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 WSe₂

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 WSe₂ with a self-limiting thickness from single- to trilayers. Exposure to ozone (O₃) below 100 °C leads to the lateral growth of tungsten oxide selectively along selenium zigzag-edge orientations on WSe₂. With further O₃ exposure, the oxide regions coalesce and oxidation terminates leaving a uniform thickness oxide film on top of unoxidized WSe₂. At higher temperatures, oxidation evolves in the layer-by-layer regime up to trilayers. The oxide films formed on WSe₂ are nearly atomically flat. Using photoluminescence and Raman spectroscopy, we find that the underlying single-layer WSe₂ 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