Crystallization kinetics of SbxSe100−x thin films

The crystallization kinetics in Sb_xSe_100−x films with 39≤x≤58is studied by monitoring the optical transmission of the films during both isothermal and constant rate heatings. The structure of the films upon crystallization and at certain intermediate stages is studied by electron microscopy techniques. The results are analyzed in the frame of the Johnson-Mehl-Avrami theory in order to determine the kinetic parameters (Avrami exponent, activation energy and frequency factor) in addition to the crystallization temperature. The results show that film crystallization is always preceeded by a relaxation process which modifies substantially the optical properties of the amorphous material. Amorphous films with compositions close to the stoichiometric compound (Sb₂Se₃) are found to show the highest activation energy for crystallization.     

Interactions of hydrogen in copper studied by internal friction technique

Internal friction (IF) in electrochemically hydrogen-charged copper was studied in the temperature range of 80–500 K. A distinct peak of relaxation caused by hydrogen was observed in the vicinity of 130 K at the frequency of about 1 Hz. The observed peak has an enthalpy and pre-exponential factor of relaxation 0.28 eV and 4.6×10⁻¹³ s, respectively. Effects of copper microstructure and oxygen content on the hydrogen internal friction peak in copper were studied and discussed.     

First investigations on twin-rolled Zr59Cu20Al10Ni8Ti3 bulk amorphous alloy by mechanical spectroscopy

Zr₅₉Cu₂₀Al₁₀Ni₈Ti₃ is one among compositions of ZrCu-based alloys giving bulk amorphous material by cooling from the melt. Twin-roll casting enabling samples suitable for our inverted torsion pendulum has been processed in strips of about 0.60 mm thick.

Low temperature IF measurements have been conducted on a specimen from room temperature to −120 °C at different heating and cooling rates. IF spectra exhibit peaks at around −40 °C (cooling) and −10 °C (heating) which are sensitive to heating rates and to the number of cycle (heating and cooling). DSC measurements have also been performed to help interpret the phenomena linked to the IF peaks.     

High-temperature internal friction on TiAl intermetallics

In order to study the microscopic mechanisms controlling the plastic deformation at high temperature of two γ-TiAl alloys with nominal compositions: Ti–46.5Al–4(Cr, Nb, Ta, B) and Ti–45Al–(5–10)Nb (in at.%), internal friction (IF) measurements have been performed. A subresonant torsion pendulum has been used working in two different modes; changing the temperature between 300 and 1200 K at a constant frequency, and varying the frequency between 0.001 and 10 Hz at a fixed temperature. The resulting mechanical spectra show an anelastic relaxation peak at about 1060 K at 1 Hz in one of the alloys and a high-temperature background in both of them. Activation parameters of the loss peak have been calculated and an activation enthalpy of about 3.8 eV is obtained. The characteristics and a possible responsible mechanism for this relaxation peak are discussed.     

Spectroscopic and structural characterisation of a VOx (x≈1) ultrathin epitaxial film on Pt (111)

VO_x ultrathin epitaxial films (0.8≤x≤1.3), grown on Pt(111) by evaporating vanadium in a controlled water background (1×10⁻⁷ Pa), have been chemically characterised by X-ray photoelectron spectroscopy (XPS) and X-ray-excited Auger electron spectroscopy (AES), which confirm the presence of V(II). The VO film shows a NaCl-type structure exposing the (111) plane, as proven by XPD. Multiple scattering calculations are compatible with an O-terminated surface and a surface relaxation of the outermost atomic layers, which leads to a V---O bond length contraction amounting to 7%.     

Hydriding effects on negative cell electrode

Internal friction (IF) and modulus measurements have been carried out on a composite material taken from the negative electrode of a commercial Ni–metal-hydride (Ni–MH) battery, both in the as-received condition and after in situ gaseous hydrogen exposure, using a sub-resonant torsion pendulum at fixed frequencies between 0.1 and 10 Hz in the temperature range 90–450 K. In both cases the IF spectrum is composed by two peaks: P1 at 190 K and P2 at 290 K, with corresponding modulus variations. The P1 data are detected to be due to a thermally activated process which frequency shift activation energy is (0.175±0.004) eV and fitted to a relaxation peak with a larger wide respect to a Debye peak, being β equal to 2.2. It is interpreted to be due to the movement of misfit dislocations within the AB₅ intermetallic-type alloy particles in the presence of nearby H atoms, acting as a Cottrell atmosphere. Peak P2 is ascribed to the decomposition and formation of hydride phase in the alloy particles upon heating and cooling, respectively. The peak heights are shown to increase in the hydrided samples, supporting the above interpretation. These results are also discussed in connection with previous measurements on an electrode material prepared at the laboratory.     

Effect of La2O3 addition and O2 atmosphere on the electric properties of SnO2TiO2

The electric properties of (Sn, Ti)O₂ doped with 1.00 mol% CoO, 0.05 mol% Nb₂O₅ and x mol% La₂O₃ (0.25≤x≤1.00) have been studied. Sn_0.25Ti_0.75Co_0.01Nb_0.005 doped with 0.50 mol% La₂O₃ has a nonlinearity coefficient of 6. An increase in the concentration of La₂O₃ raised its resistivity, thereby altering the electric properties of the material. A thermal treatment in oxygen atmosphere increased the nonlinearity coefficient to a value of 9.     

The effect of single-step low strain and annealing of nickel on grain boundary character

Combinations of a low tensile strain and annealing temperature have been successfully processed to double the fraction of special boundaries, Σ_sp, in commercially pure (C.P.) nickel. Processing sequence of one step of 6% strain followed by a 900 °C anneal for 10 min, has resulted a special boundary fraction (3 ≤ Σ ≤ 29) of 74.7%, compared to the as-received material of 36.5%. A large proportion of this increased in special boundaries were found to be made up of annealing twins Σ3 and its twin variants Σ3ⁿ. Deformation applied to the sample alone without heat treatment, caused the fraction of special boundaries, to decrease, the Σ_sp value falling, for example to 25.6% at 12% strain. Energy minimization processes such as grain boundary migration and grain growth were suggested as means of enhancing the formation of annealing twins.     

Photon frequency dependent electron relaxation time in noble metals: effect of voids

Optical properties of noble metals at frequencies below the interband transitions are well described by a simple Drude model of the free electron gas. However, a photon frequency dependent electron relaxation time τ(gW)⁻¹ = τ_o⁻¹ + βΩ² has been reported frequently for experimental data. Also, the parameters of the Drude model of silver were found to be influenced by fluids (H. Gugger et al., Phys. Rev. B, 30 (1984) 4189). On the other hand, thin silver films condensed on cold substrates contain a large amount of voids with elongated shape, which cause a strong absorption around λ ≈ 450 nm. Borensztein et al. (Surf. Sci., 211/212 (1989) 775) modelled this absorption band with an effective medium theory (EMT), taking into account the shape of the voids. In the present work it is shown that both the frequency-dependent relaxation time and the effects of fluids can be explained by this EMT.     

Correlations between structural and electrical properties of the oxyfluorides observed in the YOF-BiOF system

An investigation of the YOF-BiOF system at 850°C has allowed to isolate an ordered Y_0.75Bi_0.25OF phase and a Y_1−xBi_xOF solid solution (0.52 ≤ x ≤ 0.95).

For x ≤ 0.80 the structure is of fluorite-type and for 0.80 < x ≤ 0.95 it shows a fluorite derived rhombohedral distortion. Correlations between structural and electrical properties are established and compared with those of the analogous Pb_xMO S_8-y solid solution (0 ≤ x ≤ 0.80).     

Frequency dependent electrical conductivity and dielectric relaxation behavior in amorphous (90V2O5–10Bi2O3) oxide semiconductors doped with SrTiO3

We report on the experimental results of frequency dependent a.c. conductivity and dielectric constant of SrTiO₃ doped 90V₂O₅–10Bi₂O₃ semiconducting oxide glasses for wide ranges of frequency (500–10⁴ Hz) and temperature (80–400 K). These glasses show very large dielectric constants (10²–10⁴) compared with that of the pure base glass (≈10²) without SrTiO₃ and exhibit Debye-type dielectric relaxation behavior. The increase in dielectric constant is considered to be due to the formation of microcrystals of SrTiO₃ and TiO₂ in the glass matrix. These glasses are n-type semiconductors as observed from the measurements of the thermoelectric power. Unlike many vanadate glasses, Long's overlapping large polaron tunnelling (OLPT) model is found to be most appropriate for fitting the experimental conductivity data, while for the undoped V₂O₅–Bi₂O₃ glasses, correlated barrier hopping conduction mechanism is valid. This is due to the change of glass network structure caused by doping base glass with SrTiO₃. The power law behavior (σ_ac=A(ω^s) with s<1) is, however, followed by both the doped and undoped glassy systems. The model parameters calculated are reasonable and consistent with the change of concentrations (x).     

Influence of thermal treatments on the elastic parameters in iron rich metallic glasses

The change of magnetoelastic properties after thermal treatments has been investigated for two groups of metallic glasses. (Fe₇₉Co₂₁)_75+xSi_15−1.4xB_10+0.4x (x (at.%)=0, 2, 4, 6, 8, 10) has been studied both in the as-prepared state and after thermal annealing in an applied magnetic field, to achieve a particular domain structure, at temperatures well below the crystallization temperatures. Changes in the ΔE effect, magnetomechanical coupling (k) and internal friction coefficient (Q⁻¹) are reported, reaching values of about 60% of the saturation value E_S. Fe₆₄Ni₁₀Nb₃Cu₁Si₁₃B₉ alloys annealed in vacuum for 1 h in the temperature range 350–550 °C showed maximum values of the ΔE effect and k of 61% and 0.85, respectively, accompanied by a minimum value of Q of around 2 for the sample annealed at 460 °C. These variations are related to the progress of nanocrystalization. The properties achieved are among the best reported for magnetomechanical applications.     

钙钛矿型(La0.2Li0.2Ba0.2Sr0.2Ca0.2)TiO3高熵氧化物陶瓷的制备及性能研究

高熵陶瓷是近年来在高熵合金基础上逐渐发展起来的一种新的陶瓷材料体系,它的出现为开发具有优异性能的非金属材料提供了新的理念和路线.本研究采用固相烧结法制备A位等摩尔比的钙钛矿型高熵氧化物陶瓷(La0.2Li0.2Ba0.2Sr0.2Ca0.2)TiO3,并探索了烧结温度对高熵陶瓷的物相结构及电学性能的影响.结果表明,陶瓷...     

Characterization of GaN epitaxial layers on SiC substrates with AlxGa1−xN buffer layers

High quality GaN epitaxial layers were obtained with Al_xGa_1−xN buffer layers on 6H–SiC substrates. The low-pressure metalorganic chemical vapor deposition (LP-MOCVD) method was used. The 500 Å thick buffer layers of Al_xGa_1−xN (0≤x≤1) were deposited on SiC substrates at 1025°C. The FWHM of GaN (0004) X-ray curves are 2–3 arcmin, which vary with the Al content in Al_xGa_1−xN buffer layers. An optimum Al content is found to be 0.18. The best GaN epitaxial film has the mobility and carrier concentration about 564 cm² V⁻¹ s⁻¹ and 1.6×10¹⁷ cm⁻³ at 300 K. The splitting diffraction angle between GaN and Al_xGa_1−xN were also analyzed from X-ray diffraction curves.     

A study on the formation and characteristics of the Si---O---C---H composite thin films with low dielectric constant for advanced semiconductor devices

The Si---O---C---H composite thin films were deposited on a p-type Si(100) substrate using bis-trimethylsilane (BTMSM) and O₂ mixture gases by an inductively coupled plasma chemical vapor deposition (ICPCVD). High density plasma of approximately 10¹² cm⁻³ is obtained at low pressure (<320 mtorr) with an RF power of approximately 300 W in the inductively coupled plasma source where the BTMSM and oxygen gases are greatly dissociated. Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) spectra show that the film has Si---CH₃ and O---H related bonds. The CH₃ groups formed the void in the film and the Si atoms in the annealed sample have different chemical states from those in the deposited sample. It means that the void is formed due to the removing of O---H related bonds during the annealing process. The relative dielectric constant of the annealed sample with the flow rate ratio O₂/BTMSM as 0.3 at 500°C for 30 min is approximately 2.5.     

The effect of rapid thermal annealing on structural and electrical properties of TiB2 thin films

This work reports on the effect of post-deposition rapid thermal annealing on the structural and electrical properties of deposited TiB₂ thin films. The TiB₂ thin films, thicknesses from 9 to 450 nm, were deposited by e-beam evaporation on high resistivity and thermally oxidized silicon wafers. The resistivity of as-deposited films varied from 1820 μΩ cm for the thinnest film to 267 μΩ cm for thicknesses greater than 100 nm. In the thickness range from 100 to 450 nm, the resistivity of TiB₂ films has a constant value of 267 μΩ cm.

A rapid thermal annealing (RTA) technique has been used to reduce the resistivity of deposited films. During vacuum annealing at 7 × 10⁻³ Pa, the film resistivity decreases from 267 μΩ cm at 200 °C to 16 μΩ cm at 1200 °C. Heating cycles during RTA were a sequence of 10 s. According to scanning tunneling microscopy analysis, the decrease in resistivity may be attributed to a grain growth through polycrystalline recrystallization, as well as to an increase in film density.

The grain size and mean surface roughness of annealed films increase with annealing temperature. At the same time, the conductivity of the annealed samples increases linearly with grain size. The obtained results show that RTA technique has a great potential for low resistivity TiB₂ formation.     

On Optimizing Batch Annealing for the Production of IF Steels

Batch annealing characterized by a long heating cycle and low heating temperature is widely used to produce sheet steels including interstitial-free (IF) steels. Optimizing batch-annealing conditions would be helpful in cutting lead time and saving energy while keeping the necessary deep drawability; however, little research has been done on it. The effects of batch-annealing parameters on the deep drawability of a Ti-stabilized IF steel and Nb+Ti-stabilized IF steel have been investigated. In general, a slight improvement in r_mvalue was found with the increase of annealing temperature. Because of the higher recrystallization temperatures of Nb+Ti-IF steel, it showed higher sensitivity to annealing temperature than Ti-IF steel. In addition, greater dependency of mechanical properties and deep drawability on soaking time was observed when annealing temperature was lower. Moreover, a heat transfer analysis showed that the annealing time could be reduced by 40% if the temperature decreases from 730°C to 650°C. The industrial production has verified that the analytical results are in good agreement with the recorded annealing temperature curve. Meanwhile, it has been shown that Ti-IF steels annealed at 650°C have very close deep drawability and other tensile properties compared with these annealed at 730°C.     

The Indiana silicon sphere 4π charged-particle detector array

A low threshold charged particle detector array for the study of fragmentation processes in light-ion-induced reactions has been constructed and successfully implemented at the IUCF and Saturne II accelerators. The array consists of 162-triple-element detector telescopes mounted in a spherical geometry and covering 74% of 4π in solid angle. Telescope elements are composed of (1) an axial-field gas ionization chamber operated with C₃F₈ gas; (2) a 0.5 mm thick passivated silicon detector, and (3) a 2.8 cm thick CsI(Tl) scintillation crystal with photodiode readout. Discrete element identification is obtained for ejectiles up to Z 16 over the dynamic range 0.7 ≤ E/A ≤ 95 MeV/nucleon. Isotopes are also distinguished for H, He, Li and Be ejectiles with 8 E/A 95 MeV. Custom-designed electronics are employed for bias supplies and linear signal processing. Data are acquired via a CAMAC/VME/Ethernet system.     

Infrared optical properties of Bi2Ti2O7 thin films by spectroscopic ellipsometry

Bi₂Ti₂O₇ thin films have been grown directly on n-type GaAs (1 0 0) by the chemical solution decomposition technique. X-ray diffraction analysis shows that the Bi₂Ti₂O₇ thin films are polycrystalline. The optical properties of the thin films are investigated using infrared spectroscopic ellipsometry (3.0–12.5 μm). By fitting the measured ellipsometric parameter (Ψ and Δ) data with a three-phase model (air/Bi₂Ti₂O₇/GaAs), and Lorentz–Drude dispersion relation, the optical constants and thickness of the thin films have been obtained simultaneously. The refractive index and extinction coefficient increase with increasing wavelength. The fitted plasma frequency ω_p is 1.64×10¹⁴ Hz, and the electron collision frequency γ is 1.05×10¹⁴ Hz, and it states that the electron average scattering time is 0.95×10⁻¹⁴ s. The absorption coefficient variation with respect to increasing wavelength has been obtained.     

Textured black brass spectrally selective coating

A textured black brass selective coating has been reported in this paper. These textured black brass selective coatings have been obtained by using chemical conversion process. They exhibit initial solar absorptance ()0.96 and thermal emittance ₁₀₀0.17 and are reproducible. These have been annealed up to 250°C in air and at 150°C in vacuum (10⁻³ Torr) possessing solar absorptance ()0.90. TEM, XRD and FTIR analyses have also been reported which suggests that the coating consists of multi-phases.