We present the detection of volatile organic compounds directly in their vapor phase by surface-enhanced Raman
scattering (SERS) substrates based on lithographically-defined two-dimensional rectangular array of nanopillars. The
type of nanopillars is known as the tapered pillars. For the tapered pillars, SERS enhancement arises from the
nanofocusing effect due to the sharp tip on top. SERS experiments were carried out on these substrates using various
concentrations of toluene vapor. The results show that SERS signal from a toluene vapor is strongly influenced by the
substrate temperature, and the toluene vapor can be detected within minutes of exposing the SERS substrate to the vapor.
A simple adsorption model is developed which gives results matching the experimental data. The results also show
promising potential for the use of these substrates in environmental monitoring of gases and vapors.
Recent experimental advances have made carbon nanotubes promising material for utilizing as nano-electro-mechanical systems (NEMS). The key feature of CNT-based NEMS is the ability to drastically change electrical conductance due to a mechanical deformation. The deformation effects can be divided into two major groups: bond stretching of sp<sup>2</sup> coordinated nanotubes and transition from sp<sup>2</sup> to sp<sup>3</sup> coordination. The purpose of this work is to review the change in electrical response of nanotubes to different types of mechanical deformation. The modeling consists of a combination of universal force-field molecular dynamics (UFF), density functional theory (DFT) and Green's function theory. We show that conductance of metallic carbon nanotubes can decrease by 2-3 orders of magnitude, when deformed by an AFM tip, but is insensitive to bending. These results can explain the experiment of Ref. . Such a decrease is chirality dependent, being maximum for zigzag nanotubes. In contrast, twisting and radial deformation result in bandgap openning only in armchair nanotubes. In addition, radial deformation of armchair nanotubes leads to dramatic oscillations of conductance.
Of the myriad of potential application areas commonly associated with Nanotechnology, sensors based on carbon nanotubes (CNT) and metal-oxide nanoribbons are one of the closest to commercial reality. In the quest for practical sensing devices, molecular modeling continues to provide useful insight and guidance. In this work we review some of our recent molecular modeling investigations on: (1) CNT-based electromechanical sensors; (2) gas-sensing properties of SnO<sub>2</sub> nanowires/ribbons; and (3) CNT-metal contacts, which can significantly affect the performance of CNT-based sensors.
Thin films of binary chalcogenide synthesized on quartz and silicon single crystal substrates by CW argon ion laser and pulsed third harmonic of Nd:YAG laser irradiation of separate sandwiched Ge/Se and Sn/Se films. The alloy formation and crystalline states are characterized by observing photomicrographs, scanning electron micrographs, optical absorption and reflection spectra. EDAX measurements manifest near stoichiometric proportion of Sn and Se.