Showing papers on "Annealing (metallurgy) published in 1991"

Magnetization process in nanocrystalline ferromagnets

Abstract: Annealing of initially amorphous FeCuNbSiB alloys at temperatures above their crystallization temperature leads to an ultrafine grain structure of α-FeSi with average grain sizes down to D ≈ 10 nm and random texture. Owing to the nanocrystalline structure the magneto-crystalline anisotropy is randomly averaged out by exchange interaction. Moreover magnetostriction decreases on crystallization owing to the formation of α-FeSi. As a consequence the material reveals excellent soft magnetic properties.

Thermal treatment studies of the photoluminescence intensity of porous silicon

Abstract: Thermal annealing studies of the photoluminescence (PL) intensity and Fourier‐transform infrared spectroscopy have been performed concurrently on porous Si. A sharp reduction in the PL intensity is observed for annealing temperatures ≳300 °C and this coincides with desorption of hydrogen from the SiH2 surface species. A brief etch in HF can restore the luminescence of the samples annealed below 400 °C. We conclude that SiH2 is essential to the visible luminescence in porous Si.

Reversion Mechanism from Deformation Induced Martensite to Austenite in Metastable Austenitic Stainless Steels.

Abstract: Reversion mechanism from deformation induced martensite (α') to austenite (γ) has been investigated in two metastable austenitic stainless steels, 15.6%Cr-9.8%Ni (the 16Cr-10Ni) and 17.6%Cr08.8%Ni (the 18Cr-9Ni) steels, by means of magnetic analysis and transmission electron microscopy. Metastable γ almost completely transforms to lath α' by 90% cold rolling, and the α' again reverts to γ during annealing at temperatures above 700 K. Deformation induced α' in the 16Cr-10Ni steel undergoes a martensitic shear reversion during heating to 923 K annealing, while that in the 18Cr-9Ni steel does a diffusional nucleation-growth reversion on 923 K annealing. Grain refining processes are greatly influenced depending on the reversion mechanism. Martensitically reversed γ has a high density of dislocations immediately after the reversion and the γ grains are refined through recovery and recrystallization process just like that taking place in a deformed γ. On the other hand, diffusionally reversed γ is characterized by the nucleation of equiaxed γ grains within the α' matrix and the γ grains gradually grow during annealing.The reversion mechanism significantly depends on the chemical compositions of steels and annealing temperature. An increase in the Ni/Cr ratio causes an increase in the Gibbs free energy change between fcc and bcc structure, leading to a fall-down of austenitizing temperature for the martensitic shear reversion. The critical driving force required for the complete martensitic shear reversion is about -500 J/mol. To obtain the critical driving force in the 18Cr-9Ni steel, it should be heated to a high temperature above 1 023 K. However, the diffusional reversion can easily occur because the martensitic shear reversion temperature is too high in the 18Cr-9Ni steel. The 16Cr-10Ni steel also undergoes the diffusional reversion when it was annealed at low temperatures below the martensitic shear reversion, 923 K.

Effect of oxygen pressure on the synthesis of YBa2Cu3O7-x thin films by post-deposition annealing

Abstract: The effect of ambient oxygen pressure on the synthesis of epitaxial YBa2Cu3O7−x films on (100) SrTiO3 substrates by post‐deposition annealing of amorphous precursor films was studied for oxygen partial pressures pO2 between 1.0 and 8.0×10−5 atm and annealing temperatures between 890 and 650 °C. A pO2−1/T diagram containing recent literature data regarding YBa2Cu3O7−x oxygen stoichiometry, phase stability, and liquid‐phase formation was compiled to provide guidance for the selection and interpretation of annealing conditions. The results evidence a strong dependency of growth properties on the oxygen pressure with enhanced c‐oriented epitaxy at lower pO2 values. A particularly interesting result is the formation of predominantly c‐oriented films at 740 °C and pO2=2.6×10−4 atm (0.2 Torr). Similar to YBa2Cu3O7−x films produced by in situ laser ablation at the same temperature and oxygen pressure, the films exhibited low ion channeling yields (χmin<0.1) and a dense (smooth) surface morphology, while critical ...

Mechanical Properties and Retained Austenite in Intercritically Heat-Treated Bainite-Transformed Steel and Their Variation with Si and Mn Additions

Abstract: Processing peculiarities and functions of alloying elements, such as Si and Mn, were studied for improving formability of steel sheets with mixed microstructures. Annealing a sheet steel with 0.2 pct C in the intercritical range produced very fine particles of retained austenite which were moderately stabilized due to C enrichment by subsequent holding in the bainite transformation range. Its strength-ductility balance is greatly superior to that of other dual-phase steels due to transformation-induced plasticity (TRIP). The holding time in the bainite transformation range varies with temperature, depending on the activation energy of C diffusion in austenite, and shifts to longer times with an increase of Si or Mn additions. The optimum cooling rate from the intercritical region is reduced with an increase of Mn content but is not influenced by Si content. Additional Mn makes the retained austenite content larger, although uniform elongation remains the same. In this case, the product of tensile strength and total elongation is increased due to an increase in the tensile strength. Contrary to Mn, Si does not affect retained austenite content but improves the uniform elongation by increasing its stability.

Tantalum‐based diffusion barriers in Si/Cu VLSI metallizations

Abstract: We have studied sputter-deposited Ta, Ta36Si14, and Ta36Si14N50 thin films as diffusion barriers between Cu overlayers and Si substrates. Electrical measurements on Si n + p shallow junction diodes demonstrate that a 180-nm-thick Ta film is not an effective diffusion barrier. For the standard test of 30-min annealing in vacuum applied in the present study, the Ta barrier fails after annealing at 500 °C. An amorphous Ta74Si26 thin film improves the performance by raising the failure temperature of a /Ta74Si26(100 nm)/Cu(500 nm) metallization to 650 °C. Unparalled results are obtained with an amorphous ternary Ta36Si14N50 thin film in the Si/Ta36Si14N50 (120 nm)/Cu(500 nm) and in the Si/TiSi2(30 nm)/Ta36SiN50 (80 nm)/Cu(500 nm) metallization that break down only after annealing at 900 °C. The failure is induced by a premature crystallization of the Ta36Si14N50 alloy (whose crystallization temperature exceeds 1000 °C) when in contact with copper.

Growth of Ge Microcrystals in SiO 2 Thin Film Matrices: A Raman and Electron Microscopic Study

Abstract: The growth of Ge microcrystals in SiO2-Ge mixture films prepared by an rf co-sputtering method was studied by Raman spectroscopy and electron microscopy. It was found that in the as-deposited films, Ge clusters about 2 nm in diameter are embedded in SiO2 matrices and they are grown to Ge microcrystals by thermal annealing. It is shown that annealing at 800°C is necessary to prepare well-grown microcrystalline samples. The microcrystalline size dependence of the Raman spectrum was investigated. The increase in the linewidth observed with decreasing the size can be well explained by the phonon confinement theory, while the downward shift of the peak frequency predicted from the theory was not observed, presumably due to the stress caused by SiO2 matrices.

Optical doping of waveguide materials by MeV Er implantation

Abstract: Implantation of MeV erbium ions into micron‐thick silica and phosphosilicate glass films and 1200‐A‐thick Si3N4 films is studied with the aim of incorporating the rare‐earth dopant on an optically active site in the network. Implantation energies and fluences range from 500 keV to 3.5 MeV and 3.8×1015 to 9.0×1016 ions/cm2. After proper thermal annealing, all implanted films show an intense and sharply peaked photoluminescence spectrum centered around λ = 1.54 μm. The fluorescence lifetime ranges from 6 to 15 ms for the silica‐based glasses, depending on annealing treatment and Er concentration. Silicon nitride films show lower lifetimes, in the range <0.2–7 ms. Annealing characteristics of all materials are interpreted in terms of annealing of ion‐induced network defects. These defects are identified using photoluminescence spectroscopy at 4.2 K. Concentration quenching, diffusion and precipitation behavior of Er is also studied.

Diffusion of boron in silicon during post-implantation annealing

Abstract: The diffusion of B implanted in Si has been investigated at different concentrations in a wide range of experimental conditions (temperature from 800 to 1000 °C and time from 10 s to 8 h) by using furnace and rapid thermal treatments. In particular, the transient enhanced diffusion induced by the implantation damage in the early phase of the annealing and the precipitation occurring in concomitance with the diffusion for dopant concentration exceeding the solid solubility have been extensively analyzed. A simulation program taking these phenomena into account has been developed by modifying the supreme iii code. A satisfactory agreement with experimental data has been obtained for all the investigated conditions. The model represents a significative improvement of the diffusion simulation of B implanted in crystalline Si. In fact, the more commonly used codes of process simulation do not evaluate adequately the effects of the above considered phenomena.

Magnetic properties of FeCuMSiB (M = Cr, V, Mo, Nb, Ta, W) alloys

Abstract: Magnetic properties, microstructures and formed phases of nanocrystalline alloys prepared by annealing iron-based amorphous alloys added Cu and M (Cr, V, Mo, Nb, Ta, W) were investigated. Nb, No, Ta, W addition is very effective to improve soft magnetic properties. Especially, Nb is the most effective element to improve the soft magnetic properties. The order of the effect of decreasing the grain size is: Nb = Ta > Mo = W > V > Cr and is similar to that of the sofr magnetic properties.

Optimal Chemical Composition in Fe-Cr-Ni Alloys for Ultra Grain Refining by Reversion from Deformation Induced Martensite.

Abstract: A thermomechanical treatment, which applies reversion from deformation induced martensite (α') to ultra grain refining of austenite (γ), was proposed for metastable austenitic stainless steels. To determine optimal steels for the treatment, the effect of chamical composition on the γ-α' transformation behavior during cold rolling and the α'-γ reversion behavior by successive annealing was investigated in Fe-Cr-Ni ternary alloys. An ultra fine γ grain structure was obtained when steels satisfied the following three compositional conditions:(1) Metastable γ should be almost completely transformed to α' during cold rolling at room temperature. The amount of α' induced by 90% cold rolling can be estimated by the Ni equivalent (Ni+0.35Cr). For steels with the Ni equivalent of less than 16.0 mass%, over 90 vol% of γ transforms to α' during 90% cold rolling at room temperature.(2) Most of deformation induced α' must revert to γ again at relatively low temperatures where grain growth is difficult to occur. When the Cr equivalent (Cr-1.2Ni) is less than 4.0 mass%, most α' induced by the 90% cold rolling reverts to γ through 873K-0.6ks annealing. Retained α' is less than 10 vol%.(3) The Ms temperature of the reversed γ obtained through 873K-0.6ks annealing should be below room temperature. When the Ni equivalent (Ni+0.65Cr) of steels is more than 19.7 mass%, the reversed γ is stable at room temperature. For the Fe-Cr-Ni ternary alloys which satisfy these three conditions, an ultra fine γ grain structure might be obtained through the reversion from deformation induced α'. For example, γ grains of 0.5μm were observed in a 15.5%Cr-10%Ni steel which was subjected to 90% cold rolling and subsequent 873K-0.6ks annealing.

Epitaxial Growth of SrTiO3 Films on Si(100) Substrates Using a Focused Electron Beam Evaporation Method

Abstract: A novel epitaxial growth method of SrTiO3 films on Si(100) substrates is presented in which, in order to reduce the surface oxide layers of the substrates, thin Sr layers are deposited prior to deposition of SrTiO3 films. It has been shown that the film composition becomes nearly stoichiometric when single-crystalline SrTiO3 sources are evaporated by a focused electron beam and that SrTiO3 films grow epitaxially on Si(100) substrates under the optimum conditions of the Sr layer thickness, deposition temperature, and annealing temperature.

Oxidation and reduction of copper oxide thin films

Abstract: We have employed 16O(α,α)16O oxygen resonance measurement and transmission electron microscopy to study the oxidation and reduction of copper oxide thin films. The in‐ and out‐diffusion of oxygen‐induced oxygen concentration variations and microstructural changes in the films were monitored. The study of reduction was carried out by annealing CuO and Cu4O3thin films in vacuum. Dark‐field microscopic images show that isolated and large Cu2O grains emerge from the small CuO and Cu4O3 grain matrices. The growth of Cu2O grains in both CuO and Cu4O3 matrices has been measured to be linear with time, and have activation energies 1.1 and 0.7 eV, respectively. The main controlling mechanism to the discontinuous morphology of the Cu2O grain growth is the migration of the phase boundaries between the oxides induced by oxygen out‐diffusion along the moving boundary. An oxygen in‐diffusion study was performed by annealingCu2O and Cu4O3 in an oxygen ambient. The CuO phase nucleates randomly and rapidly in both Cu2O and Cu4O3 matrices. The small grain growth rate of CuO suggests that nucleation rather than grain growth is the predominant event during oxidation. The kinetics study of the reduction and oxidation of copper oxides shows that the two processes are asymmetrical and the latter is faster.

Enlargement of Poly-Si Film Grain Size by Excimer Laser Annealing and Its Application to High-Performance Poly-Si Thin Film Transistor

Abstract: By both numerical simulation and experimental investigation, we found it possible to enlarge the grain size (?3000 ?) of polycrystalline silicon (poly-Si) films by excimer laser annealing, using a new method to control the solidification process of molten Si - low-temperature (?400?C) substrate heating during laser annealing. Poly-Si thin-film transistors (TFTs) fabricated by this new excimer laser annealing method showed a high field-effect mobility of 230 cm2/V?s, and good uniformity of field-effect mobility (?10%) within the effective laser irradiation area.

Effects of Silicon and Manganese Addition on Mechanical Properties of High-strength Hot-rolled Sheet Steel Containing Retained Austenite

Abstract: An 80 kgf/mm2 grade high-strength hot rolled sheet steel with a significantly high product of tensile strength and total elongation (TS×EI=3 000) has been developed by utilizing transformation-induced plasticity of retained austenite in 0.2% carbon sheet steels by optimizing the silicon and manganese content and hot rolling conditions. Finish rolling temperature and coiling temperature are important factors in terms of introducing a large amount of retained austenite. Silicon addition over 1.0% results in a significant increase in the volume fraction of retained austenite due to the change in second phase from bainite+pearlite to bainitic ferrite. The maximum volume fraction of retained austenite and the consequential optimum combination of tensile strength and ductility is obtained in a 0.2%C-2.0%Si-1.5%Mn steel. The effect of retained austenite on ductility becomes small with further addition of manganese over 1.5%, because the retained austenite transforms in the early stage of the straining process due to the presence of martensite.

Granular cobalt in a metallic matrix

Abstract: Ultrafine face‐centered‐cubic Co particles in a conducting Cu matrix have been produced by annealing of sputtered metastable CoxCu1−x alloy films (0.10≤x≤0.80). The average size of the particles, and therefore the magnetic properties of these materials, can be easily controlled by the processing parameters. Single‐domain behavior results in coercivities in excess of 600 Oe, while the magnetization is determined by the choice of alloy composition. The evolution of the structural and magnetic properties have been studied as a function of annealing conditions, and are compared to those previously observed with Fe‐based materials.

Grain Growth in Microwave‐Annealed Alumina

Abstract: Normal grain growth in dense, fine-grained, aluminum oxide-0.1 wt% MgO was studied under both conventional furnace and 28-GHz microwave furnace annealing conditions. The microstructural changes that occurred were the same for both sets of samples; soap bubble microstructures were observed and the aspect ratios and shape factors did not change during the anneals. The kinetics of grain growth were greatly increased by the 28-GHz microwave anneals; e.g., the grain growth rate at 1500°C in the microwave furnace was the same as the rate at 1700°C in the conventional furnace. Also, the activation energy for grain growth was reduced by the microwave anneal from 590 kJ/mol (conventional) to 480 kJ/mol (microwave). Finally, these results demonstrate that a “microwave effect” can exist in a dense ceramic body and that no free pore-solid interfaces are necessary.

Activation energy for electromigration in Cu films

Abstract: Copper is a possible substitute for Al in very large scale integration interconnects because of its higher resistance to electromigration damage (EMD) and its lower electrical resistivity. In the present work, we report on electrical resistance measurements of the activation energy for EMD in Cu films as determined by an isothermal annealing method carried out under high vacuum conditions. Temperature measurement and control were accomplished by means of a Cu thin‐film thermistor. The activation energy for EMD of evaporated Cu films was found to be 0.79±0.02 eV.

Low‐temperature metalorganic chemical vapor deposition of InP on Si(001)

Abstract: We report successful growth of antiphase domain‐free InP on Si(001) without any preannealing of the Si substrate using low‐pressure metalorganic chemical vapor deposition in contrast to present belief that high‐temperature substrate annealing prior to growth is imperative to achieve this goal. Optimized crystallographic and optical properties are obtained for an offcut along [110] of 4°±0.4°, an InP buffer layer temperature of 400 °C±10 °C, a layer deposition temperature of 640 °C, and low growth rates r≤2.7 μm/h.

A novel preparation technique for preparing hydrogenated amorphous silicon with a more rigid and stable Si network

Abstract: A novel preparation technique, termed ‘‘chemical annealing,’’ was developed with the aim of making a stable and rigid Si network structure. The hydrogen content (CH) in the films and the optical gap could be reduced gradually without any change in substrate temperature by alternating deposition of a hydrogenated amorphous silicon layer several tens of A thick and treatment with atomic hydrogen. These films showed CH of 1.5–10 at. %, and exhibited high photoconductivities in the level of 10−5–10−4 S/cm. In the films with CH of 3 at. % or less, in particular, improvement was observed in stability against illumination with light. Their photoconductivity remained at about 65% of the initial value even after illumination with white light (AM1, 100 mW) for 60 h. In addition, time‐of‐flight experiments revealed a significant enhancement in hole drift mobility to a value of 0.2 cm2/V s at 300 K.

Influence of C Content and Annealing Temperature on Microstructure and Mechanical Properties of 400°C Transformed Steel Containing Retained Austenite

Abstract: In order to evaluate the influence of C content and annealing temperature on the mechanical properties of steels containing retained austenite, cold-rolled sheets containing 0.12 to 0.4 C, 1.2 Si, and 1.5 Mn have been intercritically annealed and isothermally transformed at 400°C. Annealing near AC1 temperature followed by the 400°C isothermal transformation for 100 to 300 sec results in the best combination of strength and ductility. The ultimate tensile strength ranges from 590 Mpa in the 0.12 C steel to 980 Mpa in the 0.4 C steel. The total elongation varies 39 to 33%, and is ranked well above that of conventional ferrite-martensite dual-phase steels at the comparable strength. Amounts of retained austenite in these specimens are 7 to 20% and linearly related to the C contents of the steel. Mechanical stability of the retained austenite is fairly improved compared to that found in conventional dual-phase steels, and enhances the ductility at high strength. Better combinations of strength and ductility are maintained even in the lower C steels due to the contribution of an increased amount of highly ductile ferrite.

Ion beam synthesis of buried α-FeSi2 and β-FeSi2 layers

Abstract: Using high dose implantation of Fe+ into (111)Si, followed by rapid thermal annealing (RTA) at 1150 °C for 10 s, we fabricated continuous buried layers of the metallic α‐FeSi2 phase. Rutherford backscattering experiments indicate that these layers contain a large number of Fe vacancies, up to 18%. By implanting through a SiO2 mask, we produced Schottky diodes with idealty factors of 1.4±0.1 and a Schottky barrier height of ΦB=0.84±0.03 eV on (111) n‐Si. In this letter we report for the first time the formation of the semiconducting stoichiometric FeSi2 (β‐FeSi2) phase by annealing the buried α‐FeSi2 layers below the phase transition temperature of 937 °C; specifically at 750 °C for 20 h.

Manufacture of p-type gallium nitride based compound semiconductor

Abstract: PURPOSE: To provide a method for manufacturing a p-type gallium nitride based compound semiconductor, by which a gallium nitride based compound semiconductor doped with a p-type impurity is made a p-type semiconductor having a low resistance and further, the value of the resistance is made uniform over the whole of its wafer independently of its film thickness and moreover, a light emitting element made of the compound semiconductor can have a double or single hetero-structure. CONSTITUTION: By a vapor growth method, a gallium nitride based compound semiconductor layer doped with a p-type impurity is formed, and thereafter, its annealing is performed at a temperature not lower than 400°C. However, it is more preferable that the annealing is performed in a pressurized atmosphere or performed by providing newly a cap layer on the gallium nitride based compound semiconductor. COPYRIGHT: (C)1993,JPO&Japio

Substrate temperature dependence of arsenic precipitate formation in AlGaAs and GaAs

Abstract: GaAs epilayers which are grown by molecular‐beam epitaxy under ‘‘normal’’ group III–V fluxes but at very low substrate temperatures contain as much as 1% excess arsenic. Upon annealing these epilayers at a temperature of 600 °C, the excess arsenic forms precipitates. We have undertaken a systematic study of the substrate growth temperature dependence of this incorporation of excess arsenic in both GaAs and Al0.3Ga0.7As epilayers. The substrate growth temperature was varied in increments of 25 °C from 225 to 375 °C after every 0.25 μm of film growth for a GaAs and an Al0.3Ga0.7As epilayer. Both epilayers were grown using a dimer arsenic source and a group V to total group III beam equivalent pressure ∼20. After growth the films were annealed for 1 h in the As2 flux at a temperature of 600 °C. Cross‐sectional samples were than prepared by the ion thinning technique and examined by transmission electron microscopy (TEM). Both epilayers contained arsenic precipitates; this is the first observation of arsenic ...

Low Core Loss of a bcc Fe86Zr7B6Cu1 Alloy with Nanoscale Grain Size

Abstract: We have investigated the possible applications potential of a newly developed bcc-nanocrystalline Fe 86 Zr 7 B 6 Cu 1 alloy by determining the core loss, permeability μ c , and magnetization B 800 (at a field 800 kA/m). The above parameters have been studied as a function of annealing temperature T a of the as-quenched amorphous alloy, maximum induction B m , and frequency (up to 100 kHz)