Effect Of Vacuum Annealing Research Articles

Effect of vacuum annealing on the characteristics of composite pellets containing DBSA-doped polyaniline and Fe nanoparticles

The DBSA-PANI-Fe composite powder with 50wt% of Fe nanoparticles was prepared by mechanically mixing the DBSA-doped polyaniline powder and Fe nanoparticles. The composite powder was compacted to pellets and the pellets were annealed in vacuum at 443, 493, 543, and 593 K for 60 and 120 min. The conductivity of the pellet increases markedly with increasing the annealing temperature up to 493 K, and then decreases with further increasing the annealing temperature. When the pellet was annealed at 493 K for 60 min, the increment of conductivity reaches a maximum value, and the conductivity is 2.6 times as large as that of the pellet unannealed. The conductivities of the pellets annealed under the conditions of 543 K/120 min, 593 K/60 min, and 593 K/120 min are lower than the conductivity of the pellet unannealed. For all the pellets, the variation in conductivity with temperature reveals that the charge transport mechanism can be considered to be 1-D variable-range-hopping (1-D VRH). The composite pellet shows a magnetic hysteresis loop independent of the annealing condition. The saturation magnetization is about 5.4×10 4 emu/kg. The saturation field and the coercivity are estimated to be 4.38×10 5 and 3.06×10 4 A/m, respectively. The crystalline structure of Fe nanoparticles in the composites does not change with the annealing condition. The annealing condition cannot destroy the polymer backbones.

Temperature-dependent electrical characterization of nitrogen-doped ZnO thin film: vacuum annealing effect

Temperature-dependent Hall effect measurements were carried out at an N-doped ZnO thin film grown by the reactive sputtering method onto (001) Si substrate before and after being vacuum annealed at 900 °C. p-Type ZnO thin film was obtained with a relatively high mobility of ∼60 cm2 V−1 s−1, a high carrier concentration of 2.5×1017 cm−3 and a low resistivity of 0.4 Ω cm. After vacuum annealing, the temperature dependence of electrical parameters such as mobility and carrier concentration showed highly different characteristics. Time-resolved photoluminescence (TRPL), PL and x-ray diffraction measurements (XRD) were performed after the annealing process to check whether the high-temperature annealing can remove the ZnO film on Si or not. The PL measurement shows band-to-band recombination at 360 nm and TRPL shows the exciton recombination lifetime to be 571.7 ps. The XRD measurement reveals highly preferred c-axis (0002) orientation. Activation energies were calculated using the ln σ versus 1000 T−1 plot to be 20 meV for the as-grown and 24 and 6.8 meV after the vacuum annealing process.

Study of thermocolored WO3 thin film under direct solar radiation

The effect of vacuum annealing on the spectral response and structure of tungsten oxidefilms prepared by electron beam evaporation was studied. The temperatures ofWO3 and glass heated in vacuum and under solar radiation were investigated.Vacuum annealing WO3 at 450 °C for 1 h was observed to change the film from transparent to a deep shade of blueand to cut off the infrared radiation as a result of increased reflectance andabsorbance. The annealing was also observed to decrease the band gap of theWO3 from 3.2 to 2.4 eV, and to change the film from an amorphous to a polycrystalline phase.The colored WO3 film was observed to increase the temperature of the substrate glass at a rate of0.06 °C (W m−2)−1 due to its solar radiation absorbance. These films were left to self-bleach outside forextended periods of time.

Influence of Cd/S ratio on photocatalytic activity of high‐vacuum‐annealed CdS–TiO2 thin film

AbstractCdS–TiO2 thin film heterojunctions were prepared on glass substrates with various Cd/S ratios to optimize the photocatalytic efficiency in UV–visible light irradiation. The CdS underlayer was prepared by the chemical bath deposition technique and subsequently annealed in high vacuum of 5 × 10–5 Pa at 400 °C. The effect of vacuum annealing of the CdS layer on optical and photocatalytic properties of the CdS–TiO2 thin film was also studied. The photocatalytic activity, evaluated by the measurement of the decomposition of methanol in the gas phase under UV–visible light irradiation, shows higher efficiency for a vacuum‐annealed CdS underlayer deposited with Cd/S ratio ≈1:4. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Structure, paramagnetic defects and light-emission of carbon-rich a-SiC:H films

The effect of vacuum annealing on local structure reconstruction, evolution of photoluminescence (PL) and paramagnetic defects in carbon-rich a-Si1−xCx:H films (x=0.7) was studied. Strong enhancement of visible (white-green) PL was observed after annealing in the temperature range of 400–500 °C. Such enhancement was correlated with increasing of the concentration of carbon-hydrogen bonds in Si:CHn accompanied with increase in the fluctuation of the interatomic potential. Complete disappearance of PL, “graphitization” of the carbon precipitates, and a strong increase in the concentration of the paramagnetic states were observed after annealing at 650 °C and above. The enhancement and the degradation of PL after different-temperature treatments are explained by the following competing effects: (1) enhancement of the radiative recombination due to passivation of paramagnetic defects with hydrogen and increase of localization of photoexcited electron-hole pairs due to formation of new Si:CH and (2) enhancement of the nonradiative recombination through the paramagnetic states due to increase in their concentration caused by graphitization of carbon precipitates after high- temperature treatment.

10.1007/s11700-008-1017-x

The effect of vacuum annealing on the morphology of hydrogenated and oxidized Si(310) surfaces is investigated by scanning tunnel microscopy, reflection high-energy electron diffraction, and low-energy electron diffraction. It is found that after desorption of a passivating coating, the surface has a strongly developed profile formed preferentially by steps two monolayers in height. Annealing at a temperature of 900±15°C with subsequent abrupt cooling leads to faceting of the surface by (510) planes. The presence of steps two monolayers in height on the Si(310) surface allows one to use Si crystals oriented along the (310) plane as the substrate for heteroepitaxy of the II–VI compounds.

Investigation of the effect of annealing on the interface structure in Fe/Cr superlattices by conversion electron Mössbauer spectroscopy

The effect of vacuum annealing on the structure of the Fe/Cr superlattice, exhibiting giant magnetoresistance effect, has been investigated by Mossbauer spectroscopy. It is shown that annealing-induced activation of diffusion leads to a decrease in the thickness of “pure” Cr and Fe layers, redistribution of atoms in the interface regions, and a change in the giant magnetoresistance. The existence of the angular spatial dispersion of the magnetic anisotropy field at the interface has also been revealed.

Effect of vacuum annealing on field emission from heavily phosphorus doped homoepitaxial (111) diamond

Vacuum anneal treatments effects on field emission properties of phosphorus doped diamond are discussed. The C1s core level of diamond is characterized by X-ray photoelectron spectroscopy (XPS). With increasing annealing temperature, firstly oxygen desorption takes place from surface, which induce surface reconstruction followed by graphitization of surface. Field emission properties, therefore, strongly depend on vacuum anneal temperature. The threshold voltage of diamond annealed at 900 °C is the lowest. Fowler–Nordheim plots indicate that diamond annealed at 900 °C has the lowest barrier height, which is in good agreement with electron affinities as measured on carbon reconstructed surface. Further increased annealing temperature induces surface graphitization, which causes a threshold voltage increase of field emission.

Effect of Vacuum Annealing on the Phase Stability of Ti3SiC2

The effect of vacuum annealing on the thermal stability and phase transition of Ti3SiC2 has been investigated by X‐ray diffraction (XRD), neutron diffraction, synchrotron radiation diffraction, and secondary ion mass spectroscopy (SIMS). In the presence of vacuum or a controlled atmosphere of low oxygen partial pressure, Ti3SiC2 undergoes a surface dissociation to form nonstoichiometric TiC and/or Ti5Si3Cx that commences at ∼1200°C and becomes very pronounced at ≥1500°C. Composition depth profiling at the near surface of vacuum‐annealed Ti3SiC2 by XRD and SIMS revealed a distinct gradation in the phase distribution of TiC and Ti5Si3Cx with depth.

Effect of Vacuum Annealing on the Surface Chemistry of Electrodeposited Copper(I) Oxide Layers as Probed by Positron Annihilation Induced Auger Electron Spectroscopy

Vacuum anneal induced changes in the surface layers of electrodeposited copper(I) oxide (Cu2O) were probed by time-of-flight positron annihilation induced Auger electron spectroscopy (TOF-PAES) and by electron induced Auger electron spectroscopy (EAES). Large changes in the intensity of the Cu PAES intensity resulting from isochronal in situ vacuum anneals made at increasing temperatures indicated that, before thermal treatment, the surface was completely covered by a carbonaceous overlayer and that this layer was removed, starting at a temperature between 100 and 200 degrees C, to expose an increasing amount of Cu in the top layer as the anneal temperature was increased. The thickness of this overlayer was estimated to be approximately 4 A based on analysis of the EAES data, and its variation with the thermal anneal temperature was mapped. This study demonstrated the order-of-magnitude enhancement in the sensitivity of PAES to the topmost surface layer in Cu2O relative to the EAES counterpart; factors underlying this contrast are discussed. Finally, the implications of ultrathin carbon layers on semiconductor surfaces are discussed.

Effect of vacuum annealing on characteristics of the DBSA-doped polyaniline pellets

Powder of DBSA-doped polyaniline was pressed to pellets. The pellets were annealed in vacuum at 140, 200, 260 and 320 °C for times up to 120 min. For all the annealing temperatures, the conductivity of the pellet is sharply reduced by a factor of 2 when the annealing time reaches 15 min. For the annealing temperatures lower than 260 °C, the conductivity does not change with further increasing the annealing time. However, under the annealing condition of 260 °C/120 min, the conductivity of the pellet decreases markedly again. Furthermore, the pellets annealed at 320 °C for the times longer than 30 min exhibit an insulating characteristic. The pellets consist of many agglomerated particles. The agglomerated particles become large with thermal aging. When the annealing temperature reaches 320 °C, some small sub-particles are formed on the surface of the agglomerated particles. The annealing results in a de-doping of DBSA from the polymer backbones and promotes the formation of reduction state in the polyaniline. The DBSA-doped polyaniline pellets annealed have a more porous and cracked morphology relative to the pellet unannealed. The degradation of the conductivity of the DBSA-doped polyaniline pellets is attributed to the de-doping, the phase separation and the porous and cracked morphology.

The effects of vacuum annealing on the structure of VO 2 thin films

Noncrystalline VO x thin films were deposited onto p-doped Si (100) substrates at 400 °C using magnetron sputtering. By vacuum annealing, we obtained polycrystalline VO 2 thin films with two different structures under a variety of annealing conditions. With the annealing temperature increasing and the annealing time developing, structures of the films underwent the following transformation: amorphous structure→metastable VO 2 (B)→VO 2 (B) + VO 2 (M). Vacuum annealing is useful of acquiring VO 2 thin films with high surface quality, but too high annealing temperature (500 °C) and too long time (15 h) are harmful, which make the surface degenerate.

Effect of Thermal Treatment on the Structure of Multi-walled Carbon Nanotubes

The effects of vacuum annealing and oxidation in air on the structure of multi-walled carbon nanotubes (MWCNTs) produced by a large-scale catalytic chemical vapor deposition (CCVD) process are studied using Raman spectroscopy and transmission electron microscopy (TEM). A detailed Raman spectroscopic study of as-produced nanotubes has also been conducted. While oxidation in air up to 400°C removes disordered carbon, defects in tube walls are produced at higher temperatures. TEM reveals that MWCNTs annealed at 1,800°C and above become more ordered than as-received tubes, while the tubes annealed at 2,000°C exhibit polygonalization, mass transfer and over growth. The change in structure is observable by the separation of the Raman G and D′ peaks, a lower R-value (I D/I G ratio), and an increase in the intensity of the second order peaks. Using wavelengths from the deep ultraviolet (UV) range (5.08 eV) extending into the visible near infrared (IR) (1.59 eV), the Raman spectra of MWCNTs reveal a dependence of the D-band position proportional to the excitation energy of the incident laser energies.

Corrosion characteristics of plasma-sprayed Ni-coated WC coatings comparison with different post-treatment

The effects of vacuum annealing and laser remelting on the microstructure and corrosion behaviour of plasma-sprayed Ni-coated WC coatings on steel substrate have been investigated. The laser remelting was operated in a continuous way while the vacuum annealing was operated with clamping the coating on the graphite face in order to avoid decarburization of WC. When compared with the as-sprayed coating, the microstructure of the post-heating treatment coatings has been found to consist of different phases. Moreover, the denser microstructure can be obtained after heating treatment, especially the laser remelting coating. Electron probe micro analyzer (EPMA) shows that the chemical composition remained largely unchanged except the “bumps” at the interface for as-sprayed and vacuum annealing coatings. The more uniform composition was obtained for laser remelting coating. The Vickers microhardness measurement shows a very slightly enhancement for post-heating treatment coatings, which may be duo to the lamellar structure, lower contemt and bulky of carbide for coatings. However, salt spray corrosion (SSC) show the laser remelting coating has the best corrosion resistance, which is due to its low number defects and uniform distribution of the phase and composition.

Effect of vacuum annealing and nitrogen alloying on gas atomised M4 high speed steel powder

In the present study the authors have used X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) to assess how surface oxides limit the gas nitriding depth of gas atomised M4 high speed steel powder and compacts. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) have been used for phase identification. In model experiments XPS and AES analyses of vacuum annealed powder were performed in an interconnected furnace, limiting reoxidation. Sintering cycles with and without vacuum annealing treatment were also evaluated. Generally, the authors found that an increased vacuum annealing treatment time decreased the amount of residual oxygen, which improved densification. AES and XPS analyses of the model experiments showed that the vacuum annealing time increased the absorption of nitrogen. In the sintered compacts, SEM, AES and XRD analysis as well as Thermo–Calc simulations showed that similar amounts of nitrogen were tied to vanadium carbonitrides. An AES comparison between the model and sintering experiments showed that the nitrogen absorption had the Sieverts' law dependence once the surface oxide had been removed.

Effect of vacuum annealing on the phase composition of In/SnO/Si, In/SnO2/Si, and Sn/In2O3/Si heterostructures

The chemical interaction between indium and thin SnO and SnO2 films and between tin and thin In2O3 films during vacuum annealing was studied. The metallic films were deposited onto single-crystal silicon substrates by magnetron sputtering, the SnO and SnO2 films were produced by heat-treating the Sn film in flowing oxygen at 673 and 873 K, respectively, and the In2O3 film was produced by heat-treating the In film at 573 K. The results indicate that annealing of the In/SnO/Si and In/SnO2/Si heterostructures in vacuum (residual pressure of 0.33 × 10−2 Pa) at 773 K gives rise to the reduction of Sn and oxidation of In, whereas annealing of Sn/In2O3/Si causes partial tin substitution for indium in the cubic indium oxide lattice.

Effect of vacuum annealing on characteristics of the HCl-doped polyaniline pellets

Powders of HCl-doped polyanilines were prepared by using a solution polymerization process and then were pressed to the polyaniline pellets. The pellets were annealed in vacuum at 140, 200 and 260 °C for times up to 120 min, respectively. Electrical property and micromorphology of the pellets were studied by using a four-point probe technique and a scanning electron microscopy. The conductivity of the pellets decreases sharply when the annealing time reaches 30 min and then decreases gradually with further increasing annealing time. When the pellets are annealed under the conditions of 200 °C/120 min, 260 °C/90 min and 260 °C/120 min, the resistance of the pellets could not be measured by the four-point probe technique and the pellets show an insulating characteristic. The breakdown voltage increases with increasing annealing temperature and time. The maximum breakdown voltage is about 875 V/cm. The degradation of the conductivity is mainly attributed to the loss of chlorine in the polyaniline pellets. The micromorphology of the pellets becomes heterogeneous with thermal aging.

Investigation of vacuum annealing effects on physical–mechanical properties of thermoplastic parts

Impact and tensile strength of polystyrene and nylon 6 samples, which have been produced by injection molding before and after annealing in different conditions are obtained. Polystyrene samples that are heated on vacuum conditions can deform highly even in temperatures much less than polystyrene glass temperature. This phenomenon is reduced significantly by heating samples to annealing temperature in atmospheric pressure and then removing air from sample environment in constant temperature. Deformation problems for nylon were not so important but due to high temperature implied for annealing of nylon parts, some color change due to oxidative degradation are observed. So for nylon parts a complete vacuum was need to eliminate such oxidative degradation. Analysis of obtained results shows some reduction in impact and strength of annealed samples that can be due to elimination of longitudinal orientation observed normally in injection-molded parts.

Effect of vacuum annealing on the edge luminescence of undoped zinc selenide

It has been established experimentally that vacuum annealing of undoped ZnSe crystals in the temperature range 700–1200 K leads to a significant increase in the intensity of the blue luminescence band and suppression of the red-orange band. A model for defect formation is proposed to explain the observed characteristics.

Effects of vacuum annealing on electrical properties of GaN contacts

To understand formation and deterioration mechanisms of Ta/Ti ohmic contacts that were previously developed for p-GaN, the electrical properties of the Ta/Ti contacts, which were deposited on undoped GaN substrates and subsequently annealed in vacuum (where a slash (/) sign indicates the deposition sequence), were studied. The Ta/Ti contacts displayed good ohmic behavior after annealing at a temperature of 800°C for 10 min in vacuum, although the undoped GaN substrates were used. However, deterioration of the present ohmic contacts was observed during room-temperature storage. These contact properties were similar to those observed in the Ta/Ti contacts prepared on p-GaN. Hall-effect measurements revealed that thin n-type conductive layers were found to form on surfaces of both the undoped GaN and p-GaN substrates after annealing at 800°C in vacuum.