Optical evidence of a quantum well channel in low temperature molecular beam epitaxy grown Ga(AsBi)/GaAs nanostructure

A Ga(AsBi) quantum well (QW) with Bi content reaching 6% and well width of 11 nm embedded in GaAs is grown by molecular beam epitaxy at low temperature and studied by means of high-resolution x-ray diffraction, photoluminescence (PL), and time-resolved PL. It is shown that for this growth regime, the QW is coherently strained to the substrate with a low dislocation density. The low temperature PL demonstrates a comparatively narrow excitonic linewidth of ∼ 40 meV. For high excitation density distinct QW excited states evolve in the emission spectra. The origins of peculiar PL dependences on temperature and excitation density are interpreted in terms of intra-well optical transitions.

Comparison of the Band Gap of Porous Silicon as Measured by Photoelectron Spectroscopy and Photoluminescence

The peak energy of the room temperature photoluminescence of porous silicon is compared with the bandgap determined from photoelectron spectroscopy measurements for a series of porous silicon samples prepared under different conditions. The photoluminescence bandgap is found to be smaller than the photoelectron spectroscopy bandgap, but exhibits the same trend with preparation conditions. The width of both the photoluminescence spectrum and the L-absorption edge increases when the current density during the preparation is increased or the sample is allowed to soak in HF after preparation.

Temperature Dependence of the Optical Absorption Edge in Indium Phosphide

Optical bandgap thermometry is a new method for measuring the temperature of semiconductor substrates. In this method, the temperature of the substrate is inferred from the wavelength of the onset of transparency of the substrate which is a measure of its bandgap. Common configurations of this technique are diffuse reflectance and transmittance. In order to calibrate these spectra to substrate temperature and to better understand the temperature dependence of the absorption edge, the transmittance spectra of semi-insulating InP:Fe and n-type InP:S substrates have been measured as a function of temperature in a tube. The width of the absorption edge (Urbach parameter) is found to increase linearly with temperature from 8.7 meV at room temperature to 15.7 meV at 595°C for semi-insulating InP:Fe while it remains independent of temperature at a value of about 21.5 meV for heavily doped (6.5×1018 cm−3) InP:S. For InP:Fe, the temperature dependent part of the width is smaller than predicted by the standard theory where the width of the edge is proportional to the phonon population. The values of the Urbach parameter for InP:Fe are higher than those of semi-insulating GaAs which is attributed to the higher ionicity of InP.

Giant spin-orbit bowing in GaAs1-xBix

We report a giant bowing of the spin-orbit splitting energy Delta0 in the dilute GaAs1-xBix alloy for Bi concentrations ranging from 0% to 1.8%. This is the first observation of a large relativistic correction to the host electronic band structure induced by just a few percent of isoelectronic doping in a semiconductor material. It opens up the possibility of tailoring the spin-orbit splitting in semiconductors for spintronic applications.

Evidence from the surface morphology for nonlinear growth of epitaxial GaAs films

The mesoscale morphology of homoepitaxial GaAs surfaces is explained with an anisotropic and nonlinear Kardar-Parisi-Zhang (KPZ) model in which adatoms are incorporated into the film from a metastable surface layer. Evaporation-condensation between the film and the metastable layer is proposed as the microscopic physical origin of the KPZ description, as well as of the excess noise observed in the power spectral density. The parabolic mounds observed experimentally in films grown on rough substrates are in good agreement with the surface shape expected from the solution of the KPZ equation in the large amplitude limit.

The role of tumor necrosis factor in the development of multiple organ failure in a murine model

OBJECTIVE

To elucidate the role of tumor necrosis factor (TNF) in the development of multiple organ dysfunction syndrome (MODS) after zymosan-induced peritonitis in mice.

DESIGN

Prospective controlled laboratory study on zymosan-induced generalized inflammation in mice. Over < or =28 days, a single intraperitoneal administration of zymosan induced a three-phase illness in C57BL mice, rendering them very ill with MODS-like symptoms from day 7 onward. Additionally, the same experiment was performed on C57BL/6 TNF-Rc-p55 knockout mice to elucidate the role of TNF and its receptor p55.

SETTING

Animal research laboratory.

SUBJECTS

Inbred C57BL mice and C57BL p55-/- mice received a single sterile intraperitoneal injection of zymosan suspended in paraffin oil (0.75 mg/g of body weight).

MEASUREMENTS AND MAIN RESULTS

The animals were monitored for survival, condition, and body weight for < or =28 days. At 3, 7, 14, and 28 days after zymosan administration, bronchoalveolar lavage was performed and lungs and livers were extracted for isolation of RNA and histopathologic evaluation. Reverse-transcriptase-polymerase chain reaction was performed to quantify TNF-alpha messenger RNA (mRNA) in the respective organs. Both animal strains went through initial shock with a high mortality rate during the first 3 days. The C57BL mice developed MODS with typical symptoms and histopathologic results correlating with excessive TNF-alpha mRNA expression from day 7 onward. In contrast, no disease, histopathologic changes, nor TNF-alpha mRNA expression in liver or lung was found within the TNF-Rc-p55-/- mice.

CONCLUSION

Organ-derived TNF-alpha plays a crucial role in the development of MODS in this murine model.