Laser doping of chromium as a double acceptor in silicon carbide with reduced crystalline damage and nearly all dopants in activated state

Chromium, a p-type dopant, has been incorporated into silicon carbide by laser doping. Secondary ion mass spectrometric data revealed enhanced solid solubility (2.29 × 10¹⁹ cm⁻³ in 6H–SiC and 1.42 × 19¹⁹ cm⁻³ in 4H–SiC), exceeding the equilibrium limit (3 × 10¹⁷ cm⁻³ in 6H–SiC above 2500 °C). The roughness, surface chemistry and crystalline integrity of the doped sample were examined by optical interferometry, energy dispersive X-ray spectrometry and transmission electron microscopy, respectively, and showed no crystalline disorder due to laser heating. Deep-level transient spectroscopy confirmed Cr as a deep-level acceptor with activation energies E_v + 0.80 eV in 4H–SiC and E_v + 0.45 eV in 6H–SiC. The Hall effect measurements showed that the hole concentration (1.942 × 10¹⁹ cm⁻³) is almost twice the average Cr concentration (1 × 10¹⁹ cm⁻³), confirming that almost all of the Cr atoms were completely activated to the double acceptor state by the laser-doping process without requiring any additional annealing step.     

Non-equilibrium grain-boundary segregation of Bi in Cu bicrystals

The observations of grain-boundary segregation of Bi in Cu bicrystals were analyzed. According to equilibrium grain boundary segregation (EGS) model and non-equilibrium grain-boundary segregation (NGS) model, respectively, the segregation kinetics of isothermal annealing at 500 °C and that of isochronal annealing for 24 h of Bi in Cu bicrystals were investigated. By qualitative analysis and quantitative analysis, it is concluded that the grain-boundary segregation of Bi agrees well with the theory of NGS. Based on the kinetics model of NGS, some parameters that are useful to predicting and controlling the Bi-induced embrittlement in Cu alloys are calculated as follows: the diffusion coefficient of Bi-vacancy complexes D_c=7.8×10^?5exp[–1.46/(kT)]; the apparent diffusion coefficient of Bi atoms D_i^A=7.66×10^at+bexp[–1.76/(kT)], where a=8.45×10^?8 and b=–13.37.     

Hot deformation behavior and microstructural evolution of beta C titanium alloy in β phase field

The hot deformation behavior of beta C titanium alloy in β phase field was investigated by isothermal compression tests on a Gleeble–3800 thermomechanical simulator. The constitutive equation describing the hot deformation behavior was obtained and a processing map was established at the true strain of 0.7. The microstructure was characterized by optical microscopy (OM), scanning electron microscopy (SEM) and electron back-scattered diffraction (EBSD) technique. The results show that the flow stress increases with increasing strain rates, and decreases with increasing experimental temperatures. The calculated apparent activation energy (167 kJ/mol) is close to that of self-diffusion in β titanium. The processing map and microstructure observation exhibit a dynamic recrystallization domain in the temperature range of 900–1000 °C and strain rate range of 0.1–1 s⁻¹. An instability region exists when the strain rate is higher than 1.7 s⁻¹. The microstructure of beta C titanium alloy can be optimized by proper heat treatments after the deformation in the dynamic recrystallization domain.     

FMR study of crystallization in the amorphous alloy Co65Fe4Ni2Si15B14 (Metglas 2714A)

The ferromagnetic resonance technique was used to study the annealing behavior of the metallic glass Co₆₅Fe₄Ni₂Si₁₅B₁₄ (Metglas 2714A). The peak-to-peak FMR linewidth, ΔH_pp, was measured at room temperature and 9.5 GHz for three isothermal annealing times in the temperature range 737–757 K. The transformed fraction, as derived from FMR data, satisfies the Johnson–Mehl–Avrami equation with the exponent n between 0.98 and 1.00. The activation energy for crystallization is estimated from the times to ΔH_pp=25–35 mT to to be 199 kJ mol⁻¹.     

Reflectance of conducting poly(3,4-ethylenedioxythiophene)

We present the reflectance spectrum of poly(3,4-ethylenedioxythiophene) (PEDOT) doped with PF₆ with dc conductivity of 230 S/cm at room temperature, measured over a wide frequency range from 50 to 5×10⁴ cm⁻¹ (0.006–6 eV). The reflectance, R(ω), of PEDOT-PF₆ is characterized by metal-like signatures in the infrared (IR), including high R(ω) in the far-IR and a plasma frequency of approximately 1.2 eV. The optical conductivity, σ(ω), is dominated by intraband contributions below 1 eV, characteristic of a disordered metal near the metal–insulator (M–I) transition. The reflectance spectrum is in good quantitative agreement with the “localization-modified Drude (LMD) model”. Since the onset of the interband absorption (below 1.5 eV) is at lower energy than in other conducting polymers, PEDOT-PF₆ shows low absorption in the visible range between 2 and 3 eV. Our spectroscopic results demonstrate that this doped PEDOT system can be utilized as a transparent electrode for optoelectronic devices.     

Deformation behavior and mechanisms of Ti- 1023 alloy

1 Introduction Beta titanium alloys offer a variety of microstructural morphologies and associated mechanical property variations thus giving considerable latitude in microstructure design. They are the most versatile class of titanium alloys and offer th…     

Electrical and impedance spectral characterisation of ITO/DAG/In device

A Schottky device, with configuration ITO/DAG/In is fabricated using diazopheny diamino glyoxime (DAG) as an n-type organic material. Current–voltage characteristics and impedance spectroscopy measurements were carried out, which reveals that the injection and transport properties are dominated by negative charge carriers. Space charge limited current theory with an exponential distribution of traps is very well followed by observations resulted through current–voltage characteristics at high voltage region. This gives a traps density N_t of about 4.5×10²¹ m⁻³ and mobility of electron is about 3.9×10⁻¹⁰ m² V⁻¹ s⁻¹. It is found that DAG behaves as an n-type materials as it forms Schottky barrier with ITO (high work function electrode) and conduction is governed by majority carriers, i.e. electrons. Using temperature and bias dependence of impedance spectral characteristics in a broad frequency range, i.e. 40 Hz to 100 kHz, it is found that the ac behaviour of In/DAG/ITO device shows several features, described by the simple double RC circuit representing a depleted junction region and an undepleted bulk region. From the large frequency range of impedance spectroscopy two distinct processes were identified, corresponding to bulk DAG layer and junction region. The activation energy of the relaxation times coincides well with the results obtained from the temperature dependent dc conductivity. The temperature dependent capacitance–voltage measurements were analysed at a frequency of 40 Hz. The obtained inherent donor concentration from 1/C²–V plots varies from 1.8×10²³ m⁻³ at room temperature to 5.9×10²³ m⁻³ at 360 K.     

The influence of the transformation of electronic structure and micro-structure on improving the thermoelectric properties of zinc antimonide thin films

Measurements of electronic structure, microstructure and thermoelectric properties of zinc antimonide thin films prepared by direct current magnetron co-sputtering were carried out. The as-deposited zinc antimonide thin film had a very high resistivity similar to insulating ceramics, which was due to a low binding energy of both zinc and antimony, with the electron scattering increases and impedes the current transport. With the increase in annealing temperature, the films became more crystalline and the thermoelectric properties were also improved. The resistivity of the film decreased rapidly with its crystallinity when the annealing temperature was above 350 °C. The Seebeck coefficients of the thin films were positive, indicating that the films were P-type. The Seebeck coefficient of those samples increased with increasing annealing temperature. The thin film annealed at 400 °C has an optimal power factor of 1.87 × 10⁻³ Wm⁻¹ K⁻² with a Seebeck coefficient of 300 μVK⁻¹ and a resistivity of 4.82 × 10⁻⁵ Ωm at 573 K.     

Surface plasmon resonance and electrical properties of RF: magnetron sputtered carbon–nickel composite films at different annealing temperatures

In this work, the optical absorption spectra of carbon–nickel films annealed at different temperatures(300–1000 °C) with a special emphasis on the surface plasmon resonance(SPR) were investigated. The films were grown on quartz substrates by radio-frequency(RF)magnetron co-sputtering at room temperature with a deposition time of 600 s. The optical absorption peaks due to the SPR of Ni particle are observed in the wavelength range of 300–330 nm. With annealing temperature increasing up to 500 °C due to the increase in Ni particle size, the intensity of the SPR peaks increases, but weakens with annealing temperature increasing over 500 °C. The Ni nanoparticle size, the dielectric function of carbon matrix(ε_m) and the plasma frequency of the free electrons(ω_p) at500 °C have the maximum values of 21.63 nm, 0.471 and5.26 9 10~(15)s~(-1), respectively. The absorption peak shows a redshift trend up to 500 °C and then turn to blueshift with annealing temperature increasing over 500 °C. These observations are in a good agreement with the electrical measurements in temperature range of 15–520 K and the Maxwell–Garnett(M–G) effective medium theory(EMT).     

Deformation mechanisms in Cr20Ni80 alloy at elevated temperatures

The mechanisms of plastic deformation of Cr20Ni80 nichrome with an initial grain size of 80 μm were studied in the temperature range 600–950°C and the strain-rate range 1.5 × 10^?6?5 × 10^?2s^?1. Nichrome is shown to exhibit anomalously high values of stress exponent n and a high deformation activation energy Q. These unusual properties were found to be caused by “threshold” stresses below which deformation does not occur. An analysis of the deformation behavior with allowance for threshold stresses reveals the regions of hot, warm, and cold deformation in nichrome. At normalized strain rates \(\dot \varepsilon \) kT/D _{1 Gb} < 10^?8, the true values of n and Q are ～4 and 285 ± 30 kJ/mol, respectively. In the normalized-strain range 10^?8?10^?4 n ～ 6 and the deformation activation energy decreases to 175 ± 30 kJ/mol. This change in the deformation-behavior characteristics is explained by the transition from high-temperature dislocation climb, which is controlled by lattice self-diffusion, to low-temperature dislocation climb, which is controlled by pipe diffusion, as the temperature decreases. At \(\dot \varepsilon \) kT/D _{1 Gb} = 10^?4, a power law break-down takes place and an exponential law (which describes the deformation behavior in the range of cold deformation) becomes operative.     

Microstructure evolution and hot deformation behavior of Cu−3Ti−0.1Zr alloy with ultra-high strength

The hot compression deformation behavior of Cu–3Ti–0.1Zr alloy with the ultra-high strength and good electrical conductivity was investigated on a Gleeble–3500 thermal-mechanical simulator at temperatures from 700 to 850 °C with the strain rates between 0.001 and 1 s⁻¹. The results show that work hardening, dynamic recovery and dynamic recrystallization occur in the alloy during hot deformation. The hot compression constitutive equation at a true strain of 0.8 is constructed and the apparent activation energy of hot compression deformation Q is about 319.56 kJ/mol. The theoretic flow stress calculated by the constructed constitutive equation is consistent with the experimental result, and the hot processing maps are established based on the dynamic material model. The optimal hot deformation temperature range is between 775 and 850 °C and the strain rate range is between 0.001 and 0.01 s⁻¹.     

Accumulation and diffusion of radiogenic helium in beryllium

Accumulation of radiogenic helium isotope ⁴He, its diffusion characteristics, and microstructure of beryllium have been studied after irradiation at 70 and 200°C by neutrons with an energy of E > 0.1 MeV to fluences of (1.0–13.3) × 10²² cm^?2. Experimental results concerning the concentration of radiogenic helium in beryllium after irradiation and subsequent isothermal annealings for 1 h in a temperature range of 700–1200°C have been obtained. The accumulation of helium corresponds to a linear dependence up to a neutron fluence of ～6 × 10²² cm^?2 (E > 0.1 MeV); at fluences from 6 × 10²² to 13 × 10²² cm^?2 (E > 0.1 MeV), a deviation from the linear dependence toward the decrease in the rate of accumulation is observed. The diffusion of radiogenic helium in beryllium at annealing temperatures of 70–200°C is low; intense diffusion and degassing of helium from beryllium start at an annealing temperature of 700°C. At annealing temperatures of 1100–1200°C, virtually all helium escapes from the irradiated beryllium.     

Superplastic behavior of a TiAl-based alloy

Superplastic behavior under the conditions of a temperature range from 850 to 1075°C and strain rates varying from 8×10⁻⁵ to 1×10⁻³ s⁻¹ was investigated for Ti–33Al–3Cr–0.5Mo (wt%) alloy with a very fine grain size obtained by the multi-step thermal mechanical treatment. The results show that the TiAl-based alloy with a hot-deformed fine grain size possesses good superplasticity. It exhibits a strain rate sensitivity coefficient of 0.9 at a strain rate of 3×10⁻⁵ s⁻¹ and temperature from 1000 to 1075°C. Moreover, the strain rate sensitivity coefficient is stable during the hot deformation, and a tensile elongation of 517% was obtained at 1075°C and a strain rate of 8×10⁻⁵ s⁻¹. The superplastic behavior of the present fine-grained TiAl-based alloy can be explained by the local strain hardening and high m value during the tensile deformation. Microstructure evolution in the superplastic deformation was also discussed.     

Thermal stability of Al1−xInxN (0 0 0 1) throughout the compositional range as investigated during in situ thermal annealing in a scanning transmission electron microscope

The thermal stability of Al_1?xIn_xN (0 ? x ? 1) layers was investigated by scanning transmission electron microscopy (STEM) imaging, electron diffraction, and monochromated valence electron energy loss spectroscopy during in situ annealing from 750 to 950 °C. The results show two distinct decomposition paths for the layers richest in In (Al_0.28In_0.72N and Al_0.41In_0.59N) that independently lead to transformation of the layers into an In-deficient, nanocrystalline and a porous structure. The In-richest layer (Al_0.28In_0.72N) decomposes at 750 °C, where the decomposition process is initiated by In forming at grain boundaries and is characterized by an activation energy of 0.62 eV. The loss of In from the Al_0.41In_0.59N layer was initiated at 800 °C through continuous desorption. No In clusters were observed during this decomposition process, which is characterized by an activation energy of 1.95 eV. Finally, layers richest in Al (Al_0.82In_0.18N and Al_0.71In_0.29N) were found to resist thermal annealing, although the initial stages of decomposition were observed for the Al_0.71In_0.29N layer.     

Electroactive langmuir-blodgett films of N-octadecylpyridinium-TCNQ charge-transfer salt

Langmuir-Blodgett films of the 1 : 1 charge-transfer salt N-octadecylpyridinium-TCNQ have been deposited onto glass substrates. The layers exhibit significant bulk lateral conductivity without doping. The value obtained at room temperature is (2.0 ± 0.2) × 10⁻² S cm⁻¹; over the temperature range 100 – 300 K, the films show typical semiconductor behaviour with an activation energy of 0.13 ± 0.005 eV. Infrared and u.v.-visible transmission spectra of the films are characteristic of an organic conductor.     

Superplastic deformation behaviour of friction stir processed 7075Al alloy

Commercial 7075Al rolled plates were subjected to friction stir processing (FSP) with different processing parameters, resulting in two fine-grained 7075Al alloys with a grain size of 3.8 and 7.5 μm. Heat treatment at 490 °C for 1 h showed that the fine grain microstructures were stable at high temperatures. Superplastic investigations in the temperature range of 420–530 °C and strain rate range of 1×10⁻³–1×10⁻¹ s⁻¹ demonstrated that a decrease in grain size resulted in significantly enhanced superplasticity and a shift to higher optimum strain rate and lower optimum deformation temperature. For the 3.8 μm 7075Al alloy, superplastic elongations of >1250% were obtained at 480 °C in the strain rate range of 3×10⁻³–3×10⁻² s⁻¹, whereas the 7.5 μm 7075Al alloy exhibited a maximum ductility of 1042% at 500 °C and 3×10⁻³ s⁻¹. The analyses of the superplastic data for the two alloys revealed a stress exponent of 2, an inverse grain size dependence of 2, and an activation energy close to that for grain boundary self-diffusion. This indicates that grain boundary sliding is the main deformation mechanism for the FSP 7075Al. This was verified by SEM examinations on the surfaces of deformed specimens.     

Behavior of magnetic and magnetoresistive properties of nanocrystalline Co/Cu/Co films during step-by-step annealing

Three-layered Co/Cu/Co films with d _Cu = 1.0 and 2.1 nm (corresponding to the first and second antiferromagnetic maxima, respectively) and single-layer Co films produced during the same manufacturing cycle of magnetron sputtering in an argon atmosphere have been studied. The behavior of the coercive force and magnetoresistance ratio during step-by-step annealing in a temperature range of 250–400°C has been investigated. The correlation factor between the magnetoresistance ratio and saturation field (or the energy of indirect exchange coupling between Co layers) upon step-by-step annealing is 0.97 and 0.95 for the first and second antiferromagnetic maxima, respectively. In a temperature range of 20–300°C, the correlation factor between the coercive force and saturation field is 0.98–0.99. At T _an > 350°C corresponding to intense grain growth, the violation of the correlation between H _c and H _s takes place. Limits of the time and temperature stability of the Δρ/ρ ratio and H _c during the step-by-step annealing of the films have been determined. The behavior of Δρ/ρ, H _c, and magnetic anisotropy of the three-layered films is shown to be due to structural changes (grain size, amplitude of roughness). The behavior of the magnetic anisotropy constants K _u ¹ and K _u ² depends on the annealing temperature and thickness of the nonmagnetic spacer.     

Characterization of hot deformation behavior of as-forged TiAl alloy

The deformation behavior of as-forged Ti–43Al–9V–Y alloy was investigated by hot compression tests in the temperature range of 1100–1225 °C and strain rate range of 0.01–0.5 s⁻¹. The results show that the alloy exhibits negative temperature sensitivity and positive strain rate sensitivity. The stress exponent (n = 3.02) and the apparent activation energy (Q = 342.27 kJ/mol) of the present alloy are lower than that of previous reported TiAl alloys, which suggests that the as-forged Ti–43Al–9V–Y alloy exhibits better deformability at low temperatures and high strain rates. A processing map for hot working was developed on the basis of a dynamic material model. The deformation mechanisms were analyzed by the processing map. The optimum processing condition at the strain of 0.6 is 1180–1210 °C/0.01–0.05 s⁻¹. A crack-free Ti–43Al–9V–Y sheet was prepared by hot rolling at these optimized parameters. EBSD results show that dynamic recrystallization is more likely to occur for γ phase.     

Thermal degradation of the dielectric relaxation of 10–90% (w/w) zeolite-conducting polypyrrole composites

The effect of thermal aging of 10–90 wt% zeolite-conducting polypyrrole composite on its dielectric properties is studied in the frequency range 10⁻² to 2 × 10⁶ Hz from room temperature to liquid nitrogen temperature. A dielectric relaxation mechanism, which appears in the fresh samples, is influenced by the thermal annealing. The frequency f_max where a maximum of a dielectric loss peak is located decays exponentially with the aging time and the intensity of the loss peaks shows a maximum at intermediate aging time. A modified Williams–Landel–Ferry law describes the temperature variation of f_max in all specimens. Increasing activation energy values on increasing the aging duration are obtained. The temperature dependence of f_max and the activation energy (regarded as the height of a potential barrier) are different from those characterizing the macroscopic conductivity, which is described by the charging energy limited tunneling model. The intensity of the dielectric mechanism in thermally treated samples deviates from the linear decrease with inverse temperature occurring in fresh polypyrrole. Although the thermal degradation of the logarithm of the dc conductivity decays proportional with the root of the aging time, the equivalent conductivity obtained from the dielectric data decays exponentially with aging duration. Time constants are obtained in both cases. The model of Barton–Nakajima–Namikawa (BNN) can hardly interconnect the dc conductivity with the relaxation process in fresh sample. The divergence augments with the aging time. The thermal aging law and the inadequacy of the BNN model probably indicates that the dc process is probably irrelevant to the relaxation process.     

Annealing behaviors of vacancy in varied neutron irradiated Czochralski silicon

The difference of annealing behaviors of vacancy-oxygen complex (VO) in varied dose neutron irradiated Czochralski silicon: (S1 5×10¹⁷ n/cm³ and S2 1.07×10¹⁹ n/cm³) were studied. The results show that the VO is one of the main defects formed in neutron irradiated Czochralski silicon (CZ-Si). In this defect, oxygen atom shares a vacancy, it is bonded to two silicon neighbors. Annealed at 200 °C, divacancies are trapped by interstitial oxygen(O_i) to form V₂O (840 cm⁻¹). With the decrease of the 829 cm⁻¹ (VO) three infrared absorption bands at 825 cm⁻¹ (V₂O₂), 834 cm⁻¹ (V₂O₃) and 840 cm⁻¹ (V₂O) will rise after annealed at temperature range of 200–500 °C. After annealed at 450–500 °C the main absorption bands in S1 sample are 834 cm⁻¹, 825 cm⁻¹ and 889 cm⁻¹ (VO₂), in S2 is 825 cm⁻¹. Annealing of A-center in varied neutron irradiated CZ-Si is suggested to consist of two processes. The first is due to trapping of VO by O_i in low dose neutron irradiated CZ-Si (S1) and the second is due to capture the wandering vacancy by VO, etc, in high dose neutron irradiated CZ-Si (S2), the VO₂ plays an important role in the annealing of A-center. With the increase of the irradiation dose, the annealing behavior of A-center is changed.