Structure and Vibrational Properties of Isolated Carbon Nanocrystallites
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STRUCTURE AND VIBRATIONAL PROPERTIES OF ISOLATED CARBON NANOCRYSTALLITES V.I. MERKULOV, J.S. LANNIN Dept. of Physics, Penn State University, University Park, PA 16802 J.M. COWLEY Dept. of Physics and Astronomy, Arizona State University, Tempe, AZ 85287-1504 ABSTRACT Small isolated nanocrystallites of carbon have been prepared on amorphous Si0 2 and studied by interference enhanced Raman scattering (IERS) and scanning transmission electron microscopy (STEM). A new mode of dark field STEM, using a thin annular detector, has allowed imaging of 1-2 nm graphite-like particles using (002) diffraction. For such small particles, the Raman spectra provide the first evidence for changes in the phonon density of states of a nanocrystalline system. INTRODUCTION As crystallites are decreased in size to the nanoscale level their electronic and vibrational properties will be modified as surface and quantum size effects play an increasing role. Experimental studies to date have focused on modification of the electronic states of nanocrystalline semiconductors, such as CdSe or Si, wherein substantial changes in the optical gap have been attributed to quantum size effects [1,2]. However, the influence of size effects on the phonon states of very small, isolated nanocrystallites
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