Gallium selenide (GaSe) is a 2D material with a thickness-dependent gap, strong non-linear optical coefficients and uncommon interband optical selection rules, making it interesting for optoelectronic and spintronic applications. In this work, we monitor the oxidation dynamics of GaSe with thicknesses ranging from 10 to 200 nm using Raman spectroscopy. In ambient temperature and humidity conditions, the intensity of all Raman modes and the luminescence decrease rapidly with moderate exposure to above-gap illumination. Concurrently, several oxidation products appear in the Raman spectra: Ga 2 Se 3 , Ga 2 O 3 and amorphous and crystalline selenium. We find that no safe measurement power exists for optical measurements on ultrathin GaSe in ambient conditions. We demonstrate that the simultaneous presence of oxygen, humidity, and abovegap illumination is required to activate this photo-oxidation process, which is attributed to the transfer of photo-generated charge carriers towards aqueous oxygen at the sample surface, generating highly reactive superoxide anions that rapidly degrade the sample and quench the optical response of the material.

The introduction of stable isotopes in the fabrication of semiconductor nanowires provides an additional degree of freedom to manipulate their basic properties, design an entirely new class of devices, and highlight subtle but important nanoscale and quantum phenomena. With this perspective, we report on phonon engineering in metal-catalyzed silicon nanowires with tailor-made isotopic compositions grown using isotopically enriched silane precursors (28)SiH4, (29)SiH4, and (30)SiH4 with purity better than 99.9%. More specifically, isotopically mixed nanowires (28)Si(x)(30)Si(1-x) with a composition close to the highest mass disorder (x ∼ 0.5) were investigated. The effect of mass disorder on the phonon behavior was elucidated and compared to that in isotopically pure (29)Si nanowires having a similar reduced mass. We found that the disorder-induced enhancement in phonon scattering in isotopically mixed nanowires is unexpectedly much more significant than in bulk crystals of close isotopic compositions. This effect is explained by a nonuniform distribution of (28)Si and (30)Si isotopes in the grown isotopically mixed nanowires with local compositions ranging from x = ∼0.25 to 0.70. Moreover, we also observed that upon heating, phonons in (28)Si(x)(30)Si(1-x) nanowires behave remarkably differently from those in (29)Si nanowires suggesting a reduced thermal conductivity induced by mass disorder. Using Raman nanothermometry, we found that the thermal conductivity of isotopically mixed (28)Si(x)(30)Si(1-x) nanowires is ∼30% lower than that of isotopically pure (29)Si nanowires in agreement with theoretical predictions.

No abstract

Background The COVID-19 pandemic has had unprecedented consequences on the world economy. The impact of the pandemic on illicit drug market remains scant. We expose the potential consequences the COVID-19 pandemic could have on the ability of people who use drugs to source their illicit drugs via cryptomarkets. Methods We analyzed 262 self-reported submissions of illicit drug transactions on the darkweb. The self-reports include the date of the transaction, the types of illicit drugs bought/sold, and whether the shipment of the illicit drugs succeeded, had issues (ex. unusually long delivery, an error in the type of drug shipped, quantity or concentration of the drug), or failed. Results Between January 1st , 2020 and March 21, 2020, successful deliveries represented 60% to 100% of transactions. Starting on March 21 however, the share of shipments that had issues or failed increased rapidly and represented a majority of all shipments. At the peak of the market disruption, the successful deliveries represented only 21% of all transactions. Conclusion Illicit drug transactions on the darkweb were disrupted at the same time as lockdowns were put in place in the United States and in the United Kingdom. While no causation link can be established, the correlation suggests that lockdowns could have disrupted drug cryptomarkets activities. We discuss the market disruption in light of the literature.

Objectives Environmental contamination by patients with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) through respiratory droplets suggests that surfaces and equipment could be a medium of transmission. We aimed to assess the surface and equipment contamination by SARS-COV-2 of an emergency department (ED) during the coronavirus infectious disease-2019 (COVID-19) outbreak. Methods We performed multiple samples from different sites in ED patients care and non-patient care areas with sterile premoistened swabs and used real-time reverse transcriptase polymerase chain reaction (RT-PCR) to detect the presence of SARS-CoV-2 ribonucleic acid (RNA). We also sampled the personal protective equipment (PPE) from health care workers (HCWs). Results Among the 192 total samples, 10 (5.2%) were positive. In patient care areas, 5/46 (10.9%) of the surfaces directly in contact with COVID-19 patients revealed the presence of SARS-CoV-2 RNA, and 4/56 (7.1%) of the surfaces that were not directly in contact with COVID-19 patients were positive. SARS-CoV-2 RNA was present only in the patients’ examination and monitoring rooms. Before decontamination SARS-CoV-2 RNA was present on the saturation clip, the scuff for blood pressure measurement, the stretcher, the plastic screens between patients and the floor. After decontamination, SARS-CoV-2 RNA remained on the scuff, the stretcher and the trolleys. All samples from non-patient care areas or staff working rooms were negative. Only one sample from the PPE of the HCWs was positive. Conclusions Our findings suggest that surfaces and equipment contamination by SARS-CoV-2 RNA in an ED during the COVID-19 outbreak is low and concerns exclusively patients’ examination and monitoring rooms, preserving non-patient care areas.