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The risk factors of environmental contamination by SARS-CoV-2 are largely unknown. We analyzed 1,320 environmental samples obtained from COVID-19 patients over 1 year. The risk factors for contamination of COVID-19 patients’ surrounding environment were higher viral load in the respiratory tract and shorter duration from symptom onset to sample collection.
Pt thin films of various thicknesses (30 nm ∼ 200 nm) were deposited on Si wafers with SiO2, Ti, TiO2, or IrO2 buffer layers at various temperatures (room temperature ∼200 °C) by a direct current magnetron sputtering process. The Pt films showed a strong (111)-preferred texture irrespective of the thickness, under-layer, and growth temperature. The authors previously reported [J-E. Lim, D-Y. Park, J.K. Jeong, G. Darlinski, H.J. Kim, and C.S. Hwang, Appl. Phys. Lett. 81, 3224 (2002)] that the films were composed of three kinds of grains with slightly different (111) lattice parameters (bulklike, 1.0% and 2.1% larger). This study details the microstructural variations of the Pt films according to the variations of experimental parameters. The different deposition conditions produced slightly different crystalline structures, but the three different (111) lattice parameters were always found. Epitaxial (200) Pt films on a (200) MgO substrate and a highly (111) textured Au thin film on a SiO2/Si did not show the same splitting in the lattice parameter. The grains with 1.0% and 2.1% larger (111) lattice parameter almost disappeared after postannealing at 1000 °C. However, surface chemical binding of the Pt film before and after annealing was unchanged. Therefore, it is believed that the lattice parameter splitting in the (111) textured Pt film originated from the interfacial grains with the distorted crystal structure due probably to growth stress.
We have investigated the electrical characteristics, junction depth and defect of ultrashallow junctions formed by using a plasma doping procedure. Compared with ultralow energy boron ion implantation at 500eV, the plasma doping process exhibits both a shallow junction depth and a low sheet resistance. The junction depths of the plasma doped samples were 15 nm and 33 nm after annealing for 10s at 900 °C and 950 °C, respectively. For the same junction depth, the sheet resistance of the B2H6 plasma doped sample is an order of magnitude less than that of the 500eV B ion implanted sample. Based on cross-sectional transmission electron microscope (TEM) and deep level transient spectroscopy (DLTS) analysis, the defects formed by the B2H6 plasma doping process can be completely removed by annealing at 950 °C for 10s.
Selective chemical etching and atomic force microscope (AFM) examination has been performed to delineate two-dimensional (2-D) dopants profiles of p/n-type well and junction areas. Selectivity strongly depended on the types of dopants and the ratio of etching solutions. Calibration showed that the carrier concentrations in both p/n-type regions could be delineated down to a level of ∼1×1017/cm3. The AFM-induced profiles were compared with the calculated data provided by the 2-D process simulators such as TRIM and SUPREM-IV.
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