Figure 1

(a) STM image ($103\times 114{\AA }^2$) of dimer structures of hydrogen atoms on the graphite surface after a 1 min deposition at room temperature. Imaging parameters: $V_t=884\mathrm{mV}$, $I_t=160\mathrm{pA}$. Examples of dimer type A and B are marked. Black arrows indicate the $⟨2\overline{1}\overline{1}0⟩$ directions and white arrows indicate the orientation of the dimers 30° off. (b) Close up of dimer A structure in top white circle in image (a). (c) Close up of dimer B structure in lower white circle in image (a).Reuse & Permissions

Figure 2

(a) A mass 4 amu, i.e., ${\mathrm{D}}_2$, TPD spectrum from the HOPG surface after a 2 min D atom dose (ramp rate: $2\mathrm{K}/\mathrm{s}$ below 450 K, $1\mathrm{K}/\mathrm{s}$ above). The arrow indicates the maximum temperature of the thermal anneal performed before recording the STM image in (b) STM image ($103\times 114{\AA }^2$) of dimer structures of hydrogen atoms on the graphite surface after a 1 min deposition at room temperature and subsequent anneal to 525 K (ramp rate: $1\mathrm{K}/\mathrm{s}$, 30 s dwell at maximum temperature). Imaging parameters: $V_t=884\mathrm{mV}$, $I_t=190\mathrm{pA}$. The inset shows a higher resolution STM image of dimer structures of hydrogen atoms on the graphite surface after a 6 min deposition at room temperature and subsequent anneal to 550 K. Imaging parameters: $V_t=-884\mathrm{mV}$, $I_t=-210\mathrm{pA}$.Reuse & Permissions

Figure 3

Calculated structure of the two most tightly bound dimer structures of hydrogen atoms on the graphite surface. (a) Dimer A structure of hydrogen atoms adsorbed on neighbor carbon atoms. (b) Dimer B structures of hydrogen adsorbed on carbon atoms at opposite sides of the graphite hexagon. (c) Simulated STM image of the dimer structure in (a). (d) Simulated STM image of the dimer structure in (b). Imaging parameters: $V_t=0.9\mathrm{V}$, ${\rho }_0=1\times {10}^{-6}(\mathrm{eV}{)}^{-1}{\AA }^{-3}$. The position of the hydrogen atoms is marked by black dots. (e) Experimental dimer A structure. (f) Experimental dimer B structure. The carbon unit cell is marked in white.Reuse & Permissions

Figure 4

Energy barriers for atomic hydrogen diffusion and recombination from dimer A and B states on the graphite surface. The barrier to desorption of a single H atom out of structures A, I, and B are 2.08, 0.92, and 1.92 eV, respectively, and is hence energetically unfavorable in all three cases.Reuse & Permissions