In situ RHEED monitor of the growth of epitaxial anatase TiO2 thin films

Epitaxial anatase TiO₂ thin films were successfully grown on (0 0 1) SrTiO₃ substrates by the laser molecular-beam epitaxy (laser-MBE) method. The whole growth process is monitored by in situ reflection high-energy electron diffraction (RHEED). RHEED monitoring shows a transition from a streaky pattern to a spot pattern during deposition, indicating different growth modes of TiO₂ film. The RHEED patterns are in consistent with the RHEED intensity oscillation results. The atomic force microscopy (AFM) and X-ray diffraction (XRD) investigation show that the thin films have single crystalline orientation with roughness less than three unit cells.     

Plastic relaxation anisotropy in epitaxial films grown on miscut Si(001) substrates

A way of calculating the structural parameters of semiconductor epitaxial layers grown on miscut (0 0 1) substrates is developed. It is shown that the difference between the tensor of film elastic strains and the spherical tensor of strains translating the film’s crystal lattice into the substrate’s lattice is a tensor whose components are proportional to X-ray strains. The technique is used to analyze GaAs and Ge_0.2Si_0.8 films grown on (1 1 13) Si substrates. The anisotropy of the degree of plastic relaxation is established for lateral directions perpendicular and parallel to the interfacial steps in the GeSi film. It is proposed that noninteger Miller indices be used to denote the direction and value of the rotation of the film’s crystal lattice with respect to the substrate lattice.     

First-principles study of ferromagnetism in epitaxial Si-Mn thin films on Si(001)

Density-functional theory calculations are employed to investigate both the epitaxial growth and the magnetic properties of thin Mn and MnSi films on Si(001). For single Mn adatoms, we find a preference for the second-layer interstitial site. While a monolayer Mn film is energetically unfavorable, a capping-Si layer significantly enhances the thermodynamic stability and induces a change from antiferromagnetic to ferromagnetic order. For higher Mn coverage, a sandwiched Si-Mn thin film (with CsCl-like crystal structure) is found to be the most stable epitaxial structure. We attribute the strong ferromagnetic intralayer coupling in these films to Mn 3d-Si 3s3p exchange.     

Room-temperature epitaxial growth of CeO2(001) films on YSZ buffered Si(001) substrates

2 (001) epitaxial thin films deposited on Si(001) with yttria-stabilized zirconia buffers have been obtained for the first time at room temperature by pulsed-laser deposition. The influence of oxygen pressure on the crystal quality of CeO₂ was studied for the films deposited at 100 °C. The rocking curve full width at half maximum of the CeO₂(002) peak for films deposited at room temperature and 100 °C was between 1° and 2°, for oxygen pressures below 3×10^-2 mbar. The best crystal quality was obtained at around 3×10^-3 mbar. Epitaxial growth at room temperature was confirmed by cross-sectional transmission electron microscopy. Scanning electron microscopy and atomic force microscopy revealed very smooth surfaces for oxygen pressure below 3×10^-2 mbar, with rms roughness values around 0.3 nm over 5 μm×5 μm. Received: 25 September 1997/Accepted: 22 April 1998     

Strain-induced polarization rotation in epitaxial (001) BiFeO3 thin films

Direct measurement of the remanent polarization of high quality (001)-oriented epitaxial BiFeO3 thin films shows a strong strain dependence, even larger than conventional (001)-oriented PbTiO3 films. Thermodynamic analysis reveals that a strain-induced polarization rotation mechanism is responsible for the large change in the out-of-plane polarization of (001) BiFeO3 with biaxial strain while the spontaneous polarization itself remains almost constant.     

Spin-dependent quantum interference from epitaxial MgO thin films on Fe(001)

Spin-dependent electron reflection from MgO thin films grown on Fe(001) was measured using spin-polarized low energy electron microscopy. The electron reflectivity exhibits quantum interference from which two MgO energy bands with Delta1 symmetry were determined in experiment. We found that a bulklike MgO energy gap is fully established for MgO film thicker than 3 atomic monolayers and that the electron reflectivity from the MgO/Fe interface exhibits a spin-dependent amplitude and a spin-independent phase change.     

Phase‐controlled epitaxial growth of iron oxide thin films on MgO(001) and LaAlO3(001) substrates

We have deposited epitaxial iron oxide thin films on MgO(001) and LaAlO₃(LAO)(001) substrates, resulting in different phase stabilities. Atomic force microscopy images revealed a smooth surface. Detailed X‐ray diffraction (XRD) measurements were performed to confirm the epitaxial growth and to analyze the atomic growth configuration. We found that (00l) oriented γ‐Fe₂O₃ was the stable phase on MgO(001) substrates, whereas $ (1\bar 102) $ oriented α‐Fe₂O₃ was stable on LAO(001). Magnetic hysteresis loop measurements revealed typical ferrimagnetic behavior for γ‐Fe₂O₃ on MgO, whereas the magnetization of α‐Fe₂O₃ on LAO was relatively small and consistent with an antiferromagnetic order. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Magnetic properties of thin epitaxial Gd films on Nb

We investigated the magnetic properties of Gd films by magnetization measurements with the transverse magnetooptic Kerr effect in the temperature range from 2 to 295 K and for magnetic field up to 0.3 T. The thicknessd _Gd of the Gd films was varied between 11 and 1000 Å. For thick films (d _Gd500 Å) the form of the hysteresis curves and especially the nonmonotonic temperature dependence of remanence and coercivity can be qualitatively reproduced with a simple model employing theT dependence of the easy-axis direction. TheT dependence of the saturation magnetizationM _s of the thick films (d _Gd>=150 Å) strongly resembles the behavior of bulk crystals, whereas for the thinnest filmsM _s approximately depends linearly onT up to the Curie temperatureT _C . The thickness dependence ofT _C follows approximately a power law with an exponent 1.6 close to the theoretical value.     

Ion-beam-induced ferromagnetism in Ca-doped LaMnO3 thin films grown on Si (100)

The ion-bean-induced room temperature ferromagnetic ordering in pulsed laser deposited Ca-doped LaMnO₃ thin films grown on Si (100) are presented in the present study. In addition to this, changes bought by the ion beam in structural, morphological and electrical properties are presented. Dense electronic excitation produced by high energy 120?MeV Ag⁹⁺ ion irradiation causes change in surface roughness, crystallinity and strain. It is also evident that these excitations induce the magnetic ordering in this system. The observed modifications are due to the large electronic energy deposited by swift heavy ion irradiation. The appearance of ferromagnetism at 300?K in these samples after irradiation may be attributed to the canting of the antiferromagnetically ordered spins due to the structural distortion. It is observed that the irradiated films show higher resistance than unirradiated films for all the compositions.     

RHEED intensity oscillations during epitaxial growth of fcc Fe on Cu(001)

Up to 14 strong intensity oscillations of the specular beam in reflection high-energy electron diffraction (RHEED) have been observed during the epitaxial growth of face-centered (fcc) Fe on Cu(001) in the temperature range between 333–370 K. The amplitudes of these oscillations are strong even in the initial stages of growth. This provides evidence that the hetero-epitaxial growth of fcc Fe on Cu(001) proceeds predominantly layer-by-layer-like in that temperature regime. For growth at 300 K, initial Fe-bilayer-island formation followed by predominant layer-by-layer growth above 2 monolayers (ML) of Fe is observed. 3D growth prevails at ˜ 100 K.     

RHEED observation of BaTiO3 thin films grown by MBE

Ferroelectric BaTiO₃ thin films with a thickness of 10 monolayers (ML) were epitaxially grown on SrTiO₃(0 0 1) substrates by very slow deposition using molecular beam epitaxy (MBE). The investigations were carried out by two growth methods: (i) codeposition and (ii) alternate deposition of the metal elements in an oxygen atmosphere. In situ observation of reflection high-energy electron diffraction confirmed that an epitaxial cube-on-cube structure was prepared. After the deposition, X-ray diffraction measurements were carried out. The 10-ML-thick BaTiO₃ films were highly c-axis oriented single crystals with good film quality.     

Superconductivity of bilayer titanium/indium thin film grown on SiO_2/Si(001)

Bilayer superconducting films with tunable transition temperature(Tc) are a critical ingredient to the fabrication of high-performance transition edge sensors. Commonly chosen materials include Mo/Au, Mo/Cu, Ti/Au, and Ti/Al systems. Here in this work, titanium/indium(Ti/In) bilayer superconducting films are successfully fabricated on SiO_2/Si(001)substrates by molecular beam epitaxy(MBE). The success in the epitaxial growth of indium on titanium is achieved by lowering the substrate temperature to-150?C during indium evaporation. We measure the critical temperature under a bias current of 10 μA, and obtain different superconducting transition temperatures ranging from 645 m K to 2.7 K by adjusting the thickness ratio of Ti/In. Our results demonstrate that the transition temperature decreases as the thickness ratio of Ti/In increases.     

Electron-stimulated desorption of thin epitaxial films of KBr grown on (100)InSb

We have measured time-of-flight (TOF) distributions of Br atoms desorbed from thin (less than 1000 Å) epitaxial films of KBr on (100) InSb with a 2 keV electron beam. Although the general structure of the TOF spectra was similar to that obtained previously for the thick crystals, both the fast and the slow (thermal) components of the distribution were strongly dependent on the film thickness. We argue that this dependence is due to two different diffusion processes involved in the transport of the primary excitation products from the bulk to the surface. By measuring the velocity resolved ESD yield for films of various thicknesses, we determined that a diffusion length of the carriers responsible for the thermal ESD component varied from 30 to 700 Å with temperature in the range 20–300°C. In contrast, for the non-thermal desorption we found the carrier diffusion length of about 140 Å which did not depend significantly on the temperature.     

Photoacoustic spectroscopy of thin SiO2 films grown on (100) crystalline Si substrates

Photoacoustic Spectroscopy (PAS) has been used to measure the thickness of thin SiO₂ films grown on (100) Si wafers. The data are in reasonable agreement with a simple theoretical model. It suggests that photoacoustic Spectroscopy is complementary to optical interferometry, in that it is capable of giving quantitative estimates of thin transparent films on opaque substrates of low reflectivity via the transmitted fraction of the optical energy incident on the sample. Both theoretical and experimental results indicate that PAS can be very useful in the measurement of thin films on substrates of low reflectivity.     

Preparation and characterization of epitaxial Fe(001) thin films on GaAs(001)-based LED for spin injection

We report on the successful fabrication and characterization of ferromagnetic Fe/Tb multilayer contacts with perpendicular magnetic anisotropy (PMA) on the clean As-terminated surface of a GaAs(001)-based light-emitting diode (LED) structure. PMA was inferred from magnetometry and ⁵⁷Fe conversion electron Mössbauer spectroscopy. Such contacts are a potential candidate for optical detection of electron spin injection from the remanent magnetic state into the semiconductor.     

In-situ imaging of the nucleation and growth of epitaxial anatase TiO2(001) films on SrTiO3(001)

The growth of TiO₂ anatase films on Nb‐doped SrTiO₃(001) molecular beam epitaxy has been studied in-situ by scanning tunneling microscopy. We show that the initial growth follows the Stranski–Krastanov mode, where islands form on top of a wetting layer consisting of two monolayers (ML) of TiO₂. The epitaxial islands subsequently nucleate and coalesce into large commonly oriented crystallites. The reconstruction observed by reflection high-energy electron diffraction (RHEED) is shown to result from the coexistence of individual (4 × 1) and (1 × 4) reconstructions present on different crystallite surfaces. The anatase grows in units of bilayers, resulting in a step height of 2 ML (~ 0.5 nm). This result explains the fact that the measured period of the RHEED specular-beam intensity oscillations corresponds to the time required for deposition of 2 ML. Ar ion sputtering and UHV annealing results in a transformation to coexisting (4 × 1) and (1 × 4) reconstructed terraces on individual crystallites, as commonly observed by ex-situ STM studies.     

Growth and structure of epitaxial diamond films grown on Si(111) single crystals

Experiments on growing single-crystal diamond films on silicon crystals with (111) surface orientation have been performed. Results attesting to the possibility of obtaining thin heteroepitaxial films are presented. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 5, 414–418 (10 March 1997)