An acoustic study of the mixed-alkali-mixed phase β-aluminas. Part 1: Naβ″/βAl2O3, Kβ″/βAl2O3 and (Na0.6K0.4)β″/βAl2O3

The relative attenuation of compressional sound waves of frequencies 10–60 MHz in mixed alkali (Na/K) mixed phase (β″/β)-aluminas is reported for temperatures 80–550 K. The internal friction peaks shift to higher frequencies at higher temperatures and are attributed to Na⁺ interactions in Naβ″/β alumina and Na⁺ and K⁺ in NaK β″/β alumina. The broad attenuation peaks occuring at low temperatures (< 300 K) and at higher temperatures (> 400 K) suggest multi-relaxation processes giving a distribution of activation energies. The estimated average activation energy for Na⁺ diffusion in Naβ″/βAl₂ O₃ at low temperatures and high temperatures is 0.183 eV and 0.387 eV respectively. In the NaK β″/βAl₂o₃ samples, the Na ⁺ values were 0.239 eV and 0.386 eV, respectively. The estimated average activation energies for K⁺ diffusion at low and high temperatures in the Kβ″/β-alumina samples were 0.269 eV and 0.371 eV and for K⁺ in the NaK β″/β samples, 0252 eV and 0.339 eV, respectively. The low temperature attenuation peaks were interpreted in terms of ionic interaction in the bulk and the high temperature peaks were related to interactions in the grain boundaries. The measured activation energies confirmed these interpretations. A reversal of the temperature appearance of the Na⁺ and K⁺ high temperature peaks in the NaKβ″/βAl₂ O₃ is explained by the disorder at the grain boundaries.     

Electroluminescence from nano-crystalline Si/ SiO2 structures embedded in pn junctions

Phosphorous-doped and boron-doped amorphous Si thin films as well as amorphous SiO₂/Si/ SiO₂ sandwiched structures were prepared in a plasma enhanced chemical vapor deposition system. Then, the p–i–n structures containing nano-crystalline Si/ SiO₂ sandwiched structures as the intrinsic layer were prepared in situ followed by thermal annealing. Electroluminescence spectra were measured at room temperature under forward bias, and it is found that the electroluminescence intensity is strongly influenced by the types of substrate. The turn-on voltages can be reduced to 3 V for samples prepared on heavily doped p-type Si (p⁺-Si) substrates and the corresponding electroluminescence intensity is more than two orders of magnitude stronger than that on lightly doped p-type Si (p-Si) and ITO glass substrates. The improvements of light emission can be ascribed to enhanced hole injection and the consequent recombination of electron–hole pairs in the luminescent nanocrystalline Si/ SiO₂ system.     

Mechanism of charge transfer in injection photodiodes based on the In-n +-CdS-n-CdS x Te1 − x -p-Zn x Cd1 − x Te-Mo structure

Photosensitive In-n ⁺-CdS-n-CdS _x Te_{1 ? x} -p-Zn _x Cd_{1 ? x} Te-Mo film structures based on II–VI semiconductors and operating in the wavelength range λ = 0.490–0.855 μm have been fabricated. These structures in the forward current direction at high bias voltages operate as injection photodiodes and exhibit a high integrated sensitivity S _int ≈ 700 A/lm (14500 A/W) at room temperature. It has been found that, in the fabricated structures at low illuminance levels and low forward bias voltages (0.05–0.50 V), the diffusion and drift fluxes of nonequilibrium charge carriers are directed toward each other. This effect leads to the sign reversal of the photocurrent, which makes it possible on the basis of these structures to create selective photodetectors with injection properties. In the reverse direction of the photocurrent, these structures also operate in the mode of internal amplification of the primary photocurrent, but the integrated sensitivity in this mode is considerably less than that in the forward current direction.     

Ionic thermocurrents in sodium fluoride thin film

Ionic thermocurrent (ITC) in NaF thin film deposited between gold electrodes has been investigated in situ in the temperature region 300–500 K. The thermally stimulated polarization current (TSPC) and thermally stimulated depolarization current (TSDC) obtained under low electric field pf polarization (E_p) at a lower temperature of polarization (T_p) exhibited current-peak temperatures (T_M) about 420 K and 450 K. The activation energies associated with the first and the second current peaks were 1.15 + 0.05 eV and 0.65 + 0.02 eV, which are assigned to cation vacancy blocking at the grain boundary barrier and the electrode contact interface barrier respectively. Polarization under a strong electric field (E_p > MV m₋₁) at T_p > 480 K causes a quasi-stable shift of the ITC peak positions to higher temperature. The current peak positions and magnitudes then depend upon the polarity of the electrode metal during polarization, and activation energies associated with the first peak positions are 0.90 + 0.02 eV and 0.79 + 0.02 eV for positive and negative bias at the counter electrode respectively, which may be attributed to the clustering of the cation vacancies and the dislocation networks at the interfaces.     

Hysteretic effects in the dc current-voltage characteristic of normal Nb/Pb tunnel junctions

High resistance normal Nb/Pb tunnel junctions have been studied. Both at 300 K and 77 K an hysteresis in the I–V characteristic has been measured: the presence of negative or positive bias voltages changes the tunneling probability. At every fixed bias current value, a voltage drift with time appears. The drift velocity increases as the voltage or the temperature increases. Moreover at 77 K anomalous low frequency oscillations arise in the junction when some positive or negative threshold voltages are exceeded.     

Low temperature ESR spectra of nickel — doped NaCl crystals

Paramagnetic resonance of Bridgman-grown NaCl crystals nominally doped with divalent nickel was studied over the temperature range from 4 K to 300 K. The broad isotropic EPR line with g = 2.12 ÷ 2.23 and ΔH _pp = 280 ÷ 780 G was detected at temperatures higher than 130 K for samples of various thermal history. The origin of these spectra was attributed to aggregated and precipitated Ni²⁺ ions. At temperatures lower than 40 K another ESR signal was registered. It was an anisotropic one, the intensity of which strongly depends upon the temperature. This spectrum results from substitutional Ni⁺ ions with tetragonally distorted surrounding along a S100T direction. The angular dependence of the ESR line positions was fitted to an appropriate spin-Hamiltonian with the g-factor components g _∥ and g _⊥ equal to 2.86 and 2.10, respectively. The temperature-dependence of the signal intensity at temperatures between 4 and 110 K has been interpreted in terms of a transition from the static to dynamic Jahn-Teller effect.     

磷化铟中离子注入硅的双性行为研究

本文研究了热靶条件下注Si⁺的磷化铟材料的电学特性和低温光致荧光特性,发现Si⁺单注入样品的薄层载流子浓度随注入剂量的增加而趋于饱和,共P⁺注入后薄层载流子浓度大大增加,低温光致荧光谱研究表明,注Si⁺的磷化铟中存在Si_p-V_p络合物缺陷,共P⁺注入能抑制其形成,表明Si⁺注入磷化铟中呈双性行为,还对Si⁺+P 关键词：     

Intensity and half-width measurements in the 1·525 μm band of acetylene

Line intensities at 150°K and 295°K, self-broadened half-widths at 171°K, 200°K, 250°K and 295°K, and hydrogen-broadened half-widths at 171°K, 200°K and 295°K have been measured in the ν₁+v₃ band of C₂H₂ at 1·525 μm. The absolute intensity of the band has been determined independently by employing the Wilson-Wells-Penner-Weber technique. Our best estimate for the absolute intensity of the band is S_v=7·82 ± 0·07 cm^?2 atm^?1 at 295°K. Line intensities calculated using this value of S_v are in good agreement with the measured intensities at the two extreme temperatures of 150°K and 295°K considered in the present study, thereby not suggesting any significant intensity anomalies. Line positions have been measured for the first time for this band for R(29)?P(25).     

Thermoelectric power and ac conductivity of A-type Nd2O3

Measurement of thermoelectric power Θ of pressed pellets of A-type Nd₂O₃ from 550 to 1180K and electrical conductivity (σ) at dc, 50 Hz, 1.542 kHz and 3 kHz at different temperatures is reported. It is concluded that electrical conduction at high temperature (T>600K) in this solid is due to positive large polarons in O²⁻ : 2p (valence) band and negative intermediate polarons in Nd³⁺ : 5d (conduction band). The energy band gap of the solid has been found to be 2.44 eV. At low temperatures, conduction by hopping of charge carriers from one impurity centre to another has been predicted.     

Growth of Ni-Mn-Ga high-temperature shape memory alloy thin films by magnetron sputtering technique

Ni-Mn-Ga thin films have been fabricated by using magnetron sputtering technique under various substrate negative bias voltages. The effect of substrate negative bias voltage on the compositions and surface morphology of Ni-Mn-Ga thin films was systematically investigated by energy dispersive X-ray spectrum and atomic force microscopy, respectively. The results show that the Ni contents of the thin films increase with the increase of the substrate negative bias voltages, whereas the Mn contents and Ga contents decrease with the increase of substrate negative bias voltages. It was also found that the surface roughness and average particle size of the thin films remarkably decrease with the increase of substrate negative bias voltages. Based on the influence of bias voltages on film compositions, a Ni₅₆Mn₂₇Ga₁₇ thin film was obtained at the substrate negative bias voltage of 30 V. Further investigations indicate that the martensitic transformation start temperature of this film is up to 584 K, much higher than room temperature, and the film has a non-modulated tetragonal martensitic structure at room temperature. Transmission electron microscopy observations reveal that microstructure of the thin film exhibits an internally (1 1 1) type twinned substructure. The fabrication of Ni₅₆Mn₂₇Ga₁₇ high-temperature shape memory alloy thin film will contribute to the successful development of microactuators.