Carbon monoxide induced ordering of benzene of Pt (111) and Rh (111) crystal surfaces

Benzene Adsorption on Rh(111): A New Perspective on Intermolecular Interactions and Molecular Ordering

“…The work presented in this section does not counter or contradict any of the prior publications where the deposition of benzene at high coverage on Rh(111) has been reported on, but the nature of this discussion will be relevant when we move on to investigate the (√19×√19)R23.4° ordering. In these previous experiments, mainly involving HREELS and LEED, benzene was found to form a short-ranged (2√3×3)rect ordered structure, with a unit cell containing two benzene molecules, each one adsorbed in a different bridge30° configuration 21,52,54 . Disordered molecules present on the surface were determined to be on three-fold hollow sites.…”

“…Benzene adsorption has been extensively studied on the surface of the Rh(111) single crystal 21,29,30,37,[49][50][51][52][53][54][55] , with a significant amount of attention given to the behavior of benzene upon coadsorption with CO. This is in part due to the difficulty in preparing such a reactive surface free of typical UHV pollutants such as CO.…”

“…Upon realizing that the 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 initial studies of benzene on Rh(111) involved coadsorbed structures with CO, research interest changed to how these different molecules interacted with one another on a catalytic substrate. As a result of benzene and CO having oppositely orientated dipoles upon binding to the substrate, a strong attractive interaction occurs 56 which induces two possible ordered overlayers: a (3×3) structure with one benzene and two CO molecules per unit cell, and a c(2√3×4)rect structure with one benzene and one CO per unit cell [50][51][52] . The formation of these ordered overlayers is dependent on the deposition conditions, with both molecules determined to adsorb on hexagonally close-packed (hcp) hollow sites irrespective of the way the molecules are ordered.…”

“…This results in the self-organization of the molecules into two different commensurate nanostructures. A (2√3×3)rect ordering (relative coverage of ʘC6H6= 0.166), with two benzene molecules per unit cell (all adsorbed on bridge sites), was first identified through LEED patterns 52 , which also suggested the ordering was 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 short-ranged. HREELS experiments revealed two out-of-plane C-H bending modes for the benzene molecule, leading to the determination of benzene adsorbed on a threefold hollow site in the disordered regions 52 .…”

“…A (2√3×3)rect ordering (relative coverage of ʘC6H6= 0.166), with two benzene molecules per unit cell (all adsorbed on bridge sites), was first identified through LEED patterns 52 , which also suggested the ordering was 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 short-ranged. HREELS experiments revealed two out-of-plane C-H bending modes for the benzene molecule, leading to the determination of benzene adsorbed on a threefold hollow site in the disordered regions 52 . Another dense structure has been identified through LEED and ARUPS to form upon annealing a benzene saturated Rh(111) surface to 363 K. This structure, with relative coverage of ʘC6H6= 0.159, contains three benzene molecules per unit cell.…”