Resolving the homology-function relationship through comparative genomics of membrane-trafficking machinery and parasite cell biology

With advances in DNA sequencing technology, it is increasingly common and tractable to informatically look for genes of interest in the genomic databases of parasitic organisms and infer cellular states. Assignment of a putative gene function based on homology to functionally characterized genes in other organisms, though powerful, relies on the implicit assumption of functional homology, i.e. that orthology indicates conserved function. Eukaryotes reveal a dazzling array of cellular features and structural organization, suggesting a concomitant diversity in their underlying molecular machinery. Significantly, examples of novel functions for pre-existing or new paralogues are not uncommon. Do these examples undermine the basic assumption of functional homology, especially in parasitic protists, which are often highly derived? Here we examine the extent to which functional homology exists between organisms spanning the eukaryotic lineage. By comparing membrane trafficking proteins between parasitic protists and traditional model organisms, where direct functional evidence is available, we find that function is indeed largely conserved between orthologues, albeit with significant adaptation arising from the unique biological features within each lineage

The effects of thermally-induced biaxial stress on the structural, electrical, and optical properties of Cu2O thin films

The effects of biaxial stress in Cu2O thin films grown by rf magnetron sputtering at different growth temperatures were investigated using X-ray diffraction (XRD), atomic force microscopy (AFM), electrical transport, and ellipsometric measurements. A predominant diffraction peak in the XRD patterns corresponds to the (111) plane direction of the Cu2O phase. Biaxial tensile stress was induced by thermal mismatch between the film and substrate and increased with increasing growth temperature. As the growth temperature and biaxial stress increased, the electrical resistivity decreased, while the carrier concentration and Hall mobility both increased. The ellipsometric data were fit using an optical dispersion model, and the decrease in refractive index was attributed to contraction of the lattice parameter with increasing biaxial stress. The optical absorption peaks shifted slightly toward higher energy with increasing stress. Our experimental data suggest that the mechanisms of stress are important for understanding the properties of Cu2O thin films and for the fabrication of devices using them.ope

Effects of temperature-induced stress on the structural, electrical, and optical properties of ZnO:Ga thin films grown on Si substrates

Crystalline ZnO:Ga thin films with highly preferential c-axis oriented crystals were prepared on Si(001) substrates at different temperatures using the reactive magnetron sputtering technique. Effects of temperature-induced stress in ZnO:Ga films were investigated using X-ray diffraction (XRD), atomic force microscopy (AFM), electrical transport, and spectroscopic ellipsometry measurements. XRD results showed that the films were highly c-axis (out-of-plane) oriented and crystallinity improved with growth temperature. The residual compressive stress in films grown at low temperature relaxes with substrate temperature and becomes tensile stress with further increases in growth temperature. Resistivity of the films decreases with increasing stress, while the carrier concentration and mobility increase as the stress increases. The mechanism of the stress-dependent bandgap of ZnO:Ga films grown at different temperatures is suggested in the present work.ope

Electronic and optical properties in ZnO:Ga thin films induced by substrate stress

The effects of biaxial stress in ZnO:Ga thin films on different substrates, e.g., sapphire(0001), quartz, Si(001), and glass have been investigated by X-ray diffraction, atomic force microscopy, and electrical transport and ellipsometric measurements. A strong dependence of orientation, crystallite size, transport, and electronic properties upon the substrate-induced stress has been found. The structural properties indicate that a tensile stress exists in epitaxial ZnO:Ga films grown on sapphire, Si, and quartz, while a compressive stress appears in films grown on glass. The resistivity of the films decreased with increasing biaxial stress, which is inversely proportional to the product of the carrier concentration and Hall mobility. The refractive index n was found to decrease with increasing biaxial stress, while the optical band gap E0 increased with stress. These behaviors are attributed to lattice contraction and the increase in the carrier concentration that is induced by the stress. Our experimental data suggest that the mechanism of substrate-induced stress is important for understanding the properties of ZnO:Ga thin films and for the fabrication of devices which use these materials.ope

Temperature dependence of the interband transition in a V2O5 film

The temperature dependence of the interband transition in an ??-V2O5 film was investigated using absorption and photoluminescence spectral measurements at a temperature range of 10–300 K. Transmission measurements in the experimental temperature range indicate that the ??-V2O5 film has two distinct interband transitions, implying indirect and direct transitions. This result was confirmed by spectroscopic ellipsometry. The blue shift of both the transitions in the ??-V2O5 film with decreasing temperature was explained by a reduction in the lattice-dilatation effect and the electron-phonon interaction. The PL measurements in the experimental temperature range showed that the emission near 530 nm is due to the indirect transition in the ??-V2O5 film.ope

Phase transition of a MoS2 monolayer through top layer desulfurization by He+ ion irradiation

Two-dimensional (2D) metal monochalcogenides have recently attracted significant interest following the extensive and intensive research into transition metal dichalcogenides (TMDs). However, the formation of transition metal monochalcogenide remains relatively unstudied. Here, we investigate the structural and electronic changes of the MoS2 monolayer by removing the top sulfur layer using low-energy He+ ion sputtering. As a result, the substoichiometric MoSx surface induces semiconducting to the metallic phase transition. Under ambient conditions, the oxidized MoSx surface restores a semiconducting state with narrowed bandgap, p-type conduction, or possibly a semimetallic state. Our findings provide an effective way to form and improve the functionality of Janus TMD monolayers. Published under an exclusive license by AIP Publishing.FALS

Enhanced ferroelectricity in perovskite oxysulfides

© 2019 American Physical Society.A sulfur element is a promising anion dopant for synthesizing new multifunctional materials and for exploring unusual physical phenomena. However, owing to its volatility, sulfur substitution to oxide materials is challenging, and thus the sulfurization effects on the associated properties have been limitedly studied. Here, a facile method for sulfurization to a perovskite oxide Pb(Zr,Ti)O3 is developed and demonstrated. A thiourea (CH4N2S) solution is used as a precursor for the sulfurization and its doping-level control. By manipulating the sulfur concentration (x), we systematically examine the physical properties of sulfur-doped Pb(Zr,Ti)O3-xSx films. An enhancement in the tetragonality and ferroelectricity by sulfurization is observed with the band-gap reduction, which is consistent with our theoretical predictions. In the sulfurized films, the ferroelectric phonon modes become softened progressively, probably due to the substitution of apical oxygens with sulfur atoms. Our work is of practical interest for designing ferroelectric photovoltaic devices with high performance

Interface Defect Engineering of a Large-Scale CVD-Grown MoS2 Monolayer via Residual Sodium at the SiO2/Si Substrate

Alkali metal halide-assisted chemical vapor deposition (CVD) methods can produce wafer-scale uniform monolayer transition metal dichalcogenides (TMDs). Further defect engineering is necessary to obtain high-performance functional devices. While defect engineering has focused on the surface of the monolayer TMDs or the contact property, interface defect engineering is rare and non-trivial. Based on a NaCl-assisted CVD-grown large-scale uniform MoS2 monolayer on SiO2/Si substrate, a trace amount of Na cations is present, residing at the SiO2 substrate during the CVD-growth process and contributes to the n-type doping into the supported monolayer MoS2. Furthermore, the residual Na cations are electrically moved toward the bottom side of monolayer MoS2 to passivate the interfacial defects.1