Epitaxial LaRh1/2Mn1/2O3 thin films have been grown on (001)-oriented LaAlO3 and SrTiO3 substrates using pulsed laser deposition. The optimized thin film samples are semiconducting and ferromagnetic with a Curie temperature close to 100 K, a coercive field of 1200 Oe, and a saturation magnetization of 1.7muB per formula unit. The surface texture, structural, electrical, and magnetic properties of the LaRh1/2Mn1/2O3 films was examined as a function of the oxygen concentration during deposition. While an elevated oxygen concentration yields thin films with optimal magnetic properties, slightly lower oxygen concentrations result in films with improved texture and crystallinity.
The technological conditions of oxygen content variation in epitaxial La0.7Sr0.3MnO3-δ films and the peculiarities of change of their transport characteristics were investigated. The films were grown onto single crystal SrTiO3 substrates by an enhanced method of dc magnetron sputtering of a ceramic target. It was revealed, that the oxygen content of the film material with initially strong deviation from stoichiometric composition (δ>0.06) changes easily in both directions at temperatures Tp >=870 K, and the result of the oxygen content variation can be well controlled via changes of conductivi…
We discuss the environmental instability of amorphous indium oxide (InOx)-based thin-film transistors (TFTs) in terms of the excess oxygen in the semiconductor films. A comparison between amorphous InOx doped with low and high concentrations of oxygen binder (SiO2) showed that out-diffusion of oxygen molecules causes drastic changes in the film conductivity and TFT turn-on voltages. Incorporation of sufficient SiO2 could suppress fluctuations in excess oxygen because of the high oxygen bond-dissociation energy and low Gibbs free energy. Consequently, the TFT operation became rather stable. The…
We have synthesized highly oxygen deficient HfO$_{2-x}$ thin films by controlled oxygen engineering using reactive molecular beam epitaxy. Above a threshold value of oxygen vacancies, p-type conductivity sets in with up to 6 times 10^{21} charge carriers per cm3. At the same time, the band-gap is reduced continuously by more than 1 eV. We suggest an oxygen vacancy induced p-type defect band as origin of the observed behavior.
The oxygen stoichiometry has a large influence on the physical and chemical properties of complex oxides. Most of the functionality in e.g. catalysis and electrochemistry depends in particular on control of the oxygen stoichiometry. In order to understand the fundamental properties of intrinsic surfaces of oxygen-deficient complex oxides, we report on in situ temperature dependent scanning tunnelling spectroscopy experiments on pristine oxygen deficient, epitaxial manganite films. Although these films are insulating in subsequent ex situ in-plane electronic transport experiments at all tempera…
We report the optical, electrical transport, and magnetotransport properties of high quality oxygen deficient SrTiO3 (STO) single crystal film fabricated by pulsed laser deposition and reduced in the vacuum chamber. The oxygen vacancy distribution in the thin film is expected to be uniform. By comparing the electrical properties with oxygen deficient bulk STO, it was found that the oxygen vacancies in bulk STO is far from uniform over the whole material. The metal-insulator transition (MIT) observed in the oxygen deficient STO film was found to be induced by the carrier freeze-out effect. The …
Strontium doped lanthanum manganite thin films were deposited by pulsed laser deposition on yttria stabilized zirconia single crystals for a comprehensive electrochemical characterization of the material acting as a cathode. A physically meaningful electrical model was employed to fit the electrochemical impedance spectroscopy results in order to extract the main oxygen mass transport parameters as a function of the temperature and oxygen partial pressure. The oxygen diffusion and surface exchange coefficients extracted from the analysis showed several orders of magnitude of enhancement with r…
The double perovskite La2NiMnO6 (LNMO) exhibits complex magnetism due to the competition of magnetic interactions that are strongly affected by structural and magnetic inhomogeneities. In this work, we study the effect of oxygen annealing on the structure and magnetism of epitaxial thin films grown by pulsed laser deposition. The key observations are that a longer annealing time leads to a reduction of saturation magnetization and an enhancement in the ferromagnetic transition temperature. We explain these results based upon epitaxial strain and oxygen defect engineering. The oxygen enrichment…
Stable oxygen sites on a PdO film over a Pd(100) thin structures with a (sqrt{5} times sqrt{5}) R27^circ surface-unit cell are determined using the first-principles electronic structure calculations with the generalized gradient approximation. The adsorbed monatomic oxygen goes to a site bridging two 2-fold-coordinated Pd atoms or to a site bridging a 2-fold-coordinated Pd atom and a 4-fold-coordinated Pd atom. Estimated reaction energies of CO oxidation by reduction of the oxidized PdO film and N_2O reduction mediated by oxidation of the PdO film are exothermic. Motion of the adsorbed oxygen …
Single-phase perovskite 5 at.% Mn-doped and undoped polycrystalline BaTiO3 thin films have been grown under different oxygen partial pressures by pulsed laser deposition on platinum-coated sapphire substrates. Ferroelectricity is only observed for the Mn-doped and undoped BaTiO3 thin films grown under relatively high oxygen partial pressure. Compared to undoped BaTiO3, Mn-doped BaTiO3 reveals a low leakage current, increased dielectric loss, and a decreased dielectric constant. Ferromagnetism is seen on Mn-doped BaTiO3 thin films prepared under low oxygen partial pressure and is attributed to …
Complex oxide functionality, such as ferroelectricity, magnetism or superconductivity is often achieved in epitaxial thin-film geometries. Oxygen vacancies tend to be the dominant type of defect in these materials but a fundamental understanding of their stability and electronic structure has so far mostly been established in the bulk or strained bulk, neglecting interfaces and surfaces present in a thin-film geometry. We investigate here, via density functional theory calculations, oxygen vacancies in the model system of a SrMnO$_3$ (SMO) thin film grown on a SrTiO$_3$ (STO) (001) substrate. …
Understanding the diffusion of oxygen vacancies in oxides under different external stimuli is crucial for the design of ion-based electronic devices, improve catalytic performance, etc. In this manuscript, using an external electric field produced by an AFM tip, we obtain the room-temperature diffusion coefficient of oxygen-vacancies in thin-films of SrTiO$_3$ under compressive/tensile epitaxial strain. Tensile strain produces a substantial increase of the diffusion coefficient, facilitating the mobility of vacancies through the film. Additionally, the effect of tip bias, pulse time, and tempe…
ITO thin films were deposited on glass substrates by d.c. magnetron sputtering with varied oxygen flow rates. It was found that the optical absorption decreases and optical absorption edge has blue shifts with the increasing oxygen flow rate. Oxygen vacancy concentration was characterized and analyzed by XPS. It is shown that the oxygen vacancy concentration increases with oxygen flow rates, which is a different observation from the current understanding. The energy band structures associated with different vacancy concentrations of ITO were calculated using the first-principle based on densit…
In many transition metal oxides (TMOs), oxygen stoichiometry is one of the most critical parameters that plays a key role in determining the structural, physical, optical, and electrochemical properties of the material. However, controlling the growth to obtain high quality single crystal films having the right oxygen stoichiometry, especially in a high vacuum environment, has been viewed as a challenge. In this work, we show that through proper control of the plume kinetic energy, stoichiometric crystalline films can be synthesized without generating oxygen defects, even in high vacuum. We us…
We report on the magnetic and structural properties of ferromagnetic-insulating La$_2$CoMnO$_6$ thin films grown on top of (001) STO substrates by means of RF sputtering technique. Careful structural analysis, by using synchrotron X-ray diffraction, allows identifying two different crystallographic orientations that are closely related to oxygen stoichiometry and to the features (coercive fields and remanence) of the hysteresis loops. Both Curie temperature and magnetic hysteresis turn out to be dependent on the oxygen stoichiometry. In situ annealing conditions allow tailoring the oxygen cont…
In oxide epitaxy, the growth temperature and background oxygen partial pressure are considered as the most critical factors that control the phase stability of an oxide thin film. Here, we report an unusual case wherein diffusion of oxygen vacancies from the substrate overpowers the growth temperature and oxygen partial pressure to deterministically influence the phase stability of $Bi_{2}WO_{6}$ thin film grown by the pulsed laser deposition technique. We show that when grown on an oxygen-deficient $SrTiO_{3}$ substrate, the $Bi_{2}WO_{6}$ film exhibits a mixture of (001) and (100)/(010)-orie…
The conductive characteristics of Bi0.9La0.1Fe0.96Mg0.04O3(BLFM) thin film are investigated at various temperatures and a negative differential resistance (NDR) is observed in the thin film, where a leakage current peak occurs upon application of a downward electric field above 80 oC. The origin of the NDR behavior is shown to be related to the ionic defect of oxygen vacancies (VO..) present in the film. On the basis of analyzing the leakage mechanism and surface potential behavior, the NDR behavior can be understood by considering the competition between the polarized distribution and neutral…
Vanadium oxides are strongly correlated materials which display metal-insulator transitions as well as various structural and magnetic properties that depend heavily on oxygen stoichiometry. Therefore, it is crucial to precisely control oxygen stoichiometry in these materials, especially in thin films. This work demonstrates a high-vacuum gas evolution technique which allows for the modification of oxygen concentration in VOX thin films by carefully tuning thermodynamic conditions. We were able to control the evolution between VO2, V3O5, and V2O3 phases on sapphire substrates, overcoming the n…
Oxygen-defect control has long been considered an influential tuning knob for producing various property responses in complex oxide films. In addition to physical property changes, modification to the lattice structure, specifically lattice expansion, with increasing oxygen vacancy concentrations has been reported often and has become the convention for oxide materials. However, the current understanding of the lattice behavior in oxygen-deficient films becomes disputable when considering compounds containing different bonding environments or atomic layering. Moreover, tensile strain has recen…
We report the enthalpy of oxygen vacancy formation in thin films of electron-doped SrTiO$_{3}$, under different degrees of epitaxial stress. We demonstrate that both compressive and tensile strain decrease this energy at a very similar rate, and promote the formation of stable doubly ionized oxygen vacancies. Moreover, we also show that unintentional cationic vacancies introduced under typical growth conditions, produce a characteristic rotation pattern of TiO$_6$ octahedra. The local concentration of oxygen vacancies can be modulated by an electric field with an AFM tip, changing not only the…
We report the formation of cubic phase, under ambient conditions, in thin films of Zirconia synthesized by electron beam evaporation technique. The stabilization of the cubic phase was achieved without the use of chemical stabilizers and/or concurrent ion beam bombardment. Films of two different thickness (660 nm, 140 nm) were deposited. The 660 nm and 140 nm films were found to be stoichiometric (ZrO2) and off-stoichiometric (ZrO1.7) respectively by Resonant Rutherford back-scattering spectroscopy. While the 660 nm as-deposited films were in the cubic phase, as indicated by X-ray diffraction …
Using Landau-Ginzburg-Devonshire theory and phase field modeling, we explore the complex interplay between the long-range structural order parameter (oxygen octahedron rotations) and polarization in EuxSr1-xTiO3 thin epitaxial films. In biaxially tensile strained films, we discover the presence of a low symmetry monoclinic phase with in-plane ferroelectric polarization that is stabilized by antiferrodistortive oxygen octahedra tilts. The monoclinic phase is stable in a wide temperature range, and is characterized by the large number of energetically equivalent polar and structural twin domains…
The structures, optical and electrical transport properties of SnO$_2$ films, fabricated by rf sputtering method at different oxygen partial pressures, were systematically investigated. It has been found that preferred growth orientation of SnO$_2$ film is strongly related to the oxygen partial pressure during deposition, which provides an effective way to tune the surface texture of SnO$_2$ film. All films reveal relatively high transparency in the visible range, and both the transmittance and optical band gap increase with increasing oxygen partial pressure. The temperature dependence of res…
Oxygen-vacancies-related dielectric relaxation and scaling behaviors of Bi0.9La0.1Fe0.98Mg0.02O3 (BLFM) thin film have been investigated by temperature-dependent impedance spectroscopy from 40 oC up to 200 oC. We found that hopping electrons and single-charged oxygen vacancies (VO.) coexist in the BLFM thin film and make contribution to dielectric response of grain and grain boundary respectively. The activation energy for VO. is shown to be 0.94 eV in the whole temperature range investigated, whereas the distinct activation energies for electrons are 0.136 eV below 110oC and 0.239 eV above 11…
Thin films of Co-TiO2 are deposited on silicon and quartz substrates using Pulse Laser Deposition (PLD) process at various oxygen partial pressures ranging from 6.6 x 10-3 Pascals (Pa) to 53 Pa. Crystal structure, transport and magnetic properties of reduced CoxTi(1-x)O2 (0 <x< 0.03) thin films are investigated and are found to have a strong dependence on the oxygen partial pressure. X-ray diffraction (XRD) data reveals the presence of mixed phase material containing both anatase and rutile. However, these phases intertransform with the change in the oxygen partial pressure in the chamber duri…
On highly oxygen deficient thin films of hafnium oxide (hafnia, HfO$_{2-x}$) contaminated with adsorbates of carbon oxides, the formation of hafnium carbide (HfC$_x$) at the surface during vacuum annealing at temperatures as low as 600 °C is reported. Using X-ray photoelectron spectroscopy the evolution of the HfC$_x$ surface layer related to a transformation from insulating into metallic state is monitored in situ. In contrast, for fully stoichiometric HfO$_2$ thin films prepared and measured under identical conditions, the formation of HfC$_x$ was not detectable suggesting that the enhanced …
Although defects on graphene can degrade electron transport and its ability for use as a protection layer, they can also be helpful to tailor the local properties or activate new sites for particular adsorbates. Here, carbon vacancy defects are formed in graphene films on Ru(0001) using low energy Ar$^+$ bombardment and the materials are then reacted at room temperature with oxygen (O$_2$). Helium low energy ion scattering shows that no oxygen attaches to the intact graphene layer. When isolated single carbon vacancy defects are present, oxygen adsorbs molecularly at the defect sites and inter…
The ability to manipulate oxygen anion defects rather than metal cations in complex oxides can facilitate creating new functionalities critical for emerging energy and device technologies. However, the difficulty in activating oxygen at reduced temperatures hinders the deliberate control of important defects, oxygen vacancies. Here, strontium cobaltite (SrCoOx) is used to demonstrate that epitaxial strain is a powerful tool for manipulating the oxygen vacancy concentration even under highly oxidizing environments and at annealing temperatures as low as 300 C. By applying a small biaxial tensil…
The quantum Hall conductance in monolayer graphene on an epitaxial SrTiO3 (STO) thin film is studied to understand the role of oxygen vacancies in determining the dielectric properties of STO. As the gate voltage sweep range is gradually increased in our device, we observe systematic generation and annihilation of oxygen vacancies evidenced from the hysteretic conductance behavior in graphene. Furthermore, based on the experimentally observed linear scaling relation between the effective capacitance and the voltage sweep range, a simple model is constructed to manifest the relationship among t…
Oxygen-containing yttrium hydride thin films exhibit a photochromic behavior: transparent thin films switch from a transparent state to a photodarkened state after being illuminated with UV or blue light. This feature has attracted much attention in recent years due to its potential applications in smart fenestration or in any device in which a response to intense light radiation is needed. However, the process responsible for the reversible change of the optical properties upon illumination is still not well understood. The objective of the present work is to shed some light on the photochrom…
Oxygen vacancies (VOs) effects on magnetic ordering in Eu0.5Ba0.5TiO3-δ (EBTO3-δ) thin films have been investigated using a combination of experimental measurements and first-principles density-functional calculations. Two kinds of EBTO3-δthin films with different oxygen deficiency have been fabricated. A nuclear resonance backscattering spectrometry technique has been used to quantitatively measure contents of the VOs. Eu0.5Ba0.5TiO3 ceramics have been known to exhibit ferroelectric (FE) and G-type antiferromagnetic (AFM) properties. While, a ferromagnetic (FM) behavior with a Curie temperatu…
Electrical conductivity, Hall effect and magnetoresistance of In$_2$O$_3$:Sn thin films deposited on a glass substrates at different temperatures and oxygen pressures, as well as the films treated in a hydrogen plasma, have been investigated in the temperature range 1.5-300 K. The observed temperature dependences of resistivity were typical for metallic transport of electrons except temperature dependence of resistivity of the In$_2$O$_3$:Sn film deposited in the oxygen deficient atmosphere. The electron concentration and mobility for the film deposited at 230$^\circ$C was larger than that for…
Despite of the tremendous efforts spent on the oxygen vacancy migration in determining the property optimization of oxygen-vacancy enrichment transition metal oxides, few has focused on their dynamic behaviors non-equilibrium states. In this work, we performed multi-timescale ultrafast X-ray diffraction measurements by using picosecond synchrotron X-ray pulses and femtosecond table-top X-ray pulses to monitor the structural dynamics in the oxygen-vacancy ordered SrCoO2.5 thin films. A giant photoinduced strain (Δc/c > 1%) was observed, whose distinct correlation with the pump photon energy ind…
Epitaxially grown SrTiO$_{3}$ (STO) thin films are material enablers for a number of critical energy-conversion and information-storage technologies like electrochemical electrode coatings, solid oxide fuel cells and random access memories. Oxygen vacancies (${\rm V_{O}}$), on the other hand, are key defects to understand and tailor many of the unique functionalities realized in oxide perovskite thin films. Here, we present a comprehensive and technically sound ab initio description of ${\rm V_{O}}$ in epitaxially strained (001) STO thin films. The novelty of our first-principles study lies in…
Zinc nitride films were synthesized by reactive radio frequency (rf) magnetron sputtering of a zinc target using an Ar+N2 mixture. The as-deposited films were annealed in the air and O2 at 300 °C for 1 hr. The XRD measurements indicated that the films had a polycrystalline structure with a preferred (400) Zn3N2 orientation. The annealing process enhanced the crystallinity. After annealing, the AFM and SEM morphology revealed no significant change in the surface morphology and surface roughness. The direct bandgap of Zn3N2 was estimated to be in the range of 1.15 -1.35 eV where annealing result…
Although rare earth nickelates (ReNiO3) exhibit abundant electronic phases and widely adjustable metal to insulator electronic transition properties, their practical electronic applications are largely impeded by their intrinsic meta stability. Apart from elevating oxygen reaction pressures, heterogeneous nucleation is expected as an alternative strategy that enables the crystallization of ReNiO3 at low meta stability. In this work, the respective roles of high oxygen pressure and heterogeneous interface in triggering ReNiO3 thin films growth at metastable state are revealed. The ReNiO3 (Re:Nd…
Reversible topotactic transitions between oxygen-vacancy-ordered structures in transition metal oxides provide a promising strategy for active manipulation of material properties. While transformations between various oxygen-deficient phases have been attained in bulk ABO$_{3-δ}$ perovskites, substrate clamping restricts the formation of distinct ordering patterns in epitaxial films. Using in-situ scanning transmission electron microscopy (STEM), we image a thermally driven reversible transition in La$_{0.5}$Sr$_{0.5}$CoO$_{3-δ}$ films on SrTiO$_3$ from a multidomain brownmillerite (BM) struct…
We use first-principles methods to investigate the effects of collective lattice excitations on the formation of oxygen vacancies in perovskite thin films. We find that phonons play a crucial role on the strain-mediated control of defect chemistry at finite temperatures. In particular, zero-temperature oxygen vacancy formation trends deduced as a function of epitaxial strain can be fully reversed near room temperature. Our first-principles calculations evidence a direct link between the lattice contribution to the oxygen vacancy free energy and the volume expansion that the system undergoes wh…
The slow kinetics of the oxygen reduction reaction (ORR) is one of the key challenges in developing high performance energy devices, such as solid oxide fuel cells. Straining a film by growing on a lattice-mismatched substrate has been a conventional approach to enhance the ORR activity. However, due to the limited choice of electrolyte substrates to alter the degree of strain, a systematic study in various materials has been a challenge. Here, we explore the strain modulation of the ORR kinetics by growing epitaxial La0.6Sr0.4CoO3-δ (LSCO) films on yttria-stabilized zirconia substrates with t…
Oriented Strontium Ferrite films with the c axis orientation were deposited with varying oxygen partial pressure on Al2O3(0001) substrate using PLD technique. The angle dependent magnetic hysteresis, remanent coercivity and temperature dependent coercivity had been employed to understand the magnetization reversal of these films. It was found that the Strontium Ferrite thin film grown at lower (higher) oxygen partial pressure shows Stoner-Wohlfarth type (Kondorsky like) reversal. The relative importance of pinning and nucleation processes during magnetization reversal is used to explain the ty…
Electrocatalysts for the oxygen reduction reaction (ORR) based on complexes of iron and nitrogen in a carbon matrix (Fe-N-C) are a promising alternative to platinum group metal (PGM) based catalysts in polymer electrolyte membrane (PEM) fuel cells. Further improvements of Fe-N-C catalysts would benefit from model thin film studies of activity and stability of catalytic sites, but synthesis of Fe-N-C model thin films is challenging. Here we report on synthesis and characterization of Fe-N-C thin films produced by co-sputtering iron and carbon in a reactive nitrogen atmosphere onto removable gla…
FeTe is known to become a superconductor when doped with oxygen. Using layer by layer growth of single crystal films by molecular beam epitaxy (MBE), we have studied how oxygen incorporates. If oxygen is supplied during growth of a layer, it substitutes for tellurium inhomogeneously in oxygen domains that are not associated with superconductivity. When oxygen is supplied after growth, it diffuses homogeneously into the crystalline film and incorporates interstitially. Only the interstitial oxygen causes superconductivity to emerge. This suggests that the superconductivity observed in this mate…
Multiferroics in which giant ferroelectric polarization and magnetism coexist are of tremendous potential for engineering disruptive applications in information storage and energy conversion. Yet the functional properties of multiferroics are thought to be affected detrimentally by the presence of point defects, which may be abundant due to the volatile nature of some constituent atoms and high temperatures involved in materials preparation. Here, we demonstrate with theoretical methods that oxygen vacancies may enhance the functionality of multiferroics by radically changing their magnetic in…
The interrelation between the epitaxial strain and oxygen deficiency in La0.7Ca0.3MnO3-δ thin films was studied in terms of structural and functional properties. The films with a thickness of 1000Å were prepared using a PLD system equipped with a RHEED facility and a pyrometric film temperature control. The epitaxial strain and the oxygen deficiency in the samples were systematically modified using three different substrates: SrTiO3, (LaAlO3)0.3-(Sr2AlTaO6)0.7 and LaSrAlO4, and four different oxygen pressures during film growth ranging from 0.27mbar to 0.1mbar. It could be demonstrated that th…
We investigated SrFeO$_{3-x}$ thin films on a SrTiO$_3$ (001) substrate prepared via pulsed laser epitaxy using an optical spectroscopy technique. The oxygen vacancy level ($x$) was controlled by post-annealing processes at different oxygen partial pressures. We achieved a brownmillerite(BM) structure at $x =$ 0.5 and observed the evolution of the crystal structure from BM into perovskite(PV) as the oxygen concentration increased. We observed the evolution of infrared-active phonons with respect to the oxygen concentration, which was closely related to the structural evolution observed via X-r…
Pitting corrosion is a much-studied and technologically relevant subject. However, the fundamental mechanisms responsible for the breakdown of the passivating oxide layer are still subjects of debate. Chloride anions are known to accelerate corrosion; relevant hypotheses include Cl insertion into positively charged oxygen vacancies in the oxide film, and Cl adsorption on passivating oxide surfaces, substituting for surface hydroxyl groups. In this work, we conduct large-scale first principles modeling of explicit metal/Al(2)O(3) interfaces to investigate the energetics and electronic structure…
In this work we report on photochromism in transparent thin film samples of oxygen-containing yttrium hydride. Exposure to visible and ultraviolet (UV) light at moderate intensity triggers a decrease in the optical transmission of visible and infrared (IR) light. The photo-darkening is colour-neutral. We show that the optical transmission of samples of 500 nm thickness can be reduced by up to 50% after one hour of illumination with light of moderate intensity. The reaction is reversible and samples that are left in the dark return to the initial transparent state. The relaxation time in the da…
Solid oxide oxygen ion and proton conductors are a highly important class of materials for renewable energy conversion devices like solid oxide fuel cells. Ba2In2O5 (BIO) exhibits both oxygen ion and proton conduction, in dry and humid environment, respectively. In dry environment, the brownmillerite crystal structure of BIO exhibits an ordered oxygen ion sublattice, which has been speculated to result in anisotropic oxygen ion conduction. The hydrated structure of BIO, however, resembles a perovskite and the protons in it were predicted to be ordered in layers. To complement the significant t…
It is generally accepted that oxygen vacancies play a central role in the emergence of ferroelectricity for HfO2-based materials, but the underlying mechanism still remains elusive. Herein, starting from the basic characterization circuit, we propose that the observed ferroelectricity is extrinsic. A key finding is that charged oxygen vacancies oscillate within the sample under repeated electric pulses, yielding a nonlinear current which behaves similarly to the polarization current for a normal ferroelectric. This unwanted current signal results in a ferroelectric-like hysteresis loop with bo…
We present a detailed ab initio study of the electronic structure and magnetic order of an Fe monolayer on the Ir(001) surface covered by adsorbed oxygen and hydrogen. The results are compared to the clean Fe/Ir(001) system, where recent intensive studies indicated a strong tendency towards an antiferromagnetic order and complex magnetic structures. The adsorption of an oxygen overlayer significantly increases interlayer distance between the Fe layer and the Ir substrate, while the effect of hydrogen is much weaker. We show that the adsorption of oxygen (and also of hydrogen) leads to a p(2$\t…
Surface Reactivity in Low Temperature Deposited Amorphous/Crystalline SnO2 Thin Films: Chemisorbed Oxygen Activity and CO Oxidation Pathways Revealed by In Situ XPS and Mass Spectrometry
该研究通过 EIS、原位 XPS、MS 等手段分析低温沉积多孔 SnO2 薄膜，证明 200°C 下 CO 氧化主要由化学吸附氧而非晶格氧驱动。
We have investigated the growth of BaTiO3 thin films deposited on pure and 1% Nb-doped SrTiO3(001) single crystals using atomic oxygen assisted molecular beam epitaxy (AO-MBE) and dedicated Ba and Ti Knudsen cells. Thicknesses up to 30 nm were investigated for various layer compositions. We demonstrate 2D growth and epitaxial single crystalline BaTiO3 layers up to 10 nm before additional 3D features appear; lattice parameter relaxation occurs during the first few nanometers and is completed at »10 nm. The presence of a Ba oxide rich top layer that probably favors 2D growth is evidenced for wel…
CoFe2O4 thin films (5 nm and 20 nm thick) were grown by oxygen assisted molecular beam epitaxy on Pt(111) at 523~K and subsequently annealed at 773 K in vacuum or oxygen. They were characterized in-situ using Auger Electron Spectroscopy, Low-Energy Electron Diffraction, Scanning Tunneling Microscopy and Conversion Electron Mössbauer Spectroscopy. The as-grown films were composed of small, nanometric grains. Annealing of the films produced an increase in the grain size and gave rise to magnetic order at room temperature, although with a fraction of the films remaining in the paramagnetic state.…
The search for chiral magnetic textures in systems lacking spatial inversion symmetry has attracted a massive amount of interest in the recent years with the real space observation of novel exotic magnetic phases such as skyrmions lattices, but also domain walls and spin spirals with a defined chirality. The electrical control of these textures offers thrilling perspectives in terms of fast and robust ultrahigh density data manipulation. A powerful ingredient commonly used to stabilize chiral magnetic states is the so-called Dzyaloshinskii-Moriya interaction (DMI) arising from spin-orbit coupl…
Improved toughness is a central goal in the development of wear-resistant refractory ceramic coatings. Extensive theoretical and experimental research has revealed that NaCl structure VMoN alloys exhibit surprisingly high ductility combined with high hardness and toughness. However, during operation, protective coatings inevitably oxidize, a problem which may compromise material properties and performance. Here, we explore the role of oxidation in altering VMoN properties. Density functional theory and theoretical intrinsic hardness models are used to investigate the mechanical behavior of cub…
The understanding of the Physics underlying the performances of organic spin-valve devices is still incomplete. According to some recent models, spin transport takes place in an impurity band inside the fundamental gap of organic semiconductors. This seems to be confirmed by recent experiments performed with La$_{0.7}$Sr$_{0.3}$MnO$_3$/Alq$_3$/AlO$_x$/Co devices. The reported results suggest a possible correlation between the magnetoresistance and the variable oxygen doping in the Alq$_3$ spacer. In this paper we investigate by means of first-principles calculations the electronic and magnetic…
