Raman Nanometrology of Graphene

Graphene is a two-dimensional honey-comb lattice of carbon atoms with very unusual electron energy dispersion. Since its recent micromechanical isolation and measurements, graphene attracted tremendous attention of the physics and engineering communities. In addition to the wealth of two-dimensional electron gas physics revealed by graphene, it is a very promising material for the electronic and sensor applications. Graphene manifests extremely high charge carrier mobility at room temperature, which is far beyond the values achievable in the materials currently used in transistor designs. For this reason, graphene is considered for applications in the integrated circuits beyond the conventional silicon complementary metaloxide semiconductor electronic technology. Some of the major problems associated with graphene research and applications are the difficulties of graphene identification, e.g. distinguishing it from other carbon materials, and verification of the number of graphene atomic layers. In this dissertation research we expand the use of the micro-Raman spectroscopy as the nanometrology tool for graphene material characterization. Raman spectroscopy is a noninvasive technique, which is widely used to characterize structural and electronic properties of carbon-based materials such as carbon nanotubes, diamond, graphite and diamond-like carbons. Graphenes Raman spectrum has clear signatures, which allow one to identify it and determine the number of atomic layers with high accuracy. The main results of this dissertation are (i) measurement of the temperature coefficients of the G and 2D peaks in Raman spectrum of graphene; (ii) the study of the effects of different substrates on Raman signatures of graphene; and (iii) the first investigation of the ultraviolet Raman spectrum of graphene. The obtained results are important for graphene identification and device applications since electric bias and gate voltages in graphene transistors result in the device self-heating while device fabrication often requires the use of various substrates with properties different from those of the standard silicon. In addition, graphene-device characterization is conducted at different temperatures. The measurements of temperature coefficients of graphene Raman peaks was also instrumental in the study of heat conduction in graphene and shed light on its anharmonic properties.