Sub - nanometer resolved measurement of the tunnelling effective mass using bulk plasmons

Superlattices are periodic structures where the constituents alternate between low and high band gap materials; the resulting quantum confinement tailors the resulting device's properties and increases their operating speed. To understand the properties of such structures on the nanoscale, the electronic structure needs to be sampled with high spatial resolution. Here we show that, in layered structures, the bulk collective oscillation of the sample's electrons can be defined for 'sandwiched' layers as thin as 5Å, due to the very effective screening at the 'sandwiched' layer's interfaces, well below the bulk plasmon extinction distances. Using this, we measure the quantum confinement in diamond-like carbon superlattices as a function of well width, as derived from the plasmon energy, and show that it is well described by the 'particle-in-a-box' model. We