We present the surface modification of Si(111) into silicon nitride by exposure to energetic N-2(+) ions. In-situ UHV experiments have been performed to optimize the energy and fluence of the N-2(+) ions to form silicon nitride at room temperature (RT) and characterized in-situ by X-ray photoelectron spectroscopy. We have used N-2(+) ion beams in the energy range of 0.2-5.0 keV of different fluence to induce surface reactions, which lead to the formation of SixNy on the Si(111) surface. The XPS core level spectra of Si(2p) and N(1s) have been deconvoluted into different oxidation states to extract qualitative information, while survey scans have been used for quantifying of the silicon nitride formation, valence band spectra show that as the N-2(+) ion fluence increases, there is an increase in the band gap. The secondary electron emission spectra region of photoemission is used to evaluate the change in the work function during the nitridation process. The results show that surface nitridation initially increases rapidly with ion fluence and then saturates. (C) 2014 Elsevier B.V. All rights reserved.