Real-space investigation of fast diffusion of hydrogen on Si(001) by a combination of nanosecond laser heating and STM

Abstract

The rearrangement of silicon dangling bonds induced by pulsed laser heating of monohydride-covered Si͑001͒ surfaces has been studied by means of scanning tunneling microscopy ͑STM͒. The initial configurations, which were created by laser-induced thermal desorption, consist of isolated pairs of dangling bonds at two adjacent dimers and represent an excited state of the surface. Hydrogen diffusion causes this arrangement to change during only a few nanosecond laser pulses into the equilibrium configuration with most of the dangling bonds being paired up at a single dimer. STM images taken after different numbers of heating pulses show snapshots of the surface configuration frozen at various stages of the fast equilibration process. In this way, hydrogen diffusion associated with rates as high as 10 8 s −1 could be monitored with atomic resolution. Comparison with Monte Carlo simulations of the diffusion processes allows for the precise determination of both the diffusion rates and the pairing energies between dangling bonds at high surface temperature.

Ab initiostudy of atomic hydrogen diffusion on the clean and hydrogen-terminated Si(001) surface

“…11 and 12͒ to examine intrarow and interrow diffusion at high temperatures. 11,13 Contrary to previous work, the authors did not start out with a clean Si͑001͒-͑2 ϫ 1͒ surface on which they adsorbed atomic hydrogen at low coverage but rather heated up a Si͑001͒-͑2 ϫ 1͒ monohydride surface to 1400 K by a laser pulse for a few nanoseconds. Within this time scale some H 2 molecules desorb and a few H hopping events may happen.…”

“…1 On clean and flat Si͑001͒ terraces, three kinds of surface diffusion processes have been discussed in the literature, namely, H hopping between Si atoms of one dimer ͑in-tradimer͒, between Si atoms of two adjacent dimers within the same dimer row ͑intrarow͒, and from one dimer row to a neighboring row ͑interrow͒. [3][4][5][6][7][8][9][10][11] According to theoretical studies, 3-6 the corresponding activation energies increase monotonically with the distance between the initial and final state positions of the H atom and get larger from intradimer through intrarow to interrow hopping, respectively. Video scanning tunneling microscopy ͑STM͒ experiments confirm this order of barrier heights.…”

“…For reference, we first briefly address diffusion of isolated H atoms on a clean and flat Si͑001͒ surface, which has been investigated in detail before. [3][4][5][6][7][8][9][10][11] Our main focus is then on H diffusion in the high-coverage regime of very few vacancies on a Si͑001͒ monohydride surface. We note in passing that even higher H coverages, which are accompanied by Si dimer cleavage and which finally end up in a dihydride surface, are beyond the scope of this paper.…”

Photostimulated desorption of Xe from Au(001) surfaces via transient Xe−formation

“…4) and Xe/Cu, 5 and has been successfully applied to the studies of surface diffusion combined with low-energy electron microscopy 6 or with scanning tunneling microscopy. 7 Nonthermal photostimulated phenomena, on the other hand, provide us with pathways that are nonaccessible in a thermal process. The nonthermal photostimulated desorption (PSD) of rare gas atoms from metal surfaces has been investigated using photons of two energy regions: At hν > 7 eV, the excitonic or ionic excitation of the mono-and multilayers of Ar and Kr induces desorption, 8 while infrared light at hν < 1 eV causes the direct excitation of the vibrational mode in the physisorption well to a continuum state.…”

Distributed Bio-Hydrogen Refueling Stations

“…For a practical hydrogen storage medium spillover hydrogens must also bond-hop or diffuse along the silicon surface [19]. Modeled as Knudsen diffusion, the coefficient for hydrogen atoms on silicon is given by Eq.…”