Microplasma-Induce Liquid Chemistry for Stabilizing of Silicon Nanocrystals Optical Properties in Water Somak Mitra, y Vladimir  Svrcek, y Davide Mariotti,* Tamilselvan Velusamy, Koiji Matsubara, Michio Kondo In this report, we demonstrate stabilization of photoluminescence (PL) properties of environmentally and biologically friendly silicon nanocrystals (SiNCs) in water through atmospheric pressure radio-frequency (RF) microplasma processing at room temperature. The PL of the SiNCs is enhanced after microplasma processing, which involves three-dimensional engineering of SiNCs directly in water avoiding degra- dation by surface functionalization. Moreover, we compare the RF microplasma process with direct-current microplasma processing, whereby the two approaches lead to very similar SiNCs optical properties and surface characteristics. The induced unique chemistry and SiNCs stability in water have wide implications for the SiNCs processability and applications in energy devices, biology and medicine. 1. Introduction Silicon nanocrystals (SiNCs), having diameter less than 10 nm exhibit quantum confinement effects that manifest a set of unique properties with consequent opportunities for diverse application fields. [1–8] In order to improve and broaden the utilization of SiNCs in different application fields, it has become essential to understand the basic optical and electronic properties of SiNCs with a range of surface characteristics. Improved processing capabilities can lead to increase the degree of surface passivation and tailor the type of terminations of tunable quantum- confined SiNCs. [9,10] Dispersion of SiNCs in water is particularly challenging due to their degradation over time and therefore surface functionalization approaches that can stabilize SiNCs in aqueous solution without using lengthy organic ligands are highly desirable. [11] Previous studies showed that, for instance, the photoluminescence (PL) stability can be somewhat improved either by capping SiNCs with bio-compatible polymers [12] or with an ultra- thin-oxide layer. [13] It follows that surface processing techniques directly in aqueous solution capable of mini- mizing contamination and other undesired effects would be very useful. [10] In this work, we report that a radio-frequency (RF) microplasma in a jet configuration is a very efficient tool for S. Mitra, D. Mariotti, T. Velusamy Nanotechnology and Integrated Bio-Engineering Centre (NIBEC), University of Ulster, Newtownabbey, BT37 0QB, UK E-mail: d.mariotti@ulster.ac.uk V.  Svrcek, K. Matsubara, M. Kondo Research Center for Photovoltaic Technologies, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8568, Japan y These authors contributed equally to this work. Full Paper Plasma Process. Polym. 2014, 11, 158–163 ß 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 158 DOI: 10.1002/ppap.201300097 wileyonlinelibrary.com