Photoelectron diffraction patterns of the different silicon sub-oxides have been recorded and compared with simulated patterns for various model structures. Each silicon sub-oxide is embedded in an ordered environment since individual diffraction patterns and differences among them were exhibited. In particular, the intensity maxima are located at different angles. In the simulation the silicon-oxide/silicon interface was assumed to be abrupt and within one atomic layer. Excellent agreement between experimental and calculated patterns was achieved. At the interface, horizontally compressed SiO2 was found. Furthermore, the highest oxidation state of silicon, Si4+, displays a diffraction pattern indicating an ordered structure for this chemical state.