualitatively different way from plasmon damping. Increased phonon damping leads to a merging of the coupled modes for a certain range of carrier density. Plasmon damping broadens the spectral linewidths of both of the coupled modes when plasmon energies are of the order of LO-phonon energies. However, when plasmon energies are larger than LO-phonon energies, increasing plasmon damping makes the higher-energy mode completely degenerate with plasmon, and may even have lower energies than plasmon. In weakly damped situations, we also discuss the low-energy optical transmission region that forms in between the coupled modes. Finally, the effect of plasmon and LO-phonon coupling on the analyses of the experimental infrared reflection data of InN films (for different electron densities) is discussed. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The electrical characteristics of a hydrogen sensor utilizing a metal/AlN/Si(111) structure, which behaves similarly to a metal-insulator-semiconductor-type capacitor, have been investigated. The AlN layer, which acts as the insulator, was deposited by plasma source molecular-beam epitaxy. The device employed alternating gates of Pd and Al, and an Al back contact, all grown by magnetron sputtering. The Pd gate structures were found to be sensitive to hydrogen, down to parts per million concentrations in the surrounding flow, while the Al gate structures showed no response to hydrogen. Both structures show similar capacitance versus voltage as well as conductance versus voltage curves. Therefore the combination of Al and Pd gates can be utilized in a balanced hydrogen sensor structure. Furthermore, the frequency dependence of the capacitance and conductance curves clearly indicated the presence of series resistance effects, but with multiple time constants, requiring a complex equivalent circuit representation. Evidence was found for the presence of carrier traps at the AlN/Si interface, with energy levels distributed throughout the silicon band gap, and with an estimated surface density ranging between 8×10[sup 14] and 1.5×10[sup 15] m[sup -2] eV[sup -1]. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Pb[sub 0.4]Sr[sub 0.6]TiO[sub 3] films with submicron size grains have been prepared on Pt substrates by the metalorganic decomposition method. X-ray diffraction analysis reveals that the films are polycrystalline with a perovskite crystal structure and negligible tetragonal splitting at room temperature. The room temperature Raman spectrum, however, shows all the characteristic phonon modes of a tetragonal ferroelectric phase. These modes lose their intensity with an increase in temperature but persist even up to 150°C. This is in agreement with the dielectric permittivity versus temperature data which show a broad peak-room temperature, and ferroelectric hysteresis persisting up to ∼140°C. Both Raman and dielectric data are interpreted as due to the presence of a distribution of phases in the film perhaps caused by a variation in Pb content along the film thickness and/or near grain boundary regions. [ABSTRACT FROM AUTHOR]

Deals with a study which assessed bilayer Co/Cu, Fe/Cu, and Ni/Cu films deposited by molecular-beam epitaxy on hydrogen-terminated silicon substrates. Background on the magnetic anisotropy of thin films; Experimental details; Results and discussion.

Provides information on a study that investigated interlayer coupling in cobalt/copper multilayer using ferromagnetic resonance and magnetization measurements. Methodologies used; Results and discussion; Conclusion.