11 research outputs found
Self-Assembled Two-Dimensional Heteromolecular Nanoporous Molecular Arrays on Epitaxial Graphene
The
development of graphene functionalization strategies that simultaneously
achieve two-dimensional (2D) spatial periodicity and substrate registry
is of critical importance for graphene-based nanoelectronics and related
technologies. Here, we demonstrate the generation of a hydrogen-bonded
molecularly thin organic heteromolecular nanoporous network on epitaxial
graphene on SiC(0001) using room-temperature ultrahigh vacuum scanning
tunneling microscopy. In particular, perylenetetracarboxylic diimide
(PTCDI) and melamine are intermixed to form a spatially periodic 2D
nanoporous network architecture with hexagonal symmetry and a lattice
parameter of 3.45 ± 0.10 nm. The resulting adlayer is in registry
with the underlying graphene substrate and possesses a characteristic
domain size of 40–50 nm. This molecularly defined nanoporous
network holds promise as a template for 2D ordered chemical modification
of graphene at lengths scales relevant for graphene band structure
engineering
Accepted for the Council:
very smooth program for me. When I was first admitted to the graduate program, I had no funding. At that time, my financial situation was very crucial, and my first and immediate goal was to find an assistantship position as soon as possible. My sincere thanks and appreciation go to Prof. Ward Plummer who let me join his research group even before I passed the qualifying exam. With Prof. Plummer’s help, I was able to travel extensively to do experiments all over the world with visits t
Coexistence of Two Electronic Nano-Phases on a CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3–<i>x</i></sub>Cl<sub><i>x</i></sub> Surface Observed in STM Measurements
Scanning
tunneling microscopy is utilized to investigate the local density
of states of a CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3–<i>x</i></sub>Cl<sub><i>x</i></sub> perovskite in cross-sectional
geometry. Two electronic phases, 10–20 nm in size, with different
electronic properties inside the CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3–<i>x</i></sub>Cl<sub><i>x</i></sub> perovskite
layer are observed by the d<i>I/</i>d<i>V</i> mapping
and point spectra. A power law dependence of the d<i>I/</i>d<i>V</i> point spectra is revealed. In addition, the distinct
electronic phases are found to have preferential orientations close
to the normal direction of the film surface. Density functional theory
calculations indicate that the observed electronic phases are associated
with local deviation of I/Cl ratio, rather than different orientations
of the electric dipole moments in the ferroelectric phases. By comparing
the calculated results with experimental data we conclude that phase
A (lower contrast in d<i>I/</i>d<i>V</i> mapping
at −2.0 V bias) contains a lower I/Cl ratio than that in phase
B (higher contrast in d<i>I/</i>d<i>V</i>)
Templating Sub-10 nm Atomic Layer Deposited Oxide Nanostructures on Graphene via One-Dimensional Organic Self-Assembled Monolayers
Molecular-scale control over the
integration of disparate materials
on graphene is a critical step in the development of graphene-based
electronics and sensors. Here, we report that self-assembled monolayers
of 10,12-pentacosadiynoic acid (PCDA) on epitaxial graphene can be
used to template the reaction and directed growth of atomic layer
deposited (ALD) oxide nanostructures with sub-10 nm lateral resolution.
PCDA spontaneously assembles into well-ordered domains consisting
of one-dimensional molecular chains that coat the entire graphene
surface in a manner consistent with the symmetry of the underlying
graphene lattice. Subsequently, zinc oxide and alumina ALD precursors
are shown to preferentially react with the functional moieties of
PCDA, resulting in templated oxide nanostructures. The retention of
the original one-dimensional molecular ordering following ALD is dependent
on the chemical reaction pathway and the stability of the monolayer,
which can be enhanced via ultraviolet-induced molecular cross-linking