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We report the epitaxial integration of phase-pure EuO on both single-crystal diamond and on epitaxial diamond films grown on silicon utilizing reactive molecular-beam epitaxy. The epitaxial orientation relationship is (001) EuO ‖ (001) diamond and [110] EuO ‖ [100] diamond. The EuO layer is nominally unstrained and ferromagnetic with a transition temperature of 68 ± 2 K and a saturation magnetization of 5.5 ± 0.1 Bohr magnetons per europium ion on the single-crystal diamond, and a transition temperature of 67 ± 2 K and a saturation magnetization of 2.1 ± 0.1 Bohr magnetons per europium ion on the epitaxial diamond film.

Epitaxial perovskite oxide thin films and heterostructures are a highly active materials research topic generating both fundamental and applied interest. This manuscript reports the roles of oxidation kinetics and film deposition rate on the growth of phase-pure complex oxides by molecular-beam epitaxy, one of the premier techniques for these materials, in a regime that is traditionally described as being governed by thermodynamics. It is found that oxidation kinetics on the film surface are surprisingly important for the growth of PbTiO${}_{3}$ and for formulating a simple kinetic theory to interpret experimental observations. The results are also enlightening to predict the conditions for improved growth of BiFeO${}_{3}$ and other complex oxides by MBE, of high interest to the broad community studying oxide films and heterostructures.

Despite their potential application in strain-engineered layer structures, the epitaxial growth of rare earth scandate films on cubic perovskite substrates is not fully understood to date. Here we report on the epitaxy of the orthorhombic GdScO3 and DyScO3 on (001) BaTiO3 and SrTiO3 thin films. In particular, the orientation relationship between the orthorhombic epilayer and the cubic substrate is examined by aberration corrected high-resolution transmission electron microscopy. For all cases investigated, the long axis of the orthorhombic unit cell was found to be perpendicular to the growth direction.

Epitaxial rare-earth scandate thin films of 100–1500 nm in thickness have been prepared by pulsed laser deposition on SrTiO3(100) and MgO(100) substrates. Stoichiometry and crystallinity were investigated by Rutherford backscattering spectrometry/channelling (RBS/C), transmission electron microscopy, and X-ray diffraction. Electrical measurements on microstructured capacitors with a SrRuO3 bottom electrode and Au top contacts reveal dielectric constants of 20 to 27, leakage currents of 0.85 to 6 μA/cm2 at 250 kV/cm, and breakdown fields of 0.6 to 1.2 MV/cm. The optical bandgaps of the films range from 5.5 to 6 eV. The results substantiate the high potential of rare-earth scandates as alternative gate oxides.

Thin films of rare-earth scandates (RE ScO"3) as well as multi-layers of scandates and titanates have been prepared using pulsed laser deposition. Epitaxial films were grown on SrRuO"3/SrTiO"3(100) as well as amorphous films on silicon substrates. The epitaxial films are investigated to measure the physical properties of the crystalline material. Electrical measurements (CV, leakage current) show for example high @e"r>20 for the scandates and @e"r>35 for the epitaxial and amorphous multi-layer films. A diffusion of the new materials into silicon is not observed.

Epitaxial thin films of LaLuO3 were deposited on SrTiO3(100) and SrRuO3/SrTiO3(100) or SrRuO3/LaAlO3(100) substrates using pulsed-laser deposition. They were investigated by means of Rutherford backscattering spectrometry, X-ray diffraction, transmission electron microscopy and atomic force microscopy. Smooth, c-axis oriented films with a channeling minimum yield of 3% were obtained. The electrical characterization of Au/LaLuO3/SrRuO3/SrTiO3(100) and Au/LaLuO3/SrRuO3/LaAlO3(100) metal–insulator–metal capacitor stacks revealed a dielectric constant of κ>45 and a breakdown field of 2 MV/cm for 100 nm thick epitaxial LaLuO3 films.

The effects of film thickness and epitaxial strain on the magnetic properties of commensurate EuO thin films grown on single crystalline (001) yttria-stabilized zirconia (YSZ) and (110) LuAlO3 substrates are presented. Magnetic measurements show a reduction in the Curie temperature (TC) for EuO/YSZ films thinner than ∼10 nm. Additionally, the EuO/LuAlO3 films exhibit a systematically lower TC than the corresponding EuO/YSZ films. This further reduction in TC is attributed to the effect of biaxial tensile strain arising from lattice mismatch: 0.0% for EuO/YSZ and +1.0% for EuO/LuAlO3.

The effect of lutetium doping on the structural, electronic, and magnetic properties of epitaxial EuO thin films grown by reactive molecular-beam epitaxy is experimentally investigated. The behavior of Lu-doped EuO is contrasted with doping by lanthanum and gadolinium. All three dopants are found to behave similarly despite differences in electronic configuration and ionic size. Andreev reflection measurements on Lu-doped EuO reveal a spin-polarization of 96% in the conduction band, despite non-magnetic carriers introduced by 5% lutetium doping. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4723570]

Rare earth doping is a standard, yet experimentally poorly understood method to increase the Curie temperature (T-C) of the ferromagnetic semiconductor EuO. Here, we report on the charge carrier density (n) and the T-C of commonly used 4.2 at. % Gd-doped EuO films grown by molecular-beam epitaxy on (110) oriented YAlO3 substrates at various substrate temperatures (T-sub). Increasing T-sub leads to a decrease in n and T-C. For high substrate temperatures the Gd-doping is rendered completely inactive: n and T-C drop to the values of undoped EuO. (C) 2011 American Institute of Physics. [doi:10.1063/1.3563708]

Homoepitaxial Sr1+xTiO3+delta films with -0.2

We have developed the means to grow BiMnO3 thin films with unparalleled structural perfection by reactive molecular-beam epitaxy and determined its band gap. Film growth occurs in an adsorption-controlled growth regime. Within this growth window bounded by oxygen pressure and substrate temperature at a fixed bismuth overpressure, single-phase films of the metastable perovskite BiMnO3 may be grown by epitaxial stabilization. X-ray diffraction reveals phase-pure and epitaxial films with omega rocking curve full width at half maximum values as narrow as 11 arc sec (0.003 degrees). Optical absorption measurements reveal that BiMnO3 has a direct band gap of 1.1 +/- 0.1 eV. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3457786]

We have studied the effect of biaxial strain on thin films of (001) La0.7Sr0.3MnO3. We deposited films by reactive molecular-beam epitaxy on different single crystalline substrates, varying the substrate-induced biaxial strain from -2.3% to +3.2%. Magnetization and electrical transport measurements reveal that the dependence of the Curie temperature on biaxial strain is in very good agreement with the theoretical predictions of Millis et al. [J. Appl. Phys. 83, 1588 (1998)]. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3213346]

Phase-pure, stoichiometric, unstrained, epitaxial (001)-oriented EuTiO3 thin films have been grown on (001) SrTiO3 substrates by reactive molecular-beam epitaxy. Magnetization measurements show antiferromagnetic behavior with T-N=5.5 K, similar to bulk EuTiO3. Spectroscopic ellipsometry measurements reveal that EuTiO3 films have a direct optical band gap of 0.93 +/- 0.07 eV.

Using molecular-beam epitaxy, we demonstrate the adsorption-controlled growth of epitaxial EuO films on single crystalline (110) YAlO3 substrates. Four-circle x-ray diffraction (XRD) reveals phase-pure, epitaxial, (001)-oriented films with rocking curve full width at half maxima as narrow as 34 arc sec (0.0097 degrees). The critical thickness for the onset of relaxation of (001) EuO on (110) YAlO3 (similar to 2% lattice mismatch) was determined from XRD measurements to be 382 +/- 25 angstrom. A saturation magnetization of 6.96 +/- 0.07 mu(B)/Eu, a value close to the theoretical limit of 7 mu(B)/Eu, is observed. (C) 2008 American Institute of Physics.

Doped EuO is an attractive material for the fabrication of proof-of-concept spintronic devices. Yet for decades its use has been hindered by its instability in air and the difficulty of preparing and patterning high-quality thin films. Here, we establish EuO as the pre-eminent material for the direct integration of a carrier-concentration-matched half-metal with the long-spin-lifetime semiconductors silicon and GaN, using methods that transcend these difficulties. Andreev reflection measurements reveal that the spin polarization in doped epitaxial EuO films exceeds 90%, demonstrating that EuO is a half-metal even when highly doped. Furthermore, EuO is epitaxially integrated with silicon and GaN. These results demonstrate the high potential of EuO for spintronic devices.

International audience; We investigate the suitability of an epitaxial CaTiO3 buffer layer deposited onto (100)Si by reactive molecular-beam epitaxy (MBE) for the epitaxial integration of thecolossal magnetoresistive material La0.7Sr0.3MnO3 with silicon. The magnetic andelectrical properties of La0.7Sr0.3MnO3 films deposited by MBE on CaTiO3-bufferedsilicon (CaTiO3/Si) are compared with those deposited on SrTiO3-buffered silicon(SrTiO3/Si). In addition to possessing a higher Curie temperature and a highermetal-to-insulator transition temperature, the electrical resistivity and 1/ f noise levelat 300 K are reduced by a factor of two in the heterostructure with the CaTiO3 bufferlayer. These results are relevant to device applications of La0.7Sr0.3MnO3 thin filmson silicon substrates.

Single crystalline (0001)ZnO films were grown by pulsed-laser deposition on (111) Si substrates containing thin Sc2O3 buffer layers (1 and 5nm) which were prepared by molecular-beam epitaxy at 700 ◦ C. Both x-ray diffraction and transmission electron microscopy reveal that the ZnO films grown at 240 and 400 ◦ C are highly crystalline with good epitaxy. The commonly seen amorphous SiOx layer has been successfully eliminated from the interface between the ZnO/Sc2O3 film and (111) Si substrate, resulting in improved electrical properties. Rectifying effects are observed in the heterojunction exhibiting a turn-on voltage of 1.08V and an ideality factor of 17.7. The room temperature mobility is 65cm 2 V −1 s −1 . A donor binding energy of 46.7meV is determined by temperature-dependent photoluminescence measurements.

Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010.

We report the structural properties of homoepitaxial (100) SrTiO3 films grown by reactive molecular-beam epitaxy (MBE). The lattice spacing and x-ray diffraction (XRD) rocking curves of stoichiometric MBE-grown SrTiO3 films are indistinguishable from the underlying SrTiO3 substrates. Off-stoichiometry for both strontium-rich and strontium-poor compositions (i.e., Sr1+xTiO3+δ films with −0.2

Epitaxial (0001) ZnO films were grown on (111) Si substrates using epitaxial (111) Sc2O3 buffer layers. The quality of the ZnO epilayers is manifested by a Hall mobility of 77 cm2/V s at room temperature, x-ray diffraction rocking curve full widths at half maximum of 300–400 arc sec, and optical properties comparable to ZnO single crystals. Transmission electron microscopy studies reveal that a thin layer of SiOx was formed at the Sc2O3/Si interface not during the Sc2O3 growth, but during the growth of the ZnO films. The thermal-mismatch induced residual strain in the films causes an energy shift of the exciton resonances in the photoluminescence spectrum. The redshifts are smaller than those of GaN films, indicating that the optical properties of ZnO are less strain sensitive.

Strained epitaxial SrTiO{sub 3} films were grown on orthorhombic (101) DyScO{sub 3} substrates by reactive molecular-beam epitaxy. The epitaxy of this substrate/film combination is cube on cube with a pseudocubic out-of-plane (001) orientation. The strain state and structural perfection of films with thicknesses ranging from 50 to 1000 {angstrom} were examined using x-ray scattering. The critical thickness at which misfit dislocations was introduced was between 350 and 500 {angstrom}. These films have the narrowest rocking curves (full width at half maximum) ever reported for any heteroepitaxial oxide film (0.0018{sup o}). Only a modest amount of relaxation is seen in films exceeding the critical thicknesses even after postdeposition annealing at 700{sup o}C in 1 atm of oxygen. The dependence of strain relaxation on crystallographic direction is attributed to the anisotropy of the substrate. These SrTiO{sub 3} films show structural quality more typical of semiconductors such as GaAs and silicon than perovskite materials; their structural relaxation behavior also shows similarity to that of compound semiconductor films.

In this work, we have investigated conditions to grow epitaxial La2O3 and Sc2O3 thin films directly on (111) Si as well as epitaxial LaScO3 thin films on (100) Si using an alkaline earth oxide buffer layer. The films were structurally characterized by reflection high-energy electron diffraction (RHEED) during growth and four-circle x-ray diffraction (XRD) and high-resolution plan-view and cross-section TEM, including Z-contrast TEM after growth. The epitaxial La2O3 thin films grew with the following epitaxial relationship (0001) La2O3 // (111) Si La2O3 // [112] Si with 1 additional rotational twin variant. Sc2O3 thin films grew epitaxially with a cube-on-cube orientation relationship on (111) silicon. It was not possible to achieve epitaxial LaScO3 thin films without the use of an alkaline earth buffer layer. The epitaxial orientation relationship between the orthorhombic LaScO3 and the underlying Si was (101) LaScO3 // (001) Si and [010] LaScO3 // [110] Si.

BiFeO3 thin films have been deposited on (001) SrTiO3 substrates by adsorption-controlled reactive molecular-beam epitaxy. For a given bismuth overpressure and oxygen activity, single-phase BiFeO3 films can be grown over a range of deposition temperatures in accordance with thermodynamic calculations. Four-circle x-ray diffraction reveals phase-pure, epitaxial films with ω rocking curve full width at half maximum values as narrow as 29arcsec (0.008°). Multiple-angle spectroscopic ellipsometry reveals a direct optical band gap at 2.74eV for stoichiometric as well as 5% bismuth-deficient single-phase BiFeO3 films.

BiFeO3 thin films have been deposited on (111) SrTiO3 single crystal substrates by reactive molecular-beam epitaxy in an adsorption-controlled growth regime. This is achieved by supplying a bismuth overpressure and utilizing the differential vapor pressures between bismuth oxides and BiFeO3 to control stoichiometry. Four-circle x-ray diffraction reveals phase-pure, untwinned, epitaxial, (0001)-oriented films with rocking curve full width at half maximum values as narrow as 25arcsec (0.007°). Second harmonic generation polar plots combined with diffraction establish the crystallographic point group of these untwinned epitaxial films to be 3m at room temperature.

Metastable lutetium scandate (LuScO3) thin films with an orthorhombic perovskite structure have been prepared by molecular-beam epitaxy and pulsed-laser deposition on NdGaO3(110) and DyScO3(110) substrates. Stoichiometry and crystallinity were investigated using Rutherford backscattering spectrometry/channeling, x-ray diffraction, and transmission electron microscopy. The results indicate that LuScO3, which normally only exists as a solid solution of Sc2O3 and Lu2O3 with the cubic bixbyite structure, can be grown in the orthorhombically distorted perovskite structure. Rocking curves as narrow as 0.05 degrees were achieved. A critical film thickness of approximately 200 nm for the epitaxially stabilized perovskite polymorph of LuScO3 on NdGaO3(110) substrates was determined. (C) 2007 American Institute of Physics.