Nanotubes and Nanoribbons in displays, NEMS, and chemical sensors: recent results from First-Principles Quantum Mechanics simulations
Accelrys Inc., US
Keywords: Nanotubes, Nanoribbons, Displays, NEMS, Sensors
Of the myriad of potential application areas commonly associated with Nanotechnology, sensors and displays are two of the closest ones to commercial reality. The two materials systems that have given rise to high hopes in these applications are carbon nanotubes (CNT) and SnO2 nanoribbons. We have used Accelrys' Density Functional Theory code DMol3  to investigate important properties in both systems. For CNT-based field-emission displays, we have investigated the effect of adsorbates at the nanotube tip on the emission current. In particular, we show that polar adsorbates like water are attracted to the tube tip under emission conditions, and make the HOMO unstable, thereby reducing the work function . The effect becomes more significant in the presence of a H-bonded cluster of water (Fig. 1). For CNT-based nano-electro-mechanical sensors (NEMS), we have computed the electrical response of CNT under two types of mechanical forces: (a) bending, and (b) pushing with an AFM tip. We show that bent tubes do not display large changes in conductance. In contrast, AFM-pushing leads to a net tensile stretching of the tube . For zigzag tubes this opens up an energy gap at the Fermi level, leading to a significant drop in the room-temperature electrical conductance . For semiconducting nanotubes a different experiment is proposed, in which the tube is pushed against a SiO2 substrate, thereby promoting charge transfer and change in electrical conductance (Fig. 2). Finally, recent experiments have revealed that SnO2 nanoribbons can be used as very efficient and re-usable chemical sensor for certain harmful gases, e.g., NO2. Based on previously known results for bulk oxides, it was believed that surface O-vacancies play an important role. However, our simulations yield a very interesting binding structure of NO2 on a defect-free SnO2 surface, which involves breaking of a surface Sn-O bond and corresponding localization of the LUMO . The resulting NO3 species have been clearly identified in subsequent spectroscopic measurement .
NSTI Nanotech 2003 Conference Technical Program Abstract