AVS 57th International Symposium & Exhibition
    Energy Frontiers Topical Conference Thursday Sessions
       Session EN-ThP

Paper EN-ThP10
Optical and Thermal Studies on CdSe Quantum Dots and Rods

Thursday, October 21, 2010, 6:00 pm, Room Southwest Exhibit Hall

Session: Energy Frontiers Topical Conference Poster Session
Presenter: H. Talaat, Ain Shams University, Egypt
Authors: H. Awad, Ain Shams University, Egypt
S. Abdallah, Ain Shams University, Egypt
K. Easawib, Benha University, Egypt
S. Negm, Benha University, Egypt
H. Talaat, Ain Shams University, Egypt
Correspondent: Click to Email
CdSe nanoparticles have attracted a great deal of scientific interest recently, because of the sensitivity of their optical and non-radiative properties to their size and shape, and their applicability in high efficiency photovoltaic solar cells [1]. As the size of a material falls to the nanometer length scale, the material properties become sensitive not only to the particles size, but also to their shapes. The optical (band gap width) and thermal properties of different sized CdSe quantum dots (QDs) and nano rods (NRs) of different aspect ratios have been characterized and compared using photoacoustic (PA) techniques. CdSe colloidal nanocrystals were prepared by the method of Talapine et al. [2], on the other hand, CdSe nanorods were prepared according to Manna et al [3]. A conventional PA setup with (PAR model 6003) PA cell was used to measure the optical absorption spectrum, and the thermal parameters. The PA absorption spectra for CdSe QDs and NRs in Figures (1.a) and (2.a), respectively, show a significant red shift in all cases as the nanoparticles increase in size. We used the second-derivative technique, to determine the peaks positions for QDs and NRs (Figure (1.b) and (2.b), respectively). The lowest energy transition is between 1S(e) and 1S3/2(h) states in case of QDs and between 1S(e) and 1S1/2 states in case of NRs. The UV-Vis absorption spectra were also obtained for the samples and give a comparable values for the first excitonic transition peaks. The band gap of the nanoparticles Eg(NC) is determined by the energy of the lowest 1S(e)-1S3/2(h) transition corrected for the coulomb e-h interaction, NOTE: WE ARE UNABLE TO INCLUDE FORMULAS where mhh is the heavy hole mass, e is the electron charge, and ε is the dielectric constant for bulk CdSe. The QDs radii were found to be within 2.52 nm and 2.86 nm in agreement with the dimensions obtained by XRD. In the case of NRs, the radial dimensions determined in the same way, were found to be between 2.28 nm and 2.89 nm in good agreement with STM measurements, which gave the rod lengths as 19-50 nm. The second peak in the PA spectra could be described by the transition coupling the 1P e electron state with the 1P 1/2 hole state. Furthermore, the thermal parameters of the CdSe nanoparticles (diffusivity α, effusivity e and conductivity k) as determined by PA technique for both the QD's and NR's show an increase by almost an order of magnitude from the bulk values, however, there is no observable variations between the QD's and the NR's thermal parameters.

NOTE: WE ARE UNABLE TO INCLUDE FIGURES

1. E. Hendry, M. Koeberg, F. Wang, H. Zhang, C. deMello Donega', D. Vanmackelbergh, and M. Bonn, Phys. Rev. Lett. 96, 057408, 2006.

2. D. V. Talapin, A. L. Rogach, A. Kornowski, et al, Nanoletters, 1, 207, 2001.

3. L. Manna, E. C. Scher, A. P. Alivisatos, J. Am. Chem. Soc. 122,12700, 2000.