| This thesis is divided into three sections. The first section describes the design and construction of an ultrahigh vacuum, low temperature, high magnetic field, scanning tunneling microscope (STM) system. This system has been designed specifically for the characterization of nanometer-scale materials with low-dimensional electronic properties, and for the manipulation and modification of these materials to fabricate novel electronic devices. The successful operation of this system marks the beginning of a long term, potentially fruitful research program.; The second section discusses experiments performed with an STM on two carbon materials. The first material is the fullerene molecule C36, which is investigated through scanning tunneling spectroscopy. These measurements prove C36 to be a material with an 0.8 eV electronic gap and sharp, molecular-like electronic energy levels. However, the spacing of these levels varies slightly from the theoretical predictions for isolated C36 molecules. Through further analysis, a new, dimerized C36 morphology is proposed and a better appreciation of the high chemical reactivity of this material is gained. Carbon nanotubes are a second material studied in this thesis. Besides conventional STM measurements, length-dependent transport characteristics of nanotubes are measured using the STM tip as a sliding electrical contact. These measurements identify unusual transport properties which appear to be initiated at particular physical positions along a nanotube. The behavior agrees with theoretical models in which a defect is incorporated in a carbon nanotube, indicating that the control of such defects may be a critical issue in the development of nanotube-based electronic devices.; The third section of this thesis discusses field emission characteristics of carbon nanotube-filled composites. Nanotube-based field emission sources are shown to have excellent device characteristics which meet or exceed all of the requirements of commercial, high intensity, field emission sources. Surprisingly, though, a quantitative analysis of the emission current reveals that the nanotubes are not conventional emitters at all. Instead, they display a variety of interesting behaviors including an unusually low voltage onset, an anomalously sharp current increase above the onset, and a high field regime in which nanotube interactions tend to smooth and stabilize the field emission current. By looking beyond conventional field emission theory, each of these behaviors may be understood in terms of nanotube properties. |
