The Hexagon, Volume 92, Number 2, Summer 2001

The Hexagon, Volume 92, Number 2, Summer 2001

Date: Summer 2001
Creator: Alpha Chi Sigma
Description: Quarterly publication of the Alpha Chi Sigma chemistry fraternity containing articles related to chemistry research and the activities of the organization, including local chapters and groups.
Contributing Partner: UNT Libraries
Reciprocal space analysis of the initial stages of strain relaxation in SiGe epilayers

Reciprocal space analysis of the initial stages of strain relaxation in SiGe epilayers

Date: January 1, 1996
Creator: Lee, S.R. & Floro, J.A.
Description: Metastable SiGe films were grown by MBE on Si (001) substrates and annealed to promote varying degrees of partial relaxation. X-ray diffraction reciprocal-space analysis was then used to monitor the structural evolution of the displacement fields of the dislocation array with increasing misfit density. The diffuse-x-ray-scattering patterns of the dislocated heterolayers were compared with lineal- misfit densities determined by defect etching, leading to the develop a geometric model which provides a framework for understanding the early-stage evolution of the displacement fields of the dislocation array, and which also explicitly links diffuse x-ray intensity to misfit density. At low misfit density, the diffuse intensity arises from two-dimensional displacement fields associated with single-nonoverlapping dislocations. As misfit density increases, the displacement fields of individual dislocations increasingly overlap producing three-dimensional displacements. The evolving diffuse intensity reflects the transition from 2-D to 3-D displacement fields. Finally, it is demonstrated that the diffuse x-ray intensity of the strained epilayer can be used to accurately measure lineal misfit- dislocation densities from 400 to 20,000 lines/cm.
Contributing Partner: UNT Libraries Government Documents Department
Modification to the Klein-Nishina cross section for Ge electrons at high statistics limit

Modification to the Klein-Nishina cross section for Ge electrons at high statistics limit

Date: November 3, 1995
Creator: Wang, T.F.
Description: Modification factors for the Klein-Nishina cross-sections for gamma-ray with energies between 50 keV and 250 keV incident on Ge electrons have been obtained at the high statistics limit. In this limit, the Ge electrons can then be treated as they are obtained from the self-consistent augmented plane wave calculations, without considering the orientation of crystal lattice with respect to incident photons. The kinematics corrections (i.e. outgoing momenta), on the other hand, have to be taken into account on an event by event basis. Even so, the computing time has been reduced dramatically since the relativistic calculation of the modifications to the Klein-Nishina cross sections is the most tedious one. The modification factors are almost linear with respect to incident photon energy in the interesting energy range with respect to a given photon outgoing angle.
Contributing Partner: UNT Libraries Government Documents Department
Microstructure of amorphous-silicon-based solar cell materials by small-angle x-ray scattering. Annual subcontract report, 6 April 1994--5 April 1995

Microstructure of amorphous-silicon-based solar cell materials by small-angle x-ray scattering. Annual subcontract report, 6 April 1994--5 April 1995

Date: August 1, 1995
Creator: Williamson, D.L.
Description: The general objective of this research is to provide detailed microstructural information on the amorphous-silicon-based, thin-film materials under development for improved multijunction solar cells. The experimental technique used is small-angle x-ray scattering (SAXS) providing microstructural data on microvoid fractions, sizes, shapes, and their preferred orientations. Other microstructural features such as alloy segregation, hydrogen-rich clusters and alloy short-range order are probed.
Contributing Partner: UNT Libraries Government Documents Department
Plasma analysis and diagnostics for high efficiency amorphous solar cell production. Final report

Plasma analysis and diagnostics for high efficiency amorphous solar cell production. Final report

Date: December 21, 1994
Creator: Klepper, C.C.
Description: This is a project that sought to improve the amorphous silicon-germanium (SiGe) thin film deposition process in the production of solar cells. To accomplish this, the electron cyclotron resonance (ECR) plasma discharge, employed for the thin film deposition, was modified. Changes in the parameters of the plasma were monitored with diagnostic techniques, similar to those used in fusion plasma studies. That was the primary contribution from ORNL. Only one phase was contained in the statement of work, with the following tasks: (1) Develop a detailed program for plasma characterization. (2) Carry-out plasma modeling and analysis to support deposition systems design. (3) Operate experimental deposition systems for the purpose of plasma characterization. (4) Analyze data. (5) Modify deposition as directed by measurements. (6) This final report, which was deemed to be the only deliverable of this small project. And while the modified ECR discharge did not show measurable improvement of the conditions relevant to the deposition process, much was learned about the plasma parameters in the process. Some ideas on alternative designs are being discuss and funding options for testing such designed are being sought.
Contributing Partner: UNT Libraries Government Documents Department
Electronic processes in uniaxially stressed p-type germanium

Electronic processes in uniaxially stressed p-type germanium

Date: February 1, 1996
Creator: Dubon, O.D. Jr.
Description: Effect of uniaxial stress on acceptor-related electronic processes in Ge single crystals doped with Ga, Be, and Cu were studied by Hall and photo-Hall effect measurements in conjunction with infrared spectroscopy. Stress dependence of hole lifetime in p-type Ge single crystals is used as a test for competing models of non-radiative capture of holes by acceptors. Photo-Hall effect shows that hole lifetime in Ga- and Be-doped Ge increases by over one order of magnitude with uniaxial stress at liq. He temps. Photo-Hall of Ge:Be shows a stress-induced change in the temperature dependence of hole lifetime. This is consistent with observed increase of responsivity of Ge:Ga detectors with uniaxial stress. Electronic properties of Ge:Cu are shown to change dramatically with uniaxial stress; the results provide a first explanation for the performance of uniaxially stressed, Cu-diffused Ge:Ga detectors which display a high conductivity in absence of photon signal and therefore have poor sensitivity.
Contributing Partner: UNT Libraries Government Documents Department
Epitaxial growth simulation employing a combined molecular dynamics and Monte Carlo approach

Epitaxial growth simulation employing a combined molecular dynamics and Monte Carlo approach

Date: July 1, 1995
Creator: Grein, C.H.; Benedek, R. & Rubia, T. de la
Description: The epitaxial growth of Ge on Si(OO1) is simulated by employing a hybrid approach based on molecular dynamics to describe the initial kinetic behavior of deposited adatoms and Monte Carlo displacements to account for subsequent equilibration. This method is well suited to describe initial nucleation and growth. Stillinger-Weber potentials are employed to describe interatomic interactions.
Contributing Partner: UNT Libraries Government Documents Department
Nanocrystals and quantum dots formed by high-dose ion implantation

Nanocrystals and quantum dots formed by high-dose ion implantation

Date: January 1, 1996
Creator: White, C.W.; Budai, J.D.; Zhu, J.G.; Withrow, S.P.; Hembree, D.M.; Henderson, D.O. et al.
Description: Ion implantation and thermal annealing have been used to produce a wide range of nanocrystals and quantum dots in amorphous (SiO{sub 2}) and crystalline (Al{sub 2}O{sub 3}) matrices. Nanocrystals of metals (Au), elemental semiconductors (Si and Ge), and even compound semiconductors (SiGe, CdSe, CdS) have been produced. In amorphous matrices, the nanocrystals are randomly oriented, but in crystalline matrices they are three dimensionally aligned. Evidence for photoluminescence and quantum confinement effects are presented.
Contributing Partner: UNT Libraries Government Documents Department
Morphological stability of thin films

Morphological stability of thin films

Date: December 31, 1993
Creator: Gray, L.J.; Chisholm, M.F. & Kaplan, T.
Description: The boundary element method for elastostatics is applied to a thin stability problem arising in solid state surface science. An aim of this work is to determine the morphology of Ge deposited on a Si substrate. Nonstandard boundary conditions at the material interface are used to model the epitaxially grown film. In addition to determining the deformed geometry, it is also necessary to compute the surface stress tensor. Although the surface displacement at the junction between the interface and the Si free surface is not differentiable, the hypersingular integral equation for surface stress can still be used. These techniques are described along with results from 2-D calculations.
Contributing Partner: UNT Libraries Government Documents Department
Chemical and electrical properties of cavities in silicon and germanium

Chemical and electrical properties of cavities in silicon and germanium

Date: December 31, 1994
Creator: Myers, S.M.; Follstaedt, D.M.; Petersen, G.A.; Seager, C.H.; Stein, H.J. & Wampler, W.R.
Description: Cavities were formed in Si and Ge by He ion implantation and annealing, and resultant chemical and electrical properties were investigated. The dissociation energies for Si-H and Ge-H surface monohydride bonds were determined, showing that H chemisorption on Si is energetically stable with respect H{sub 2} gas whereas H chemisorption on Ge is not. Cavity walls in Si were found to trap transition metals strongly, suggesting application to impurity gettering in devices. Measurement and modeling of cavity electrical properties elucidated surface electronic states and indicated a potential for controlled electrical isolation in devices. 35 refs.
Contributing Partner: UNT Libraries Government Documents Department
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