Isothermal Annealing In Vacuum Research Articles

Annealing effect of Ca3TaGa3Si2O14 catangasite crystals on their optical activity

The spectral dependences of transmission and absorption in the wavelength range of 200–2500 nm were measured for Ca3TaGa3Si2O14 crystals cut perpendicular to the optical axis in the initial state (without annealing) and after isothermal annealing in vacuum and in air. It was found that annealing in vacuum leads to a decrease, and annealing in air leads to an increase in the intensity of absorption bands. A spectrophotometric method for measuring and calculating the specific rotation angle ρ of the plane of polarization of light in gyrotropic crystals from the transmission coefficient spectra at different angles between the polarizer and the analyzer is considered. The transmission spectra were normalized in order to eliminate shifts in the spectra associated with measurement features. Spectral dependences of the values of ρ for all three samples, which are approximated by the extended Drude formula, are obtained; the influence of the annealing atmosphere on the values of the coefficients of this formula is established.

Effect of isothermal annealing on the optical properties of Ca<sub>3</sub>TaGa<sub>3</sub>Si<sub>2</sub>O<sub>14</sub> crystals

The effect of post-growth isothermal annealing in vacuum and in air on the optical properties of Ca3TaGa3Si2O14 crystal samples of Z and X-cuts has been studied. Spectral dependences of transmission coefficients were measured in the wavelength range (240–700) nm taking into account anisotropy and dichroism. On the Z-cut samples in the initial state an absorption band at λ = 360 nm in the ultraviolet range is observed, in the visible region – two absorption bands at λ = 460 nm and λ = 605 nm. Additionally, a band at λ = 290 nm was observed on the X-cut samples. When the sample was rotated around the direction of the light beam by 90 degrees, a change in the intensity of the absorption bands was observed. Annealing in vacuum leads to a decrease in the intensity of the absorption bands in the near ultraviolet and visible range, except for the absorption band at λ = 605 nm. Annealing in air leads to the opposite effect – an increase in the intensity of the absorption bands, except for the band λ = 605 nm. The value of the anomalous birefringence of the samples was estimated by the Mallard method. The degree of linear dichroism is calculated. It is shown that the degree of dichroism decreases as a result of annealing in vacuum, and increases during annealing in air.

Исследование эволюции структурно-фазового состояния образцов сплава W – Сu в графитовой оболочке в процессе вакуумных отжигов и воздействия высокотемпературной плазмы

The change in porosity during isothermal vacuum annealing of the pseudo alloy W – 18 wt. % Cu obtained by powder metallurgy methods in the temperature range of 800 – 1200 °C and the resistance to oxidation under the action of high-temperature plasma of the outer surface of a hybrid laboratory structure, consisting of two composite elements made of dissimilar materials: graphite and alloy W – 18 wt. % Cu. The process of evolution of the microstructure controlled by diffusion along the internal interfaces (grain and subgrain boundaries) of copper atoms from copper particles located on these surfaces in the near-surface layers of the sample has been studied.

A model of interdiffusion occurring during the formation of thin metal films on single-crystal silicon under conditions of limited solubility of the components

Thin metal films are used in semiconductor and microelectronic devices to form ohmic and non-ohmic contacts to singlecrystal silicon. A common feature of the used Ме–Si systems is the low mutual solubility of elements and the polycrystalline nature of metal films. Solid-phase interactions during the deposition of metals on single-crystal silicon and the subsequent vacuum annealing results in the redistribution of the elements near the Me/Si interface. An important task facing the material science of solid-state electronics is to develop a mechanism of solid-phase interaction of metal thin films and single-crystal silicon. The aim of our study – was to develop a quantitative model of interdiffusion in the Ме–Si system under conditions of limited solubility of the components. The article suggests a mechanism of formation of Me–Si systems based on the diffusion and segregation of silicon near the intergrain boundaries of the metal and the limited formation of complexes during the diffusion-induced penetration of metal into silicon. The article suggests a model of reactive interdiffusion in thin metal film – single-crystal silicon systems under conditions of limited solubility of the components. Mathematical modelling was used to study the interaction of magnetron-sputtered metals Ti, W, and Nb with single-crystal silicon during isothermal vacuum annealing. The numerical analysis of experimental distributions of concentrations of Me and Si obtained by Rutherford backscattering spectroscopy allowed us to determine their individual diffusion coefficients in Me-Si systems. The model can be used for empirical studies of the redistribution of the elements of two-layer systems with limited solubility, as well as to forecast the technological conditions for the production of electronic devices.

STRUCTURAL-PHASE TRANSFORMATIONS IN MAGNETRON DEPOSITED FILMS OF Ti-Zr-Ni SYSTEMS DURING ANNEALING IN VACUUM

Structural and phase changes in thin films obtained by magnetron sputtering of a target with the composition Ti41Zr38.3Ni20.7 (at.%) were studied under isothermal vacuum annealing in the temperature range from 400 to 800 C. The boundaries of the thermal stability of the phases have been determined. Coatings consisting of a single icosahedral quasicrystalline phase, as well as films consisting of the 2/1 crystal-approximant phase were obtained. The features of the phase transformation of a quasicrystal into an approximant crystal were investigated, and the activation energy of this transformation was determined at a level of 94 kJ/mol. The dependence of the degree of phase transformation on the temperature and duration of annealing has been established.

High-strength carbon nanotube fibers with near 100% purity acquired via isothermal vacuum annealing

The Fe and carbonaceous particles are the main impurities in a carbon nanotube fiber (CNTF) fabricated by the floating catalyst chemical vapor deposition (FCCVD) method, which have an adverse effect on various applications, leading to strong demand for purification process to obtain high-purity CNTFs. However, the commonly used purification methods combining oxidation and acid refluxing cannot remove the impurities thoroughly, and will introduce undesired damage onto CNT wall at the same time. Herein, we propose an efficient purification strategy involving an isothermal annealing process under high vacuum to achieve mass preparation of CNTFs with high purity and mechanical/electrical properties. The Fe and carbonaceous impurities can be almost completely removed after vacuum annealing at 1800 °C. The purified CNTFs exhibit enhanced oxidation resistance due to the removal of Fe catalyst particles. The diffusion and evaporation of Fe atoms are most likely responsible for the removal of Fe particles enclosed with graphitic shells. The purified CNTF shows a high specific tensile strength of 1.82 ± 0.04 N/tex due to the high alignment of the CNT bundles within fibers, which can retain 80% of the value for pristine CNTF. The purified CNTF exhibits similar trends of electrical conductivity as the specific tensile strength and has a high conductivity of 3.65 ± 0.11 × 105 S/m. The large-scale preparation of high-purity CNTFs with high-performance will promote the real application of CNTFs.

Interdiffusion and phase formation in the Fe–TiO2 thin-film system

The interaction of magnetron-sputtered metal iron with titanium-oxide films upon isothermal vacuum annealing is studied by X-ray phase analysis, secondary-ion mass spectrometry, atomic-force microscopy, and mathematical simulation. A mechanism for the formation of complex oxides at grain boundaries is suggested. The mechanism is based on the reaction diffusion of metal iron into titanium oxide. A quantitative model of reaction interdiffusion in two-layer polycrystalline metal–oxide film systems with limited component solubility is developed. From numerical analysis of the experimental distributions of the metal concentrations in the Fe–TiO2 film system, the individual diffusion coefficients are determined. It is found that, under the conditions of vacuum annealing at 1073 K, the diffusion coefficients of iron and titanium are 8.0 × 10–13 and 3.0 × 10–15 cm2 s–1, respectively.

Study of iodine diffusion in silicon carbide

Diffusion of iodine in 6H-SiC and polycrystalline CVD-SiC was investigated using Rutherford backscattering spectroscopy and electron microscopy. A fluence of 1 × 10 16 cm −2 of 127I + was implanted with an energy of 360 keV at room temperature, producing an amorphous surface layer of approximately 220 nm thickness. The implantation profile reached an atomic density of approximately 1.3% at the projected range of about 95 nm. Broadening of the implantation profile and iodine loss through the front surface during isochronal and isothermal vacuum annealing was determined. At a temperature of 1100 °C no iodine loss was observed after 120 h and a diffusion coefficient of less than 10 −21 m 2 s −1 was extracted from the analysis of profile widths. Relatively strong broadening occurred after 60 h annealing at 1200 °C with the iodine profile extending beyond 300 nm into the bulk, accompanied by a surprisingly modest iodine loss through the surface. Electron microscopic studies reveal a drastic restructuring of the surface region at this temperature, indicating possible chemical reactions between iodine and silicon carbide.

Surface properties of Fe76Mo8Cu1B15 alloy after annealing

NANOPERM-type alloy Fe76Mo8Cu1B15 is investigated in amorphous and in partially crystallized state. Samples were prepared by 1 h isothermal annealing in vacuum at temperatures ranging from 330°C up to 700°C. Bulk and surface microstructural characteristics were studied using transmission and conversion electron Mossbauer effect techniques, respectively. Surface features were checked by the help of atomic force microscopy. Presence of nanocrystalline bcc-Fe phase was detected during the first crystallization stage. The crystallization process starts at 450°C and it is more pronounced in surface regions than in the bulk. With progressing crystallization, hyperfine parameters especially of the amorphous residual phase are altered. Distinctions in surface morphology are revealed between wheel and air side of the ribbon-shaped samples.

Effect of Sublimation in Vacuum Annealing on the Limit of Elasticity of Nonferrous Alloys

Results of analytical and experimental studies of the effect of annealing in vacuum on the limit of elasticity of nonferrous alloys are presented. Vacuum annealing changes the chemical composition of the surface layers due to sublimation of the highly volatile component of the alloy, which leads to a decrease in its limit of elasticity due to the accumulation of crystal structure defects. An empirical equation is suggested for predicting the variation of the limit of elasticity of heterophase alloys as a function of the duration of isothermal annealing in vacuum. The results obtained by solving this equation agree satisfactorily with experimental data.

Self-diffusion of iron in amorphous iron nitride

The measurement of self-diffusion of iron in amorphous ${\mathrm{FeN}}_{0.7}$ using secondary-ion mass spectroscopy is reported. Diffusion broadening of tracer layers of ${}^{57}{\mathrm{FeN}}_{0.7}$ was observed after isothermal vacuum annealing of the films at different temperatures. Strong structural relaxation effects on diffusion coefficient were observed below crystallization temperature of the amorphous phase. In the well-relaxed state, the values of preexponential factor ${D}_{0}$ and activation energy q are given by $\mathrm{ln}{D}_{0}=\ensuremath{-}16.6\ifmmode\pm\else\textpm\fi{}2{\mathrm{m}}^{2}/\mathrm{s}$ and $q=1.3\ifmmode\pm\else\textpm\fi{}0.2\mathrm{eV}.$ On the basis of correlation between $\mathrm{ln}{D}_{0}$ and q, it is suggested that the mechanism of self-diffusion of iron in amorphous iron nitride is very similar to that in metallic glasses.

Effect of hydrogen treatment on structure and phase state and hydrogen permeability of low-activation 10Cr12Mn20W and 10Cr9WVA steels

Phase composition, hydrogen diffusion parameters (permeability, solubility, and diffusion coefficient) and electro-physical properties of low-activation 10Cr12Mn20W and 10Cr9WVA steels were studied in 673–1173 K temperature range in the initial normalized state and after isothermal annealing in vacuum and hydrogen under 873 K for 600 h. It is shown that thermal treatment decreases hydrogen permeability in 10Cr12Mn20W steel and increases it in 10Cr9WVA steel. Hydrogen flux in 10Cr9WVA ferritic/martensitic steel increases due to hydrogen decarbonization, this agrees with electrical and magnetic property changes under hydrogen treatment. Permeability of tritium through the analyzed steels is estimated and compared with the values for 2.25Cr–1Mo, 9Cr–1Mo and 316 steels.

Correlation between Hall effect, structural relaxation and magnetoelastic coupling in Fe 81B 13Si 4C 2 amorphous alloy

The expected high positive value of the extraordinary Hall coefficient R s in a ferromagnetic alloy was confirmed in the amorphous system Fe 81B 13Si 4C 2. At the same time the increase of R s produced by the thermal structural relaxation was experimentally verified by means of Hall potential measurements in Fe 81B 13Si 4C 2 sheets after isothermal annealing in vacuum at increasing temperatures. Moreover, a direct relaxation between magnetoelasticity and Hall conduction mechanism was demonstrated by means of the effect of a tensile stress σ on the spontaneous Hall coefficient. It was shown that R s has an appreciable increase with σ. By this result one deduces that Hall effect can be useful to measure local axial stresses.

The Influence of Obtainment Conditions of Didymium-Iron-Boron Permanent Magnets on their Structure and Properties

The structure, phase composition and properties of cast and sintered didymium-iron-boron powder alloys have been studied. It has been shown that an increase in size of the initial powder particles leads to a decrease in i H c and Br of sintered magnets (this relation is to a great extent of a quantitative character). The dependence of magnetic characteristics ( i H c and Br) on the grain size of the main R 2 Fe 14 B magnetic phase and also on its volumetric part has been shown. As determined the grain size produced an effect on coercitivity without changing the value of residual magnetism. It has been established that the chemical composition declines from an optimum one and inaccurate observance of technical regimes leads to the lowering of magnetic properties of sintered magnets. The properties of structure-phase transformations in didymium-iron-boron alloys under isothermal annealing in vacuum have been investigated in order to establish a link between their structure and properties.

Stress Evolution During Crystallization and Isothermal Annealing of Titanium-Nickel on (100) Si

ABSTRACTThin films of near-equiatomic titanium-nickel are capable of thermally induced shape-strains and have recently been applied to silicon-based micromachined reversible actuators in force-production devices requiring energy-density levels substantially exceeding those available from piezoelectric, electromagnetic, electrostatic, or bimetal systems. Reversible actuation requires the presence of a resetting agent, or ‘bias’ force, capable of deforming the martensite phase during the exothermic transformation on cooling. Here, we show that both the initial martensite ‘programming’ force, and the bias force for subsequent reversible actuation, can readily be provided by manipulating intrinsic and extrinsic stresses developed during low-pressure sputter deposition of TiNi, and subsequent cooldown from either the deposition process temperature or from the crystallization annealing temperature. The stability of both intrinsic and extrinsic stresses at temperatures below the deposition temperature allows considerable flexibility in the design of the force-producing system, and reversible stress-production to levels beyond 0.7 GPa are shown to be readily achieved, corresponding to energy-density levels approaching 10 MJ-m−2. The present paper will review recent results from our group on the development of residual stresses in TiNi sputtered on (100) Si, using the wafer-curvature method applied during isochronal and isothermal vacuum annealing of both amorphous and crystalline thin films, with an emphasis on the combined influence of deposition temperature and annealing temperature on stress-relaxation rates, and on the response of the system to temperature cycling in the displacive transformation range.

Multiple free energies of activation of the chain oxygen atoms in the YBa2Cu3O7??

The desorption kinetics of the chain oxygen atoms in the YBa2Cu3O7−δ (YBCO) superconductor were studied using isothermal vacuum annealing (VA). The number of the O(1) atoms per unit cell in the crystal was measured at three temperatures of 390, 415, and 450°C for various annealing times. From these measurements it was found that at high temperatures the loss of the O(1) atoms from the YBCO is very rapid, and so, low annealing temperatures must be used in order to see the fine details of the desorption phenomena. When the log of the instantaneous O(1) occupancy vs. time was plotted, three distinct linear segments were obtained for each temperature. This, I think is an indication of the existence of multiple desorption processes. From the slopes of these lines, I have evaluated three free energies of activation to be 1.14(6), 1.45(3), and 1.91(13) eV. These results are explained in terms of oxygen ordering in the chains.

Anomalous properties of oxygen-deficient YBa 2Cu 3O 7−δ

A simple technique is described for the control and determination of the oxygen stoichiometry between 6.95–5.83 of pure deoxygenated YBa 2Cu 3O 7−δ (YBCO). By studying samples prepared using this method, two anomalous properties, namely (1) the step-like increase of the c-axis length of the crystal unit cell, and (2) the changes of the superconducting (SC) transition temperature, T c, clearly showing the presence of two familiar plateaus as oxygen is gradually removed from YBCO have been reproduced. These two properties, first observed by Cava et al. by a Zr gettering technique thus appear to be inherent to pure YBCO. In addition, it is also found that the crystal structure of YBCO does not break down for an oxygen stoichiometry as low as 5.83. The extra (0.17) O atom per unit cell difference between 6.0 and 5.83 is believed to be lost from the O(4) sites. The technique adopted in this study which involves isothermal vacuum annealing (VA) can, therefore, be used as an alternative to the Zr gettering method for tuning various amounts of oxygen per unit cell in YBCO.

Time Resolved X-Ray Diffraction Study of the Transformation Kinetics of TiSi2-C49 in Amorphous Si/Ti Multilayers

ABSTRACTAmorphous Si/Ti multilayers transform at high temperatures (above 700°C) to TiSi2-C54. This phase is important for microelectronics applications because of its low resistivity, stability up to 900°C, and compatibility with silicon processing. However, an unfavorable metastable TiSi2-C49 phase is usually formed at lower temperatures. Thus, an understanding of the C49 phase formation kinetics is useful to the device processing strategy. The kinetics of the transformation of TiSi2-C49 phase can be characterized as a process of nucleation and growth, using the well known Johnson Mehl Avrami (JMA) equation. In the present work the formation kinetics of the C49 phase has been studied by an in situ x-ray diffraction technique. Isothermal annealing in vacuum was done at four temperatures, in the range of 275"C to 310°C. A position sensitive detector (PSD) was used to simultaneously collect the diffracted beams of (131) and (150) peaks of the C49 phase. From the data, the Avrami exponent, n, was determined to be 2.0±0.1. The reaction rate constant k follows a familiar Arrhenius-type equation with a measured activation energy of 2.5eV. Comparison of our x-ray results with kinetic data obtained by other means will be discussed.

Crystallized amorphous silicon for low-cost solar cells

Abstract Hydrogenated amorphous silicon (a-Si:H), 1–10 μm thick, was deposited onto stainless steel and molybdenum sheets using catholic d.c. glow discharge in a gradient field and by plasma-enhanced chemical vapor deposition. The films were subsequently crystallized by isothermal heating in N2, rapid thermal processing, isothermal annealing in vacuum (IAV) or isothermal annealing after vycor encapsulation (IAE). All techniques led to crystallization as revealed by X-ray diffraction. Annealing by IAV at 1000 °C for 7 h or IAE at 700 °C for 8 h gave the most intense (111) silicon diffraction peaks. Auger electron spectroscopy showed significant diffusion of iron into the silicon for stainless steel substrates. Energy recoil detection of as-deposited a-Si:H showed good uniformity of both silicon and hydrogen.