Reactions of Metal Ions at Fluorinated SAM (Self-Assembled Monolayer) Surfaces: Formation of MFn+ (M = Ti, Cr, Fe, Mo, and W; n = 1-5)

Abstract

Low-energy (<100 eV) ion/surface reactions of metal ions, Ti*+, Cr*+, Fe,+, Mo*+, and W,+, at a fluorinated self-assembled monolayer surface give fluorine-containing scattered ions, MF"+, n < 5. The metal fluorides are the most abundant products in the scattered ion spectra. The single fluorine abstractions are all endothermic and driven by the projectile translational energy. Multiple fluorine abstraction occurs with high efficiency for Mo,+ and W,+ projectiles, where the thermochemistry is most favorable. Polyatomic projectile ions derived by partial fragmentation of the Cr, Mo, and W hexacarbonyls also yield metal fluoride scattered ions, in addition to more complex species formed by fluorine abstraction by ions which retain one or more carbon atoms or carbonyl groups. Fe-and Ti-containing projectile ions, bearing one or two cyclopentadienyl (Cp) groups, also exhibit fluorine abstraction products, with and without retention of a Cp group. TiCl"+ (n = 1-4) projectiles exhibit fluorine abstraction, as well. Similar fluorine abstraction products are generated upon collisions at a liquid perfluorinated polyether surface. Gas-phase ion/molecule reactions and thermochemical considerations suggest that multiple fluorine abstractions can occur by a direct reaction mechanism within a single scattering event and that multiple fluorine atoms are probably derived from a single fluorocarbon chain. Angle-resolved scattering data support a single-collision, multiple-atom abstraction mechanism. The scattered ions leave the surface with very low translational energy and collision energy variations suggest that in these ion/surface reactions, projectile dissociation is concerted with or occurs prior to fluorine abstraction. There is no evidence that electron transfer to the surface is involved, as it is in alkyl group abstraction reactions by ions at hydrocarbon surfaces.

Ion/Surface Reactions at Monolayers in Solution: A Combined Surface Enhanced Raman–X-Ray Photoelectron Spectroscopic Investigation of the Chemical Modification of a 2-Mercaptobenzothiazole Monolayer on Polycrystalline Au Films

“…The same as the mechanism proposed for gas-phase ion/surface encounters, reaction between the ionic surfaces and the neutralized projectile can be one of the important means of relaxation of the excited surface species (2,4). This reaction could occur with high efficiency, the same as similar gas-phase processes.…”

“…Since the efficiency of energy transfer is high, even endothermic processes occur with high probability (4). One of the important events when an ion approaches a surface is electron transfer from the surface, leading to an ionized surface species (2,10).…”

“…This is particularly the case for a molecular surface. Various low-energy ion/surface collision experiments have been used to understand the details of the interfacial ion processes (3)(4)(5)(6). In an electrochemical system, an ion approaching the electrode has little translational energy and the energy transfer induced by collision cannot be a driving force in the chemical processes.…”

Probing Molecular Solids with Low-Energy Ions

“…. 5) with a unique intensity pattern (89). Such transition-metal chemistry was subsequently extended to many ions and surfaces in an effort to better understand the chemical nature of surfaces with extreme surface sensitivity.…”

Trapping of molecules in alkanethiol self-assembled monolayer matrices

“…Since the centre of mass collision energies in these experiments are comparable with bond energies, the process can be used very e ectively in breaking (by a process called surface induced dissociation) or making of chemical bonds (referred to as ion± surface reactions). In ion± surface reactions [3], a process of particular interest to this work, a mass selected ion is made to collide with a surface at a desired collision energy, generally of the order of a few tens of eV, and the scattered-ion mass spectrum is analysed. A large number of ions undergo reactions at the surface; the most intensely researched are the hydrogen and¯uorine atom pick-up reactions [1].…”