ABSTRACT
The spontaneous ordering of molecules into two-dimensional self-assembled arrays is commonly stabilized by directional intermolecular interactions that may be promoted by the addition of specific chemical side groups to a molecule. In this paper, we show that self-assembly may also be driven by anisotropic interactions that arise from the three-dimensional shape of a complex molecule. We study the molecule Mn(12)O(12)(O(2)CCH(3))(16)(H(2)O)(4) (Mn(12)(acetate)(16)), which is transferred from solution onto a Au(111) substrate held in ultrahigh vacuum using electrospray deposition (UHV-ESD). The deposited Mn(12)(acetate)(16) molecules form filamentary aggregates because of the anisotropic nature of the molecule-molecule and molecule-substrate interactions, as confirmed by molecular dynamics calculations. The fragile Mn(12)O(12) core of the Mn(12)(acetate)(16) molecule is compatible with the UHV-ESD process, which we demonstrate using near-edge X-ray adsorption fine-structure spectroscopy. UHV-ESD of Mn(12)(acetate)(16) onto a surface that has been prepatterned with a hydrogen-bonded supramolecular network provides additional control of lateral organization.
Subject(s)
Gold/chemistry , Manganese Compounds/chemistry , Nanotechnology/methods , Anisotropy , Models, MolecularABSTRACT
Zinc-protoporphyrin, adsorbed on the rutile TiO(2)(110) surface, has been studied using photoemission spectroscopy and near-edge absorption fine structure spectroscopy to deduce the nature of the molecule-surface bonding and the chemical environment of the central metal atom. To overcome the difficulties associated with sublimation of the porphyrin molecules, samples were prepared in situ using ultrahigh vacuum electrospray deposition, a technique which facilitates the deposition of nonvolatile and fragile molecules. Monolayers of Zn protoporphyrin are found to bond to the surface via the oxygen atoms of the deprotonated carboxyl groups. The molecules initially lie largely parallel to the surface, reorienting to an upright geometry as the coverage is increased up to a monolayer. For those molecules directly chemisorbed to the surface, the interaction is sufficiently strong to pull the central metal atom out of the molecule.
ABSTRACT
The adsorption of the dye molecule N3 [cis-bis(isothiocyanato)bis(2,2(')-bipyridyl-4,4(')-dicarboxylato)-ruthenium(II)] on the Au(111) surface has been studied using core-level and valence photoemission and scanning tunneling microscopy (STM). The dye molecules were deposited in situ using ultrahigh vacuum electrospray deposition. The core-level spectra reveal that the molecule bonds to the surface via sulfur atoms with no deprotonation of the carboxylic groups. The STM images show that at low coverage the molecules decorate the Au(111) herringbone reconstruction and form uniform monolayers as the coverage is increased.
ABSTRACT
An experimental study of the bonding geometry and electronic coupling of cis-bis(isothiocyanato)bis(2,2(')-bipyridyl-4,4(')-dicarboxylato)-ruthenium(II) (N3) adsorbed on rutile TiO(2)(110) is presented, along with supporting theoretical calculations of the bonding geometry. Samples were prepared in situ using ultrahigh vacuum electrospray deposition. Core-level photoemission spectroscopy was used to characterize the system and to deduce the nature of the molecule-surface bonding. Valence band photoemission and N 1s x-ray absorption spectra were aligned in a common binding energy scale to enable a quantitative analysis of the bandgap region. A consideration of the energetics in relation to optical absorption is used to identify the photoexcitation channel between the highest occupied and lowest unoccupied molecular orbitals in this system, and also to quantify the relative binding energies of core and valence excitons. The core-hole clock implementation of resonant photoemission spectroscopy is used to reveal that electron delocalization from N3 occurs within 16 fs.
ABSTRACT
Here we report on a novel and effective technique for the deposition of carbon nanotubes onto surfaces in vacuum directly from a liquid suspension. The technique, based on in-vacuum electrospray ionization, has the potential to bridge the gap between high resolution techniques requiring ultra-high vacuum conditions, and non-volatile molecules and nanostructures such as carbon nanotubes. Atomic force microscopy of double-walled nanotubes deposited onto silicon surfaces in vacuum show individual nanotubes and low density bundles.
