Clustering of Chemisorbed H(D) Atoms on the Graphite (0001) Surface due to Preferential Sticking

Abstract

We present scanning tunneling microscopy experiments and density functional theory calculations which reveal a unique mechanism for the formation of hydrogen adsorbate clusters on graphite surfaces. Our results show that diffusion of hydrogen atoms is largely inactive and that clustering is a consequence of preferential sticking into specific adsorbate structures. These surprising findings are caused by reduced or even vanishing adsorption barriers for hydrogen in the vicinity of already adsorbed H atoms on the surface and point to a possible novel route to interstellar H2 formation.

Cooperative Interplay of van der Waals Forces and Quantum Nuclear Effects on Adsorption: H at Graphene and at Coronene

“…As expected, and in agreement with many previous DFT GGA studies, the barrier between the gas phase and the chemisorbed state is about 200 meV. 16,19,[32][33][34][35] The chemisorption well is 800 meV with a H−C bond length of 1.13 Å and puckering of the top site carbon atom away from the surface by ∼ 0.4 Å. With PBE there is no physisorption state, which is again consistent with previous work and understandable given the lack of a long-range correlation term in GGA exchange-correlation functionals.…”

“…Hornekaer et al 16 and Rougeau et al 33 determined that once a single H atom has chemisorbed the barrier for subsequent H atoms to chemisorb locally is much smaller. Considered in concert with our findings this therefore facilitates the low temperature hydrogenation of large regions of graphene.…”

“…This barrier -which includes vdW, ZPE effects, quantum tunneling and finite temperature effects -is approximately half the height of barriers typically predicted for H atom chemisorption at graphene using traditional DFT-GGA methods. 16,19,[32][33][34][35] Although the barrier is substantially reduced the physisorption well remains relatively unperturbed, being a similar depth and shifted towards the gas phase by just ∼ 0.1 Å.…”

“…Hydrogen adsorption on carbon based materials such as graphite and graphene is relevant to hydrogen storage, 9 band gap engineering, [10][11][12][13] and potentially as the first step in H 2 formation in the interstellar medium. [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] Although there is enormous interest in H adsorption on carbonaceous surfaces, with graphene, graphite and polycyclic aromatic hydrocarbons (PAHs) being the most widely studied model systems, we still don't fully understand the seemingly simple process of how a single H atom adsorbs on the surface.…”

Modeling of hydrogen and hydroxyl group migration on graphene

“…Calculated value of hydrogen migration is smaller that achieved in previous calculations [5][6][7][8][9]. For verify used method and choice of technical parameters I have been performed calculations for different sizes of supercell.…”