Production of nanoparticles composed of ionic liquid [C(4)mpyrr][NTf2], N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl) imide, was demonstrated by a gas aggregation technique under low pressure. The diameter spectra were measured by a differential mobility analyzer (DMA) and were dependent on the heating temperature. Photoelectron spectra for the nanoparticles diameter-selected at 10 nm were also measured by X-ray photoelectron spectroscopy (XPS), and their chemical composition and structure were identified by comparison with photoelectron spectra for neat ionic liquid. The form and surface structure of the nanoparticles deposited onto an Au-coated Si substrate were also determined. (C) 2008 Elsevier B.V. All rights reserved.