We have measured the bias dependence of the threshold voltage shift in a series of amorphous silicon-silicon nitride thin-film transistors, where the composition of the nitride is varied. There are two distinct instability mechanisms: a slow increase in the density of metastable fast states and charge trapping in slow states. State creation dominates at low fields and charge trapping dominates at higher fields. The state creation is found to be independent of the nitride composition, whereas the charge trapping depends strongly on the nitride composition. This is taken as good evidence that state creation takes place in the hydrogenated amorphous silicon (a-Si:H) layer, whereas the charge trapping takes place in the a-SiN:H. The metastable states are suggested to be Si dangling bonds in the a-Si:H, and the state creation process similar to the Staebler–Wronski effect. The confirmation of state creation in a thin-film transistor means that states can be created simply by populating conduction-band states in the undoped material. The slow states are also thought to be Si dangling bonds, but located in the silicon nitride matrix.
Using a dynamic fabrication process, hybrid, photoactivated microswimmers made from two different semiconductors, titanium dioxide (TiO ) and cuprous oxide (Cu O) are developed, where each material occupies a distinct portion of the multiconstituent particles. Structured light-activated microswimmers made from only TiO or Cu O are observed to be driven in hydrogen peroxide and water most vigorously under UV or blue light, respectively, whereas hybrid structures made from both of these materials exhibit wavelength-dependent modes of motion due to the disparate responses of each photocatalyst. It is also found that the hybrid particles are activated in water alone, a behavior which is not observed in those made from a single semiconductor, and thus, the system may open up a new class of fuel-free photoactive colloids that take advantage of semiconductor heterojunctions. The TiO /Cu O hybrid microswimmer presented here is but an example of a broader method for inducing different modes of motion in a single light-activated particle, which is not limited to the specific geometries and materials presented in this study.
We investigate the dynamics of structured photoactive microswimmers and show that morphology sensitively determines the swimming behavior. Particular to this study, a major portion of the light-activated particles' underlying structure is built from a photocatalytic material, made possible by dynamic physical vapor deposition (DPVD). We find that swimmers of this type exhibit unique shape-dependent autonomous swimming that is distinct from what is seen in systems with similar structural morphology but not fabricated directly from the catalyst. Notably, the direction of motion is a function of these parameters. Because the swimming behavior is strongly correlated with particle shape and material composition, DPVD allows for engineering small-scale propulsion by adjusting the fabrication parameters to match the desired performance.
An iridium (Ir) modified silicon (001) (Si(001)) surface is studied using low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). The surface exhibits p(2 × 2) domains in LEED intensity images. The STM images show that the basis of the crystal lattice consists of an Ir atom and a Si dimer and, like Si(001) dimer rows, they are aligned parallel to the orthogonal [110] directions.
Copper(II) meso-tetra (4-carboxyphenyl) porphyrin (Cu-TCPP) is studied on a 5-(octadecyloxy) isophthalic acid covered highly ordered pyrolytic graphite surface with a scanning tunneling microscope (STM) at the solid-liquid interface. STM images of individual, chains, and two-dimensional domains of Cu-TCPP molecules were measured. The stability of individual Cu-TCPP molecules and Cu-TCPP chains indicates that the interaction between the Cu-TCPP molecules and the underlying 5-OIA layer is strong enough to immobilize Cu-TCPP molecules.
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