Showing papers by "Mildred S. Dresselhaus published in 1979"

Near Infrared Reflectivity of Graphite under Hydrostatic Pressure. I. Experiment

Abstract: We report here the dependence on hydrostatic pressure up to 2.79 kbars of the two structures associated with the A 1 and A 2 transitions in the reflectivity spectra of graphite measured at room temperature in the photon energy range from 0.655 to 1.125 eV. By considering explicitly the effect of the trigonal warping upon the probabilities of these transitions, their spectral shapes are shown to be a step and a peak, respectively, resulting in new locations of critical points on the spectral features A 1 and A 2 which are different from those previously given by Bellodi et al. The observed shifts of these structures due to pressure provide the first direct experimental determination of the fractional change per unit pressure increment of the Slonczewski-Weiss-McClure band parameters γ 1 and γ 5 , yielding values of ∂ln γ 1 /∂ p =0.028 ±0.003 (kbar) -1 and ∂ln γ 5 /∂ p =0.055 ±0.016 (kbar) -1 .

Lattice Mode Structure of Graphite Intercalation Compounds

Abstract: At first sight, a discussion of the lattice, electronic and structural properties of graphite intercalation compounds would appear to be an exceedingly difficult task in view of the large number of intercalate species which form intercalation compounds. A great simplification of the discussion of the graphite intercalation compounds results from emphasis on the strong intralayer bonding in both the graphitic and intercalate layers and the relatively weak interlayer bonding between graphite-intercalate layers and graphite-graphite layers in the intercalation compounds. Thus many of the properties of the graphite intercalation compounds can be understood by identification of the graphite and intercalate layers with their respective parent materials. For this reason, knowledge of the structural, lattice and electronic properties of the parent materials is important for understanding the properties of the corresponding intercalation compounds. To be sure, differences in these properties are found for compounds formed by the various intercalate species but the similarities are more significant. The largest differences occur between classes of intercalation compounds, such as donor and acceptor compounds. For the donors, the intercalate species tends to be ionic and the interlayer interaction is greater than for pristine graphite, while acceptor intercalates tend to be molecular and have a weaker interlayer interaction than for pristine graphite. The similarities between various classes of intercalation compounds are great, and by emphasizing these similarities, a more coherent picture of this class of materials can be presented.