Band‐like Transport in Surface‐Functionalized Highly Solution‐Processable Graphene Nanosheets

Abstract

Graphenes are attracting renewed interests owing to recent advances in micromechanical exfoliation and epitaxial growth methods that make macroscopic 2D sheets of sp 2 -carbon atoms available.[1] A variety of simple yet elegant physics relating to its zero-gap semiconductor character has thus been demonstrated. [2][3][4][5] It would be very desirable to make these materials solution (or more accurately, dispersion) processable by coating or printing, which will open applications for large and/or flexible substrates. Graphite oxide (GO) is a possible candidate for this because it is a precursor to graphene through deoxidation either thermally or by chemical reduction. [6][7][8] Although GO itself has been studied for over a century, [9] its structure and properties remain elusive, and progress has been made only recently to give materials with limited dispersability and electronic quality. [10][11][12][13][14] Here we show that substoichiometric GO nanosheets can be surface-functionalised and purified to show excellent dispersability at the single-sheet level, >15 mg mL À1 in organic solvents, sufficient for spincoating and printing onto a variety of substrates. The films could then be deoxidised to graphene (ca. 80% completion at 300 8C) to give a network of low-dimensional ''graphenite'' tracks and dots on the nanosheets. Though imperfect and disordered, these show well-behaved and trap-free field-effect transistor charge-carrier mobilities for both electrons and holes of the order of 10 cm 2 V À1 s À1 , limited presently by the density of this graphenite network. Devices can be operated continuously in air for both p-and n-channels. The transport activation energies are in the meV region at low temperatures which together with the delocalisation of carriers indicate bandlike transport. The density-of-states at the Fermi level deduced by electrical measurements is higher than in graphite. MNDO-PM3 semiempirical electronic structure calculations relate this to defects in the 1D graphenite network. The fact that charge carriers can still be sufficiently delocalised in such disordered graphenites opens new opportunities for graphenes. It is well-known that chemical oxidation of graphite crystals gives GO which can be exfoliated by rapid-thermal-anneal >1000 8C, [15] or in solvents to give few-layer stacks that aggregate over time. [16,17] Recent work has shown that chemical functionalisation of GO can improve dispersability, particularly in the presence of stabilising polyelectrolytes. [10][11][12][13] However it is crucial to achieve more stable and concentrated dispersions without the added polyelectrolytes or ions, for electronic applications. We show here that substoichiometric (i.e. under-oxidised) GO can be obtained by a modified Staudenmaier oxidation of graphite with potassium chlorate [15] in a concentrated sulphuric-nitric acid mixture to give a material with an empirical formula containing less oxygen than the fully oxidised GO (C 2.0 O 1.0 H x ), [8,9,18] for example, C 2.0 O 0.77 H 0.75 . This material...

Insulator to Semimetal Transition in Graphene Oxide

“…Here, we examine the minimum conductivity  min of r-GO instead of (V g = 0 V) in order to exclude the effects of charged impurities 19 . Fig Fig 3a) decreases with the extent of reduction, which is in agreement with the prediction that restoration of percolating sp 2 carbon network allows band-like transport 20 .…”

Design and Synthetic Scheme of Water Dispersible Graphene Oxide-Coumarin Complex for Ultra-Sensitive Fluorescence Based Detection of Copper (Cu2+) Ion in Aqueous Environment

“…The terminal amine group of the compound #4 will take part in the epoxy ring opening reaction. Similar epoxy ring opening reactions involving primary amine containing molecules and the GO have been reported in the literature [37] [41] [42].…”

Functionalized Graphene Nanocomposites

“…The preferred mechanism for this type of reaction involves a nucleophilic attack of amines to α-carbon. The study performed by Wang et al based on this methodology allowed the surface modification of GO with octadecylamine (Wang, Chia et al 2008). Another author used the same procedure to establish links between an ionic liquid with terminal amine groups and epoxide groups at the surface of graphene oxide.…”