Multi-wavelength Raman spectroscopy of natural nanostructured carbons

Abstract

9 There is an extensive range of carbon substances with poorly ordered structures that are not 10 well understood. Yet they are important as indicators of conditions of related geological 11 processes. The carbon minerals include nanocrystalline graphite, natural analogues of glass-like 12 carbon (GLC) – shungite and impact ultrahigh-pressure GLC, recently discovered 13 ultranocrystalline diamond, as well as natural carbon nanocomposites of diamond, lonsdaleite 14 and graphite. Studying these natural carbon substances using a standard Raman approach with 15 excitation by visible radiation may lead to a significant distortion of the understanding of their 16 phase states. This paper presents in detail for the first time the spectral features of natural, poorly 17 ordered and multiphase sp 2 -sp 3 carbon composites by multi–wave Raman spectroscopy using 18 laser excitations from visible to ultraviolet light applied to natural low-ordered carbon substances 19 - nanocrystalline graphite and shungite, nanocrystalline and ultranocrystalline diamond, and 20 multiphase carbon aggregates. The carbon state resolution advantages of ultraviolet Raman 21 spectroscopy for phase analysis of nanostructured and poorly ordered polycomponent carbon 22