Epitaxial growth, optical properties and structural studies of GaN nanorods and related heterostructures

Group three-nitride nanorods have attracted substantial research focus thanks to their direct bandgap, full solar spectrum coverage, and wide optoelectronic applications. GaN nanorod growth has been achieved by several growth methods, and among them, self-assembled nanorod growth by metalorganic chemical vapour deposition (MOCVD) is an optimal and time-saving method due to its catalyst-free and minimal substrate preparation requirements. This approach has been applied in devices that do not demand precise positionings, such as single nanorod light-emitting diodes (LEDs) and flexible nanorod array LEDs. This dissertation presents a detailed growth study of GaN self-assembled nanorods on sapphire substrates by MOCVD. Both the pre-growth and growth parameters have been systemically studied. Due to their wurtzite crystal structure, how to control their polarity has been a critical issue in the nanomaterial growth and nano-device fabrication. In this thesis, we show and discuss how the polarity and optical properties are affected by nitridation, one of the pre-growth conditions. With appropriate nitridation, the nanorods can be grown with uniform hexagonal morphology and N-polar, resulting in homogenous luminescence with a strong near-band edge emission. This thesis also studies the effect of growth parameters such as silane co-injection, growth temperature and growth time on the morphology and density of the nanorods. A rosette-shaped cathodoluminescence (CL) pattern is found in GaN nanodisks and nanorods. This unique pattern forms at a very early stage of nanorod growth and consists of yellow luminescence (YL) and non-luminous regions. To explore its origin, CL, electron microscopy and nanoscale secondary ion mass spectrometry studies are conducted. These studies found optical resonance modes and polarity inversion do not contribute to this phenomenon. Higher concentration of carbon and nitrogen clusters are found at the pattern area, which indicates pattern could be related to facet preferential distribution of defects related to excess carbon/nitrogen. This study adds the knowledge of defect-related emission in GaN nanorod, which is essential for future optoelectronic applications. Finally, this dissertation presents InxGaN1-x/GaN multi-quantum well (MQW) core-shell structures and the formation of InxGa1-xN quantum dots (QDs). Through high-resolution CL and transmission electron microscopy (TEM) studies, the strong QW emission is found only at the tip area and indium segregation is observed at the nanorod sidewall MQW area. The InxGa1-xN MQW emission shows high sensitivity to minor changes in trimethylindium source flow and quantum barrier growth temperature. The MQW emission shifts to longer wavelengths due to increasing indium source supply and decreasing quantum barrier growth temperature as a result of higher indium incorporation. This study extends our knowledge of growth & optical properties of InxGaN1-x/GaN MQW and QDs, which also demonstrates the potential of application in LEDs in the future

Modified Glucose-Insulin-Potassium Regimen Provides Cardioprotection With Improved Tissue Perfusion in Patients Undergoing Cardiopulmonary Bypass Surgery

Background Laboratory studies demonstrate glucose-insulin-potassium (GIK) as a potent cardioprotective intervention, but clinical trials have yielded mixed results, likely because of varying formulas and timing of GIK treatment and different clinical settings. This study sought to evaluate the effects of modified GIK regimen given perioperatively with an insulin-glucose ratio of 1:3 in patients undergoing cardiopulmonary bypass surgery. Methods and Results In this prospective, randomized, double-blinded trial with 930 patients referred for cardiac surgery with cardiopulmonary bypass, GIK (200 g/L glucose, 66.7 U/L insulin, and 80 mmol/L KCl) or placebo treatment was administered intravenously at 1 mL/kg per hour 10 minutes before anesthesia and continuously for 12.5 hours. The primary outcome was the incidence of in-hospital major adverse cardiac events including all-cause death, low cardiac output syndrome, acute myocardial infarction, cardiac arrest with successful resuscitation, congestive heart failure, and arrhythmia. GIK therapy reduced the incidence of major adverse cardiac events and enhanced cardiac function recovery without increasing perioperative blood glucose compared with the control group. Mechanistically, this treatment resulted in increased glucose uptake and less lactate excretion calculated by the differences between arterial and coronary sinus, and increased phosphorylation of insulin receptor substrate-1 and protein kinase B in the hearts of GIK-treated patients. Systemic blood lactate was also reduced in GIK-treated patients during cardiopulmonary bypass surgery. Conclusions A modified GIK regimen administered perioperatively reduces the incidence of in-hospital major adverse cardiac events in patients undergoing cardiopulmonary bypass surgery. These benefits are likely a result of enhanced systemic tissue perfusion and improved myocardial metabolism via activation of insulin signaling by GIK. Clinical Trial Registration URL: clinicaltrials.gov. Identifier: NCT01516138

Recent developments in chemical vapor deposition of 2D magnetic transition metal chalcogenides

In recent years, two-dimensional (2D) magnetic transition metal chalcogenides (TMCs) have attracted tremendous research interests thanks to their intriguing properties that are essential in developing future electronic and spintronic devices in this modernizing era. This review aims to introduce recent developments in the preparation of 2D magnetic TMCs, especially chromium and iron-based chalcogenides, their structures, as well as the related intriguing magnetic phenomena. First, the common crystal structures of magnetic TMCs including both layered and nonlayered structures are introduced. Various chemical vapor deposition strategies for synthesizing 2D magnetic TMCs are then introduced with emphasis on the key synthesis parameters. Moreover, the intriguing physical properties associated with 2D TMCs such as magnetic anisotropy, thickness, and phase-dependent magnetic response as well as stability are summarized. Last but not least, challenges and future research directions are briefly discussed in light of recent advances in the field.Ministry of Education (MOE)National Research Foundation (NRF)Submitted/Accepted versionZ.L. acknowledges support from National Research Foundation Singapore Programme Grants NRF-CRP22-2019-0007, NRF-CRP21-2018-0007, and NRF-CRP22-2019-0004. This research is also supported by the Ministry of Education, Singapore, under its AcRF Tier 3 Programme “Geometrical Quantum Materials” (Grant MOE2018-T3-1-002), and AcRF Tier 1 Grant RG161/19

Analogous Anti-Ferroelectricity in Y2O3-Coated (Pb0.92Sr0.05La0.02)(Zr0.7Sn0.25Ti0.05)O3 Ceramics and Their Energy-Storage Performance

Antiferroelectric analogous (Pb0.92Sr0.05La0.02)(Zr0.7Sn0.25Ti0.05)O3 (PSLZSnT) ceramics were prepared by the solid-state sintering method by introducing a Y2O3-coating via the self-combustion method. The synthesized Y2O3-doped PSLZSnT ceramics present pseudo-cubic structure and rather uniform microstructural morphology accompanied by relatively small grain size. Excellent energy-storage performance is obtained in the Y2O3-doped PSLZSnT ceramics, in which the value of the energy-storage density presents a linearly increasing trend within the electric field measurement range. Such excellent performance is considered as relating to the rather pure perovskite structure, high relative density accompanied by relatively small grain size, and the antiferroelectric-like polarization-electric field behavior

Genetic subtypes and phenotypic characteristics of 110 patients with Prader-Willi syndrome

Abstract Background Prader-Willi syndrome (PWS) is a complex disorder caused by impaired paternally expressed genes on chromosome 15q11-q13. Variable findings have been reported about the phenotypic differences among PWS genetic subtypes. Methods A total of 110 PWS patients were diagnosed from 8,572 pediatric patients included from July 2013 to December 2021 by MLPA and MS-MLPA assays. Atypical deletions were defined by genomic CNV-sequencing. Maternal uniparental disomy (UPD) was subgrouped by microsatellite genotyping. Clinical data were collected for phenotype-genotype associations. Twenty-one patients received growth hormone (GH) treatment, and the anthropometric and laboratory parameters were evaluated and compared. Results Genetically, the 110 patients with PWS included 29 type I deletion, 56 type II deletion, 6 atypical deletion, 11 heterodisomy UPD, and 8 isodisomy UPD. The UPD group had significantly higher maternal age (31.4 ± 3.4 vs 27.8 ± 3.8 years), more anxiety (64.29% vs 26.09%) and autistic traits (57.14% vs 26.09%), and less hypopigmentation (42.11% vs 68.24%) and skin picking (42.86% vs 71.01%) than the deletion group. The type I deletion group was diagnosed at earlier age (3.7 ± 3.3 vs 6.2 ± 3.2 years) and more common in speech delay (95.45% vs 63.83%) than the type II. The isodisomy UPD group showed a higher tendency of anxiety (83.33% vs 50%) than the heterodisomy. GH treatment for 1 year significantly improved the SDS of height (− 0.43 ± 0.68 vs − 1.32 ± 1.19) and IGF-I (− 0.45 ± 0.48 vs − 1.97 ± 1.12). No significant changes were found in thyroid function or glucose/lipid metabolism. Conclusion We explored the physical, psychological and behavioral phenotype-genotype associations as well as the GH treatment effect on PWS from a large cohort of Chinese pediatric patients. Our data might promote pediatricians' recognition and early diagnosis of PWS

Synthesis and characterization of Pb(Yb

xPb(Yb1/2Nb1/2)O3-(1 − x)Pb(Zr0.36Ti0.64)O3 (xPYN-(1 − x)PZT) piezoelectric ceramics were prepared by the conventional ceramic processing via a B-site oxide mixing route. The synthesized xPYN-(1 − x)PZT ceramics exhibit majority of perovskite structure with slight content of impurity, which exhibit typical tetragonal structure with slight orthorhombic distortion depending on compositions. All the xPYN-(1 − x)PZT ceramics exhibit high Curie temperature (TC/Tm), higher than 380 °C, and their dielectric behavior above TC/Tm can be fitted well by the Curie-Weiss law. The xPYN-(1 − x)PZT ceramics exhibit large resistivity, and excellent ferroelectric and piezoelectric properties, which provide promising for the high-power and high-temperature piezoelectric applications. However, electric energy density of the xPYN-(1 − x)PZT ceramics is small due to their nearly rectangular shape of polarization-electric field (P-E) hysteresis loop and early electric displacement saturation, which is not suitable for high energy and power storage applications

Optimizing structure and electrical properties of high-Curie temperature PMN-PHT piezoelectric ceramics via tailoring sintering process

Pseudo-ternary high-Curie temperature 0.15Pb(Mg1/3Nb2/3)O3-0.4PbHfO3-0.45PbTiO3 (PMN-PHT) piezoelectric ceramics were prepared by the conventional ceramic processing via the columbite precursor method. The influences of sintering temperature and sintering time on structure and electrical properties of the PMN-PHT ceramics were investigated in order to tailor their performance further. The sintered PMN-PHT ceramics exhibit pure perovskite structure with composition locating at the rhombohedral side around the morphotropic phase boundary (MPB) of the PMN-PHT system. The PMN-PHT ceramics sintered at 1260 °C for 2 h exhibit the best dielectric, ferroelectric and piezoelectric properties. The high piezoelectric response of the PMN-PHT ceramics is considered as relating to the MPB effect and their dense microstructure obtained via tailoring sintering conditions. The sintered PMN-PHT ceramics exhibit good thermal stability of piezoelectricity and ferroelectricity within the common usage temperatures, indicating that such ceramics are promising candidates for piezoelectric devices at elevated temperatures

A Two-Step Annealing Method to Enhance the Pyroelectric Properties of Mn:PIMNT Chips for Infrared Detectors

Mn:0.15Pb(In1/2Nb1/2)O3-0.55Pb(Mg1/3Nb2/3)O3-0.30PbTiO3 (Mn:PIMNT) pyroelectric chips were prepared by a two-step annealing method. For the two steps, annealing temperatures dependence of microstructure, defects, surface stress, surface roughness, dielectric properties and pyroelectric properties were studied comprehensively. The controlling factors influencing the pyroelectric properties of the Mn:PIMNT crystals were analyzed and the optimum annealing temperature ranges for the two steps were determined: 600–700 °C for the first step and 500–600 °C for the second step. The pyroelectric properties of the thin Mn:PIMNT chips were significantly enhanced by the two-step annealing method via tuning oxygen vacancies and eliminating surface stress. Based on Mn:PIMNT pyroelectric chips annealed at the most favorable conditions (annealed at 600 °C for the first step and 500 °C for the second step), infrared detectors were prepared with specific detectivity D* = 1.63 × 109 cmHz1/2W−1, nearly three times higher than in commercial LiTaO3 detectors

Tumor-vasculature-on-a-chip for investigating nanoparticle extravasation and tumor accumulation

Nanoparticle tumor accumulation relies on a key mechanism, the enhanced permeability and retention (EPR) effect, but it remains challenging to decipher the exact impact of the EPR effect. Animal models in combination with imaging modalities are useful, but it is impossible to delineate the roles of multiple biological barriers involved in nanoparticle tumor accumulation. Here we report a microfluidic tumor-vasculature-on-a-chip (TVOC) mimicking two key biological barriers, namely, tumor leaky vasculature and 3D tumor tissue with dense extracellular matrix (ECM), to study nanoparticle extravasation through leaky vasculature and the following accumulation in tumor tissues. Intact 3D tumor vasculature was developed with selective permeability of small molecules (20 kDa) but not large ones (70 kDa). The permeability was further tuned by cytokine stimulation, demonstrating the independent control of the leaky tumor vasculature. Combined with tumor spheroids in dense ECM, our TVOC model is capable of predicting nanoparticles' in vivo tumor accumulation, thus providing a powerful platform for nanoparticle evaluation