Scanning tunneling microscopy studies of pulse deposition of dinuclear organometallic molecules on Au(111)

Abstract

Ultrahigh-vacuum scanning tunneling microscopy (STM) was used to study trans-[Cl(dppe)2Ru(C Triple Bond C)6Ru(dppe)2Cl] [abbreviated as Ru2, diphenylphosphinoethane (dppe)] on Au(111). This large organometallic molecule was pulse deposited onto the Au(111) surface under ultrahigh-vacuum (UHV) conditions. UHV STM studies on the prepared sample were carried out at room temperature and 77 K in order to probe molecular adsorption and to characterize the surface produced by the pulse deposition process. Isolated Ru2 molecules were successfully imaged by STM at room temperature; however, STM images were degraded by mobile toluene solvent molecules that remain on the surface after the deposition. Cooling the sample to 77 K allows the solvent molecules to be observed directly using STM, and under these conditions, toluene forms organized striped domains with regular domain boundaries and a lattice characterized by 5.3 and 2.7 A intermolecular distances. When methylene chloride is used as the solvent, it forms analogous domains on the surface at 77 K. Mild annealing under vacuum causes most toluene molecules to desorb from the surface; however, this annealing process may lead to thermal degradation of Ru2 molecules. Although pulse deposition is an effective way to deposit molecules on surfaces, the presence of solvent on the surface after pulse deposition is unavoidable without thermal annealing, and this annealing may cause undesired chemical changes in the adsorbates under study. Preparation of samples using pulse deposition must take into account the characteristics of sample molecules, solvent, and surfaces.

Scanning Tunneling Microscopy of Mixed Valence Dinuclear Organometallic Cations and Counterions on Au(111)

“…Ru2 on Au(111) samples were prepared by the pulse-injection technique discussed in previous publications. 22,23,29,30 The mixed-valence complex Ru2 þ [PF 6 ] -was made by mixing Ru2 with ferrocenium hexafluorophosphate ([Fe(η 5 -C 5 H 5 ) 2 ][PF 6 ]) in a 1:1 mol ratio in toluene solution in a nitrogen-purged drybox Ru2 þ ½Feðη 5 -C 5 H 5 Þ 2 ½PF 6 s f toluene ½Ru2 þ ½PF 6 -þ Feðη 5 -C 5 H 5 Þ 2 After the oxidation reaction, the Ru2 þ [PF 6 ] -solution was pulse-deposited without further purification onto Au(111) under vacuum to make Ru2 þ [PF 6 ] -on Au(111). Samples were imaged at room and low temperatures using a UHV STM (Omicron Nanotechnology LT-STM) in constant-current mode using mechanically cut Pt-Ir tips.…”

UHV-STM Investigations and Numerical Calculations of a Ruthenium β-Diketonato Complex with Protected Ethynyl Ligand: [Ru(dbm)2(acac-TIPSA)]

“…[33][34][35] Among molecules with magnetic centres, ruthenium complexes may be of particular interest to study charge transfer or transport phenomena at the nanometer scale. [36][37][38][39][40][41][42] In a previous paper, we reported the investigation of a series of ruthenium tris( -diketonato)complexes by UHV-STM. 43 Here, the synthesis and characterization of a new ruthenium -diketonato complex with Scheme 1.…”

Adsorption of diferrocenylacetylene on Au(111) studied by scanning tunneling microscopy

“…The technique of pulse-deposition allows for large, delicate molecules to remain intact as they are deposited onto a surface. 39,[44][45][46][47][48][49] We have deposited DFA dissolved in benzene, which results in a surface with both solute and solvent molecules coadsorbed, as without post-deposition annealing, even low-boiling-point solvents will remain on the surface at sub-monolayer concentrations. 39 Benzene and DFA are observed in a variety of configurations: we see benzene in both the 2D gas phase and solid phase, DFA sitting on and around benzene, and a partial monolayer of DFA absorbed onto a partial monolayer of benzene.…”

“…A 1 mM solution of diferrocenylacetylene in benzene was prepared and several mL of solution were pulse deposited onto the Au(111) surface in vacuum at room temperature using a pulsed solenoid valve (Parker Instrumentation 9-series, 0.5 mm nozzle diameter, IOTA One driver). 39,[44][45][46][47][48][49] The samples were cooled to 77 K prior to imaging with a low-temperature ultra-high-vacuum scanning tunneling microscope (LT-UHV STM from Omicron NanoTechnology) at pressures below 3 Â 10 À10 Torr. All images were obtained with the sample bias voltage applied to the sample.…”

“…[11][12][13] As part of a longer-range plan to investigate mixed-valence DFA, as well as more complex organometallic systems based upon it, 38 we are interested in preparing molecules in a solution environment before deposition on a solid surface. With this approach, solvent molecules are necessarily deposited on the surface alongside solutes; 39 here, benzene is co-deposited with DFA. The result is a fairly complex surface arrangement of molecules, and solvent coadsorption can potentially modify the interaction of solute molecules with the surface and with each other.…”