Mammalian cells are exposed to complex microenvironments of varying micro-and nanoscale structural features. These multiscale extracellular cues dictate important aspects of cell behavior, including migration, proliferation and differentiation. In this study, we fabricated anodized aluminum oxide (AAO) membranes of either 80 or 40 nm pore diameters. We utilized these membranes as extracellular matrix scaffolds to culture NIH-3T3 fibroblast cells and investigated how the surface nanotopography might regulate their motility. We observed faster and more persistent fibroblast migration on AAO membranes with larger pores. Through various cell−matrix interaction markers, we found that the surfaces with higher nanoporosity enhance motility through larger focal adhesions, aligned actin fibers, and polarized cell morphology. Our findings reveal the importance of nanoscale topographical cues present in the matrix environment in regulating submicrometer-scale subcellular mechanisms of stress fiber organization and adhesion formation, micrometer-scale cell−matrix interactions, and cell motility over hundreds of micrometers.

High quality BiOCl nanosheets were fabricated using facile, room temperature hydrolysis of Bi(NO3)3 and HCl. The resulting nanosheets had dimensions of 500 nm with the exposed {001} facet. The band gap of the nanosheets was found to be 3.34 eV with conduction and valence band edges at -3.63 eV and -6.97 eV with respect to vacuum, respectively. The electrical conductivity of drop-cast BiOCl nanosheets was measured between aluminum patterned electrodes as a function of temperature and oxygen partial pressure (pO2). The activation energy for conduction in BiOCl was found to be 862 meV in the temperature range of 300-425 K and below 1000 mbar. The electrical conductivity varied with pO2, indicating σ ∝ pO2(1/4.05) and σ ∝ pO2(1/32) for low and sub atmospheric pressures, respectively. A prototypical device for low temperature (425 K) O2 sensing was demonstrated.

The reduction of CuO nanowires (NWs) to Cu2O NWs undergoes an indirect phase transformation on the surface: from single crystalline CuO, to a disordered Cu2-δO phase, and then to crystalline Cu2O. A 9-12 nm disordered Cu2-δO is formed on the NW surface by exposing CuO NWs to CO at 1 Torr, 300 °C for 30 min. After 60 min, this layer decreases to 2-3 nm and is eliminated after 180 min. Energy dispersive X-ray spectroscopy using a scanning tunneling electron microscope and across a single NW reveals the disordered layer to be O-rich with respect to Cu2O with a maximum at. % Cu:O = 1.8. X-ray photoelectron spectroscopy shows adsorbed CO on the surface as evidence of the reduction reaction. Micro-Raman spectroscopy tracks the transformation in NWs as a function of reduction time. A CO enabled surface reduction reaction coupled to diffusion-limited transport of "nonlattice" O to the surface is proposed as a mechanism for Cu2-δO formation. The initial buildup of out-diffusing O to the surface appears to aid the formation of the disordered surface layer. The transformation follows Ostwald-Lussac's law which predicts formation of unstable phases over stable phases, when phase transformation rates are limited by kinetic or diffusional processes. The study provides a generalized approach for facile growth of few nanometer transient layers on multivalent, metal oxide NW surfaces.

Cation substitution of Bi with Fe in BiOCl leads to the formation of ionically layered BiFeOCl nanosheets. The synthesis follows a hydrolysis route using bismuth(III) nitrate and iron(III) chloride, followed by postannealing at 500 °C. Room temperature electrical conductivity improves from 6.11 × 10 S/m for BiOCl to 6.80 × 10 S/m for BiFeOCl. Correspondingly, the activation energy for electrical conduction reduces from 862 meV for pure BiOCl to 310 meV for BiFeOCl. These data suggest improved charge mobility in BiFeOCl nanosheets. Density functional theory calculations confirm this behavior by predicting a high density of states near the Fermi level for BiFeOCl. The improvement in electrical conductivity is exploited in the electrochemical performance of BiFeOCl nanosheets. The insertion capacity of Li ions shows an increase of 2.5×, from 215 mAh·.g for undoped BiOCl to 542 mAh·g for BiFeOCl after 50 cycles at a current density of 50 mA·g. Thus, the direct substitution of Bi sites with Fe in BiOCl results in nanosheets of an ionically layered ternary semiconductor compound which is attractive for Li ion battery anode applications.

We demonstrated room-temperature gas sensing of volatile organic compounds (VOCs) using SnO nanostructured thin films grown via the aerosol chemical vapor deposition process at deposition temperatures ranging from 450 to 600 °C. We investigated the film's sensing response to the presence of three classes of VOCs: apolar, monopolar, and biopolar. The synthesis process was optimized, with the most robust response observed for films grown at 550 °C as compared to other temperatures. The role of film morphology, exposed surface planes, and oxygen defects were explored using experimental techniques and theoretical calculations to improve the understanding of the room-temperature gas sensing mechanism, which is proposed to be through the direct adsorption of VOCs on the sensor surface. Overall, the improved understanding of the material characteristics that enable room-temperature sensing gained in this work will be beneficial for the design and application of metal oxide gas sensors at room temperature.