Структура, оптические и фотоэлектрические свойства пленок сульфида свинца, легированных стронцием и барием

The morphological evolution of composition, structural characteristics (lattice constant, microdeformations, texturing), optical and photoelectric properties of PbS films obtained by chemical bath deposition in the presence of ammonium iodide and strontium/barium chlorides at a concentration range up to 5 mmol/l was studied. According to elemental EDX analysis, the strontium content in PbS films was 0.4−0.7 at%, whereas barium concentration was beyond the determination error interval. The size of the particles forming the PbS films ranged from ~ 200 to ~ 400 nm with monomodal particle size distribution. The introduction of NH4I and SrCl2/BaCl2 into the bath retained the cubic B1 structure of PbS films, but led to a nonmonotonic change in the lattice parameter, which was associated with the defects, namely, vacancies or interstitial ions. The introduction of strontium and barium salts had no effect on the PbS band gap, but led to a change in the intensities of the impurity absorption bands in the depth and near the bottom of the conduction band. The dependence of the volt−watt sensitivity of the PbS films upon the concentration of strontium/barium in the solution was extreme with maxima at 0.05 and 0.1 mmol/l, respectively.

DESORPTION OF IMPURITIES FROM DETONATION NANODIAMOND DURING THE SYNTHESIS OF INTERMATALLIC COMPOUNDS OF THE Ni-Al SYSTEM

The results of modification of the impurity subsystem of detonation nanodiamonds (DND) (from the “Altai” Federal Research and Production Center (Biysk)) with active metals and mixtures of nickel and aluminum metals are presented. Samples made from three different metal-diamond mixtures were investigated: 1) 70 wt % of DND and 30 wt % of Al, 2) 50 wt % of DND and 50 wt % of mixture of nickel and aluminum in NiAl stoichiometry, 3) 70 wt % of DND and 30 wt % of mixture of nickel and aluminum in Ni3Al stoichiometry. The heating of samples of nanodiamonds in a vacuum volume (VUP-5) is accompanied by thermal desorption of volatile compounds. Analysis of the samples using differential scanning calorimetry and mass-spectrometry (DSC - on STA 409 PC Luxx NETZSCH, MS - on QMS 403 D Aeolos NETZSCH) allowed us to study the kinetics of desorption and the molecular composition of volatile compounds desorbed by heating nanodiamonds. Annealing of the charge with aluminum is accompanied by a nonmonotonic change in the weight of the sample during heating. Heating mixtures of nanodiamond with nickel and aluminum is accompanied by an almost monotonic decrease in weight. Weight loss at up to 950 °C annealing can reach 20%. When samples are heated to 950 °C, H2O (up to 200 °С), O2 (up to 60 °С), H2S (up to 700 °С), CO2 (up to 600 °С), SO2 (up to 450 °С), N2 (up to 60 °С) evaporate from the surface of the samples. Endo- and exo-effects indicate the occurrence of chemical reactions between impurities and metals. The cleaning process most actively takes place during the annealing of the metal-diamond mixture containing Ni and Al in Ni3Al stoichiometry.

Photoconductivity and Conductivity Processes in Si-Sn Films Grown on Si(100) Substrate at Room Temperature

Photoresistors based on amorphous Si-Sn thin films (270-285 nm) with different concentration of tin were studied by spectral measurements of photoconductivity at room temperature and by low-temperature measurements of the Hall effect . Electrical contacts to the Si-Sn film was formed by aluminum layer deposition. When the Al contact is illuminated, the spectral sensitivity of the photoresistor with Sn consentration of 19% extends to 2060 nm due to Schottky barrier influence. It was proved that the Si-Sn alloy film provides photoresponse with cut-off energy of 0.98 eV that is close to the indirect band gap in the Si-Sn film. Three deep acceptor levels with activation energies of 90, 114, and 173 meV were found in the Si-Sn thin film (20% Sn) in the temperature range of 50 – 300 K. Sequential activation of the deep levels and their competition leads to a nonmonotonic change of the Si-Sn film conductivity (0.025 - 5.0 (Ω×cm)-1) and mobility of holes (100 – 500 cm2/(V·s)). The transition to the intrinsic conductivity region of the amorphous Si-Sn film was not observed up to room temperature.

Anomalous anisotropic compression behavior of superconducting CrAs under high pressure

CrAs was observed to possess the bulk superconductivity under high-pressure conditions. To understand the superconducting mechanism and explore the correlation between the structure and superconductivity, the high-pressure structural evolution of CrAs was investigated using the angle-dispersive X-ray diffraction (XRD) method. The structure of CrAs remains stable up to 1.8 GPa, whereas the lattice parameters exhibit anomalous compression behaviors. With increasing pressure, the lattice parameters a and c both demonstrate a nonmonotonic change, and the lattice parameter b undergoes a rapid contraction at ∼0.18−0.35 GPa, which suggests that a pressure-induced isostructural phase transition occurs in CrAs. Above the phase transition pressure, the axial compressibilities of CrAs present remarkable anisotropy. A schematic band model was used to address the anomalous compression behavior of CrAs. The present results shed light on the structural and related electronic responses to high pressure, which play a key role toward understanding the superconductivity of CrAs.

A Componential Model of Human Interaction with Graphs. III. Spatial Orientation

The Mixed Arithmetic-Perceptual (MA-P) model of graph comprehension proposes that graph users apply combinations of component processes — including Searching for indicators, Encoding the value of indicators, performing Arithmetic Operations on the values, making Spatial Comparisons among the indicators, and Responding — when they answer questions from a graph. The model further suggests that the combination and order of the components that the user applies depends on a user's task and the type of graph. The present research investigated the use of another component process — mental rotation — in interacting with star graphs. Subjects used two star graphs to answer comparison and difference questions in which the differences in orientation of the indicators in question varied from 0 to 288°. The results showed a nonmonotonic change in response time with the difference in orientation. The discussion addresses the effects of mental rotation in reading displays and the role that rotation may play in the hierarchy of graph effectiveness proposed by Cleveland and McGill.

Investigation of Polymer Relaxation after Deformation by Positron Annihilation

ABSTRACTThe relaxation of polyimid films after the axial tension has been investigated by measuring life-time of positrons and angular correlation of annihilation photons. The nonmonotonic change of mean life-time while relaxing the free film has been found. Two range of changes of positron-sensitive properties can be seen: “rapid” relaxation for 4–5 hours (characterized by reducing life-time of short-lived component) and “slow” relaxation (characterized by reducing the intensity of long-lived component). The results of this investigation have been compared with those of measuring of sample density and dielectric losses. The possible explanations and the- changes of mechanizms of relaxation with the conditions of deformation and “the rest” of polymers are analyzed.