Preparation and thermal stability of silicon nanoparticles

Silicon nanoparticles were prepared in a homemade apparatus by means of a dc sputtering method in which the condensates were collected directly from the cold surface of a liquid nitrogen trap. They were dispersed in 2-propanol under ultrasonic agitation, and dried in the atmosphere. The particles were found to compose of tiny silicon crystals and were only mildly oxidized. Various samples were prepared with different annealing times and temperatures 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 unoxidised state Si0. The intermediate oxidation states are the least stable; they exist only at suf®ciently low temperatures (3008C or lower) and are converted to either Si0 or Si4‡ at higher temperatures. # 2001 Elsevier Science B.V. All rights reserved.