Type of presentation: Oral

MS-2-O-2445 Atomic Resolution Structure Study of Fluorinated Graphene by Phase Restoration of Focal Series of Images

J Kashtiban R.¹, Dyson M. A.¹, Raveendran-Nair R.², Zan R.⁴, Bangert U.³, Sloan J.¹, Geim A. K.²

¹University of Warwick, Coventry, UK, ²University of Manchester, Manchester, Uk, ³University of Limerick, ⁴Niğde University, Niğde, Turkey

r.jalilikashtiban@warwick.ac.uk

One approach towards band gap engineering of the graphene(Gr) which is scalable and cost effective is the chemical modification route to produce 2D derivatives of wonder material of suitable quality for monolayer devices although few such phases exist. GO and (CH)_n are disordered or unstable while stoichiometric fluorographene(FG) exhibits significant corrugation. Fluorination of a Gr sheet results in FG, a Gr derivative with each fluorine atom connected to one carbon atom at the basal plane of Gr by a stronger SP3 bonding. Chair-C₂F is a highly ordered material that demonstrates selective alternating fluorination and presents with an undistorted 2D morphology in contrast with stoichiometric but corrugated CF with the consequence that the former is a potentially much more tractable material for 2D device fabrication [1].A structural and morphological study of this material by means of atomic resolution TEM has yet not been reported. Exit wave restoration(EWR) by means of focal series of HRTEM images [2] can be performed to recover phase at the exit plane of the sample. Here we reveal, by atomic resolution EWR for the first time , that chair-C₂F is a stable Gr derivative and demonstrates long-range order limited only by the size of a functionalized domain. Monolayer C₂F was produced by partially fluorinating a suspended CVD grown Gr sample using direct fluorination method [3]. Focal series of images of Gr and chair-C₂F were obtained at 80 kV in an aberration-corrected TEM instrument. EWR images reveal that imaged single carbon atoms and carbon-fluorine pairs in chair-C²F alternate strictly over domain sizes of at least 150 nm² with electron diffraction indicating ordered domains up to ~0.16 μm². Our results[4] also indicate that, within an ordered domain, functionalization occurs on one side only as theory predicts[1].

Figure 1 EWR and SIM EWRs of pristine Gr and monolayer chair C₂F and figure 2 is a demonstration of long-range order within a 64 nm² domain of C₂F.

Refrences:

[1] Şahin, H, et al., Phys. Rev. B, 83 (2011)
[2] Coene, W.M.J., et al., Ultramicroscopy 64(1996) 109
[3] Nair, R.R., et al., Small, 6(2010) 2877
[4] Kashtiban et al., submitted.

We thank the EPSRC for funding through a studentship for M. A. D. and for a P. D. R. A. Fellowship for R. J. K. and additional support provided by the Warwick Centre for Analytical Science (EP/F034210/1).

Fig. 1: Figure 1 a-b, Graphene(Gr) and C₂F models.c-d, Equivalent domains of EXP. and SIM. phase for Gr and chair-C₂F respectively. e,f line profiles for the EXP and SIM phase for Gr and chair-C₂F.g overlaid full plots of the EXP and SIM phase contrast for Gr, respectively.h overlaid full plots of the EXP and SIM phase contrast for chair-C₂F, respectively.

Fig. 2: EWR image of a 250 nm² sheet of highly ordered sheet C₂F with an unrippled 64 nm² domain highlighted. b, 64 nm² domain in a exhibiting a high degree of order (scale bar = 2 nm). c, Surface plot from b in which the orange-yellow apexes correspond to ordered –CF< units. d, Line profiles (I-III) obtained through either >C–CF< or >C–CF< dumbbells.