Applied Surface Science 257 (2011) 3603–3606 Contents lists available at ScienceDirect Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc Potential barrier generation at the BeW interface blocking thermonuclear radiation Yan Wang a , Yanguang Nie b , L.K. Pan c , Zhuo Sun c , Chang Q. Sun b,∗ a School of Information and Electronic Engineering, Hunan University of Science and Technology, Xiangtan 411201, China b School of Electrical & Electronic Engineering, Nanyang Technological University, Singapore 639798, Singapore c Engineering Research Center for Nanophotonics & Advanced Instrument, Ministry of Education, Department of Physics, East China Normal University, Shanghai 200062, China article info Article history: Received 23 August 2010 Received in revised form 12 November 2010 Accepted 12 November 2010 Available online 19 November 2010 Keywords: Potential barrier Alloy Binding energy shift abstract BeW is an important medium for radiation protection in the International Thermonuclear Experimental Reactor (ITER) devices. However, the mechanism for the radiation-protection ability of BeW remains unclear. An extension of the BOLS correlation mechanism [12] into the X-ray photoelectron spectroscopy (XPS) has enabled us to examine the energy and charge distribution of the specimen and clarify that the Be 1s and W 4f 7/2 energy levels undergo an elevation by 0.136 and 0.184 times those of the respective bulk constituents standing alone up-on BeW compound formation associated with polarization of the valence density of states. It is suggested that the interface potential barrier creation due to bond order distortion and bond nature alteration perturbs essentially the Hamiltonian and hence leads to the binding energy shifts. The established interface potential barrier and the polarized charge may screen the nuclear irradiation in the thermonuclear fusion devices. Findings may provide guideline for searching materials for such purpose. © 2010 Elsevier B.V. All rights reserved. 1. Introduction The study of interface alloy is motivated by their use in many industrial applications such as catalysis, anticorrosion, fric- tion reduction, thermonuclear radiation protection, and electronic devices. Varying composition or thermal annealing upon contin- uous deposition of dissimilar metals has provided an effective method to modify lattice distance and redistribute charges around the bonded atoms [1–3]. As the first wall materials in a fusion device, BeW alloying easily occurs in the plasma-wall interaction processes, which forms an important medium for radiation pro- tection in the International Thermonuclear Experimental Reactor (ITER) [4–7]. However, understanding the energetic and electronics of the alloy and the interface is crucial to realizing such functional materials design. Due to the different electronic structures of tung- sten (6S 2 5d 4 , delocalized d electrons dominate) and beryllium (2S 2 states dominate), a strong influence of the alloying on both the core and the valence bands should be expected, but insofar, poorly understood [8]. In order to understand the physical origin of the unusual behav- ior of BeW compound, we have studied the binding energetic and the electronic behavior of BeW compound from analyzing the bind- ∗ Corresponding author. E-mail address: Ecqsun@ntu.edu.sg (C.Q. Sun). ing energy shift of their surfaces before and after alloy formation [9–11] from the perspective of chemical bond – crystal potential – energy band correlation [12]. Findings revealed that the energy shifts of the resultant valence charge and the core electrons of the constituents for BeW compound are consistent in their polarization directions and for the first time that the Be 1s and W 4f 7/2 energy levels undergo an elevation by 0.134 and 0.187 times those of the respective bulk constituents standing alone. It is evidenced that the bond order distortion and bond nature alteration and the associ- ated interface charge polarization are responsible for the negative binding energy shifts and the functionality in radiation protection. 2. Principle 2.1. Bond–potential–band correlation Hetero-junction interfaces can be prototyped using an atom with fully or partially coordinated heterogeneous atoms. Many processes take place surrounding the atoms such as alloy forma- tion associated with the delocalized valence charge intermixing, compound formation with repopulation and polarization of the localized valence electrons, and structure distortion and lattice mismatching. Due to the bond order distortion and bond nature alteration, the interface energy will change [13]. Hence, the inter- face produces locally perturbation in the Hamiltonian, binding energy density, electroaffinity, and atomic cohesive energy, which 0169-4332/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2010.11.086