The ionic model applied to vacancy ordering in NaCl-type materials

An order-disorder transition in Sc_0.8S (NaCl structure type) was studied by high-temperature X-ray diffraction and 700 ± 20°C was found to be the ordering temperature. A group of ordered sublattices on the rock-salt lattice was generated and a Madelung energy and a configurational entropy were calculated for each assuming the lattice was made up of point charges. Mean field and pair interaction approximations were used to model long-range and short-range orderings, respectively. Results indicate that the ionic model is seriously in error in predicting short-range or long-range orderings of the type observed.     

3D-analysis of semiconductor structures by electron tomography

The analysis of advanced nano-devices by the classical 2D imaging with transmission or scanning transmission electron microscopy suffers from projection effects over the sample thickness that result in e.g. blurring due to interfacial roughness or superposition of different structures. Electron tomography allows to overcome these problems. The method involves the acquisition of tilted series of 2D-images, the accurate alignment of these images and the 3D volume reconstruction. Slicing in any direction through this volume yields sections through the device structure with resolution of a few nanometer. The methodology is discussed and illustrated with some case studies.     

Efficiency-limiting defects in silicon solar cell material

The precipitation rate of intentionally introduced iron during low-temperature heating is studied among a variety of single-crystal and polycrystalline silicon solar cell materials. A correlation exists between the iron precipitation rate and the carrier recombination rate in dislocation-free as-grown material, suggesting that diffusion-length-limiting defects in as-grown material are structural defects which accelerate iron precipitation. Phosphorous diffusion gettering was found to be particularly ineffective at improving diffusion length after intentional iron contamination in materials with high iron precipitation rates. We propose that intragranular structural defects in solar cell silicon greatly enhance transition metal precipitation during cooling from the melt and become highly recombination-active when decorated with these impurities. The defects then greatly impair diffusion length improvement during phosphorus gettering and limit carrier lifetimes in as-grown material.     

The determination of local structural units in amorphous SiBN 3C by means of X-ray photoelectron and X-ray absorption spectroscopy

X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge structure (XANES) spectroscopy at the K-edge of Si, N, and B are presented as techniques suited to determine structural units in amorphous SiBN₃C. The measurements reported give evidence for the presence of tetrahedral (SiN₄)- and planar (BN₃)-groups. It is concluded that these structural elements dominate the atomic surroundings of B and Si, respectively. From the spectroscopic results we conclude that C is mainly bonded to N and is not present as a pure carbide.     

Tiegelloses Zonenschmelzen hochschmelzender Metalle mit Hilfe von punktfokussierten Elektronenstrahlen

Summary In conventional systems for floating-zone melting with electron bombardment the use of ring-cathode electron guns is widely spread. However, little is known about the applicability of point-focus electron-beams for floating-zone melting. To study this type of process a floating-zone melting device with a horizontal specimen position and a single point-focus electron-beam has been constructed. The experiment showed that in spite of sagging of the molten zone due to gravity, it is possible to melt rods of all refractory metals with rod diameters up to 5 mm with well controllable operating characteristics. This method easily allows the growth of exactly oriented crystals of W, Ta, Mo and Nb using a goniometric holder with a seed crystal on one side. Some characteristics of this type of zone melting and some preliminary results of an investigation of the single crystals grown in this way are discussed.

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Gekürzte deutsche Fassung eines Vortrages, gehalten an «Second Internat. Conf. on Electron and Ion Beam Science and Technology», New York, April 1966.