Nitrogen-enhanced indium segregation in (Ga,In)(N,As)/GaAs multiple quantum wells grown by molecular-beam epitaxy

Transmission electron microscopy (TEM) is used to determine the composition of quaternary (Ga,In)(N,As) quantum wells (QWs). Through a combined analysis of the chemically sensitive (002) dark-field (DF) images and the lattice-resolving high-resolution TEM images, the local distributions of nitrogen and indium in the growth direction are determined. In particular, we are able to directly detect the existence of indium segregation in (Ga,In)(N,As) QWs. A comparison with the indium distribution profile in the nitrogen-free (In,Ga)As QWs, grown under similar conditions, revealed that incorporating N into the alloy enhanced indium segregation

Ni+-irradiated InGaAs/GaAs quantum wells: picosecond carrier dynamics

Room-temperature carrier dynamics as functions of heavy-ion implantation and subsequent thermal annealing were investigated for technologically important InGaAs/GaAs quantum wells (QWs) by means of a time-resolved up-conversion method. Sub-picosecond lifetimes were achieved at 10 MeV Ni+ doses of (20-50) x 1010 ions cm-2. The decay rates reached a maximum at the highest irradiation dose, yielding the shortest lifetime of the confined QW states of 600 fs. A simple theoretical model is proposed for the photodynamics of the carriers. The relaxation rate depended on the irradiation dose according to a power law of 1.2, while the irradiated and subsequently annealed samples exhibited a power law of 0.35. The results are qualitatively interpreted.Room-temperature carrier dynamics as functions of heavy-ion implantation and subsequent thermal annealing were investigated for technologically important InGaAs/GaAs quantum wells (QWs) by means of a time-resolved up-conversion method. Sub-picosecond lifetimes were achieved at 10 MeV Ni+ doses of (20-50) x 1010 ions cm-2. The decay rates reached a maximum at the highest irradiation dose, yielding the shortest lifetime of the confined QW states of 600 fs. A simple theoretical model is proposed for the photodynamics of the carriers. The relaxation rate depended on the irradiation dose according to a power law of 1.2, while the irradiated and subsequently annealed samples exhibited a power law of 0.35. The results are qualitatively interpreted.Room-temperature carrier dynamics as functions of heavy-ion implantation and subsequent thermal annealing were investigated for technologically important InGaAs/GaAs quantum wells (QWs) by means of a time-resolved up-conversion method. Sub-picosecond lifetimes were achieved at 10 MeV Ni+ doses of (20-50) x 1010 ions cm-2. The decay rates reached a maximum at the highest irradiation dose, yielding the shortest lifetime of the confined QW states of 600 fs. A simple theoretical model is proposed for the photodynamics of the carriers. The relaxation rate depended on the irradiation dose according to a power law of 1.2, while the irradiated and subsequently annealed samples exhibited a power law of 0.35. The results are qualitatively interpreted.Peer reviewe

Metastability of Band-Gap Energy in GaInNAs Compound Investigated by Photoreflectance

The band-gap energy of GaInNAs layers lattice-matched to GaAs substrate and annealed under different temperatures is investigated by photoreflectance spectroscopy. Different nitrogen nearest-neighbor environments of N atom appear in GaInNAs layers due to the post-growth annealing. It leads to an energy-fine structure of the band gap, i.e. well separated photoreflectance resonances related to different nitrogen nearest-neighbor environments (N-Ga$\text{}_{4-m}$In$\text{}_{m}$ (0≤ m≤ 4) short-range-order clusters). The temperature dependence of the band gap E(T) related to different N-Ga$\text{}_{4-m}$In$\text{}_{m}$ clusters is investigated in 10-280 K temperature range, and Varshni and Bose-Einstein parameters for E(T) are determined

Metastability of Band-Gap Energy in GaInNAs Compound Investigated by Photoreflectance

The band-gap energy of GaInNAs layers lattice-matched to GaAs substrate and annealed under different temperatures is investigated by photoreflectance spectroscopy. Different nitrogen nearest-neighbor environments of N atom appear in GaInNAs layers due to the post-growth annealing. It leads to an energy-fine structure of the band gap, i.e. well separated photoreflectance resonances related to different nitrogen nearest-neighbor environments (N-Ga$\text{}_{4-m}$In$\text{}_{m}$ (0≤ m≤ 4) short-range-order clusters). The temperature dependence of the band gap E(T) related to different N-Ga$\text{}_{4-m}$In$\text{}_{m}$ clusters is investigated in 10-280 K temperature range, and Varshni and Bose-Einstein parameters for E(T) are determined

TEENAGER WITH UPPER GASTROINTESTINAL OBSTRUCTION – KEEP IN MIND THE RARE CAUSES

Introduction. Superior mesenteric artery syndrome is a rare cause of upper gastrointestinal tract obstruction. Case presentation. A 17-year-old adolescent is admitted in the Pediatrics Department of “Grigore Alexandrescu” Hospital in Bucharest in July 2018 for episodes of vomiting associated with epigastric pain. The patient started presenting persistent abdominal pain since five years before, apparently after an appendectomy. In the last year, he associated heartburn, dysgeusia, food vomiting and postprandial plenitude. A diagnosis of H. pylori acute gastritis was initially set and he received triple therapy with temporary relief. Due to chronic digestive symptoms, the adolescent presented anxiety related to food intake with extremely reduced appetite, food selectivity and lack of weight gain. The clinical examination revealed marfanoid phenotype, low weight, chest deformity, excavated abdomen, epigastric pain and clapotage. Laboratory investigations were within normal limits. Esogastroduodenal barium examination showed an important gastric stasis with an elongated stomach, dilation of the second part of the duodenum with delayed distal passage. Abdominal ultrasound revealed reduced aorto-mesenteric distance at the third part of the duodenum. Upper gastrointestinal endoscopy found barium residue in the stomach 24 hours after the contrast study and a spastic pylorus, with impossible safe duodenal passage. Abdominal computed tomography confirmed obstruction of the third part of the duodenum by vascular compression at the aorto-mesenteric angle, a specific image for superior mesenteric artery syndrome. The patient underwent laparoscopic surgery with a good outcome. Conclusions. Although a rare entity, duodenal obstruction by aorto-mesenteric clamp must be taken into account in the differential diagnosis of vomiting. An early radiologic diagnostic spares the patient of chronic digestive disease with negative impact on nutritional status and quality of life

Nanostructured W-Cu Electrical Contact Materials Processed by Hot Isostatic Pressing

Nanostructured W-Cu-Ni electrical contact materials to be used in low voltage vacuum switching contactors for nominal currents up to 630 A were developed successfully by hot isostatic pressing. W-Cu-Ni composite powder mixtures with copper content of 20 to 40 wt% and 1 wt% Ni were mechanically alloyed in Ar atmosphere by high-energy ball milling with a ratio of milling steel balls: powders mixtures of 8:1 and rotation speed of 400 rpm for 10 and 20 h. The effect of mechanical alloying on the sintering response of composite compacts was investigated. Also, the sintered contacts were characterized from the point of view of physical, microstructural, mechanical, and functional properties. The nanostructured electrical contacts presented very good sinterability and homogeneous structures with a maximum compactity degree of about 89%. The best W-Cu-Ni compositions with relative density of about 80%, chopping currents lower than 5 A, copper content lower than 40% as W-20Cu-1Ni (10 h of mechanical alloying and 20 h of mechanical alloying) and W-30%Cu-Ni (10 h of mechanical alloying) were selected to be used in vacuum contactors

CAUZĂ RARĂ DE OBSTRUCȚIE DE TRACT DIGESTIV SUPERIOR – IMPORTANȚA UNEI ABORDĂRI MULTIDISCIPLINARE

Introducere. Sindromul de arteră mezenterică superioară este o cauză rară de obstrucție intestinală. Prezentare de caz. Un adolescent în vârstă de 17 ani a fost spitalizat în iulie 2018 în Departamentul Pediatrie al Spitalului Clinic de Urgență pentru Copii „Grigore Alexandrescu“ din Bucureşti pentru vărsături recurente și epigastralgii. Durerile abdominale au debutat cu 5 ani anterior, sunt prezente cvasiconstant, aparent după apendicectomie, şi de aproximativ un an asociază pirozis, disgeuzie, vărsături recurente și senzație de plenitudine postprandială. Inițial, se stabilește diagnosticul de gastrita acută cu Helicobacter pylori și se inițiază triplă terapie, cu remiterea parțială a simptomatologiei. Din cauza simptomatologiei cronice digestive, pacientul își limitează aportul alimentar, cu scădere ponderală consecutivă. La examenul clinic, se remarcă fenotip marfanoid, deformarea cutiei toracice, abdomen excavat, dureros în epigastru și clapotaj. Investigațiile de laborator sunt în limite normale. Tranzitul baritat esogastroduodenal evidențiază stază gastrică importantă cu stomac alungit, dilatare duodenală cu pasaj distal lent. Ecografia abdominală arată reducerea marcată a distanței aorto-mezenterice. La endoscopia digestivă superioară se observă reziduu baritat la 24 de ore de la efectuarea tranzitului și spasm piloric, fiind imposibil pasajul în duoden. Computer tomografia abdominală confirmă obstrucția intestinală la nivelul celei de-a treia porțiuni duodenale prin compresie vasculară la nivelul unghiului aorto-mezenteric, descoperire radiologică specifică sindromului de arteră mezenterică superioară. Se practică tratament chirurgical laparoscopic, cu evoluție postoperatorie favorabilă. Concluzii. Deși este o entitate rară, obstrucția duodenală prin pensă aorto-mezenterică trebuie luată în considerare în diagnosticul diferențial al vărsăturilor recurente. Un diagnostic radiologic precoce evită consecințele negative asupra statusului nutrițional și asupra calitații vieții la pacienții cu această patologie