Proton channeling in ionic and semiconducting single crystals

Measurements have been made of the energy distributions of protons passing through NaCl, KCl, Si, and Ge single crystals at various angles with respect to the {100} and {110} planes. The fraction of protons passing through lattice channels has been evaluated, and its dependences on the angle of incidence, the chemical composition of the sample, and the proton energy have been found.     

Electrical conductivity of the semiconducting phase in vanadium dioxide single crystals

The electrical conductivity of the semiconducting phase of vanadium dioxide single crystals is studied over a wide range of temperatures. It is shown that the electrical conductivity varies with temperature as log σ ～ T in the range 340–170 K and as log σ ～ 1/T at temperatures below 120 K. The experimental results are described in the framework of the model in which the temperature dependence of the hopping conductivity of small-radius polarons is determined by the dependence of the resonance integral on the amplitude of thermal lattice vibrations.     

Diamagnetism and muon knight shift in semimetallic and semiconducting BiSb single crystals

A series of single crystalline Bi_1−x Sb _x alloys (x=0,0.03, 0.14, 0.19, 0.37) covering both the semimetallic (0≤x≤0.07 orx≥0.22) and the semiconducting region (0.07≤x≤0.22) was examined using the stroboscopic μ⁺ SR method. The μ⁺ Knight shift, negative for all Sb concentrations, shows pronounced temperature dependences and large anisotropies. A scaling with the-negative-total magnetic susceptibility [1] is found in the semiconducting alloys. In detail, the isotropic part of the μ⁺ Knight shift is proportional to the isotropic part of the susceptibility, and the anisotropic Knight shift scales with the anisotropic susceptibility. Possible mechanisms leading to this relation are investigated.     

Study of deep photoluminescence levels in CuInS2 crystals

Deep PL levels in bulk single-crystals of CuInS₂ have been investigated. The PL spectra show three broad peaks at 0.83, 0.99, and 1.24 eV in the low energy region. The emissions are considered to be due to recombination between deep donors and deep acceptors. The deep localized levels are more likely to be attributed to deformation of the crystalline structure rather than any deviation from the stoichiometric composition.     

Low temperature thermal conductivity of pure and doped single crystals of semiconducting SmS

We measured the thermal conductivity of pure SmS and of SmS doped with P, As and Se between 1.5 and 350 K. The lattice thermal conductivity of pure samples and of SmSSe obeys a T^{?$\text{3}\text{2}$} law for temperatures T greater than 150 K, and is very sensitive to point defects in the lattice. The highest values are measured on samples close to the stoichiometric composition. P and As dopants act as phonon scattering centers and considerably reduce the low temperature lattice conductivity.     

Optical properties of V6O13 single crystals in the metallic and the semiconducting phase

The optical reflection of V₆O₁₃ single crystals has been studied between 0.06 and 3 eV at temperatures both below and above the semiconductor-to-metal transition temperature (T_t?150K). In addition to the metallic reflection, present only at T>T_t, discrete resonances are observed in both phases: four with polarization E//b and three with E⊥b.The results of a dispersion analysis using classical-oscillator and Drude terms are presented. The resonances above 2 eV are attributed to oxygen 2p - vanadium 3d interband transitions. The maxima at the lower energies are interpreted as transitions between vanadium 3d subbands.     

Ultrasonic studies on bismuth single crystals

Studies of ultrasonic velocities and attenuation are carried out in bismuth single crystals along the trigonal axis and perpendicular to the trigonal axis and the results are interpreted in terms of the changes in carrier concentration with change of direction. Temperature dependence of ultrasonic attenuation is also reported.     

Pressure studies of deep levels in semiconductors

Abstract

The effects of pressure on the energetics and kinetics of electron emission and capture processes by several important deep levels in Si are discussed. The results yield the first quantitative measures of the breathing mode lattice relaxations accompanying these processes.     

Infrared studies of single crystals of polycaprolactam

Infrared studies of the α-crystalline form of polycaprolactam (nylon 6) have confirmed the assignment of the 1288 and 1210-cm^?1 bands to a unique fold conformation. The γ-crystalline phase has a band at 1212 cm^?1 which overlaps the 1210-cm^?1 fold band in samples containing both α and γ phases. The 1288-cm^?1 band was, therefore, used to monitor regular fold content. No unique fold bands were detected in the γ form. Irregular folds present in solution-grown crystals regularize to the unique fold conformation upon annealing. Crystals which originally exhibit slight differences in regular folding as a result of different crystallization history have similar amounts of regular folds upon annealing at 220°C. Crystals grown from solutions of very dilute concentrations of polymer have different amounts of regular folding. The annealing behavior of crystals prepared from two different solution concentrations reflect the processes of regularization and long period increase.     

Paired gap states in a semiconducting carbon nanotube: deep and shallow levels

Several paired, localized gap states were observed in semiconducting single-wall carbon nanotubes using spatially resolved scanning tunneling spectroscopy. A pair of gap states is found far from the band edges, forming deep levels, while the other pair is located near the band edges, forming shallow levels. With the help of a first-principles study, the former is explained by a vacancy-adatom complex while the latter is explained by a pentagon-heptagon structure. Our experimental observation indicates that the presence of the gap states provides a means to perform local band-gap engineering as well as doping without impurity substitution.     

Photoelectric studies of gallium monosulfide single crystals

Photoconductivity (PC) studies were carried out on GaS single crystals prepared from melt by directional solidification. We studied the effect of light intensity, applied voltage on both the PC and the lifetime of carriers. The V-I characteristics and the absorption spectra were checked for different sample thickness. The present investigation was extended to study the spectral distribution of the photocurrent for GaS. It was found that the photocurrent curves are practically independent of the bias voltage. The energy gap for GaS was found to be 2.5 eV.     

Photoemission studies of single crystals of titanium carbide

The electron distribution in the valence band from single crystals of titanium carbide has been studied by photoelectron spectroscopy with photon energies h?ω = 16.8, 21.2, 40.8 and 1486.6 eV. The most conspicious feature of the electron distribution curves for TiC is a hybridization between the titanium 3d and carbon 2p states at ca. 3–4-eV binding energy, and a single carbon 2s band at ca. 10 eV. By taking into account the strong symmetry and energy dependence of the photoionization crosssections, as well as the surface sensitivity, we have identified strong emission from a carbon 2p band at ? 2.9-eV energy. Our results are compared with several recent energy band structure calculations and other experimental data. Results from pure titanium, which have been used for reference purposes, are also presented.The valence band from single crystals of titanium carbide have been studied by means of photoelectron spectroscopy, with photon energies ranging from 16.8 to 1486.6 eV.By taking into account effects such as the symmetry and energy dependence of the photoionization cross-sections and surface sensitivity, we have found the valence band of titanium carbide to consist of two peaks. The upper part of the valence band at 3–4 eV below the Fermi level consists of a hybridization between Ti 3d and C 2p states. The C 2p states observed in our spectra were mainly excited from a band about 2.9 eV below the Fermi level. The APW^5–9, MAPW¹⁰ and EPM¹¹ band structure calculations predict a flat band of p-character between the symmetry points X′₄ and K₃, most likely responsible for the majority of C 2p excitations observed. The C 2s states, on the other hand, form a single band centered around ?10.4 eV.The results obtained are consistent with several recent energy band structure calculations^{5–11, 13} that predict a combined bonding of covalent, ionic and metallic nature.     

Mössbauer studies in β-AgI single crystals

The Mössbauer effect has been used to study the valence state and the impurity-vacancy dipole formation in single crystal of Co⁵⁷:β-AgI.     

Optical studies in gamma irradiated Mg doped CaF2 single crystals

Pure and Mg doped CaF₂ single crystals grown by the Bridgman method were irradiated with gamma rays (γ-rays) for doses ranging from 97 Gy to 9.72 KGy. The pristine samples showed minimal absorption indicating the purity of the samples. The γ-irradiated pure CaF₂ crystals showed prominent and strong absorption with a peak at ~ 374 nm besides three weak ones at ~ 456, 523 and 623 nm. However γ-rayed Mg doped crystals showed a prominent absorption with a strong peak at ~ 370 nm and a broad one at ~ 530 nm. The absorption indicated the generation of F and F-aggregate centers in the irradiated crystals. The photoluminescence (PL) emission spectrum of both pure and Mg doped crystals showed prominent emission at ~ 390 nm when they were excited at ~ 250 nm. Also, when the samples were excited at 323 and 363 nm strong emissions were observed at ~ 430 and 422 nm respectively. The optical absorption and PL intensities were found to increase with increase in dose.     

Computer studies of boron ion channeling in silicon single crystals

The motion of 200 keV B ions in the [111] direction in a silicon single crystal has been investigated using a computer simulation method. Profiles of the depth distribution of implanted ions for both an ideal crystal and a crystal with thermal vibrations have been obtained. A study of the defect distribution has been carried out.