Spatio-Temporal Electron Propagation Dynamics in Au/Fe/MgO(001) in nonequilibrium: Revealing Single Scattering Events and the Ballistic Limit

Understanding the microscopic spatio-temporal dynamics of nonequilibrium charge carriers in heterosystems promises optimization of process and device design towards desired energy transfer. Hot electron transport is governed by scattering with other electrons, defects, and bosonic excitations. Analysis of the energy dependence of scattering pathways and identification of diffusive, super-diffusive, and ballistic transport regimes are current challenges. We determine in femtosecond time-resolved two-photon photoelectron emission spectroscopy the energy-dependent change of the electron propagation time through epitaxial Au/Fe(001) heteostructures as a function of Au layer thickness for energies of 0.5 to \unit[2.0]{eV} above the Fermi energy. We describe the laser-induced nonequilibrium electron excitation and injection across the Fe/Au interface using real-time time-dependent density functional theory and analyze the electron propagation through the Au layer by microscopic electron transport simulations. We identify ballistic transport of minority electrons at energies with a nascent, optically excited electron population which is determined by the combination of photon energy and the specific electronic structure of the material. At lower energy, super-diffusive transport with 1 to 4 scattering events dominates. The effective electron velocity accelerates from 0.3 to \unit[1]{nm/fs} with an increase in the Au layer thickness from 10 to 100~nm. This phenomenon is explained by electron transport that becomes preferentially aligned with the interface normal for thicker Au layers, which facilitates electron momentum / energy selection by choice of the propagation layer thickness

Mortality and pulmonary complications in patients undergoing surgery with perioperative SARS-CoV-2 infection: an international cohort study

Background: The impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on postoperative recovery needs to be understood to inform clinical decision making during and after the COVID-19 pandemic. This study reports 30-day mortality and pulmonary complication rates in patients with perioperative SARS-CoV-2 infection. Methods: This international, multicentre, cohort study at 235 hospitals in 24 countries included all patients undergoing surgery who had SARS-CoV-2 infection confirmed within 7 days before or 30 days after surgery. The primary outcome measure was 30-day postoperative mortality and was assessed in all enrolled patients. The main secondary outcome measure was pulmonary complications, defined as pneumonia, acute respiratory distress syndrome, or unexpected postoperative ventilation. Findings: This analysis includes 1128 patients who had surgery between Jan 1 and March 31, 2020, of whom 835 (74·0%) had emergency surgery and 280 (24·8%) had elective surgery. SARS-CoV-2 infection was confirmed preoperatively in 294 (26·1%) patients. 30-day mortality was 23·8% (268 of 1128). Pulmonary complications occurred in 577 (51·2%) of 1128 patients; 30-day mortality in these patients was 38·0% (219 of 577), accounting for 81·7% (219 of 268) of all deaths. In adjusted analyses, 30-day mortality was associated with male sex (odds ratio 1·75 [95% CI 1·28–2·40], p\textless0·0001), age 70 years or older versus younger than 70 years (2·30 [1·65–3·22], p\textless0·0001), American Society of Anesthesiologists grades 3–5 versus grades 1–2 (2·35 [1·57–3·53], p\textless0·0001), malignant versus benign or obstetric diagnosis (1·55 [1·01–2·39], p=0·046), emergency versus elective surgery (1·67 [1·06–2·63], p=0·026), and major versus minor surgery (1·52 [1·01–2·31], p=0·047). Interpretation: Postoperative pulmonary complications occur in half of patients with perioperative SARS-CoV-2 infection and are associated with high mortality. Thresholds for surgery during the COVID-19 pandemic should be higher than during normal practice, particularly in men aged 70 years and older. Consideration should be given for postponing non-urgent procedures and promoting non-operative treatment to delay or avoid the need for surgery. Funding: National Institute for Health Research (NIHR), Association of Coloproctology of Great Britain and Ireland, Bowel and Cancer Research, Bowel Disease Research Foundation, Association of Upper Gastrointestinal Surgeons, British Association of Surgical Oncology, British Gynaecological Cancer Society, European Society of Coloproctology, NIHR Academy, Sarcoma UK, Vascular Society for Great Britain and Ireland, and Yorkshire Cancer Research

Band-edge exciton fine structure and recombination dynamics in InP/ZnS colloidal nanocrystals

We report on a temperature-, time-, and spectrally resolved study of the photoluminescence of type-I InP/ZnS colloidal nanocrystals with varying core size. By studying the exciton recombination dynamics we assess the exciton fine structure in these systems. In addition to the typical bright-dark doublet, the photoluminescence stems from an upper bright state in spite of its large energy splitting (similar to 400 meV). This striking observation results from dramatically lengthened thermalization processes among the fine structure levels and points to optical-phonon bottleneck effects in InP/ZnS nanocrystals. Furthermore, our data show that the radiative recombination of the dark exciton scales linearly with the bright -dark energy splitting for CdSe and InP nanocrystals. This finding strongly suggests a universal dangling bonds-assisted recombination of the dark exciton in colloidal nanostructures

Band-Edge Exciton Fine Structure and Recombination Dynamics in InP/ZnS Colloidal Nanocrystals

We report on a temperature-, time-, and spectrally resolved study of the photoluminescence of type-I InP/ZnS colloidal nanocrystals with varying core size. By studying the exciton recombination dynamics we assess the exciton fine structure in these systems. In addition to the typical bright–dark doublet, the photoluminescence stems from an upper bright state in spite of its large energy splitting (∼100 meV). This striking observation results from dramatically lengthened thermalization processes among the fine structure levels and points to optical-phonon bottleneck effects in InP/ZnS nanocrystals. Furthermore, our data show that the radiative recombination of the dark exciton scales linearly with the bright–dark energy splitting for CdSe and InP nanocrystals. This finding strongly suggests a universal dangling bonds-assisted recombination of the dark exciton in colloidal nanostructures