Bulding Better Quantum
Dots-Doping and Going 'Green'
Quantum dots are potential materials for next generation solar cells, but manipulating the conductivity of these materials remains a challenge. A goal of our research is develop economically viable colloidal methodologies to produce doped quantum dots and study their fundamental properties. Doping nanoparticles and quantum dots results in new and interesting science. Critical components of this research are to find ways to circumvent challenges and to understand the underlying mechanisms of doping quantum dots. In addition, the currently available quantum dot materials are not sustainable materials to address global electricity needs. We are developing materials that are potentially more environmentally friendly and abundant. The young artist's (Hyeon Jung Kim) conception below shows the structure of a single quantum dot that is used as a model in our doping studies.
Roy, S.; Aguirre, A.; Higgins, D. A.; Chikan, V., Investigation of Charge Transfer Interactions in CdSe Nanorod P3HT/PMMA Blends by Optical Microscopy. The Journal of Physical Chemistry C (2011), 116 (4), 3153-3160.
•Chikan, V., Challenges and Prospects of Electronic Doping of Colloidal Quantum Dots: Case Study of CdSe. J. Phys. Chem. Lett. (2011), 2 (21), 2783-2789.
•Santanu Roy, C. T., Fadzai Fungura, Pinar Dagtepe, Jacek Jasinski and Viktor Chikan, Progress towards Producing n-type CdSe Quantum Dots: Tin and Indium Doped CdSe Quantum Dots. J. Phys. Chem. C (2009), 113 (30), 13008–13015.
•Christopher Tuinenga, Jacek Jasinski, Valerie J. Leppert; Takeo Iwamoto, Viktor Chikan, In situ Observation of Heterogeneous Growth of CdSe Quantum Dots; Effect of Indium Doping on the Growth Kinetics, ACS Nano, 2(7), 1411–1421, (2008)
• Mandal, P. K. & Viktor Chikan Terahertz Conductivity of n-type (charged) CdSe Quantum Dots. Nano Lett., 7 (8), 2521 -2528, (2007)
Colloidal Synthesis of Novel Nanomaterials
Our group has developed a variety of new nanomaterials at Kansas State University over the years. Many of the materials are the result of the hypothesis driven research where we intend to investigate a particular material in terms of its function, however in some instances we stumbled across some new materials. The picture below shows a gallery of nanoparticles developed by our group taken with high resolution transmission electron microscope.
•Dahal, N.; Jacek Jasinski; Valerie J. Leppert; Viktor Chikan, Synthesis of Water-Soluble Iron-Gold Alloy Nanoparticles. Chem. Mater., 20 (20), 6389–6395, (2008)
•Dahal, N.; Chikan, V., Phase-Controlled Synthesis of Iron Silicide (Fe3Si and FeSi2) Nanoparticles in Solution. Chem. Mater. (2010) 22, (9), 2892-2897.
Dahal, N.; Chikan, V., Synthesis of Hafnium Oxide-Gold Core-Shell Nanoparticles. Inorganic Chemistry 2012, 51 (1), 518-522.
Growth Kinetics of Nanoparticles
Colloidal synthesis of nanomaterials is cheap process that can be easily scaled up for industrial production. Controlling the growth of nanoparticles in colloidal solution is an important step towards developing materials with well-defined optical and physical properties. Our goal is to understand how the interplay of thermodynamics and growth kinetics determines the size and the size distribution of nanoparticles. The thermodynamic control of the nanoparticle growth may lead to the formation of magic sized nanoparticles. In the example below, we are observing the birth of magic sized CdTe quantum dots and its 'quantized' aggregation into larger quantum dots. LEFT figure shows the 'usual' monomer induced growth of CdSe quantum dots. RIGHT figure shows the time evolution of the absorption spectra of CdTe quantum dot solution during the synthesis. The first step is the formation of magic sized CdTe quantum dot, which subsequently undergoes aggregation.
•Dagtepe, P.; Chikan, V., Quantized Ostwald Ripening of Colloidal Nanoparticles. J. Phys. Chem. C (2010), 114, (39), 16263-16269.
•Dagtepe, P.; Chikan, V., Effect of Cd/Te Ratio on the Formation of CdTe Magic-Sized Quantum Dots during Aggregation. J. Phys. Chem. A (2008), 112, (39), 9304-9311.
•Dagtepe, P., Jacek Jasinski, Valerie J. Leppert; Viktor Chikan, Quantized Growth of CdTe Quantum Dots; Observation of Magic Sized CdTe Quantum Dots. J. Phys. Chem. C, 111 (41), 14977 -14983, (2007)
Magnetic Hyperthermia by Superparamagnetic Nanoparticles
Magnetic hyperthermia represents a one step development towards selective and uniform heating of cancerous tissue by introducing nanometer sized magnetic particles close to a tumor site. The temperature increase of the tissue can significantly contribute to the destruction of the cancerous cells. Heating takes place by power absorption of the nanometer sized superparamagnetic and ferromagnetic particles from alternating magnetic field. Our research explores ideas to utilize these relaxation processes of superparamagnetic nanoparticles more effectively, therefore reducing the required nanoparticle load to effectively eliminate cancer cells. The images below show the conceptual difference between Brownian and Neel relaxation of a magnetic spin in a superparamagnetic nanoparticle, respectively. Ultimately, these two mechanisms are the key components that we want to understand and control in biological systems for developing effective cancer treatments.
•Dani, R. K.; Wang, H.; Bossmann, S. H.; Wysin, G.; Chikan, V., Faraday rotation enhancement of gold coated Fe2O3 nanoparticles: Comparison of experiment and theory. J. Chem. Phys. (2011), 135 (22), 224502-9.
•Balivada, S.; Rachakatla, R. S.; Wang, H.; Samarakoon, T.; Dani, R. K.; Pyle, M.; Kroh, F.; Walker, B.; Leaym, X.; Koper, O.; Tamura, M.; Chikan, V.; Bossmann, S.; Troyer, D., A/C magnetic hyperthermia of melanoma mediated by iron(0)/iron oxide core/shell magnetic nanoparticles: a mouse study. BMC Cancer (2010) 10, (1), 119.
•Raj Kumar Dani, Myungshim Kang, Mausam Kalita, Paul E. Smith, Stefan H. Bossmann and Viktor Chikan MspA Porin-Gold Nanoparticle Assemblies: Enhanced Binding through a Controlled Cysteine Mutation. Nano Lett., 8(4); 1229-1236, (2008)
Kansas State University, Department of Chemistry, NSF (ELECT, PHOTONICS, & MAG DEVICE),COBRE (NIH) Center for Cancer Experimental Therapeutics, The Terry C. Johnson Center for Basic Cancer Research, Harvey McCarter, University Small Research Grant, President’s Faculty Development Award, American Chemical Society Doctoral New Investigator