Highly dense amorphous Nb2O5 films with closed nanosized pores

This study is focused on tailoring the porosity of Nb2O5 films during reactive pulsed magnetron sputtering. Dense amorphous films containing nanopores only in deeper regions have been grown at a high rate using substrate temperatures below 60 degrees C. The films exhibit a high refractive index, n(400)=2.54, a low extinction coefficient, k(400)similar to 6x10(-4), a low mechanical stress (-90 MPa), and a negligible thermal shift. The specific depth distribution of the nanopores is believed to be the reason for the optimum trade-off between a high refractive index and low mechanical stress.