Yongling Guo

Coordination-resolved bonding and electronic dynamics of Na atomic clusters and solid skins

Density functional theory calculations confirmed the bond-order-length-strength (BOLS) predictions regarding the local bond length, bond energy and electron binding energy (BE) of Na atomic clusters and shell-resolved monolayer skins. A reproduction of the photoelectron spectroscopic measurements leads to the following observations: (i) local lattice maximal strain of 12.67%, (ii) BE density of 71.92%, (iii) atomic cohesive energy drops to 62.31% and (iv) the 2p core-level shifts deeper by 2.749 eV for under-coordinated Na atoms. This information helps in understanding the unusual behaviour of the under-coordinated Na solid skins and atomic clusters.

Skin Bond Electron Relaxation Dynamics of Germanium Manipulated by Interactions with H2, O2, H2O, H2O2, HF, and Au

Although germanium performs amazingly well at sites surrounding hetero-coordinated impurities and under-coordinated defects or skins with unusual properties, having important impact on electronic and optical devices, understanding the behavior of the local bonds and electrons at such sites remains a great challenge. Here we show that a combination of density functional theory calculations, zone-resolved X-ray photoelectron spectroscopy, and bond order length strength correlation mechanism has enabled us to clarify the physical origin of the Ge 3d core-level shift for the under-coordinated (111) and (100) skin with and without hetero-coordinated H2 , O2 , H2 O, H2 O2 , HF impurities. The Ge 3d level shifts from 27.579 (for an isolated atom) by 1.381 to 28.960 eV upon bulk formation. Atomic under-coordination shifts the binding energy further to 29.823 eV for the (001) and to 29.713 eV for the (111) monolayer skin. Addition of O2 , HF, H2 O, H2 O2 and Au impurities results in quantum entrapment by different amounts, but H adsorption leads to polarization.

Electronic binding energy relaxation of Sc clusters by monatomic alloying: DFT-BOLS approximation

Monatomic alloying of atomic clusters emerges as a promising means for efficient catalyst development with a yet unclear mechanism. Here we show that such monatomic cluster alloying takes the advantages of both atomic undercoordination and atomic heterocoordination that enhance each other in the local quantum entrapment and polarization. Atomic undercoordination shortens the Sc–Me bond by up to 30% and reduces the atomic cohesive energy by 25% (Me = Ag, Au, Ca, Cd, Cu, Ni, Ir, Ti, Rh, Pd, Fe, Pt, Y, Zn), resulting in local energy density gain and charge polarization. Monatomic alloying enhanced the effect of undercoordination on the quantum entrapment and local polarization, which is fundamentally significant in modulating the catalytic ability of metal-doped Sc clusters.

Skin-depth lattice strain, core-level trap depression and valence charge polarization of Al surfaces

Clarifying the origin for surface core-level shift (SCLS) and gaining quantitative information regarding the coordination-resolved local strain, binding energy (BE) shift and cohesive energy change have been a challenge. Here, we show that a combination of the bond order–length–strength (BOLS) premise, X-ray photoelectron spectroscopy (XPS) and the ab initio density functional theory (DFT) calculations of aluminum (Al) 2p3/2 energy shift of Al surfaces has enabled us to derive such information, namely, (i) the 2p3/2 energy of an isolated Al atom (72.146 ± 0.003eV) and its bulk shift (0.499 eV); (ii) the skin lattice contracts by up to 12.5% and the BE density increases by 70%; and (iii) the cohesive energy drops up to 38%. It is affirmed that the shorter and stronger bonds between under-coordinated atoms provide a perturbation to the Hamiltonian and hence lead to the local strain, quantum entrapment and valence charge polarization. Findings should help in understanding the phenomena of surface pre-melting and skin-high elasticity, in general.