Magnetization reversal of ultrathin Fe film grown on Si（111） using iron silicide template

Ultrathin Fe films were epitaxially grown on Si（lll） by using an ultrathin iron silicide film with p（2 × 2） surface reconstruction as a template. The surface structure and magnetic properties were investigated in situ by low energy electron diffraction （LEED）, scanning tunnelling microscopy （STM）, and surface magneto-optical effect （SMOKE）. Polar SMOKE hysteresis loops demonstrate that the Fe ultrathin films with thickness t 〈 6 ML （monolayers） exhibit perpen-dicular magnetic anisotropy. The characters of M-H loops with the external magnetic field at difference angles and the angular dependence of coercivity suggest that the domain-wall pinning plays a dominant role in the magnetization reversal process.[第一段]     

Study of the structural and magnetic characteristics of epitaxial Fe3Si/Si(111) films

The results of the structural and magnetic studies of the epitaxial structure prepared during the simultaneous evaporation from two iron and silicon sources on an atomically pure Si(111)7 × 7 surface at a substrate temperature of 150°C have been presented. The epitaxial structure has been identified as a single-crystal Fe₃Si silicide film with the orientation Si[111]‖Fe₃Si[111] using methods of the X-ray structural analysis, transmission electron microscopy, and reflection high-energy electron diffraction. It has been established that the epitaxial Fe₃Si film at room temperature has magnetic uniaxial anisotropy (H _a = 26 Oe) and a relatively narrow uniform ferromagnetic resonance line (ΔH = 11.57 Oe) measured at a pump frequency of 2.274 GHz.     

Optical properties of epitaxial CuGaS2 layers on Si(111)

CuGaS₂ films epitaxially grown on Si(111) substrates by molecular beam epitaxy from elemental sources were investigated by various optical methods. Photoluminescence studies at low temperatures reveal a strong dependence of the near-bandgap emission on the composition. Ga-rich films show predominantly donor–acceptor pair recombination, while additionally free-to-bound and excitonic transitions are found for stoichiometric and Cu-rich films. Low lineshape broadening of the free excitonic transitions FX^A and FX^B/C in the photoreflectance spectra up to room temperature demonstrates the high crystal quality. The assignment of these transitions is confirmed by polarisation dependent photocurrent measurements making use of the optical selection rules and the three different growth directions for the c-axis of CuGaS₂ relative to the Si-substrate. A fit to the photocurrent measurements yields the relative volume fraction of each c-axis orientation.     

Origin of the metallic to insulating transition of an epitaxial Bi(111) film grown on Si(111)

Transport characteristics of single crystal bismuth films on Si(111)-7×7 are found to be metallic or insulating at temperatures below or above T_C, respectively. The transition temperature T_C decreases as the film thickness increases. By combining thickness dependence of the films resistivity, we find the insulating behaviour results from the states inside film, while the metallic behaviour originates from the interface states. We show that quantum size effect in a Bi film, such as the semimetal-to-semiconductor transition, is only observable at a temperature higher than T_C.     

The electronic structures of epitaxial CrSi2 film prepared on Si(111) substrate

The valence band (VB) electronic structures of CrSi₂ were studied by synchrotron radiation photoemission. Overall features of the VB photoemission spectra measured at room temperature (RT) and 20 K by using synchrotron radiation (photon energy, hν=20–120 eV) were similar. Two characteristic emissions were observed corresponding to the bonding and the nonbonding Cr-d partial density of states (PDOS) in the CrSi₂. The onset of the VB photoemission measured at 20 K was located at about 0.32 eV below Fermi level, due to the energy band gap of CrSi₂ more than 0.32 eV.     

FMR study of the anisotropic properties of an epitaxial Fe<Subscript>3</Subscript>Si film on a Si(111) vicinal surface

The anisotropic characteristics of an iron silicide (Fe₃Si) epitaxial thin magnetic film grown on a Si(111) silicon vicinal surface with a misorientation angle of 0.14° have been measured by the ferromagnetic resonance method. It has been shown that the polar and azimuth misorientation angles of the crystallographic plane of the substrate can be determined simultaneously from the angular dependences of the ferromagnetic resonance field of the epitaxial film. The effective saturation magnetization of the film M _eff = 1105 G and the constant of the cubic magnetocrystalline anisotropy K ₄ = 1.15 × 10⁵ erg/cm³ have been determined. The misorientation of the substrate plane leads to the formation of steps on the film surface and, as a result, to the appearance of uniaxial magnetic anisotropy of the magnetic dipole nature with the constant K ₂ = 796 erg/cm³. Small unidirectional magnetic anisotropy (K ₁ = 163 erg/cm³), which may be associated with symmetry breaking on the steps of the film and is due to the Dzyaloshinskii–Moriya interaction, has been detected.     

Growth of an Eu-Si(111) thin film structure: The stage of silicide formation

Silicide formation in thin films produced by depositing Eu atoms on the Si(111) surface is studied using LEED, Auger electron spectroscopy, contact potential difference, and isothermal thermal-desorption spectroscopy. It is shown that if Eu is deposited on a substrate at room temperature, the growing film is disordered and consists of almost pure Eu. At high temperatures (T≥500 K), the Eu-Si(111) system forms through the Stranski-Krastanow mechanism; namely, first a two-dimensional transition layer (reconstruction) with the (2×1) structure forms and then three-dimensional silicide crystallites grow on it. A specific feature of this system is a low rate of diffusion of Si atoms in the europium silicides. This feature accounts for the concentration gradient of Si atoms across the silicide film thickness and, as a consequence, the multiphase film composition.     

New optoelectronic materials: Effects of annealing upon the formation of epitaxial iron silicide nanostructures on Si(001)

Iron silicide nanostructures were grown on Si(001) by a strain-induced, self-assembly method. 1 nm iron was deposited by electron gun evaporation and subsequently annealed at 850 °C for different times, between 10 and 50 min. The formation of nanostructures was traced by reflection high energy electron diffraction, and the formed nanoobjects were characterized by scanning electron microscopy and atomic force microscopy. The electrical features were measured by I–V, C–V, deep level transient spectroscopy and conductive atomic force microscopy. As a function of the annealing time the size and the shape of the iron silicide nanoobjects varied, while they were orientated in normal directions. With the rising duration of annealing time the height of the nanostructures emerged, with moderate lateral size enhancement. The electrical characterization shows that the Fe-related defects dominated in all samples in a depth below the surface depending on the time of annealing. These defects are closer to the conduction band at the beginning of the annealing, and after 30 min their concentration is much reduced and they are closer to the valence band.     

Thermal stability of Mg2Si epitaxial film formed on Si（111） substrate by solid phase reaction

A single crystalline Mg2 Si film was formed by solid phase reaction(SPR) of a Si(111) substrate with an Mg overlayer capped with an oxide layer(s),which was enhanced by post annealing from room temperature to 100 ℃in a molecular beam epitaxy(MBE) system.The thermal stability of the Mg2 Si film was then systematically investigated by post annealing in an oxygen-radical ambient at 300℃,450℃ and 650 ℃,respectively.The Mg2 Si film stayed stable until the annealing temperature reached 450 ℃ then it transformed into amorphous MgO x attributed to the decomposition of Mg2 Si and the oxidization of dissociated Mg.