Electronic Doping in Semiconductor Nanocrystals
Final Report Abstract
The challenge in obtaining and understanding functional doping of nanocrystals is, to control and determine the distribution of the dopant atoms relative to the particle surface and the location of the dopant atoms relative to the crystal lattice. Our project shed light on optical, electronic and especially structural changes involved with the doping of CdSe and ZnO nanocrystals. The observed changes are intriguing and complex. In case of CdSe nanocrystals doped with Ag by ion exchange Ag is located on tetrahedral interstitial sites with a local structure similar to Ag2Se. Ag is not located at the particle surface but incorporated into the nanocrystals. Already a few Ag atoms enhance the fluorescence of the CdSe nanocrystals dramatically. In antimony doped zinc oxide generated by gas phase synthesis Sb atoms substitute Zn and are coordinated to five oxygen atoms similar to Sb in Sb2O3 whereas Mn is substituting Zn in ZnO with tetrahedral oxygen coordination. We also observed that the surface of the nanocrystals can alternatively be employed for charge carrier transfer – ‘surface doping’ – as has been shown for cysteine chemisorbed on ZnO nanocrystals in colloidal dispersion. Here, with increasing cysteine concentration the intensity of the defect luminescence decreases by orders of magnitude, the near band edge increases in intensity substantially and displays a large blue shift. Initially, Ag doped CdSe was thought to be an ideal candidate for EXAFS analysis of dopant location in nanocrystals as all K-edge spectra are easily accessible. Surprisingly, the EXAFS data of Ag doped CdSe showed very little contribution beyond the first coordination shell which made the localization of the Ag dopant even more challenging. Although an excess of oxygen was supplied during CVS of Cu containing samples (CuAlO2, copper oxide, etc.), the conditions are still reducing as shown by the synthesis of Cu2O from Cu(acac)2 and might be one reason for the so far unsuccessful direct CVS of Cu-Al delafossite. The control of the gas phase reduction potential seems, therefore, a key parameter to generate complex metal oxides containing elements which are able to form various oxidation states. This is the topic of our project in the DFG Research Unit FOR 2284.
Publications
- Electronic impurity doping on CdSe nanocrystals, Nano Lett., 12 (2012) 2587–2594
A. A. Sahu, M. Sung Kang, A. Kompch, C. Notthoff, A. W. Wills, D. Deng, M. Winterer, C. D. Frisbie, and D. J. Norris
(See online at https://doi.org/10.1021/nl300880g) - The Quest for Direct Gas-Phase Synthesis of p-Type TCOs, MRS fall meeting 2012, Boston, USA, 25.11.2012 - 30.11.2012
K. A. Kompch and M.Winterer
- Towards Functional Nanoparticles: Gas-Phase Doping of Zinc Oxide, Nano 2012 – International Conference on NanoStructured Materials, Rhodos, Greece 26.8.-31.8.2012
E. M. Winterer
- Chemical Vapor Synthesis and Characterization of Sb-Doped ZnO Nanoparticles – Where is the Dopant Located? MRS fall meeting 2014, Boston, USA, 30.11.2014 - 05.12.2014
I. A. Kompch, S. Lorenz and M. Winterer
- . A. Sandmann, A. Kompch, V. Mackert, C. H. Liebscher, and M. Winterer, Interaction of L-cysteine with ZnO: Structure, surface chemistry, and optical properties, Langmuir, 31 (2015) 5701–5711
B. A. Sandmann, A. Kompch, V. Mackert, C. H. Liebscher, and M. Winterer
(See online at https://doi.org/10.1021/la504968m) - EXAFS investigation of Sb-doped ZnO nanoparticles. XAFS16, Karlsruhe, Germany 23.08.2015 - 28.08.2015
L. A. Kompch, S. Lorenz and M. Winterer
- Localization of Ag dopant atoms in CdSe nanocrystals by reverse monte carlo analysis of EXAFS spectra, J. Phys. Chem. C 119 (2015) 18762–18772
C. A. Kompch, A. Sahu, C. Notthoff, F. Ott, D. J. Norris, and M. Winterer
(See online at https://doi.org/10.1021/acs.jpcc.5b04399)
