Producing Atomically Abrupt Axial Heterojunctions in Silicon-Germanium Nanowires by Thermal Oxidation.

Compositional abruptness of the interfaces is one of the important factors to determine the performance of Group IV semiconductor heterojunction (Si/Ge or Si/SiGe) nanowire devices. However, forming abrupt interfaces in the nanowires using the common vapor-liquid-solid (VLS) method is restricted because large solubility of Si and Ge in the Au eutectic liquid catalyst makes gradual composition change at the heterojunction after switching the gas phase components. According to the VLS growth mechanism, another possible approach to form an abrupt interface is making a change of the semiconductor concentration in the eutectic liquid before precipitation of the second phase. Here we show that the composition in AuSiGe eutectic liquid on SiGe nanowires of low Ge concentration (≤6%) can be altered by thermal oxidation at 700 °C. During the oxidation process, only Si is oxidized on the surface of the eutectic liquid, and the Ge/Si ratio in the eutectic liquid is increased. The subsequently precipitated SiGe step at the liquid/solid interface has a higher Ge concentration (∼20%), and a compositionally abrupt interface is produced in the nanowires. The growth mechanism of the heterojunction includes diffusion of Si and Ge atoms on nanowire surface into the AuSiGe eutectic liquid and step nucleation at the liquid/nanowire interface.

Endotoxin Activity in Patients With Extracorporeal Membrane Oxygenation Life Support: An Observational Pilot Study.

Background: Extracorporeal membrane oxygenation (ECMO) life support has become an integral part of intensive care. The endotoxin activity assay (EAA) is a useful test to measure endotoxemia severity in whole blood. To date, no information is available regarding the EAA levels and their effect on clinical outcomes in critically ill patients with ECMO support. Methods: This prospective observational pilot study enrolled adult critically ill patients with ECMO support from August 2019 to December 2020. The EAA levels were measured within 24 h (T1), and at 25-48 (T2), 49-72 (T3), and 73-96 h (T4) after ECMO initiation. This study primarily aimed to investigate the incidence of high EAA levels (≥0.6) at each time point. Subsequent exploratory analyses were conducted to compare the EAA levels of venoarterial ECMO (VA-ECMO) patients between 30-day survivors and non-survivors. Post-hoc analysis was performed to compare the clinical outcomes of VA-ECMO patients with elevated EAA levels at T3 (vs. T1) and those without elevated EAA levels. Results: A total of 39 VA-ECMO patients and 15 venovenous ECMO (VV-ECMO) patients were enrolled. At T1, the incidence of high EAA level (≥0.6) was 42% in VV-ECMO patients and 9% in VA-ECMO patients (P = 0.02). At T2, the incidence of high EAA level was 40% in VV-ECMO patients and 5% in VA-ECMO patients (P = 0.005). In VA-ECMO patients, EAA levels at T3 were significantly higher in 30-day non-survivors than in survivors (median [interquartile range]: 0.49 [0.37-0.93] vs. 0.31 [0.19-0.51], median difference 0.16 [95% confidence interval [CI], 0.02-0.31]; P = 0.024). Moreover, VA-ECMO patients with elevated EAA levels at T3 (vs. T1) had lower 30-day survival than patients without elevated EAA levels (39 vs. 83%, P = 0.026) and fewer ECMO free days by day 30 (median: 3 vs. 23 days, median difference 12 days [95% CI, 0-22]; P = 0.028). Conclusions: A certain proportion of patients experienced high EAA levels (≥0.6) after VV-ECMO or VA-ECMO initiation. VA-ECMO patients with an elevated EAA level at 49-72 h were associated with poor clinical outcomes.