Thermal Treatment In Vacuum Research Articles

Reversible plasma switching in epitaxial BiFeO3 thin films

Reversible plasma switching in epitaxial multiferroic BiFeO3 thin films was directly observed and analyzed using piezoresponse force microscopy. The polarization could be reversibly switched using oxygen plasma and a subsequent thermal annealing treatment in vacuum, respectively. The domain wall velocity during plasma switching, estimated to about 10−8 m/s, is much slower compared to the normal electrical switching, however a large area of square centimeter scale could be stably switched. The results demonstrate that reversible plasma switching can be achieved by oxygen plasma treatment and it can be a useful tool for an electrode-less control of ferroelectric switching on large area.

Synthesis and photoelectric characterization of delafossite conducting oxides CuAlO 2 laminar crystal thin films via sol–gel method

Thin films of delafossite of CuAlO 2 laminar crystals on metal substrates (Ni plates) were prepared by sol–gel processing and subsequent thermal treatment in vacuum. The influence of annealing treatment on surface morphologies and structure of the samples is discussed. Field-emission scanning electron microscope (FESEM) shows the laminar surface architecture of the as-prepared CuAlO 2 thin films. The electrical property of sample was investigated by current–voltage analysis, which indicates that a rectifying junction between CuAlO 2 film and metal substrate is formed and forward current exceeds reverse current by a factor of up to three. Otherwise, the photoelectrochemical characteristics recorded under 250 mW/cm 2 illumination show that the as-prepared thin film electrode which was annealed at 1150 °C for 4 h in vacuum possesses the highest photocurrent density, which is 0.7 mA/cm 2 at 0 V vs Ag/AgCl.

Structural, optical, and ferromagnetic properties of Co-doped TiO2 films annealed in vacuum

Polycrystalline anatase Ti1−xCoxO2 (x=0–0.06) films have been fabricated by sol-gel spin coating. The effects of Co doping on the structural, optical, and magnetic properties are investigated. It is shown that oxygen vacancies and/or defects in the films are generated during thermal treatment in vacuum. Co doping reduces crystal quality and inhibits crystalline grain growth. Due to the introduction of Co, photoluminescence (PL) spectra become weak and the band gap emission has a blueshift. PL spectra reveal that the solubility of Co is lower than 0.02. At 300 K, the saturated magnetization is around 1.8 μB/Co, which is independent of the concentration of Co. This value is approximately equivalent to the average magnetic moment of bulk metallic cobalt (1.75 μB/Co). Zero-field-cooling/field-cooling measurements indicate that room temperature ferromagnetism in Co-doped TiO2 films is not an intrinsic property of the material. The presence of Co metal is identified by x-ray photoelectron spectroscopy and scanning electron microscopy.

Structure and Properties of Nickel Aluminide Layers on INCONEL 100

The paper presents the results of investigations into the structure and properties of Ni-Al diffusion layers produced on INCONEL 100 by Chemical Vapour Deposition (CVD). The process was carried out in aluminium chloride (AlCl3) mixed with hydrogen atmosphere. The as-deposited layers were subjected to thermal treatment in vacuum to optimize their adhesion, hardness and temperature-resistance. Microstructural characterization of the coatings was carried out by scanning electron microscopy (SEM) The chemical composition was measured via EDS and the phase content was investigated by X-ray diffraction XRD. The resistance to high temperature of the coatings at atmospheric pressure was tested by applying 24-hours cycles at 950 °C. Scratch-tests provided data on the microhardness and adhesion of the coatings. The results indicate that the layers produced on the INCONEL 100 exhibit a very good adhesion combined with exceptional corrosion resistance at high temperatures.

Physical and sensing properties of ZnO:F:Al thin films deposited by sol–gel

Fluorine and aluminum-doped zinc oxide thin films, ZnO:F:Al, were prepared on soda–lime glass substrates by the sol–gel method and repeated dip-coating. The effect of the solution ageing and film thickness on the physical characteristics of the films was studied. Two ageing times, namely, two and seven days, and three different thicknesses, in the order of 220, 330, and 520 nm, were the main variables used in this work. As-deposited ZnO:F:Al films showed a high electrical resistivity, however after a vacuum thermal treatment, it was registered a significant decrease. Structural, optical, and morphological characterizations were carried out in vacuum-annealed films. The X-ray diffraction (XRD) patterns revealed that both as-deposited and vacuum-annealed ZnO:F:Al thin films were polycrystalline with a hexagonal wurtzite-type structure with a well-defined (002) diffraction peak, irrespective of the ageing time of the starting solution. The (002) peak shows a proportional increase with the thickness magnitude. An average crystallite size of about 20 nm was estimated using the well-known Scherrer's formula. From the surface morphological study it was observed that the grain size is almost independent of the ageing time of the starting solution, and the film thickness. Films presented an average optical transmittance in the visible range (400–700 nm) in the order of 90%, as well as a band gap of 3.3 eV. The gas-sensing properties of ZnO:F:Al thin films in an atmosphere containing different concentrations of carbon monoxide, and at different operation temperatures were probed. The highest sensitivity registered was of the order of 93%.

XPS study of annealing induced effects on surface and interface electronic properties of Si/Ge nanostructures

The present study is focused on the influence of vacuum thermal treatment on surface/interface electronic properties of Si/Ge multilayer structures (MLS) characterized using X-ray photoelectron spectroscopy (XPS) technique. Desired [Si(5 nm)/Ge(5 nm)] ×10 MLS were prepared using electron beam evaporation technique under ultra high vacuum (UHV) conditions. The core-level XPS spectra of as-deposited as well as multilayer samples annealed at different temperatures such as 100 °C, 150 °C and 200 °C for 1 h show substantial reduction in Ge 2p peak integrated intensity, whereas peak intensity of Si 2p remains almost constant. The complete interdiffusion took place after annealing the sample at 200 °C for 5 h as confirmed from depth profiling of annealed MLS. The asymmetric behaviour in intensity patterns of Si and Ge with annealing was attributed to faster interdiffusion of Si into Ge layer. However, another set of experiments on these MLS annealed at 500 °C suggests that interdiffusion can also be studied by annealing the system at higher temperature for relatively shorter time duration.

Carbon nanotube thin film transistors based on aerosol methods

We demonstrate a fabrication method for high-performance field-effect transistors(FETs) based on dry-processed random single-walled carbon nanotube networks(CNTNs) deposited at room temperature. This method is an advantageous alternativeto solution-processed and direct CVD grown CNTN FETs, which allows usingvarious substrate materials, including heat-intolerant plastic substrates, and enablesan efficient, density-controlled, scalable deposition of as-produced single-walledCNTNs on the substrate directly from the aerosol (floating catalyst) synthesisreactor. Two types of thin film transistor (TFT) structures were fabricated toevaluate the FET performance of dry-processed CNTNs: bottom-gate transistors onSi/SiO2 substrates and top-gate transistors on polymer substrates. Devices exhibited on/off ratios up to105 and field-effectmobilities up to 4 cm2 V−1 s−1. The suppression of hysteresis in the bottom-gate device transfer characteristics by meansof thermal treatment in vacuum and passivation by an atomic layer depositedAl2O3 film was investigated.A 32 nm thick Al2O3 layer was found to be able to eliminate the hysteresis.

Thermal stability of structure and properties of CHx doped SiCOH low dielectric constant films

This paper investigates the effect of vacuum thermal treatment on current-voltage (I-V) and capacitance-voltage (C-V) characteristics, hydrophobic properties and microstructure of CH4 doped SiCOH low dielectric constant films deposited by decamethylcyclopentasiloxane (D5) electron cyclotron resonance plasma. The results show that the desorption of thermally unstable CHx groups during the heat treatment can lead to the decrease of leakage current, the variation of SiCOH/Si interface state and the decrease of surface roughness. However, the desorption of CHx groups also leads to the deterioration of hydrophobic property.

High Temperature Mechanical Properties of Free-Standing HVOF CoNiCrAlY Coatings by Lateral Compression of Circular Tube

MCrAlY, M means Co and/or Ni, sprayed coating is used to protect a super alloy substrate from corrosion or oxidation in a gas turbine blade. However, the mechanical properties are not well-known, because there are few proper measurement methods for a thin coating at high temperature. Authors have developed the new easy method to measure the mechanical properties using the lateral compression of a circular tube. The method is useful to apply to a thin coating because it does not need chucking and manufacturing a test piece is very easy. The method is also easily applicable to high temperature measurement. In this study, high temperature mechanical properties, Young's modulus, bending strength and fracture strain, of CoNiCrAlY coatings by HVOF were systematically measured. The results obtained were as follows: Young's modulus and bending strength suddenly decreased beyond 400∼450°C. The Young's modulus and bending strength thermally treated at higher than 1050°C was significantly higher than that of virgin CoNiCrAlY coating. It was found that higher thermal treatment in atmosphere was the most effective in increasing the Young's modulus and bending strength. It was also found that the improvement of Young's modulus was primarily caused by not the effect of TGO but the sintering and diffusion of unfused particles. On the contrary, the fracture strain increased beyond 400°C differently from the bending strength. The fracture strains of CoNiCrAlY thermally treated in vacuum were higher than those of CoNiCrAlY treated in atmosphere. It was found that higher thermal treatment in vacuum was the most effective in increasing the fracture strain.

Influence of annealing conditions on the structural quality of CuInSe 2 thin films

CuInSe 2 (CIS) films have been prepared by one-step electrodeposition technique. The effect of thermal treatment in vacuum and under selenium vapour pressure on the composition and structure of CIS electrodeposited layers has been investigated. The structure and composition of these samples have been investigated by SEM, XRD, EDX and Raman spectroscopy. It was found that recrystallization of CIS thin film occurs with segregation of Cu–Se phases onto the bottom of films and formation of CIS grains different by size and composition.

Magnetic susceptibility of quasicrystalline Al65Cu22Fe13 powders

Magnetic properties of quasicrystalline Al65Cu22Fe13 powders synthesized by the solid-phase diffusion method via thermal treatment in vacuum or a hydrogen atmosphere have been studied. The powders synthesized in vacuum are found to contain a ferromagnetic fraction. The formation of iron oxide Fe3O4 is shown to be the most probable cause of the existence of this fraction. It is possible to avoid the formation of the ferromagnetic fraction in the powders synthesized or annealed in hydrogen. Removal of the ferromagnetic fraction from the powder by repeated magnetic separation made it possible to obtain a quasicrystalline fraction, for which the behavior of the magnetic susceptibility can be explained by the formation of nanoclusters. Such behavior is a general and integral property of quasicrystalline powders synthesized in both vacuum and hydrogen.

Changes in the density of alloy ZhS6U in the process of operation

The density of alloy ZhS6U in cast state is studied after testing for long-term strength, hot isostatic pressing, thermal vacuum treatment, and long-term operation. The density of the alloy is determined using the method of hydrostatic weighing of test specimens and specimens cut from turbine blades.

Thermal degradation of anodic niobia on niobium and oxygen-containing niobium

Thermal treatment of anodized niobium and oxygen-containing niobium has been carried out to elucidate the thermal degradation mechanism of niobium capacitors and to clarify the influence of oxygen dissolved in niobium on thermal degradation. The capacitance and leakage current of the anodized specimens increase with thermal treatment above 423 K in air, although the oxygen content in the substrate has no significant effect up to 523 K. At increased temperatures, the changes in capacitance and leakage current are suppressed with increasing oxygen content. The anodic film formed on the Nb-50 at.% O substrate thickens significantly during thermal treatment at 623 K in air, while only a slight reduction of the thickness is evident for those on the niobium and Nb-20 at.% O substrates. In contrast, vacuum thermal treatment at 623 K causes thinning of the anodic film on niobium, with evidently no change in the film thickness on the Nb-50 at.% O substrate. These are interpreted in terms of oxygen diffusion from the anodic film to the substrate as well as thermal oxide growth.

Structure and Morphology of Annealed Gold Films Galvanically Displaced on the Si(111) Surface

The effects of thermal treatment in ultrahigh vacuum (UHV) of gold films galvanically displaced on the Si(111) surface are studied with low-energy electron diffraction, Auger electron spectroscopy, atomic force microscopy, Kelvin probe force microscopy, and X-ray photoelectron spectroscopy. Annealing the galvanically displaced gold on Si substrates to 1100 K produces films with similar structure, composition, and morphology to annealed gold films evaporated on Si in UHV. The surface morphology is consistent with the Stranski−Krastanov growth mode. Compared to the unannealed film, an interfacial gold silicide layer forms upon annealing, although with limited improvement in adhesion. We report the formation of submicrometer Au/Si islands with narrow size dispersion, separated by deep trenches and with local order and shape dictated by the symmetry of the substrate. A mechanism for the formation of these islands is proposed.

Impact of vacuum thermal treatments on the structure and magnetic properties of titaniumoxide films doped with Co

The structure and magnetic properties of different titanium oxide films doped withmagnetic impurities are investigated both in the as-deposited state and after thermaltreatments in a vacuum. The samples were characterized by x-ray diffraction (XRD), x-rayphotoelectron spectroscopy (XPS), x-ray absorption spectroscopy (XAS) and vibratingsample magnetometry. In the as-deposited films, ferromagnetism was shown to becaused by the formation of magnetic clusters during the deposition. Heating ofTi1−xCoxO2−δ films in a vacuum up to high temperatures and the following quenching thereof result inpartial dissolution of the clusters with the magnetic ions being incorporated into thematrix. The low-temperature vacuum annealing leads to an increase of weakferromagnetism in the semiconductor solid solution.

Ferromagnetism of 3-D transition metals solid solutions in titanium oxides

The structure and magnetic properties of the films of titanium oxides doped with magnetic impurities are investigated both in as-deposited state and after thermal treatments in vacuum. In the as-deposited films, ferromagnetism was shown to be caused by magnetic cluster formation during deposition. The vacuum quenching of Ti 1− x Co x O 2− δ films results in the partial transition of a magnetic impurity from clusters into a matrix. The low-temperature vacuum annealing leads to a rise of weak ferromagnetism in the semiconductor solid solution.

Effect of the [Al/Zn] ratio in the starting solution and deposition temperature on the physical properties of sprayed ZnO:Al thin films

Aluminum-doped zinc oxide thin films (ZnO:Al) were deposited on sodocalcic glass substrates by the chemical spray technique, using zinc acetate and aluminum pentanedionate as precursors. The effect of the [Al/Zn] ratio in the starting solution, as well as the substrate temperature, on the physical characteristic of ZnO:Al thin films was analyzed. We have found that the addition of Al to the starting solution decreases the electrical resistivity of the films until a minimum value, located between 2 and 3 at.%; a further increase in the [Al/Zn] ratio leads to an increase in the resistivity. A similar resistivity tendency with the substrate temperature was encountered, namely, as the substrate temperature is increased, a minimum value of around 475 °C in almost all the cases, was obtained. At higher deposition temperatures the film resistivity suffers an increase. After a vacuum-thermal treatment, performed at 400 °C for 1 h, the films showed a resistivity decrease about one order of magnitude, reaching a minimum value, for the films deposited at 475 °C, of 4.3 × 10 − 3 Ω cm. The film morphology is strongly affected by the [Al/Zn] ratio in the starting solution. X-ray analysis shows a (002) preferential growth in all the films. As the substrate temperature increases it is observed a slight increase in the transmittance as well as a shift in the band gap of the ZnO:Al thin films.

The surface structure of titania and the effect of reduction

Recent developments in the elucidation of the structure of the titania surface are reviewed, and they reveal a rich panoply of behaviour. The pristine TiO 2(1 1 0) surface shows the expected (1 × 1) bulk termination, but very mild deviations from stoichiometry of the bulk have significant effects on the surface structure which evolves successively with increasing reduction to (1 × 3), (1 × 2), ‘cross-linked’ (1 × 2), the appearance of crystallographic shear planes, and eventually to gross surface roughening due to a high density of the latter features. This reduction is induced by thermal treatment in vacuum or by sputtering. STM has shown that reduced surface species, such as Ti 3+, which are present at low temperatures after sputtering, are lost by dissolution into the bulk of the sample, and this process begins to occur at ∼700 K. In oxidation the reverse occurs above about 600 K, that is, titanium cations return to the surface where they are re-oxidised and grow new surfaces of titania in a layer-by-layer fashion. STM has revealed that anion vacancies can remain in the surface region if the sample is not annealed to high temperatures. These have recently been shown to consist of missing oxygen atoms in the [0 0 1]-strings of surface oxygen and are very reactive to gas phase oxidants, including oxygen and water.

Anelastic Spectroscopy in Superconducting Oxides

Since the discovery of the high Tc superconductors, several works have been made about the different properties of these materials. Anelastic spectroscopy experiments are sensitive tools to the study of defects in solids and phase transitions. By this technique, we can distinguish the different types of atomic jumps that happen to different temperatures. The intensity of the peaks in the anelastic spectrum and the "step" in the torsional modulus are related with the concentration of the relaxing entities, and the position of the peaks is determined by its mobility. In this paper, the study on Bi and Sm based superconducting oxides was made by anelastic relaxation measurements using a torsion pendulum. The samples were submitted to successive thermal treatments in high vacuum, in the temperature range between 100 K and 650 K, heating rate about 1 K/min. For Bi based superconducting oxides the results shown two peaks, that were associated to interstitial oxygen mobility and to orthorhombic to monoclinic phase transition. For Sm based superconducting oxides the results shown a relaxation peak that was attributed to the jumps of the oxygen atoms in the inter-chains O1 and O5 of the lattice.

Electron spin resonance probing of E′-type defects in fumed silica nanoparticles

Results are presented of an electron spin resonance (ESR) characterization of E′ type defects observed in fumed ∼ 7-nm sized silica nanoparticles. This is accomplished through K- and Q-band ESR following 10-eV irradiation used to photo-dissociate H from passivated defects. The defect analysis provides access to the structure of the nanoscale on atomic level, herewith adding an extra dimension for analysis. To assess specific physico-chemical structural aspects of the particles, the E′ centers have been monitored as a function of thermal treatment in vacuum in the range 850–1115 °C, revealing the presence of two systems of E′ centers. The first one exhibits ESR parameters very similar to those of the familiar E′ γ center encountered in bulk fused silica, while the second bath exhibits an altered zero crossing g value and line shape, attributed to variations in local structure. While the first E′ system most likely resides in the core regions of the nanoparticles, the second system may mainly be confined to the outer SiO 2 layers exposing a structurally different, possibly more strained nature than macroscopic glassy SiO 2. Probing of fundamental point defects in nanometer-sized silica particles thus reveals structural variations and non-uniformity, indicative of a structure different from bulk material.