Hematite or α-Fe2O3 has emerged as a highly promising photoanode candidate for photoelectrochemical cells. While significant improvements in its performance have recently been achieved, it remains unclear why the maximum photocurrents still remain well below their theoretical predictions. Here, we report, for the first time, a detailed correlation between the electrical conductivity of undoped and 1 atom% Ti doped hematite and the conditions under which it was annealed (20 ≤ T ≤ 800 °C and 10(-4) ≤ pO2 ≤ 1 atm). Hematite thin films grown by pulsed laser deposition onto sapphire single crystals were evaluated by impedance spectroscopy. Hematite's room temperature conductivity can be increased from ∼10(-11) S cm(-1) for undoped films by as much as nine orders of magnitude by doping with the Ti donor. Furthermore, by controlling the non-stoichiometry of Ti-doped hematite, one can tune its conductivity by up to five orders of magnitude. Depending on processing conditions, donor dopants in hematite may be compensated largely by electrons or by ionic defects (Fe vacancies). A defect model was derived to explain this phenomenon. In addition, a temperature independent value for the electron mobility of 0.01 cm(2) V(-1) s(-1) for a donor density of 4.0 × 10(20) cm(-3) (1% Ti) was derived. These results highlight the importance of carefully controlling photoanode processing conditions, even when operating within the material's extrinsic dopant regime, and more generally, provide a model for the electronic properties of semiconducting metal oxide photoanodes.

The ability to control the size of nanostructures still presents one of the biggest challenges in nanosciences. While impressive progress has been made toward diameter-controlled synthesis of nanocrystals via solutionphase chemical techniques, control over nanowire diameters grown via the gas-phase vapor-liquid-solid mechanism is still challenging. Diameter-controlled growth of nanowires have been reported by controlling the size of the metal nanocatalysts, which is a general technique. However, the complex dynamics of gasphase reactants and their reaction with catalysts requires in-depth understanding of the effect of various growth parameters on the size of catalysts during growth, which makes diameter-controlled growth of nanowires challenging. Here, we report diameter-controlled growth of GeTe nanowires, which are important materials for phase-change memory devices. Recently, several groups have investigated phase-change nanowires for memory applications, but the ability to control their diameters has been lacking. This lack of nanowire size control has made investigation of phase-change memory switching difficult for both fundamental science and device applications. We find that by controlling the rate of supercooling and the reactant supply rate we can produce large quantities of nanowires with uniform, narrow diameter distributions. The effects of various growth parameters such as temperature, pressure, and reactant supply rate on nanowire morphologies are discussed.

Cholesterol is considered indispensable for cell motility, but how physiological cholesterol pools enable cells to move forward remains to be clarified. The majority of cells obtain cholesterol from the uptake of Low-Density lipoproteins (LDL) and here we demonstrate that LDL stimulates A431 squamous epithelial carcinoma and Chinese hamster ovary (CHO) cell migration and invasion. LDL also potentiated epidermal growth factor (EGF) -stimulated A431 cell migration as well as A431 invasion in 3-dimensional environments, using organotypic assays. Blocking cholesterol export from late endosomes (LE), using Niemann Pick Type C1 (NPC1) mutant cells, pharmacological NPC1 inhibition or overexpression of the annexin A6 (AnxA6) scaffold protein, compromised LDL-inducible migration and invasion. Nevertheless, NPC1 mutant cells established focal adhesions (FA) that contain activated focal adhesion kinase (pY397FAK, pY861FAK), vinculin and paxillin. Compared to controls, NPC1 mutants display increased FA numbers throughout the cell body, but lack LDL-inducible FA formation at cell edges. Strikingly, AnxA6 depletion in NPC1 mutant cells, which restores late endosomal cholesterol export in these cells, increases their cell motility and association of the cholesterol biosensor D4H with active FAK at cell edges, indicating that AnxA6-regulated transport routes contribute to cholesterol delivery to FA structures, thereby improving NPC1 mutant cell migratory behaviour.

A novel method for performing in situ characterization of the electrical properties of pristine, ultrafine nanopowders is reported. A modified dilatometer, with a spring‐loaded push rod and electrodes, allows for the simultaneous monitoring of the packed nanopowder's lateral displacement as well as its complex impedance spectroscopy as a function of temperature within a controlled environment. Anatase TiO2 quantum dots of 2 nm diameter, on average, are examined and found to simultaneously shrink and become more resistive upon initial heating. The resistance changes by approximately 3 orders of magnitude upon heating, associated with the desorption of adsorbed water, demonstrating the need for sample preconditioning. Subsequent electrical resistivity measurements, as a function of oxygen partial pressure, over approximately 40 orders of magnitude, at temperatures between 300 °C and 400 °C, exhibit nearly 9 orders of magnitude change in conductivity. The data are consistent with a Frenkel‐based defect disorder model characterized by an enthalpy of reduction of 5.5 ± 0.5 eV.

Summary 1. We investigated the effects of local disturbance history and several biotic and abiotic habitat parameters on the microdistribution of benthic invertebrates after an experimental disturbance in a flood‐prone German stream. 2. Bed movement patterns during a moderate flood were simulated by scouring and filling stream bed patches (area 0.49 m2) to a depth of 15–20 cm. Invertebrates were investigated using ceramic tiles as standardized substrata. After 1, 8, 22, 29, 36 and 50 days, we sampled one tile from each of 16 replicates of three bed stability treatments (scour, fill and stable controls). For each tile, we also determined water depth, near‐bed current velocity, the grain size of the substratum beneath the tile, epilithic algal biomass and standing stock of particulate organic matter (POM). 3. Shortly after disturbance, total invertebrate density, taxon richness and density of the common taxa Baetis spp. and Chironomidae were highest in stable patches. Several weeks after disturbance, by contrast, Baetis spp. and Hydropsychidae were most common in fill and Leuctra spp. in scour patches. The black fly Simulium spp. was most abundant in fill patches from the first day onwards. Community evenness was highest in scour patches during the entire study. 4. Local disturbance history also influenced algal biomass and POM standing stock at the beginning of the experiment, and water depth, current velocity and substratum grain size throughout the experiment. Scouring mainly exposed finer substrata and caused local depressions in the stream bed characterized by slower near‐bed current velocity. Algal biomass was higher in stable and scour patches and POM was highest in scour patches. In turn, all five common invertebrate taxa were frequently correlated with one or two of these habitat parameters. 5. Our results suggest that several ‘direct’ initial effects of local disturbance history on the invertebrates were subsequently replaced by ‘indirect’ effects of disturbance history (via disturbance‐induced changes in habitat parameters such as current velocity or food).