Layer and orientation resolved bond relaxation and quantum entrapment of charge and energy at Be surfaces

Yan Wang; Yan Guang Nie; Ji Sheng Pan; Likun Pan; Zhuo Sun; Chang Q. Sun

doi:10.1039/C0CP00088D

Layer and orientation resolved bond relaxation and quantum entrapment of charge and energy at Be surfaces

Yan Wang,^a Yan Guang Nie,^b Ji Sheng Pan,^c Likun Pan,^d Zhuo Sun^d and Chang Q. Sun*^be

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* Corresponding authors

^a School of Information and Electronic Engineering, Hunan University of Science and Technology, Xiangtan 411201, China

^b School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798

^c Institute of Materials Research and Engineering, A*STAR, Singapore 117602

^d Engineering Research Center for Nanophotonics & Advanced Instrument, Ministry of Education, Department of Physics, East China Normal University, Shanghai 200062, China

^e Institute of Quantum Engineering and Micro-nano Energy, Key Laboratory of Low-dimensional Materials and Application Technologies, Xiangtan University, Changsha 411105, China

Abstract

The chemistry and physics of under-coordination at a surface, which determines the process of catalytic reactions and growth nucleation, is indeed fascinating. However, extracting quantitative information regarding the coordination-resolved surface relaxation, binding energy, and the energetic behavior of electrons localized in the surface skin from photoelectron emission has long been a great challenge, although the surface-induced core level shifts of materials have been intensively investigated. Here we show that a combination of the theories of tight binding and bond order-length-strength (BOLS) correlation [C. Q. Sun, Prog. Solid State Chem., 2007, 35, 1–159], and X-ray photoelectron spectroscopy (XPS) has enabled us to derive quantitative information, by analyzing the Be 1s energy shift of Be(0001), (10 [1 with combining macron] 0), and (11 [2 with combining macron] 0) surfaces, for demonstration, regarding: (i) the 1s energy level of an isolated Be atom (106.416 ± 0.004 eV) and its bulk shift (4.694 eV); (ii) the layer- and orientation-resolved effective atomic coordination (3.5, 3.1, 2.98 for the first layer of the three respective orientations), local bond strain (up to 19%), charge density (133%), quantum trap depth (110%), binding energy density (230%), and atomic cohesive energy (70%) of Be surface skins up to four atomic layers in depth. It is affirmed that the shorter and stronger bonds between under-coordinated atoms perturb the Hamiltonian and hence the fascinating localization and densification of surface electrons. The developed approach can be applied to other low-dimensional systems containing a high fraction of under-coordinated atoms such as adatoms, atomic defects, terrace edges, and nanostructures to gain quantitative information and deeper insight into their properties and processes due to the effect of coordination imperfection.

Physical Chemistry Chemical Physics

Layer and orientation resolved bond relaxation and quantum entrapment of charge and energy at Be surfaces

Abstract

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