Dehydrogenation induced phase transitions of p-aminobenzoic acid on Cu(110)

Temperature and coverage dependent studies of p-aminobenzoic acid on a Cu(110) single crystal surface show a novel sequence of periodic structures linked to successive removal of hydrogen from the adsorbed species, as shown by LEED, STM, HREELS, and TPD. At room temperature, flat-lying molecules with a primitive unit cell of (3x4) periodicity with glide plane along the < 001 > direction are observed. Annealing this surface to 464 K causes partial desorption of H-2 and a variation of the intensity in HREELS of various bands and formation of a ((5) (2)(4)(-2)) periodicity. STM images suggest the formation of dimers, as a result of the dehydrogenation. On annealing to higher temperatures (510 K), further dehydrogenation forms ((1)(2)(6)(-5)) structure. Finally, at 540 K, a ((4) (1)(2)(-3)) periodicity is revealed in which all species correspond to dehydrogenated dimers. Through this sequence, all species retain a flat-lying orientation on the surface. (C) 2002 American Institute of Physics.