The interfacial chemistry of a barium/silicon oxynitride (SiOxNy)/silicon nanostructure was investigated with x-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS) to determine if SiOxN(y) can serve as a barrier for the barium strontium titanate high-k dielectric. The structure consisted of 17 Angstrom of (4 ML) Ba on a 12 Angstrom SiOxNy barrier layer on a Si(100) substrate. Both XPS and SIMS results suggest that barium oxide (BaO) and silicon dioxide (SiO2) at the Ba/SiOxNy interface react to form similar to 10 Angstrom of multiphase barium silicate even at 300 K. The kinetics of this reaction were accelerated by annealing the structure in a stepwise fashion to 1000 K. During the annealing, the BaO and SiO2 XPS chemical states attenuate leaving two silicate states. Below the silicate layer, in the oxygen poor region of the nanostructure, similar to 10 Angstrom BaSix formed. Annealing the nanostructure to 1000 K for 5 min tested the barrier capabilities of the 12 Angstrom SiOxNy layer. SIMS Ba+, BaSi+, BaSiO+ and Si2N+ signals reveal that Ba containing species do not significantly penetrate below the N drop Si-3 bonds characteristic of SiOxNy. Comparison of similar to 11 Angstrom SiO2 and similar to 12 Angstrom SiOxNy confirms that the N drop Si-3 bonds are the key to the barrier properties. Without N atom incorporation, the Ba+ SIMS signal increased 66% and penetrated similar to 24 Angstrom deeper into the Si substrate after a 5 min 600 K anneal.