Comments on some experimental measures of the non–metal to metal transition in thin films

Monodisperse Pt nanoparticles with atomic structures that span the cluster to crystal transition have recently been synthesized in electrostatically stabilized, aqueous-based suspensions. In the present study, the anionic charge from the stabilizing SnCl(2) sheath adsorbed on the surface of these particles is used for the first time to assemble Pt directly onto porous carbon supports via electrostatic assembly. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) reveals that these assemblies have substantially higher Pt-C dispersions than obtained from precipitation methods commonly used for commercial electrocatalyst systems. Energy dispersive spectroscopy (EDS) and inductively coupled plasma-mass spectrometry (ICP-MS) are used to determine that loadings of 10-30% by weight Pt (particle packing fractions from 0.05 to 0.25) are obtained through a single electrostatic application of these particles on Vulcan carbon, depending on particle size. The highest average oxygen reduction reaction (ORR) mass activity obtained using this approach is 90.4 A/g(Pt) at 0.9 V vs RHE in 0.1 M perchloric acid is with 1-2 nm particles that exhibit a transitional atomic structure. This activity compares to an average value of 74.0 A/g(Pt) obtained from densely packed electrostatic layer-by-layer (LbL) assemblies of unsupported particles and 36.7 A/g(Pt) commercial Vulcan electrocatalyst from Tanaka Kikinzoku Kogyo (TKK). Enhanced activity is observed with electrostatic assembly of any particle size on Vulcan relative to unsupported or commercial electrocatalyst with comparable durability. Such enhanced activity is attributed to improved reactant accessibility to the catalyst surface due to the increase in particle dispersion. An extinction coefficient of 7.41 m(2)/g at 352 nm is obtained across the entire cluster to crystal transition from 20 atom clusters to 2.9 nm single crystal nanoparticles, indicating that observed variation in ORR activity with particle size may be associated primarily with changes in atomic surface structure as opposed to the metallic character of the nanoparticles as assessed by UV-vis spectroscopy.

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Phase transition in the surface structure in copolymer films of vinylidene fluoride (70%) with trifluoroethylene (30%)

Choi

et al. 2000

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Lee; Fridkin, V.M.; Petukhova, N.N.; and Yudin, S.G., "Phase transition in the surface structure in copolymer films of vinylidene fluoride (70%) with trifluoroethylene (30%)" (2000). Surface structures and a surface structure phase transition are identified that are distinct from the known bulk ferroelectric-paraelectric phase transition of crystalline copolymer films of vinylidene fluoride ͑70%͒ with trifluoroethylene ͑30%͒. The temperature-dependent changes in the surface structure are accompanied by the physical rotation of the polar group ͑CH 2 -CF 2 ͒. These changes in the surface structure are compared to the bulk phase transition. We show that the bulk structural transition, while distinct from the surface, is qualitatively similar in both thick and thin Langmuir-Blodgett-grown films.

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Comments on some experimental measures of the non–metal to metal transition in thin films

Abstract: A brief review is presented of experimental indicators of metallicity and the metalnon-metal transition, with particular emphasis on studies of thin films. Problems of definition and measurement are emphasized.

Cited by 3 publications

References 110 publications

Inner-shell absorption spectra of potassium fluoride clusters

Inner-shell absorption spectra of potassium fluoride clusters

Enhanced Electrocatalytic Oxygen Reduction through Electrostatic Assembly of Pt Nanoparticles onto Porous Carbon Supports from SnCl₂-Stabilized Suspensions

Phase transition in the surface structure in copolymer films of vinylidene fluoride (70%) with trifluoroethylene (30%)

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Comments on some experimental measures of the non–metal to metal transition in thin films

Abstract: A brief review is presented of experimental indicators of metallicity and the metalnon-metal transition, with particular emphasis on studies of thin films. Problems of definition and measurement are emphasized.

Cited by 3 publications

References 110 publications

Inner-shell absorption spectra of potassium fluoride clusters

Inner-shell absorption spectra of potassium fluoride clusters

Enhanced Electrocatalytic Oxygen Reduction through Electrostatic Assembly of Pt Nanoparticles onto Porous Carbon Supports from SnCl2-Stabilized Suspensions

Phase transition in the surface structure in copolymer films of vinylidene fluoride (70%) with trifluoroethylene (30%)

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Product

Resources

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Enhanced Electrocatalytic Oxygen Reduction through Electrostatic Assembly of Pt Nanoparticles onto Porous Carbon Supports from SnCl₂-Stabilized Suspensions