ALBERT

Notes: Thin films of the high Tc superconducting Y-Ba-Cu metal oxide have been prepared for the first time by plasma-assisted organometallic chemical vapor deposition using β-diketonate chelates of Y, Ba, and Cu, Y(C11H19O2)3, Ba(C11H19O2)2, and Cu(C11H19O2)2 as starting materials, followed by post-annealing under a reduced pressure of oxygen stream. X-ray diffraction spectra indicate that the films deposited on the yttria-stabilized zirconia (YSZ) substrate have a significant preferential orientation of the crystallite c axis being perpendicular to the substrate surface. Four-probe resistivity measurements reveal the temperature of the onset of superconductivity at 91.6 K and zero resistance by 78.5 K.

Notes: Epitaxial PbTiO3 films were prepared by metalorganic chemical-vapor deposition on MgO(001)-, SrTiO3(001)-, and LaAlO3(001)-oriented substrates. Four-circle x-ray diffraction, transmission electron microscopy, Rutherford backscattering (RBS) channeling, and optical waveguiding were performed to characterize the deposited films. Epitaxial, single-crystal films were obtained on all three substrate materials under the same growth conditions. However, the defect structure of the films, including grain tilting, threading dislocation density, and 90° domain formation, was strongly dependent on the choice of substrate material. Films grown on MgO(001) and LaAlO3(001) (pseudocubic indices) substrates are nominally c-axis oriented; however, the PbTiO3 grains in the film form a fourfold domain structure, with the grains tilted ∼0.6° and ∼0.7°, respectively, toward the [100] directions (cubic or pseudo-cubic) of the substrates. In addition, these films contain a significant volume fraction of 90°-domain (a-axis) structures with a critical thickness hc for domain formation below the detection level of our experiments (hc≥100 A(ring)). Together, these structural defects result in a low RBS channeling yield reduction. In contrast, films grown on SrTiO3(001) substrates showed no tilting of the c-axis grains and a minimum RBS channeling yield of as low as ∼3%. In addition, we observed that below a critical film thickness of hc∼1500 A(ring), 90° domain formation was completely suppressed resulting in a nearly perfect single-crystal structure.The refractive indices and optical birefringence of the films were measured as a function of wavelength using the film-prism coupling method. Both the ordinary and extraordinary refractive indices for films grown on MgO(001) and LaAlO3(001) were higher than that of single-crystal PbTiO3; however, the optical birefringence of films grown on MgO(001) was reduced from that of the bulk. For films grown on SrTiO3(001), the ordinary refractive index was very close to that of single-crystal PbTiO3. We correlate the refractive index values and the reduced birefringence to the degree of residual strain and the volume fraction of 90° domains in the samples, respectively. © 1995 American Institute of Physics.

Notes: Epitaxial lead titanate (PbTiO3) thin films were grown on MgO(100) single-crystal substrate by metal-organic chemical-vapor deposition at a growth temperature of 650 °C. The films were dense, stoichiometric, and epitaxial. The domain structure was studied via x-ray-diffraction ω scans and in-plane Φ scans. Existence of c and a domains in the PbTiO3 films was evident. Consistent with literature reports, the a domains were found to have four variants 90° apart from each other, tilting about 2.2° away from the surface normal. The population ratio between c and a domain of the PbTiO3 films was determined to be approximately 2.3 to 1. The domain structure was found to be stable and reproducible during repeated thermal cycling above and below Tc. Furthermore, lattice parameters and Curie temperatures of PbTiO3 thin films were measured during the thermal cycles. The lattice parameters were found to be smaller and the Curie temperatures were shifted lower than the corresponding bulk values. This is attributed to the film stress effect. A theory based on the Landau–Ginzburg–Devonshire function has been developed to explain the shift of the Curie temperatures. © 1996 American Institute of Physics.

Notes: We present in situ surface x-ray scattering measurements of PbTiO3 epitaxy by metal–organic chemical-vapor deposition. Oscillations in crystal truncation rod intensity corresponding to layer-by-layer growth are observed under a variety of growth conditions. At lower PbO overpressures, we observe a transition to step-flow growth and an increased rate of recovery after growth, indicating a higher surface mobility. © 2002 American Institute of Physics.

Notes: A grain-size-dependent reduction in the room-temperature thermal conductivity of nanocrystalline yttria-stabilized zirconia is reported for the first time. Films were grown by metal-organic chemical vapor deposition with controlled grain sizes from 10 to 100 nm. For grain sizes smaller than approximately 30 nm, a substantial reduction in thermal conductivity was observed, reaching a value of less than one-third the bulk value at the smallest grain sizes measured. The observed behavior is consistent with expectations based on an estimation of the phonon mean-free path in zirconia.© 2000 American Institute of Physics.

Notes: Metal-organic chemical vapor deposition was used to prepare Pb(Mg1/3Nb2/3)O3 (PMN) thin films on (001) SrTiO3 and SrRuO3/SrTiO3 substrates, using solid Mg β-diketonate as the Mg precursor. Parameters including the precursor ratio in the vapor phase, growth temperature, growth rate, and reaction pressure in the reactor chamber were varied in order to determine suitable growth conditions for producing phase-pure, epitaxial PMN films. A cube-on-cube orientation relationship between the thin film and the SrTiO3 substrate was found, with a (001) rocking curve width of 0.1°, and in-plane rocking-curve width of 0.8°. The root-mean-square surface roughness of a 200-nm-thick film on SrTiO3 was 2 to 3 nm as measured by scanning probe microscopy. The zero-bias dielectric constant and loss measured at room temperature and 10 kHz for a 200-nm-thick film on SrRuO3/SrTiO3 were approximately 1100 and 2%, respectively. The remnant polarization for this film was 16 μC/cm2. © 2000 American Institute of Physics.

Notes: Single-crystal thin films of Pb(ZrxTi1−x)O3 (PZT) covering the full compositional range (0≤x≤1) were deposited by metal-organic chemical vapor deposition. Epitaxial SrRuO3(001) thin films grown on SrTiO3(001) substrates by rf-magnetron sputter deposition served as template electrode layers to promote the epitaxial growth of PZT. X-ray diffraction, energy-dispersive x-ray spectroscopy, atomic force microscopy, transmission electron microscopy, and optical waveguiding were used to characterize the crystalline structure, composition, surface morphology, microstructure, refractive index, and film thickness of the deposited films. The PZT films were single crystalline for all compositions exhibiting cube-on-cube growth epitaxy with the substrate and showed very high degrees of crystallinity and orientation. The films exhibited typical root mean square surface roughness of ∼1.0–2.5 nm. For tetragonal films, the surface morphology was dominated by grain tilting resulting from ferroelectric domain formation. We report the systematic compositional variation of the optical, dielectric, polarization, and electronic transport properties of these single-crystalline PZT thin films. We show that the solid-solution phase diagram of the PZT system for thin films differs from the bulk due to epitaxy-induced strains and interfacial defect formation. High values of remanant polarization (30–55 μC/cm2) were observed for ferroelectric compositions in the range of 0.8≤x≤0.2. Unlike previous studies, the dielectric constant exhibited a clear dependence on composition with values ranging from 225 to 650. The coercive fields decreased with increasing Zr concentration to a minimum of 20 kV/cm for x=0.8. The undoped films exhibited both high resistivity and dielectric-breakdown strength (1013–1014 Ω cm at 100 kV/cm and 300–700 kV/cm, respectively). © 1997 American Institute of Physics.

Notes: Single-crystal PbZrO3 thin films have been grown on (001) SrTiO3 substrates by metalorganic chemical vapor deposition. The single-crystal nature of c-axis oriented PbZrO3 film is confirmed by x-ray diffraction, selective area electron diffraction, and transmission electron microscopy. The epitaxial relationship between the PbZrO3 film and the SrTiO3 substrate was found to be (001)[100]PbZrO3(parallel)(001)[110]SrTiO3.

Notes: Single-crystal films of PbTiO3 have been deposited on (100) SrTiO3 substrates by metalorganic chemical vapor deposition. X-ray diffraction spectra and transmission electron microscopy images revealed that the development of 90° domains was directly related to the thickness of the film. Single-domain, single-crystal films were obtained for film thickness less than 150 nm. The minimum yields of the films in ion-channeling experiments were only 3 %, similar to that of a perfect single crystal. The ordinary refractive index of the film measured by optical waveguiding experiment was also the same as that of PbTiO3 single crystals.