On splitting of dislocations at a reverse motion in germanium single crystals

In the preceding paper, Paper I, we described an analytical technique, based on ion-induced x-ray yields, for detecting low-Z impurities in medium-Z targets. In this paper, Paper II, we report the application of this method to the lattice location of impurity atoms. Two systems have been examined to test the method, viz., P and S implants in Ge single crystals. The channeling effect was applied to the phosphorus and sulfur K x-ray yields excited by 0.5-MeV protons. Some 93% of implanted 31P (0.7 × 1015 atoms cm−2, room-temperature implant, 450°C anneal), were found to occupy substitutional sites; the fraction dropped to [inverted lazy s] 63% for an implant dose of 2.7 × 1015 atoms cm−2. Channeling effect results in 〈110〉, 〈111〉, and 〈100〉 directions for Ge(S), implanted at room temperature and annealed at 450°C, prescribe a preferred off-lattice (> 0.3 Å) site for the sulfur, necessarily different from the regular tetrahedral or hexagonal interstitial sites. For hot (220°C) implantation conditions, poorer crystal annealing and weaker channeling effects were observed.

Nuclear interactions for 15 GeV/ c protons and pions under random and channeling conditions in germanium single crystals

Analysis of reordering of Ge amorphous surface by ruby laser; kinetics of the surface annealing after ion implantation using the optical reflectivity; occurrence of laser induced periodical structures; nanohills formation by Nd:YAG laser allowed us to resume common features for these process which belong to Thermogradient effect. Experimental data on annealing of p-Si (111) and i-Ge (111) mechanically polished surfaces by Nd:YAG laser radiation using of optical microscopes and atomic force microscopes, optical reflectivity of He-Ne laser and the four-probe method confirmed the main role of Thermogradient effect in the reordering process of the mechanically polished surface of Si and Ge to single crystal. It was found that row of nanohills arises on the irradiated surface of Ge and Si single crystal after irradiation by Nd:YAG. Photoluminescence of nanohills row in visible range of spectra was established. The photoluminescence of Ge and Si samples after irradiation by Nd:YAG laser is explained with quantum confinement effect on the top of nanohills - quasi quantum dots. For explanation of this effect gathering of interstitial atoms at the irradiated surface is proposed.

In order to clarify the formation mechanism of work-hardened layer introduced at the time of frictional or abrasive working, (001) planes of pure Al and Cu single crystals are scratch-deformed by diamond cone styli as a simplified model of working. The deformed structures around the end of the scratch-grooves in [100] and [110] directions and also the cross-section of the groove are examined by selected area ECP using SEM, and the results are compared with those by TEM. The following results are obtained:(1) By the scratch deformation, the regions where crystals are bent and rotated are introduced around the end of scratch groove and under the groove. The form of the region, the amount of crystal rotation and the direction of rotation depend on the scratch direction. The amount of rotation, especially, depends on the cone angle of stylus.(2) In the case of Cu single crystal, the regions, in which crystal has rotated with respect to 〈211〉 axis, can be classified by comperatively clear boundaries between them. Thus the activated region of slip systems contributing to the crystal rotation can be estimated at the time of scratch deformation.(3) Through the observations around the end of the groove by TEM, the process of variation of dislocation structures during the procession of stylus can be traced. As the result shows, cell walls are formed along the slip planes which are activated at the time of crystal rotation. Also, the increment of dislocation density is recognized in the regions which suffer several different slip processes and at the boundary regions which are formed by the regions of different rotational direction.

Previous investigations showed that kinematics and muscle activity associated with natural whole-body movements along the gravity direction present modular organizations encoding specific aspects relative to both the motor plans and the motor programmes underlying movement execution. It is, however, still unknown whether such modular structures characterize also the reverse movements, when the displacement of a large number of joints is required to take the whole body back to a standing initial posture. To study what motor patterns are conserved across the reversal of movement direction, principal component analysis and non-negative matrix factorization were therefore applied, respectively, to the time series describing the temporal evolution of the elevation angles associated with all the body links and to the electromyographic signals of both natural and reverse whole-body movements. Results revealed that elevation angles were highly co-varying in time and that despite some differences in the global parameters characterizing the different movements (indicating differences in high-level variable associated with the selected motor plans), the level of joint co-variation did not change across movement direction. In contrast, muscle organization of the forward whole-body pointing tasks was found to be different with respect to that characterizing the reverse movements. Such results agree with previous findings, according to which the central nervous system exploits, dependently on the direction of motion, different motor plans for the execution of whole-body movements. However, in addition, this study shows how such motor plans are translated into different muscle strategies that equivalently assure a high level of co-variation in the joint space.

Microhardness of single crystals La 3 Ga 5 SiO 14 , La 3 Ta 0.5 Ga 5.5 O 14 , Ca 3 TaGa 3 Si 2 O 14 family of lantanum gallium silicate of trigonal symmetry class of 32 space group P 321 has been researched by Knoop method. Anisotropy of microhardness determined by the ability to bring the material under the indenter, which determines the value of microhardness on different planes and in different crystallographic directions in the plane. The technique of measuring the microhardness by Knupp method for semi − automatic hardness tester Tukon 2100B for single crystals of langasite family. Anisotropy of the I group of microhardness (microhardness polar dependence on indentor position relatively crystallography directions in the plane of measurement) on the crystallography planes (112 − 0), (011 − 0), (0001) has been founded. Anisotropy of microhardness in fragile crystals of langasite family determined by the possibility of mass transfer under the indenter due to the movement of interstitial atoms and vacancies of oxygen and gallium. Measurements have shown that microhardness on all investigated planes of CTGS single crystals, as base, and the prismatic lower than the respective planes of LGS and LGT single crystals; wherein in CTGS single crystals there is no anisotropy of microhardness microhardness as I, and II type. Polar dependence of the mechanical properties of langasite and langatate single crystals should be taken into account in the surface treatment technology and manufacturing techniques of piezo − and acoustoelements.

Dislocation configurations in germanium single crystals developed during tensile deformation at 600°C were frozen in by the rapid cooling of deformed crystals under load and investigated with etch pit technique. Distribution patterns of dislocation etch pits at various deformation stages were observed on two kinds of surfaces which were cut out parallel to the cross slip plane (1\bar11) and to the primary slip plane (111). Peculiar distribution patterns of etch pits were developed during stage I, namely, the stripe on the (1\bar11) surface and the dense zone on the (111) surface. Stripe patterns of dislocation etch pits were also observed on the surfaces cut out parallel to the critical slip plane (\bar111) and to the conjugate slip plane (\bar1\bar11). It was found that the stripes on (1\bar11), (\bar111), and (\bar1\bar11) surfaces and the dense zone on (111) surface were interrelated each other. Characteristics of the distribution pattern of etch pits were compared with those observed on f.c.c. metals.

ABSTRACTFracture experiments with silicon specimens in recent years have shown the need for a new approach to the analysis of rapidly propagating cracks in single crystals. Behaviour and phenomena have been revealed that fracture in these materials is rather different from the fracture of both amorphous and polycrystalline materials. We show that continuum mechanics is insufficient for analyzing crack propagation in single crystals since it is unable to consider atomistic‐scale phenomena. Accordingly, we describe basic phenomena associated with rapid crack propagation in silicon: (i) anisotropic velocity‐dependent R‐curve behaviour, as a key phenomenon dictating atomistic scale behaviour, (ii) crack deflection from one cleavage plane to another as a mesoscopic scale phenomenon in single‐crystal fracture, (iii) the Rayleigh surface wave speed as the limiting crack tip velocity is re‐examined, (vi) the lowest crack velocity in brittle crystals is examined, and finally (v) the interaction between crack path and preferred cleavage planes in single crystals is depicted.

The core structure of a/2 〈110〉 dislocations in PbS has been analysed by high resolution transmission electron microscopy. Dislocations on {100} and {110} slip planes are dissociated while those on {111} are perfect. The dissociation width d of 45° dislocations on {100} and edge dislocations on {110} has been estimated to about 5 and 2 Burgers vectors, respectively. The results support a correlation of d with the ionicity of the material as it is expected from elasticity theory: an increase of d on {100} and decrease of d on {110} and {111} with decreasing ionicity. Finally the slip behaviour of dislocations in ionic crystals is discussed in terms of dislocation dissociation and plastic anisotropy.

Anomalous effects of dopant distribution in Ge single crystals grown by FZ-technique aboard spacecrafts

Adsorption of tetraethylammonium ions on Cd(0 0 0 1) single crystal plane from solutions in ethanol

Grooving wear of single-crystal tungsten carbide

Isotopically enriched [sup 70]Ge and [sup 74]Ge single crystals were successfully gown by a newly developed vertical Bridgman method. The system allows us to reliably grow high purity Ge single crystals of approximately 1 cm[sup 3] volume. To our knowledge, we have grown the first [sup 70]Ge single crystal. The electrically active chemical impurity concentration for both crystals was found to be [approximately]2 [times] cm[sup [minus]3] which is two order of magnitude better that of [sup 74]Ge crystals previously grown by two different groups. Isotopic enrichment of the [sup 70]Ge and the [sup 74]Ge crystals is 96.3% and 96.8%, respectively. The residual chemical impurities present in both crystals were identified as phosphorus, copper, aluminum, and indium. A wide variety of experiments which take advantage of the isotopic purity of our crystals are discussed.

Flow stress measurements were made on single crystals of Ni3Ge with several different orientations. Slip systems were determined by two-surface trace analysis, and dislocation arrangements due to deformation were observed by transmission electron microscopy. The yield stress increases with increasing temperature in the temperature range of −196∼800°C where {111} slip operates (positive temperature dependence), but it decreases as {001} slip commences. Critical resolved shear stress for {111}〈10\bar1〉 slip is orientation-dependent. The positive temperature dependence is pronounced even below room temperature, and the yield stress nearly doubles as the temperature is raised from −196 to 27°C. Electron microscope observation on dislocation arrangements in the specimens deformed at −196 and 27°C has revealed that the mobility of screw dislocations decreases with increasing temperature. These observations indicate that the positive temperature dependence of the yield stress is controlled by the mobility of screw dislocations. This decrease of mobility leading to the positive temperature dependence of the yield stress can be explained by thermally activated cross-slip of screw dislocations from the (111) plane to the (010) plane.

: The Knoop hardness of 4H and 6H single crystals of silicon carbide (SiC) was determined at room temperature. X-ray diffraction techniques confirmed the crystal structure and orientation of each polytype verifying that both discs had the six-fold symmetry expected for a hexagonal crystal and that the c-axis was oriented approximately perpendicular to disc faces. This symmetry was confirmed by the Knoop hardness values on the (0001) plane of the 4H crystal, but the symmetry was not as apparent in the 6H crystal, which may indicate that the c-axis was not as nearly aligned to the faces of the 6H as it was in the 4H crystal. The Knoop hardness was determined at 15 increments around the c-axis using 0.98 and 2.94 N indentation loads. The average Knoop hardness on the (0001) plane at 0.98 N was approximately 30 GPa for both crystals with the average dropping to around 24 GPa for the 6H crystal and 23 GPa for the 4H when the indentation load was increased to 2.94 N. The difference between the maximum and minimum hardness values on the (0001) plane of both crystals at the 0.98 N indentation load was approximately 2 GPa but the difference was significantly less at 2.94 N.