Epitaxial Growth and Band Structure Effects at the Si/Ge(111) Interface

1987 ◽  
Vol 102 ◽  
Author(s):  
J.C. Woicik ◽  
R.S. List ◽  
B.B. Pate ◽  
P. Pianetta
Keyword(s):  
Band Structure ◽  
Lattice Constant ◽  
Absorption Edge ◽  
Elevated Temperatures ◽  
Solid Phase ◽  
Many Body ◽  
White Line ◽  
Low Energy Electron ◽  
Excitonic Effects ◽  
X Ray Absorption

ABSTRACTX-ray absorption fine structure, Auger electron spectroscopy and low energy electron diffraction have been used to study the evolution of the lattice constant and the degree of intermixing of thin (∼5 Å) silicon films grown on the germanium(111) surface by solid phase epitaxy. Our results indicate that as the system is annealed, the silicon intermixes with the germanium at elevated temperatures to form a pseudomorphic Si-Ge alloy with the germanium bulk lattice constant. We further observe a splitting of the ‘white line’ Is absorption edge in crystalling Si, SiGe and dilute (<10% silicon) SiGe. The measured splittings agree with band structure calculations for Si, SiGe, and Ge, respectively, indicating that the density of conduction band states of SiGe behaves as the interpolation between the states of Si and Ge. Qualitatively, our spectra may be interpreted in terms of a one electron picture without invoking many body excitonic effects. The absorption edge of amorphous silicon is also presented and the features of the density of states due to long versus short range order are extracted.

Structural Studies of Metal-Semiconductor Interfaces by Means of Surface Extended X-Ray Absorption Edge Fine Structure

1982 ◽  
Vol 18 ◽  
Author(s):  
J. Stohr ◽  
R. Jaeger ◽  
T. Kendelewicz ◽  
G. Rossi ◽  
I. Lindau
Keyword(s):  
Fine Structure ◽  
Absorption Edge ◽  
Elevated Temperatures ◽  
Complete Information ◽  
Interface Layer ◽  
Silver Clusters ◽  
Strong Reaction ◽  
Weak Reaction ◽  
X Ray ◽  
X Ray Absorption

We report surface extended X-ray absorption edge fine structure (SEXAFS) studies of the early stages of Schottky barrier formation. Results will be presented for aluminum, silver and palladium on Si(111) 7 × 7 in the range from ⅓ monolayer to five monolayers. The SEXAFS signal reveals the local structure around the metal atoms in terms of bond lengths and coordination numbers. Complex ordered and disordered surface structures are observed ranging from weak reaction between the components (e.g. silver clusters on silicon) to strong reaction (e.g. Pd2Si formation). At elevated temperatures the Ag–Si interface is particularly interesting and consists of a well-defined ordered interface layer (√3 × √3 Ag on Si(111)) with silver clusters growing on top. While most other surface structural techniques fail to yield complete information the power of SEXAFS as a local structural technique becomes most apparent for such complex systems. Structure determinations for some metalsemiconductor interfaces will be presented.

Investigation by X-Ray Absorption Spectroscopy of Platinum Clusters Supported on Zeolites

1979 ◽  
Vol 34 (1) ◽  
pp. 40-42 ◽  
Author(s):  
P. Gallezot ◽  
R. Weber ◽  
R. A. Dalla Betta ◽  
M. Boudart
Keyword(s):  
Particle Size ◽  
Absorption Spectrum ◽  
Catalytic Activity ◽  
Absorption Edge ◽  
White Line ◽  
Y Zeolites ◽  
X Ray ◽  
Platinum Clusters ◽  
Spectral Area ◽  
X Ray Absorption

Abstract The onset of the LIII edge of the X-ray absorption spectrum of platinum in F-zeolites involves an electronic transition from core to band levels producing a so-called white line. The spectral area of this increases and the edge position shifts to higher energies, first when the platinum particle size becomes small enough so that the clusters are in the supercages, second when the clusters are covered with oxygen, and third when multivalent cations are introduced in the zeolite. Both features of the absorption edge indicate that under the three above circumstances, platinum becomes more electron deficient. This conclusion had been inferred earlier from the enhanced catalytic activity of Pt clusters in Y zeolites.

X-Ray absorption edge elemental imaging of B. thuringienis

1989 ◽  
Vol 47 ◽  
pp. 212-213
Author(s):  
R. L. Stears
Keyword(s):  
Absorption Edge ◽  
Elemental Distribution ◽  
X Rays ◽  
Differential Absorption ◽  
Synchrotron Source ◽  
High Brightness ◽  
X Ray ◽  
Elemental Imaging ◽  
Cellular Integrity ◽  
X Ray Absorption

Because of the nature of the bacterial endospore, little work has been done on analyzing their elemental distribution and composition in the intact, living, hydrated state. The majority of the qualitative analysis entailed intensive disruption and processing of the endospores, which effects their cellular integrity and composition.Absorption edge imaging permits elemental analysis of hydrated, unstained specimens at high resolution. By taking advantage of differential absorption of x-ray photons in regions of varying elemental composition, and using a high brightness, tuneable synchrotron source to obtain monochromatic x-rays, contact x-ray micrographs can be made of unfixed, intact endospores that reveal sites of elemental localization. This study presents new data demonstrating the application of x-ray absorption edge imaging to produce elemental information about nitrogen (N) and calcium (Ca) localization using Bacillus thuringiensis as the test specimen.

EELS white line intensities calculated for the 3d and 4d metals

1989 ◽  
Vol 47 ◽  
pp. 388-389
Author(s):  
C. C. Ahn ◽  
D. H. Pearson ◽  
P. Rez ◽  
B. Fultz
Keyword(s):  
Experimental Data ◽  
Line Intensity ◽  
Transition Probabilities ◽  
Initial Increase ◽  
White Line ◽  
Hartree Fock ◽  
Line Intensities ◽  
Integrated Intensity ◽  
X Ray Absorption ◽  
The Continuum

Previous experimental measurements of the total white line intensities from L2,3 energy loss spectra of 3d transition metals reported a linear dependence of the white line intensity on 3d occupancy. These results are inconsistent, however, with behavior inferred from relativistic one electron Dirac-Fock calculations, which show an initial increase followed by a decrease of total white line intensity across the 3d series. This inconsistency with experimental data is especially puzzling in light of work by Thole, et al., which successfully calculates x-ray absorption spectra of the lanthanide M4,5 white lines by employing a less rigorous Hartree-Fock calculation with relativistic corrections based on the work of Cowan. When restricted to transitions allowed by dipole selection rules, the calculated spectra of the lanthanide M4,5 white lines show a decreasing intensity as a function of Z that was consistent with the available experimental data.Here we report the results of Dirac-Fock calculations of the L2,3 white lines of the 3d and 4d elements, and compare the results to the experimental work of Pearson et al. In a previous study, similar calculations helped to account for the non-statistical behavior of L3/L2 ratios of the 3d metals. We assumed that all metals had a single 4s electron. Because these calculations provide absolute transition probabilities, to compare the calculated white line intensities to the experimental data, we normalized the calculated intensities to the intensity of the continuum above the L3 edges. The continuum intensity was obtained by Hartree-Slater calculations, and the normalization factor for the white line intensities was the integrated intensity in an energy window of fixed width and position above the L3 edge of each element.

scholarly journals Theoretical description of optical and x-ray absorption spectra of MgO including many-body effects

2021 ◽  
Vol 103 (19) ◽  
Author(s):  
Vijaya Begum ◽  
Markus E. Gruner ◽  
Christian Vorwerk ◽  
Claudia Draxl ◽  
Rossitza Pentcheva
Keyword(s):  
Absorption Spectra ◽  
Theoretical Description ◽  
Many Body ◽  
X Ray ◽  
Many Body Effects ◽  
X Ray Absorption

In-Situ Characterization of Growth and Intermixing at a Heteroepitaxial Interface: Fe on Au(001)

1993 ◽  
Vol 318 ◽  
Author(s):  
Q. Jiang ◽  
A. Chan ◽  
Y.-L. He ◽  
G.-C. Wang
Keyword(s):  
Elevated Temperatures ◽  
Chemical Elements ◽  
Background Intensity ◽  
In Situ Characterization ◽  
Initial Stage ◽  
Monolayer Growth ◽  
Low Energy Electron ◽  
Energy Dependent

ABSTRACTThe growth and chemical intermixing of submonolayer and a few monolayer thick Fe films on a Au(001) surface was studied by High Resolution Low Energy Electron Diffraction (HRLEED) technique. Through the analysis of the energy dependent angular profiles as a function of time, we obtained the distribution of islands and distribution of spacings during submonolayer growth. The interference of electron waves from different chemical elements in terraces at different heights in the surface contributes to the background intensity and broadening in the angular profiles of diffraction beams. A subsurface Fe capped by Au islands as a result of atomic place exchange was observed at the initial stage of monolayer growth. From the energy dependent angular profiles as a function of temperature, we determine the quantitative change of inhomogeneity length (∼20 Å) at the interface of ultrathin films at elevated temperatures due to intermixing.

Racemization in stepwise solid-phase peptide synthesis at elevated temperatures

Tetrahedron ◽  
2004 ◽  
Vol 60 (21) ◽  
pp. 4671-4681 ◽  
Author(s):  
Marcos P. Souza ◽  
Marina F.M. Tavares ◽  
M.Terêsa M. Miranda
Keyword(s):  
Peptide Synthesis ◽  
Elevated Temperatures ◽  
Solid Phase ◽  
Solid Phase Peptide Synthesis

Evidence of x-ray absorption-edge shift as a function of luminescence wavelength in porous silicon

2000 ◽  
Vol 62 (15) ◽  
pp. 9911-9914 ◽  
Author(s):  
G. Dalba ◽  
N. Daldosso ◽  
P. Fornasini ◽  
M. Grimaldi ◽  
R. Grisenti ◽  
...  
Keyword(s):  
Porous Silicon ◽  
Absorption Edge ◽  
X Ray ◽  
Absorption Edge Shift ◽  
X Ray Absorption
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