Photoacoustic (PA) spectra were obtained for CdSe nanorods (NRs) of different
aspect ratios, prepared via the organometallic synthesis. The second derivative spectra were
used to have an accurate determination of the different excitonic transitions. Using the lowest
transition energy (band gap) 1S(e)-1S1/2(h) and applying the effective mass model, the NRs
diameters were determined. The obtained diameters were then compared to direct
measurements of scanning tunneling microscopy (STM) and XRD. It is observed that the band
gap depends on the diameter of the rods due to quantum confinement effect, since diameters
are of the order of the bulk CdSe Bohr radius. The second derivative of the PA spectra for
CdSe NRs also shows clearly a second excitonic transition1P(e)-1P1/2(h) in contrast to UVVis
absorption spectra carried out for colloidal samples. The thermal parameters for samples
were also measured and compared to the bulk values. |
