The effect of small elongations on the electronic and optical signatures in InAs nanocrystal quantum dots

We present a detailed theoretical investigation of the electronic structure and optical properties of InAs nanocrystals at the transition from spheres to rods. Using a semiempirical pseudopotential approach, we predict that, despite the qualitative similarity of both intra- and inter-band optical spectra, for NCs with R > 15 Å even slight elongations should result in shifts of the order of hundreds of meV in the spacings between STM peaks measured in the positive bias regime, in the position of the intra-band absorption peaks associated with transitions within the conduction band and in the separation between the first and the fifth peak in PLE experiments. Our results show that, based on the spectroscopic data, it should be possible to discriminate between spherical and elongated NCs with aspect ratios of length over diameter as small as 1.2. Indeed our results suggest that many nominally spherical experimental samples contained a large fraction of slightly elongated structures.