Epitaxial Mg-Fe-O spinel thin films were prepared by solid state reactions between MgO(lOO) substrates and thin films or vapors of iron oxide. Iron or iron oxide was deposited by electron beam evaporation in an oxygen background pressure onto a heated MgO crystal. The formation of MgFe2O4 at high temperatures proceeds via cation counter-diffusion in the fixed oxygen sublattice. Depending on substrate temperature, oxygen partial pressure and target material, epitaxial spinel films of different composition and magnetic properties were obtained. Crystal structure, composition and sub-micron morphology were investigated by RBS, XRD, TEM/SAED and EDX. Magnetic hysteresis loops were recorded at room temperature using the magneto-optic Kerr effect. Thickness interference fringes observed by XRD confirm the growth of smooth films. The main feature found in TEM plane view samples is a network of cation antiphase boundaries. The film composition measured by RBS varied from Fe2+ɛO3 films deposited at 340 °C substrate temperature to a solid solution of Fe2+E03 and MgFe2O4 at 500 °C to MgFe2O4 above 800 °C. EDX line-scans show a single phase MgFe2O4 spinel for a substrate temperature of 850 °C, without variation of composition with position or depth. At substrate temperatures higher than 800 °C Fe2+ was additionally dissolved in the MgO substrate, forming a FexMg1-xO solid solution.

We report on the growth and properties of (Sr1-xCax)Ru03 and Sr(Ru1-xTix)O3 thin films obtained by pulsed laser deposition. A sequential deposition of sub-monolayers from SrTiO3 and CaRuO3 end members has been successfully used to substitute Ca- and Ti- in the SrRuO3 perovskite structure. Magnetization measurements as well as transport properties exhibit very different behavior for each type of substitution. In the case of Ca- substituted samples, the resistivity remains metallic and is consistent with the expected behavior for intermediate compositions. A progressive reduction of the Curie temperature with higher doping is reported. In the case of Ti- substituted samples, we observe a stronger reduction of the Curie temperature and remanent magnetization with increasing Ti substitution. Resistivity as a function of temperature shows a crossover from metallic to semiconducting behavior with variable range hopping process for a high level of Ti doping and points out the clear differences between the two substitutions sites. In both cases, the observed reduction of the magnetization with increasing doping concentration can be well described by assuming a random distribution of substituted sites in the perovskite structure.

The compound V20O13 undergoes a metal-insulator-transition (MIT) at T=150K with an optical gap in the insulating phase of ∼0.6eV. Therefore epitaxial films of V2O3 are of interest for infrared (IR) applications. We present the results of a systematic study of the growth conditions of such films utilizing electronic transport and infrared transmission measurements in addition to studies of crystal and microstructure.

Epitaxial V2O3 thin films were grown in a reactive oxygen atmosphere on c-axis oriented sapphire substrates by electron beam evaporation. While V2O3 single crystals show a MIT in a narrow temperature range ΔT < 1K, the MIT broadened in epitaxial thin films due to defects and stress induced by the film-substrate interaction.

In our study we defined the quality of the films by the width ΔT of the transition and the change of resistivity p and IR transmission at the MIT. We found the most important growth parameter to be the growth temperature. Only in a narrow region around 600°C the growth of high quality films was observed. The optical constants of such films were determined from IR transmission measurements in combination with an oscillator fit method. While the spectra in both the metallic and the insulting phase are dominated by d-d-transitions for photon energies above leV, in the IR region (λ > 2μm) a high transmission contrast between the two phases was almost independent of the wavelength. This behavior suggests e.g. applications as a non mechanical IR shutter or as switchable interference filter in the IR regime.

Epitaxial PbTiO3 and Bi4Ti3O12 thin films have been grown on (100) SrTiO3 and (100) LaAlO3 substrates by reactive molecular beam epitaxy (MBE). Titanium is supplied to the film in the form of shuttered bursts each containing a one monolayer dose of titanium atoms for the growth of PbTi03 and three monolayers for the growth of Bi4Ti3O12. Lead, bismuth, and ozone are continuously supplied to the surface of the depositing film. Growth of phase pure, c-axis oriented epitaxial films with bulk lattice constants is achieved using an overpressure of these volatile species. With the proper choice of substrate temperature (600 – 650 °C) and ozone background pressure (PO3 = 2×10−5 Torr), the excess of the volatile metals and ozone desorb from the surface of the depositing film leaving a phase-pure stoichiometric crystal. The smooth PbTiO3 surface morphology revealed by atomic force microscopy (AFM) suggests that the PbTiO3 films grow in a layer-by-layer fashion. In contrast the Bi4Ti3O12 films contain islands which evolve either continuously or around screw dislocations via a spiral-type growth mechanism.

We show our recent development on the epitaxial growth of oxide thin films by laser molecular beam epitaxy directed towards a possible new field of electro-photonics based on metal-oxide quantum structures. Examples of quantum structures include superlattices and tunnel junctions (2-dimensional), superconducting quantum wire arrays (1-dimensional), and quantum dots for photonic application (O-dimensional). For fabricating such structures, it is vitally important to prepare the substrate surface and to understand the growth dynamics. Such electro-phptonic functions as Josephson effect in high Tc tunnel junctions and excitonic UV-laser operation at room temperature in self-organized hexagonal nanocrystal ZnO films are presented.

We report on ferroelectric field effect experiments in ultrathin layers of the metallic perovskite SrRuC<3 using Pb(Zr0.52Ti0.48)O3/SrRuO3 epitaxial heterostructures. Switching the ferroelectric polarization of the Pb(Zr0.52Ti0.48)O3 layer induces a ∼ 10% change in the sheet resistance of the SrRuO3 layer that is nonvolatile and also reversible. Hall effect measurements that take into account the anomalous Hall effect reveal a carrier concentration of n ∼ 2 × 1022 electrons/cm3 and allow us to understand quantitatively the sign and magnitude of the observed resistance change. Of key importance for these experiments is the crystalline and surface quality of the SrRuO3 and Pb(Zr0.52Ti0.48)O3 layers. We also discuss how this general approach of nonvolatile doping using ferroelectrics opens new possibilities of directly creating small electronic structures without using traditional lithographic techniques.

With the aim of lowering epitaxial growth temperature, the effect of electron incidence is studied in the epitaxial growth of CeO2(110) layers on Si(100) substrates by electron-beam evaporation in an ultrahigh vacuum. Two growth methods are employed: evaporation under substrate bias application and electron-beam assisted evaporation. In evaporation at positive substrate bias, electrons and anions from an evaporation source are attracted to the substrate surface, resulting in successful epitaxial temperature lowering. It is clarified that facilitation of the epitaxial growth is attributed only to electron incidence. The electronic current component is measured to be on the order of 10−4 A, about half of the total current. In using electron-beam assisted evaporation for higher current (10−3 A), electron-beam irradiation is demonstrated to have a much greater effect in both the growth temperature lowering and the crystalline quality improvement. The epitaxial growth facilitation effect increases with electron energy in both evaporation methods. It is clarified that the epitaxial growth temperature is lowered to 720°C, i. e., epitaxial growth temperature lowering of ∼100°C compared with the conventional growth method, both by evaporation with substrate bias at +240 V and 240 eV-electron-beam assisted evaporation, wherein the latter produces higher crystalline quality layers.

The growth mechanism and surface morphology of epitaxial SrRuO3 thin films deposited on exact and vicinal (001) SrTiO3 and exact (001) LaAlO3 substrates has been studied. Vicinal substrates with miscut angle, a, up to 4° toward [010] direction were used. Atomic force microscope images show that the films grown on exact (001) SrTiO3 substrate had a growth mechanism involving two dimensional nucleation. In contrast, characteristic step patterns were observed on the films deposited on vicinal substrates, suggesting that these films had a step flow growth mode. The films deposited on exact (001) LaAlO3 substrates had a three dimensional island growth, due to the incoherence between the film and substrate lattice. These results were found to be consistent with the results of x-ray diffraction analysis of the in-plane domain structure.

A perplexing issue in the growth of epitaxial oxide films on (100) silicon is the observed (110) orientation of yttria (Y2O3) and ceria (CeO2) despite the (100) orientation having a lower lattice mismatch. As expected, yttria-stabilized zirconia (YSZ) grows with the (100) orientation, yet it has a worse lattice match than both Y2O3(100) and CeO2(100) with silicon (100). The orientations observed would be expected if an epitaxial metal suicide layer forms initially during growth, before the oxidizing ambient is introduced. Calculation of the ensuing lattice mismatch between the oxide and suicide layer and multiplicity (σoxide) of the near coincident-site lattice for the oxide lattice shows that the (110) orientation is better lattice-matched than the (100) orientation for both Y2O3 (+2.3% × -2.4%, σoxide= 2, vs. -2.4% × +3.5%, σoxide = 4) and CeO2 (+1.8% × -4.0%, σoxide = 5, vs. 1.9% × 1.9%, σoxide= 5) and that for YSZ, (100) is better lattice matched than (110) (-0.8% × -1.6%, σoxide = 1, vs. -1.1 % × +4.8%, σoxide = 3). In each case, the in-plane orientation yielding the lowest mismatch with the suicide layer is consistent with the in-plane orientation observed between the oxide film and silicon substrate. Furthermore, the commonly observed rotational twinning in the oxide film can be accounted for by the expected orthogonal domain multipositioning in both the suicide and oxide layers. In CeO2, multipositioning allows two equally matched sets of orthogonal domains. One set consists of the two experimentally observed orientations (related by a 90° rotation). The other set is rotated 37° from the commonly observed orientations. Only the set with orientations aligned to the surface steps of Si(100) is observed, indicating the likely influence of graphoepitaxy in selecting between the two degenerate sets of orientations. When grown on Pt(100), Y2O3 grows with predominantly the (100) orientation and no (110) orientation, suggesting that without suicide formation, Y2O3 will grow with the expected well matched (100) orientation even when polar interfaces are involved.

CeO2 is nearly lattice matched to Si and has the CaF2 cubic structure thus it offers the potential for the epitaxial growth of an insulating film on Si. Laser ablation of a CeO2 target in an ultra high vacuum system was used for the deposition of single crystal CeO2. The effect of post growth thermal and rapid thermal annealing in O2, N2 and Ar atmosphere was found to have pronounced effects on the electrical properties measured by C-V and the optical properties measured by photoluminescence.

We report on our initial results for the growth of epitaxial Si on the deposited CeO2 using low pressure CVD. Both RHEED and TEM studies showed that single crystal epitaxial Si was deposited on CeO2. The details of the Si deposition on CeO2 films for potential of SOI (silicon on insulator) structures will be discussed.

In this study, the Y2O3 films on p-type Si(100) have been fabricated by UHV reactive ionized cluster beam deposition(r-ICB) systems. The crystallinity of the films was investigated by glancing X-ray diffraction(GXRD) and in-situ reflection of high energy electron diffraction(RHEED) analyses. The results show that the preferentially oriented crystallinity of the films was increased with acceleration voltages as well as substrate temperatures. Especially, at the substrate temperature of 700 °C and the acceleration voltage of 5kV, the Y2O3 films grow epitaxially in direction of Y2O3(110)//Si(100). The characteristics of Al/Y2O3/Si MIS structure were obtained by C-V, and I-V measurements. The breakdown field strength of the epitaxially grown films increases up to 2MV/cm without any interface silicon oxide layer, and the dielectric constant is found to be ε=15.6. these results demonstrated that the yttrium oxide films have potential application to the gate insulator of the future VLSI/ULSI devices.

In this paper, we have reported our investigations related to the growth of high temperature superconducting YBa2Cu3O7-δ (YBCO) and colossal magnetoresistive La0.7MnxO3-δ (LMO) thin films in presence of silver. The films were grown using pulsed laser deposition (PLD) techniques and characterized using x-ray diffraction, scanning electron microscopy, Squid magnetometer. The focus of our work is on the realization of significant improvement in microstructural and physical properties of these films by the addition of a common material (silver) to the films during their in-situ formation. Optical emission studies of plumes emanating from Ag target have been carried out to find the role of Ag acting as additional source of oxygen-supply to oxide lattices during film-growth.

The interaction of molecular oxygen, at room temperature, with a reduced TiO2(110) surface has been studied in situ by scanning tunneling microscopy (STM). Oxygen vacancies (point defects) were created on a clean TiO2(110) surface by annealing in ultra-high vacuum and successfully imaged on the atomic scale. These point defect sites were stable under ultrahigh vacuum conditions. During exposure to molecular oxygen, new point defects appear at different locations on the surface although their overall number is reduced. A mechanism for this dynamic healing process is proposed.

Epitaxially grown oxides of both SrTiO3 (STO) and YBa2Cu3O7-δ (YBCO) have been removed from their growth substrate and transferred for integration into other circuits (microwave devices) and onto other substrate material (glass). The enabling element in the separation process is the high selectivity of etching between YBCO and other oxide materials. Thus, a thin layer of YBCO is used as the sacrificial layer in the structure, allowing rapid etchant ingress under the device structures and separation from the growth substrate. Initial demonstrations of microwave device tuning using a lifted-off STO layer is detailed.

We introduce a new annealing procedure to prepare well defined surfaces of SrTiO3 single crystal and bicrystal substrates. Annealing SrTiO3 (001) substrates in oxygen and then in ultra high vacuum produces a uniformly TiO2-terminated, atomically flat and ordered SrTiO3 (001) surfaces, as revealed by Auger electron spectroscopy, low energy electron diffraction, and high resolution scanning tunneling microscopy. Applying this annealing procedure to slightly off-cut (∼1.2°) SrTiO3 (001) surfaces has a strong influence on the resulting step structure. Particular annealing procedures can be used to tailor the structure and morphology of the surface and of bicrystal boundaries down to the atomic level. For example, steps of SrTiO3 (001) surfaces can be adjusted to a height of one, two, or multiple times the unit-cell size of STO (aSTO=0.3905 nm). Atomically flat SrTiO3 (001) substrates were used for deposition of SmBa2Cu3O7-δ (SBCO) thin films. The thickness (in a range from 10 nm to 200 nm) dependency of the surface morphology of SmBa2Cu3O7-δ films was investigated with UHV-STM. No spiral growth was observed. Surfaces of all films exhibit stacks of flat terraces which are frequently separated by steps, smaller than the c-axis length cSBCO of SBCO (cSBCO=1.17 nm).

Here we present our recent work on the fabrication of high crystalline and optical quality ZnO films on sapphire (001) by pulsed laser deposition. The influence of deposition parameters such as the substrate temperature, oxygen pressure, laser fluence, and pulse repetition rate on the crystalline quality of ZnO layers has been studied. The Ω-rocking curve FWHM of the (002) peak for the films grown at 750°, oxygen pressure 10−5 Torr was 0.17°. The XRD-Ф scans studies revealed that the films were epitaxial with a 30° rotation of the unit cell with respect to the sapphire to achieve a low energy configuration for epitaxial growth. The high degree of crystallinity was confirmed by ion channeling technique providing a minimum Rutherford backscattering yield of 2–3% in the near surface region (-2000Å). The atomic force microscopy revealed smooth hexagonal faceting of the films. The optical absorption edge measured by UV-Visible spectroscopy was sharp at 383 nm. Excellent crystalline properties of these epi-ZnO/sapphire heterostractures are thus promising for III-V nitride heteroepitaxy.

The topmost atoms of TiO2 - terminated SrTiO3(001) annealed at temperatures between room temperature and 800°C in ultra high vacuum (UHV), have been studied by means of in-situ coaxial impact collision ion scattering spectroscopy (CAICISS). Both time-of-flight spectra at the incident angle of 45.0°C along [ 100] azimuth and of 35.3°C along [110] azimuth revealed Ti and weak O peaks and no Sr peak at 150°C, which means that the topmost layer at 150°C is terminated by TiCh-plane, completely. On the other hand, as increasing the substrate temperature, Sr peak began to appear above 400°C. This Sr peak intensity from both directions was drastically increased with elevating the substrate temperature. This indicates that the topmost O and Ti atoms desorb from the surface at the higher substrate temperature. The ratio Sr/Ti corresponds to the amount of the topmost oxygen or titanium vacancies due to the desorption. It was found that 40 % of the topmost oxygen atoms and 32% of the topmost titanium atoms desorb from TiO2-terminated SrTiO3(001) surface at 800°C. The activation energies for oxygen and titanium desorption were 0.28eV and 0.40eV, respectively.

Epitaxial ZnO films were grown on c-plane sapphire substrate at low temperature using the electron cyclotron resonance-assisted molecular beam epitaxy(ECR-assisted MBE) technique. In this method, Zn vapor provided by a Knudsen cell reacts with oxygen activated in an ECR source on the surface of sapphire substrate. The crystal structure, surface morphology and epitaxial relationship of the films were investigated. It was confirmed that the ECR-assisted MBE technique was capable of growing a high quality epitaxial ZnO films on c-plane sapphire substrates at low temperatures in comparison with CVD and RF sputtering. The FWHM of an x-ray rocking curve of the (0002) peak for a 0.33μ-thick ZnO film was as narrow as 0.58°. The epitaxial relationship between ZnO film and c-plane sapphire substrate was determined to be (0001)ZnO//(0001)Al2O3 with in-plane alignment of [1100]ZnO//[2110]Al2O3, which is equivalent to the 30° rotation of ZnO relative to sapphire in the c-plane.

The epitaxial growth of CeO2 on various (001) metal surfaces using pulsed-laser deposition is discussed. In particular, the growth of (001) CeO2 on (001) Pd, Ag, and Ni is described. Emphasis is given to the specific deposition conditions which successfully alleviate the formation ornative oxides at the metal/metal oxide interface. The control of the epitaxial relationships between the oriented oxides films and the underlying noble and oxidizing metal surfaces is addressed.

Possible equilibrium domain structures due to elastic interactions between the film and the substrate as a result of a cubic-tetragonal transformation observed in epitaxial perovskite ferroelectric films are analyzed. The formation of both two- and three-domain states is taken into account. A stability map which shows domain stability regions as a function of temperature is developed in coordinates of misfit strain and tetragonality of the lattice of the ferroelectric phase. Misfit dislocation generation at the growth temperature is found to have a profound effect on domain selection. As an example a PbTiO3(001) film grown on a MgO(001) substrate is considered and theoretical findings are compared with experimental results in the literature.