Huge shift of fundamental electronic absorption edge in Sr1−xBaxNb2O6 crystals at elevated temperatures

1995 ◽  
Vol 188 (2) ◽  
pp. K43-K45 ◽  
Author(s):  
J. Seglins ◽  
S. Kapphan
Keyword(s):  
Electronic Absorption ◽  
Absorption Edge ◽  
Elevated Temperatures

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.

scholarly journals Direct correlation between aromatization of carbon-rich organic matter and its visible electronic absorption edge

Carbon ◽  
2015 ◽  
Vol 88 ◽  
pp. 139-147 ◽  
Author(s):  
Nicola Ferralis ◽  
Yun Liu ◽  
Kyle D. Bake ◽  
Andrew E. Pomerantz ◽  
Jeffrey C. Grossman
Keyword(s):  
Organic Matter ◽  
Electronic Absorption ◽  
Absorption Edge

The Electronic Absorption Edge of Petroleum

1992 ◽  
Vol 46 (9) ◽  
pp. 1405-1411 ◽  
Author(s):  
Oliver C. Mullins ◽  
Sudipa Mitra-Kirtley ◽  
Yifu Zhu
Keyword(s):  
Electronic Absorption ◽  
Absorption Edge ◽  
Spectral Region ◽  
Population Distribution ◽  
Fluorescence Emission ◽  
Crude Oils ◽  
Excitation Wavelength ◽  
Urbach Tail ◽  
Wide Range ◽  
Peak Widths

The electronic absorption spectra of more than 20 crude oils and asphaltenes are examined. The spectral location of the electronic absorption edge varies over a wide range, from the near-infrared for heavy oils and asphaltenes to the near-UV for gas condensates. The functional form of the electronic absorption edge for all crude oils (measured) is characteristic of the “Urbach tail,” a phenomenology which describes electronic absorption edges in wide-ranging materials. The crude oils all show similar Urbach widths, which are significantly larger than those generally found for various materials but are similar to those previously reported for asphaltenes. Monotonically increasing absorption at higher photon energy continues for all crude oils until the spectral region is reached where single-ring aromatics dominate absorption. However, the rate of increasing absorption at higher energies moderates, thereby deviating from the Urbach behavior. Fluorescence emission spectra exhibit small red shifts from the excitation wavelength and small fluorescence peak widths in the Urbach regions of different crude oils, but show large red shifts and large peak widths in spectral regions which deviate from the Urbach behavior. This observation implies that the Urbach spectral region is dominated by lowest-energy electronic absorption of corresponding chromophores. Thus, the Urbach tail gives a direct measure of the population distribution of chromophores in crude oils. Implied population distributions are consistent with thermally activated growth of large chromophores from small ones.

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.

Properties of Carbon-doped TiO2 (Anatase) Photo-Electrodes

2005 ◽  
Vol 885 ◽  
Author(s):  
Cristina S. Enache ◽  
Joop Schoonman ◽  
Roel van de Krol
Keyword(s):  
Thermal Treatment ◽  
Visible Light ◽  
Spray Pyrolysis ◽  
Absorption Edge ◽  
Light Absorption ◽  
Elevated Temperatures ◽  
Visible Light Absorption ◽  
Tio2 Anatase ◽  
Carbon Doped ◽  
Post Deposition

ABSTRACTTo enhance the visible light absorption of anatase TiO2 photo-electrodes, the material was doped with carbon by two different methods: i) by spray pyrolysis under a CO2 atmosphere, and ii) by a post-deposition thermal treatment in a hexane-containing environment. For the hexane-treated samples, most of the carbon is located at the surface, from which it can be removed by re-oxidation at elevated temperatures. In addition, both methods seem to result in the presence of small amounts of carbon in the bulk of the material, as deduced from a small red-shift of the absorption edge of TiO2.

Characterization of Rare-Earth Fluoride Anti-Stokes Phosphors by Scanning arid Transmission Electron Microscopy

1971 ◽  
Vol 29 ◽  
pp. 142-143
Author(s):  
N. M. P. Low ◽  
L. E. Brosselard
Keyword(s):  
Electron Microscopy ◽  
Rare Earth ◽  
Elevated Temperatures ◽  
Stoichiometric Composition ◽  
Rare Earth Ions ◽  
Crystalline Solid ◽  
Precipitation Process ◽  
Rare Earth Fluoride ◽  
Earth Fluoride ◽  
Rare Earth Fluorides

There has been considerable interest over the past several years in materials capable of converting infrared radiation to visible light by means of sequential excitation in two or more steps. Several rare-earth trifluorides (LaF3, YF3, GdF3, and LuF3) containing a small amount of other trivalent rare-earth ions (Yb3+ and Er3+, or Ho3+, or Tm3+) have been found to exhibit such phenomenon. The methods of preparation of these rare-earth fluorides in the crystalline solid form generally involve a co-precipitation process and a subsequent solid state reaction at elevated temperatures. This investigation was undertaken to examine the morphological features of both the precipitated and the thermally treated fluoride powders by both transmission and scanning electron microscopy.Rare-earth oxides of stoichiometric composition were dissolved in nitric acid and the mixed rare-earth fluoride was then coprecipitated out as fine granules by the addition of excess hydrofluoric acid. The precipitated rare-earth fluorides were washed with water, separated from the aqueous solution, and oven-dried.

Sign in / Sign up

Export Citation Format

Share Document