A medium-frequency dielectric barrier discharge (DBD) plasma gun was used to deposit SiO2-like films at ambient temperature under atmospheric pressure. SiO2-like films were deposited on Si and stainless-steel surfaces by flowing Ar gas containing hexamethyldisiloxane (HMDSO) monomer through the gun. The authors found that the chemical structure of the deposited SiO2-like film strongly depended on the HMDSO monomer ratio in the flowing gas and on the incident power. Fourier transform infrared spectroscopy showed no hydroxyl group in the chemical structure under the low HMDSO ratio in flowing gas or high incident plasma power. Scanning electron microscopy and atomic force microscopy revealed that SiO2-like films began to grow as islands and then formed in columns having porosity. Oxygen added to the plasma-gun flow plays a lesser role in the SiO2-like deposition from a DBD plasma gun at atmospheric pressure, and the critical temperature for pure SiO2 formation is also greatly lowered. (c) 2006 American vacuum Society.