Perspective: Bonding and electronic origin of Au atomic-undercoordination-derivacy and nanoscale-size-dependency.

Atomic undercoordination entitles the inert gold even more noble at sites pertained to adatoms, defects, kinks, and skins of bulk and sized crystals with unclear mechanism. Systematic analysis of the electron emission spectra of XPS and STM/S of the undercoordinated gold atoms revealed that the 4 f and 5 d bands undergo quantum entrapment while the 6 s level is subject to localization and polarization because of the undercoordination-induced local bond contraction and bond strength gain – named bond order-length-strength correlation and nonbonding electron polarization (BOLS-NEP). Such a bonding and electronic relaxation result in the undercoordination derivacy of properties such as its extraordinary catalytic ability that the bulk gold does never demonstrate. The BOLS-NEP in the skin-electrical-double-layer shell dictates the nanostructure size dependency of the known bulk properties such as the chemical potential, inner potential constant, elasticity, and thermal stability. The exercise not only establishes a powerful means monitoring the Hamiltonian perturbation by atomic undercoordination but also offers information on the atomic-site-resolved local bond length, bond energy, chemical potentials, energy density, and atomic cohesive energy and the associated properties. Image 1 • Atomic undercoordination shortens the local bond and polarizes nonbonding electrons. • Polarization derives the intriguing properties of catalytic ability and chemical reactivity. • Bond relaxation in the skin EDL results in the size dependency of sized crystals. • Electron spectrometrics offers information of local bonding and electronic dynamics. [ABSTRACT FROM AUTHOR]