bluuebunny/crossref_metadata_2025_split huggingface dataset:
Role of Ag in the Epitaxial Growth of Oxide Thin Films
Authors: Lee Clinton B. , Kumar D. , Singh Rajiv K. , Mathis Derrick , Moxey Donovan 
Published: April 2011

ABSTRACTIn 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.
Heteroepitaxial Growth Of ZnO Films BY PLD
Authors: Vispute R. D. , Talyansky V. , Trajanovic Z. , Choopun S. , Downes M. , Sharma R. P. , Venkatesan T. , Wood M. C. , Lareau R. T. , Jones K. A. , Li Y. X. , Salamanca-Riba L. 
Published: April 2011

ABSTRACTHere 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.
In-Situ Caiciss Study Of Dynamic Process Of Oxygen Desorption On TiO2-Terminated SrTiO3(001) Surface
Authors: Nishihara T. , Ishiyama O. , Hayashi S. , Shinohara M. , Yoshimoto M. , Ohnishi T. , Koinuma H. 
Published: April 2011

ABSTRACTThe 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.
Growth of ZnO Thin Films on Sapphire Substrates by ECR-Assisted MBE
Authors: Kang Hee-Bog , Nakamura Kiyoshi , Ishikawa Kazuo 
Published: April 2011

ABSTRACTEpitaxial 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.
Improved Dielectric Response in Strontium Titanate Thin Films Grown by Pulsed Laser Ablation
Authors: Dalberth M. J. , Stauber R. E. , Price J. C. , Rogers C. T. , Galt David 
Published: April 2011

ABSTRACTWe have grown epitaxial strontium titanate films on lanthanum aluminate substrates at a range of oxygen pressures and substrate temperatures. The complex dielectric function was measured versus frequency (10 kHz to 1 MHz) and temperature (room temperature to 4.2 K) on coplanar capacitors patterned on the films. Preliminary data from 1.5 to 2.5 GHz is also presented. The dielectric constant εr was as high as 4600 at 65 K, a factor of two greater than previously reported for strontium titanate thin films and a factor of 1.8 greater than the bulk value at the same temperature. Tuning the capacitor by applying a dc bias of ±15 V across the 3 μm coplanar gap at 4.2 K yielded a ratio of maximum to minimum dielectric constant of 2.8. At 101 K this ratio was 2.2. A bulk capacitor does not show tuning over such a large temperature range.
Mechanism of Oxygenation of YBaCuO Thin Films During in Situ Growth by Cathodic Sputtering: Thermodynamic and Kinetic Aspects
Authors: Siejka J. , Garcia-Lopez J. , Lemaître Y. , Mercandalli L. M. 
Published: April 2011

ABSTRACTThe recent experimental results obtained for c-axis oriented YBaCuO thin films deposited at the optimized conditions for the microwave applications are presented and discussed. The emphasis is on the study of the relationship between oxygen profiles, crystallographic structure and electrical and physical properties of the films formed in situ at the same and optimized conditions of sample deposition and further submitted to the different conditions of sample cooling. The studies of the oxygen depth concentration profiles and of the oxygen contents are carried out using the recently developed Nuclear Reaction Analysis (NRA). These results are correlated, on one hand, with the measurements of the atomic composition and structure by RBS, XRD and TEM and, on the other hand, by the measurements of the electrical and physical properties Tc, Jc and microwave surface resistance Rs. All results are consistent with the idea that the fully oxygenated films are formed during in situ growth at T∼ 700°C. For T< 300°C, the oxygen interface transfer coefficient is very small and the oxygen content is practically preserved. However a large room temperature oxidation (corrosion like) takes place in the presence of water vapor. The fundamental and applied consequences of these findings for the mechanism of thin films growth and for the properties of the films in the presence of cathodic plasma or laser plume are analysed.
Epitaxial YBa2Cu3O7-δ/Sr2RuO4 Heterostructures
Authors: Schlom D. G. , Merritt B. A. , Madhavan S. , Liu Ying , Hawley M. E. , Brown G. W. , Dabkowski A. , Dabkowska H. A. , Uecker R. , Reiche P. 
Published: April 2011

ABSTRACTThe anisotropie oxide superconductors YBa2Cu3O7-Dgr; and Sr2RuO4 have been epitaxially combined in various ways (c-axis on c-axis, c-axis on a-axis, and a-axis on a-axis) though the use of appropriate substrates. Phase-pure a-axis oriented or c-axis oriented epitaxial Sr2RuO4 films were grown by pulsed laser deposition. YBa2Cu3O7-δ films were then grown on both orientations of Sr2RuO4 films and the resulting epitaxy was characterized.
Microstructural Defects in SrTiO3 Bicrystals and Their Influence on YBa2Cu3O7 Film Growth and Junction Performance
Authors: Hsu J. W. P. , McDaniel E. B. , Rao R. A. , Eom C. B. 
Published: April 2011

ABSTRACTWe use a near-field scanning optical microscope (NSOM) to investigate microstructural defects at the fusion boundaries of SrTiO3 bicrystal substrates. The optical transmission across the fusion boundary shows circular dark spots with diameters varying from 0.1 to 1 μm that are distributed non-uniformly along the boundary. After detailed characterization of the substrates, a thin YBa2Cu3O7 (YBCO) film (∼ 40 nm) was deposited on a 24° bicrystal. Combining NSOM and scanning force microscopy, we show that these substrate defects can cause the grain boundary of a YBCO thin film grown on the bicrystal to wander up to 0.8 micron in the film. Strain fields associated with these substrate defects are attributed to their influence on YBCO growth. The relation between these structural defects and the electrical characteristics of YBCO grain boundary junctions are also discussed.
Magnetic easy axis switching in ultrathin Co/Cu(110) films
Authors: Hope S. , Gu E. , Tselepi M. , Bland J.A.C. 
Published: April 2011

AbstractWe have studied the magnetic properties of the Co/Cu(110) system at 300K, using the magneto-optic Kerr effect. After a given deposition of Co in the thickness range 5ML<dCo<40ML, the M-H loop is observed to evolve continuously in time until the magnetic easy axis has switched 90° from the [001] to [1–10] direction. We attribute this behaviour to the reversal in sign of the effective in-plane uniaxial anisotropy constant, due to the adsorption of submonolayer quantities of a residual gas from the UHV environment. STM images reveal the growth of elongated Co island structures preferentially oriented along the [001] direction providing ‘step like’ edge sites for gas adsorption. We find the easy axis can be switched back to the [001] direction by depositing a submonolayer Cu overlayer, and that for relatively thick Co films (>15ML) the Cu overlayer can cause the magnetisation to take up intermediate angles. We analyse this behaviour using a simple model of the effective anisotropy energies.
Structural and Magnetotransport Properties of NiMnSb/Cu and NiMnSb/Ag Multilayers
Authors: Caballero J.A. , Petroff F. , Cabbibo A. , Park Y.D. , Childress J.R. 
Published: April 2011

ABSTRACTWe report on the integration of the predicted half-metallic (100% spin-polarized) ferromagnetic Heusler alloy NiMnSb into NiMnSb/Cu and NiMnSb/Ag multilayer structures, and on their magnetic, microstructural and magnetotransport properties. The NiMnSb layer thickness was fixed at 30Å and those of Cu and Ag were varied from 5 to 60Å. The multilayers were characterized using x-ray diffraction (XRD), four-wire resistivity measurements, atomic force microscopy, SQUID magnetometry and magnetotransport measurements. Moderate substrate temperatures (250°C) are shown to be sufficient to produce stochiometric Clb-structured NiMnSb. XRD data confirm that the NiMnSb ultra-thin layers retain their crystalline quality and texture. SQUID measurements shows that the bulk saturation magnetization (∼740 emu/cm3) is maintained and that it is strongly sensitive to interlayer diffusion and roughness. AFM studies show that the surface roughness, which can be as low as 4Å, depends on the choice of spacer layer, layer thickness and substrate temperature. The relationship between the measured magnetoresistance, NiMnSb crystalline quality, magnetic properties and interfacial roughness are discussed.
Perpendicular Magnetic Anisotropy in Nanostructured Pseudomorphic Fe(110) Films on W(110)
Authors: Elmers H.J. , Weber N. , Wagner K. , Hauschild J. , Gradmann U. 
Published: April 2011

ABSTRACTPseudomorphic Fe(110) films, deposited on W(110) at room temperature, with a mean thickness of 1.5 monolayers. are composed of double layer islands with a diameter of the order of 10 nm on a monolayer sea. The double layer islands are ferromagnetic (superparamagnetic) below 500 K, the monolayer sea becomes ferromagnetic below 222 K. Magnetic anisotropy is uniaxial in both components. The easy axis is perpendicular to the film plane in the double layer islands and within the film plane (along [110]) in the monolayer sea. The perpendicular anisotropy in the double layer islands apparently is caused by the pseudomorphic strain. The lateral scale for the anisotropy switching roughly coincides with the exchange lengths in both media. The strength of the exchange interaction between double layer islands rapidly increases when the monolayer sea becomes ferromagnetic.
Magnetization Reversal by Rotation in Magnetic Thin Films Deposited on Step Bunched Si(111) Substrates
Authors: Sussiau M. , Encinas A. , Nguyen Van Dau F. , Vaurès A. , Schuhl A. , Galtier P. 
Published: April 2011

ABSTRACTMagnetic and magnetoresistive properties of magnetic thin films deposited on periodically structured substrates have been studied. By using a thermodynamical heat treatment, we activate the step bunching phenomenon on vicinal Si(111) substrates misoriented towards [112] which results in a laterally modulated surface with a period around 0.1 μm. Epitaxial magnetic thin films deposited on these substrates exhibit an in-plane uniaxial anisotropy and a specific magnetoresistive behavior which characterizes the magnetization reversal process. In this contribution, we demonstrate that these properties can also be observed in non-epitaxial structures grown either by molecular beam epitaxy or by sputtering. In particular, magnetotransport measurements show that by varying parameters such as the nature of the magnetic metal, the layer thickness or the strength of the induced anisotropy, we can modulate the interplay between the anisotropy and the exchange stiffness, and, consequently, observe gradual magnetization reversal behaviors between a Stoner-Wohlfarth uniform mode and a non-uniform mode.
Structural and Magnetic Properties of XMnSb/PtMnSb Clb Heusler Alloy Superlattices (X=Ni,Cu)
Authors: Bobo J.F. , Bessho K. , Mancoff F.B. , Johnson P.R. , Kautzky M.C. , White R.L. , Clemens B.M. 
Published: April 2011

ABSTRACTWe have grown superlattices based on the Clb Heusler alloys PtMnSb, CuMnSb and NiMnSb between 200–500°C on A12O3 (0001). X-ray diffraction (XRD) indicates (111) oriented ordered structures for growth at 300°C. Higher deposition temperature leads to interdiffusion, loss of the multilayer structure and appearance of extra phases. Growth at 200°C slightly reduces the intermixing but also reduces the quality of the crystal structure. For PtMnSb/CuMnSb, we found an enhancement of the saturation magnetization compared to equivalent PtMnSb single layer films and a CuMnSb spacer thickness dependence of the squareness of the M(H) 100ps suggestive of interlayer coupling. Short periodicity NiMnSb/PtMnSb superlattices show an in-plane magnetic easy axis, but correction for shape anisotropy indicates a tendency for perpendicular anisotropy.
Magnetic Domain Structure and Spin Reorientation Transition in the System Co/Au/W(110)
Authors: Duden T. , Bauer E. 
Published: April 2011

ABSTRACTUltrathin epitaxial Co layers grown on Au(111) show strong perpendicular magnetic aniso-tropy resulting in out-of-plane magnetization in thin films. With increasing Co thickness the increasing contribution of the shape anisotropy leads to a reorientation transition of the magnetization which has already been subject of many other studies. In the dynamic in-situ experiments reported here bulk Au(111) is replaced by epitaxially grown Au(111)/W(110). The high time resolution (0.05 ML Co deposition per acquisition cycle) allows to extract several mechanisms which occur during the spin reorientation transition.
Macroscopic Magnetic Measurements on Microscopic Quantities of Materials
Authors: Foner Simon 
Published: April 2011

ABSTRACTThe principles of several of the most popular macroscopic magnetic measurement techniques are discussed for the vibrating sample magnetometer, SQUID magnetometer, ac susceptometer, ac force magnetometer, and torque magnetometers. These types of instruments are available commercially as stand-alone computer-controlled systems, Selected examples of recent measurements on thin films, small particles, and clusters of magnetic ions are presented.
Growth and Magnetic Anisotropy of Polycrystalline (110) (NiFe/Ni/NiFe)/Cu Multilayer on 4 ° TILT-CUT Si(111)
Authors: Song Yong-Jin , Lee Byung-Il , Joo Seung-Ki 
Published: April 2011

ABSTRACT[Cu(20Å)/NiFe(7Å)/Ni(6Å)/NiFe(7Å)]10Cu(50Å) multilayers were deposited on 4 ° tilt-cut Si(lll) using 3-gun rf magnetron sputtering system. An in-plane uniaxial magnetic anisotropy was found and the uniaxial magnetic anisotropy constant was about 3×104 erg/cm3. The multilayers on non tilt-cut Si(lll) with Cu underlayer did not show any anisotropy. The crystal structure of the multilayer on 4 ° tilt-cut Si(111) was studied using TEM work and the magnetic anisotropy is originated from the growth of (110) preferred orientation of the multilayer. When other material such as Ni or NiFe was used as an underlayer for the multilayer, the magnetic anisotropy disappeared and the crystal structure was (111). The multilayer without underlayer did not show any magnetic anisotropy either. It is thought that Cu underlayer was grown with (110) orientation on 4 ° tilt-cut Si(111) through the ledges in Si wafer and worked as a template for the growth of the multilayer.
Magnetic Thin Films of Cobalt Nanocrystals Encapsulated in Graphite-Like Carbon
Authors: Hayashi T. , Hirono S. , Tomita M. , Umemura S. , Delaunay J.-J. 
Published: April 2011

ABSTRACTGranular thin films consisting of cobalt nanocrystals encapsulated in graphite-like carbon were fabricated by co-deposition of cobalt and carbon with subsequent annealing. The gram size and the crystal structure of the Co-C films depended on the substrate temperature, the carbon concentration, and the annealing temperature. The film deposited with 36 at.% carbon at 200°C consisted of crystalline carbide and hep cobalt, which transformed into hep cobalt and graphite-like carbon by annealing at ≥300 °C. The as-deposited film with a carbon of 46 at.% had an amorphous-like phase and grain sizes of ≤10 nm. By annealing at ≥300°, the amorphous-like phase transformed into cobalt grains with a random stacking structure encapsulated in graphite-like carbon, and the initial size of the grains was unchanged. The saturation magnetization and the in-plane coercivity of these films were also reported.
Magnetic Dichroism in Resonant Photoemission and Photoabsorption from Gd Metal
Authors: Starke K. , Van Der Laan G. , Hu Z. , Arenholz E. , Navas E. , Bauer A , Mühlig A. , Langeheine C. S- , Weschke E. , Goodkoep J. , Brookes N. , Kaindl G. 
Published: April 2011

ABSTRACTWe report on the study of MCD in resonant PE, using Gd metal as an example. When the photon energy is changed across the Gd 4d → 4ƒ excitation region, the PE-MCD spectrum varies substantially. Based on atomic-multiplet theory, we present a consistent picture of MCD in resonant 4d → 4ƒ PE and x-ray absorption at the 4d-edge, where all spectral changes can be explained by the angular-momentum of the intermediate absorption state. The present analysis shows: when tuning to a specific line of the 4d x-ray absorption spectrum with a total angular momentum J', only the associate multiplet component is found to resonate. At the ‘giant resonance’, the shape of the MCD-PE signal closely resembles the off-resonance case; this finding is explained within atomic-multiplet theory allowing a straightforward use of MCD in 4d-resonant PE (i) for element-specific analysis of multicomponent magnetic systems with high surface sensitivity and (ii) for surface-domain imaging by PE microscopy.
Anisotropic Local Structure of Co-Pd Alloy and Pd/Co Multilayer Films Having Perpendicular Magnetic Anisotropy
Authors: Kim Sang-Koog , Chernov V.A. , Kortright J. B. , Koo Yang-Mo 
Published: April 2011

ABSTRACTAnisotropie short-range structure in Co-Pd alloy and Pd/Co multilayer films is determined using polarized Co K-edge extended x-ray absorption fine structure. A local modulation of Co fraction exists along the growth direction in the alloy films. Pd underlayer and Pd spacers alternated with the alloy layer influence an effective strain anisotropy. Pd/Co multilayers have an alloy-like region near nominal interfaces by diffuse interface. Pd spacers in the multilayer play a role in coherency strain rather than on broken symmetry of Co atoms. Local structural anisotropy of both strain and chemical environment contribute to the perpendicular magnetic anisotropy observed in these films.
Interaction of Magnetic Impurities with Surfaces
Authors: Szunyogh L. , Györffy B.L. 
Published: April 2011

ABSTRACTThe interaction of a magnetic (Fe) impurity with the surface of a non-magnetic (Au) semi-infinite host is investigated in terms of fully relativistic spin-polarized first principles calculations. It is shown that the surface induces a magnetic anisotropy on the impurity which is considerably larger than in the bulk. It is also found that the anisotropy constant K(d) is an oscillating function of the distance d between the impurity and the surface with an amplitude which falls as 1/d2 and a period which is determined by the shape of the Fermi Surface of the bulk Au host. However, the question still remains open whether the magnitude of the anisotropy energy is sufficiently large to explain the thickness dependence of the Kondo amplitude B in thin films of dilute FecAu1-c alloys.
Magnetic and Transport Properties of Ga1-xMnxAs, a New III-V Diluted Magnetic Semiconductor
Authors: Van Esch A. , Van Bocksta L. , De Boeck J. , Verbanck G. , Van Steenbergen A. , Bogaerts R. , Herlach F. , Borghs G. 
Published: April 2011

ABSTRACTGa1-xMnxAs is a new III-V diluted magnetic semiconductor that can be grown by MBE with Mn concentrations up to x ∼ 0.09. Below a critical temperature Tc, determined by the Mn concentration (about 50 K for x = 0.05) the material becomes ferromagnetic. This is attributed to the magnetic long-range order of Mn-hole complexes, the latter being the result of the strong antiferromagnetic interaction between the holes and Mn 3d spins. Transport and magnetic properties of the Ga1-xMnxAs system are strongly correlated. Above Tc, all samples show transport behaviour characteristic for materials near the metal insulator transition. Below Tc, resistivity decreases as the magnetic ordering sets in. When the magnetisation has reached its saturation value (below ∼ 20 K), variable range hopping is the main transport mechanism. Also, a negative magnetoresistance is observed below Tc.