Physical and chemical manipulation of carbon nanotubes and graphene for nanoelectronics

Abstract

The electron confinement in carbon nanomaterials provides them with many interesting electronic, mechanical and optical properties, thus making them one of the best suited materials for electronic and sensor applications. However, at present practical realization of nano-scale electronics faces two major challenges: their assembly into functional electronic circuits, and precise engineering of these building blocks. New methods of physical and chemical manipulation are needed to address these challenges. The work presented in this thesis aims to understand and design physical and chemical manipulation methods for carbon nanostructures. More specifically, this thesis is concerned with two main topics on manipulation of carbon nanomaterials: First, the problem of the top-down, parallel placement of anisotropic nanoparticles and secondly, chemical manipulation via controlled chemical functionalization. Physical manipulation of nanostructures has been achieved by designing a method for creating high aspect ratio cylindrical droplets with nano-to-micro scale diameters on a wafer by engineering the substrate surface chemistry, liquid surface tension and liquid film thickness. The substrate surface is manipulated by chemisorption of monolayers of hydrophobic and hydrophilic molecules in form of alternating rectangular strips. The cylindrical droplets selectively form on the hydrophilic strips. The hydrodynamic flow patterns that evolve within the droplets during evaporation are able to orient and position the entrained carbon nanotubes with parallel alignment with nanometer precision. With respect to chemical manipulation, this thesis work focuses on graphene and graphene nanoribbons (GNR). In this work first detailed structure-reactivity relationships for electron-transfer chemistries of graphene and GNR are developed. For GNR, these relationships demonstrate the dependence of the ribbon reactivity on width and orientation of carbon atoms along the edges. Large variations in reactivity are predicted for ribbons of different widths and family type suggesting selective chemistries may be developed to sort or preferentially modify the GNRs. For graphene these structure reactivity relationships include regio-selective chemistry and reactivity dependence on the number of graphene layers on chip. This work demonstrates high reactivity of graphene edges and reports a spectroscopic method to analyze the edge reactivity. This study should aid studies to control the disordered edge structure of GNR by edge selective chemical functionalization and chemically modify graphene depending on the number of layers stacked. The electron transfer chemistries developed in this work have also been used to understand the role of covalent defects on graphene electron conduction. This work may be used in future to assemble graphene sheets in three dimensions to fabricate supermolecular structures (i.e. graphene super lattices).