Gresback et al. Nanoscale Research Letters 2011, 6:68 http://www.nanoscalereslett.com/content/6/1/68 Page 5 of 6 Figure 6 Representative PL spectra of InP/ZnS core/shell NCs synthesized with various plasma residence times. residence time of NCs in the plasma. This synthesis pro- cess yields NCs which are bare and free-standing, which may simplify device integration. In addition, we find that these NCs can easily form a colloid with a variety of ligands, which then enables application of well-estab- lished colloidal-processing techniques. After capping the InP NCs with a ZnS shell, PL QYs between 10 and 15% were observed. This study has demonstrated that it is Figure 7 Effect of plasma residence time on peak PL emission from InP/ZnS core/shell structures. Inset: Layer-by-layer effect of ZnS growth on PL intensity where whole layers represent a full cycle of Zn and S injections. possible to synthesize compound semiconductor NCs with plasma, opening up the possibility of a wider range of the plasma-synthesized NC materials. Acknowledgements This study was supported primarily by the MRSEC Program of the National Science Foundation under Award Number DMR-0819885. Partial support through the University of Minnesota Center for Nanostructure Applications is acknowledged. The authors utilized the University of Minnesota Characterization Facility which receives partial support from the NSF under the NNIN program. Author details 1Department of Mechanical Engineering, University of Minnesota, Minneapolis, MN, USA 2Department of Chemistry, University of Minnesota, Minneapolis, MN, USA Authors’ contributions RG synthesized the InP quantum dots, contributed to the ZnS shell functionalization, and drafted the manuscript. RH contributed to the ZnS shell functionalization. UK and WLG were involved in the scientific guidance of the research and in revising the manuscript. Competing interests The authors declare that they have no competing interests. Received: 24 August 2010 Accepted: 12 January 2011 Published: 12 January 2011 References 1. Murray CB, Norris DJ, Bawendi MG: Synthesis and characterization of nearly monodisperse CdE (E = sulfur, selenium, tellurium) semiconductor nanocrystallites. J Am Chem Soc 1993, 115:8706-8715. 2. Efros A, Rosen M, Kuno M, Nirmal M, Norris D, Bawendi M: Band-edge exciton in quantum dots of semiconductors with a degenerate valence band: Dark and bright exciton states. Phys Rev B 1996, 54:4843-4856. 3. Hines MA, Guyot-Sionnest P: Synthesis and Characterization of Strongly Luminescing ZnS-Capped CdSe Nanocrystals. J Phys Chem 1996, 100:468-471. 4. Alivisatos AP: Semiconductor Clusters, Nanocrystals, and Quantum Dots. Science 1996, 271:933-937. 5. Yamaguchi M, Uemura C, Yamamoto A: Radiation damage in InP single crystals and solar cells. J Appl Phys 1984, 55:1429-1436. 6. Micic OI, Curtis CJ, Jones KM, Sprague JR, Nozik AJ: Synthesis and Characterization of InP Quantum Dots. J Phys Chem 1994, 98:4966-4969. 7. Micic OI, Sprague JR, Curtis CJ, Jones KM, Machol JL, Nozik AJ, Giessen H, Fluegel B, Mohs G, Peyghambarian N: Synthesis and Characterization of InP, GaP, and GaInP2 Quantum Dots. J Phys Chem 1995, 99:7754-7759. 8. Battaglia D, Peng X: Formation of High Quality InP and InAs Nanocrystals in a Noncoordinating Solvent. Nano Lett 2002, 2:1027-1030. 9. Xu S, Kumar S, Nann T: Rapid Synthesis of High-Quality InP Nanocrystals. J Am Chem Soc 2006, 128:1054-1055. 10. Mangolini L, Thimsen E, Kortshagen U: High-Yield Plasma Synthesis of Luminescent Silicon Nanocrystals. Nano Lett 2005, 5:655-659. 11. Knipping J, Wiggers H, Rellinghaus B, Roth P, Konjhodzic D, Meier C: Synthesis of High Purity Silicon Nanoparticles in a Low Pressure Microwave Reactor. J Nanosci Nanotechnol 2004, 4:1039-1044. 12. Gresback R, Holman Z, Kortshagen U: Nonthermal plasma synthesis of size-controlled, monodisperse, freestanding germanium nanocrystals. Appl Phys Lett 2007, 91:093119-3. 13. Shenai-Khatkhate DV, DiCarlo RL Jr, Ware RA: Accurate vapor pressure equation for trimethylindium in OMVPE. J Cryst Growth 2008, 310:2395-2398. 14. Xie R, Battaglia D, Peng X: Colloidal InP Nanocrystals as Efficient Emitters Covering Blue to Near-Infrared. J Am Chem Soc 2007, 129:15432-15433. 15. Kruis FE, Fissan H, Peled A: Synthesis of nanoparticles in the gas phase for electronic, optical and magnetic applications–a review. J Aerosol Sci 1998, 29:511-535.