Journal of Alloys and Compounds 509 (2011) 4603–4607 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom X-ray photoelectron spectroscopic study of catalyst based zinc oxide thin films S.S. Shinde, K.Y. Rajpure ∗ Electrochemical Materials Laboratory, Department of Physics, Shivaji University, Kolhapur 416004, India article info Article history: Received 18 December 2010 Received in revised form 12 January 2011 Accepted 15 January 2011 Available online 22 January 2011 Keywords: Catalyst XPS Chemical shifts Bond iconicity Auger parameter abstract X-ray photoelectron spectroscopy (XPS) is a powerful tool for surface and interface analysis, providing an elemental composition of surfaces and the local chemical environment of adsorbed species. The surface composition and chemical states of the F/ZnO and In/ZnO catalysts deposited using spray technique have been studied by high resolution and high sensitivity X-ray photoelectron spectroscopy. A hybrid multiline method is proposed for quantitative XPS analysis that combines the first principles approach with the experimental determination of overall response function. The chemical shifts of XPS core lines for Zn (2P 3/2 , F 1s and In 3d) and Auger parameter for zinc (ˇ Zn = 2012.6, 2011.48 eV for F/ZnO and In/ZnO, respectively) have been calculated. The results have been used to determine the bond iconicity (0.55). © 2011 Elsevier B.V. All rights reserved. 1. Introduction The understanding of the interaction of a catalyst’s with the host surface plays a key role in a detailed description of catalytic pro- cesses. However, a spectroscopic characterization of the reacting surface under ambient conditions is challenging. While photon-in photon-out techniques can be employed at higher gas pressures, which typically show a lack of surface sensitivity. On the other hand, photon-in electron-out techniques like XPS are intrinsically more surface sensitive due to the strong interaction of (low energy) electrons with matter. Thus, the use of XPS as a tool for char- acterization of catalysts is an attractive tool for several apparent reasons. XPS shows a universal chemical sensitivity by probing the different core levels of the element. The surface sensitivity of XPS critically depends on the kinetic energy of the released photo- electrons and thus on the energy difference between the incoming photon and the binding energy of the core level. Low energy elec- trons of 50–150 eV show the smallest inelastic mean free path in a solid and thus the highest surface sensitivity [1]. Thus, XPS devel- ops into an ultimate surface sensitive tool for characterizing the topmost layers of a material when it is operated with a tunable X-ray source at a storage ring. Synchrotron based XPS makes it fea- sible to ensure a low kinetic energy of the released photoelectrons for all core levels. Zinc oxide, with a direct band gap of 3.37 eV and a large exciton binding energy of 60 meV at room temper- ature, is attracting worldwide attention because of its potential ∗ Corresponding author. Tel.: +91 231 2609435; fax: +91 231 2691533. E-mail address: rajpure@yahoo.com (K.Y. Rajpure). applications in short-wavelength optoelectronic devices, such as piezoelectric sensors/actuators [2], high frequency electro-acoustic devices [3] due to their piezoelectric properties and high acous- tic velocity, ultraviolet (UV) light-emitting diodes (LEDs), and laser diodes (LDs) operating at high temperatures and in harsh envi- ronments [4–9]. However, in order to develop ZnO-based optical devices, stable and high-quality n-type ZnO films are required. The major difficulty in fabrication of n-type ZnO films is the self- compensating process of doping. The electrochemical removal of the oxides present on the host surface enhances the catalytic prop- erties of the host, indicating that the oxide(s) inhibit rather than catalyzing the evolution reaction. Since the electronic properties of the host surfaces play an important role in the catalytic activity. These arguments are based on X-ray photoelectron spectroscopy (XPS) results such as measured core level energy shifts between ele- ments in elemental states. The measurable chemical shift is one of the main advantages of XPS technique. The chemical shift is defined as the variation in measured photoelectron (and/or Auger elec- tron) energy arising from changes in the atomic potential, which are in turn strongly related to changes in the atomic environment. Photoelectron binding energy values are susceptible to energy ref- erencing and/or sample electrostatic charging effects. XPS is used in this study to differentiate the species of F and In found in ZnO:F, In films. To understand how the electronic properties of the films are affected by F and In doping, XPS is used to determine posi- tions of the valence band edge with respect to the Fermi level. Ballerini et al. [10] reported the acid–base properties of the sur- face of native zinc oxide layers by XPS study of adsorption of 1,2-diaminoethane. Islam et al. [11] depicted the XPS and X-ray diffraction studies of aluminum-doped zinc oxide transparent con- 0925-8388/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2011.01.117