Engineered Semiconductor Nanocrystals: From Synthesis to Application

Jennifer Hollingsworth
Los Alamos National Lab

Abstract:
Particle size or ‘quantum-­?confinement’ effects have been used for decades to tune semiconductor optical and electronic properties. More recently, however, particle size control as the primary means for properties control has been succeeded by nanoscale hetero-­?structuring. In this case, the nanosized particle is further modified to include internal, nanoscale interfaces, generally defined by compositional variations that induce additional changes to semiconductor properties. These changes can entail enhancements to the size-­?induced properties as well as unexpected or ‘emergent’ behaviors. Common structural motifs include enveloping a spherical semiconductor nanocrystal, i.e., a quantum dot, within a shell of a different composition, or converting a semiconductor nanowire into a superlattice nanowire by introducing compositional variations along the nanowire length. In this talk, I will discuss how solution-­?phase synthesis techniques can be used to create these structures with precisely ‘engineered’ complexity and, in many cases, for realizing relevant functionality. Most notably, I will review our experiences with so-­?called ‘giant’ quantum dots, which due to their structure exhibit a range of novel behaviors, including non-­?blinking and non-­?photobleaching behavior with both visible-­? and near-­?infrared-­?emitting examples,1-­?3 as well as remarkably efficient ‘multi-­?exciton’ emission as a result of suppressed non-­?radiative Auger recombination.4 Extending toward  a range of light-­?emission applications, including ‘building blocks’ for solid-­?state devices5,6 and as aqueous-­?phase molecular probes in biology.7 I will also discuss the development of a new synthetic technique—‘flow’ solution-­?liquid-­?solid  growth—for controlled growth of semiconductor nanowires that has permitted new understanding of solution-­?phase nanowire growth mechanisms and the ability to fabricate complex axial heterostructures8 toward optimized nanostructures for thermoelectric energy conversion.

1. Y. Chen et al. J. Am. Chem. Soc. 2008, 130, 5026-­?5027.
2. Y. Ghosh et al. J. Am. Chem. Soc. 2012, 134, 9634.
3. A. M. Dennis et al. Nano Lett. 2012 12, 5545.
4. H. Htoon et al. Nano Lett. 2010, 10, 2401.
5. J. Kundu et al. Nano Lett., 2012, 12, 3031.
6. B. N. Pal et al. Nano Lett. 2012, 12, 331.
7. A. M. Keller, A. M. et al. Adv. Funct. Mater. DOI: 10.1002/adfm.201400349 2014.
8. R. Laocharoensuk et al. Nat. Nanotechnol. 2013, 8, 660.