Theory and Applications of X-ray Standing Waves in Real Crystals

Theoretical aspects of x-ray standing wave method for investigation of the real structure of crystals are considered in this review paper. Starting from the general approach of the secondary radiation yield from deformed crystals this theory is applied to different concreat cases. Various models of deformed crystals like: bicrystal model, multilayer model, crystals with extended deformation field are considered in detailes. Peculiarities of x-ray standing wave behavior in different scattering geometries (Bragg, Laue) are analysed in detailes. New possibilities to solve the phase problem with x-ray standing wave method are discussed in the review. General theoretical approaches are illustrated with a big number of experimental results.Comment: 101 pages, 43 figures, 3 table

Simulation of mass interferences considering charge exchange events and dissociation of molecular ions during extraction

Contamination due to mass interferences generally leads to severe problems in ion implantation. To be able to prevent this kind of contamination, the cause of the respective mass interference has to be known. Frequently, however, the transport mechanisms of the contamination are unknown and the search for potential transport mechanisms is troublesome. Simulation of mass interferences, therefore, is an excellent means to find potential transport mechanisms. In this paper, the simulation software ENCOTION (ENergetic COntamination simulaTION) is explained. In the latest version, an enhanced model was implemented in order to calculate the apparent mass of ions. The relevance of the new model is discussed by the example of tungsten contamination in the case of BF2+ implants. A new module that allows for the simulation or mass spectra was recently added to ENCOTION as a new feature

The effect of average soft segment length on morphology and properties of a series of polyurethane elastomers. II. SAXS-DSC annealing study

A series of eight thermoplastic polyurethane elastomers were synthesized from 4,4′-methylene diphenyl diisocyanate (MDI) and 1,4-butanediol (BDO) chain extender, with poly(hexamethylene oxide) (PHMO) macrodiol soft segments. The PHMO molecular weights employed ranged from 433 g/mol to 1180 g/mol. All materials contained 60% (w/w) of the macrodiol. The materials were characterized by differential scanning calorimetry (DSC) following up to nine different thermal treatments. In addition, three of the materials were selected for characterization by small-angle x-ray scattering (SAXS) following similar thermal treatments. The DSC experiments showed the existence of five hard segment melting regions (labelled T1-T5), which were postulated to result from the disordering or melting of sequences containing one to five MDI-derived units, respectively. Evidence for urethane linkage dissociation and reassociation during annealing at temperatures above 150°C is presented. This process aids in the formation of higher melting structures. Annealing temperatures of 80–100°C provided the maximum SAXS scattering intensity values. Materials containing longer soft segments (and, therefore, longer hard segments) were observed to develop and sustain higher melting hard domain structures and also develop maximum average interdomain spacing values at higher annealing temperatures. Another additional series of three PHMO-based polyurethanes having narrower hard segment length distributions, was synthesized and characterized by DSC in the as-synthesized and annealed states. The resulting DSC endotherms provided further evidence to suggest that the T1-T5 endotherms were possibly due to melting of various hard segment length populations

A new determination method of very low Fe contamination by UFS

We have produced very low Fe-dose (108-109 Fe/cm2) implanted Si samples. A new method of Ultraviolet Fluorescence Spectra (UFS) measurements has been used to determine the contents of Fe on the surfaces of Fe-implanted samples. We find that the Fe-impurities have their own ultraviolet fluorescent peak wavelength at room temperature and their characteristic spectral peak intensities are proportional to the Fe-doses (Fe-concentrations) in Fe implanted Si samples. This method is very sensitive, efficient and nondestructive for testing the Fe contamination on silicon. Some SOI (Silicon on Insulator) wafers and VLSI chips were evaluated with the UFS method. The results indicate that the UFS method is able to measure the very low Fe-contamination. The limit is below (108-109) Fe/cm2 or (1013-1014) Fe/cm3 in Si samples.</p

Solid-phase epitaxy of silicon amorphized by implantation of the alkali elements rubidium and cesium

The redistribution of implanted Rb and Cs profiles in amorphous silicon during solid-phase epitaxial recrystallization has been investigated by Rutherford backscattering spectroscopy and secondary ion mass spectroscopy. For the implantation dose used in these experiments, the alkali atoms segregate at the a-Si/c-Si interface during annealing resulting in concentration peaks near the interface. In this way, the alkali atoms are moved towards the surface. Rutherford backscattering spectroscopy in ion channeling configuration was performed to measure average recrystallization rates of the amorphous silicon layers. Preliminary studies on the influence of the alkali atoms on the solid-phase epitaxial regrowth rate reveal a strong retardation compared to the intrinsic recrystallization rate