4 research outputs found
Effect of Gas Pressure on the Density of Horizontally Aligned Single-Walled Carbon Nanotubes Grown on Quartz Substrates
We
investigate the influence of gas pressure on the growth of horizontally
aligned single-walled carbon nanotubes (SWCNTs) on R-cut and r-cut
crystal quartz substrates by alcohol catalytic chemical vapor deposition
(CVD). The density of horizontally aligned SWCNTs was found to depend
highly on gas pressure. A study of the SWCNT growth as a function
of CVD time revealed that the density of horizontally aligned SWCNTs
continued to increase for 10 min at reduced pressure, whereas the
density saturated rapidly at higher pressure even though catalysts
were not deactivated. We argue that variation of incubation time for
low-pressure CVD is key for independent growth of horizontally aligned
SWCNTs and hence higher density growth
Highly Stable and Tunable n‑Type Graphene Field-Effect Transistors with Poly(vinyl alcohol) Films
The
intrinsic p-type behavior of graphene field-effect transistors (FETs)
under ambient conditions poses a fundamental challenge for the assembly
of complex electronic devices, such as integrated circuits. In this
work, we present a protocol for tunable n-type doping of graphene
FETs via poly(vinyl alcohol) (PVA) coating. Using graphene grown by
alcohol catalytic chemical vapor deposition, functionalization of
the surface by this hydroxyl anion-rich polymer results in an evolution
of the FETs from p-type to ambipolar or n-type even under ambient
air conditions. The doping level of graphene is strongly related to
the PVA film coating parameters, such as solution concentration, hardening
temperature, and hardening time. This PVA coating proves to be a simple
and stable approach to tuning the Dirac point and doping level of
graphene, which is highly desirable and of great significance for
the future of graphene-based electronic devices
Self-Limiting Layer-by-Layer Oxidation of Atomically Thin WSe<sub>2</sub>
Growth of a uniform oxide film with
a tunable thickness on two-dimensional transition metal dichalcogenides
is of great importance for electronic and optoelectronic applications.
Here we demonstrate homogeneous surface oxidation of atomically thin
WSe<sub>2</sub> with a self-limiting thickness from single- to trilayers.
Exposure to ozone (O<sub>3</sub>) below 100 °C leads to the lateral
growth of tungsten oxide selectively along selenium zigzag-edge orientations
on WSe<sub>2</sub>. With further O<sub>3</sub> exposure, the oxide
regions coalesce and oxidation terminates leaving a uniform thickness
oxide film on top of unoxidized WSe<sub>2</sub>. At higher temperatures,
oxidation evolves in the layer-by-layer regime up to trilayers. The
oxide films formed on WSe<sub>2</sub> are nearly atomically flat.
Using photoluminescence and Raman spectroscopy, we find that the underlying
single-layer WSe<sub>2</sub> is decoupled from the top oxide but hole-doped.
Our findings offer a new strategy for creating atomically thin heterostructures
of semiconductors and insulating oxides with potential for applications
in electronic devices
Commissioning engineers compendium Revision 3: 2000
First edition published 1991, ISBN 1-873623-00-3SIGLEAvailable from British Library Document Supply Centre-DSC:m01/15145 / BLDSC - British Library Document Supply Centre3. rev. ed.GBUnited Kingdo