Interband absorption in alpha-Sn/Ge short-period superlattices

Band-to-band infrared absorption has been studied in a series of Sn1Gem (m=11, 15, and 21) strained layer superlattices for the first time. The absorption coefficient shows a quadratic increase with two onsets, characteristic for indirect transitions. From a numerical fit to the absorption spectra, band gap energies are determined in the energy range between 0.55 and 0.75 eV, in accordance with theoretical calculations. The temperature dependence of the band gaps show the usual behavior, at low temperatures quadratic and at higher temperatures linear decrease with increasing temperature. Applied Physics Letters is copyrighted by The American Institute of Physics

Infrared optical properties and band structure of α-Sn/Ge superlattices on Ge substrates

Short-period α-Sn/Ge strained-layer superlattices have been prepared on [001] Ge substrates by low-temperature molecular-beam epitaxy. We have achieved almost-defect-free and thermally stable single-crystalline structures. Photocurrent measurements in a series of Sn1Gem (m>10) superlattices reveal a shift of the fundamental energy gap to smaller energies with decreasing Ge layer thickness m, in good agreement with band-structure calculations. A direct fundamental energy gap is predicted for a slightly increased lateral lattice constant in α-Sn/Ge superlattices

Electronic structure and optical properties of short-period α-SnnGem superlattices

Short period α-Sn/Ge strained layer superlattices have been prepared on Ge(001) substrates by low temperature molecular beam epitaxy. We have achieved almost defect free and thermally stable single crystalline structures. Photourrent measurements in a series of Sn1Gem(m>10) superlattices reveal a shift of the fundamental energy gap to smaller energies with decreasing Ge layer thickness m, in good agreement with band structure calculations. A direct fundamental energy gap and large direct band gap absorption is predicted for a slightly increased lateral lattice constant in α-Sn/Ge superlattices

Fabrication and properties of epitaxially stabilized Ge / α-Sn heterostructures on Ge(001)

We have investigated the influence of the growth parameters during molecular beam epitaxy on the realizibility of diamond crystal structure Ge / α-Sn alloys and superlattices on Ge(001) substrates. The segregation behaviour of Sn during Ge overgrowth has been studied. We find that for growth temperatures higher than 300°C the incorporation rates are less than 0.005 ML-1. The low-energy electron diffraction data of a series of Ge0.9Sn0.1 films deposited at substrate temperatures in the range of 185 to 275°C indicate a transition to amorphous growth for thicknesses beyond 20 Å. Single-crystal GenSnm superlattices with α-Sn layer thicknesses m of 1 and 2 monolayers and periodicities n + m between 10 and 22 monolayers have been fabricated by an unconventional molecular beam epitaxy technique which involves large substrate temperature modulations during growth. Structural characterization of the samples by means of transmission electron microscopy. Raman spectroscopy and X-ray diffraction exhibits distinct superlattice effects. The downward shift of the fundamental energy gap of the superlattices with increasing Sn content, as extracted from absorption measurents with a Fourier transform spectrometer, is in excellent agreement with theoretical values obtained from pseudopotential band structure calculations. The films were found to be stable against phase transition up to temperatures of 430–465°C, depending on the average Sn content

Properties of Sn/Ge superlattices

Short-period strained-layer alpha -Sn/Ge superlattices have been synthesized recently by a low temperature molecular beam epitaxy technique which allows a large variation of substrate temperature. Thin, tetragonally distorted alpha Sn layers h ave been stabilized on Ge substrates by growth conditions far way from thermal equilibrium. The fundamental bandgap of Sn/Ge superlattices is shifted towards lower energies with increasing average Sn concentration, as expected from theory

NO-induced migraine attack: Strong increase in plasma calcitonin gene-related peptide (CGRP) concentration and negative correlation with platelet serotonin release

The aim of the present study was to investigate changes in the plasma calcitonin gene-related peptide (CGRP) concentration and platelet serotonin (5-hydroxytriptamine, 5-HT) content during the immediate headache and the delayed genuine migraine attack provoked by nitroglycerin. Fifteen female migraineurs (without aura) and eight controls participated in the study. Sublingual nitroglycerin (0.5 mg) was administered. Blood was collected from the antecubital vein four times: 60 min before and after the nitroglycerin application, and 60 and 120 min after the beginning of the migraine attack (mean 344 and 404 min; 12 subjects). In those subjects who had no migraine attack (11 subjects) a similar time schedule was used. Plasma CGRP concentration increased significantly ðP , 0:01Þ during the migraine attack and returned to baseline after the cessation of the migraine. In addition, both change and peak, showed significant positive correlations with migraine headache intensity ðP , 0:001Þ: However, plasma CGRP concentrations failed to change during immediate headache and in the subjects with no migraine attack. Basal CGRP concentration was significantly higher and platelet 5-HT content tended to be lower in subjects who experienced a migraine attack. Platelet serotonin content decreased significantly ðP , 0:01Þ after nitroglycerin in subjects with no migraine attack but no consistent change was observed in patients with migraine attack. In conclusion, the fact that plasma CGRP concentration correlates with the timing and severity of a migraine headache suggests a direct relationship between CGRP and migraine. In contrast, serotonin release from platelets does not provoke migraine, it may even counteract the headache and the concomitant CGRP release in this model