Direct Determination of the Local Polarity in Wurzite Crystals; published as Direct Determination on Local Lattice Polarity in Crystals

In hexagonal crystals with wurtzite structure, physical and chemical properties are different not only along the major c and a axes, but they are also different parallel and anti-parallel to the c-axis. This unique property of wurtzite (A-B) compounds is the result of non-symmetric stacking of the atomic layers along the [0001] direction (Fig. 1, A). Polarity, therefore, was introduced to describe the sequence of the A and B layers along c-axis. In the age of nano-science, these compounds are becoming useful for many applications ranging from CdSe quantum dots and rods to GaN-AlN quantum wells and nano-wires. And in most cases, like in wurtzite III-V nitrides, the existence of directional polarization is the driving force behind their applications. Therefore, the ability to measure polarity at the atomic scale would open new prospects for understanding new phenomena present in these nanosctructures, such as: selective growth of PbSe with a rock-salt structure on the tips of wurtzite colloidal nanorods (1) and classifying of the grain boundaries between zincblend CdTe core and wurtzite CdTe/CdSe branches in nanocrystals (2).