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Epitaxial Films (epitaxial + film)
Kinds of Epitaxial Films Selected AbstractsFunctional Perovskites , From Epitaxial Films to Nanostructured Arrays,ADVANCED FUNCTIONAL MATERIALS, Issue 24 2008Ionela Vrejoiu Abstract Functional perovskite materials gain increasing significance due to their wide spectrum of attractive properties, including ferroelectric, ferromagnetic, conducting and multiferroic properties. Due to the developments of recent years, materials of this type can conveniently be grown, mainly by pulsed laser deposition, in the form of epitaxial films, multilayers, superlattices, and well-ordered arrays of nanoislands. These structures allow for investigations of preparation,microstructure,property relations. A wide variation of the properties is possible, determined by strain, composition, defect contents, dimensional effects, and crystallographic orientation. An overview of our corresponding work of recent years is given, particularly focusing on epitaxial films, superlattices and nanoisland arrays of (anti)ferroelectric and multiferroic functional perovskites. [source] Vertical Interface Effect on the Physical Properties of Self-Assembled Nanocomposite Epitaxial FilmsADVANCED MATERIALS, Issue 37 2009Hao Yang Vertical interface effect on the physical properties of epitaxial metal-oxide films is demonstrated. Self-assembled (BiFeO3)0.5:(Sm2O3)0.5 nanocomposite films are fabricated with three-dimensional heteroepitaxy having an ordered nano-columnar structure on a large scale. The vertical interface effect on lattice parameters, dielectric properties, and leakage currents is investigated. [source] Thermoelectric Performance of Epitaxial Thin Films of Layered Cobalt Oxides Grown by Reactive Solid-Phase Epitaxy with Topotactic Ion-Exchange MethodsINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 4 2007Kenji Sugiura This article reviews high-quality epitaxial film growth of layered cobalt oxides by reactive solid-phase epitaxy (R-SPE) with topotactic ion-exchange methods. Epitaxial film of Na0.8CoO2 was grown on a (0001)-oriented ,-Al2O3 substrate by R-SPE using CoO film as the starting material. The Na0.8CoO2 epitaxial films were converted into high-quality epitaxial films of Sr0.32Na0.21CoO2 and [Ca2CoO3]xCoO2 by topotactic ion-exchange methods. The Sr0.32Na0.21CoO2 film exhibited better stability against moisture than that of the Na0.8CoO2 film, while it retained the good thermoelectric properties of Na0.8CoO2. The [Ca2CoO3]xCoO2 film exhibited a high electrical conductivity of 2.95 × 102 S/cm and a large Seebeck coefficient of +125 ,V/K at 300 K. [source] Do we really need another PL study of CuInSe2?PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 9 2004Susanne Siebentritt Abstract A detailed composition, intensity and temperature dependent photoluminescence (PL) study of CuInSe2 has been performed to obtain data on defects, directly comparable to the defects in CuGaSe2, prepared under the same conditions. Epitaxial films are grown by metal organic vapour phase epitaxy on GaAs. The PL study reveals three shallow defects, which are responsible for the doping behaviour in CuInSe2: two acceptors, 40 and 60 meV deep, and a donor, approximately 12 meV deep. The shallower acceptor dominates for low or no Cu-excess, whereas the deeper one dominates material grown under high Cu-excess. These defects and their compositional dependence are the same as observed in CuGaSe2. Thus no fundamental difference concerning the shallow defects exists between these two materials. [source] Spontaneous Outcropping of Self-Assembled Insulating Nanodots in Solution-Derived Metallic Ferromagnetic La0.7Sr0.3MnO3 FilmsADVANCED FUNCTIONAL MATERIALS, Issue 13 2009César Moreno Abstract A new mechanism is proposed for the generation of self-assembled nanodots at the surface of a film based on spontaneous outcropping of the secondary phase of a nanocomposite epitaxial film. Epitaxial self-assembled Sr,La oxide insulating nanodots are formed through this mechanism at the surface of an epitaxial metallic ferromagnetic La0.7Sr0.3MnO3 (LSMO) film grown on SrTiO3 from chemical solutions. TEM analysis reveals that, underneath the La,Sr oxide (LSO) nanodots, the film switches from the compressive out-of-plane stress component to a tensile one. It is shown that the size and concentration of the nanodots can be tuned by means of growth kinetics and through modification of the La excess in the precursor chemical solution. The driving force for the nanodot formation can be attributed to a cooperative effect involving the minimization of the elastic strain energy and a thermodynamic instability of the LSMO phase against the formation of a Ruddelsden,Popper phase Sr3Mn4O7 embedded in the film, and LSO surface nanodots. The mechanism can be described as a generalization of the classical Stranski,Krastanov growth mode involving phase separation. LSO islands induce an isotropic strain to the LSMO film underneath the island which decreases the magnetoelastic contribution to the magnetic anisotropy. [source] Study of magnetization processes using higher harmonic ac-susceptibilityPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 8 2008S. Prüfer Abstract The ac-susceptibility of a La0.7Sr0.3MnO3 epitaxial film was measured up to the 11th harmonic as a function of ac-field amplitude, superimposed dc-field and temperature. The experimental data reflect the magnetization hysteresis-loop shape in a very precise and detailed way. This is further elucidated by numerical simulations of the ac-susceptibility within a Preisach model with Gaussian distribution function. Using parameters from magnetization measurements the simulated ac-susceptibility curves were found to be in good agreement with the experimental results. This shows that measurements of higher harmonic susceptibilities are a powerful tool for the precise study of magnetization processes. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Unusual current-voltage characteristics of single crystalline and bicrystalline La0.7Ca0.3MnO3 filmsANNALEN DER PHYSIK, Issue 10 2004A. Sawa Abstract The current-voltage characteristics of single crystalline and bicrystalline La0.7Ca0.3MnO3 films were measured and analyzed. Several epitaxial films, as well as 45° [001]-tilt grain boundaries, display current-voltage characteristics which are asymmetric with respect to polarity reversal of the bias current. One epitaxial film has a polarity dependent resistance of ,340k, and of ,670k, in forward and in reverse direction, respectively. [source] Functional Perovskites , From Epitaxial Films to Nanostructured Arrays,ADVANCED FUNCTIONAL MATERIALS, Issue 24 2008Ionela Vrejoiu Abstract Functional perovskite materials gain increasing significance due to their wide spectrum of attractive properties, including ferroelectric, ferromagnetic, conducting and multiferroic properties. Due to the developments of recent years, materials of this type can conveniently be grown, mainly by pulsed laser deposition, in the form of epitaxial films, multilayers, superlattices, and well-ordered arrays of nanoislands. These structures allow for investigations of preparation,microstructure,property relations. A wide variation of the properties is possible, determined by strain, composition, defect contents, dimensional effects, and crystallographic orientation. An overview of our corresponding work of recent years is given, particularly focusing on epitaxial films, superlattices and nanoisland arrays of (anti)ferroelectric and multiferroic functional perovskites. [source] Thermoelectric Performance of Epitaxial Thin Films of Layered Cobalt Oxides Grown by Reactive Solid-Phase Epitaxy with Topotactic Ion-Exchange MethodsINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 4 2007Kenji Sugiura This article reviews high-quality epitaxial film growth of layered cobalt oxides by reactive solid-phase epitaxy (R-SPE) with topotactic ion-exchange methods. Epitaxial film of Na0.8CoO2 was grown on a (0001)-oriented ,-Al2O3 substrate by R-SPE using CoO film as the starting material. The Na0.8CoO2 epitaxial films were converted into high-quality epitaxial films of Sr0.32Na0.21CoO2 and [Ca2CoO3]xCoO2 by topotactic ion-exchange methods. The Sr0.32Na0.21CoO2 film exhibited better stability against moisture than that of the Na0.8CoO2 film, while it retained the good thermoelectric properties of Na0.8CoO2. The [Ca2CoO3]xCoO2 film exhibited a high electrical conductivity of 2.95 × 102 S/cm and a large Seebeck coefficient of +125 ,V/K at 300 K. [source] Amphoteric Phosphorus Doping for Stable p-Type ZnO,ADVANCED MATERIALS, Issue 20 2007A. Allenic The role of dislocations in stable p-type phosphorus-doped ZnO epitaxial films is investigated. It is shown that good p-type conductivity is always associated with a considerable increase in the density of dislocations, which can aid the formation of shallow complex acceptors and provide sinks for native donors. [source] Threading dislocations in domain-matching epitaxial films of ZnOJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 5 2007W.-R. Liu The structures of high-quality ZnO epitaxial films grown by pulsed-laser deposition on sapphire (0001) without an oxygen gas flow were investigated by X-ray diffraction and transmission electron microscopy. The great disparity of X-ray diffraction line widths between the normal and in-plane reflections reveals the specific threading dislocation geometry of ZnO. Most threading dislocations are pure edge dislocations. From a combination of scattering and microscopic results, it is found that threading dislocations are not uniformly distributed in the ZnO films, but the films consist of columnar epitaxial cores surrounded by annular regions of edge threading dislocations in large density. The local surface morphology and capacitance signal obtained from atomic force and scanning capacitance microscopes indicate that the aggregation of threading dislocations leads to high interface traps at the annular regions. [source] Growth behavior and microstructure of ZnO epilayer on ,-LiAlO2(100) substrate by chemical vapor depositionPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 2 2009Liuwen Chang Abstract Low lattice-mismatched ,-LiAlO2(100) substrates were employed to grow ZnO epitaxial films by chemical vapor deposition. The influence of growth temperature on growth behavior of ZnO was investigated. Results indicated that the low lattice-matched (100) crystallites nucleate on substrate at all growth temperatures employed. However, a second type of crystallites having an (0001) orientation can also nucleate on substrate at low growth temperature of 575 °C and 640 °C. The growth rate of the later crystallite is, however, higher than that of the (100) one and finally results in a single crystalline ZnO film having an [0001] azimuthal orientation. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Oxygen induced band-gap reduction in ZnOxSe1,x alloysPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2004W. Shan Abstract The effect of alloying a small amount of ZnO with ZnSe on the electronic band structure has been studied. Optical transitions in MBE-grown ZnOxSe1,x epitaxial films (0 , x , 0.0135) were investigated using photoreflectance and photoluminescence spectroscopies. The fundamental band-gap energy of the alloys was found to decrease at a rate of about 0.1 eV per atomic percent of oxygen. The pressure dependence of the band gap was also found to be strongly affected by the O incorporation. Both effects can be quantitatively explained by an anticrossing interaction between the extended states of the conduction band of ZnSe and the highly localized oxygen states located at approximately 0.22 eV above the conduction band edge. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Growth of GaN on a -plane sapphire: in-plane epitaxial relationships and lattice parametersPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2003T. Paskova Abstract We have studied GaN films grown on a -plane sapphire substrates by both hydride vapor phase epitaxy (HVPE) and metalorganic vapor phase epitaxy (MOVPE). The in-plane orientation relationships between the epitaxial films and the substrate are determined to be [11,20]GaN , [0001]sapphire and [1,100]GaN , [1,100]sapphire in the HVPE growth, while [1,100]GaN , [0001]sapphire and [11,20]GaN , [1,100]sapphire are found in the MOVPE growth. The different orientation preferences are attributed to the atom termination of the sapphire surface determined by the substrate treatment used in the different growth methods. The effect of the lattice matches on the in-plane lattice parameters and strain anisotropy in the two cases is studied. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Molecular and biomolecular interfaces to metal oxide semiconductorsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2010Robert J. Hamers Abstract Previous work has shown that organic alkenes will graft to covalent semiconductors such as diamond and silicon. Here, we demonstrate that organic alkenes can be grafted to the surfaces of metal oxide semiconductors, including TiO2 in nanocrystalline thin films and as single-crystal anatase(001) epitaxial films grown on SrTiO3(001) substrates. The resulting layers can be used as a starting point for linking biomolecules such as DNA to metal oxide surfaces. Initial results are presented showing that this chemistry can also be applied to graft molecular layers to zirconium oxide thin films. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Electro-optic property of ZnO:Mn epitaxial filmsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 9 2008T. Oshio Abstract Mn doping effect on the dielectric and electro-optic (E-O) property of ZnO epitaxial films was studied. The leakage current of the ZnO film is drastically decreased by doping Mn with the concentration of 3-5 at%. Although, ZnO: 4 at% Mn with the lowest leakage current has the largest frequency dispersion of birefringence shift (, n) at 1 kHz, and its E-O coefficient (rc) was larger than that of ZnO single crystal. It is presumably caused by another polarization effect but spontaneous polarization, such as space charge. To investigate the origin of the dispersion of , n, discharging property was evaluated. When the signal at 1 kHz was applied, ZnO: 3 and 5 at% Mn showed the discharging with relaxation time of 5 msec. Furthermore, the discharging property with same relaxation time was observed at 20 kHz at where the dispersion of , n was not observed. However, ZnO: 4 at% Mn does not show such a discharging behavior. Therefore, it is considered that the space charge is not the origin of the dispersion of , n. On the other hand, the dispersion of , n was minimum and no dielectric dispersion was observed at 20 kHz for all samples. The rc of ZnO: 3, 4 and 5 at% Mn measured at 20 kHz, which should be the rc originated from the spontaneous dipolar polarization, were derived to be 0.81, 0.81 and 0.62 pm/V, respectively. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Photoluminescence depth-profiling of lattice-mismatched InGaN thick film on GaN using inductively coupled plasma etchingPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2006Ji-Myon Lee Abstract Photoluminescence depth profiling of highly strained In0.1Ga0.9N and In0.15Ga0.85N epitaxial films have been studied employing an inductively coupled Cl2 plasma etching. The photoluminescence measurements showed that thick InGaN films (0.2 ,m) consist of three different structural phases; (i) an InN-rich region near the InGaN film surface, (ii) a region that was free from InN-rich phase under stress-relaxation in the middle of the film, and (iii) an InGaN/GaN interface region. In region (i), a higher wavelength peak from the InN-rich phase was dominant. After removing the surface layer of 500 Å, the PL peaks from InN-rich phases completely disappeared, suggesting that the InN-rich phase region is confined to a depth of 500 Å. In regions of (ii) and (iii), the strain-relaxation between InGaN and GaN had a significant influence on the luminescence properties of InGaN. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Epitaxial strain energy measurements of GaN on sapphire by Raman spectroscopyPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2005H. J. Park Abstract This study reports a non-destructive method of measuring the residual strain in the GaN epilayer grown on sapphire substrate by micro-Raman spectroscopy. Operating in confocal mode this method allows a depth-dependent measurement of residual strain in the epitaxial layer without prior treatment of the sample. This approach to measurement of residual strain is demonstrated on GaN epitaxial films grown by both MOCVD and H-MOVPE. In the case of MOCVD grown films, the biaxial strain energy was found to vary from 0 (GaN surface) to 5.0 kJ/mole (GaN/sapphire interface), but in the case of H-MOVPE grown samples the strain energy varied from 6.5 kJ/mole , hydrostatic strain (GaN surface) to 25.0 kJ/mole , biaxial strain (GaN/sapphire interface), indicating that the surface layer of the N-terminated H-MOVPE material is not free from strain. Estimates are given for the curvature of substrate, lattice parameter of epitaxial layer, and the interface shear modulus. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Optical in-situ study of the oxidation and reduction kinetics of Yb-substituted YAG epitaxial filmsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2005N. V. Martynyuk Abstract The optical spectra of the Yb-substituted Yb3Al5O12 (YAG) epitaxial films and the Yb ions recharging kinetics have been investigated by means of in-situ optical spectroscopy in the temperature range between 900 and 1100 °C at oxidation and reduction condition. This work continues the studies of the spectral properties of Yb:YAG epitaxial films represented in [1] and optical in-situ study of the re-oxidation kinetics of Yb3Al5O12 (YbAG) crystal represented in [2] where the model of internal oxidation of ytterbium ions Yb2+ , Yb3+ in the bulk crystal was developed and proofed. The changes of the absorption spectra of Yb:YAG film during oxidation and reduction were attributed to the recharging process Yb3+ , Yb2+. It was found that the oxidation kinetics in epitaxial films do not agree to the model [2] and do not follow a parabolic rate law in contrary to bulk YbAG single crystal. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Properties of n-layers formed by low-energy ion beam milling of chalcogenides epitaxial filmsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2003N. N. Berchenko Abstract The paper presents the preliminary results of experiments performed to study the influence of low-energy Ar ions on the electrical properties of p- and n-type PbTe epitaxial films under ion beam milling. We demonstrate that this treatment causes p-to-n conversion in p-PbTe and increases the electron concentration in n-PbTe, with the electron mobility decreasing. The character of changes in the electrical properties allows to conclude that ion beam milling creates additional donor centres due to the preferential sputtering of tellurium. [source] Unusual current-voltage characteristics of single crystalline and bicrystalline La0.7Ca0.3MnO3 filmsANNALEN DER PHYSIK, Issue 10 2004A. Sawa Abstract The current-voltage characteristics of single crystalline and bicrystalline La0.7Ca0.3MnO3 films were measured and analyzed. Several epitaxial films, as well as 45° [001]-tilt grain boundaries, display current-voltage characteristics which are asymmetric with respect to polarity reversal of the bias current. One epitaxial film has a polarity dependent resistance of ,340k, and of ,670k, in forward and in reverse direction, respectively. [source] | |||||||||||||