Vacuum Annealing Process Research Articles

Reversible Charge-Transfer Doping in Graphene due to Reaction with Polymer Residues

Chemical doping in graphene due to polymer molecules adsorption has attracted much recent interest because of the modification of electrical, magnetic, and optical properties of graphene. We show a reversible charge-transfer doping effect in graphene due to the reaction with poly(methyl methacrylate) (PMMA) residues. By helium ion irradiation and vacuum annealing without introducing an external dopant, reversible shifts in Raman G and 2D bands are observed as well as the change in the relative 2D band intensity to the G band. Chemical bonds between functional groups from PMMA residues and graphene could be formed due to He+ ion irradiation, and the desorption of functional groups from graphene is dominant during the vacuum annealing process. Meanwhile, PMMA residue on the graphene surface is mostly removed and the surface morphology becomes smooth after irradiation and annealing. Both electrical conductance and Raman band shifts show nonmonotonic dependence on the dose density, which remains after anneali...

Temperature-resistant high-infrared transmittance indium molybdenum oxide thin films as an intermediate window layer for multi-junction photovoltaics

For optimal performance, the intermediate window layer in multijunction photovoltaics should transmit as much light as possible to guarantee maximum device efficiency. In this work, we demonstrate that indium molybdenum oxide (IMO) is a more suitable intermediate layer, compared to indium tin oxide (ITO), as it would absorb significantly less infrared light with comparable electrical conductivity once integrated into a multijunction solar cell. In fact, we show that IMO optoelectronic properties are virtually unchanged by the typical thermal budgets used in solar absorber deposition processes used in low-cost high-performance multijunction photovoltaics (e.g. CuInGaSe2). Specifically, IMO and ITO thin films were reactively sputtered onto glass substrates at 150°C, then subjected to a vacuum annealing process (550°C, 2h) identical to that of co-evaporated copper gallium diselenide (CGSe), a candidate material for the top absorber in multijunction cells. We found that annealing substantially reduces the infrared transmittance of ITO starting at 900nm, reducing by 2.5% per 100nm, while IMO only started experiencing a reduction at 1400nm and decaying more slowly at 1.6% per 100nm. Furthermore, the resistivity of IMO was comparable to that of ITO after annealing. The resilience of IMO to such high temperature processes show that it has potential to enhance the performance of multijunction devices.

Long lasting blue phosphorescence and photostimulated luminescence in 12CaO⋅7Al2O3:Eu thin films grown by pulsed laser deposition

Long lasting blue emitting Eu-doped 12CaO⋅7Al2O3 thin films have been prepared on quartz substrates by pulsed laser deposition combined with post-annealing. The 12CaO⋅7Al2O3 phase is formed after annealing the films above 900°C in vacuum ambient. Upon 323nm excitation, the thin films exhibit a blue long lasting emission peaked at 444nm, assigned to the 5d–4f transitions of Eu2+. The films annealed at 950°C have stronger luminescence and longer lasting time than that annealed at 900°C. The phosphorescence intensity of vacuum annealed film is better than that annealed in H2/N2 atmosphere, which might be due to the increase of shallow trap numbers during the vacuum annealing process. Thermoluminescence curves demonstrate that vacuum and H2/N2 atmosphere annealing could introduce a large number of both shallow and deep traps into 12CaO⋅7Al2O3:Eu thin films. After UV irradiation, excellent photostimulated luminescence can be observed under 980nm excitation. Our results suggest that 12CaO⋅7Al2O3:Eu phosphor may serve as a promising blue luminescent materials used in fabrication of optical storage and illumination in dark environments.

Native NIR-emitting single colour centres in CVD diamond

Single-photon sources are a fundamental element for developing quantum technologies, and sources based on colour centres in diamonds are among the most promising candidates. The well-known nitrogen vacancy centres are characterized by several limitations, and thus few other defects have recently been considered. In the present work, we characterize, in detail, native efficient single colour centres emitting in the near infra-red (λ = 740–780 nm) in both standard IIa single-crystal and electronic-grade polycrystalline commercial chemical vapour deposited (CVD) diamond samples. In the former case, a high-temperature (T > 1000 °C) annealing process in vacuum is necessary to induce the formation/activation of luminescent centres with good emission properties, while in the latter case the annealing process has marginally beneficial effects on the number and performance of native centres in commercially available samples. Although displaying significant variability in several photo-physical properties (emission wavelength, emission rate instabilities, saturation behaviours), these centres generally display appealing photophysical properties for applications as single photon sources: short lifetimes (0.7–3 ns), high emission rates (∼50–500 × 103 photons s−1) and strongly (>95%) polarized light. The native centres are tentatively attributed to impurities incorporated in the diamond crystal during the CVD growth of high-quality type-IIa samples, and offer promising perspectives in diamond-based photonics.

Room-Temperature Ferromagnetism in Fe/Sn-Codoped In2O3 Powders and Thin Films

Fe/Sn-codoped In2O3 powders and films are prepared by a vacuum annealing process and a pulsed laser deposition technique, respectively. The structural and magnetic properties of the samples are investigated. The obvious room-temperature ferromagnetism is observed in both (In0.92Fe0.05Sn0.03)2O3 powders and films, but their magnetic behaviors are very different. The ferromagnetism of the vacuum-annealed powders is partially due to precipitated Fe3O4 impurity. By contrast, the ferromagnetism of the films is intrinsic and does not originate from any magnetic impurity, as confirmed by the extensive x-ray absorption spectroscopy and magnetization studies.

Size Effect of Silver Nanoparticle Melted into ZnO Nanorods for Photocatalytic Activity

Ag/ZnO nanorod structure was synthesized by using the hydrothermal method to grow ZnO nanorods and melted silver nonoparticles into ZnO nanorods by thermal annealing process in vacuum at 700 oC. The photocatalytic activity for methylene blue decolorization is enhanced by silver nanoparticles melted into a ZnO nanorod structure owing to the formation of Schottky barrier near the Ag/ZnO interface prolongs the recombination of electron-hole pairs effectively. The size effect of silver nanoparticles in the Ag/ZnO nanorod structure for photocatalytic activity was discussed which was changed from 12 to 34 nm. The smaller silver nanoparticle size sample shows better decolorization efficiency of methylene blue solution owing to the higher surface area of Ag/ZnO nanoroad. Ag/ZnO nanorod films have been characterized by X-ray diffraction (XRD), UV-vis spectroscopy, field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The dye decolorization significantly increased from 69 to 99 % after UV light irradiation for 8 hr by the optimum Ag/ZnO nanorod film.

Effects of vacuum annealing on the optical and electrical properties of p-type copper-oxide thin-film transistors

We have investigated the effects of vacuum annealing on the optical and electrical properties of the p-type copper-oxide thin-film transistors (TFTs). The vacuum annealing of the copper-oxide thin-film was performed using the RF magnetron sputter at various temperatures. From the x-ray diffraction and UV-vis spectroscopy, it is demonstrated that the high-temperature vacuum annealing reduces the copper-oxide phase from CuO to Cu2O, and increases the optical transmittance in the visible part of the spectrum. The fabricated copper-oxide TFT does not exhibit the switching behavior under low-temperature vacuum annealing conditions. However, as the annealing temperature increases, the drain current begins to be modulated by a gate voltage, and the TFT exhibits a high current on–off ratio over 104 as the vacuum annealing temperature increases over 450 °C. These results show that the vacuum annealing process can be an effective method of simultaneously improving the optical and electrical performances in p-type copper-oxide TFTs.

Fabrication of Al/Al3Mg2 composite by vacuum annealing and accumulative roll-bonding process

Al3Mg2 produced by the reaction between 1060-Al plates and AZ31-Mg foil was introduced homogeneously in the 1060-Al matrix during an accumulative roll-bonding (ARB) process. A type of aluminum metal matrix composite (AMMC) called intermetallic compound-reinforced AMMC was manufactured. Investigations regarding the hardness and tensile properties of the composites showed that the Vickers microhardness, tensile strength, and elongation of the Al/Al3Mg2 composites increased with the number of ARB cycles. Compared with the annealed and ARB monolithic 1060-Al, the Al/Al3Mg2 composites showed excellent mechanical properties and low density after the sixth ARB cycle.

Preparation and electrochemical characterization of NiO nanostructure-carbon nanowall composites grown on carbon cloth

This study provided a simple method to form NiO nanostructures onto the carbon nanowalls (CNWs) surface to enhance the performance of electric double layer capacitor (EDLC) characteristics. The CNWs were synthesized on carbon cloth by rf magnetron sputtering without any catalyst. Ni film was then deposited on the synthesized CNWs by e-beam evaporator. Subsequently, the vacuum annealing process and oxygen plasma treatment were used to form the NiO nanostructures. The crystallize structures of NiO nanostructures and CNWs were examined by Raman scattering spectroscopy. To realize the electrochemical properties of NiO/CNWs/carbon cloth composite, cyclic voltammetry (CV) and galvanostatic charge–discharge tests were investigated. Due to the relatively larger surface area of CNWs and the quickly reversible redox reaction and pseudo-capacitive properties of NiO nanostructures, the measured results demonstrated that the NiO/CNWs/carbon cloth is a suitable electrode material for EDLC applications.

Freestanding diamond films phototransistor

High quality freestanding diamond (FSD) films with smooth nucleation surfaces were grown by microwave plasma chemical vapor deposition (MPCVD) method. A p-type hydrogenated surface conductivity of FSD film was obtained by using hydrogen plasma treatment. The annealing process in vacuum on the p-type behavior of FSD nucleation surfaces was investigated by Hall effect measurement. H-terminated diamond phototransistors were fabricated and the results suggest that they may be ideally suited for ultraviolet (UV) switching applications.

Thermoelectric and mechanical properties of Zn4Sb3 polycrystals sintered by spark plasma sintering

β-Zn4Sb3 has attracted much interest as a thermoelectric material because of its potential for power-generation applications in a moderate temperature range (450 ∼ 650 K). In general, three kinds of considerations have been reported for the fabrication of a polycrystalline β-Zn4Sb3 bulk sample: (i) a problem in chemical stability, (ii) cracks in bulk specimens owing to a phase transition of the Zn4Sb3 composition resulting in stress during cooling, and (iii) the requirement for high bulk density. In this study, a pure Zn4Sb3 phase with a high define ZT(figure of merit) value was synthesized by using a vacuum melting process and a vacuum annealing process, followed by a spark plasma sintering (SPS) method. Fabricating a single-phase specimen with high bulk density by means of optimizing the SPS conditions (temperature and pressure) was significant for obtaining high performance in the Zn4Sb3 thermoelectric system. The maximum ZT value (0.98) was attained at a 573 K measurement temperature for the specimen sintered with the optimized SPS conditions (723 K, 40 MPa).

Improvement of interfacial electron scattering by introduced NiFe nanoparticles

Ta/MgO/NiFe/MgO/Ta ultrathin films with and without intercalation of NiFe nanoparticles in MgO layers were prepared by magnetron sputtering, followed by a vacuum annealing process. The measured and calculated results show that the former has higher specular electron scattering (SES) parameter at MgO/NiFe interfaces, lower resistivity, and higher magnetoresistance (MR). The improved transport properties (TPs) are mainly attributed to the suppressed diffuse electron scattering by means of the introduction of NiFe nanoparticles.

Effects of oxygen vacancy and local spin on the ferromagnetic properties of Ni-doped In2O3 powders

(In1−xNix)2O3 (x=0.03 and 0.06) powders were prepared by a solid-state reaction and a vacuum annealing process. The air-sintered samples initially showed paramagnetism, and then exhibited obvious room temperature ferromagnetism after vacuum annealing. The ferromagnetic signal almost disappeared after air annealing and reappeared after vacuum annealing. Hence, the ferromagnetism can be switched “on” and “off” by alternate air and vacuum annealing. X-ray diffraction, high-resolution transmission electron microscopy, and field-cooled/zero-field-cooled measurements were performed. These analyses confirmed that there was no detectable trace of Ni or Ni oxide secondary phase in vacuum-annealed (In1−xNix)2O3 samples, and that the Ni ions were incorporated into the indium oxide lattice (substituting the In3+ ions). No ferromagnetic signal emerged from pure In2O3 powders regardless of undergoing vacuum or air annealing. These results revealed that oxygen vacancy and local spin are two factors that indispensably affect the ferromagnetic properties of the Ni-doped In2O3 system.

Influence of vacuum annealing and irradiation on magnetic properties of Fe-3%Y2O3 films

Yttria (Y) dispersed ferrum (Fe) films were prepared by a double-target magnetron co-sputtering method. Vacuum annealing and xenon ion irradiation were conducted to investigate the influence on the magnetic and mechanical properties of the films. The crystal grain growth mechanism and second phase precipitation mechanism were conducted simultaneously in the vacuum annealing process. These two effects led to an opposite variation of nano-hardness and coercivity in the films. Xenon ion irradiation played a role in rapid annealing, which also affected the magnetic performance of the yttria dispersed ferrum films.

Enhanced reactivity of nanoscale iron particles through a vacuum annealing process

A reactivity study was undertaken to compare and assess the rate of dechlorination of chlorinated aliphatic hydrocarbons (CAHs) by annealed and non-annealed nanoscale iron particles. The current study aims to resolve the uncertainties in recently published work studying the effect of the annealing process on the reduction capability of nanoscale Fe particles. Comparison of the normalized rate constants (m2/h/L) obtained for dechlorination reactions of trichloroethene (TCE) and cis-1,2-dichloroethene (cis-1,2-DCE) indicated that annealing nanoscale Fe particles increases their reactivity ~30-fold. An electron transfer reaction mechanism for both types of nanoscale particles was found to be responsible for CAH dechlorination, rather than a reduction reaction by activated H2 on the particle surface (i.e., hydrogenation, hydrogenolysis). Surface analysis of the particulate material using X-ray diffraction (XRD) and transmission electron microscopy (TEM) together with surface area measurement by Brunauer, Emmett, Teller (BET) indicate that the vacuum annealing process decreases the surface area and increases crystallinity. BET surface area analysis recorded a decrease in nanoscale Fe particle surface area from 19.0 to 4.8 m2/g and crystallite dimensions inside the particle increased from 8.7 to 18.2 nm as a result of annealing.

Improved sorption characteristics of NH 3 molecules on the solution-processed graphene sheets

In this report, we investigated solution-processed graphene chemical sensors. A vacuum-annealing process after the graphene sheets were deposited on the wafer enhanced the response and sensitivity of the sensors by increasing the number of pristine sites on graphene. The presence of defect sites with higher binding energies and lower populations was related with slow adsorption/desorption. In contrast, fast adsorption/desorption were observed from the pristine sites. A two-step adsorption/desorption mechanism was observed when graphene sheets were exposed to ammonia molecules.

Electrical Properties of Hydrogen Terminated P-Type Diamond Film

Undoped high quality polycrystalline diamond films were grown by the microwave plasma chemical vapor deposition (MPCVD) method. The effects of hydrogen plasma treatment and vacuum annealing process on the p-type behavior of diamond films were investigated by the Hall effect method. The sheet carrier concentration increased and the sheet resistivity decreased with the treating time of hydrogen plasma and a stable value was achieved finally. After annealing the samples in vacuum at temperature above 600 °C, the sheet carrier concentration dropped dramatically. The origin of this hydrogen terminated p-type conductive layers is also discussed.

Molecular Dynamic Simulation on Graphitization and Dehydrogenization of Hydrogenated Carbon Films in Vacuum

The thermal stability of hydrogenated carbon films with H fraction from zero to 51.5% is studied by carrying out a molecular dynamical simulation on the annealing process in vacuum. Our simulations show that both graphitization temperature and dehydrogenization temperature decrease with H fraction in the films, which is in good agreement with the available experimental data. The dehydrogenization temperature is found to be much higher than the graphitization temperature. It is indicated that graphitization is the dominant process causing the degeneration of hydrogenated carbon films.

Effect of nano-oxide layers on the magnetoresistance of ultrathin permalloy films

Ta/NiFe/Ta ultrathin films with and without nano-oxide layers (NOLs) were prepared by magnetron sputtering followed by a vacuum annealing process. The influence of NOLs on the magnetoresistance (MR) ratio of ultrathin permalloy films was studied. The results show that the influence of grain size and textures on the MR ratio becomes weak when the thickness of the NiFe layer is below 15 nm. A higher MR ratio was observed for the thinner (< 15 nm) NiFe film with NOLs. The MR ratio of a 10 nm NiFe film can be remarkably enhanced by NOLs. The enhanced MR ratio for these ultrathin films can be attributed to the enhanced specular reflection of conduction electrons.

Growth and characterization of ZnIn 2Se 4 buffer layer on CuInSe 2 thin films

The p-type CuInSe 2 (CIS) films were prepared by electrodeposition following the vacuum annealing process. Zn element was diffused into the CIS film samples at 350 °C by heating Zn grains in vacuum. Then, ZnIn 2Se 4 (ZIS) buffer layer was fabricated on CIS thin film by this thermal diffusion process. The formation of ZIS phase was confirmed by X-ray diffraction pattern (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). Dark I– V measurement shows that the Zn-doped CIS (0.89 at%)/Mo structure reveals the rectifying property, which indicates that a p–n junction was formed.