Semiconductor nanocrystals : synthesis, characterization, and instrumentation for femtosecond spectroscopy

Semiconductor nanocrystals exhibit strongly size-dependent absorption spectra and consequently are of great interest for use in nanoscale devices. As the excited states of these crystals are short-lived, spectroscopic investigation of the nature and size dependence of their energy levels requires femtosecond laser pulses. We have synthesized cadmium selenide nanocrystals and constructed a femtosecond instrument around a commercial laser system from Coherent to study them.The instrument is capable of measuring the autocorrelation and crosscorrelation of laser pulses and can measure the transient absorption dynamics of nanocrystals via pump-probe spectroscopy. A novel means of simultaneously measuring the dynamics associated with two different excitation wavelengths has also been employed.I have written a LabVIEW program for data acquisition from this instrument, capable of reducing measurement noise through averaging and rejection of bad measurements. We have successfully used this software in probing specific transitions in cadmium selenide nanocrystals