| In this research, the optical and electrical properties of graphene-based materials are investigated. In particular, "graphene oxide", which is an individual layer of graphite oxide, and its chemically reduced form, is probed in terms of its properties, and the properties of graphene oxide and chemically modified graphene oxide are compared with the properties of graphene. Although graphite oxide was synthesized more than a hundred years ago (by Brodie 1859), the individual layers have not been investigated until recently. In parallel with our work on graphene oxide, physicists have discovered remarkable transport physics in pristine graphene (a layer of graphite) and showed that it has a potential for use in nano-electronics; this heightens interest in chemically modified graphenes, including graphene oxide.; In terms of characterizing the optical properties of graphene oxide, a straightforward method is presented for identifying and measuring the effective optical properties of graphene-based materials, based on the use of substrates consisting of a thin dielectric layer on silicon. With this approach and by optimizing the thickness of the dielectric layer, strong contrast between the graphene-based individual platelets and the substrate is obtained. By choosing appropriate optical properties and thickness of the dielectric layer, the effective refractive index and optical absorption coefficient of graphene oxide, thermally reduced graphene oxide, and graphene were obtained by comparing the predicted and measured contrasts.; Imaging ellipsometry is a method that holds potential for optical imaging and for characterizing the optical properties of extremely thin materials (∼1nm), such as an individual chemically modified graphene platelet, and few-layer graphene oxide platelets. Of interest is whether it is possible to determine the optical properties as well as the thickness, through use of imaging ellipsometry alone. A conventional spectroscopic ellipsometer can also be applied to a multi-layer stack of graphene oxide several millimeters in width---much wider than the individual platelets. By using the results from both imaging as well as conventional ellipsometry, a significant difference in the optical properties of single vs. multilayer stacks and a strong difference in optical properties for "as is" graphene oxide (whether individual layer or multilayer stacks) vs. thermally treated individual or multilayer stacks, is observed. By separately obtaining thickness from profilometry or AFM, a model for explaining the thickness and optical properties, and their changes upon thermal treatment, is proposed.; Electrical characterization is of both fundamental and technological interest, given the aforementioned, exceptional, properties of pristine graphene. The resistivity of the material was monitored by heating the individual-layer graphene oxide (deposited on a substrate) in vacuum. Through monitoring the time and temperature response of electrical conductivity, it was possible to show that the rate changes in conductivity could be correlated with an activated chemical process, and the activation energy (the barrier height) could be obtained. It was also learned that the electrical conductivity of individual layers of graphene oxide following such time-temperature exposures could be as high as 85 S/m. A several-fold higher conductivity was obtained by chemical reduction with gas phase hydrazine, followed by heating in vacuum. As in the case with pristine graphene, the resistivity of graphene oxide was sensitive to the electric field. The current-voltage measurements that were made however also revealed electrical properties different from graphene.; A preliminary measurement of the sensitivity of single graphene oxide on specific gas suggests the possibility of using this material as a sensor. A plan for measuring sensitivity of specific gases and their concentrations is suggested and discussed. This method would rely on... |
