Electrical Transport in Devices Based on Edge‐Fluorinated Graphene

Abstract

When considering fluorinated graphene (FG)-based functional device technology, the device architectures must be chosen adequately. Typically, functionalized graphene devices can be envisaged as either large scale (area)-based thin film structures or as systems integrated from individual nanoobjects. This implies potentially significant qualitative and quantitative differences in the device response. Specifically, the presence of edges in graphene can be decisive. Considering the electrical conductivity of individual mono-and fewlayer flakes, it is dominated by the type, amount, and bonding position (basal or edge) of functional groups attached to the C(sp 2 ) matrix. In thin film-based systems, however, the charge transport also is largely affected by the properties of edge/edge, edge/plane, and plane/plane junctions. [22] Therefore, electrical characterization is a primary means to evaluate and benchmark whether or not a given derivative meets the requirements for selected applications.In the present work we study the impact of F content and bonding position on the electronic properties of graphene fluorinated by BrF 3 vapor at room temperature [8,20] in the range of 2.4-16.6 at%. We compared the electrical conductivity of thin films with the conductivity of corresponding individual FG flakes which constitute the former. We found a significant difference in the conductivity dependence on the degree of fluorination for the two device architectures: While in the case of thin films, a strong decrease in conductivity with fluorine content was observed, individual flakes showed an increase in conductivity and exhibited graphene-like bipolar transfer characteristics with electron and hole mobilities of the order of few 1000s cm 2 V −1 s −1 for F content approaching 17 at%. With further aid of scanning electron and Raman microscopy, this qualitative difference between films and single flakes was attributed to the circumstance that the preferred sites for fluorination are at the edges rather than basal planes of the FG.For the characterization of thin film devices, 3 mm long and 1 mm wide structures were defined using a hard-mask technique (Figure 1a). FG dispersions were sprayed onto Si wafers with 300 nm thermal SiO 2 on top, resulting in homogeneous and continuous films (Figure 1b), which were then electrically contacted with conducting silver paste. For electrical characterization of individual flakes, small amounts of the dispersionsThe conductivity of few-and monolayer graphene with covalently bound moieties is a key-point in the potential application of these materials in any electrical and optoelectronic device. In particular, fluorination of such graphene-based systems is of interest, as fluorine is expected to have a strong influence on the charge-carrier density due to its high electronegativity, and therefore modify the electrical transport properties significantly. Here it is shown that, depending on the device architecture, the electrical properties of fluorinated graphene-based devices are significantly d...

Chemiresistive Properties of Imprinted Fluorinated Graphene Films

“…These defects led to reliable p-type doping of the graphene layers and, as a result, to an increase in the resistivity of FG films (Table 1). Such behavior is consistent with previous works on the fluorination [47] and oxidation [50] of graphene. For the FG films obtained using the sedimentation procedure without or with the centrifugation treatment, we observed a decrease in the conductivity by more than three orders of magnitude when the fluorine content in parent fluorinated graphite increased from ca.…”

“…The electrical transport properties of partially fluorinated graphene can be adjusted by tuning the fluorination degree for application in chemical sensors. The charge carrier mobility for single flake devices was found to increase with an increase in the fluorination degree, reaching 2000-3000 cm 2 V −1 s −1 [47]. In case of thin films, the charge transport is largely affected by edge/edge, edge/plane, and plane/plane junctions.…”

Effect of Fluorine Patterns on Electronic Transport in Fluorinated Graphene

“…It should be noted that a similar maximum in conductivity has been recently found experimentally in thin films of few‐layer graphene with fluorine content at the same concentration. [ 33 ] For mol kcal −1 this maximum moves to higher energies eV. Since the transport measurements in ref.…”

“…Since the transport measurements in ref. [ 33 ] were performed at zero gate voltage, we can conclude that the appearance of conductivity maximum at 10% is a direct consequence of a more ordered distribution of fluorine atoms.…”

“…We found that electrons for considered fluorine concentrations (1–25%) exhibit localized behavior in a wide range of energies close to the neutrality point. The transport simulations allow us to reproduce i) the recently found conductivity peak at 10% fluoride content [ 33 ] associated with the emergency of quasiperiodical structures in electron density and ii) experimentally observed electron–hole asymmetry in fluorinated graphene [ 7 ] which can be connected with specific patterns in the density of states. We have shown that transport properties of fluorinated graphene are strongly correlated with system ordering, which confirm that account of real fluorine distribution is important for modeling the electron transport phenomena in such systems.…”