It was reported [H. Hosono &etal;, Appl. Phys. Lett.65, 1632 (1994)] that nanometer-sized crystalline (nc) Ge colloid particles were formed by implantation of protons into 0.1GeO2–0.9 SiO2glasses at room temperature. The depth profiles of Ge colloids and the density of Si–OH or Ge–OH created by the implantation were measured and compared with those of energy deposition in order to examine the formation mechanism of Ge colloids by proton implantation. The depth region of nc-Ge particles was found to correspond to the overlapped region between the OH distribution and the peak of electronic energy deposition. Transmission electron microscopic observation revealed that the size of Ge colloid particles created by proton implantation was close to that ofGeO2-rich particles occurring in the substrate glasses. These results indicate thatGeO2-rich particles are converted into Ge particles by a combined effect of the electronic excitation and the chemical reaction of implanted protons. A mechanism was proposed consisting of displacement of bridging oxygen into interstitials by electronic excitation and subsequent trapping of the oxygen interstitials by a formation of OH groups. ©1997 American Institute of Physics.