Although hydrogen adsorbed on aluminum surfaces is a simple-looking adsorption system, the interaction between them has been found to be very peculiar; that is, a large amount of aluminum hydride molecules such as Al2H6 and/or AlH3 desorb from H/Al(111), while they desorb hardly from H/Al(110). In order to investigate the adsorption states of hydrogen on the two different aluminum surfaces, we have studied these systems by TPD, LEED, and HREELS. Hydrogen atoms adsorb in the island-growth manner on Al(111) at 85 K from the initial stage of adsorption and form a surface aluminum hydride after annealing the surface. The hydrogen adsorption on Al(110) at 85 K exhibits sequential site filling in contrast to H/Al(111) and displays a (1 × 2) reconstruction after annealing.
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