Carbon nanotube field effect transistors and ferrofluids

Abstract

The thesis presents transport measurements of isolated single wall carbon nanotube field effect transistors (SWNTFETs), magnetic fluids and their derivatives independently and in combination. Some of the challenges that plague the performance of the SWNTFETs are found to be hysteresis, incessant 1/f noise and low value of quantum capacitance. The extracted device parameters are strongly influenced by the growth, fabrication, device geometry, environment, material and instrumentation factors. The numerically simulated transistor characteristics are found to qualitatively explain the Schottky barrier transport in SWNTFET, but do not bring out the richness of the characteristics observed at DC, constant (time-domain) and AC bias. The study of SWNTFET characteristics under a magnetic fluid environment forms the core of the present work. Measurement of electrical characteristics of the SWNT in the vicinity of single-domain magnetic nanoparticles introduced from a ferrofluid dispersion reveals an apparent change in the semi conducting state of the SWNT to a metallic state. This dramatic change is indicated by gate independence of the drain - source current and increase in off - current by orders of magnitude beyond a threshold level of nanoparticle concentration in the magnetic fluid. The effect of fluid concentration, device geometry, time, SWNT current, particle nature and fluid stabilizing mechanism are explored to identify plausible physical or chemical nature of the observed phenomena. The studies point to a charge transfer mechanism from the surfactant adsorbed on the magnetic nanoparticle to the SWNT. Finally, the macroscopic problem of field induced instability is studied in magnetic gels (magnetoelastic derivative of ferrofluids). Measurements on the dielectric properties of these gels with and without magnetic field are observed to magnify sources of error which are normally hidden in the capacitance voltage curves.