Journal of Alloys and Compounds 470 (2009) 452–460 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom Electronic structure of layer type tungsten metal dichalcogenides WX 2 (X = S, Se) using Compton spectroscopy: Theory and experiment Gunjan Arora a , Yamini Sharma b , Vinit Sharma c , Gulzar Ahmed c , S.K. Srivastava d , B.L. Ahuja c,∗ a Department of Physics, Geetanjali Institute of Technical Studies, Udaipur 313022, Rajasthan, India b Department of Physics, Feroze Gandhi College, Rae Bareli 229001, U.P., India c Department of Physics, University College of Science, M. L. Sukhadia University, Udaipur 313001, Rajasthan, India d Department of Chemistry, Indian Institute of Technology, Kharagpur 721302, India article info Article history: Received 8 January 2008 Received in revised form 18 February 2008 Accepted 28 February 2008 Available online 16 April 2008 PACS: 13.60.Fz 71.15.Ap 72.80.Ey 78.70.Ck Keywords: Transition-metal alloys and compounds Electronic band structure X-ray and gamma-ray spectroscopies abstract In this paper, we report the first ever experimental Compton profile study of WS 2 and WSe 2 employing 20 Ci 137 Cs Compton spectrometer. To interpret our experimental data, the electronic properties of these compounds have been determined by linear combination of atomic orbitals, full potential linearised augmented plane-wave and spin polarised relativistic Korringa–Kohn–Rostoker (SPR-KKR) schemes. The band structure calculations show that both the WS 2 and WSe 2 are indirect-gap semiconductors. The SPR- KKR calculations are found to be relatively in poor agreement with the experimental electron momentum densities. The relative nature of bonding in both the dichalcogenides is explained in terms of equal- valence-electron-density profiles, Mulliken’s population and valence band charge densities. © 2008 Elsevier B.V. All rights reserved. 1. Introduction The Compton scattering is an inelastic process in which an ener- getic photon collides with a single electron and transfers part of its energy to the electron. This technique has been recognised as a powerful and versatile experimental tool to probe the consistency of band structure models of the ground-state electron momentum density. Compton study of materials is based upon the Doppler broadening of the scattered radiation by the motion of electrons in the target [1,2]. The energy spectrum of inelastically scattered pho- tons at a fixed angle reflects the electron momentum distribution, and hence the electronic structure of materials. From such exper- iments, one measures the double differential cross section that is related to Compton profile J(p z ) as follows d 2  d˝ dω 2 ∝ J (p z ) =  n(p)dp x dp y (1) where n(p) is the ground-state electron momentum density. The momentum density, within an independent-particle model, is ∗ Corresponding author. Tel.: +91 294 2423322; fax: +91 294 2411950. E-mail address: blahuja@yahoo.com (B.L. Ahuja). given by n(p) = 1 (2) 3  Occ.      (r ) exp(ip · r)dr     2 (2) where (r) represents the electron wave function and the summa- tion extends over all the occupied states. Since last three decades, there is a considerable interest in the layered transition-metal dichalcogenides (MX 2 : M = transition- metal atom from IVB, VB or VIB group, X = S, Se or Te). In photoelectrochemical cells [3,4] they have frequent applications as electrode materials and exhibit band gaps well matched with the solar spectrum, hence can be treated as prototype materials for photovoltaic and opto-electronic devices [5]. They also possess very good antifriction properties and are extensively employed as solid lubricant. Particularly, in the case of WSe 2 , the electrochem- ical devices possess conversion efficiencies up to 17% [6]. Unlike other conventional semiconductors, the optical gap in WSe 2 is determined by orbitals that contribute only weakly to the chemical bonding. As a consequence, the generation of electron–hole pairs by light absorption does not break any bond, which makes it sta- ble against photocorrosion and is used for photovoltaic applications [7]. 0925-8388/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2008.02.098