Methods and apparatus are provided for non-volatile semiconductor devices. The apparatus comprises a substrate having therein a source region and a drain region separated by a channel region extending to a first surface of the substrate, and a multilayered gate structure containing nano-crystals located above the channel region. The gate structure comprises, a gate dielectric substantially in contact with the channel region, spaced-apart nano-crystals disposed in the gate dielectric, one or more impurity blocking layers overlying the gate dielectric and a gate conductor layer overlying the one more impurity blocking layers. The blocking layer nearest the gate conductor can also be used to adjust the threshold voltage of the device and/or retard dopant out-diffusion from the gate conductor layer.