Deformation mechanism and dislocation structure of high-purity molybdenum single crystals at low temperatures

High purity molybdenum single crystals were deformed in tension and compression along the symmetric double slip orientation [110] in the temperature range from 300 K down to 0.5 K with strain rates between 10⁻³ and 10⁻⁵ s⁻¹. The activation volume was measured by stress relaxation tests. The dislocation structure of the deformed crystals (T → 1.85 K) was examined by high voltage electron microscopy. It was established that the low temperature increase of the critical shear stress exhibits three distinct temperature regimes with different temperature dependences. These non-uniformities are discussed in terms of recently developed theories of kink-pair formation and kink-kink interactions on screw dislocations in bcc metals. The HVEM observations suggest that the mobility of screw dislocations at very low temperatures should be determined by the combined effects of the PEIERLS barriers and the jog dragging.     

High-temperature Localization of Plastic Deformation in Lithium Fluoride Single Crystals

Experimental results on the superlocalization of plastic deformation at high strains and high temperatures in LiF single crystals are described. The physical conditions of transition to a localized plastic flow in the temperature range of 603 K to 1073 K T (0.53–0.94T_mp) using constant strain rate compression tests under strain rates from 10⁻³s⁻¹ to 10⁻²s⁻¹ are found. The results indicate that the deformation mechanism involves dislocation climb, controlled by diffusion. The connection of high temperature flow instability with an excessive concentration of point defects (strain vacancies) in zone of shear has been confirmed.     

DCXS and RHEED characterization of effectiveness of annealing implanted Si crystals by using pulsed UV excimer laser and sample scanning technique

In the experiment (111) oriented silicon plates were implanted with 80 keV Ge ions (dose 5 × 10¹⁵ cm⁻²) and with 150 keV Kr ions (dose 5 × 10¹⁵ cm⁻²). Then the samples were annealed with the pulsed excimer laser by using the sample scanning technique. The effectiveness of the annealing has been analyzed by means of double crystal X-ray spectrometry (DCXS) and reflection high energy electron diffraction (RHEED). The results of the experiment show that the applied technique of annealing considerably improves the perfection of the structure of the implanted silicon crystals.     

Convergent beam camera for structure analysis of microcrystals

An X-ray tube with external miniature anode was constructed and mounted inside of a cylindrical diffraction camera in the immediate vicinity of the crystal holder. The distance of specimen from tube focus is 15 mm. This special construction allows to obtain diffractograms of small crystal specimens (∼ 10⁻³ mm in diameter) at reasonable exposure time (several hours).     

Confrontation of the BCF theory and computer simulation experiments with measured (R, σ) curves

A brief summary of crystal growth models – the surface diffusion model of Burton, Cabrera and Frank and computer simulation models – is given and these models are confronted with measured (R, σ) curves. It was found that the most (R, σ) curves measured so far can be fitted by BCF curves with 10⁻² ≲ σ₁ ≲ 10⁻¹ and C having an order of magnitude of 10⁻⁴ cm ≲ s⁻¹. ΔG turns out to be 12 ± 5 kcal ≲ mol⁻¹. – Some of the (R, σ) curves can be described better by a nucleus above nucleus formalism. The order of magnitude of A is 10⁻⁴ cm · s⁻¹ and 10⁻² ≲ B ≲ 10⁻¹. – It is concluded what kind of work should be done in future to check theoretical models.     

Stresses in silicon after boron diffusion (III) determination of lattice contraction coefficient in consideration of residual stresses

Rocking curves of boron diffused silicon obtained by a double crystal spectrometer in (n, -n) position permit a rather simply determination of the relative variation of the lattice constant of the doped layer with high accuracy. For the calculation of the lattice contraction coefficient it is important to take into consideration the residual stresses found after boron diffusion in order to correct the value obtained from the double crystal spectrometer. The corrected lattice contraction coefficient is 2.5 · 10⁻²⁴cm³/atom.     

Pressure Dependence of C–V Curve for Ferroelectric PbTiO3 Thin Films Prepared by RF Multi-target Magnetron Sputtering

Lead titanate thin films were prepared in-situ by RF magnetron sputtering method in the substrate temperature region of 550 °C ˜ 650 °C using Ti and Pb metal targets and oxygen gas. The films deposited at 650 °C for 60 min – when the applied power to the Ti and Pb target and deposition pressure were 200 W, 40 W, and 1.8 × 10⁻² Torr, respectively — had stoichiometric composition ratio and shown X-ray diffraction patterns of tetragonal structure like that of the powder. For the application to the piezoelectric field effect transistor (PI-FET), the substrate of SiO₂ (50 nm)/p-Si(100) was used. Leakage current density of the thin film was 7 × 10⁻⁸ A/cm² at 100 kV/cm, dielectric breakdown voltage was 1.8 MV/cm, and so it showed high insulator characteristics. Capacitance-voltage curve was measured as a function of pressure. The variation width of the capacitance was 6.5 pF at bias voltage of –4 volts, and the value increased linearly according to the pressure up to about 6 kgf/cm², and was saturated at the pressure of 8 kgf/cm².     

Crystal growth of PbTe and (Pb,Sn)Te by the bridgman method and by THM

Synthesis and growth of PbTe and (Pb, Sn)Te single crystals by the Bridgman method and by the Travelling Heater Method (THM) from Te-rich solutions are described. It is to be seen from comparative investigations that seeded THM growth reproducibly provides oriented single-crystalline ingots free of low-angle grain boundaries and with etch pit densities of 8–12 × 10⁴ cm⁻². All the materials were p-type with carrier concentrations from 1 to 2 × 10¹⁸ cm⁻³.     

Determination of carbon,silicon and boron content in semi-insulating GaAs by infrared absorption spectroscopy

Measurements of the local vibrational mode (LVM) absorption of ¹²C_As at 582 cm⁻¹, ²⁸Si_Ga at 384 cm⁻¹ and ⁽¹⁰⁾¹¹B_Ga at (540 cm⁻¹) 517 cm⁻¹ can be used to determine the concentration of these residual impurities in semi-insulating (SI) GaAs. Although the energy-limited resolution of a grating spectrometer does not allow measuring the line shape of the narrow LVM bands in GaAs the intensity of it determined with definite spectral slit width (SSW) is a reliable measure for the respective impurity content. Calibration factors given in the literature and peculiarities in the measurements and evaluations for the different impurities are discussed.     

An AES/XPS study of oxygen involved reactions on InSb

The oxidation of ion-etched InSb(110)-cleavage planes was investigated by means of AES and XPS, respectively. Whereas the sticking coefficient of oxygen at indium sites was found to reach a saturation value after slight ion bombardment, the oxygen uptake rate of antimony remains low (sticking probability in the 10⁻⁷ range) with raising ion dose to a point where a drastical change in oxidation behaviour occurs at ion doses in the 10⁻² As · cm⁻² range. Then indium and antimony are nearly simultaneously oxidized with sticking coefficients of roughly 10⁻³. Cluster formation is discussed as one possible mechanism to explain the experimental findings. Adsorption experiments on disordered surfaces can contribute to a better understanding of surface reactions during gas phase growth of single crystals, since the in-growth situation of the top layer of the latter is far away from the ideal situation that is prepared by in situ cleaving only.     

IR and X-Ray Powder Diffraction Studies on Ba2Me(HCOO)6. 4 H2O (Me = Co,Ni, Zn)

It has been established that the double salts Ba₂Me(HCOO)₆. 4 H₂O (Me = Co, Ni, Zn) are isostructural with Ba₂Cu(HCOO)₆. 4 H₂O (trinclinic space group P1 = C¹_i). The infrared spectra of the double salts and their deuterated analogues have been recorded and the internal modes of the formate groups and the water molecules are reported. The analysis of the infrared spectra indicates that some of the internal formate modes (v₃ and v₄) reflect the existence of three crystallographically independent formate ions. The comparatively large frequency separations between the asymmetric and symmetric C–O stretching modes is a criterion for the different C–O bond lengths within each formate groups. The number and the positions of the bands in the high frequency range (4000–2300 cm⁻¹) are evidence for the existence of two inequivalent water molecules. The apearance of four uncoupled O–D modes in the spectra of the isotopically dilute samples shows that the water molecules are asymmetric. The librational modes of the water molecules are discussed as well.     

Vapor growth and characterization of pyrite (FeS2) doped with Co,Ni, and As: Variations in semiconducting properties

Pyrite (FeS₂) crystals doped with As, Ni and Co were synthesized with chemical vapor transport over an 18 cm horizontal gradient of 700–600 °C in evacuated quartz tubes, from a mixture of FeS and S, with FeBr₃ as a transport agent. Sulfur fugacity and thus S:Fe stoichiometry was constrained by the Fe_1−xS/FeS_2−y buffer. As, Ni and Co concentrations were ∼3–800 ppm, ∼200–1500 ppm and ∼ 450–3700 ppm, respectively.Semiconducting properties were measured at room temperature using a van der Pauw and Hall measurement system. Ni and Co-doped pyrite are n-type while As-doped pyrite tends to be p-type. Resistivity for Co-doped pyrite ranged from 0.009 to 0.02 Ω cm while for Ni- and As-doped pyrite, resistivity ranged from 2 to 17 Ω cm. Undoped pyrite resistivity ranged from 15 to 85 Ω cm. Carrier concentration was similar for undoped and Ni-doped pyrite, ranging from 10¹⁵ to 10^16.6 cm⁻³, while for Co-doped pyrite it ranged from 10^18.7 to 10^19.3 cm⁻³ and for As-doped pyrite it ranged from 10¹⁴ to 10¹⁸ cm⁻³. Hall mobility was similar for Co and Ni-doped pyrite ranging from 60 to 270 cm² v⁻¹ s⁻¹ while for undoped pyrite it ranged from 8 to 70 cm² v⁻¹ s⁻¹. Hall mobility for As-doped pyrite ranged from 55.0 to 0.2 cm² v⁻¹ s⁻¹ for electrons and from 0.1 to 11.3 cm² v⁻¹ s⁻¹ for holes with the exception of one sample (of 22). These values should be viewed more as trends than as definitive. The results obtained for Ni, Co, and undoped pyrite are similar to those reported in the literature while results for As-doped synthetic pyrite have not previously been reported.     

Dislocation densities in copper single crystals after thermal treatment

Copper crystals of high purity and doped with nickel were subjected to a long time thermal treatment at 1050°C, in order to reduce the as-grown dislocation density of about 10⁷ cm⁻². A dissolution of the dislocations during their motion to the crystal surface was observed. Regions of different dislocation densities arose. Finally the crystals exhibited constant dislocation densities of 10² cm⁻². Such a perfection or a better one of the crystals is reached only by a long time treatment, since the dislocation velocity without external stresses cannot exceed 1 · 10⁻⁷ cm · s⁻¹ in copper single crystals of high purity.     

Growth Kinetics of Barium Sulphate in Suspension

The growth rate of barium sulphate seed crystals from stirred solutions was studied conductometrically at 25°C by a stopped-flow technique. The supersaturation ranged from 3 × 10⁻⁷ to 3 × 10⁻⁸ mol BaSO₄/cm³. The seed crystals were grown in the system during the initial (steady-state) period of the experiment. Crystal size distributions were determined by optical microscopy. The growth rate of barium sulphate under the conditions of the experiments can be expressed by a quadratic function of supersaturation. The results, which suggest an interface rate-controlling mechanism, are discussed with respect to published data.     

The interaction of oxygen with the iron (111) surface,mainly studied by AES

The cleaned surface was oxidized by means of pure oxygen at a pressure of 3 × 10⁻⁶ – 3 × 10⁻³ pa and at temperatures of 300 K, 370 K, and 620 K. The Auger peaks of high energy (for oxygen at 510 eV and for iron at 703 eV) were used for the quantitative determination of the oxygen coverage on the iron surface. The experimental results on the change of oxygen coverage as a function as a function of the dose are interpreted by means of a theoretical model and provided definite informations about the bonding state of the adsorbate. In the lower energy part of the Auger spectrum there appear peak shape modifications during oxidation. These observations allow us to suppose that in the process of oxidation there are in action two kinds of chemical bonding of oxygen with iron differing by density of states in the valence band.     

Zur Realstruktur von Ga1–xInxAs LPE-Schichten

Ga_1–xIn_xAs epitaxial layers (0.02 ≦ × ≦ 0.12) are grown on (111)-oriented GaAs substrates from nonstoichiometric melts. The etch pit densities – determined by chemical etching – yield values between 2 · 10⁵ cm⁻² and 3 · 10⁷ cm⁻² and were found to be dependent on composition, layer thickness and cooling rate. X-ray topography of cleaved {110}-planes gives information on layer quality and indicates the existence of stress in the substrate lattice near the heterojunction. The validity of Vegard's law in the investigated concentration range was confirmed by X-ray determination of the lattice constants. The half width of double crystal spectrometer rocking-curves, the epd and the relative intensity of photoluminescence show similar dependence on the composition of the mixed crystal layers.     

Sub-boundaries on (002) cleavages of Li2CO3 single crystals

Linear arrays of dislocations (straight, terminating and curved) are observed on etching with 2% citric acid (002) cleavages of lithium carbonate (Li₂CO₃) single crystals, grown by zone melting technique. As the dislocations are non-uniformly spaced and disappear on successive etching, they may not be revealing low-angle grain boundary, nor slip traces as they are terminating and curved meaning crystallographically non-oriented. On the observation of experiments on successive etching and etching of matched pairs, it is concluded that the arrays of etch pits reveal dislocation walls (dislocation density 1.1 × 10⁶ — 1.5 × 10⁷ pits cm⁻²) probably created due to the localized thermal stresses released as a result of high temperature annealing of the crystal during growth. The implications are discussed.     

Initiation and propagation of shear bands in Zr-based bulk metallic glass under quasi-static and dynamic shear loadings

The effect of strain rate on the initiation and propagation of shear bands in the Zr_41.2Ti_13.8Cu_12.5Ni₁₀Be_22.5 bulk metallic glass under shear loading was investigated. The quasi-static (at a strain rate of 1.5 × 10⁻³ s⁻¹) and the dynamic shear tests (at a strain rate of 1.4 × 10³ s⁻¹) were conducted at room temperature using a GATAN Microtest-2000 instrument and a split Hopkinson pressure bar (SHPB) with a specially designed ‘Plate-shear’ specimen, respectively. The complete process of shear band initiation, propagation, and shear band unstable propagation-induced fracture was revealed. The experimental results demonstrated that the macroscopic shear strength is relatively insensitive to the strain rate, whereas shear band initiation and fracture are significantly dependent on strain rate. A dimensionless Deborah number was introduced to characterize the effect of the strain rate on the formation of shear bands. Additionally, the observed numerous liquid droplets and melted belts on the fracture surface at high-strain rates demonstrate that the adiabatic heating exerts a significant effect on fracture behavior of the material.     

Dynamic deformation of silicon-rich V3Si single crystals at elevated temperatures

The plastic deformation behaviour of the intermetallic phase V₃Si (Cr₃Si type) was investigated under dynamic conditions. The experiments revealed that V₃Si deforms plastically at a strain rate of about 4.7 × 10⁻⁵s⁻¹ above 1200°. Flow stress depends strongly on deformation temperature and strain rate. An alloy hardening by deviation from stoichiometric composition within the range of homogeneity is observed.     

Structure and electrical resistance of thin scandium films (III). Study on electrical properties

The specific resistance-thickness of ScH_x (vacuum 10⁻⁵ to 5 · 10⁻⁶ Torr) and Sc films (vacuum 1 · 10⁻⁸ to 3 · 10⁻⁸ Torr) relationships have been obtained by keeping a record of a film resistance directly in the course of condensation. The results are discussed according to the theory FUCHS -SONDHEIMER (ScH_x, Sc) and MAYADAS -SHATZKES (Sc) assuming a diffuse scattering of the carriers (P = 0) on the external surface of the films. A mean free path of the current carriers is 188 to 355 Å (T ⋍ 300 K) for ScH_x and 400 Å with grain-boundary scattering parameter from 0.1 to 0.3 for Sc. The temperature dependence of specific resistivity of Sc films was obtained in the interval from 300 to 650 K during the annealing in vacuum 5 · 10⁻⁹ Torr.