Showing papers by "Meyya Meyyappan published in 2015"

Carbon Nanotube Synthesis Using Coal Pyrolysis.

Abstract: This study investigates carbon nanotube (CNT) production from coal pyrolysis wherein the output gases are used in a chemical vapor deposition reactor. The carbon products are similar to those using commercial coal gas as feedstock, but coal is a relatively cheaper feedstock compared to high purity source gases. A Gibbs minimization model has been developed to predict the volume percentages of product gases from coal pyrolysis. Methane and carbon monoxide were the largest carbon components of the product stream and thus formed the primary source for CNT synthesis. Both the model and the observations showed that increasing the furnace temperature led to a decrease in the absolute quantities of "useful" product gases, with the optimal temperature between 400 and 500 °C. Based on the experimental data, a kinetic rate law for CNT from coal pyrolysis was derived as d[CNT]/dt = K([CO][CH4])(1/2), where K is a function of several equilibrium constants representing various reactions in the CNT formation process.

Chemical functionalization of graphene with aromatic molecule

Abstract: We investigated the doping effects of chemical functionalization on graphene field-effect transistors (G-FETs). A pyrene backbone with an electron-withdrawing group (1-pyrenebutanoic acid succinimidyl ester, PBASE) and DMF acting as a solvent were used. The pyrene derivative was stably immobilized onto the graphene surface via π-π stacking between the two highly conjugated systems, confirmed by electric measurements with different incubation times and linker molecule concentrations. Dimethyl formamide (DMF) can decrease the conductivity of the FET devices and showed an n-doping effect while the pyrene derivative showed a p-doping effect. Because of this, the functionalization with PBASE in DMF could be regarded as a competitive process. This study provides a new insight into chemical functionalization with aromatic molecule, and understanding of doping effects about electron donor and electron acceptor on graphene during the functionalization process.

Nanotechnology: Development of practical systems and nano-micro-macro integration

Abstract: There are strong nanotechnology research programs across the world with every conceivable application in all economic sectors. Basic discoveries have progressed at an amazing pace, as evidenced by the accumulation of publications in the literature. At present, the development of practical systems and commercial products is the next big challenge. Nanoscale is not a human scale. In many cases, development of practical systems demands seamless integration of nano-micro-macro to produce scaled components and processes. While the ultimate vision in nanotechnology may be an entirely bottom-up approach to building systems, it is unrealistic to expect this to happen anytime in the foreseeable future. Only realistic possibility to achieve tangible results in a reasonable time frame, before the stakeholders run out of patience, is to use nanomaterials in a hybrid approach that involves a systematic nano-micro-macro integration. Such an approach will also allow us to utilize the existing infrastructure in the micro area (MEMS, microelectronics) from the last couple of decades, which would make economic sense. This talk will expand on this theme on product and system development using nanomaterials and nanotechnology. Examples will include a carbon nanotube (CNT) based chemical sensor that has been tested for monitoring air quality in the crew cabin in the International Space Station in 2009 and further developed for security applications; a CNT based biosensor for water quality monitoring and health monitoring; CNT-based X-ray tubes for security and other applications; supercapacitors, and several other developments we have been working on for the last 5–8 years. The author thanks all past and present NASA Ames colleagues for their contributions to the application development efforts, especially Jing Li, Yijiang Lu, Jessica Koehne, Cattien Nguyen, Jinwoo Han, Beomsok Kim, Ami Hannon and Michael Oye.

Effects of buffer concentration on sensing performances of ion-sensitive field-effect transistors wth si-nanowires

Abstract: We have experimentally investigated the effect of buffer-dilution on sensing characteristics of the Si-nanowire (Si-NW) ion-sensitive field-effect transistors (ISFETs). Phosphate-buffered saline (PBS) with various buffer concentrations was prepared. The result showed that the sensitivity increases as the buffer concentration decreases for bio-molecule detection, while the pH sensitivity of the Si-NW FETs is insensitive to the buffer solutions. The Debye length of the buffer solution can be a crucial factor to detect biomolecules using FET sensors. For the buffer solution with high ionic strength, the Debye length becomes shorter than the distance between the sensing membrane and the target-molecules so that the charges of target-molecules are screened out. For the pH sensing, however, small hydrogen ions can be bound close to the channel surface and thus little dependence on the buffer concentration.