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Aram Mailian: Structural Features and Identification of Allotropic Nanostructures in Carbon Tribolayers

posted 4 Aug 2016, 01:26 by info admin
Aram Mailian1,2, Zhozef Panosyan2, Yeremia Yengibaryan2, Manuel Mailian3 
1 Institute for Informatics, 1 P. Sevak str., 0014, Yerevan, Armenia
2 State Engineering University, 105, Teryan str. Yerevan, Armenia 
3 LTX-Credence Armenia, 2 Adonts str., 0014, Yerevan, Armenia

The carbon tribolayer (CTL) spontaneously developed within the boundary strata during rubbing of graphite bulk against the surface of insulating substrate, displays properties of a solid material fundamentally different those of bulk graphite. 
The optical absorption in as-obtained CTL exposes a resonance in ultraviolet (at 4.8 eV), which refers to excitonic transitions and is assumed to be a fingerprint of sp2 structure [1]. With step-by-step removal (peeling) of topmost layers of CTL the peak in absorption fades out whereas the absorption above ~5 eV progressively dominates the optical absorption spectrum. The latter is characteristic to sp3 carbon allotrope.
X-ray diffraction (XRD) study also reveals a crystalline structure on the CTL surface.  The XRD pattern has a (002) diffraction peak at 2=26.5510 emerging over a broad noise background.  No additional feature is observed. Such a pattern is characteristic of two-layer graphene [2]. With the removal of surface layer of CTL the peak on XRD pattern disappears leaving only the flat background. Evidently X-ray diffraction is enabled by a periodical crystalline structure on the CTL surface.
In Raman spectra, the width and symmetrical line shape of 2D band, the equal peak intensity of G and 2D peaks, reveal that the observed features are characteristic to the crystal lattice of turbostratic sp2 carbon [3].  
Observed features in combination with other observations testify that the CTL is morphologically anisotropic through the layer thickness; sp2 phase of turbostratic bi-layer grapheme is formed at the top, and thicker sp3 allotrope sub-layer is formed beneath it. 

[1] K.F. Mak, et al. Sol. St. Comms. 152 (2012) 1341-1349.
[2] Z. Q. Li et al. Carbon 45, 8, (2007) 1686–1695.     
[3] M. S. Dresselhaus et al.  Phil. Trans. R. Soc. A (2010) 368, 5355–5377.

Aram Mailian is a senior researcher at the Institute for Informatics and at the Laboratory of Solar Engineering at State Engineering University, Yerevan, Armenia. He got his PhD degree in 1987 from Yerevan State University, Armenia. He is experienced in experimental investigation of surface properties of semiconductors, especially optical transitions at semiconductor surface. During recent years he deals with the carbon layers developed by rubbing.