Order-disorder processes fundamentally determine the structure and properties of many important oxide systems for energy and computing applications. While these processes have been intensively studied in bulk materials, they are less investigated and understood for nanostructured oxides in highly non-equilibrium conditions. These systems can now be realized through a range of deposition techniques and probed at exceptional spatial and chemical resolution, leading to a greater focus on interface dynamics. Here we survey a selection of recent studies of order-disorder behavior at thin film oxide interfaces, with a particular emphasis on the emergence of order during synthesis and disorder in extreme irradiation environments. We summarize key trends and identify directions for future study in this growing research area.
To better understand the electronic and chemical properties of wide-gap oxide surfaces at the atomic scale, experimental work has focused on epitaxial films on metal substrates. Recent findings show that these films are considerably thinner than previously thought. This raises doubts about the transferability of the results to surface properties of thicker films and bulk crystals. By means of density-functional theory and approximate GW corrections for the electronic spectra we demonstrate for three characteristic wide-gap oxides (silica, alumina, and hafnia) the influence of the substrate and…
This paper discusses questions of synthesizing and pressing vanadium oxides to create film-forming materials that can be used in producing optical coatings. Based on the film-forming materials thus created, technological processes have been developed for fabricating coatings from vanadium dioxide by two methods of producing thin films: vacuum evaporation and magnetron sputtering. Questions of using films made from vanadium oxide in optical instrumentation are considered.
We present an efficient and general method to identify promising candidate configurations for thin-film oxides and to determine structural characteristics of (metastable) thin-film structures using ab initio calculations. At the heart of this method is the complexity of the oxide bulk structure, from which a large number of thin films with structural building blocks, that is motifs, from metastable bulk oxide systems can be extracted. These span a coarse but well-defined network of initial configurations for which density functional theory (DFT) calculations predict and implement dramatic atom…
In this study, we report on face-centered cubic structured CoCrFeNi high-entropy alloy thin films with finely dispersed nano-oxide particles which are formed by internal oxidation. Analytical scanning transmission electron microscopy imaging found that the particles are Cr2O3. The oxide particles contribute to the hardening of the film increasing its hardness by 14% compared to that of the film without precipitates, through the Orowan-type strengthening mechanism. Our novel approach paves the way to design medium- and high-entropy alloys with high strength by making use of oxide phases.
The applicability of standard methods for compositional analysis is limited for H-containing films. Neutron reflectometry is a powerful, non-destructive method that is especially suitable for these systems due to the large negative scattering length of H. In this work we demonstrate how neutron reflectometry can be used to investigate thin films of yttrium hydride. Neutron reflectometry gives a strong contrast between the film and the surface oxide layer, enabling us to estimate the oxide thickness and oxygen penetration depths. A surface oxide layer of 5-10 nm thickness was found for unprotec…
Transition metal oxide heterostructures and interfaces host a variety of exciting quantum phases and can be grown with atomic-scale precision by utilising the intensity oscillations of $in$ $situ$ reflection high-energy electron diffraction (RHEED). However, establishing a stable oscillation pattern in the growth calibration of complex oxides films is very challenging and time consuming. Here, we develop a substantially more efficient and reliable growth calibration method for complex oxide films using molecular beam epitaxy.
We perform first-principles density functional calculations to explore the role of substrate proximity effects on the octahedral rotation patterns in perovskite oxide superlattices. With cubic perovskite SrFeO$_3$ as our model film and tetragonal SrTiO$_3$ as the substrate, we show that in most cases the substrate octahedral rotation patterns propagate into the film across the heterointerface. We also identify elastic boundary conditions for which the enforced structural coherence induces atomic displacement patterns that are not found in the bulk phase diagram of either individual constituent…
The structure of thin terminated Bi(1 1 1) films of approximately 1 nm thickness is investigated from first principles. Our density functional theory calculations show that covalent bonds to the surface can change the orientation of the films completely. For thicker films, the effect is limited to the surface only. Based on these observations, we further present a simple model structure for the native oxide and chemically similar oxides, which form a protective capping layer, leaving the orientation of the films unchanged. The advantages of this energetically favorable layered termination are …
High Frequency (GW) Post Processing of Transparent Conductive Oxide, ITO, leads to a significant improvement of Optical Transmission and Electrical Conduction. This is also true in case of ITO films in multilayered structures. The improvements happen without any affecting the lower layers (other layers of the multilayered Device). This Method is extremely selective and can process only the targeted film (layer).
The micro-properties (structure and composition), and macro-properties (electrical and optical properties) of zinc oxide (ZnO) thin films deposited on glass substrates using a filtere vacuum arc deposition (FVAD) system were investigated as a function of oxygen pressure (0.37 - 0.5 Pa) and arc current (100 - 300 A). Correlations between the various properties were investigated.
We report layer-resolved measurements of the \textit{unoccupied} electronic structure of ultrathin MgO films grown on Ag(001). The metal-induced gap states at the metal/oxide interface, the oxide band gap as well as a surface core exciton involving an image-potential state of the vacuum are revealed through resonant Auger spectroscopy of the Mg $KL_{23}L_{23}$ Auger transition. Our results demonstrate how to obtain new insights on \textit{empty} states at interfaces of metal-supported ultrathin oxide films.
Oxide thin films exhibit versatile physical properties such as magnetism, ferroelectricity, piezoelectricity, metal-insulator transition (MIT), multiferroicity, colossal magnetoresistivity, switchable resistivity, etc. More importantly, the exhibited multifunctionality could be tuned by various external fields, which has enabled demonstration of novel electronic devices. In this article, recent studies of the multi-fields modulation of physical properties in oxide thin films have been reviewed. Some of the key issues and prospects about this field are also addressed.
We report the epitaxial growth of Ca3SnO antiperovskite oxide films on (001)-oriented cubic yttria-stabilized zirconia (YSZ) substrates by using a conventional pulsed laser deposition (PLD) technique. In this work, a sintered Ca3SnO pellet is used as the ablation target. X-ray diffraction measurements demonstrate the (001) growth of Ca3SnO films with the antiperovskite structure and a cube-on-cube orientation relationship to the YSZ substrate. The successful synthesis of the antiperovskite phase is further confirmed by x-ray photoemission spectroscopy. These results strongly suggest that antip…
An original modification of the standard Pulse Laser Deposition (PLD) method for preparing both undoped and indium doped zinc oxide (ZnO:In) thin films at low substrate temperature is proposed. This preparation method does not demand any further post-deposition annealing treatment of the grown films. The developed method allows to grow thin films at low substrate temperature that prevents them from the considerable loss of their intrinsic electrical and optical properties. The influence of deposition parameters on the electrical and optical parameters of the undoped and the indium doped ZnO th…
Auger electron spectroscopy (AES) and electron energy loss spectroscopy (EELS) in a reflection mode are compared as the methods for phase composition investigation of thin film oxide systems by ion profiling. As an example, the Al/Al2O3/Si and YBa2Cu3O7/CeO2/Al2O3 systems are considered. The adaptation of applied statistics methods for AES and EELS data treatment is discussed.
Thin aluminum oxide films were deposited by a new and simple physicochemical method called chemical liquid phase deposition (CLD) on semiconductor materials. Aluminum sulfate with crystallized water and sodium bicarbonate were used as precursors for film growth, and the control of the system pH value played an important role in this experiment. The growth rate is 12 nm/h at room temperature. Post-growth annealing not only densifies and purifies the films, but results in film crystallization as well. Excellent quality of Al2O3 films in this work is supported by electron dispersion spectroscopy,…
Ordering of mobile defects in functional materials can give rise to fundamentally new phases possessing ferroic and multiferroic functionalities. Here we develop the Landau theory for strain induced ordering of defects (e.g. oxygen vacancies) in thin oxide films, considering both the ordering and wavelength of possible instabilities. Using derived analytical expressions for the energies of various defect-ordered states, we calculated and analyzed phase diagrams dependence on the film-substrate mismatch strain, concentration of defects, and Vegard coefficients. Obtained results open possibiliti…
Amorphous metal oxide thin-film transistors (TFT) are fabricated using InOx-based semiconductors doped with TiO2, WO3 or SiO2. Although density of dopant is low in the film, change in the electrical properties showed strong dependence on the dopant species. We found that the dependence could be reasonably explained by the bond-dissociation energy. By incorporating the dopant with higher bond-dissociation energy, the film becomes less sensitive to oxygen partial pressure used during sputtering deposition and remains electrically stable to thermal annealing treatment. The concept of bond-dissoci…
We have used the classical Hall effect to electrically characterize Indium Tin Oxide (ITO) films grown by two different techniques on silica substrates. ITO films have the unique property that they can be both electrically conducting (and to be used for a gate electrode for example) as well as optically transparent (at least in the visible part of the spectrum). In the near infrared (NIR) the transmission typically reduces. However, the light absorption can in principle be compensated by growing thinner films.
Chemical oxidation of multilayer graphene grown on silicon carbide yields films exhibiting reproducible characteristics, lateral uniformity, smoothness over large areas, and manageable chemical complexity, thereby opening opportunities to accelerate both fundamental understanding and technological applications of this form of graphene oxide films. Here, we investigate the vertical inter-layer structure of these ultra-thin oxide films. X-ray diffraction, atomic force microscopy, and IR experiments show that the multilayer films exhibit excellent inter-layer registry, little amount (<10%) of int…
We observe remarkably strong room temperature ferromagnetism (~1.5 Bohr Magneton/Mn) in optically transparent Mn(II)-doped indium tin oxide (ITO) films. The nanocrystalline films with average grain size 10-22 nm and thickness 150-350 nm are prepared by sol-gel coating technique on sodalime silica glass substrate. The ferromagnetic property is, of course, weak for films deposited on pure silica glass substrate. The structural parameters of the films appear to be governing the magnetic property strongly which vary appreciably depending on the substrate. The observation of room temperature ferrom…
The effects of wet chemical processing conventionally employed in device fabrication standards are systematically studied on molybdenum oxide (MoOx) ultra-thin films. We have combined x-ray photoelectron spectroscopy (XPS), angle resolved XPS and x-ray reflectivity techniques to provide deep insights into the changes in composition, structure and electronic states upon treatment of films with different initial stoichiometry prepared by reactive sputtering. Our results show significant reduction effects associated with the development of gap states in MoOx, as well as changes in the composition…
The observation of ferroelectric, ferromagnetic and ferroelastic phases in thin films of binary oxides attract the broad interest of scientists and engineers. However, the theoretical consideration of observed behaviour physical nature was performed mainly for HfO2 thin films from the first principles, and in the framework of Landau-Ginzburg-Devonshire (LGD) phenomenological approach with a special attention to the role of oxygen vacancies in both cases. Allowing for generality of the LGD theory we applied it to the group of binary oxides in this work. The calculations have been performed in t…
Thin films of thulium and ytterbium-doped titanium oxide were grown by metal-organic spray pyrolysis deposition from titanium(IV)oxide bis(acetylacetonate), thulium(III) tris(2,2,6,6-tetramethyl-3,5-heptanedionate) and ytterbium(III) tris(acetylacetonate). Deposition temperatures have been investigated from 300°C to 600°C. Films have been studied regarding their crystallity and doping quality. Structural and composition characterisations of TiO2:Tm,Yb were performed by electron microprobe, X-ray diffraction and Fourier transform infrared spectroscopy. The deposition rate can reach 0.8 \mum/h. …
Recently high density (HD) nonmagnetic (NM) cobalt has been discovered in a cobalt thin film, grown on Si(111). This cobalt film had a natural cobalt oxide at the top. The oxide layer forms when the film is taken out of the electron-beam deposition chamber and exposed to air. Thin HD NM cobalt layers were found near the cobalt/silicon and the cobalt-oxide/cobalt interfaces, while the thicker mid-depth region of the film was hcp cobalt with normal density and normal magnetic moment. If an ultrathin film of gold is grown on the cobalt layer, before exposing it to air, the oxidation of the cobalt…
Oxide passive films are a key for the durability of metals and alloys components as well as a central issue in corrosion science and engineering. Herein, we discuss current developments of the nanometer and sub-nanometer scale knowledge of the barrier properties and adsorption properties of passive oxide films brought by recent model experimental and theoretical investigations. The discussed aspects include (i) the chromium enrichment and its homogeneity at the nanoscale in passive films formed on Cr-bearing alloys such as stainless steel, (ii) the corrosion properties of grain boundaries in e…
In this paper we report: the use of GO in aqueous solution as a gate dielectric material, its application to a MOS transistor based on organic semiconductor and the use of paper as substrate material.
A detailed spectroscopic and structural characterization of ultrathin cobalt oxide films grown by O-assisted molecular beam epitaxy on a-Al2O3(0001) single crystals is reported. The experimental results show that the cobalt oxide films become progressively more disordered with increasing thickness, starting from the early stages of deposition. Low energy electron diffraction patterns suggest that the unit cell remains similar to that of a-Al2O3(0001) up to a thickness of 17 A, while at larger thicknesses a pattern identified with that of Co3O4(111) becomes visible. X-ray photoelectron spectros…
Vacancy defects in thin film laser ablated SrTiO3 on SrTiO3 were identified using variable energy positron annihilation lifetime measurements. Strontium vacancy related defects were the dominant positron traps and, apart from in the top ~ 50 nm, were found to be uniformly distributed. The surface layer showed an increase in annihilation from larger open-volume defects, large vacancy clusters or nanovoids.
We show that the thermal stability of thin films of the organic semiconductor diindenoperylene (DIP) can be strongly enhanced by aluminum oxide capping layers. By thermal desorption spectroscopy and in-situ X-ray diffraction we demonstrate that organic films do not only stay on the substrate, but even remain crystalline up to 460C, i.e. 270 deg. above their desorption point for uncapped films (190C). We argue that this strong enhancement of the thermal stability compared to uncapped and also metal-capped organic layers is related to the very weak diffusion of aluminum oxide and the structurall…
We report on sexithiophene films, about 150nm thick, grown by thermal evaporation on single crystal oxides and, as comparison, on Si/SiO2. By heating the entire deposition chamber at 100 C we obtain standing-up oriented molecules all over the bulk thickness. Surface morphology shows step-like islands, each step being only one monolayer height. The constant and uniform warming of the molecules obtained by heating the entire deposition chamber allows a stable diffusion-limited growth process. Therefore, the regular growth kinetic is preserved when increasing the thickness of the film. Electrical…
In spite of being highly relevant for the development of a new generation of information storage devices, not many single-phase materials displaying magnetic and ferroelectric orders above room temperature are known. Moreover, these uncommon materials typically display insignificant values of the remanent moment in one of the ferroic orders or are complex multicomponent oxides which will be very challenging to integrate in devices. Here we report on the strategy to stabilize the metastable epsilon-Fe2O3 in thin film form, and we show that besides its already known ferrimagnetic nature, the fil…
In this review, we propose a summary of the most recent advances in the first-principles study of ferroelectric oxide epitaxial thin films and multilayers. We discuss in detail the key roles of mechanical and electrical boundary conditions, providing to the reader the basic background for a simple and intuitive understanding of the evolution of the ferroelectric properties in many nanostructures. Going further we also highlight promising new avenues and future challenges within this exciting field or researches.
NaOH-reacted graphite oxide film was prepared by decomposing epoxy groups in graphite oxide into hydroxyl and -ONa groups with NaOH solution. Ultrafast carrier dynamics of the sample were studied by time-resolved transient differential reflection (\DeltaR/R). The data show two exponential relaxation processes. The slow relaxation process (\sim2ps) is ascribed to low energy acoustic phonon mediated scattering. The electron-phonon coupling and first-principles calculation results demonstrate that - OH and -ONa groups in the sample are strongly coupled. Thus, we attribute the fast relaxation proc…
Understanding early stages of low-temperature hydrogen-driven direct co-reduction of Fe-Ni mixed oxide thin films at the near atomic scale
Chair for Materials Discovery and Interfaces, Institute for Materials, Ruhr-Universität Bochum（鲁尔大学材料研究所材料发现与界面讲席）；Max Planck Institute for Sustainable Materials（马克斯·普朗克可持续材料研究所）；Center for Interface Dominated High Performance Materials (ZGH), Ruhr-Universität Bochum（鲁尔大学界面主导高性能材料中心）
Improved thermomechanical properties have been reported for various high-entropy oxides containing typically five metal cations. This study further investigates a series of duodenary (11 metals + oxygen) high-entropy oxides by mixing different fractions of a five-cation fluorite-structured niobate and a seven-cation pyrochlore (both containing Yb) with matching lattice constants. Nine compositions of duodenary high-entropy oxides have been examined. All of them exhibit single high-entropy phases of either disordered fluorite or ordered pyrochlore structure. An order-disorder transition (ODT) i…
Perovskite transition-metal oxides are networks of corner-sharing octahedra whose tilts and distortions are known to affect their electronic and magnetic properties. We report calculations on a model interfacial structure to avoid chemical influences and show that the symmetry mismatch imposes an interfacial layer with distortion modes that do not exist in either bulk material, creating new interface properties driven by symmetry alone. Depending on the resistance of the octahedra to deformation, the interface layer can be as small as one unit cell or extend deep into the thin film.
To clarify the electronic density of states (DOS) around the conduction band bottom for state of the art transparent amorphous oxide semiconductors (TAOSs), InGaZnO4 and In2MgO4, we fabricated TAOS-based transparent thin film transistors (TTFTs) and measured their gate voltage dependence of thermopower (S). TAOS-based TTFTs exhibit an unusual S behavior. The |S|-value abruptly increases, but then gradually decreases as Vg increases, clearly suggesting the anti-parabolic shaped DOS is hybridized with the original parabolic shaped DOS around the conduction band bottom.
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 …
This review covers the important advances in recent years in the physics of thin film ferroelectric oxides, the strongest emphasis being on those aspects particular to ferroelectrics in thin film form. We introduce the current state of development in the application of ferroelectric thin films for electronic devices and discuss the physics relevant for the performance and failure of these devices. Following this we cover the enormous progress that has been made in the first principles computational approach to understanding ferroelectrics. We then discuss in detail the important role that stra…
Cupric oxide single crystal thin films were grown by plasma-assisted molecular beam epitaxy. X-ray diffraction, Raman spectrum and in situ reflection high-energy electron diffraction show that the thin films are 2x2 reconstructed with an in-plane compression and out-of-plane stretching. Thermal stimulated current measurement indicates that the electric polarization response presents in the special 2D cupric oxide single crystal thin film over a wide temperature range from 130 K to near-room temperature. We infer that the abnormal electric response involves the changing of phase transition temp…
Tin doped indium oxide (ITO) thin films are being used extensively as transparent conductors in several applications. In the present communication, we report the electrical transport in DC magnetron sputtered ITO thin films in low temperatures (25-300 K). The low temperature Hall effect and resistivity measurements reveal that the ITO thin films are moderately dis-ordered (kfl~1) and degenerate semiconductor. The transport of charge carriers in these disordered ITO thin films takes place via the de-localized states. The disorder effects lead to the well- known metal-insulator transition; this …
Cation disorder is an important design criterion for technologically relevant transition-metal (TM) oxides, such as radiation-tolerant ceramics and Li-ion battery electrodes. In this letter, we use a combination of first-principles calculations, normal mode analysis, and band-structure arguments to pinpoint a specific electronic-structure effect that influences the stability of disordered phases. We find that the electronic configuration of a TM ion determines to which extent the structural energy is affected by site distortions. This mechanism explains the stability of disordered phases with …
Control of order-disorder phase transitions is a fundamental materials science challenge, underpinning the development of energy storage technologies such as solid oxide fuel cells and batteries, ultra-high temperature ceramics, and durable nuclear waste forms. At present, the development of promising complex oxides for these applications is hindered by a poor understanding of how interfaces affect lattice disordering processes and defect transport. Here we explore the evolution of local disorder in ion-irradiated La$_2$Ti$_2$O$_7$ / SrTiO$_3$ thin film heterostructures using a combination of …
Mastery of order-disorder processes in highly non-equilibrium nanostructured oxides has significant implications for the development of emerging energy technologies. However, we are presently limited in our ability to quantify and harness these processes at high spatial, chemical, and temporal resolution, particularly in extreme environments. Here we describe the percolation of disorder at the model oxide interface LaMnO$_3$ / SrTiO$_3$, which we visualize during in situ ion irradiation in the transmission electron microscope. We observe the formation of a network of disorder during the initia…
SrVO3 (SVO) is a prospective candidate to replace the conventional indium-tin-oxide (ITO) among the new transparent conducting oxide (TCO) generation. In this study, the structural, electrical, and optical properties of SVO thin films, both epitaxial and polycrystalline, are determined during and after heat treatments in the 150-250 °C range and under ambient environment in order to explore the chemical stability of this material. The use of these relatively low temperatures speeds up the natural ageing of the films, and allows to follow the evolution of their related properties. The combinati…
Highly-ordered and spatially-coherent cobalt slanted columnar thin films were deposited by glancing angle deposition onto silicon substrates, and subsequently oxidized by annealing at 475 $^{\circ}$C. Scanning electron microscopy, Raman scattering, generalized ellipsometry, and density functional theory investigations reveal shape-invariant transformation of the slanted nanocolumns from metallic to transparent metal-oxide core-shell structures with properties characteristic of spinel cobalt oxide. We find passivation of Co-SCTFs yielding CoAl$_2$O$_3$ core-shell structures produced by conforma…
Electrostatic control of the metal-insulator transition (MIT) in an oxide semiconductor could potentially impact the emerging field of oxide electronics. Vanadium dioxide is of particular interest due to the fact that the MIT happens in the vicinity of room temperature and it is considered to exhibit the Mott transition. We present a detailed account of our experimental investigation into three-terminal field effect transistor-like devices using thin film VO2 as the channel layer. The gate is separated from the channel through an insulating gate oxide layer, enabling true probing of the field …
Ultrathin (111)-oriented polar iron oxide films were grown on a Pt(111) single crystal either by the reactive deposition of iron or oxidation of metallic iron monolayers. These films were characterized using low energy electron diffraction, scanning tunneling microscopy and conversion electron Mossbauer spectroscopy. The reactive deposition of Fe led to the island growth of Fe3O4, in which the electronic and magnetic properties of the bulk material were modulated by superparamagnetic size effects for thicknesses below 2 nm, revealing specific surface and interface features. In contrast, the ox…
The manufacture of solid oxide fuel cells (SOFCs) involves fabrication of a multilayer ceramic structure, for which constrained sintering is a key processing step in many cases. Defects are often observed in the sintered structure, but their formation during sintering is not well understood. In this work, various ceramic films were fabricated by screen printing and a variety of defects observed. Some films showed mud-cracking defects, whereas others presented distributed large pores. Mud cracking defects were found to originate from a network of fine cracks present in the green film and formed…
The sensitivity of materials properties, particularly those of perovskite oxides, to epitaxial strain has been exploited to great advantage to create materials with new or enhanced properties. Although it has certainly been recognized that mismatch in the thermal expansion coefficients of the bulk and substrate material will contribute to the misfit strain, the significance of this contribution for ferroelectric perovskite thin-films has not been systematically explored. We use first-principles density functional theory and the example of ferroelectric PbTiO$_3$ thin-films on various substrate…
Here we report on the preparation of transparent and flexible polymerized graphite oxide, which is composed of carbons with sp3-hybridized orbitals and a non-planar ring structure, and which demonstrates dispersion in its dielectric constant at room temperature. This frequency dependence renders the material suitable for creating miniaturized, flexible, and transparent variable capacitors, allowing for smaller and simpler integrated electronic devices. We discuss this polarizability in terms of space charge effects.
Magnetic insulators with strong perpendicular magnetic anisotropy (PMA) play a key role in exploring pure spin current phenomena and developing ultralow-dissipation spintronic devices, thereby it is highly desirable to develop new material platforms. Here we report epitaxial growth of La2/3Sr1/3MnO3 (LSMO)-SrIrO3 (SIO) composite oxide films (LSMIO) with different crystalline orientations fabricated by sequential two-target ablation process using pulsed laser deposition. The LSMIO films exhibit high crystalline quality with homogeneous mixture of LSMO and SIO at atomic level. Ferrimagnetic and …
The thermal growth of silicon oxide films on Si in dry O2 is modelled as a dynamical system, assuming that it is basically a diffusion-reaction phenomenon. Relevant findings of the last decade are incorporated, as structure and composition of the oxide/Si interface and O2 transport and reaction at initial stages of growth. The present model departs from the well established Deal and Grove framework (Deal, B.E. and Grove, A. S. General Relationship for the Thermal Oxidation of Silicon, J. Appl. Phys. 36, 3770-3778 (1965)) indicating that its basic assumptions, steady-state regime and reaction b…
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…
Barrier films preventing permeation of gases and moistures are important for many industries ranging from food to medical and from chemical to electronic. From this perspective, graphene has recently attracted particular interest because its defect free monolayers are impermeable to all gases and liquids. However, it has proved challenging to develop large-area defectless graphene films suitable for industrial use. Here we report barrier properties of multilayer graphitic films made by chemical reduction of easily and cheaply produced graphene oxide laminates. They are found to provide a pract…
RF sputtered ZnO and Al:ZnO films are attractive transparent conductive oxides for fabrication of opto-electronic devices. In this paper we present efforts to control carrier concentration and mobility of ZnO/Al:ZnO thin films by controlling deposition parameters (RF power, pressure and substrate temperature. Al:ZnO thin film with resistivity as low as $ρ$ = $3.8\times 10^{-4}$ $Ω$.cm at deposition temperature of 250°C has been achieved. Zinc oxide thin film with low resistivity of $ρ$ = $3.7\times 10^{-2}$ $Ω$.cm and high electron mobility of $30$ $\mathrm{cm^{-2}V^{-1}s^{-1}}$ at deposition …
