Grant Johnson - Coverage-Dependent Charge Reduction of Cationic Gold Clusters on Surfaces Prepared Using Soft Landing of Mass-Selected Ions

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      Publication Details (including relevant citation   information):


      Volume:   116

        Issue: 47

        Pages: 24977-24986


    Published: NOV 29 2012


        The ionic charge state of monodisperse multiply charged cationic   gold clusters on surfaces may be controlled by selecting the   coverage of mass selected ions soft landed onto a substrate.   Polydisperse diphosphine-capped gold clusters were synthisized in   solution and introduced into the gas phase by electrospray   ionization. Miss selection was employed to isolate a multiply   charged cationic cluster species (Au11L53+, m/z = 1409, L=   1,3,bis(diphenylphosphino)-propane) which was delivered to the   surfaces of four different self-assembled mjonolayers on gold   (SAMs) at controlled coverages of 10(11) and 10(12) clusters.   Employing the spatial profiling capabilities of in situ   time-of-flight secondary ion mass spectrometry (TOF-SIS), it is   shown that, in addition to the chemical functionality of the   monolayer (as demonstrated previously ACS Nano 2012, 6, 573); the   coverage of cationic gold clusters on the surface may be used to   control the relative abundance of different charge states of the   soft landed multiply charged clusters. In the case of a   1H,1H,2H,2H-perfluorodecanethiol monolayer (FSAM) almost complete   retention of charge by the deposited Au11L53+ clusters was   observed at a lower coverage of 10(11) clusters. In contrast, at   a higher coverage of 10(12) clusters, pronounced reduction of   charge to Au11L52+ and Au11L5+ was observed on the FSAM. When   soft landed onto 16- and 11-mercaptohexadecanoic acid surfaces on   gold (16,11-COOH-SAMS), the mass selected Au11L53+ clusters   exhibited partial reduction of charge to Au11L52+ at lower   coverage and additional reduction of charge to both Au11L52+ and   Au11L5+ at higher coverage on the surface of the 1-dodecanethiol   (HSAM) monolayer, the most abundant charge state was found to be   Au11L52+ at lower coverage and Au11L53+ at higher coverage,   respectively. A coverage-dependent electron tunneling mechanism   is proposed to account for the observed reduction of charge of   mass-selected multiply charged gold clusters soft landed on SAMs.   The results demonstrate that one of the critical parameters that   influence the chemical and physical properties of supported metal   clusters, ionic charge state, may be controlled by selecting the   coverage of charged species soft landed onto surfaces.

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