STM and AFM characterization of thin metal oxide films electrodeposited from [P2Mo18O62]6−

Abstract

Two groups of techniques have been devised for the electrodeposition of new electroactive oxide ®lms from [P 2 Mo 18 O 62 ] 6) . In the ®rst group, two adsorption procedures were used: simple immersion of the electrode in a solution containing 10 )4 M [P 2 Mo 18 O 62 ] 6) in a pH 3.50 medium or cycling of the electrode in this solution in the potential domain of the ®rst three twoelectron waves of the heteropolyanion results in surfaces which retain the oxometalate by mere adsorption. Strikingly, during the cycling, it was found that a fourth wave appears in the potential domain of the ®rst three two-electron waves of [P 2 Mo 18 O 62 ] 6) , indicating an evolution of the heteropolyanion in the solution. Such an evolution was also observed with aged solutions. Then, the potential program for the actual modi®cation step was run by cycling either of these electrodes from )0.2 V to )0.87 V vs. SCE in pure supporting electrolyte. Analysis of the STM images of the surfaces show essentially monomers 1.2±1.5 nm in diameter just after adsorption and a sizeable increase of the dimensions of the patterns after modi®cation. The predominant sizes of these aggregates after modi®cation remain in the range 10±12 nm. The second group of techniques consists in a modi®cation of the electrode surface directly in the solution containing the heteropolyanion. A ®xed potential as well as cycling prove ecient. Thick ®lms are obtained readily, which are better imaged by tapping mode AFM. An increase of the pH to 4.50, in appropriate conditions, seems to be favourable to the deposition kinetics. The aggregates in the topmost layers are up to 40 nm in diameter and are assembled in interconnected islands. As a whole, these two groups of techniques appear to exert an important in¯uence on the aggregate sizes. The paper demonstrates that these sizes might be relatively well controlled by the choice of experimental conditions.

Nanotribological Study of Supramolecular Template Networks Induced by Hydrogen Bonds and van der Waals Forces

“…As mentioned in the Experimental Section, the measurements were conducted after the solvent was evaporated, so that the effect of the solvent on friction forces could be excluded. It should be noted that the drying process may have an effect on the assembly structures owing to the potential shear flow and defects. , To avoid such an effect, the samples were characterized at the gas–solid interface by STM before friction measurements. Experimental results show that the structures of TMA and BTB networks are with no observable changes after the solvent evaporation.…”

Superlubricity of Fullerene Derivatives Induced by Host–Guest Assembly

“…To eliminate the solvent effect on the friction forces, the measurements were conducted at the gas–solid interface after the solvent was evaporated. However, due to the potential shear flow and defects, the solvent evaporation may have an impact on the assembly structures. , Before each measurement, the samples were characterized by STM to confirm the host–guest assembly structures in case of the impact of the drying process. The silicon CSG10 probe with a rectangular cantilever (nominal normal spring constant 0.1 N m –1 ) was used.…”

Direct Imaging of the Ligand Monolayer on an Anion-Protected Metal Nanoparticle through Cryogenic Trapping of its Solution-State Structure

“…By contrast, organized arrays of individual POMs on graphite and metal surfaces have been investigated by scanning tunneling microscopy , (STM), atomic force microscopy (AFM), , and X-ray specular reflectivity .…”