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Notes: Abstract A sedimentological study of the early Proterozoic Black Reef Quartzite Formation in the south-western parts of the Transvaal province of South Africa was undertaken with the primary aim of examining the sedimentological controls of gold mineralization in the Black Reef placer, which occurs at the base of this Formation. A second aim of the study was to investigate the early history of the basin in which the Transvaal Sequence of South Africa was deposited. The thin, siliciclastic Black Reef Quartzite Formation, which is informally subdivided into a lower Conglomerate Unit and an upper Quartzite Unit, is underlain by Archaean rocks belonging to the basement complex and the Witwatersrand and Ventersdorp Supergroups, and is overlain by a thick succession of carbonate rocks of the Malmani Subgroup. The pre-Transvaal palaeosurface is characterised by elongated northeast to southwest trending grabens and partly-eroded horst blocks. The Black Reef Quartzite Formation, which has a maximum thickness of about 30 m in the study area, typically comprises a succession of interbedded arenites and mudstones, with a sporadically-developed basal Conglomerate Unit. Thickness trends are similar to the dominant structural trend of the pre-Transvaal palaeosurface. At localities where the Conglomerate Unit is absent, the Formation invariably overlies quartzites of the Witwatersrand Supergroup directly. The palaeocurrent distribution of the Conglomerate Unit is unimodal, with modes towards the southwest in the southern parts of the study area and towards the north in the northern regions. Most of the palaeocurrent distributions of the Quartzite Unit are unimodal, too, but bimodal distributions were found at three localities. Pebble size of the Black Reef placer is largest in the northeastern parts of the study area, but no orderly lateral size variation was found. Pebble roundness, too, varies greatly and apparently randomly. The composition of the pebble assemblage is not constant, but no systematic lateral change could be detected. A petrographic study of the arenites of the Formation reveals a remarkable textural and mineralogical maturity, especially for the upper beds. It is concluded that the pre-Transvaal palaeosurface had a palaeorelief of up to 30 m and that the topography of the palaeo-landscape was the dominant factor controlling early sedimentation in the basin. The palaeo-grabens probably constituted the valleys of shallow braided stream systems that drained south-westwards and northwards from a palaeo-drainage divide in the northern parts of the study area. Sediment, including detrital gold, was derived from erosion of Witwatersrand rocks and fed to the graben valleys via several alluvial fans. During a subsequent transgression, the fluvial systems became drowned and transgressive estuarine conditions ensued. During the final stages of siliciclastic sedimentation, the upper quartzite beds of the Formation were probably reworked by shallow marine processes before carbonate precipitation commenced. The cause of the marine transgression is not known beyond doubt. It is suggested, however, that lithospheric rifting, which initiated the extrusion of the underlying Ventersdorp lavas, resumed during early Transvaal times, resulting in complete severing of the continental crust and the creation of a linear sea.

Notes: Abstract Two bioavailability studies of S(+)-ibuprofen (dexibuprofen) were conducted in healthy volunteers to define the relationship between the bioavailability of the drug after administration of dexibuprofen alone or as part of ibuprofen racemate. Enantioselective plasma drug analysis was used throughout. In the first study, the bioavailability of dexibuprofen from a 400 mg tablet formulation was compared with that from 400 mg in aqueous solution. The tablet formulation did not influence the bioavailability of the drug and dexibuprofen was well absorbed from the gastro-intestinal tract. The second study was divided into three identical parts. Bioavailability of dexibuprofen 200, 400 and 600 mg was compared with its bioavailability from ibuprofen racemate 400, 800 and 1200 mg. The second study showed that the mean relative bioavailability of dexibuprofen to ibuprofen racemate was 0.66, thus enabling the estimation of clinically useful dexibuprofen doses from the usual doses of the racemate. The 95% confidence interval limits did not include 0.5, leading to the conclusion that administering half of the racemate dose would not provide patients with an adequate amount of therapeutically active drug.

Notes: The interfacial reactions in the structures of Si/SiO2 (500 nm)/Ru (65 nm) (up to 950 °C) and Si/SiO2 (500 nm)/Ru (72 nm)/Al-0.8 wt % Si (630 nm) (up to 700 °C), were studied by Rutherford backscattering spectrometry, Auger electron spectroscopy, x-ray diffractometry, selected-area electron diffraction, energy-dispersive x-ray spectroscopy, scanning electron microscopy, and transmission electron microscopy. A thin film of Ru was stable on a SiO2 substrate up to 30 min in a vacuum anneal at 950 °C. In vacuum, a fast interfacial reaction between the Ru thin film and the Al-Si overlayer started between 550 and 575 °C, resulting in the formation of a Si/SiO2/ RuAl2/(Ru4Al13)Al-Si layer sequence. Similar to the reactions between Pt group metals and Al, the Ru/Al reaction is nonuniform. It is controlled by a nucleation mechanism and is accompanied by void formation. © 1995 American Institute of Physics.

Notes: We have studied the incorporation of heavily supersaturated C into Si using solid-phase epitaxy (SPE) of implanted amorphous layers. The strain in the Si1−xCx/Si heterostructures was measured using rocking curve x-ray diffraction. The microstructure and defect introduction were examined using ion channeling and transmission electron microscopy (TEM). The fraction of C located on substitutional lattice sites in the Si was monitored using Fourier transform infrared absorption spectroscopy and ion channeling at resonance energies. Carbon-depth profiles were monitored by secondary ion mass spectroscopy. The metastable solubility limit for the incorporation of C into Si by SPE was found to be 3.0–7.0×1020 atoms/cm3, which is over three orders of magnitude above the equilibrium solubility at the Si melting point. This limit was determined by the ability to regrow without the introduction of microtwins and stacking faults along {111} planes. We postulate the local bond deformation resulting from the atomic size difference between C and Si leads to the faceting of the amorphous–crystalline interface and allows defect introduction, thus limiting the C supersaturations achieved in Si by SPE. It was also found that the defect density in the regrown alloys could be reduced by higher SPE regrowth temperatures in rapid thermal anneal processing. © 1996 American Institute of Physics.

Notes: The self-encapsulation kinetics of Ag/Al bilayers were studied both experimentally and theoretically as part of the effort to introduce Ag as an alternative metallization scheme for future ultra-large-scale-integrated technologies. Theoretical modeling was based on an analytical solution of a modified diffusion equation, which incorporated the diffusion of Al atoms through the Ag layers during the Ag/Al bilayer encapsulation progress. The amount of segregated Al atoms was monitored by both Rutherford backscattering spectrometry and film resistivity measurements, and correlated well with the theoretical predictions. These findings showed that the kinetics of the self-encapsulation could be significantly affected by both (i) the chemical affinity between Al and Ag atoms, and (ii) the interfacial energy between the metal layer (Ag) and the newly formed AlxOyNz diffusion barriers. Higher anneal temperatures were shown to accelerate the encapsulation process, and hence, achieved a lower resistivity in the underneath Ag layer. This model, in addition, confirmed the self-passivating characteristics of AlxOyNz diffusion barriers formed by Ag/Al bilayers annealed between 500 and 725 °C. © 1999 American Institute of Physics.

Notes: We report the first study of interfacial reactions of a metal with Si1−x−yGexCy epitaxially grown on Si. The Ti/Si1−x−yGexCy/Si (0〈y〈1.7%) contact system was studied after isochronal heat treatments from 500 to 800 °C. The results for Ti/Si1−xGex phase formation agree with recent published works. However, C incorporation in the epilayer causes a dramatic decrease in strain relaxation during the Ti reaction with the epilayer, a delay in the appearance of the C54 phase, a decreased Ge concentration in the silicide–germanide phases, and carbon accumulation (probably in the form of TiC) at the silicide–germanide/epilayer interface. Also, at high annealing temperatures, a roughing of the silicide–germanide/epilayer interface was detected for the C-containing samples. A possible explanation for the reduced strain relaxation is based on mobility of dislocations. © 1996 American Institute of Physics.

Notes: Thickness profiles of silicon dioxide films deposited by ozone-augmented tetraethoxysilane have been experimentally measured in ultra-high-aspect ratio capillaries. The deposition profiles exhibit a sharp drop in film thickness near the capillary entrance followed by a gradual decrease in thickness along the capillary. A feature-scale model for this process has been developed which includes the effect of by-products on the reaction kinetics and transport inside the structure. Simulated deposition profiles agree well with the experimental data, indicating that a trapped by-product inside the capillary inhibits the film-forming reaction, thus producing the characteristic film profile. © 1995 American Institute of Physics.

Notes: Pseudomorphic SiGeC films have been grown on (100) Si by atmospheric pressure chemical vapor deposition at 600 and 700 °C using SiH2Cl2, GeH4, and C2H4 precursors. Films with C concentrations of up to 2.5 at. % were entirely pseudomorphic and a 120-nm-thick Si66.5Ge31C2.5 film had 90% substitutional carbon. With increasing C incorporation due to increased ethylene flow, a layered structure was formed consisting of an amorphous film overlaying a buried pseudomorphic film. The crystalline-to-amorphous transition was initiated by the accumulation of C on the epitaxial growth surface. This deteriorated surface resulted in the formation of stacking faults along {111} planes and subsequent amorphization. Defect formation and amorphization could be prevented by periodically growing a thin Si epilayer. © 1997 American Institute of Physics.

Notes: Si1−x−yGexCy films ( x≈0.90, y≤0.02) were grown by molecular beam epitaxy on Si substrates. Infrared optical absorption was used to obtain the band gap energy at room temperature. Biaxial strain obtained from x-ray diffraction measurements verified the presence of nearly relaxed films, and the total and substitutional C contents were obtained from channeling C-resonance backscattering spectrometry. We show by direct measurements that interstitial C had a negligible impact on the band gap, but substitutional C was found to increase the band gap with respect to equivalently strained Si1−xGex alloys. While strain decreases the band gap, the effect of substitutional C on the band gap depends on the Si and Ge fractions. © 1996 American Institute of Physics.