Effect Of Vacuum Annealing Research Articles

Effects of vacuum annealing on the electron mobility of epitaxial La-doped BaSnO3 films

Wide bandgap (Eg ∼ 3.1 eV) La-doped BaSnO3 (LBSO) has attracted increasing attention as one of the transparent oxide semiconductors since its bulk single crystal shows a high carrier mobility (∼320 cm2 V−1 s−1) with a high carrier concentration (∼1020 cm−3). For this reason, many researchers have fabricated LBSO epitaxial films thus far, but the obtainable carrier mobility is substantially low compared to that of single crystals due to the formation of the lattice/structural defects. Here we report that the mobility suppression in LBSO films can be lifted by a simple vacuum annealing process. The oxygen vacancies generated from vacuum annealing reduced the thermal stability of LBSO films on MgO substrates, which increased their carrier concentrations and lateral grain sizes at elevated temperatures. As a result, the carrier mobilities were greatly improved, which does not occur after heat treatment in air. We report a factorial design experiment for the vacuum annealing of LBSO films on MgO substrates and discuss the implications of the results. Our findings expand our current knowledge on the point defect formation in epitaxial LBSO films and show that vacuum annealing is a powerful tool for enhancing the mobility values of LBSO films.

The effect of vacuum annealing on microstructure, adhesion strength and electrochemical behaviors of multilayered AlCrTiSiN coatings

A multilayered AlCrTiSiN coating, mainly consisting of an inner AlCrN buffer layer and an outermost AlCrTiSiN layer, was deposited on the 316L austenite stainless steel (ASS), and then isochronally annealed at below 900 °C. The effects of microstructures on adhesion strength and corrosion resistance of the AlCrTiSiN coatings annealed at different temperatures were systematically investigated in 3.5 wt% NaCl solution and 10 wt% H2SO4 solution. The results show that the Ti addition notably retards spinodal decomposition of the AlCrTiSiN coating compared with AlCrSiN one. The phase structures of the AlCrTiSiN layer vary from fcc-AlMeN (Me = Cr or/and Ti) solid solution to rich-Me and rich-Al fcc-domains, and then to hcp-AlN, Cr, Cr2N and TiN. Surface defects of the coatings decrease notably with the increasing annealing temperature. Annealing at above 800 °C leads to a notable loss in adhesion strength due to the formation of brittle Cr2N, hcp-AlN and σ-CrFe of the buffer layer. The coatings annealed at 800 °C show the best corrosion resistance in 3.5 wt% NaCl solution, whereas the ones annealed at 700 °C reveals best corrosion resistance in 10 wt% H2SO4 solution.

Spatial and Contamination-Dependent Electrical Properties of Carbon Nanotubes.

Two-point probe and Raman spectroscopy have been used to investigate the effects of vacuum annealing and argon bombardment on the conduction characteristics of multiwalled carbon nanotubes (MWCNTs). Surface contamination has a large effect on the two-point probe conductivity measurements which results in inconsistent and nonreproducible contacts. The electric field under the contacts is enhanced which results in overlapping depletion regions when probe separations are small (<4 μm) causing very high resistances. Annealing at 200 and 500 °C reduced the surface contamination on the MWCNT, but high resistance contacts still did not allow intrinsic conductivity measurements of the MWCNT. The high resistance measured due to the overlapping depletion regions was not observed after annealing to 500 °C. Argon bombardment reduced the surface contamination more than vacuum annealing at 500 °C but caused a slight increase in the defects concentration, enabling the resistivity of the MWCNT to be calculated, which is found to be dependent on the CNT diameter. The observations have significant implications for future CNT-based devices.

An Effect of Vacuum Annealing , Tempering Process on AISI431 Grade Stainless Steel Material

An Effect of Vacuum Annealing , Tempering Process on AISI431 Grade Stainless Steel Material

Effect of vacuum annealing on structural and optical properties of nanocrystalline ZnTe thin films

In present study, dependence of structural and optical properties of nanocrystalline $$\hbox {Zn}_{40}\hbox {Te}_{60}$$ (ZnTe) thin films on vacuum thermal annealing has been investigated. ZnTe alloy was prepared by melt quenching technique and thermally evaporated on cleansed glass substrates to deposit thin films. These films were annealed in vacuum ( $$\sim 1\times 10^{-3}$$ mbar) for an hour at three different temperatures 100, 200 and 300 °C. X-ray diffraction results revealed the presence of cubic ZnTe phase in all the films along with some hexagonal Te phase. The crystallite size of ZnTe thin films improved on annealing with larger size at elevated temperatures (from 32 to 80 nm). Micro strain and dislocation density reduced owing to improvement in crystallinity after annealing. The IR transmittance increased with increase in annealing temperature. Field emission scanning electron microscopy images suggested the formation of smooth and uniform thin films with thickness of $$\sim$$ 480 nm. Optical properties revealed the decrease in transmittance and absorption edge shift due to crystallinity improvement on annealing. The optical band gap decreased from 1.37 to 0.91 eV on annealing. Experimental results show that thermal annealing has significant impact on structural and optical properties of ZnTe thin films.

Effects of Thermal Annealing on the Properties of Mechanically Exfoliated Suspended and On-Substrate Few-Layer Graphene

Graphene’s novel electrical, optical, and mechanical properties are affected both by substrate interaction and processing steps required to fabricate contacts and devices. Annealing is used to clean graphene devices, but this can lead to doping and defect changes and strain effects. There is often disagreement about which of these effects are occurring and which result in observed changes in Raman spectra. The effects of vacuum annealing on mechanically exfoliated pristine, suspended, and attached thin and thick few-layer graphene on SiO2/Si are investigated here using scanning electron microscopy (SEM), Raman spectroscopy, and atomic force microscopy (AFM). Before annealing, Raman shows that the differences in 2D and G band positions and the appearance of a disorder-induced D band of all regions were mainly because of compressive or tensile structural deformations emerging through mechanical exfoliation instead of charge doping. Annealing at low temperature is sufficient to eliminate most of the defects. However, compressive strain is induced in the sheet by annealing at high temperature, and for thin regions increased substrate conformation leads to the apparent disappearance of the sheets. The intensity ratio of the 2D and G bands also reduces with induced compressive strain, and thus should not be used to detect doping.

Tuning the photoelectrochemical properties of hierarchical TiO2 nanostructures by control of pulsed laser deposition and annealing in reducing conditions

Nanostructured TiO2 films with hierarchical morphology were synthesized by Pulsed Laser Deposition (PLD) and tested as photoanodes for photoelectrochemical water splitting. The tuning of their photoresponse was addressed by employing oxygen-poor conditions both during the growth and the post-deposition annealing of the material: depositions were performed in different Ar/O2 background gas mixtures from both TiO2 and Ti targets, while thermal treatments, after standard air annealing for crystallization, were performed in a Ar/H2 mixture. By testing the double-annealed photoanodes in a three-electrode cell with solar simulator illumination, clear trends with optimal synthesis conditions for each target material appeared; for these conditions, also the effect of vacuum annealing was studied. The morphological, structural and optical properties were investigated by SEM, Raman spectroscopy and UV-visible-IR spectroscopy. From these observations, it emerged that the films deposited in the presence of oxygen do not show substantial differences in their morphology/structure, on the contrary of pure Ar-deposited films; thus, the trends in photoresponse can be related to differences in the defect concentration of the material, induced by depositions in the different Ar/O2 atmospheres and by annealing in Ar/H2 mixture or vacuum. In particular, the reported results suggest that some degree of oxygen shortage in the deposition process leads to a better photoelectrochemical performance, and a combination between improved charge transport and surface hydrogenation/reduction effect, leading to enhanced photoresponse, is suggested. This work elucidates the possibility of an accurate tuning of the material photoactivity by control of the deposition and annealing conditions.

The effect of post-sintering annealing on the erosion resistance of infiltrated W-Cu composites

In this work, the effect of vacuum annealing on the erosion resistance of infiltrated W-10wt%Cu composite against the impact of alumina droplets at 3000°C, was studied. SEM images were employed to identify the microstructure evolution. The obtained results indicated that the post-sintering annealing reduced erosion rate from 19.7% to 11.2%.

Effect of Vacuum Annealing on the Compositions of U-0.79wt%Ti Alloy Surface Exposed in a Salt Fog Environment

The evolution of the compositions in two typical regions on U-0.79wt%Ti alloy surface exposed in a salt fog environment was investigated by x-ray photoelectron spectroscopy (XPS) during vacuum annealing. The results show that pitting corrosion tends to occur around titanium inclusions on the alloy surface in the environment containing chloride ions. The compositions in the two regions were transformed with experimental temperature increasing. The complex oxide compound, α-U3O8, was detected by both XPS and Raman spectrum in the blackened region, while UO2+x/UO2 were the main oxide compounds in the other region where pitting corrosion did not occur. The different compositions in the two typical regions were slightly changed as temperature ramps up from room condition to 200°C. The α-U3O8 in the blackened region started to be reduced to UO2 while UO2+x in the other region to be converted into UO2 at 300°C. An oxycarbide (UOxCy) compound was observed due to the reaction between UO2 and carbon at 400°C. Betwe...

Protected Vacuum Annealing Effect on Single Crystals of Pr1-xLaCexCuO4 in the Overdoped Regime

We report the effect of protected vacuum annealing on the superconducting (SC) and magnetic properties of Pr1-xLaCexCuO4 (PLCCO) single crystals in the overdoped regime (x = 0.13 – 0.20). The powders and single crystals of PLCCO with all x were synthesized by the solid state reaction and grown by the travelling solvent floating zone (TSFZ) method, respectively. The powder x-ray diffraction (XRD) results analyzed by the Rietveld method have shown that there is a systematic decrease in the c-axis length with increasing x, suggesting the proper substitution of Ce for Pr in overdoped PLCCO up to x = 0.20. The so-called two-step annealing performed in the overdoped regime was essential for increasing the SC volume fraction estimated from the magnetic susceptibility measurements. Furthermore, the temperature dependence of the normal-state magnetic susceptibility for reduced crystals of PLCCO with all x has exhibited a Curie-Weiss-like behavior regardless of various steps of the protected vacuum annealing process.

Vacuum-annealing induces sub-surface redox-states in surfactant-structured α-Fe2O3 photoanodes prepared by ink-jet printing

Transparent nano-structured hematite (α-Fe2O3) films of approximately 550nm thickness on tin-doped indium oxide (ITO) have been obtained conveniently by ink-jet printing of a Fe(NO3)3/Brij® O10 precursor ink and subsequent annealing at 500°C in air. When illuminated with a blue LED (λ=455nm, ca. 100mWcm−2), the hematite films exhibited photocurrents of up to 70μAcm−2 at 0.4V vs. SCE in 0.1M NaOH electrolyte. Thermal annealing in vacuum at 500°C for 2h increased photocurrents more than three times to 230μAcm−2 in agreement with previous literature reports for pure hematite materials. These results suggest that a simple ink-jetting process with surfactants is viable. The effects of vacuum-annealing on the photoelectrical properties of α-Fe2O3 films are discussed in terms of a sub-surface state templating hypothesis based on data gathered from photo-transients, field emission scanning electron microscopy, X-ray photoelectron spectroscopy analysis, X-ray diffraction, photocurrent spectra, and cyclic voltammetry.

Effect of vacuum annealing on structural, electrical and thermal properties of e-beam evaporated Bi2Te3 thin films

Nanocrystalline thin films of a V-VI compound Bi2Te3 are fabricated with uniform thickness by e-beam evaporation at room temperature. The as-deposited films are stoichiometric, monophasic, highly strained and polycrystalline. We studied the effect of vacuum annealing (at a pressure of ~3×10−6mbar) on composition, structure, optical and electrical properties of these films. It is observed that, as the annealing temperature increases (from 100°C to 300°C), the crystallites grow with a preferential orientation along (110) planes with slight increase in the crystallite size from ~14nm to 30nm. This is associated with the breaking of quintuple layers and rearrangement of crystallographic planes in the crystallites with Te rich surface emerging on vacuum annealing as evidenced from the XRD, Raman and high-resolution TEM studies. The direct bandgap (0.116eV) of as-deposited Bi2Te3 changes from 0.092eV to 0.113eV on annealing at 100°C to 300°C, respectively. Interestingly, we observe a gradual change from a semiconductor to metallic behavior on annealing the samples from 100°C to 300°C. Such a transition from negative temperature coefficient (NTC) to positive temperature coefficient (PTC) is seen mainly due to the percolation of Te - rich crystallite surfaces, which evolve as the annealing temperature increases. While the films annealed at 200°C and 250°C shows a broad semiconductor to metallic transition at ~150K and 200K respectively, the thin films annealed at 300°C are found to exhibit complete metallic behavior below room temperature. The electrical property and Seebeck coefficient studies with power factors in the range of ~4 to 12×10−4W/K2m for films annealed above 200°C suggest that the vacuum annealed Bi2Te3 thin films are favorable for thermoelectric applications.

Effects of vacuum annealing on carrier transport properties of band gap-tunable semiconducting amorphous Cd–Ga–O thin films

The effect of vacuum annealing on the amorphous oxide semiconductor Cd–Ga–O system with a tunable band gap was examined. While the amorphous halo peak in XRD patterns of the films with Cd concentration of ~70% started sharpening after annealing at a temperature ≥200°C. In contrast, the films with Cd content of ~50% and ~20% were not crystallized for annealing temperatures up to 700°C. Carrier concentrations and Hall mobilities of ~70% and ~50% films were maximized by annealing at 400°C and 500°C, respectively, regardless of the properties of the as-deposited films, which were varied because of the unintended variation of deposition conditions such as the residual water vapor pressure in the deposition chamber. The initial electrical conductivity of ~20% films widely varied from <10−8 to 11S·cm−1, and annealing at 500°C was required for obtaining conductive films from the insulating as-deposited films. The maximum Hall mobility for films with Cd content of ~70% and ~50% films was ≥10cm2V−1s−1 and that for the film with ~20% Cd content was ≥3cm2V−1s−1.

Effect of heat treatment on the structure and the thermoelectric properties of Sb0.9Bi1.1Te2.9Se0.1 thin films and composites based on them

This work considers the effect of vacuum annealing on the thermoelectric properties of Sb0.9Bi1.1Te2.9Se0.1 thin film and Sb0.9Bi1.1Te2.9Se0.1–C composites with various carbon contents produced by ion-beam deposition in an argon atmosphere. The electrical resistivity and the thermopower of Sb0.9Bi1.1Te2.9Se0.1–C nanocomposites are found to be dependent on not only the carbon concentration but also the type and the concentration of intrinsic point defects of the Sb0.9Bi1.1Te2.9Se0.1 solid solution, which determine the type of conductivity of Sb0.9Bi1.1Te2.9Se0.1 granules. The power factors are estimated for films of Sb0.9Bi1.1Te2.9Se0.1 solid solution and films of Sb0.9Bi1.1Te2.9Se0.1–C composites and found to have values comparable with the values for nanostructured materials on the basis of (Bi,Sb)2(Te,Se)3 solid solutions.

真空热处理对硫化锌薄膜光学与微结构特性的影响

真空热处理对硫化锌薄膜光学与微结构特性的影响

Structural modification and band gap engineering of sol–gel dip-coated thin films of Zn0.75Mg0.25O alloy under vacuum annealing

In the present study, we investigated the effect of vacuum annealing on the structural and optical properties of sol–gel dip-coated thin films of Zn0.75Mg0.25O alloy. XRD studies revealed that all these films were polycrystalline with hexagonal wurtzite structure and there was no trace of additional phases other than ZnO. With increase in annealing temperature, the samples showed preferred orientation along the c-axis, (0 0 2) plane and also peak narrowing and peak shift towards higher angles. The calculated values of mean crystallite size increased with annealing temperature indicating the improvement in crystallinity. Heat treatment caused lattice contraction and a decrease in film thickness. The optical transmittance in the visible spectral range enhanced with increase in annealing temperature while the fundamental absorption edge in the near ultra-violet region got red-shifted with annealing. The calculated values of optical energy gap of the samples showed a decrease with heat treatment due to the improvement in crystallinity during annealing and hence the subsequent decrease in quantum size effect.

Effects of post-deposition vacuum annealing on film characteristics of p-type Cu2O and its impact on thin film transistor characteristics

Annealing of cuprous oxide (Cu2O) thin films in vacuum without phase conversion for subsequent inclusion as the channel layer in p-type thin film transistors (TFTs) has been demonstrated. This is based on a systematic study of vacuum annealing effects on the sputtered p-type Cu2O as well as the performance of TFTs on the basis of the crystallographic, optical, and electrical characteristics. It was previously believed that high-temperature annealing of Cu2O thin films would lead to phase conversion. In this work, it was observed that an increase in vacuum annealing temperature leads to an improvement in film crystallinity and a reduction in band tail states based on the X-ray diffraction patterns and a reduction in the Urbach tail, respectively. This gave rise to a considerable increase in the Hall mobility from 0.14 cm2/V·s of an as-deposited film to 28 cm2/V·s. It was also observed that intrinsic carrier density reduces significantly from 1.8 × 1016 to 1.7 × 1013 cm−3 as annealing temperature increases. It was found that the TFT performance enhanced significantly, resulting from the improvement in the film quality of the Cu2O active layer: enhancement in the field-effect mobility and the on/off current ratio, and a reduction in the off-state current. Finally, the bottom-gate staggered p-type TFTs using Cu2O annealed at 700 °C showed a field-effect mobility of ∼0.9 cm2/V·s and an on/off current ratio of ∼3.4 × 102.

Effect of vacuum annealing on evaporated pentacene thin films for memory device applications

Thin films of pentacene were deposited thermally onto glass substrates and annealed at 323K, 373K, 423K, 473K and 523K in high vacuum. Effect of annealing on the morphological and structural properties of these films was studied. X-ray diffraction patterns confirmed the crystalline nature of the films. Electrical studies for the use as write once read many (WORM) memory devices were done for the vacuum deposited pentacene thin films on indium tin oxide coated glass. Due to annealing, a sharp increase in the ON/OFF ratio of current and a decrease in threshold voltage were observed at around 373K. This device showed a stable switching with an ON/OFF current ratio as high as 109 and a switching threshold voltage of 1.35V. The performance of the device degraded above 423K due to the changes in the crystallinity of the film.

Effect of vacuum annealing on the photoconductivity of CuO thin films grown using sequential ionic layer adsorption reaction

Using sequential ionic layer adsorption reaction technique, Cupric Oxide (CuO) thin films were deposited on a glass substrate at relatively low bath temperature of 338 ± 5 K. The as deposited films were polycrystalline in nature with preferential orientation along the (200) plane. The films were found to exhibit negative photoconductivity. Vacuum annealing of the films resulted in preferential growth along the (111) and (200) plane for temperatures 373 K, 473 K and 573 K. Vacuum annealing at 673 K resulted in preferential growth along the (200) plane. The vacuum annealed films showed normal photoconductivity behavior. The optical band gap of the films was found to increase from 1.57 eV for the as prepared films to 2.06 eV for films annealed in vacuum at 673 K. Surface photo voltage measurements indicate that the direction of band bending is reversed when the as deposited CuO thin films are subjected to vacuum annealing. We conclude that surface state passivation is leading to change in the photoconductive behavior of the thin film samples when subjected to post deposition vacuum annealing.

Shape control of self-organized porous silica submicron particles and their strength evaluation

In this paper, precise control of the shape, size, and porosity of porous silica submicron particles and their strength evaluation are described. Self-organization phenomenon of silica nanopowders and submicron polystyrene latex (PSL) balls in an atomized mist is used for the fabrication of the particles. When temperatures of lower- and upper-zone heaters are 100 and 600 °C, and N2 gas flow rate is 0.4 l/min, spherical particles are produced. When PSL concentration increases, the number of pores increases. Particles with uniformly-arranged pores are produced at the PSL concentration of around 3 wt %. By using the PSL balls of different diameters, porous silica particles including different size pores are made. Also, compressive fracture test is conducted to check the effect of vacuum annealing on the strength of particles. The annealed particle shows higher fracture force than the unannealed particle, which indicates that the annealing would be effective for improving the mechanical reliability.