Exciton confinement in strain-engineered InAs quantum dots in metamorphic In_{x}Ga_{1-x}As

In this work, magneto-photoluminescence at low temperature, 4.2 K, is used to probe the exciton confinement in strain-engineered InAs/In_{x}Ga_{1-x}As/GaAs metamorphic quantum dots (QDs), emitting at telecom wavelengths (1.3 µm - 1.6 µm). The emission wavelength can be tuned by changing two independent parameters, i.e.,indium content, x, in In_{x}Ga_{1-x}As upper and lower confining layers and thickness of lower confining layer (LCL), d. Varying x changes the band offset and QD-CLmismatch (strain inside the QD), while varying d changes only QD-CL mismatch.We investigate the dependence of confinement on the QD-CL mismatch and band offset. Zero-magnetic-field spectra showed that wavelength (PL energy) increases(decreases) with increasing x, for a constant d, and with increasing d, for a constant x, which was attributed to be due to relaxation of strain inside the QD that is, in turn,a function of x and d. No correlation between wavelength and intensity was observed. Magneto-photoluminescence results revealed that for a subset of samples, the exciton effective mass increases linearly, more or less, with increasing QD-CL mismatch (QD strain), while its Bohr radius has no correlation with mismatch. The diamagneticshift coefficient increases 12-fold with decreasing mismatch from ∼ 7.5 % to 4.5 %, which is attributed to low effective mass, which in turn, is due to low QD strain. For high mismatch (> 5.8 %), the Bohr radius is not determined, implying that it is less than10 nm, smaller than the dot radius. For indium composition x = 0.28 and 0.31, and for d > 1000˚A, the wave-function spills over out of the dot. For x = 0.35, the Bohr radii are, counter intuitively, found to be smaller than for samples with larger band offset (x = 0.31). Initially, it was explained as a spilling of the wave-function over vertically resulting in strong lateral confinement of exciton, but this explanation is not supported by our model calculations. Another explanation is, therefore, presented by carrying out temperature dependence and magnetic field dependence, at various temperatures, of PL energy: there are different dots, at x = 0.35, with different size where thermal escape of carriers from smaller dots to bigger ones occurs with increasing temperature, and the PL energy, in magnetic field, is contributed more by smaller dots than the bigger ones

Exciton confinement in strain-engineered metamorphic InAs/InxGa1-xAs quantum dots

We report a comprehensive study of exciton confinement in self-assembled InAs quantum dots (QDs) in strain-engineered metamorphic InxGa1-xAs confining layers on GaAs using low temperature magneto-photoluminescence. As the lattice mismatch (strain) between QDs and confining layers (CLs) increases from 4.8% to 5.7% the reduced mass of the exciton increases, but saturates at higher mismatches. At low QD-CL mismatch there is a clear evidence of spillover of the exciton wave-function due to small localisation energies. This is suppressed as the In content, x, in the CLs decreases (mismatch and localisation energy increasing). The combined effects of low effective mass and wave-function spillover at high x result in a diamagnetic shift coefficient that is an order of magnitude larger than for samples where In content in the barrier is low (mismatch is high and localisation energy is large). Finally, an anomalously small measured Bohr radius in samples with the highest x is attributed to a combination of thermalisation due to low localisation energy, and its enhancement with magnetic field, a mechanism which results in small dots in the ensemble dominating the measured Bohr radius

Influence of preparation methods on textural properties of purified bentonite

The aim of this work was to study the effect of three different purification methods, using chemical solution of (Na(PO3))(6) (method-I), NaCl (method-II) and Na2CO3 (method-III), followed by stokes law of sedimentation, on the textural properties of a Pakistani bentonite, containing &gt; 70% Ca2+-montmorillonite. The raw and the purified samples were examined through X-ray Diffraction (XRD), N-2 adsorption-desorption, and laser diffraction method (LDM). The quartz contents were found absent in all the purified samples. It was confirmed that the sample obtained by the method-I and other two methods resulted in to be,typically, Ca2+-bentonite and Na+-bentonite, respectively. In comparison with the raw sample, higher percentage volume of fine particles was detected in purified samples. The fine particles, however, exhibited significant enhancement in the samples purified by method-II and method-III. Higher pore volume and specific surface area were noticed for samples purified by the trio methods in comparison with the raw sample. Specific surface area of the sample obtained by the method-III was much higher than that of the other purified samples. Mesopores volume was increased significantly by purification, especially by the method-I and III. Considerably higher value of micropores volume/area and mesopores volume/area were detected for sample purified by method-III than for the samples purified by the other methods. A highly porous sample with the excellent surface area and small particle size was obtained by purification method-III which can be used as a good adsorbent, catalyst and catalyst support.</p

Evaluation of a quality improvement intervention to reduce anastomotic leak following right colectomy (EAGLE): pragmatic, batched stepped-wedge, cluster-randomized trial in 64 countries

Background Anastomotic leak affects 8 per cent of patients after right colectomy with a 10-fold increased risk of postoperative death. The EAGLE study aimed to develop and test whether an international, standardized quality improvement intervention could reduce anastomotic leaks. Methods The internationally intended protocol, iteratively co-developed by a multistage Delphi process, comprised an online educational module introducing risk stratification, an intraoperative checklist, and harmonized surgical techniques. Clusters (hospital teams) were randomized to one of three arms with varied sequences of intervention/data collection by a derived stepped-wedge batch design (at least 18 hospital teams per batch). Patients were blinded to the study allocation. Low- and middle-income country enrolment was encouraged. The primary outcome (assessed by intention to treat) was anastomotic leak rate, and subgroup analyses by module completion (at least 80 per cent of surgeons, high engagement; less than 50 per cent, low engagement) were preplanned. Results A total 355 hospital teams registered, with 332 from 64 countries (39.2 per cent low and middle income) included in the final analysis. The online modules were completed by half of the surgeons (2143 of 4411). The primary analysis included 3039 of the 3268 patients recruited (206 patients had no anastomosis and 23 were lost to follow-up), with anastomotic leaks arising before and after the intervention in 10.1 and 9.6 per cent respectively (adjusted OR 0.87, 95 per cent c.i. 0.59 to 1.30; P = 0.498). The proportion of surgeons completing the educational modules was an influence: the leak rate decreased from 12.2 per cent (61 of 500) before intervention to 5.1 per cent (24 of 473) after intervention in high-engagement centres (adjusted OR 0.36, 0.20 to 0.64; P &lt; 0.001), but this was not observed in low-engagement hospitals (8.3 per cent (59 of 714) and 13.8 per cent (61 of 443) respectively; adjusted OR 2.09, 1.31 to 3.31). Conclusion Completion of globally available digital training by engaged teams can alter anastomotic leak rates. Registration number: NCT04270721 (http://www.clinicaltrials.gov)

Evaluation of a quality improvement intervention to reduce anastomotic leak following right colectomy (EAGLE): pragmatic, batched stepped-wedge, cluster-randomized trial in 64 countries

Background: Anastomotic leak affects 8 per cent of patients after right colectomy with a 10-fold increased risk of postoperative death. The EAGLE study aimed to develop and test whether an international, standardized quality improvement intervention could reduce anastomotic leaks. Methods: The internationally intended protocol, iteratively co-developed by a multistage Delphi process, comprised an online educational module introducing risk stratification, an intraoperative checklist, and harmonized surgical techniques. Clusters (hospital teams) were randomized to one of three arms with varied sequences of intervention/data collection by a derived stepped-wedge batch design (at least 18 hospital teams per batch). Patients were blinded to the study allocation. Low- and middle-income country enrolment was encouraged. The primary outcome (assessed by intention to treat) was anastomotic leak rate, and subgroup analyses by module completion (at least 80 per cent of surgeons, high engagement; less than 50 per cent, low engagement) were preplanned. Results: A total 355 hospital teams registered, with 332 from 64 countries (39.2 per cent low and middle income) included in the final analysis. The online modules were completed by half of the surgeons (2143 of 4411). The primary analysis included 3039 of the 3268 patients recruited (206 patients had no anastomosis and 23 were lost to follow-up), with anastomotic leaks arising before and after the intervention in 10.1 and 9.6 per cent respectively (adjusted OR 0.87, 95 per cent c.i. 0.59 to 1.30; P = 0.498). The proportion of surgeons completing the educational modules was an influence: the leak rate decreased from 12.2 per cent (61 of 500) before intervention to 5.1 per cent (24 of 473) after intervention in high-engagement centres (adjusted OR 0.36, 0.20 to 0.64; P < 0.001), but this was not observed in low-engagement hospitals (8.3 per cent (59 of 714) and 13.8 per cent (61 of 443) respectively; adjusted OR 2.09, 1.31 to 3.31). Conclusion: Completion of globally available digital training by engaged teams can alter anastomotic leak rates. Registration number: NCT04270721 (http://www.clinicaltrials.gov)