Low-Temperature Reduction of Graphene Oxide: Electrical Conductance and Scanning Kelvin Probe Force Microscopy

Oleksandr M Slobodian,Alexei N Nazarov,Oleg Yu Khyzhun,Peter M Lytvyn,Andrii S Nikolenko,Stanislav V Sevostianov,Victor M Naseka,Andrey V Vasin,Andrey V Vasin,Alexei N Nazarov

doi:10.1186/s11671-018-2536-z

Oleksandr M Slobodian, Alexei N Nazarov + Show 8 more

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https://doi.org/10.1186/s11671-018-2536-z

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Abstract

Graphene oxide (GO) films were formed by drop-casting method and were studied by FTIR spectroscopy, micro-Raman spectroscopy (mRS), X-ray photoelectron spectroscopy (XPS), four-points probe method, atomic force microscopy (AFM), and scanning Kelvin probe force (SKPFM) microscopy after low-temperature annealing at ambient conditions. It was shown that in temperature range from 50 to 250 °C the electrical resistivity of the GO films decreases by seven orders of magnitude and is governed by two processes with activation energies of 6.22 and 1.65 eV, respectively. It was shown that the first process is mainly associated with water and OH groups desorption reducing the thickness of the film by 35% and causing the resistivity decrease by five orders of magnitude. The corresponding activation energy is the effective value determined by desorption and electrical connection of GO flakes from different layers. The second process is mainly associated with desorption of oxygen epoxy and alkoxy groups connected with carbon located in the basal plane of GO. AFM and SKPFM methods showed that during the second process, first, the surface of GO plane is destroyed forming nanostructured surface with low work function and then at higher temperature a flat carbon plane is formed that results in an increase of the work function of reduced GO.

Highlights

A necessity of inexpensive mass production of these materials directed the interest of a great army of researchers into the study of graphene oxide (GO) reduction [11] which allows obtaining a graphene material with needed properties using chemical [12] or radiation [13] methods
Chemical bonds in the GO film deposited on silicon wafer were detected by FTIR spectroscopy using Bruker Vertex 70 V spectrometer and X-ray photoelectron spectroscopy (XPS) using the UHVAnalysis-System (SPECS Surface Nano Analysis Company) possessing the residual pressure less than 5 × 10− 10 mbar and equipped with a PHOIBOS 150 energy analyzer
FTIR Spectroscopy and XPS The FTIR spectra of the initial GO films demonstrate the appearance of OH bonds (Fig. 2)

Summary

Introduction

Graphene and graphene-based materials have very attractive physical and optical properties [1–3] which can be employed into a lot of applications such as nanoelectronics [4], chemical and biosensors [5, 6], solar-cells [7], effective catalysts [8], and supercapacitors [9, 10]. A necessity of inexpensive mass production of these materials directed the interest of a great army of researchers into the study of graphene oxide (GO) reduction [11] which allows obtaining a graphene material with needed properties using chemical [12] or radiation [13] methods. One of the simplest reduction techniques is the thermal one which is usually performed in vacuum to desorb oxygen molecules from carbon π bonds [11]. The C1s XPS spectrum of GO clearly indicates a considerable degree of oxidation with four components that correspond to carbon atoms in different functional groups: 52.6% of the non-oxygenated C in sp3/sp state (284.7 eV), 26.6% of the C in C–O bonds (286.7 eV), 11.5% of the carbonyl carbon (C=O, 287.6 eV), and 8.3% of the carboxylate carbon (O– C=O, 289.0 eV) [19]

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