18 research outputs found
<i>p</i>‑Channel Field-Effect Transistors Based on C<sub>60</sub> Doped with Molybdenum Trioxide
Fullerene
(C<sub>60</sub>) is a well-known n-channel organic semiconductor.
We demonstrate that p-channel C<sub>60</sub> field-effect transistors
are possible by doping with molybdenum trioxide (MoO<sub>3</sub>).
The device performance of the p-channel C<sub>60</sub> field-effect
transistors, such as mobility, threshold voltage, and on/off
ratio is varied in a controlled manner by changing doping concentration.
This work demonstrates the utility of charge transfer doping to obtain
both n- and p-channel field-effect transistors with a single organic
semiconductor
Ripping Graphene: Preferred Directions
The understanding of crack formation due to applied stress
is key
to predicting the ultimate mechanical behavior of many solids. Here
we present experimental and theoretical studies on cracks or tears
in suspended monolayer graphene membranes. Using transmission electron
microscopy, we investigate the crystallographic orientations of tears.
Edges from mechanically induced ripping exhibit straight lines and
are predominantly aligned in the armchair or zigzag directions of
the graphene lattice. Electron-beam induced propagation of tears is
also observed. Theoretical simulations account for the observed preferred
tear directions, attributing the observed effect to an unusual nonmonotonic
dependence of graphene edge energy on edge orientation with respect
to the lattice. Furthermore, we study the behavior of tears in the
vicinity of graphene grain boundaries, where tears surprisingly do
not follow but cross grain boundaries. Our study provides significant
insights into breakdown mechanisms of graphene in the presence of
defective structures such as cracks and grain boundaries
Tuning the Sharing Modes and Composition in a Tetrahedral GeX<sub>2</sub> (X = S, Se) System via One-Dimensional Confinement
The packing and connectivity of tetrahedral units are
central themes
in the structural and electronic properties of a host of solids. Here,
we report one-dimensional (1D) chains of GeX2 (X = S or
Se) with modification of the tetrahedral connectivity at the single-chain
limit. Precise tuning of the edge- and corner-sharing modes between
GeX2 blocks is achieved by diameter-dependent 1D confinement
inside a carbon nanotube. Atomic-resolution scanning transmission
electron microscopy directly confirms the existence of two distinct
types of GeX2 chains. Density functional theory calculations
corroborate the diameter-dependent stability of the system and reveal
an intriguing electronic structure that sensitively depends on tetrahedral
connectivity and composition. GeS2(1–x)Se2x compound chains are also
realized, which demonstrate the tunability of the system’s
semiconducting properties through composition engineering
Reduced Defect Density in MOCVD-Grown MoS<sub>2</sub> by Manipulating the Precursor Phase
Advancements
in the synthesis of large-area, high-quality two-dimensional
transition metal dichalcogenides such as MoS2 play a crucial
role in the development of future electronic and optoelectronic devices.
The presence of defects formed by sulfur vacancies in MoS2 results in low photoluminescence emission and imparts high n-type
doping behavior, thus substantially affecting material quality. Herein,
we report a new method in which single-phase (liquid) precursors are
used for the metal–organic chemical vapor deposition (MOCVD)
growth of a MoS2 film. Furthermore, we fabricated a high-performance
photodetector (PD) and achieved improved photoresponsivity and faster
photoresponse in the spectral range 405–637 nm compared to
those of PDs fabricated by the conventional MOCVD method. In addition,
the fabricated MoS2 thin film showed a threshold voltage
shift in the positive gate bias direction owing to the reduced number
of S vacancy defects in the MoS2 lattice. Thus, our method
significantly improved the synthesis of monolayer MoS2 and
can expand the application scope of high-quality, atomically thin
materials in large-scale electronic and optoelectronic devices
Structural and Electrical Investigation of C<sub>60</sub>–Graphene Vertical Heterostructures
Graphene, with its unique electronic and structural qualities, has become an important playground for studying adsorption and assembly of various materials including organic molecules. Moreover, organic/graphene vertical structures assembled by van der Waals interaction have potential for multifunctional device applications. Here, we investigate structural and electrical properties of vertical heterostructures composed of C<sub>60</sub> thin film on graphene. The assembled film structure of C<sub>60</sub> on graphene is investigated using transmission electron microscopy, which reveals a uniform morphology of C<sub>60</sub> film on graphene with a grain size as large as 500 nm. The strong epitaxial relations between C<sub>60</sub> crystal and graphene lattice directions are found, and van der Waals <i>ab initio</i> calculations support the observed phenomena. Moreover, using C<sub>60</sub>–graphene heterostructures, we fabricate vertical graphene transistors incorporating n-type organic semiconducting materials with an on/off ratio above 3 × 10<sup>3</sup>. Our work demonstrates that graphene can serve as an excellent substrate for assembly of molecules, and attained organic/graphene heterostructures have great potential for electronics applications
Ripping Graphene: Preferred Directions
The understanding of crack formation due to applied stress
is key
to predicting the ultimate mechanical behavior of many solids. Here
we present experimental and theoretical studies on cracks or tears
in suspended monolayer graphene membranes. Using transmission electron
microscopy, we investigate the crystallographic orientations of tears.
Edges from mechanically induced ripping exhibit straight lines and
are predominantly aligned in the armchair or zigzag directions of
the graphene lattice. Electron-beam induced propagation of tears is
also observed. Theoretical simulations account for the observed preferred
tear directions, attributing the observed effect to an unusual nonmonotonic
dependence of graphene edge energy on edge orientation with respect
to the lattice. Furthermore, we study the behavior of tears in the
vicinity of graphene grain boundaries, where tears surprisingly do
not follow but cross grain boundaries. Our study provides significant
insights into breakdown mechanisms of graphene in the presence of
defective structures such as cracks and grain boundaries
Ripping Graphene: Preferred Directions
The understanding of crack formation due to applied stress
is key
to predicting the ultimate mechanical behavior of many solids. Here
we present experimental and theoretical studies on cracks or tears
in suspended monolayer graphene membranes. Using transmission electron
microscopy, we investigate the crystallographic orientations of tears.
Edges from mechanically induced ripping exhibit straight lines and
are predominantly aligned in the armchair or zigzag directions of
the graphene lattice. Electron-beam induced propagation of tears is
also observed. Theoretical simulations account for the observed preferred
tear directions, attributing the observed effect to an unusual nonmonotonic
dependence of graphene edge energy on edge orientation with respect
to the lattice. Furthermore, we study the behavior of tears in the
vicinity of graphene grain boundaries, where tears surprisingly do
not follow but cross grain boundaries. Our study provides significant
insights into breakdown mechanisms of graphene in the presence of
defective structures such as cracks and grain boundaries
3D Motion of DNA-Au Nanoconjugates in Graphene Liquid Cell Electron Microscopy
Liquid-phase transmission electron
microscopy (TEM) can probe and
visualize dynamic events with structural or functional details at
the nanoscale in a liquid medium. Earlier efforts have focused on
the growth and transformation kinetics of hard material systems, relying
on their stability under electron beam. Our recently developed graphene
liquid cell technique pushed the spatial resolution of such imaging
to the atomic scale but still focused on growth trajectories of metallic
nanocrystals. Here, we adopt this technique to imaging three-dimensional
(3D) dynamics of soft materials instead, double strand (dsDNA) connecting
Au nanocrystals as one example, at nanometer resolution. We demonstrate
first that a graphene liquid cell can seal an aqueous sample solution
of a lower vapor pressure than previously investigated well against
the high vacuum in TEM. Then, from quantitative analysis of real time
nanocrystal trajectories, we show that the status and configuration
of dsDNA dictate the motions of linked nanocrystals throughout the
imaging time of minutes. This sustained connecting ability of dsDNA
enables this unprecedented continuous imaging of its dynamics via
TEM. Furthermore, the inert graphene surface minimizes sample–substrate
interaction and allows the whole nanostructure to rotate freely in
the liquid environment; we thus develop and implement the reconstruction
of 3D configuration and motions of the nanostructure from the series
of 2D projected TEM images captured while it rotates. In addition
to further proving the nanoconjugate structural stability, this reconstruction
demonstrates 3D dynamic imaging by TEM beyond its conventional use
in seeing a flattened and dry sample. Altogether, we foresee the new
and exciting use of graphene liquid cell TEM in imaging 3D biomolecular
transformations or interaction dynamics at nanometer resolution
3D Motion of DNA-Au Nanoconjugates in Graphene Liquid Cell Electron Microscopy
Liquid-phase transmission electron
microscopy (TEM) can probe and
visualize dynamic events with structural or functional details at
the nanoscale in a liquid medium. Earlier efforts have focused on
the growth and transformation kinetics of hard material systems, relying
on their stability under electron beam. Our recently developed graphene
liquid cell technique pushed the spatial resolution of such imaging
to the atomic scale but still focused on growth trajectories of metallic
nanocrystals. Here, we adopt this technique to imaging three-dimensional
(3D) dynamics of soft materials instead, double strand (dsDNA) connecting
Au nanocrystals as one example, at nanometer resolution. We demonstrate
first that a graphene liquid cell can seal an aqueous sample solution
of a lower vapor pressure than previously investigated well against
the high vacuum in TEM. Then, from quantitative analysis of real time
nanocrystal trajectories, we show that the status and configuration
of dsDNA dictate the motions of linked nanocrystals throughout the
imaging time of minutes. This sustained connecting ability of dsDNA
enables this unprecedented continuous imaging of its dynamics via
TEM. Furthermore, the inert graphene surface minimizes sample–substrate
interaction and allows the whole nanostructure to rotate freely in
the liquid environment; we thus develop and implement the reconstruction
of 3D configuration and motions of the nanostructure from the series
of 2D projected TEM images captured while it rotates. In addition
to further proving the nanoconjugate structural stability, this reconstruction
demonstrates 3D dynamic imaging by TEM beyond its conventional use
in seeing a flattened and dry sample. Altogether, we foresee the new
and exciting use of graphene liquid cell TEM in imaging 3D biomolecular
transformations or interaction dynamics at nanometer resolution
3D Motion of DNA-Au Nanoconjugates in Graphene Liquid Cell Electron Microscopy
Liquid-phase transmission electron
microscopy (TEM) can probe and
visualize dynamic events with structural or functional details at
the nanoscale in a liquid medium. Earlier efforts have focused on
the growth and transformation kinetics of hard material systems, relying
on their stability under electron beam. Our recently developed graphene
liquid cell technique pushed the spatial resolution of such imaging
to the atomic scale but still focused on growth trajectories of metallic
nanocrystals. Here, we adopt this technique to imaging three-dimensional
(3D) dynamics of soft materials instead, double strand (dsDNA) connecting
Au nanocrystals as one example, at nanometer resolution. We demonstrate
first that a graphene liquid cell can seal an aqueous sample solution
of a lower vapor pressure than previously investigated well against
the high vacuum in TEM. Then, from quantitative analysis of real time
nanocrystal trajectories, we show that the status and configuration
of dsDNA dictate the motions of linked nanocrystals throughout the
imaging time of minutes. This sustained connecting ability of dsDNA
enables this unprecedented continuous imaging of its dynamics via
TEM. Furthermore, the inert graphene surface minimizes sample–substrate
interaction and allows the whole nanostructure to rotate freely in
the liquid environment; we thus develop and implement the reconstruction
of 3D configuration and motions of the nanostructure from the series
of 2D projected TEM images captured while it rotates. In addition
to further proving the nanoconjugate structural stability, this reconstruction
demonstrates 3D dynamic imaging by TEM beyond its conventional use
in seeing a flattened and dry sample. Altogether, we foresee the new
and exciting use of graphene liquid cell TEM in imaging 3D biomolecular
transformations or interaction dynamics at nanometer resolution