Transition Metal Oxide Films Research Articles

Thermal Phase Transformation of ZnO-Based Transparent Ferromagnetic Composite Films and the Change in Magnetic Characteristics

Transparent ferromagnetic semiconducting composite Fe–Zn–O films composed of wurtzite ZnO matrix and Zn-incorporated magnetite particles have been prepared by novel chemical solution processes followed by thermal annealing, performed at different temperatures between 200 and under vacuum at around . The effects of the thermal annealing on the structure and magnetic, electrical, and optical properties of the heterogranular transition metal oxides (Fe–Zn–O) films have been studied by using X-ray diffraction, X-ray absorption fine structure (XAFS), vibrating sample magnetometer, soft X-ray magnetic circular dichroism (SXMCD), and so on. These properties strongly depended on the annealing temperature and could be correlated to the changes in the ZnO matrix and/or the Zn-incorporated magnetite phase. The XAFS and SXMCD measurements using synchrotron radiation elucidated the growth process of the Zn-incorporated magnetite phase in the ZnO matrix.

Electron beam evaporated molybdenum oxide films: a study of elemental and surfacemorphological properties

Thin films of transition metal oxides are very important in electrochromic applications. Molybdenumoxide (MoO3) thin films were prepared by using one of the physical vapour depositionsof the electron beam evaporation technique in a vacuum of the order of10−6 mbar. The detailed elemental analysis of the films was performed by a particle-inducedx-ray emission (PIXE) study and the nanosurface nature of the films was studied by usingan atomic force microscopy (AFM) analysis. To the best of our knowledge this is the firsttime PIXE analysis has been used for the elemental studies of electron beam evaporatedMoO3 films.

The Ultrasmoothness of Diamond-like Carbon Surfaces

The ultrasmoothness of diamond-like carbon coatings is explained by an atomistic/continuum multiscale model. At the atomic scale, carbon ion impacts induce downhill currents in the top layer of a growing film. At the continuum scale, these currents cause a rapid smoothing of initially rough substrates by erosion of hills into neighboring hollows. The predicted surface evolution is in excellent agreement with atomic force microscopy measurements. This mechanism is general, as shown by similar simulations for amorphous silicon. It explains the recently reported smoothing of multilayers and amorphous transition metal oxide films and underlines the general importance of impact-induced downhill currents for ion deposition, polishing, and nanopattering.

Controlled preparation of well-ordered transition metal oxide layers on a metallic surface

A method to create various well-ordered two dimensional transition metal oxide films on a metallic substrate has been exploited. The formation of an intermediate amorphous layer with controllable metal–oxygen stoichiometry serves as an important precursor condition for the final transformation into a mono-phase, crystalline oxide layer via mild annealing. As a key ingredient serves a Cu 3Au(1 0 0) substrate covered by oxygen. The flat Cu–O topmost layer stops completely intermixing of the substrate material with the subsequently evaporated transition metal film. Likewise the wetting of the surface is considerably enhanced and a homogeneous oxidation of the film is strongly promoted. The proposed technique appears to be widely efficient for preparation of various two dimensional oxide films covering the entire Cu 3Au(1 0 0) substrate. Its usefulness is demonstrated successfully for vanadium, niobium and molybdenum to produce a set of single-phase transition metal oxides of different stoichiometry and geometrical structure. All created oxides are found to be thermally stable at least up to a substrate temperature of 800 K.

Structure formation upon reactive direct current magnetron sputteringof transition metal oxide films

A comparative study of reactive direct current magnetron sputtering for different transition metal oxides reveals crystalline films at room temperature for group 4 and amorphous films for groups 5 and 6. This observation cannot be explained by the known growth laws and is attributed to the impact of energetic particles, originating from the oxidized target, on the growing film. This scenario is supported by measured target characteristics, the evolution of deposition stress of the films, and the observed backsputtering.

Photochromism of novel molybdate/alkylamine composite thin films.

Novel inorganic/organic composite films of molybdates with photochromic properties have been prepared by self-assembly using alkylammonium ions as a supramolecular template. Both 1-hexadecylammonium/polyoxomolybdate (C16-Mo) and 1-octadecylammonium/polyoxomolybdate (C18-Mo) composite films have been successfully fabricated. The elemental analysis and thermal gravimetric analysis show that the main product in the C16-Mo film was (C16H33NH3)4Mo8O26. The X-ray diffraction (XRD) results indicate that the composite films were lamellar in nature. The IR, Raman and X-ray photoelectron spectroscopy (XPS) results show that the polyoxomolybdate anions present as MoO6 octahedra and that the Mo species exists as Mo6+ in the freshly prepared films. The alkyl chains in the 1-hexadecylammonium chains were linear and the alkyl groups are an all-trans configuration. Upon UV irradiation of the C16-Mo films, some Mo6+ was reduced to Mo5+, some -NH3+ became -NH2 with a concomitant increase in the concentration of -OH groups on the molybdate moieties, and the films were colored. Thus, the photochromism of the films involves the reduction of Mo6+ to Mo5+, coupled with a proton transfer from 1-hexadecylammonium ions to an oxygen atom at the Mo site. In contrast to thin films of transition-metal oxides, which all show photochromism in the blue region of the electromagnetic spectrum, these composite films show photochromism in the violet region with the greatest absorbance change at 472 nm.

Ion beam analysis of electrochromic and thermochromic oxide films

Thin transition metal oxide films with known electrochromic and thermochromic behavior have been investigated for ion beam induced changes in their optical properties. Films of WO 3 and VO 2 deposited on glass and sapphire substrates by RF sputter deposition were subjected to ion bombardment with 400 keV Xe + and Au + ions. Both the ions seem to induce mixing at the interface resulting in a mixed oxide layer whose thickness is dose dependent. Optical transmission measurements in the visible and IR region show moderate modification of electrochromic behavior in the visible and thermochromic characteristic in the IR region.

Efficient photocarrier injection to transition metal oxides

We have fabricated transition metal oxide (TMO) films on n-type titanium oxide substrates, and measured in-plane resistance under ultraviolet light irradiation. A dramatic decrease in the resistance and enhancement of the superconducting critical temperature are observed for VO 2/TiO 2:Nb and YBa 2Cu 3O z /SrTiO 3:Nb, respectively. Out-of-plane voltage measurements under light irradiation indicate hole-carrier injection from the substrate to the film in both the cases. The present photocarrier injection technique could apply to many TMOs to control the hole carrier density externally.

High quality r.f. sputtered metal oxides (Ta 2O 5, HfO 2) and their properties after annealing

Thin films of transition metal oxides have many applications like gate dielectrics in field effect transistors (FETs) and sensors, high- ε materials for capacitors or protective transparent coatings for photonic applications. Important are favorable electrical, optical and mechanical properties as well as high chemical inertness. Silicon oxide has been a standard material since the beginning of CMOS production. Tantalum pentoxide has been investigated for some years. Quite a new candidate in this area is hafnium oxide. Besides favorable properties, the material of choice must offer the possibility of reproduceable homogenous deposition at acceptable rates. The material properties should be adjustable, for example by thermal annealing, but must not change afterwards on a long term basis. Ta 2O 5 and HfO 2 have been deposited by r.f. sputtering of high purity targets in Ar/O 2 mixtures. Due to the sensor application planned, thicknesses of 150 nm were deposited. The total thickness variation (TTV) across the whole 150 mm wafer was below ±6%. After deposition, the layers were annealed with different methods. The mechanical stress can be adjusted through the annealing regime. The chemical inertness increases with the annealing temperature. All layers are insulating and transparent. Especially HfO 2 annealed at 950 °C revealed favorable results: The layers are crystalline with a fine grained structure, smooth, dense and withstand NaOH as well as HF very well. It was verified, that these materials will be suitable for the applications desired, especially in contact with harsh environments.

High quality r.f. sputtered metal oxides (Ta2O5, HfO2) and their properties after annealing

Thin films of transition metal oxides have many applications like gate dielectrics in field effect transistors (FETs) and sensors, high-ε materials for capacitors or protective transparent coatings for photonic applications. Important are favorable electrical, optical and mechanical properties as well as high chemical inertness. Silicon oxide has been a standard material since the beginning of CMOS production. Tantalum pentoxide has been investigated for some years. Quite a new candidate in this area is hafnium oxide. Besides favorable properties, the material of choice must offer the possibility of reproduceable homogenous deposition at acceptable rates. The material properties should be adjustable, for example by thermal annealing, but must not change afterwards on a long term basis. Ta2O5 and HfO2 have been deposited by r.f. sputtering of high purity targets in Ar/O2 mixtures. Due to the sensor application planned, thicknesses of 150 nm were deposited. The total thickness variation (TTV) across the whole 150 mm wafer was below ±6%. After deposition, the layers were annealed with different methods. The mechanical stress can be adjusted through the annealing regime. The chemical inertness increases with the annealing temperature. All layers are insulating and transparent. Especially HfO2 annealed at 950 °C revealed favorable results: The layers are crystalline with a fine grained structure, smooth, dense and withstand NaOH as well as HF very well. It was verified, that these materials will be suitable for the applications desired, especially in contact with harsh environments.

Continuous composition-spread thin films of transition metal oxides by pulsed-laser deposition

We have designed an improved pulsed-laser deposition–continuous composition-spread (PLD–CCS) system that overcomes the difficulties associated with earlier related techniques. Our new PLD–CCS system is based on a precisely controlled synchronization between the laser firing, target exchange, and substrate translation/rotation, and offers more flexibility and control than earlier PLD-based approaches. Most importantly, the deposition energetics and the film thickness are kept constant across the entire composition range, and the resulting samples are sufficiently large to allow characterization by conventional techniques. We fabricated binary alloy composition-spread films composed of SrRuO 3 and CaRuO 3. Alternating ablation from two different ceramic targets leads to in situ alloy formation, and the value of x in Sr x Ca x−1 RuO 3 can be changed linearly from 0 to 1 (or over any arbitrarily smaller range) along one direction of the substrate.

A high-resolution synchrotron-radiation angle-resolved photoemission spectrometer with in situ oxide thin film growth capability

We have constructed a high-resolution synchrotron-radiation angle-resolved photoemission (ARPES) spectrometer combined with a combinatorial laser molecular-beam epitaxy (laser MBE) thin film growth system in order to investigate the electronic structure of transition metal oxide thin films. An ARPES spectrometer GAMMADATA SCIENTA SES-100 was selected for the high-throughput and high-energy and angular-resolution ARPES measurements. A total energy resolution of 6.3 meV and a momentum (an angular) resolution of 0.02 Å−1 (0.2°) were obtained at a photon energy of 40 eV. The system is installed at the high-resolution vacuum-ultraviolet beamline BL-1C or the soft-x-ray undulator beamline BL-2C at the Photon Factory as an end-station. Another distinctive feature of this system is the direct connection from the spectrometer to a laser MBE chamber. Thin film samples can be transferred quickly into the photoemission chamber without breaking ultrahigh vacuum. Laser MBE is one of the best methods to grow thin films of many different transition metal oxides and to achieve well-ordered surfaces, which are indispensable for the ARPES measurements. The capabilities of the system and the importance of the in situ sample transfer between ARPES and laser MBE are demonstrated by studying the band structure of La0.6Sr0.4MnO3 thin films epitaxially grown on SrTiO3 substrates by laser MBE.

Deterministic noise in vanadium dioxide based structures

As is known [1], approaching the region of instability of a homogeneous state in a system featuring the metal‐insulator phase transition may be accompanied by low-frequency fluctuations analogous to the turbulent flow oscillations in hydrodynamics, alternatively referred to as deterministic chaos. The extensive investigation of noise in the structures based on transition metal oxide films is explained both by the prospects of using the steep temperature dependence of the physical properties of these structures, as well as by the basic interest in the physics of such phase transitions. A large proportion of investigations devoted to the metal‐insulator phase transition in vanadium dioxide (VO 2 ) was concentrated on the switching effect, which provides information on the phenomenon of interest and determines the practical applications of this material [2]. Electric switching in VO 2 , related to the metal‐ insulator phase transition, was observed in single crystal samples [3], planar thin-film structures [4], sandwich structures of the V‐VO 2 ‐metal type [5], and in various other systems containing VO 2 layers [6, 7].

Solution-processed anodes from layer-structure materials for high-efficiency polymer light-emitting diodes.

The development of low-cost, large-area electronic applications requires the deposition of active materials in simple and inexpensive techniques at room temperature, properties usually associated with polymer films. In this study, we demonstrate the integration of solution-processed inorganic films in light-emitting diodes. The layered transition metal dichalcogenide (LTMDC) films are deposited through Li intercalation and exfoliation in aqueous solution and partially oxidized in an oxygen plasma generator. The chemical composition and thickness of the LTMDC and corresponding transition metal oxide (TMO) films are investigated by X-ray photoelectron spectroscopy. The morphology and topography of the films are studied by atomic force microscopy. X-ray powder diffraction is used to determine the orientation of the LTMDC film. Finally, the LTMDC and their corresponding oxides are utilized as hole-injecting and electron-blocking materials in polymer light-emitting diodes with the general structure ITO/LTMDC/TMO/polyfluorene/Ca/Al. Efficient hole injection and electron blocking by the inorganic layers result in outstanding device performance and high efficiency.

3-D Nanoengineering of Metal Oxides and Oxyhydroxides by Aqueous Chemical Growth

ABSTRACTAdvanced nanoparticulate thin films of transition metal oxides consisting of nanorods with different orientations onto various substrates have been successfully grown by aqueous chemical growth without template, surfactant, or applied electric/magnetic field. The synthesis involves the aqueous condensation of metal ions from solutions of metal salts or metal complexes. Such low-cost fabrication of nanoengineered 3-D arrays consisting of 1-D nanorods of iron oxide (hematite), zinc oxide (zincite), and manganese oxyhydroxide (manganite) with parallel and perpendicular orientations onto various substrates are presented.

3D Highly Oriented Nanoparticulate and Microparticulate Array of Metal Oxide Materials

AbstractAdvanced nano and micro particulate thin films of 3d transition and post-transition metal oxides consisting of nanorods and microrods with parallel and perpendicular orientation with respect to the substrate normal, have been successfully grown onto various substrates by heteronucleation, without template and/or surfactant, from the aqueous condensation of solution of metal salts or metal complexes (aqueous chemical growth). Three-dimensional arrays of iron oxide nanorods and zinc oxide nanorods with parallel and perpendicular orientation are presented as well as the oxygen K-edge polarization dependent x-ray absorption spectroscopy (XAS) study of anisotropic perpendicularly oriented microrod array of ZnO performed at synchrotron radiation source facility.

Ablation of transition metal oxides by different laser pulse duration and thin films deposition

Thin films of transition metal oxides are of interest in many applications such as anticorrosion coatings and optical and electrochromic devices. In this work, the effect of different wavelength and pulse duration on ablation of oxides target has been investigated. The plume has been characterized by mass spectrometry and optical spectroscopy. Ablation thresholds have been measured by detecting ion emission from the target and from the onset of the plume luminescence. Morphology and optical properties of thin films deposited in different conditions are presented.

Vanadium transition metal oxide films obtained by annealing under room atmosphere of metal layers sequentially deposited

Metallic thin films M/V/M/V... /V/M (M=Fe, Ni) sequentially deposited under vacuum were annealed for 1 2 h in room atmosphere. The samples were characterised by X-rays diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and optical absorption (OA) and near-infrared absorption. The annealing temperature and the substrate were taken as parameters. In addition some pre-annealing treatment was used. The results showed that monoclinic Ni 2V 2O 7 and triclinic FeVO 4, homogeneous thin films can be synthesised by this simple technique. Best results were obtained when the glass substrate used was coated with SnO 2 thin films. The results were improved when, before air-annealing, a first annealing under vacuum was proceeded in order to homogenise the metal distribution in the sample.

Combined effects of small gold particles on the optical gas sensing by transition metal oxide films

The combination of small Au particles with NiO, CuO and CO 3O 4 films led to improved or new optical gas sensitivity via different mechanisms. The deposition of small Au particles on NiO film enhanced the detection of CO in air through a decreasing change of absorbance in the whole visible-near IR region. This can be explained by the change in positive hole density change of NiO, which was enhanced by an increase in catalytic formation and decomposition of surface carbonates with Au. In the case of CO-insensitive CuO film, gold deposition made it sensitive only at plasmon absorption region. This might be because the absorbance by small Au particles in plasmon band was influenced by the change in the dielectric constant of copper oxide which surrounded small Au particles. A Au-Co 3O 4 composite film showed a novel function to recognize CO and H 2, probably for the first time as inorganic materials for optochemical sensors. This owes to the fact that CO and H 2 bring about the specific absorbance change of the film at different wavelengths. Carbon monoxide decreased the absorbance of CO 3O 4 moiety, while H 2 not only decreased the absorbance of CO 3O 4 moiety but also increased plasmon absorbance of Au.

Hydrated Transition Metal Oxide Films for Reversible Switching in Near IR Region

AbstractElectro-optical properties of thin films of hydrated transition metal oxides, WO3 2(H2O) and WO3 1/3(H2O), have been investigated in situ using photoelectrochemical methods. These films can reversibly change their light absorption in the near IR region due to the double charge injection upon the applied electric field in electrolyte media. Taking into account the high stability and fast switching time, these hydrated tungsten oxide films can be utilized for efficient light modulation in the near infrared region of the spectrum.