4 research outputs found
Electrochemical Nanoscale Templating: Laterally Self-Aligned Growth of Organic–Metal Nanostructures
The electrodeposition of Ag into organized surfactant
templates
adsorbed onto (22 × √3) reconstructed Au(111) is investigated
by in situ electrochemical scanning tunneling microscopy. Ag<sup>+</sup> concentrations of as low as 2.5 × 10<sup>–6</sup> M
allow the visualization of the electrochemical molecular templating
effect of a sodium dodecyl sulfate (SDS) adlayer. The SDS hemicylindrical
stripes determine the adsorption sites of the Ag<sup>+</sup> ions
and the directionality of Ag nanodeposition. The SDS-Ag nanostructures
grow along the long axis of SDS hemicylindrical stripes, and an interaction
of Ag with the Au(111) substrate leads to a structural change in the
SDS stripe pattern. The SDS-Ag nanostructures undergo dynamic rearrangement
in response to changes in the applied electrode potential. At negative
potentials, the orientations of SDS-Ag nanostructures are pinned by
the (22 × √3) reconstructed pattern. Furthermore, observed
differences in Ag nanostructuring on Au(111) without molecular templates
(i.e., on a bare Au(111) surface) confirm the role of self-assembled
organic templates in producing metal–organic nanostructures
under control of the surface potential, which can determine the feature
size, shape, and period of the metal nanostructure arrays
Nitrogen-Doped Partially Reduced Graphene Oxide Rewritable Nonvolatile Memory
As memory materials, two-dimensional (2D) carbon materials such as graphene oxide (GO)-based materials have attracted attention due to a variety of advantageous attributes, including their solution-processability and their potential for highly scalable device fabrication for transistor-based memory and cross-bar memory arrays. In spite of this, the use of GO-based materials has been limited, primarily due to uncontrollable oxygen functional groups. To induce the stable memory effect by ionic charges of a negatively charged carboxylic acid group of partially reduced graphene oxide (PrGO), a positively charged pyridinium N that served as a counterion to the negatively charged carboxylic acid was carefully introduced on the PrGO framework. Partially reduced N-doped graphene oxide (PrGO<sub>DMF</sub>) in dimethylformamide (DMF) behaved as a semiconducting nonvolatile memory material. Its optical energy band gap was 1.7–2.1 eV and contained a sp<sup>2</sup> CC framework with 45–50% oxygen-functionalized carbon density and 3% doped nitrogen atoms. In particular, rewritable nonvolatile memory characteristics were dependent on the proportion of pyridinum N, and as the proportion of pyridinium N atom decreased, the PrGO<sub>DMF</sub> film lost memory behavior. Polarization of charged PrGO<sub>DMF</sub> containing pyridinium N and carboxylic acid under an electric field produced N-doped PrGO<sub>DMF</sub> memory effects that followed voltage-driven rewrite-read-erase-read processes
Vertical Alignments of Graphene Sheets Spatially and Densely Piled for Fast Ion Diffusion in Compact Supercapacitors
Supercapacitors with porous carbon structures have high energy storage capacity. However, the porous nature of the carbon electrode, composed mainly of carbon nanotubes (CNTs) and graphene oxide (GO) derivatives, negatively impacts the volumetric electrochemical characteristics of the supercapacitors because of poor packing density (<0.5 g cm<sup>–3</sup>). Herein, we report a simple method to fabricate highly dense and vertically aligned reduced graphene oxide (VArGO) electrodes involving simple hand-rolling and cutting processes. Because of their vertically aligned and opened-edge graphene structure, VArGO electrodes displayed high packing density and highly efficient volumetric and areal electrochemical characteristics, very fast electrolyte ion diffusion with rectangular CV curves even at a high scan rate (20 V/s), and the highest volumetric capacitance among known rGO electrodes. Surprisingly, even when the film thickness of the VArGO electrode was increased, its volumetric and areal capacitances were maintained
Inductive Effect of Lewis Acidic Dopants on the Band Levels of Perovskite for a Photocatalytic Reaction
Band-edge modulation of halide perovskites as photoabsorbers
plays
significant roles in the application of photovoltaic and photochemical
systems. Here, Lewis acidity of dopants (M) as the new descriptor
of engineering the band-edge position of the perovskite is investigated
in the gradiently doped perovskite along the core-to-surface (CsPbBr3–CsPb1–xMxBr3). Reducing M–bromide bond
strength with an increase in hardness of acidic M increases the electron
ability of basic Br, thus strengthening the Pb–Br orbital coupling
in M–Pb–Br, noted as the inductive effect of dopants.
Especially, the highly hard Lewis acidic Mg localized in the outer
position of the perovskite induces the increase of work function and
then shifts band edge upward along the core-to-surface of the perovskite.
Thus, charge separation driven by the dopant-induced internal electric
field induces the slow annihilation of the excited holes, improving
the slow aromatic Csp3–H dissociation
in the photocatalytic oxidation process by ∼211% (491.39 μmol
g–1 h–1) enhancements, compared
with undoped nanocrystals