B. H. Hoerman

Dielectric properties of epitaxial BaTiO3 thin films

The dielectric response of epitaxial BaTiO3 thin films deposited on MgO was measured through surface electrodes as a function of applied bias, frequency, and temperature. The room temperature value of the dielectric constant was ∼500 with a dissipation factor, tan(δ), of 0.05 at 100 kHz. Measurements varying the bias field showed hysteresis of the dielectric response and a tunability of 30% for a maximum applied field of ∼7 MV/m. The frequency response of the dielectric constant is well described by a Curie–von Schweidler power law with an exponent ∼0.04 in the range 1 kHz–13 MHz. The films undergo a diffuse phase transition at temperatures higher than the bulk Curie temperature. The behavior of the dielectric response is attributed to the presence of residual strain in the epitaxial thin films.

Epitaxial thin films of MgO on Si using metalorganic molecular beam epitaxy

Epitaxial cubic MgO thin films have been deposited on single crystal Si(001) substrates by metalorganic molecular beam epitaxy. The Mg source was the solid precursor magnesium acetylacetonate and a rf excited oxygen plasma was the oxidant. The growth process involved initial formation of an epitaxial β-SiC interlayer followed by direct deposition of a MgO overlayer. The films were characterized by in situ reflection high energy electron diffraction, x-ray diffraction, conventional and high resolution transmission electron microscopy, atomic force microscopy, Auger electron spectroscopy, and Fourier transform infrared spectroscopy. The β-SiC interlayer had an epitaxial relationship such that SiC(001)∥Si(001) and SiC [110]∥Si [110]. The SiC interlayer showed a columnar grain structure with planar defects including twin bands and stacking faults. The MgO overlayer showed an epitaxial relationship given by MgO(001)∥Si(001) and MgO[110]∥Si[110]. No evidence of twins in the MgO layers was observed.

Dynamic response of the electro-optic effect in epitaxial KNbO3

The dynamic response of the electro-optic coefficient of epitaxial KNbO3 thin films was measured at room temperature. The effective electro-optic coefficient for these films at 100 kHz is 12 pm/V. The magnitude of the electro-optic response increased by seventy percent as the duration of the applied field was increased from 10 ns to 10 μs. A dispersion of the electro-optic coefficient is observed which follows a power law given by Atm.

Dynamic response of the dielectric and electro-optic properties of epitaxial ferroelectric thin films

An analysis of the dynamic dielectric and electro-optic relaxation response of thin-film ferroelectrics is presented. The analysis is based upon the relaxation of ferroelectric domains with a continuous distribution of sizes given by percolation theory. The resulting temporal response is described by the expression

Fast time-resolved x-ray diffraction in BaTiO3 films subjected to a strong high-frequency electric field

\ensuremath{\Phi}(t)\ensuremath{\propto}{t}^{\ensuremath{-}m}\mathrm{exp}[\ensuremath{-}(t/\ensuremath{\tau}{)}^{\ensuremath{\beta}}].

Phase stability of epitaxial KTa x Nb 1− x O 3 thin films deposited by metalorganic chemical vapor deposition

The analysis was applied to

Nanosecond-Scale Domain Dynamics in BaTiO 3 Probed by Time-Resolved X-Ray Diffraction

{\mathrm{KNbO}}_{3}

Growth and microstructure of MgO thin films on Si(100) substrates by metal–organic molecular beam epitaxy

thin films. Measurements of the polarization, birefringence, and dielectric transients show qualitative agreement with the model over 11 orders of magnitude in time.

Growth of MgO by metal-organic molecular beam epitaxy

The pulsed synchrotron radiation from the Advanced Photon Source of Argonne National Laboratory was used to measure the dynamic structural response in 200-nm-thick BaTiO3 ferroelectric films, in situ, under the application of a high-frequency electric field. X-ray diffraction measurements were performed in the stroboscopic mode, i.e., by synchronizing the x-ray bursts with the electric-field periodicity. Time-dependent variations of lattice parameters were derived from the electric-field-induced distortions of the diffraction profiles. Drastic reduction of the relaxation time, from 6.9 ns at 71.69 MHz down to 0.7 ns at 521.36 MHz, was found with an increase of the electric-field frequency.

Oxide thin films and composites and related methods of deposition

The phase stability of epitaxial KTa x Nb 1− x O 3 (0 ≤ x ≤ 1) thin films, with compositions over the entire solid solution range, was investigated. KTa x Nb 1− x O 3 thin films were deposited on (100) MgAl 2 O 4 substrates by metalorganic chemical vapor deposition. Films with compositions x ≤ 0.30 were orthorhombic, as determined by x-ray diffraction. Dielectric measurements at room temperature indicated the presence of morphotropic phase boundaries at x = 0.30 and at x = 0.74. Temperature-dependent measurements of the dielectric constant for KNbO 3 from 80 to 800 K indicated three structural phase transitions at 710, 520, and 240 K. For intermediate compositions, a decrease in the Curie and tetragonal–orthorhombic transition temperatures was observed with increasing Ta atomic percent, similar to the bulk phase equilibrium. In contrast to bulk materials, an increase in the orthorhombic–rhombohedral transition temperature with increasing x was observed for the films, resulting in the stabilization of a rhombohedral phase at room temperature for compositions 0.45 ≤ x ≤ 0.73. Differences between the phase stability for the thin films and bulk were attributed to lattice misfit strain.