Nanocomposites and nanomaterials

Structure and electrical properties of the freestanding N-doped reduced graphene oxide paper

O. O. Voitsihovska 1, R. M. Rudenko1, A. A. Abakumov2, 
I. B. Bychko2, V.N. Poroshin1
1 Institute of Physics, National Academy of Sciences of Ukraine, 46 avenu Nauky, Kyiv, 03680, Ukraine, e-mail: voleyna@ukr.net
2L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 31 avenu Nauky, Kyiv, 03028, Ukraine

The investigation of structural and electrical properties of graphene is  inspired by both fundamental and practical interest. Reduced graphene oxide (rGO) is a graphene-derived material. Due to its scalable production rGO may be a perspective candidate for novel electronics production. Therefore, understanding of rGO properties is necessary. Reducing parent graphene oxide with hydrazine is one of the most widely used technique for rGO synthesis. Hydrazine treatment inevitably leads to nitrogen-doping of rGO layers giving N-doped rGO. This work presents structural and electrical parameters of freestanding rGO paper (rGOP), manufactured by dead-end filtration of pre-sonicated rGO water dispersion.
The analysis of cross-section obtained by scanning electron microscopy shows that the film is formed by layering up to 40 separate parallel multilayer flakes. Therefore, obtained film can  be   regarded as oriented film. Carbon, oxygen and nitrogen content are 69 at. %, 15 at. % and 16 at.%, respectively, according to chemical elemental analysis and energy-dispersive X-ray spectroscopy data. The analysis of C1s, N1s and O1s X-ray photoelectron spectra show that functional groups are presented by sp2 C=C areas, sp3 and/or defect carbons, ether, hydroxyl, carbonyl and carboxylic groups. Nitrogen-containing groups are mostly  presented by pyrazole cycles. 
The room temperature resistivity about 8×10-3 Ohm*m and sp2/sp3-defects ratio values about 5.8 for studied rGOP are in agreement with the data reported for rGO sheets on a substrate [1]. The study of current-voltage (I–V) characteristics of rGOP in a temperature range of 4.2–300 K show non-linear behavior of I–V characteristics at low temperature. The results obtained are in good agreement with the data of our previous work [2], which shows the presence of variable range hopping (VRH) conductivity in the wide temperature range for freestanding rGOP. Nonlinear behavior in sufficiently high electric fields indicates VRH conductivity according to Efros-Shklovskii model. At low electric field   I–V characteristics of rGOP may be described by model of quantum dot like conductivity [3]. 
1. D. Joung, S.I. Khondaker, Phys. Rev. B.-2012.-86.-P. 235423. 
2. O.O. Voitsihovska, R.M. Rudenko, et al, Materials Letters.-2019.-236.-P.334. 
3. D. Joung, L. Zhai, S.I. Khondaker, Phys.Rev.B.-2011.-83.-P. 115323.