Journal of Electron Spectroscopy and Related Phenomena 176 (2010) 35–45 Contents lists available at ScienceDirect Journal of Electron Spectroscopy and Related Phenomena journal homepage: www.elsevier.com/locate/elspec Study of neutralization kinetics in charged polymer–metal nanocomposite systems by photoemission spectroscopy S. Mukherjee, M. Mukherjee ∗ Surface Physics Division, Saha Institute of Nuclear Physics, 1/AF, Bidhannagar, Kolkata 700064, India article info Article history: Available online 7 October 2009 Keywords: Photoemission Charging Neutralization Insulating polymer Nanocomposite Thin film abstract In case of photoelectron spectroscopy of an insulating material the data obtained from the charged surface are often distorted due to differentially charged surface domains. Recently we have developed a controlled surface neutralization technique to study the kinetics of the surface charging. Here we demonstrate the application of the technique to study the neutralization kinetics of both thick and thin films of charged polymer–metal nanocomposite material using photoemission. Neutralization kinetics of grounded and floated pure polymer thin films was also studied. It was observed that for the thick sample the transition of positively charged domains to overcompensated ones occurs through percolation. In case of grounded thin films the growth of overcompensated domains exhibit a linear behavior followed by saturation. When electrons appear at both surfaces of a floated thin film, the neutralization kinetics show a completely different behavior. Present investigation indicates that for thin films of insulating materials appearing to be neutral in presence of an electron source, controlled neutralization technique may be an important tool to distinguish between presence of multiple chemical species and differential charging. © 2009 Elsevier B.V. All rights reserved. 1. Introduction In photoemission spectroscopy, bombardment of photons on insulating polymers leaves behind positive charges in the speci- men [1,2] that remains trapped for a very long time [3] owing to their low conductivity. If the sample is perfectly homogeneous then the entire sample is likely to have one charging level. However, for reasons like surface or bulk inhomogeneity in the structure or in the electrical properties, an insulating sample almost always gives rise to differential charging [4–14]. Although these charges may become trapped inside the bulk of a polymer sample, it is the sur- face which is mostly responsible for the charging effects. As for real polymers, due to the presence of defects and impurities, there is a low but finite density of surface states (∼10 16 eV -1 m -2 ) that are localized in nature and can act as charging sites. Superb sen- sitivity of the XPS technique in terms of shifting of the peaks by several tens of electron volts for an extremely low charge density (∼10 -8 C/m 2 ) [7,15] allows this method to become an effective tool to study bombardment induced charging phenomena and related physical properties of materials. On one hand several efforts were made towards circumventing the effect of charging through bias- ing of sample [2,6] or using electron flood gun and positive ions [6,8,16] through effective surface neutralization of the sample. On the other hand, there have been a number of studies to utilize the ∗ Corresponding author. E-mail address: manabendra.mukherjee@saha.ac.in (M. Mukherjee). phenomena of charging as such for the understanding of different sample properties [17–26]. In our recent studies [4,5] we have used a controlled surface neutralization technique using an electron gun to demonstrate the kinetics of neutralization of charged polymer surfaces. This tech- nique enables us to have continuously varying equilibrium surface charging conditions on insulating polymer surfaces under X-ray irradiation. In those studies it was possible to explain the systematic behavior in the apparently distorted spectra with a model of dif- ferentially charged surface domains. The spectra were analyzed as a combination of two peaks one of which was transient with varia- tion of electron flux and the other was locked at a fixed energy value at all electron flux. The transient and locked peaks were described as due to the positively charged and slightly negatively charged or overcompensated surface domains respectively. We have also shown that the non-linear kinetic response in the growth of the area of the overcompensated domains was due to a percolation transition. These studies on neutralization kinetics were focused on homo- geneous thick samples. However, it has been observed earlier that for samples heterogeneous in composition, charging depends on the electron affinity and band gap values of the constituent materials [6,8]. It has also been predicted that in a composite mate- rial trapped charge density of a particular component increases when the dimension of the same in the material is reduced [6]. An ideal specimen to investigate neutralization kinetics in a multiphase system could be a nanocomposite material where microscopic conducting islands are embedded in an insulating 0368-2048/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.elspec.2009.09.010