Buried dislocation networks designed to organize the growth of III-V semiconductor nanostructures

We first report a detailed transmission electron microscopy study of dislocation networks (DNs) formed at shallowly buried interfaces obtained by bonding two GaAs crystals between which we establish in a controlled manner a twist and a tilt around a k110l direction. For large enough twists, the DN consists of a twodimensional network of screw dislocations accommodating mainly the twist and of a one-dimensional network of mixed dislocations accommodating mainly the tilt. We show that in addition the mixed dislocations accommodate part of the twist and we observe and explain slight unexpected disorientations of the screw dislocations with respect to the k110l directions. By performing a quantitative analysis of the whole DN, we propose a coherent interpretation of these observations which also provides data inaccessible by direct experiments. When the twist is small enough, one screw subnetwork vanishes. The surface strain field induced by such DNs has been used to pilot the lateral ordering of GaAs and InGaAs nanostructures during metal-organic vapor phase epitaxy. We prove that the dimensions and orientations of the nanostructures are correlated with those of the cells of the underlying DN and explain how the interface dislocation structure governs the formation of the nanostructures

Developing a corpus of strategic conversation in The Settlers of Catan

International audienceWe describe a dialogue model and an implemented annotation scheme for a pilot corpus of annotated online chats concerning bargaining negotiations in the game The Settlers of Catan. We will use this model and data to analyze how conversations proceed in the absence of strong forms of cooperativity, where agents have diverging motives. Here we concentrate on the description of our annotation scheme for negotiation dialogues, illustrated with our pilot data, and some perspectives for future research on the issue

Nanoscale Footprints of Self-Running Gallium Droplets on GaAs Surface

In this work, the nanoscale footprints of self-driven liquid gallium droplet movement on a GaAs (001) surface will be presented and analyzed. The nanoscale footprints of a primary droplet trail and ordered secondary droplets along primary droplet trails are observed on the GaAs surface. A well ordered nanoterrace from the trail is left behind by a running droplet. In addition, collision events between two running droplets are investigated. The exposed fresh surface after a collision demonstrates a superior evaporation property. Based on the observation of droplet evolution at different stages as well as nanoscale footprints, a schematic diagram of droplet evolution is outlined in an attempt to understand the phenomenon of stick-slip droplet motion on the GaAs surface. The present study adds another piece of work to obtain the physical picture of a stick-slip self-driven mechanism in nanoscale, bridging nano and micro systems

Correlations between spatially resolved Raman shifts and dislocation density in GaN films

Spatially resolved Raman spectra were measured on thick GaN samples with known dislocation density grown by hydride vapor phase epitaxy. The frequencies of the E-2 (high) and E-1 (transverse optical) phonons shift to lower wave number over a distance of 30 mum from the sapphire substrate/GaN interface. The shifts are linearly correlated with the dislocation density suggesting that the strain due to the lattice mismatch at the interface determines both quantities

Aharonov-Bohm interference in quantum ring exciton: effects of built-in electric fields

We report a comprehensive discussion of quantum interference effects due to the finite structure of excitons in quantum rings and their first experimental corroboration observed in the optical recombinations. Anomalous features that appear in the experiments are analyzed according to theoretical models that describe the modulation of the interference pattern by temperature and built-in electric fields.Comment: 6 pages, 7 figure

InAs/GaAs quantum-dot superluminescent light-emitting diode monolithically grown on a Si substrate

Building optoelectronic devices on a Si platform has been the engine behind the development of Si photonics. In particular, the integration of optical interconnects onto Si substrates allows the fabrication of complex optoelectronic circuits, potentially enabling chip-to-chip and system-to-system optical communications at greatly reduced cost and size relative to hybrid solutions. Although significant effort has been devoted to Si light generation and modulation technologies, efficient and electrically pumped Si light emitters have yet to be demonstrated. In contrast, III–V semiconductor devices offer high efficiency as optical sources. Monolithic integration of III–V on the Si platform would thus be an effective approach for realizing Si-based light sources. Here, we describe the first superluminescent light-emitting diode (SLD) monolithically grown on Si substrates. The fabricated two-section InAs/GaAs quantum-dot (QD) SLD produces a close-to-Gaussian emission spectrum of 114 nm centered at 1255 nm wavelength, with a maximum output power of 2.6 mW at room temperature. This work complements our previous demonstration of an InAs/GaAs QD laser directly grown on a Si platform and paves the way for future monolithic integration of III–V light sources required for Si photonics

Influence of Dopants on Defect Formation in GaN

Influence of p-dopants (Mg and Be) on the structure of GaN has been studied using Transmission Electron Microscopy (TEM). Bulk GaN:Mg and GaN:Be crystals grown by a high pressure and high temperature process and GaN:Mg grown by metal-organic chemical-vapor deposition (MOCVD) have been studied. Structural dependence on growth polarity was observed in the bulk crystals. Spontaneous ordering in bulk GaN:Mg on c-plane (formation of Mg-rich planar defects with characteristics of inversion domains) was observed for growth in the N to Ga polar direction (N polarity). On the opposite site of the crystal (growth in the Ga to N polar direction) Mg-rich pyramidal defects empty inside (pinholes) were observed. Both these defects were also observed in MOCVD grown crystals. Pyramidal defects were also observed in the bulk GaN:Be crystals

ПРЕДВАРИТЕЛЬНАЯ ОЦЕНКА СТАБИЛЬНОСТИ ЦВЕТА ТАБЛЕТОК ИЗ ФИНИКОВ

This paper reports on preliminary qualitative evaluation of relationship between color change and water activity (aw) of date (Phoenix dactylifera L., var. Mech-Degla) fruit tablets (DFTs) as natural supplement, in view to optimize their storage conditions. Eight types of DFTs were obtained, according to: i) mean particle size (225 and 282 μm) of the used fruit powder, and ii) compression pressure (5, 10, 15 and 20 kN) applied during the tableting process. The experimental adsorption curves, determined at 25°C using static-gravimetric method, were fitted to GAB (Guggenheim–Anderson–de Boer) and BET (Brunauer–Emmett–Teller) models. Results showed that the DFT color is significantly sensitive to aw since beyond the aw threshold value of 0.44, the DFT color changes from light grey to dark brown, independently of the particle size of fruit powder and compression pressure. Concerning the isotherm modeling, the both models tested seem especially suitable (R≈0,96 0.3≤MRE≤5 and SE≈0.03) for describing the experimental data for DFT obtained under a compression pressure of 5 kN from date fruit powder with mean particle size of 225 μm. The DFT color stability is considerably influenced by the environmental humidity. Considering the importance of color for consumer acceptance, the study deserves to be deepened concerning the quantitative analysis of the color (CIELab system), packaging of the tablets, etc.В данной статье сообщается о предварительной качественной оценке взаимоотношения между изменением цвета и активностью воды (aw) таблеток из фиников (Phoenix dactylifera L., var. Mech-Degla) (DFT) как натуральной добавки с целью оптимизации условий их хранения. Было получено восемь типов DFT в соответствии с: i) средним размером частиц (225 и 282 μм) используемого порошка плодов и ii) давлением сжатия (5, 10, 15 и 20 kN), примененном во время процесса таблетирования. Экспериментальные кривые адсорбции, определенной при 25°C, используя статический гравиметрический анализ, были приспособлены к моделям GAB (Гугенгейма — Андерсона — Де Бура) и BET (Брунауэр, Эммет и Теллер). Результаты показали, что цвет DFT в большой степени чувствителен к aw, т. к. за пределами порогового уровня aw порошка плодов цвет DFT изменяется от светло серого до темно коричневого, независимо от размера частиц порошка плодов и давления сжатия. Что касается изотермического моделирования, то обе тестированные модели особенно пригодны (R≈0,96 0,3≤MRE≤5 и SE≈0,03) для описания экспериментальных данных для DFT, полученных при давлении сжатия 5 kN из порошка фиников со средним размером частиц 225 μм. Влажность окружающей среды оказывает значительное влияние на стабильность цвета DFT. Что касается, значения цвета для принятия потребителями, то исследование необходимо углубить в отношении количественного анализа цвета (система CIELab), упаковки таблеток и т. д