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The structural, optical, and room-temperature electrical properties of strained La-doped SrTiO3 epitaxial thin films are investigated. Conductive La-doped SrTiO3 thin films with concentration varying from 5 to 25% are grown by molecular beam epitaxy on four different substrates: LaAlO3, (LaAlO3)0.3(Sr2AlTaO6)0.7, SrTiO3, and DyScO3, which result in lattice mismatch strain ranging from −2.9% to +1.1%. We compare the effect of La concentration and strain on the structural and optical properties, and measure their effect on the electrical resistivity and mobility at room temperature. Room temperature resistivities ranging from ∼10−2 to 10−5 Ω cm are obtained depending on strain and La concentration. The room temperature mobility decreases with increasing strain regardless of the sign of the strain. The observed Drude peak and Burstein-Moss shift from spectroscopic ellipsometry clearly confirm that the La addition creates a high density of free carriers in SrTiO3. First principles calculations were performed to help understand the effect of La-doping on the density of states effective mass as well as the conductivity and DC relaxation time.

Thermal GeO2 oxides up to 136 nm thickness were produced by annealing Ge wafers in pure oxygen at 550 °C and 270 kPa pressure for up to 10 h. The oxidation kinetics followed the Deal–Grove law. Using multisample spectroscopic ellipsometry for a series of five thermal oxides with different thicknesses, the complex dielectric functions of Ge and GeO2 were determined from 0.5 to 6.6 eV, for thin-film metrology applications in Ge-based microelectronics and photonics. The dispersion of the GeO2 layer was modeled with a simple Tauc-Lorentz oscillator model, but a more complicated dispersion with eight parametric oscillators was required for Ge. A reasonable fit to the ellipsometric angles could be obtained by assuming that all thermal oxides can be described by the same dielectric function, regardless of thickness, but a slight improvement was achieved by allowing for a lower density oxide near the surface of the thickest films. The authors compare their results with literature data for Ge and bulk and thin-film GeO2.

Articles you may be interested inMagnetic and structural properties of BiFeO3 thin films grown epitaxially on SrTiO3/Si substrates J. Appl. Phys. 113, 17D919 (2013) The (110) plane of Co 3 O 4 spinel exhibits significantly higher rates of carbon monoxide conversion due to the presence of active Co 3þ species at the surface. However, experimental studies of Co 3 O 4 (110) surfaces and interfaces have been limited by the difficulties in growing high-quality films. We report thin (10-250 Å ) Co 3 O 4 films grown by molecular beam epitaxy in the polar (110) direction on MgAl 2 O 4 substrates. Reflection high-energy electron diffraction, atomic force microscopy, x-ray diffraction, and transmission electron microscopy measurements attest to the high quality of the as-grown films. Furthermore, we investigate the electronic structure of this material by core level and valence band x-ray photoelectron spectroscopy, and first-principles density functional theory calculations. Ellipsometry reveals a direct band gap of 0.75 eV and other interband transitions at higher energies. A valence band offset of 3.2 eV is measured for the Co 3 O 4 /MgAl 2 O 4 heterostructure. Magnetic measurements show the signature of antiferromagnetic ordering at 49 K. FTIR ellipsometry finds three infrared-active phonons between 300 and 700 cm À1

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