Si nanoparticles with diameter of 1-20 nm have been fabricated from Si swarf by use of a beads milling method. Treatment with dilute hydrofluoric acid stabilizes Si nanoparticles, and the thickness of the SiO2 layer formed by leaving nanoparticles in air for one week is only 1.2 nm. p-Si nanoparticles/crystalline n-Si structure shows rectifying behavior, indicating formation of pn-junction. Treatment with nitric acid followed by heating at 900 degrees C greatly decreases series resistance, showing that the ultrathin SiO2 layer formed by nitric acid oxidation melts and is bound to surrounding nanoparticles. p-type Si nanoparticles/n-type crystalline Si structure shows rectifying behavior and the photovoltaic effect, indicating that Si nanoparticles are applicable to solar cells. (C) 2014 Elsevier B.V. All rights reserved.