4 research outputs found
Ultrathin Oxide Films by Atomic Layer Deposition on Graphene
In this paper, a method is presented to create and characterize
mechanically robust, free-standing, ultrathin, oxide films with controlled,
nanometer-scale thickness using atomic layer deposition (ALD) on graphene.
Aluminum oxide films were deposited onto suspended graphene membranes
using ALD. Subsequent etching of the graphene left pure aluminum oxide
films only a few atoms in thickness. A pressurized blister test was
used to determine that these ultrathin films have a Young’s
modulus of 154 ± 13 GPa. This Young’s modulus is comparable
to much thicker alumina ALD films. This behavior indicates that these
ultrathin two-dimensional films have excellent mechanical integrity.
The films are also impermeable to standard gases suggesting they are
pinhole-free. These continuous ultrathin films are expected to enable
new applications in fields such as thin film coatings, membranes,
and flexible electronics
Chemical Vapor Deposition-Derived Graphene with Electrical Performance of Exfoliated Graphene
While chemical vapor deposition (CVD) promises a scalable
method
to produce large-area graphene, CVD-grown graphene has heretofore
exhibited inferior electronic properties in comparison with exfoliated
samples. Here we test the electrical transport properties of CVD-grown
graphene in which two important sources of disorder, namely grain
boundaries and processing-induced contamination, are substantially
reduced. We grow CVD graphene with grain sizes up to 250 μm
to abate grain boundaries, and we transfer graphene utilizing a novel,
dry-transfer method to minimize chemical contamination. We fabricate
devices on both silicon dioxide and hexagonal boron nitride (h-BN)
dielectrics to probe the effects of substrate-induced disorder. On
both substrate types, the large-grain CVD graphene samples are comparable
in quality to the best reported exfoliated samples, as determined
by low-temperature electrical transport and magnetotransport measurements.
Small-grain samples exhibit much greater variation in quality and
inferior performance by multiple measures, even in samples exhibiting
high field-effect mobility. These results confirm the possibility
of achieving high-performance graphene devices based on a scalable
synthesis process
In Situ Imaging of an Anisotropic Layer-by-Layer Phase Transition in Few-Layer MoTe<sub>2</sub>
Understanding the phase transition mechanisms in two-dimensional
(2D) materials is a key to precisely tailor their properties at the
nanoscale. Molybdenum ditelluride (MoTe2) exhibits multiple
phases at room temperature, making it a promising candidate for phase-change
applications. Here, we fabricate lateral 2H–Td interfaces with laser irradiation and probe
their phase transitions from micro- to atomic scales with in situ heating in the transmission electron microscope
(TEM). By encapsulating the MoTe2 with graphene protection
layers, we create an in situ reaction cell compatible
with atomic resolution imaging. We find that the Td-to-2H phase transition initiates at
phase boundaries at low temperatures (200–225 °C) and
propagates anisotropically along the b-axis in a
layer-by-layer fashion. We also demonstrate a fully reversible 2H-Td-2H phase
transition cycle, which generates a coherent 2H lattice
containing inversion domain boundaries. Our results provide insights
on fabricating 2D heterophase devices with atomically sharp and coherent
interfaces
In Situ Imaging of an Anisotropic Layer-by-Layer Phase Transition in Few-Layer MoTe<sub>2</sub>
Understanding the phase transition mechanisms in two-dimensional
(2D) materials is a key to precisely tailor their properties at the
nanoscale. Molybdenum ditelluride (MoTe2) exhibits multiple
phases at room temperature, making it a promising candidate for phase-change
applications. Here, we fabricate lateral 2H–Td interfaces with laser irradiation and probe
their phase transitions from micro- to atomic scales with in situ heating in the transmission electron microscope
(TEM). By encapsulating the MoTe2 with graphene protection
layers, we create an in situ reaction cell compatible
with atomic resolution imaging. We find that the Td-to-2H phase transition initiates at
phase boundaries at low temperatures (200–225 °C) and
propagates anisotropically along the b-axis in a
layer-by-layer fashion. We also demonstrate a fully reversible 2H-Td-2H phase
transition cycle, which generates a coherent 2H lattice
containing inversion domain boundaries. Our results provide insights
on fabricating 2D heterophase devices with atomically sharp and coherent
interfaces