title: Molecular calipers control atomic separation at a metal surface.
abstract: If a molecule controls the length of some other moiety, it can be termed a "molecular caliper". Here we image individual molecular calipers of this type by scanning tunneling microscopy. These consist of linear polymers of p-diiodobenzene, (pDIB)n, of varying length, 0.7-2.9 nm, physisorbed on Cu(110) at 4.6 K. Through electron-induced reaction these chemically imprint their terminal I-atoms on the copper, 0.7 nm further apart than their initial separations. The physisorbed monomer or polymer, therefore, constitutes a molecular-caliper with variable terminal I..I separation. The localized nature of the I-atom reaction at the copper surface relative to the parent molecule, constitutes a novel finding reported here. It ensures that the separation of the I-atoms in the physisorbed molecular caliper correlates with their subsequent separation when chemisorbed at the surface.
authors: Lash Miller Chemical Laboratories, Department of Chemistry and Institute of Optical Science,  University of Toronto , 80 St. George Street, Ontario, M5S 3H6, Canada.
authors: Lydie
authors: L
authors: Leung
authors: Tingbin
authors: T
authors: Lim
authors: John C
authors: JC
authors: Polanyi
authors: Werner A
authors: WA
authors: Hofer