The application of quasi-one dimensional nano-materials in nanoelectronic devices

As the scaling of silicon based electronic devices is approaching limitations set by the physical and materials properties, several nano-sized materials have gained much interest as possible substitutions of silicon for future electronics. This thesis focuses on carbon nanotubes (CNTs), graphene nanoribbons (GNRs) and germanium nanowires (GeNWs) due to their unique properties.;Graphene is single layer graphite, which is predicted to exhibit bandgaps useful for room temperature transistor operations with excellent switching speed and high mobilities when made into narrow ribbons (sub-10 nm). The all-semiconducting nature of sub-10 nm GNRs could bypass the problem of extreme chirality dependence of metal or semiconductor carbon nanotubes (CNTs) for future electronics. Currently, making GNRs remains challenging by lithographic, chemical or sonochemical methods. It is difficult to obtain GNRs with smooth edges and controllable width at high yields. In the second part of the thesis, I will show an interesting approach to making GNRs by unzipping multiwalled carbon nanotubes (MWNTs) by plasma etching of nanotubes partially embedded in a polymer film. The GNRs exhibit smooth edges and a narrow width distribution between 10-20 nm. Raman spectroscopy and electrical transport measurements reveal high quality of the GNRs.;Germanium nanowires (GeNWs) are another potential material to address the future device scaling limitations owing to their high hole and electron mobilities. However, the device performance is limited due to insufficient electrostatic control over charge carriers in the channel in the typical back-gate or top-gate geometry. Mobility analysis based on capacitance modeling alone without direct measurement could give errors due to various uncertainties. In the last part of this dissertation, I will demonstrate a novel surround gate structure of GeNW FETs using a novel self-aligned fabrication approach. Individual surround gate (SG) GeNW FETs show improved switching over GeNW FETs with planar gate stacks owing to improved electrostatics. FET devices comprised of multiple quasi-aligned SG GeNWs in parallel afford on-currents exceeding 0.1 mA at low source-drain bias voltages. Direct experimental evidence show that SG nanowire transistors exhibit higher capacitance and better electrostatic gate control than top-gated devices, and are the most promising structure for future high performance nanoelectronics.;Single walled carbon nanotubes are molecular quantum wires (diameter ∼1nm) which are highly chemically stable and exhibit outstanding electrical conductivity. However, typical synthesis of SWNTs yields a mixture of both metallic and semiconducting varieties with a range of diameters. Several methods have been reported to separate SWNTs and anion exchange (IEC) chromatography has shown the most promise for electronic type separation. In the first part of the dissertation, I will discuss the characterization of IEC separation efficiency by combining spectroscopy and electrical measurements. In the early experiment, the SWNTs were separated according to diameter and electronic types and the separation efficiency decreased with increasing tube diameter. The separation efficiency was much improved by using the new DNA sequence to suspend the SWNTs and single-chirality-enrichment was achieved.