ABSTRACT
Atomically thin two dimensional hexagonal boron nitride (2D h-BN) is one of the key materials in the development of new van der Waals heterostructures due to its outstanding properties including an atomically smooth surface, high thermal conductivity, high mechanical strength, chemical inertness and high electrical resistance. The development of 2D h-BN growth is still in the early stages and largely depends on rapid and accurate characterization of the grown monolayer or few layers h-BN films. This paper demonstrates a new approach to characterizing monolayer h-BN films directly on metal substrates by grazing-incidence infrared reflection absorption spectroscopy (IRRAS). Using h-BN films grown by atmospheric-pressure chemical vapor deposition on Cu and Ni substrates, two new sub-bands are found for the A2u out-of-plane stretching mode. It is shown, using both experimental and computational methods, that the lower-energy sub-band is related to 2D h-BN coupled with substrate, while the higher energy sub-band is related to decoupled (or free-standing) 2D h-BN. It is further shown that this newly-observed fine structure in the A2u mode can be used to assess, quickly and easily, the homogeneity of the h-BN-metal interface and the effects of metal surface contamination on adhesion of the layer.
ABSTRACT
We report the first evidence for functionalization of Ga(2)O(3) nanowires (NWs), which have been incorporated as the active material in room temperature capacitance gas-sensing devices. An adsorbed layer of pyruvic acid (PA) was successfully formed on Ga(2)O(3) NWs by simple room temperature vapor transport, which was confirmed by Fourier transform infrared spectroscopy. The effect of the adsorbed PA on the surface properties was demonstrated by the change in the response of the NW gas-sensing devices. Results indicate that the adsorption of PA reduced the sensitivity of the Ga(2)O(3) NW device to common hydrocarbons such as nitromethane and acetone while improving the response to triethylamine by an order of magnitude. Taking into account the simplicity of this functionalization together with the ease of producing these capacitance-based gas-sensing devices, this approach represents a viable technique for sensor development.
ABSTRACT
The preparation and functionalization of ITO surfaces has been studied using primarily X-ray photoemission spectroscopy and infrared reflection-absorption spectroscopy (IRRAS) and the reagents n-hexylamine and n-octyltrimethoxysilane (OTMS). Particular attention has been paid to characterization of the surfaces both before and after functionalization. Surfaces cleaned by ultraviolet (UV)/ozone treatment and subsequently exposed to room air have approximately 0.5-0.8 monolayers (ML) of adsorbed impurity C. Most is in the form of aliphatic species, but as much as one-half is partially oxidized and consists of C-OH, C-O-C, and/or >C=O groups. The coverage of these species can be reduced by cleaning in organic solvents prior to UV/ozone treatment. The OH coverage on the ITO surfaces studied here is relatively small (approximately 1.0 OH nm-2), based on the Si coverage after reaction with OTMS. A satellite feature in the O 1s XPS spectrum, often suggested to be a quantitative measure of adsorbed OH, receives a significant contribution from sources not directly related to hydroxylated ITO. n-Hexylamine adsorbs, at a saturation coverage of approximately 0.08 ML, via a Lewis acid-base interaction. The particular acid site has not been conclusively identified, but it is speculated that surface Sn sites may be involved. For OTMS, a saturation coverage of about 0.21 ML is found, and the C/Si atom ratios suggest that some displacement of preadsorbed organic impurities occurs during adsorption. The alkyl chain of adsorbed OTMS is disordered, with no preferred stereoisomer. However, the chain appears to lie mainly parallel to the surface with the plane defined by the terminal CH3-CH2-CH2- segment oriented essentially perpendicular to the surface.
