It is clear that low-dimensional films can have significantly different properties than those of their bulk counterparts. We felt that the ALD body of literature would be significantly advanced if QC were experimentally demonstrated, as it would then offer an alternative process to the more standard molecular beam epitaxy (MBE) to fabricate such structures. ALD offers the added advantage of not being line-of-sight dependent, as the gas-phase molecules only chemisorb to surfaces (and surfaces of any geometry) that have proper functional groups. So developing ALD techniques that deposit quantum-confined layers can allow QC attributes to be added to innumerable flat, porous or even particle-based substrates and enhance a variety of applications.

In this study, recently published in Nanotechnology, amorphous TiO2 ALD films of 4–15 nm in total thickness were deposited on wafers and the absorbance band edge for each was measured using spectroscopic ellipsometry (figure 1). We used sound statistical methods to effectively design the experiments and were subsequently able to model the parameters that best described the change in bandgap. Using a regression line based on significant factors, we obtained values for the static dielectric constant and the effective mass of the electrons and holes as described in the Brus model shift. We explicitly showed that even in nanoscale amorphous TiO2 films, QC can occur and that the effective mass is approximately an order of magnitude lower than literature values. ALD may become a commercially viable technique to fabricate quantum-confined nanostructures.