Secondary Electron Emission Spectroscopy of Crystalline and Non-Crystalline Carbon Allotropes
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SECONDARY ELECTRON EMISSION SPECTROSCOPY OF CRYSTALLINE AND NON-CRYSTALLINE CARBON ALLOTROPES ALON HOFFMAN AND STEVEN PRAWER Department of Applied Physics and Microelectronics and Materials Technology Centre, Victoria University of Technology, (RMIT), G.P.O. Box 2476V, Melbourne, Victoria, 3001, Australia.
ABSTRACT The Secondary Electron Emission (SEE) spectra of type Ila diamond, highly oriented pyrolytic graphite (HOPG), amorphous carbon (e-beam evaporated), glassy carbon and amorphic-diamond (filtered arc evaporated) were measured in the 0 - 80 eV electron kinetic energy range, and found to be very distinctive for the different carbon allotropcs. The sensitivity of SEE spectroscopy to crystal damage for the type Ila diamond surface was studied by performing SEE measurements as function of I keV argon ion irradiation dose. Two examples of the use of SEE in the characterization of diamond surfaces are presented. In the first, the crystalline quality of the back and front surfaces of a chemically vapour deposited diamond thin film which had delaminated from a fused quartz substrate were compared using SEE and, in the second, SEE was used to provide a qualitative estimate of the damage induced by mechanical polishing of a natural diamond surface.
INTRODUCTION Secondary electrons may be emitted from the surface of solids via primary excitation by electrons or photons. The energy dependence of the secondary electron yield consists of a slowly varying band peaking at a few cV. Superimposed on this large slowly varying electron energy distribution of secondary electron is a fine structure which has been shown to reflect features in the empty density of states above the vacuum level [I]. Qualitatively, the basic process involved in secondary electron emission is that electrons can be promoted to empty levels above the Fermi level (Er), whereafter those above the vacuum level (Ev) can escape into the vacuum. The contribution of these electrons to the emission current will be proportional to the density of states at each energy. Thus in general any fine structure in the SEE spectrum is expected to correspond to regions in the Brillouin zone with a high density of states. Work by our group over the past year has shown that the SEE spectrum of diamond, graphite (in the form of highly oriented pyrolytic graphite (HOPG)) and amorphous carbon (electron beam evaporated) are highly distinctive of the particular carbon allotrope under study
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In particular, the SEE spectrum fine structure of HOPG was reported by several groups and found to reflect high energy conduction band states in agreement with band structure calculations [1,3,4,51. For diamond, the SEE spectrum has been measured in the 0 - 50 eV range by us 121, and been shown to reflect high energy conduction band states in agreement with other spectroscopic techniques sensitive to the empty density of states and band structure calculations [6,7,8]. It has also been shown that the SEE spectrum of HOPG is very sensitive to damage induced under controlled Ar+ ion bea
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