3 research outputs found
Recrystallized Arrays of Bismuth Nanowires with Trigonal Orientation
We
demonstrate methods to improve the crystalline-quality of free-standing
Bi nanowires arrays on a Si substrate and enhance the preferred trigonal
orientation for thermoelectric performance by annealing the arrays
above the 271.4 °C Bi melting point. The nanowires maintain their
geometry during melting due to the formation of a thin Bi-oxide protective
shell that contains the molten Bi. Recrystallizing nanowires from
the melt improves crystallinity; those cooled rapidly demonstrate
a strong trigonal orientation preference
Atomic Resolution Imaging of Grain Boundary Defects in Monolayer Chemical Vapor Deposition-Grown Hexagonal Boron Nitride
Grain boundaries are observed and
characterized in chemical vapor
deposition-grown sheets of hexagonal boron nitride (h-BN) via ultra-high-resolution
transmission electron microscopy at elevated temperature. Five- and
seven-fold defects are readily observed along the grain boundary.
Dynamics of strained regions and grain boundary defects are resolved.
The defect structures and the resulting out-of-plane warping are consistent
with recent theoretical model predictions for grain boundaries in
h-BN
Superlinear Composition-Dependent Photocurrent in CVD-Grown Monolayer MoS<sub>2(1–<i>x</i>)</sub>Se<sub>2<i>x</i></sub> Alloy Devices
Transition
metal dichalcogenides (TMDs) have emerged as a new class of two-dimensional
materials that are promising for electronics and photonics. To date,
optoelectronic measurements in these materials have shown the conventional
behavior expected from photoconductors such as a linear or sublinear
dependence of the photocurrent on light intensity. Here, we report
the observation of a new regime of operation where the photocurrent
depends superlinearly on light intensity. We use spatially resolved
photocurrent measurements on devices consisting of CVD-grown monolayers
of TMD alloys spanning MoS<sub>2</sub> to MoSe<sub>2</sub> to show
the photoconductive nature of the photoresponse, with the photocurrent
dominated by recombination and field-induced carrier separation in
the channel. Time-dependent photoconductivity measurements show the
presence of persistent photoconductivity for the S-rich alloys, while
photocurrent measurements at fixed wavelength for devices of different
alloy compositions show a systematic decrease of the responsivity
with increasing Se content associated with increased linearity of
the current–voltage characteristics. A model based on the presence
of different types of recombination centers is presented to explain
the origin of the superlinear dependence on light intensity, which
emerges when the nonequilibrium occupancy of initially empty fast
recombination centers becomes comparable to that of slow recombination
centers