Basal dislocation interactions with a forest of non-basal dislocations in zinc

The mobility of basal dislocations in 99•999% pure zinc crystals with controlled densities of non-basal forest dislocations has been measured as a function of stress at temperatures of 298°K and 84°K. The range of the forest dislocation density was 10^2 to 10^6cm^(−2) and the range of the resolved shear stress was 0 to 34•2 × 10^6 dyne/cm^2. The mobility of dislocations was characterized by three distinct regions: a low-stress region showing no dislocation motion, a high-stress region with a linear velocity-stress relationship and, in between, a transition region, in accordance with theoretical predictions. The critical stress for basal edge dislocation motion was found to be proportional to the square root of the forest density and to be temperature-independent. A temperature-dependent critical stress for basal screw dislocations was observed. A strong interaction between basal dislocations and forest dislocations is indicated. In the high-stress region where dislocation velocity is a linear function of the stress the velocity is independent of the forest density. The values of drag coefficient B in this region are in good agreement with those previously reported for specimens with low forest densities (10^2 to 10^3 cm^(−2))

Misoriented Epitaxial Growth of (111)CoSi_2 on Offset (111)Si Substrates

Single crystal epitaxial films of CoSi_2 were grown by MBE on various (111)Si single crystal substrates, whose surfaces were purposely tilted towards the _g, direction by small angles ϕ_g,†, 0°, ≤ ϕ_g, ≤, 4° measured between the surface normal and the _g, direction of Si. The actual offset angle, ϕ_g was determined by back Laue reflection method. The average perpendicular strain of the CoSi_2 epilayer, ε┵, and the _f orientation of the epitaxial CoSi_2 film were determined by double crystal diffractometry. We find that the misorientation angle, a, measured between the Si _g, and CoSi_2 _f directions, increases linearly with the offset angle, ϕ_g, up to ϕ_g = 4°. A simple geometrical model is developed which predicts that α = ε┵ × tan ϕ_g. The model agrees quantitatively with the experimental data. The equivalent strain energy associated with the misorientation is approximated by that of a low angle tilt boundary. The misorientation angle α of the equilibrium state, determined by minimizing the total strain energy of the epitaxial film, is nonzero in general

Defects Annealing of Si^+ Implanted GaAs at RT and 100°C

Annealing behavior of point defects near room temperature is studied by measuring the strain relaxation of Si+ implanted GaAs. Polished semi-insulating GaAs wafers were implanted with 300keV Si^+ at liquid nitrogen (LN_2) and room temperature (RT). The strain profile was obtained by the X-ray Double Crystal Diffraction (DCD) technique and kinematical fitting. The maximum strain of the samples stored at RT and elevated temperature 100°C in air, decreases with time, which indicates the reduction of point defects. Relaxation is exponential in time. At least two time constants of 0.24hrs and 24hrs are needed to fit the data, suggesting that two different processes are responsible for annealing defects. Time constants are obtained for different doses at RT and LN_2 implantation temperature, and found to be insensitive to both these quantities. The activation energy for defect migration is estimated using simple diffusion model

Characterization of high-energy heavy-ion implanted InP crystals by a variety of techniques

MeV ion implantation into InP compound semiconductor crystals with 5 MeV nitrogen ions has been investigated. The subsequent characterization was undertaken by a variety of techniques such as nuclear resonant reaction analysis, channeling Rutherford backscattering spectrometry, X-ray rocking curve measurement and cross-sectional transmission electron microscopy. These techniques have clearly revealed substantial changes in structural properties and radiation-induced damage distribution as well as the influence of post-implantation annealing in ^(15)N ion-implanted InP samples. The results from these measurements, which are presented in this paper, are shown to be consistent with each other, and have led to a coherent description of the effects of the implantation and subsequent annealing. In a practical sense this has demonstrated the complementary nature of the analytical capabilities of all of these techniques used for the investigation of the processes involved in high-energy heavy-ion implantation

Amorphization and recrystallization in MeV ion implanted InP crystals

A comprehensive study of MeV-^(15)N-ion-implanted InP by a variety of analytical techniques has revealed the physical processes involved in MeV ion implantation into III-V compound semiconductors as well as the influence of post-implantation annealing. It provides a coherent picture of implant distribution, structural transition, crystalline damage, and lattice strain in InP crystals induced by ion implantation and thermal annealing. The experimental results from the different measurements are summarized in this report. Mechanisms of amorphization by implantation and recrystallization through annealing in MeV-ion-implanted InP are proposed and discussed in light of the results obtained

Wear Properties of A Shock Consolidated Metallic Glass and Glass-Crystalline Mixtures

Powder flakes prepared from 50 μm thick melt spun ribbons of Markomet 1064 (Ni_(52.5)Mo_(38)Cr_8 B_(1.5) wt%) were shock consolidatedin the unannealed and annealed condition. The unannealed flakes (microhardness 933 kg/mm^2) are amorphous while flakes annealed at 900ºC for 2 hours have an fcc structure with a grain size of 0.3 μm and microhardness of 800 kg/mm^2. The shock consolidated amorphous powder compact (250 kJ/kg shock energy) shows no crystal peaks in an X-ray diffractometer scan. Compacts of annealed powder (400 to 600 kJ/kg shock energies) contain amorphous material (18-21%) which was rapidly quenched from the melt formed at interparticle regions during the consolidation process. The microhardness of the amorphous interparticle material is 1100 kg/mm^2. Wear properties of the compacts measured in low velocity pin on disk tests show low average dynamic friction values (∿0.03). The 60 hour cumulative wear appears to correlate with the energy of shock compaction and surface porosity of the compacts rather than the metallic glass content

Total Synthesis of Clavatadine A

The first total synthesis of the potent and selective human blood coagulation factor XIa inhibitor clavatadine A (1) is described. Direct, early-stage guanidinylation enabled rapid, convergent access to an immediate clavatadine A precursor. Concomitant lactone hydrolysis and guanidine deprotection with aqueous acid cleanly provided clavatadine A (1) in only four steps (longest linear sequence, 41–43% overall yield)

Formation of Buried Oxide in MeV Oxygen Implanted Silicon

We have studied the formation of buried oxide in MeV oxygen implanted Si. A continuous oxide layer is formed in the samples implanted with 2x10^(18)/cm^2 oxygen and annealed at 1300° C. The microstructures are studied by cross-sectional transmission electron microscopy and high resolution electron microscopy. Chemical information was obtained by electron energy loss spectroscopy. The effects of implantation temperature are studied. Implantation at a low substrate temperature leads to a well-defined buried SiO_2 layer, inhibits the formation of oxide precipitates in the silicon, and reduces silicon inclusions in the SiO_2