EDITORIAL pubs.acs.org/JPCL
A New Decade for Semiconductor Nanocrystal Research in Physical Chemistry their frequency spectrum and the elastic modulus.6 Krauss and Peterson7 give an enlightening account of single NC photoluminescence blinking. Blinking,8 which is caused by surface trap states and how they interact with excitons, has both puzzled and frustrated researchers for more than a decade. This Perspective explains the fundamental processes at play in blinking, how researchers have designed nonblinking NCs, and what questions remain for the future. Zhong Lin Wang9 describes how the electrical potential results from strain deformation of wurtzite structure crystals. Applications of this effect for future technologies are envisioned, for example, to trigger or switch devices by applying force-piezotronics. I hope that these Perspectives inspire readers and set the scene for future research. Some of the very recent papers from J. Phys. Chem. C suggest, in addition to the areas highlighted in the Perspectives, that opportunities remain, for example for femtosecond studies of NCs.10-13 Indeed, as researchers apply sophisticated new tools and theories to high-quality samples, deeper insights into NCs and new phenomena will be discovered over the coming decade. I look forward to reading about those ground-breaking contributions in future issues of J. Phys. Chem. Lett.!
The nanoscience revolution has impacted physical chemistry, essentially inspiring a host of new materials to study and questions to address. Recognizing the importance of nanoscale systems in current research, the Journal of Physical Chemistry introduced Part C in 2007. This section of the journal has been hugely successful and published 3076 high-quality papers in 2009. Communications are now published solely in the Journal of Physical Chemistry Letters, enhancing the visibility, impact, and citability of that work. One area of prominence is the synthesis and study of semiconductor nanocrystals (NCs). Acharacteristic of the field is that synthesis and study of the electronic properties of NCs have progressed synergistically. That comes as no surprise, given that early attempts to prepare small, crystalline semiconductor colloids were inspired by predictions that quantum confinement would yield striking size-tunable optical properties. High quality NCs;uniform, crystalline, well-characterized materials with narrow size and shape distributions;are central to successful studies of optical and electronic properties, and leading researchers in the field strive for optimal materials to serve as a foundation of their literature reports. These qualities are epitomized in the breakthrough work of Murray et al.,1 providing a splendid example for graduate students. Synthetic creativity has extended the field to realizations of additional tuning of optical properties by shape, strain, and elemental composition,2 while light-initiated dynamics have been manipulated by epitaxial growth of one semiconductor to another to produce NC heterostructures.3 Thus, over the past decade, the synthetic “toolbox” for colloidal chemistry has expanded enormously. In parallel, new questions for physical chemistry have emerged, including how physical properties like melting point are modified in NCs compared to bulk materials and how we can understand the spectroscopy of NCs. Deeper consideration of the latter question shows why nanoscale systems are justifiably unique because their spectroscopy cannot satisfactorily be understood using wellestablished theories for molecules or bulk semiconductors. The four Perspectives in this issue of J. Phys. Chem. Lett. give a flavor of the field of NCs. They span the topics of synthesis, physical properties, and light-induced dynamics. Song Jin and co-workers4 describe the subtleties of crystal growth mechanisms that can be exploited to grow extraordinarily complex nanostructures with surprising reproducibility. They show how formation of dislocations during crystal growth can be used to control structure;another addition to the toolbox. Anne Myers Kelly5 surveys vibrations in semiconductor NCs, known as phonons (vibrational quasiparticles from solid-state physics). She describes their origins and highlights some lack of consensus in literature reports; something to be addressed in future studies. A notable and relatively little explored feature of acoustic phonons unique to NCs is the interrelationship between the size dependence of
r 2010 American Chemical Society
AUTHOR INFORMATION Corresponding Author: *E-mail:
[email protected].
Gregory D. Scholes* Department of Chemistry, Institute for Optical Sciences and Centre for Quantum Information and Quantum Control, University of Toronto, 80 St. George Street, Toronto, Ontario, M5S 3H6 Canada
REFERENCES (1)
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Murray, C. B.; Norris, D. J.; Bawendi, M. G. Synthesis and Characterization of Nearly Monodisperse CdE (E = S, Se, Te) Semiconductor Nanocrystallites. J. Am. Chem. Soc. 1993, 115, 8706–8715. Yin, Y.; Alivisatos, A. P. Colloidal Nanocrystal Synthesis and the Organic-Inorganic Interface. Nature 2005, 437, 664–670. Scholes, G. D. Controlling the Optical Properties of Inorganic Nanoparticles. Adv. Funct. Mater. 2008, 18, 1157–1172. Jin, S.; Bierman, M. J.; Morin, S., A. A New Twist on Nanowire Formation: Screw Dislocation-Driven Growth of Nanowires and Nanotubes. J. Phys. Chem. Lett. 2010, 1, 1472–1480. Kelley, A. M. Electron-Phonon Coupling in CdSe Nanocrystals. J. Phys. Chem. Lett. 2010, 1, 1296–1300.
Received Date: March 28, 2010 Accepted Date: April 7, 2010 Published on Web Date: May 06, 2010
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DOI: 10.1021/jz100408r |J. Phys. Chem. Lett. 2010, 1, 1504–1505
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Huxter, V. M.; Lee, A.; Lo, S. S.; Scholes, G. D. CdSe Nanoparticle Elasticity Scales with Size. Nano Lett. 2009, 9, 405–409. (7) Krauss, T. D.; Peterson, J. J. A Bright Future for Fluorescence Blinking in Semiconductor Nanocrystals. J. Phys. Chem. Lett. 2010, 1, 1377–1382. (8) Nirmal, M.; Dabbousi, B. O.; Bawendi, M. G.; Macklin, J. J.; Trautman, J. K.; Harris, T. D.; Brus, L. E. Fluorescence Intermittency in Single Cadmium Selenide Nanocrystals. Nature 1996, 383, 802–804. (9) Wang, Z. L. Piezotronic and Piezophototronic Effects. J. Phys. Chem. Lett. 2010, 1, 1388–1393. (10) Rawalekar, S.; Kaniyankandy, S.; Verma, S.; Ghosh, H. N. Ultrafast Charge Carrier Relaxation and Charge Transfer Dynamics of CdTe/CdS Core-Shell Quantum Dots as Studied by Femtosecond Transient Absorption Spectroscopy. J. Phys. Chem. C 2010, 114, 1460–1466. (11) McKimmie, L. J.; Lincoln, C. N.; Jasieniak, J.; Smith, T. A. Three-Pulse Photon Echo Peak Shift Measurements of Capped CdSe Quantum Dots. J. Phys. Chem. C 2010, 114, 82–88. (12) Boulesbaa, A.; Huang, Z. Q.; Wu, D.; Lian, T. Q. Competition between Energy and Electron Transfer from CdSe QDs to Adsorbed Rhodamine B. J. Phys. Chem. C 2010, 114, 962–969. (13) Peng, P.; Sadtler, B.; Alivisatos, A. P.; Saykally, R. J. Exciton Dynamics in CdS-Ag2S Nanorods with Tunable Composition Probed by Ultrafast Transient Absorption Spectroscopy. J. Phys. Chem. C 2010, 114, 5879–5885.
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