Viktor Chikan, PhD , Kansas State University
We have also found that the addition of ZnS shell greatly impacts the temperature dependent photoluminescence of the particles. The strong temperature dependent component of the doped nanoparticles disappears when the ZnS shell thickness is increased. At this point, we speculate that the dopant could migrate into the shell as a result of the better size match of with the ZnS crystal lattice.
In addition to the above studies, we realized that CdSe material will not be sufficient to address solar energy needs on the global scale. We started exploring the synthesis of sustainable nanoparticles that could be used as a platform for our doping studies. We are the first to develop the colloidal synthesis of crystalline b-FeSi2 nanoparticles.[v] These particles will be used in our future doping studies. In addition, based on our previous observation of heterogeneous growth of the CdSe nanoparticles, we have developed an approach called the quantized Ostwald Ripening[vi] that could be a potential method to produce size focusing of nanoparticles in a colloidal solution.
We hypothesize that the doped CdSe quantum dots will be more electronegative than the neutral quantum dots. We have performed in situ photoluminescence experiments to observe the dissolution and etching of quantum dots. We found increased etching rates in doped quantum dots. The rate of etching increases with the lower ionization energy of the dopant.[vii]
We have successfully secured a larger collaborative NSF funding to address “Climate Change and Energy: Basic Science, Impacts, and Mitigation Science Initiative”. Within this proposal we just started investigating indium doped CdSe nanorod/P3HT composites with single molecule spectroscopy. The results on indium doped CdSe quantum dots from the ACS funding were important to secure our NSF funding.
Several students have worked on the project over the period of years. Summer REU student Fadzai Fungura helped us obtaining terahertz data on doped cDSe quantum dots. Dr. Pinar Dagtepe, Dr. Naween Dahal and Dr. Christopher Tuinenega finished their PhD. Dr. Dagtepe and Dr. Dahal have secured postdoc positions and Dr. Tuinenga is currently in the process of finding postdoc position. Christopher Lewis also secured a job very recently at Halliburton. The ACS grant provided opportunity to all of these students to obtain the necessary experience to secure their employment. In 2009, Chris Tuinenga obtained funds from German Academic Exchange Service and spent a semester in Germany at BASF to learn how prepare solar cells. In 2010, Pinar Dagtepe received a travel fellowship to present her research on conference (Nanomaterials and Nanocatalysis for Energy, Petrochemicals and Environmental Applications) in Cairo sponsored by the US-Egypt Advanced Studies Institute.
[i] Tuinenga, C.; Jasinski, J.; Iwamoto, T.; Chikan, V., In Situ Observation of Heterogeneous Growth of CdSe Quantum Dots: Effect of Indium Doping on the Growth Kinetics. ACS Nano 2008, 2(7), 1411-1421.
[ii] Roy, S.; Tuinenga, C.; Fungura, F.; Dagtepe, P.; Chikan, V.; Jasinski, J., Progress toward Producing n-Type CdSe Quantum Dots: Tin and Indium Doped CdSe Quantum Dots. Journal of Physical Chemistry C 2009, 113(30), 13008-13015.
[iii] Tuinenga, C.; Roy, S.; Heather, S.; Moore, D.; Chikan, V., Gallium Doped CdSe Quantum Dots. Chemistry of Materials 2011, submitted.
[iv] Tuinenga, C. J.; Tvrdy, K.; Chikan, V.; Kamat, P. V., Blue Shift in Transient 1S Bleach Signal in Indium Doped CdSe Quantum Dots. Journal of Physical Chemistry Letters 2011, in preparation.
[v] Dahal, N.; Chikan, V., Phase-Controlled Synthesis of Iron Silicide (Fe3Si and b-FeSi2) Nanoparticles in Solution. Chemistry of Materials 2010,22, (9), 2892-2897.
[vi] Dagtepe, P.; Chikan, V., Quantized Ostwald Ripening of Colloidal Nanoparticles. The Journal of Physical Chemistry C 2010,114, (39), 16263-16269.
[vii] Lewis, C.; Chikan, V., Etching of doped CdSe Quantum Dots in APOL. Journal of Physical Chemistry C 2011, under preparation.