Polarization fluorescence microscopy was used to study the nature of the emission and nonlinear absorption dipole of single CdSe/ZnS quantum rods. Rods, with aspect ratios ranging from 2.75 to 15, showed strongly polarized emission consistent with previous one-photon studies. Non- linear excitation showed a sharp angular dependence fully consistent with the predicted two- photon absorption process. Two-photon absorption probes different transitions than linear absorption due to modified parity and angular momentum selection rules. The two-photon absorption dipole was found to be parallel to the emission polarization, and allows achieving highly orientation selective excitation of quantum rods. This is yet a further demonstration of single molecule measurements in unraveling basic principles of light-matter interaction that are otherwise masked by ensemble averaging.

The development of solution based synthesis approaches for preparing nanocrystals of III-V semiconductor presents a significant & important challenge especially with relation to shape control to achieve rod growth. To this end, a novel approach for synthesis of soluble semiconductor quantum rods using metal nanoparticles to direct and catalyze one-dimensional growth is developed. The synthesis method is useful in particular for III-V semiconductor with cubic lattice, where the utilization of surfactant-controlled rod-growth is not easily realized. The growth takes place via the solution–liquid–solid (SLS) mechanism where proper precursors are injected into a coordinating solvent as we reported in earlier work for InAs nanorods. Herein, we report the synthesis of high quality InP nanorods using Indium Acetate and myristic acid with gold nanoparticles as the catalysts in the SLS growth mode. A similar route was successfully developed for the growth of InAs nanorods. We find that the amount of Au catalyst in the reaction is an important parameter to achieving shape control. Transmission electron microscope (TEM) images of InP and InAs nanocrystals revealed that the crystals are mostly rod-shaped. XRD measurements, absorption spectra were preformed for the nanorods characterization.

Optical spectroscopy and Scanning Tunneling Microscopy are used to study the size and shape dependence of the electronic states in CdSe quantum rods. The quantum rods were grown using colloidal chemistry synthesis methods, with good control over size and size distribution. Samples having average rod dimensions ranging from 10 to 60 nm in length and 3.5 to 7 nm in diameter, with aspect ratios varying between 3 to 12, were investigated. Both optical (at 10 K) and tunneling (at 4.2 K, on single rods) spectra show that the level structure depends primarily on the rod diameter and not on length. With increasing diameter, the band gap and the excited state level spacings shifted to the red. The level structure is assigned using a multi-band effective-mass model, showing relatively good agreement with experiment. We shall also discuss the effect of single electron charging on the tunneling spectra, possibly reflecting the quantum rod level degeneracy.