The structural characteristics of a silica layer and Si/SiO2 interface formed on Si single-crystal by oxidation in hyperthermal atomic oxygen (AO) and molecular oxygen (MO) at 493K were compared by wide variety of experimental techniques. The hyperthermal AO with kinetic energy of 5.1eV was created by the pulsed laser detonation of oxygen gas. The oxide formed by AO and MO on Si single crystal is amorphous as observed by HRTEM and selected area electron diffraction (SAED). However, the oxide formed by AO has a less random distribution of silicon and oxygen atoms as compared to the oxide formed by MO, as evidenced by the SAED patterns and EELS spectra. In contrast to MO formed silica, initial EELS results across the Si/SiO2 interface revealed no region of suboxides exists near the interface in the AO formed silica. The Si/SiO2 interface formed by AO species was found to be very abrupt and the oxide homogeneous, as opposed to the broad interface and non-homogeneous oxide created by MO, as determined by HRTEM and EELS.