## 5 ALD on Prefunctionalized EG
### Fluorine Prefunctionalization  
[PERSON] et al. [39] investigated fluorine prefunctionalization of EG for uniform deposition of thin high-k dielectrics. Due to its high electronegativity (4.0) and its ability to adhere to carbon surfaces [55], fluorine is a suitable reactive species to enhance graphene surface reactions with ALD precursors. Fluorination of the EG grown onto on-axis 6H-SiC (0001) was carried out at room temperature exposing the EG surface to XeF\({}_{2}\) gas pulses, with the total fluorine dosing time varied in the range from 0 to  
Figure 11: **(a)** XPS spectra from C1s core-level for pristine EG on SiC(0001) (solid line) and after 20 O\({}_{3}\) pulses at 250 \({}^{\circ}\)C. The two spectra are overlapped indicating negligible etching of graphene by the O\({}_{3}\) treatment. **(b)** C 1s core level spectrum of EG after 20 O\({}_{3}\) pulses at 350 \({}^{\circ}\)C, showing the appearance of an additional peak associated to uncovered SiC, which indicates partial etching of EG. **(c)** AFM image of a 50 nm thick Al\({}_{2}\)O\({}_{3}\) film grown by 500 TMA/water cycles on EG pretreated with 20 O\({}_{3}\) pulses at 250 \({}^{\circ}\)C. Figures adapted with permission from Ref [38], copyright [PERSON] 2010. 200 s. Core level XPS was used to preliminary determine the bonding characteristics of fluorine with the EG surface with increasing XeF\({}_{2}\) exposure time. Figure 12a,d shows the C1s XPS spectra acquired on as-grown EG (a) and on EG subjected to 40 s (b), 120 s (c) and 200 s (d) XeF\({}_{2}\) exposure times. For as-grown EG (a), the contributions associated to the SiC substrate, to EG and to the interfacial buffer layer were visible. A very similar XPS spectrum was found after 40 s XeF\({}_{2}\) exposure (b), whereas the appearance of a feature at 288.5 eV, associated to C-F bonds, could be observed after 120 s (c) and 200 s (d) XeF\({}_{2}\) exposure times. Such bonds are created by breaking the sp\({}^{2}\) symmetry of the EG lattice resulting in carbon sp\({}^{3}\) bonds with fluorine. A decrease in the EG peak intensity was observed corresponding to the appearance of C-F bonds, which further supports the transition from sp\({}^{2}\) to sp\({}^{3}\) bonded carbon on the surface. For the largest exposure time (d), an additional small peak associated to C-F\({}_{2}\) bonds was detected at 290 eV. The formation of C-F\({}_{2}\) was accompanied by a significant deformation of the EG lattice, leading to a degradation of EG electrical properties. Hence, it was chosen to work in a fluorination regime where C-F bonding only occurred. The C-F sp\({}^{3}\) bond configuration was found to provide additional reaction sites of oxide nucleation and growth during the subsequent ALD process. After the initial assessment of the effect of XeF\({}_{2}\) exposure on EG chemical properties, Al\({}_{2}\)O\({}_{3}\) films (15 nm thickness) were deposited by thermal ALD at 225 \({}^{\circ}\)C using TMA/H\({}_{2}\)O precursors. Figure 12: XPS C1s spectra on as-grown EG (**a**) and after XeF\({}_{2}\) exposure for 40 s (**b**), 120 s (**c**) and 200 s (**d**). AFM images of Al\({}_{2}\)O\({}_{3}\) morphology for samples treated with varying amounts of fluorine: (**e**) no pretreatment and (**f**) 40 s XeF\({}_{2}\) exposure results in large areas of no oxide deposition; (**g**) 120 s XeF\({}_{2}\) exposure yields a conformal, uniform film and (**h**) 200 s XeF\({}_{2}\) exposure shows pinholes throughout the oxide. Figures adapted with permission from Ref. [39], Copyright Elsevier 2012. AFM characterization of the Al\({}_{2}\)O\({}_{3}\) uniformity was carried out for all the fluorine prefunctionalization conditions. Figure 12e,h shows four representative AFM images of Al\({}_{2}\)O\({}_{3}\) deposited on pristine EG (c) and after fluorine prefunctionalization at 40 s (f), 120 s (g) and 200 s (h), respectively. An inhomogeneous Al\({}_{2}\)O\({}_{3}\) coverage, especially close to the SiC step edges, was observed on the untreated EG (e) and after 40 s XeF\({}_{2}\) exposure (f).