Berlin 2015 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 59: Graphene: Applications, luminescence and spin relaxation (HL with O/TT)

HL 59.4: Talk

Wednesday, March 18, 2015, 17:30–17:45, ER 270

Correlation of the crystallite sizes and D band frequency of non-graphitic carbons — •Dominique B. Schuepfer¹, Kristin Faber², Bernd M. Smarsly², Roman V. Yusupov³, and Peter J. Klar¹ — ¹Institute of Experimental Physics I, Justus-Liebig-University Giessen, Germany — ²Institute of Physical Chemistry, Justus-Liebig-University Giessen, Germany — ³Institute of Physics, Kazan Federal University, Russia

Raman spectroscopy is often used to determine the crystallite size L_a of non-graphitic carbons by taking into account the intensity ratio of the defect-induced D band and the G band. We present an analysis of soft pitches via Raman spectroscopy in comparison to wide-angle X-ray spectra revealing discrepancies for L_a. Significant errors can be caused by known issues, for example the superposition of certain bands while estimating the intensities. Therefore, we introduce an alternative approach: An analysis of the D band revealed a correlation between its position and the crystallite size in the range of crystallite sizes less than 2 nm. The Raman shift significantly increases for smaller L_a using an excitation wavelength in the visible range. UV light yields the opposite behavior of the D band position, probably because of resonant absorption processes. To further characterize the samples in different L_a-ranges (L_a < 2 nm and L_a > 2 nm) electron paramagnetic resonance spectroscopy (EPR) has been carried out. Isotropic shaped EPR spectra are observed up to a crystallite size of 2 nm and samples containing crystallite sizes larger 2 nm show anisotropic signals. This behavior correlates with the detected Raman shift.