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One of the important parameters in understanding the mechanism of the early stage of organic thin-film growth is the critical nucleus size i*. Here, submonolayer films of para-sexiphenyl grown on amorphous silicon dioxide substrates were investigated by means of atomic-force microscopy and have been analyzed using the recently proposed capture-zone scaling. Applying the generalized Wigner surmise we determine from the capture-zone distribution i* at room temperature and 373 K. The results are compared to traditional analysis by island-size scaling and the applicability of the capture-zone scaling is critically discussed with respect to island shape.
The formation of the silicide MnSi1.7 by reactive deposition of Mn onto Si(001) has been studied using Sb as a surfactant. The growth was performed under UHV conditions by simultaneous or consecutive exposure of the Si substrates, held at high temperatures (550°C, 600 °C), to a flux of Sb and Mn atoms. The presence of Sb during the growth strongly increases the island density and changes the crystalline orientation of the MnSi1.7 grains. The morphology and the orientation of the resulting silicide are the same both for the deposition of Mn on a Sb terminated Si(001) surface and for the co-deposition of Mn and Sb on Si(001). A residual Sb coverage close to one monolayer (ML) at the sample surface has been determined for both of the preparation modes at Tsub = 550 °C. The transition from the growth mode without Sb to the surfactant-controlled growth has been studied for Tsub = 600 °C. It has been found that the silicide morphology and orientation strongly depend on the thickness of Sb pre-coverage, which was increased from 0 to about 0.7 ML (1 ML = 6.78·1014 atoms cm-2).
RHEED pattern of SiC layers on both (100) and (111)Si grown by carbonization were studied. Different deviations from the single crystalline structure were found ranging from twinning up to changes in the orientation and textured growth. Special attention was drawn on lattice relaxation and morphology evolution during the growth of the formed SiC. Relationships between the occurrence of typical RHEED pattern and the morphology and process parameters are presented.
Photothermal methods provide a valuable complement to the destructive measurement techniques for the detection of the optimal process conditions in ion beam synthesis of wide band gap semiconductor compounds. In addition to their nondestructive and non contact qualities, they are highly sensitive to changes of thermophysical properties due to structural changes. Analyses have been carried out with (SiC)l-x(AIN)x compounds, formed by ion beam synthesis.
The electrical transport properties of β-FeSi2 single crystals have been investigated in dependence on the purity of the source material and on doping with 3d transition metals. The transport properties included are electrical conducticvity, Hall conductivity and thermopower mainly in the temperature range from 4K to 300K. The single crystals have been prepared by chemical transport reaction in a closed system with iodine as transport agent. In undoped single crystals prepared with 5N Fe both electrical conductivity and thermopower depend on the composition within the homogeinity range of β-FeSi2 which is explained by different intrinsic defects at the Sirich and Fe-rich phase boundaries. In both undoped and doped single crystals impurity band conduction is observed at low temperatures but above 100K extrinsic behaviour determined by shallow impurity states. The thermopower shows between 100K and 200K a significant phonon drag contribution which depends on intrinsic defects and additional doping. The Hall resistivity is considered mainly with respect to an anomalous contribution found in p-type and n-type single crystals and thin films. In addition doped single crystals show at temperatures below about 130K an hysteresis of the Hall voltage. These results make former mobility data uncertain. Comparison will be made between the transport properties of single crystals and polycrystalline material.
The preparation of buried epitaxial layers of a compound ABx in a matrix of the material A can be performed by allotaxy . In the first process step a distribution of ABx precipitates is prepared in the matrix A by codeposition of A and B. This contribution reports on the spatial distribution and the crystallographic orientation of NiSi2precipitates in the Si- matrix. Cross-section transmission electron microscopy was utilized to characterize the samples. The observed depth distribution of Ni in the Si matrix differs remarkably from the calculated distribution given by the deposition rates of Si and Ni. This redistribution of Ni results in two well distinguishable bands of NiSi2precipitates - a narrow one and a broad one - in the Si matrix. The narrow band consists of epitaxial NiSi2 precipitates; and a mixture of epitaxially and twinned grown NiSi2precipitates is formed in the broad band. Under certain deposition conditions self-ordering of the NiSi2precipitates in the narrow band has been observed parallel and perpendicular to the growth direction. In these cases the diameter of the epitaxial NiSi2precipitates varies between 12 and 50 A and the distance between them is in the order of some 10 Å.
There is debate on the neurological impact of chronic exposure to Manganese (MN).
MN burden from rural well water was studied cross-sectionally in two proband cohorts from rural dwellings located in northern Germany. Both cohorts had exposure times for up to 40 years and were separated on the basis of well water MN content. Group A (41 subjects; mean age 57.5 years) was exposed to MN water contents of at least 0.300 mg/l (range 0.300 to 2.160), while group B (74 subjects; mean age 56.9 years) was exposed to concentrations of less than 0.050 mg/1. Both proband groups were homogenous with regard to age, sex, nutritional habits, and drug intake. Neurological assessments by clinical investigators blinded for proband’s exposure status was done using structured questionnaires, standardized neurological examination with assessment of possible Parkinsonian signs by the Columbia University Rating Scale, and instrumental tests of fine motor coordination.
No significant difference in any neurological measure was found between groups. Results were not confounded by demographic and dietary features.
Exposure to high body burden of MN does not result in detectable neurological impairment. Exposure to MN in drinking water does not seem to be a risk factor for idiopathic Parkinson’s disease.
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