Preparation and thermal stability of silicon nanoparticles

Silicon nanoparticles were prepared in a homemade apparatus by means of a d c sputtering method in which the condensates were collected directly from t he cold surface of a liquid nitrogen trap. They were dispersed in 2-propano l under ultrasonic agitation, and dried in the atmosphere. The particles we re found to compose of tiny silicon crystals and were only mildly oxidized. Various samples were prepared with different annealing times and temperatu res in ultrahigh vacuum. XPS results show that, in the particles, the Si-O bonds of the Si4+ state are the most stable, followed next by the unoxidise d state Si-0. The intermediate oxidation states are the least stable; they exist only at sufficiently low temperatures (300 degreesC or lower) and are converted to either Si-0 or Si4+ at higher temperatures. (C) 2001 Elsevier Science B.V. All rights reserved.