Thermal Treatment In Vacuum Research Articles

Electrical and Photoelectric Properties of Polycrystalline Silicon after High-Intensity Short-Pulse Ion Implantation

Electrical and photoelectric properties of polycrystalline silicon after high-intensity short-pulse implantation of carbon ions have been studied. It has been found that vacuum annealing (10–2 Pa, 300–1200 K) of silicon affects the surface dark and photoconductivity. Optimal conditions of thermal vacuum treatment of silicon have been found that provide the most heat and field resistant changes in its properties. Probable causes for the changes in electric and photoelectric characteristics of the material have been revealed.

Comparative analysis of thermally induced degradation of condensation-grown (1 0 0)Ge0.75Si0.25/SiO2 interfaces by electron spin resonance

An electron spin resonance study has been carried out on the influence of isochronal annealing on the GeSi/SiO2 interfaces of the condensation grown (100)Si/SiO2/Ge0.75Si0.25/SiO2 structure. The thermal interface stability has been monitored in terms of the evolution of occurring paramagnetic interface defects, in particular, here involving the Ge dangling bond GePb1 point defect, previously identified as a detrimental interface trap. This reveals thermal post-growth interface degradation, initiating from annealing at the temperature ∼440°C onward, identified as substantial generation of GePb1 interface traps in addition to those naturally introduced into the system during sample manufacturing. In terms of GePb1 density, the interface thus appears only robust for thermal treatment in vacuum up to 440°C. For Tan reaching ∼520°C, a drastic degradation occurs as exposed by an about two-fold increase in GePb1 density, which state is maintained up to Tan∼900°C. Annealing in H2 (∼1atm) has a similar effect, except that the interface degrades more gradually. Above 900°C, the structure's integrity gradually collapses because of disintegration (Ge escape) of the SiGe layer. As to device implementation, the data indicate that temperatures of processing steps in O-deficient ambient should be kept below ∼440°C.

Bacterial colonisation of porous titanium coatings for orthopaedic implant applications – effect of surface roughness and porosity

Bone ingrowth into and through porous coatings on orthopaedic implants can substantially improve fixation. However, the introduction of pores increases surface roughness and also the risk of bacterial adherence, which can lead to infection (in extreme cases, to death) and complicate implant surgery due to the high risk of revision being required. Improving osseointegration without increasing infection risk is therefore a major challenge in implantology. Staphylococcal adhesion and biofilm formation on Ti surfaces of varying roughness and porosity have been investigated in vitro. Porous pure titanium coatings, obtained by a PM processing route based on the electrophoretic deposition of TiH2 followed by thermal treatment in vacuum, significantly reduced bacterial colonisation of the surface compared with a state-of-the-art vacuum plasma sprayed coating. Further reduction of biofilm formation could be obtained by additional surface modification.

Characterization of graphene layers by Kelvin probe force microscopy and micro‐Raman spectroscopy

AbstractThis paper considers a synthesis of graphene flakes on the Ni surface by vacuum thermal treatment of the “sandwich” a‐SiC/Ni multilayer deposited on silicon wafer by magnetron sputtering technique. Lateral size of graphene flake is estimated to be about hundreds of microns while thickness estimated by Raman scattering varied from one to few layers. Atom force microscopy (AFM) is not able to detect graphene flakes in regime of surface topology examination due to large roughness of Ni surface. Employment of scanning Kelvin probe force microscopy (SKPFM) demonstrates a correlation of surface potential and graphene flakes visible by optical microscopy. Moreover, the SKPFM allows to detect the graphene layer even in case of absence of optical contrast from single graphene layer on nickel surface. Using of KPFM the potential differences between Ni and graphene is determined. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Free-standing and binder-free lithium-ion electrodes based on robust layered assembly of graphene and Co3O4 nanosheets

Free-standing and binder-free Co3O4/graphene films were fabricated through vacuum filtration and thermal treatment processes, in which sheet-like Co3O4 and graphene were assembled into a robust lamellar hierarchical structure via electrostatic interactions. The morphological compatibility coupled with strong interfacial interactions between Co3O4 and graphene significantly promoted the interfacial electron and lithium ion transport. When used as a binder-less and free-standing electrode for lithium-ion batteries, the hybrid film delivered a high specific capacity (~1400 mA h g(-1) at 100 mA g(-1) based on the total electrode weight), enhanced rate capability and excellent cyclic stability (~1200 mA h g(-1) at 200 mA g(-1) after 100 cycles). This effective strategy will provide new insight into the design and synthesis of many other composite electrodes for high-performance lithium-ion batteries.

Palladium–zinc catalysts on mesoporous titania prepared by colloid synthesis. II. Synthesis and characterization of PdZn/TiO2 coating on inner surface of fused silica capillary

Nanoparticle-doped mesoporous titania coating was synthesized by incorporation of PdZn nanoparticles into TiO2 sol followed by dip coating of the sol on inner surface of fused silica capillary. Monodispersed PdZn bimetallic colloidal particles with average particle diameters of approximately 2 nm have been prepared by an ethylene glycol reduction of ZnCl2 and Pd(CH3COO)2 in the presence of polyvinylpyrrolidone. The textural properties, surface structure, chemical composition, and morphology of the samples were investigated by means of N2 sorption measurements, TEM, and X-ray diffraction. PdZn/TiO2 coating has been further analyzed by quantitative analysis of the SAXS data in combination with the density contrast method, providing direct structural-dispersion information about the active component and support. Calcination conditions suitable for surfactant removal have been optimized to obtain PdZn/TiO2 coatings with required metal particle size and composition. The high dispersion and chemical composition of the nanoparticles embedded in mesoporous titania coating have been retained with no modification after thermal treatment in vacuum at 300 °C. Results suggest how porous structure of the PdZn coating may be fine-tuned to improve the accessibility of the pores to reactants. The control of the pore size in the range of 4.9–6.8 nm of the mesoporous titania was achieved by adding co-surfactants, such as n-butanol.

Influence of oxidation-Reduction conditions of synthesis on oxidation states of Cr, Mo, and Co Ions in high-silica glasses

Investigations of porous high-silica glasses treated by aqueous solutions of Cr, Mo, and Co salts and subjected to thermal treatment in air and vacuum have been carried out. The results have been analyzed using EPR spectra and electron absorption spectra. The influence of the oxidation-reduction conditions of synthesis of high-silica glasses on the oxidation states of ions introduced into the glass has been demonstrated. It has been shown that chromium ions are strongly affected by the ambient environment and that their introduction into the glass structure is accompanied by a change in the oxidation state; this effect is less pronounced for molybdenum, and cobalt ions are most stable.

Reversible switching of room temperature ferromagnetism in CeO2-Co nanoparticles

We investigated the reversible ferromagnetic (FM) behavior of pure and Co doped CeO2 nanopowders. The as-sintered samples displayed an increasing paramagnetic contribution upon Co doping. Room temperature FM is obtained simply by performing thermal treatments in vacuum at temperatures as low as 500 °C and it can be switched off by performing thermal treatments in oxidizing conditions. The FM contribution is enhanced as we increase the time of the thermal treatment in vacuum. Those systematic experiments establish a direct relation between ferromagnetism and oxygen vacancies and open a path for developing materials with tailored properties.

Coordination variation of hydrated Cu2+/Br1− ions traversing the interfacial water in mesopores

Resolution of the atomistic and electronic details about the coordination structure variation of hydrated ions in the interfacial water is still a tough challenge, which is, however, essentially important for the understanding of ion adsorption, permeation and other similar processes in aqueous solutions. Here we report the tracing of coordination structure variation for hydrated Cu2+/Br1- ions traversing the interfacial water in Vycor mesopores (ϕ = 7.6 nm) by employing both X-ray absorption near edge structure and extended X-ray absorption fine structure spectroscopies. By controlled desorption/adsorption of water, the filling fraction of the mesopores, thus the water layer thickness, can be adjusted, which in turn effects the variation of coordination structure of the ions therein. It is found that both Cu2+ and Br1- ions prefer staying exclusively in the core water, and in this circumstance no ion pairs have been detected in the solution of concentrations up to 1.0 M. Following capillary decondensation occurring at a filling fraction of ∼35% which corresponds to a water layer of about three monolayers, Br1- ions begin immediately to reconstruct their first coordination shell, characterized by ionic dehydration, shrinkage of ion-water bond length, and formation of ion pairs. In contrast, Cu2+ ions can retain a bulk-like coordination structure till being driven to bond directly to the pore surface when the filling fraction is below 20%. At the final stage of dehydration via thermal vacuum treatment at 110°C, Cu2+ ions can be completely reduced to the Cu1+ state, and recover at room temperature only when the filling fraction is above 14%. These results may be inspirable for the investigation of similar problems concerning hydrated ions in water solution under different confining conditions.

Enhanced endothelialization guided by fibronectin functionalized plasma polymerized acrylic acid film

The plasma polymerized acrylic acid (PPAA) films with high carboxyl concentration were fabricated by low temperature plasma polymerization technology. Vacuum thermal treatment was used to modify the PPAA films. The stability of the PPAA film was evidenced by scanning electron microscopy (SEM). The result of toluidine blue-O (TBO) method showed that the –COOH concentration on the surface of the PPAA films decreased from 20.73nM to17.90nM after vacuum thermal treatment. Fibronectin (Fn) was successfully covalently immobilized onto the modified surface PPAA via a covalent bond reacted with carboxyl groups. Diffuse reflectance Fourier infrared transform spectroscopy (DRFTIR) and X-ray photoelectron spectroscopy (XPS) were utilized to characterize the layer-by-layer PPAA surface modification. From the evaluation of immunostaining for actin and Cell Counting Kit-8 (CCK-8), the surface of Fn-immobilized thermal treated PPAA films could be used to enhance the adhesion and proliferation of human umbilical vein endothelial cells (HUVECs). Especially, the exposure of RGD domain existing in the immobilized Fn was ascertained by ELISA, which was one of main improvement factors of HUVEC's adhesion and proliferation. This study demonstrated a promising surface modification used for vascular devices.

Investigation of temporary stiction in poly-SiGe micromirror arrays

Stiction, permanent but also temporary, remains one of the most critical reliability concerns for micro-electro-mechanical systems (MEMS). In this paper, we present an investigation of temporary stiction of standard poly-SiGe MEMS. This is done by analyzing the hysteresis in the displacement-versus-voltage characteristics of electrostatically actuated micromirrors. The anomalous widening of the “pull-in window”, caused by stiction-induced delay of the pull-out, is used as an indication of the amount of mirror-to-surface stiction. Differences in the pull-out voltage of micromirrors within an array indicate varying levels of stiction from mirror to mirror. It is shown that a 1H,1H,2H,2H-perfluorodecyltrichlorosilane (FDTS) self-assembled monolayer (SAM) can reduce this in-use stiction. Analytical and finite element methods are used to quantify the stiction forces. Also the impact of the relative humidity and of a vacuum thermal treatment is studied. The results show that humidity at the surface is the main cause of the stiction in these devices.

Photoelectrochemical study of oxygen deficient TiO2 nanowire arrays with CdS quantum dot sensitization

Oxygen-deficient TiO(2) nanowires show substantially increased donor density due to an increase in oxygen vacancies introduced intentionally by thermal treatment in ammonia, vacuum, or hydrogen. By coupling oxygen-deficient TiO(2) nanowires with CdS quantum dots, a significant enhancement in their photoactivities was observed in the entire wavelength region from 350 to 550 nm. These new nanocomposites hold great promise for solar hydrogen generation.

Effect of thermal treatment in vacuum on Fe-doped SnO2 powders

A sample of 10at% Fe-doped SnO2 powder was prepared by mechanical alloying and then thermally treated at 773K in vacuum. The fit of the diffraction patterns and X-ray absorption spectroscopy measurements revealed that the as milled sample was pure doped rutile. Fe dissolved into SnO2 was found in Fe2+/Fe3+ ionic valence with mainly paramagnetic behavior. After the thermal treatment all techniques indicate the formation of the ternary Sn0.36Fe2.64O4 spinel phase, which is responsible for the observed ferromagnetism.

High purity chemical etching and thermal passivation process for Ge(001) as nanostructure template

An advanced two-step cleaning process of the Ge(001) surface for nanoscience requirements is presented. First, wet-chemical etching with a variant of the Piranha solution (H(2)SO(4), H(2)O(2), H(2)O) is used to remove contaminants as well as the native oxide layer. Second, passivation of the surface is achieved by a rapid thermal oxidation step, leading to a homogeneous protective oxide layer. The thickness of the oxide layer is tuned to be thick enough to protect the surface, yet thin enough to be completely removed by thermal treatment in ultra-high vacuum. The application of this recipe results in an outstandingly clean and atomically flat surface, with carbon contamination at the detection limit of x-ray photoelectron spectroscopy. Scanning tunneling microscopy and electron diffraction reveal a long range ordered surface with typical terrace diameters of ~100 nm, suitable for the growth of atomic-scale nanostructures.

A structural study of the proton conducting B-site ordered perovskiteBa3Ca1.18Ta1.82O8.73

The proton conducting materialBa3Ca1.18Ta1.82O8.73 (BCT18) was synthesized and characterized using diffraction methodsand thermal analysis. It was shown that BCT18 is structurally similarto its niobium analogue (BCN18). At synthesis temperatures up to1500 °C however, BCT18 forms a mixture of Ca- and Ta-site ordered phases, with both1:1 type and 1:2 type ordering. The phase ratio seems to depend solely onthe synthesis conditions, with 1:1 type ordering being the dominant formin most cases. Thermal treatment in vacuum, wet and dry hydrogen, andCO2 suggests that bothforms contain defects (CaTa′′′ and ), allowing the material to absorb water andCO2. The uptake andthe release of H2O and of CO2 are all reversible, as evidenced by x-ray diffraction studies and thermal analysis, suggestingthat the molecules are present as structural defects ( and CO3O × ), rather than surface species or separate hydroxide or carbonate phases. Solid state 1H nuclear magnetic resonance also confirms the presence of protons, and the peak broadeningsuggests that they are mobile at room temperature.

Impurity and phase compositions of the surface of Cd x Hg1−x Te solid solutions

The results of our studies of the real surface impurity and phase compositions of CdxHg1 − xTe solid solutions and changes in the compositions induced by thermal evacuation and ion bombardment are presented. The impurity and phase compositions of the surface of CdHgTe solid solutions exposed to air included the gases and vapors (CO, O2, H2O) and hydrocarbons adsorbed from the atmosphere. Thermal vacuum treatment of the samples at 615 K led to surface purification from organic impurities, oxygen, water, and mercury microinclusions. The CdxHg1 − xTe sample surface was completely cleaned and its stoichiometric composition achieved by ion etching to a depth of 100 A.

Optical properties of GaAs films deposited via pulsed ion ablation

Optical reflectance and absorbance of gallium arsenide films formed on polycrystalline corundum, quartz glass, and copper foil are investigated in the energy interval of 1.1–6.2 eV. The films have been deposited from ablation plasma induced by a high-power ion beam. The exponential and interband absorbance spectra of the material of films are determined by defects in the GaAs crystalline lattice and the intricate composition of the material with predominance of nanocrystalline inclusions in the amorphous phase. Films deposited on polycor at the plasma flame center with the use of a low-resistance target have optimal properties for application in devices of optoelectronics and solar power engineering. Thermal vacuum treatment at 300–850 K modifies the optical properties of films owing to annealing of defects and changing of the structural-phase composition of a material.

Magnetic properties of quasicrystalline Al65Cu22Fe13 powders synthesized by solid-phase diffusion

The magnetic properties of quasicrystalline Al65Cu22Fe13 powders synthesized by solid-phase diffusion as a result of thermal treatment in vacuum and in a hydrogen atmosphere have been studied. The magnetic properties of the samples synthesized in hydrogen were found to be much better than those of the samples synthesized in vacuum. It is shown that an increase in the treatment time in vacuum decreases the number of magnetic nanoclusters and elimninates the time instability of their magnetic properties (magnetic susceptibility and magnetization).

Effect of thermal treatment in vacuum on ignition of titanium compacts in hydrogen

Investigated were the dynamics of gas evolution during heat treatment of Ti powder compacts in vacuum and the parameters of Ti ignition in hydrogen. Heat treatment of Ti compacts was found to decrease the critical ignition temperature down to room-temperature values.

Undoped tin oxide thin films obtained by the sol gel technique, starting from a simple precursor solution

In this work, we report the synthesis and the structural, optical and electrical properties of undoped tin oxide thin films obtained by the sol–gel technique. The films have been prepared from a simpler precursor solution than other ones reported; it is based on stannous chloride (SnCl2·2H2O), ethanol, glycerol and triethylamine. The films are deposited on glass slide substrates and sintered at temperatures in the 300–550 °C range, in an open atmosphere. A second thermal treatment in vacuum is made in order to decrease the resistivity of the films. The X-ray diffraction patterns show the tetragonal phase of SnO2 with a small preferential orientation in the (110) plane. All films show high optical transmission (~85%) and a direct band gap value around of 3.8 eV. The minimum resistivity value, 2 × 10−1 Ohm-cm, is obtained for the films sintered at 300 and 350 °C and thermal treated in vacuum at 500 °C for 1 h. The decrease of the resistivity with the thermal treatment in vacuum is associated with an increase in the oxygen vacancies concentration.