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We report an improved photosensitivity in few-layer tin disulfide (SnS2) field-effect transistors (FETs) following doping with CdSe/ZnS core/shell quantum dots (QDs). The hybrid QD-SnS2 FET devices achieve more than 500% increase in the photocurrent response compared with the starting SnS2-only FET device and a spectral responsivity reaching over 650 A/W at 400 nm wavelength. The negligible electrical conductance in a control QD-only FET device suggests that the energy transfer between QDs and SnS2 is the main mechanism responsible for the sensitization effect, which is consistent with the strong spectral overlap between QD photoluminescence and SnS2 optical absorption as well as the large nominal donor-acceptor interspacing between QD core and SnS2. We also find enhanced charge carrier mobility in hybrid QD-SnS2 FETs which we attribute to a reduced contact Schottky barrier width due to an elevated background charge carrier density. [ABSTRACT FROM AUTHOR]

Atomic steps, a defect common to all crystal surfaces, can play an important role in many physical and chemical processes. However, attempts to predict surface dynamics under nonequilibrium conditions are usually frustrated by poor knowledge of the atomic processes of surface motion arising from mass transport from/to surface steps. Using low-energy electron microscopy that spatially and temporally resolves oxide film growth during the oxidation of NiAl(100) we demonstrate that surface steps are impermeable to oxide film growth. The advancement of the oxide occurs exclusively on the same terrace and requires the coordinated migration of surface steps. The resulting piling up of surface steps ahead of the oxide growth front progressively impedes the oxide growth. This process is reversed during oxide decomposition. The migration of the substrate steps is found to be a surface-step version of the well-known Hele-Shaw problem, governed by detachment (attachment) of Al atoms at step edges induced by the oxide growth (decomposition). By comparing with the oxidation of NiAl(110) that exhibits unimpeded oxide film growth over substrate steps we suggest that whenever steps are the source of atoms used for oxide growth they limit the oxidation process; when atoms are supplied from the bulk, the oxidation rate is not limited by the motion of surface steps. [ABSTRACT FROM AUTHOR]

We use in situ observations during high-temperature transmission electron microscopy to quantify the exchange of semiconductor material between Au-Ge vapor--liquid--solid seed drops and Ge nanowires (NWs). By performing simultaneous measurements under identical conditions on arrays with systematic variations in NW diameter, we establish the nanoscale size dependence of the temperature-dependent equilibrium composition of the Au-Ge binary alloy. We find a significantly enhanced Ge solubility for drops on thin NWs compared to thicker ones. The controlled modification of the surface of the NW by an ordered carbon shell leads to drastic changes in the solubility.