III–V nanostructures have the potential to revolutionize optoelectronics and energy harvesting. For this to become a reality, critical issues such as reproducibility and sensitivity to defects should ...be resolved. By discussing the optical properties of molecular beam epitaxy (MBE) grown GaAs nanomembranes we highlight several features that bring them closer to large scale applications. Uncapped membranes exhibit a very high optical quality, expressed by extremely narrow neutral exciton emission, allowing the resolution of the more complex excitonic structure for the first time. Capping of the membranes with an AlGaAs shell results in a strong increase of emission intensity but also in a shift and broadening of the exciton peak. This is attributed to the existence of impurities in the shell, beyond MBE-grade quality, showing the high sensitivity of these structures to the presence of impurities. Finally, emission properties are identical at the submicron and submillimeter scale, demonstrating the potential of these structures for large scale applications.
In order to realize many devices based on semiconductor nanowires, reliable doping is essential. For such devices, it is important that the electron mobility is not compromised by doping ...incorporation. Here, we show that core-shell GaAs/AlGaAs nanowires can be modulation n-type doped with negligible loss of electron mobility. Optical pump terahertz probe spectroscopy is used as a novel, reliable, noncontact method of determining the doping density, carrier mobility and charge carrier lifetimes for these n-type nanowires and an undoped reference. A carrier concentration of 1.10 ± 0.06 × 10 16 cm -3 was extracted proving the effectiveness of modulation doping in GaAs nanowires. The room-temperature electron mobility was found to be high at 2200 ± 300 cm 2 V -1 s -1 with no degradation in comparison to undoped reference nanowires. In addition, modulation doping was found to enhance both the photoconductivity and photoluminescence lifetimes to 3.9 ± 0.3ns and 2.4 ± 0.1ns respectively, revealing that modulation doping can passivate interfacial trap states. 1
Reliable doping in semiconductor nanowires is essential for the development of novel optoelectronic devices. Dopant incorporation within the nanowire can allow for optimisation of key optoelectronic ...properties, such as electron mobility and carrier lifetime. Thus, in-depth characterisation of doping mechanisms in semiconductor nanowires and their effect on the nanowire optoelectronics properties is crucial. However, extraction of the dopant concentration by conventional electrical methods remains difficult due to the associated challenges with fabricating lateral contacts onto the nanowire. In this work, we present a non-contact technique based on optical pump terahertz-probe spectroscopy for examining the extrinsic carrier concentration and optoelectronic properties of semiconductor nanowires. By extracting the temperature-dependent charge carrier dynamics, we show for the first time that the dopant activation energy and underlying scattering mechanisms affecting charge carrier mobility in these nanostructures can be determined via terahertz spectroscopy.
III-V nanostructures have the potential to revolutionize optoelectronics and energy harvesting. For this to become a reality, critical issues such as reproducibility and sensitivity to defects should ...be resolved. By discussing the optical properties of MBE grown GaAs nanomembranes we highlight several features that bring them closer to large scale applications. Uncapped membranes exhibit a very high optical quality, expressed by extremely narrow neutral exciton emission, allowing the resolution of the more complex excitonic structure for the first time. Capping of the membranes with an AlGaAs shell results in a strong increase of emission intensity but also to a shift and broadening of the exciton peak. This is attributed to the existence of impurities in the shell, beyond MBE-grade quality, showing the high sensitivity of these structures to the presence of impurities. Finally, emission properties are identical at the sub-micron and sub-millimeter scale, demonstrating the potential of these structures for large scale applications.
Reliable doping in GaAs nanowires is essential for the development of novel optoelectronic devices. Previously, GaAs nanowires have been shown to exhibit extremely short photoconductivity lifetimes ...of a few picoseconds due to their high surface recombination velocity, which is detrimental for nanowire devices, such as solar cells and nanowire lasers. Here, we show that, by exploiting engineered band-bending via selective doping, this parasitic surface recombination can be reduced. We utilise non-contact time-resolved terahertz spectroscopy to characterise the doping efficiency in n-type and p-type doped GaAs nanowire 8 and show high carrier concentrations of the order of 10 18 cm -3 . The carrier lifetimes were increased by an order of magnitude from 0.13ns for undoped to 3.8ns and 2.5ns for n-doped and p-doped GaAs nanowires respectively; showing that surface recombination is greatly suppressed as a result of shell doping. We also present a novel effect of p-doping in GaAs nanowires: a rapid decay in photoconductivity within 25ps after photoexcitation. This fast decay is attributed to rapid electron trapping at the nanowire surface due to doping related band bending. Thus, we demonstrate the advantages of selective doping for enhancement of desirable transport properties in GaAs nanowires, as well as highlighting terahertz spectroscopy as a reliable technique for characterising doped GaAs nanowires 1 .
Abstract One of the main problems in transplant surgery is the preservation of the organ during the cold ischemic time. The interrupted blood supply triggers a cascade of biological modifications ...resulting in cell death, which predisposes to discharge of a large quantity of toxic metabolites at the moment of organ reperfusion. Many approaches have been studied to prevent the toxic processes. Immediately after procurement, kidneys are flushed with these solutions. Two main: techniques of organ preservation are cold static storage and hypothermic machine perfusion (HMP). Based on age and comorbidities, individuals can be generally divided into 2 groups: ideal and marginal donors. Characteristics of organs from marginal donors are associated with an increased rate of delayed graft function and primary graft nonfunction (PNF), which reduce transplant survival and increase the acute rejection risk. In the last 20 years, the United Network of Organ Sharing has reported a 170% increase in deceased donors older than 50 years of age. Techniques of perfusion have been demonstrated to play a pivotal role in graft function after transplantation. Some studies suggest that HMP may improve outcomes after transplantation.
Abstract Background Combined liver-kidney transplantation (LKT) is considered to be a safe procedure, but the appropriate immunosuppressive regimen is unclear. Patients and methods Between January ...1997 and October 2011, 55 patients were listed for LKT: 45 (82%) were effectively transplanted, 5 (9.2%) died whereon here the waiting list, 3 (5.5%) temporarily out of waiting list, 1 (1.8%) was on waiting list and 1 (1.8%) refused LKT. Five LKTs treated with cyclosporine (CyA) were excluded from the analysis. Mean recipient age was 50.32 ± 10.32 years (14–65), MELD score at time of LKT was 19.22 ± 4.69 (8–29), mean waiting list time was 8.14 ± 9.50 months (0.1–35.76), and follow-up, 4.09 ± 3.02 years (0.01–10.41). Main indications for LKT were policystic disease (n = 15; 37%), hepatitis virus C (HCV)-related cirrhosis (n = 9; 22%) metabolic disease (n = 5; 13%), hepatitis virus B (HBV) cirrhosis (n = 4; 10%), alcoholic cirrhosis (n = 4; 10%), and cholestatic disease (n = 3; 8%). Immunosuppressive regimen was based on tacrolimus and steroids in 40 cases with induction therapy with alemtuzumab (Campath; 0.3 mg/kg) in 13 of 40 instances cases administered on day 0 and day 7. Results Postoperative mortality was 2.5%. Acute cellular rejection episodes were biopsy-proven in 2 (5%) cases, post-LKT infections developed in 17 cases (42.5%), and de novo cancer developed in 3 (7.5%) cases. Similar 5-year overall survivals were obtained irrespective of the LKT indication: 100% in cholestatic and alcoholic cirrhosis patients, 86% in policystic disease, 75% in metabolic disease and HBV patients, and 66% in HCV cirrhosis. Overall survivals for the alemtuzumab vs without-induction therapy groups at 1, 3, and 5-years were 100%, 85.7%, and 85.7% vs 76%, 76%, and 70%, respectively ( P = .04). Conclusion An immunosuppressive regimen based on tacrolimus and steroids with induction therapy with alemtuzumab was safe, with excellent long-term results for combined LKT.
Abstract Background Few studies have measured cadaveric kidney weight to investigate its relation to recipient kidney function related to it. The aim of this study was to evaluate kidney weight ...(cadaveric donor) and its relationship to creatinine clearance (CrCl) after 12 months posttransplantation. Methods We evaluated 81 renal transplantation recipients from cadaveric donors. We collected donor and recipient demographic, clinical and anthropometric data. Data about kidney weight were obtained through kidney measurement using an electronic machine at the moment of transplantation. Results The mean kidney weight was 201.4 ± 10.2 g (200.5 ± 11.6 g in women and 210.3 ± 14.1 g in men). Kidney weight correlated with CrCl at 12 months (0.001). The CrCl at 12 months showed a significant correlation of graft weight/recipient weight ratio ( P < .01). Conclusion The cadaveric donor kidney weight significantly influenced the CrCl at 12 months after transplantation.
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