Symmetry-Driven Band Gap Engineering in Hydrogen Functionalized Graphene

Abstract

Band gap engineering in hydrogen functionalized graphene is demonstrated by changing the symmetry of the functionalization structures. Small differences in hydrogen adsorbate binding energies on graphene on Ir(111) allow tailoring of highly periodic functionalization structures favoring one distinct region of the moiré supercell. Scanning tunneling microscopy and X-ray photoelectron spectroscopy measurements show that a highly periodic hydrogen functionalized graphene sheet can thus be prepared by controlling the sample temperature (T) during hydrogen functionalization. At deposition temperatures of T = 645 K and above, hydrogen adsorbs exclusively on the HCP regions of the graphene/Ir(111) moiré structure. This finding is rationalized in terms of a slight preference for hydrogen clusters in the HCP regions over the FCC regions, as found by density functional theory calculations. Angle-resolved photoemission spectroscopy measurements demonstrate that the preferential functionalization of just one region of the moiré supercell results in a band gap opening with very limited associated band broadening. Thus, hydrogenation at elevated sample temperatures provides a pathway to efficient band gap engineering in graphene via the selective functionalization of specific regions of the moiré structure.

Patterned formation of enolate functional groups on the graphene basal plane

“…We propose that the CO peak corresponds both to carbon atoms bound to O-atoms, via formation of an enolate, and to neighbouring carbon atoms simultaneously bound to the underlying Ir substrate. 5 These percentages concur with analysis of STM images for surface coverage (S1). The size of such a cluster corresponds to the size of the FCC site in the moiré unit cell.…”

“…Experiments and DFT calculations illustrate that the position of an Ir atom directly beneath a carbon atom, and C-Ir bond formation, significantly increases the energy gain for C-H bond formation in FCC and HCP regions compared to similar bond formation in TOP regions, with a slight energetic preference for FCC regions. 5 The C=C) stretching vibration does not originate from phonons as in graphene but appears with similar energy losses. c The region between 120-140 meV is complex for oxidized nano-diamond films and peaks assigned to (C-O-O-C), CH3),C=CH), aromatic ring-H) and (C-O-H) in the literature overlap with the clear peak at 130 meV identified in Fig.…”

Hydrogen interaction with graphene on Ir(1 1 1): a combined intercalation and functionalization study

“…Functionalization can also be based on a substitution reaction where carbon in the graphene sheet is replaced with other elements such as nitrogen [19] or boron [20,21]. For chemical functionalization with hydrogen, it has been shown earlier that an addition of this most simple element can turn graphene into a gapped semiconductor [11,22], induce enhanced spin-orbit coupling [23] or even induce ferromagn etic order [24][25][26]. By combining intercalation and functionalization schemes one may therefore facilitate development of hybrid materials, acquiring properties from individual manipulation steps.…”

Crystalline hydrogenation of graphene by scanning tunneling microscope tip-induced field dissociation of H2

“…Currently, the evidence for ordered H-Gr (or graphane at complete coverage) is somewhat limited. Most reports of H-Gr via electron beam irradiation [14][15][16], chemical [17], plasma, [5,[18][19][20] or thermal cracker [21][22][23][24][25][26][27][28][29][30][31][32][33] methods indicate insulating behavior [5,16,20,21,24,25,27] but little or no evidence for crystalline order. STM experiments have shown some ordering associated with Moiré patterns [27] or in ~nm 2 patches, [32] and other techniques have provided indirect evidence of ordered structures.…”