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We propose a BaCeO3/BaZrO3 double-layer buffer template, grown on a SrTiO3 substrate, for epitaxial growth of a target oxide film with large lattice constants of over 4.1 Å. Lattice mismatch from the substrate was mostly accommodated for by a BaZrO3 arbitrating layer. Having an ideal in-plane lattice structure, BaCeO3 served as the main-buffer to grow the target material. We demonstrated commensurate epitaxy of BaBiO3 (BBO, a = 4.371 Å) utilizing the new buffer template. Our results can be applied to heteroepitaxy and strain engineering of novel oxide materials of sizable lattice constants.

We grow Zn1-xMnxO/Al2O3 (0<=x<=0.08) thin films on sapphire (0001) using radio-frequency sputtering deposition method with Ar and various N2 flow rates. We examine the effect of N2 codoping on the band gap and Mn-related midgap absorption of (Zn,Mn)O. Using spectroscopic ellipsometry, we measure pseudodielectric functions in the spectral range between 1 and 4.5 eV. Using the model of Holden et al. [T. Holden et al., Phys. Rev. B 56, 4037 (1997)], we determine the uniaxial (Zn,Mn)O dielectric function and the E0 band-gap energy. The fitted band gap does not change appreciably with increasing Mn composition up to 2%. We find a very large broadening of both the E0 band gap and its exciton partner E0x peaks even for less than 2% of optically determined Mn composition. In ellipsometric spectra, we also find Mn-related 3 eV optical structure. In particular, optical absorption spectra with varying N2 gas flow rate show that the Mn-related peak intensity decreases with increasing N2 flux. The decrease of the 3 eV Mn-related peak intensity is attributed to increasing N2 flow rate and Mn–N hybridization. [ABSTRACT FROM AUTHOR]

We measured the pseudo-dielectric functions of several nonlinear optical (NLO) polymeric systems using spectroscopic ellipsometry in the spectral range between 0.8 and 4.7 eV. We fabricated the thin films after doping the nonlinear optical active chromophores into amorphous polycarbonate to show good optical transparency. We measured the ultraviolet-visible absorption spectra of the NLO chromophores in the film state. In order to determine the dielectric functions, we employed the Bruggeman effective medium approximation, assuming a mixture of two phases: host and guest. We used the Cauchy model for the dielectric function of the host polymer and a parametric optical constant model for that of the guest chromophore. We discussed the variation of the dielectric functions and the transition energies for various host-guest systems. In the gradient donor structural chromophores, we observed a decrease of the highest occupied molecular orbital (HOMO) lowest-unoccupied-molecular-orbital (LUMO) transition energy, and found a transition at about 3 eV. The decrease of HOMO—LUMO transition energy is attributed to the increase of electron donability and conjugative effect. We could fit the volume fractions of host and guest using spectroscopic ellipsometry, and compared them with the values estimated from the chemical structures of the molecules. [ABSTRACT FROM AUTHOR]

Spectroscopic ellipsometry is used for studying the electro-optic effect in lead zirconate titanate (PZT) thin films grown epitaxially on Nb-doped SrTi[O.sub.3](001) substrates by RF magnetron sputtering. The presence of the linear electro-optic effect in unpoled PZT films is attributed to the existence of a built-in polarization and simultaneous poling during measurements.

The effect of corona poling on the optical functions of the nonlinear-optical (NLO) polymers is investigated. A new peak [E.sub.c] is attributed to lower symmetry, possibly Stark effect, which is induced in the chromophores by the corona poling.

Pseudodielectric functions in the visible-deep ultraviolet spectral range of Pb(Zr(sub x)Ti(sub 1-x))O3 (PZT), Pb0.98Nb0.04(Zr0.2Ti0.8)0.96O3, Pb0.91La0.09(Zr0.65Ti0.35)0.98O3 and Pb0.85La0.15Ti0.96O3 films grown on platinized silicon substrates using a sol-gel method and on (0001) sapphire using a radio-frequency sputtering method is measured. The near constancy of the lowest bind-gap energy independent of Zr composition is consistent with the band-structure calculations.

We propose a BaCeO3/BaZrO3 double-layer buffer template, grown on a SrTiO3 substrate, for epitaxial growth of a target oxide film with large lattice constants of over 4.1 Å. Lattice mismatch from the substrate was mostly accommodated for by a BaZrO3 arbitrating layer. Having an ideal in-plane lattice structure, BaCeO3 served as the main-buffer to grow the target material. We demonstrated commensurate epitaxy of BaBiO3 (BBO, a = 4.371 Å) utilizing the new buffer template. Our results can be applied to heteroepitaxy and strain engineering of novel oxide materials of sizable lattice constants. [ABSTRACT FROM AUTHOR]

In this study, we investigated the structural and optical properties of Ge-doped SbTe (Ge-ST) thin films with three differing compositions: Ge0.06Sb0.77Te0.17 (Ge-STH), Ge0.05Sb0.70Te0.25 (Ge-STM), and Ge0.05Sb0.64Te0.31 (Ge-STL), grown on Si substrate by radio-frequency sputtering method. The films were annealed at 250°C for crystallization and their crystal structures were examined by X-ray diffraction. Compared to the X-ray diffraction spectra of the undoped SbTe, the Ge-ST thin films had a hexagonal structure with large stacking periods. Using Raman spectroscopy, we investigated the shift of the phonon mode frequencies (A1g and Eg) of the films with varying Sb:Te ratios. We compared the dependence of the phonon frequencies of Ge-ST on the Sb content to those of the corresponding undoped SbTe. The composition dependence of the A1g phonon frequency could be explained in terms of the linear extrapolation of Sb and Sb2Te3 crystals. By using spectroscopic ellipsometry, we measured the dielectric function of the thin films in the near-IR, visible, and ultraviolet spectral regions. The optical energy gaps and bandgaps of the amorphous and crystalline phases, respectively, were determined using linear extrapolation of the absorption coefficient. The optical gap energies of the amorphous Ge-ST films were determined to be about 0.5-0.6 eV, whereas the indirect bandgap energies of the crystalline films shrank substantially to about 0.15-0.2 eV. [ABSTRACT FROM AUTHOR]

Single crystalline PbTiO3 films have been epitaxially grown on SrTiO3 (001) substrates by molecular beam epitaxy using H2O2 as the source of active oxygen. The optimum growth conditions have been determined by analyzing a range of growth parameters affecting growth and used to attain single phase and stoichiometric PbTiO3 thin films. In situ reflection high-energy electron diffraction pattern indicated the PbTiO3 films to be grown under a two-dimensional growth mode. The full width at half maximum of the rocking curve of a relatively thin 65 nm (001) PbTiO3 film is 6.2 arc min which is indicative of high crystal quality. The band gap of PbTiO3, as determined by ellipsometric measurement, is 3.778 eV. [ABSTRACT FROM AUTHOR]

We measured pseudodielectric functions in the visible-ultraviolet spectral range of Pb(ZrxTi1-x)O3 (x=0.2, 0.56, 0.82) (PZT) grown on platinized silicon substrate using the sol-gel method and also on (0001) sapphire using radio frequency sputtering method. Using a parametric optical constant model, we estimated the dielectric functions of the PZT thin films. Taking the second derivative of the fitted layer dielectric functions and using the standard critical point model, we determined the parameters of the critical points. In the second derivative spectra, the lowest bandgap energy peak near 4 eV is fitted as a double peak for annealed PZTs associated with the perovskite phase. As-grown PZTs have mainly pyrochlore phase and the lowest bandgap is fitted as a single peak. We compared the bandgap energies with literature values. [ABSTRACT FROM AUTHOR]

Barium bismuth oxide (BaBiO3) is the end member of two families of high-Tc superconductors, i.e., BaPb1-xBixO3 and Ba1-xKxBiO3. The undoped parent compound is an insulator, exhibiting a charge density wave that is strongly linked to a static breathing distortion in the oxygen sublattice of the perovskite structure. We report a comprehensive spectroscopic and x-ray diffraction study of BaBiO3 thin films, showing that the minimum film thickness required to stabilize the breathing distortion and charge density wave is ≈11 unit cells, and that both phenomena are suppressed in thinner films. Our results constitute the first experimental observation of charge density wave suppression in bismuthate compounds without intentionally introducing dopants. [ABSTRACT FROM AUTHOR]