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1.
We report on the identification of Fe3O4 (magnetite) and α-Fe2O3 (hematite) in iron oxide thin films grown on α-Al2O3(0 0 0 1) by evaporation of Fe in an O2-atmosphere with a thickness of a few unit cells. The phases were observed by Raman spectroscopy and confirmed by X-ray diffraction (XRD). Magnetite appeared independently from the substrate temperature and could not be completely removed by post-annealing in an oxygen atmosphere as observed by X-ray diffraction. In the temperature range between 400 °C and 500 °C the X-ray diffraction shows that predominantly hematite is formed, the Raman spectrum shows a mixture of magnetite and hematite. At both lower and higher substrate temperatures (300 °C and 600 °C) only magnetite was observed. After post-annealing in an O2-atmosphere of 5 × 10?5 mbar only hematite was detectable in the Raman spectrum.  相似文献   

2.
In this paper we report epitaxial tetragonal iron selenide thin films grown on single crystal SrTiO3 (STO) (0 0 1) and MgO (0 0 1) substrates by a pulsed laser deposition (PLD) technique. Deposition temperature and annealing process are found to be critical for achieving the tetragonal phase and the optimum superconducting properties of the films. The critical transition temperature of the thin films ranges from 2 K to 11.5 K depending on the deposition temperature and annealing condition. The samples with higher critical transition temperatures show better film crystallinity along with self-assembled Fe3O4 nanoparticles (~15 nm in average particle size) in the films according to both X-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis. Besides the better crystallinity achieved in the films, the formation of Fe3O4 nanoparticles could assist the formation of the tetragonal FeSe phase and thus lead to the enhanced superconducting properties.  相似文献   

3.
The structure of propanethiol self-assembled monolayers (SAMs) on Au(1 0 0) in 0.1 M H2SO4 has been investigated as a function of electrode potential by in situ scanning tunnelling microscopy (STM). These studies reveal a potential-induced, reversible transition between an in essence quadratic and a distorted hexagonal structure. We suggest that a thiolate-driven surface reconstruction, similar to Au(1 0 0)-(hex), is responsible for the hexagonal SAM structure, whereas the quadratic one refers to the unreconstructed substrate.  相似文献   

4.
The interaction between Au nano-particles and oxide supports is recently discussed in terms of the catalytic activities. This paper reports the electronic charge transfer between Au nano-particles and TiO2-terminated SrTiO3(0 0 1) substrate, which is compared with that for stoichiometric(S)-, pseudo-stoichiometric(S1)- and reduced(R)-TiO2(1 1 0) supports. We observed the photoelectron spectra of Au 4f, O 2s, Ti 3p, and Sr 4p lines and also measured the work functions for Au/oxides supports using synchrotron-radiation light. As the results, all the O 2s, Ti 3p, and Sr 4p lines for Au/SrTiO3(0 0 1) show lower binding energy shifts in a quite same manner and abrupt increase in the work function is seen in an initial stage. This clearly evidences an electronic charge transfer from the substrate to Au probably due to a much larger work function of Au than SrTiO3(0 0 1), which leads to an upward band bending (0.3 eV) just like a Schottky contact. Electronic charge transfers also take place at Au/S- and Au/S1-TiO2(1 1 0) and Au/R-TiO2(1 1 0) interfaces, where electrons are transferred from Au to S- and S1-TiO2 and from R-TiO2 to Au, as predicted by ab initio calculations.  相似文献   

5.
The growth of ultrathin films of Y2O3(111) on Pt(111) has been studied using scanning tunneling microscopy (STM), X-ray photoemission spectroscopy (XPS), and low energy electron diffraction (LEED). The films were grown by physical vapor deposition of yttrium in a 10? 6 Torr oxygen atmosphere. Continuous Y2O3(111) films were obtained by post-growth annealing at 700 °C. LEED and STM indicate an ordered film with a bulk-truncated Y2O3(111)–1 × 1 structure exposed. Furthermore, despite the lattices of the substrate and the oxide film being incommensurate, the two lattices exhibit a strict in-plane orientation relationship with the [11?0] directions of the two cubic lattices aligning parallel to each other. XPS measurements suggest hydroxyls to be easily formed at the Y2O3 surface at room temperature even under ultra high vacuum conditions. The hydrogen desorbs from the yttria surface above ~ 200 °C.  相似文献   

6.
Mixed Fe–Mo oxides are used in industrial catalytic processes of selective oxidation of methanol to formaldehyde. For better understanding of the structure-reactivity relationships of these catalysts we aim to prepare well-ordered iron–molybdate thin films as model catalysts. Here we have studied Mo deposition onto Fe3O4 (111) thin films produced on Pt(111) as a function of Mo coverage and annealing temperature using LEED, AES, STM and IRAS. At low temperatures, the iron oxide film is covered by Mo = O terminated molybdena nanoparticles. Upon oxidation at elevated temperatures (T > 900 K), Mo species migrate into the film and form new bonds with oxygen in the film. The resulting films maintain the crystal structure of Fe3O4, and the surface undergoes a (√3 × √3)R30° reconstruction. The structure is rationalized in terms of Fe substitution by Mo in the surface layers.  相似文献   

7.
Iron films have been grown on (1 1 0) GaAs substrates by atmospheric pressure metalorganic chemical vapor deposition at substrate temperatures (Ts) between 135°C and 400°C. X-ray diffraction (XRD) analysis showed that the Fe films grown at Ts between 200°C and 330°C were single crystals. Amorphous films were observed at Ts below 200°C and it was not possible to deposit films at Ts above 330°C. The full-width at half-maximum of the rocking curves showed that crystalline qualities were improved at Ts above 270°C. Single crystalline Fe films grown at different substrate temperature showed different structural behaviors in XRD measurements. Iron films grown at Ts between 200°C and 300°C showed bulk α-Fe like behavior regardless of film thickness (100–6400 Å). Meanwhile, Fe films grown at 330°C (144 and 300 Å) showed a biaxially compressed strain between substrate and epilayer, resulting in an expanded inter-planar spacing along the growth direction. Magnetization measurements showed that Fe films (>200 Å) grown at 280°C and 330°C were ferromagnetic with the in-plane easy axis along the [1 1 0] direction. For the thinner Fe films (⩽200 Å) regardless of growth temperature, square loops along the [1 0 0] easy axis were very weak and broad.  相似文献   

8.
Epitaxial thin films of Sr2FeMoO6 (SFMO) were prepared by pulsed laser deposition on SrTiO3(1 0 0) substrate. Thin films have been grown under different gas environments and they were structurally characterised by XRD. In contrast to previous reports, deposition carried out in the presence of a small amount of O2 with Ar yields high-quality SFMO films with a saturation magnetic moment of 3.8 μB. These SFMO films were strained in such a way that they were elongated along the c-axis and compressed in the ab-axes directions. The large low-field magnetoresistance seen in these films has been attributed to the tunneling across the antisite boundaries.  相似文献   

9.
The magnetic properties of epitaxial iron films up to 80 monolayers (ML) thickness grown on Si(0 0 1) by using a template technique were investigated by means of superconducting quantum interference device and magneto-optic Kerr effect techniques. The thinnest films investigated (∼3 ML) exhibit a composition close to Fe3Si with a Curie temperature below room temperature (RT) and strong out-of-plane remanent magnetization that reflects the presence of a dominant second order surface anisotropy term. Thicker films (⩾4 ML) are ferromagnetic at RT with remanent magnetization in film-plane and a composition closer to pure Fe with typically 8–10% silicon content. When deposited at normal incidence such films show simple in-plane fourfold anisotropy without uniaxial contribution. The relevant fourth-order effective anisotropy constant K4eff was measured versus film thickness and found to change its sign near 18 ML. The origin of this remarkable behavior is investigated by means of a Néel model and mainly traced back to fourth-order surface anisotropy and magneto-elastic effects related to the large biaxial in-plane compressive strain up to 3.5% in the thinnest (⩽25 ML) films.  相似文献   

10.
《Solid State Ionics》2006,177(9-10):863-868
Layered Li(Ni0.5Co0.5)1−yFeyO2 cathodes with 0  y  0.2 have been synthesized by firing the coprecipitated hydroxides of the transition metals and lithium hydroxide at 700 °C and characterized as cathode materials for lithium ion batteries to various cutoff charge voltages (up to 4.5 V). While the y = 0.05 sample shows an improvement in capacity, cyclability, and rate capability, those with y = 0.1 and 0.2 exhibit a decline in electrochemical performance compared to the y = 0 sample. Structural characterization of the chemically delithiated Li1−x(Ni0.5Co0.5)1−yFeyO2 samples indicates that the initial O3 structure is maintained down to a lithium content (1  x)  0.3. For (1  x) < 0.3, while a P3 type phase is formed for the y = 0 sample, an O1 type phase is formed for the y = 0.05, 0.1 and 0.2 samples. Monitoring the average oxidation state of the transition metal ions with lithium contents (1  x) reveals that the system is chemically more stable down to a lower lithium content (1  x)  0.3 compared to the Li1−xCoO2 system. The improved structural and chemical stabilities appear to lead to better cyclability to higher cutoff charge voltages compared to that found before with the LiCoO2 system.  相似文献   

11.
A multilayer structure has been proposed that demonstrates improved (0 0 1) texture for FePt-based L10 perpendicular media. Achieving a strong perpendicular magnetic anisotropy requires aligning the L10 crystallographic c-axis along the film normal. The ordered L10 FePt structure is tetragonal with a c/a ratio close to 0.965. This makes discriminating between the three crystallographic variants ([1 0 0], [0 1 0], and the desired [0 0 1]) difficult. Alloying FePt with Cu to reduce the c/a ratio and using a multilayer approach to keep the magnetic layers thin results in a structure with an adjustable Mrt and a strong (0 0 1) texture (rocking curve widths around 2°). This is a remarkable improvement in texture from pure FePt multilayered films or monolithic FePt(X) films. The proposed [MgO(2 nm)/Fe50−xPt50Cux(5 nm)]×n structure limits grain size in the vertical (perpendicular) direction albeit not in the plane of the film. Carbon can be added to the FePtCu layer to reduce the grain size with minimal degradation of the (0 0 1) orientation.  相似文献   

12.
《Applied Surface Science》2005,239(3-4):451-457
Well-ordered ultra-thin Al2O3 films were grown on NiAl (1 1 0) surface by exposing the sample at various oxygen absorption temperatures ranging from 570 to 1100 K at dose rates 6.6 × 10−5 and 6.6 × 10−6 Pa. From the results of low-energy electron diffraction (LEED), Auger electron spectrometer (AES) and X-ray photon spectroscopy (XPS) observations, it was revealed that oxidation mechanism above 770 K is different from well-known two-step process. At high temperature, oxidation and crystallization occurred simultaneously while in two-step process oxidation and crystallization occurred one after another. At high-temperature oxidation well-ordered crystalline oxide can be formed by a single-step without annealing. Well-ordered Al2O3 layer with thickness over 1 nm was obtained in oxygen absorption temperature 1070 K and a dose rate 6.6 × 10−6 Pa at 1200 L oxygen.  相似文献   

13.
In this work we report on the optical properties of single-crystalline iron thin films. For this, Cr-capped Fe films with thickness, t, in the range 30–300 Å were prepared on MgO (0 0 1) by DC magnetron sputtering, and then studied by optical absorption technique within the range from 1.0 to 3.6 eV. All measurements were carried out at room temperature using a fiber optics spectrophotometer. The intensity of the transmitted light decreases with increasing film thickness. The optical constants of the films are deduced from a model that considers the transmission of light by two absorbing films on an absorbing substrate. The absorption coefficient of the Fe films is also calculated from the transmission data. The absorption spectra show the following characteristics: (i) two large absorption peaks centered at about 1.20 and 2.65 eV; and (ii) a sharp step near 1.40 eV. These structures are associated with conventional interband transitions of the iron film.  相似文献   

14.
First-principles calculations are employed to study the structural and magnetic properties of fully-relaxed cubic Fe4N(0 0 1) surfaces with both Fe2- and Fe2N-termination. The results of surface stability calculations show that the (0 0 1) surface of Fe4N is most possibly existing with Fe2N-termination. Slab structures have more localized features in the density of states especially for the Fe2N-terminated surface due to structure relaxation. The average magnetic moments of Fe atoms increase with increasing thickness of slabs. The calculated interlayer distances indicate that the decreases of d12 and d23 result in stronger hybridization and shorter bond distances between Fe2 atom in the second layer and other atoms in surface or the third layers, which lead to variation of magnetic moments with different slab thicknesses.  相似文献   

15.
Biaxially textured yttria stabilized zirconia (YSZ) thin films, were deposited on glass substrates by ion beam assisted deposition method with different deposition time. As contrasts, films were also fabricated without assisting ion beam. The orientation properties of the films were characterized by X-ray diffraction. A comparative study shows that there is a competition between (0 0 1) and (0 1 1) alignments during the growth process. Assisting ions make the films (0 0 1)-advantaged and biaxially textured. The competitive growth and the orientation development are explained by selective resputtering and anisotropic damage on growing films induced by assisting ions.  相似文献   

16.
The effects of 100 MeV Ni ion irradiation on magnetic properties of nanoparticles of Ni0.8Cu0.2Fe2O4 with average particle sizes of 40 Å and 60 Å, synthesized by chemical co-precipitation method have been studied. The spinel cubic structures were confirmed by XRD. The average particle size estimated by XRD and by Langevin function fitting are in good agreement for both the pristine and irradiated samples. The blocking temperature increases with particle size and does not change after irradiation. On irradiation by 100 MeV Ni ions, significant changes in the hysteresis loop features are observed, which may be attributed to formation of cluster of defects in the nanocrystalline samples due to swift heavy ion (SHI) irradiation. It is also found that SHI irradiation produces more dominant changes in the hysteresis loop of smaller particle size of 40 Å as compared to that of 60 Å.  相似文献   

17.
In the present work, a special solid phase epitaxy method has been adapted for the preparation of CoSi2 film. This method includes an epitaxial growth of Co films on Si (1 0 0) substrate, and in situ annealing of the Co/Si films in vacuum. It has been found that at the substrate temperature of 360°C, fcc cobalt film grows epitaxially on the Si (1 0 0) surface. The crystallographic orientation relations between fcc Co film and Si substrate determined from the electron diffraction result are: (0 0 1) Co//(0 0 1) Si, [1 0 0] Co//[1 1 0]Si. Upon annealing at temperatures range from 500 to 600°C, Co film reacts with Si substrate and transforms into CoSi2. The CoSi2 films prepared by this way are characterized by XTEM, XPS and AFM.  相似文献   

18.
In thin layered Fe/Co (0 0 1), grown on MgO (0 0 1), both Fe and Co crystallize in the body-centered cubic (BCC) structure, as seen in a series of superlattices where the layer thickness of the components is varied from two to twelve atomic monolayers. These superlattices have novel magnetic properties as observed by magnetization and polarized neutron reflectivity measurements. There is a significant enhancement of the magnetic moments of both Fe and Co at the interfaces. Furthermore, the easy axis of the system changes from [1 0 0] for films of low cobalt content to [1 1 0] for a Co content exceeding 33%. No indication of a uniaxial anisotropy component is found in any of the samples. The first anisotropy constant (K1) of BCC Co is found to be negative with an estimated magnitude of 110 kJ/m3 at 10 K. In all cases, the magnetic moments of Fe and Co have parallel alignment.  相似文献   

19.
Stefan F?rster  Wolf Widdra 《Surface science》2010,604(23-24):2163-2169
The growth of epitaxial ultrathin BaTiO3 films upon rf magnetron sputter deposition on a Pt(111) substrate has been studied by scanning tunnelling microscopy, low-energy electron diffraction, and X-ray photoelectron spectroscopy. The BaTiO3 films have been characterized from the initial stages of growth up to a film thickness of 4 unit cells. The deposited films develop a long-range order upon annealing at 1050 K in UHV. In the submonolayer regime a wetting layer is formed on Pt(111). Thicker films reveal a Stranski–Krastanov-like structure as observed with STM. By XPS a good agreement of the thin film stoichiometry with BaTiO3 single crystal data is determined. Due to annealing at 1150 K BaTiO3 forms large two-dimensional islands on the Pt(111) substrate. Different surface structures develop on the islands depending on the O2 partial pressure during annealing.  相似文献   

20.
We present a summary of results of systematic first principles calculations of the electronic and geometric structures of the Cu2O(1 0 0) surface and the process of CO oxidation on this surface (energetics and pathways of adsorption, diffusion and reactions of CO and O2 on the surface). The (p, T) phase diagram of the Cu2O(1 0 0) in equilibrium of with gas phase O2 built using the ab initio thermodynamics approach suggests that the O-terminated surface is preferred over the Cu-terminated one within the entire ranges of pressures and temperatures in which the compound exists. Metastable Cu-terminated Cu2O(1 0 0) is found to undergo a surface reconstruction in agreement with experiment. We find CO to oxidize spontaneously on the O-terminated Cu2O(1 0 0) surface by consuming surface O atoms. Our calculations also show that the surface O-vacancies left in the course of the CO oxidation can be easily filled with dissociative adsorption of the gas phase O2 molecules, which are usually present in reaction environment.  相似文献   

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