@article {1212,
	title = {Formation of quantum-dot quantum-well heteronanostructures with large lattice mismatch: ZnS/CdS/ZnS},
	journal = {Journal of Chemical Physics},
	volume = {114},
	number = {4},
	year = {2001},
	note = {Little, RB El-Sayed, MA Bryant, GW Burke, S},
	month = {Jan},
	pages = {1813-1822},
	abstract = {Two-dimensional heterostructures have been exploited extensively in the synthesis of optoelectronic devices. Structures with small lattice mismatch can be synthesized readily. Large lattice mismatch in II-VI film heterostructures makes synthesis of devices with these materials more difficult. However, these large mismatch heterostructures usually have useful optical properties. One such heterostructure is the ZnS/CdS system with a large exciton binding energy and a large band gap useful for blue-green emitting devices. In this work, small II-VI nanoparticles are studied. We show that II-VI heterostructures can be made in quantum dots, despite the large bulk lattice mismatch. Two well-known techniques are combined to synthesize first very small ZnS and CdS seed nanoparticles and then do nanoepitaxy on them to produce ZnS/CdS core/shell quantum-dot quantum-well heteronanostructures. These structures are characterized by UV visible absorbance. Measured spectra are compared with electronic level structures calculated for the fabricated heteronanostructures with a tight-binding model. The consistency of the observed spectra with the predicted transitions indicates that the desired core/shell and core/shell/clad structures were grown. The metastability of the ZnS/CdS/ZnS heteronanostructures is attributed to low-temperature construction and small crystal size (<3 nm). The small particle size should produce large surface forces and ZnS core contraction. Also, the small particle size should accommodate strain, as a result of the ZnS/CdS interfacial curvature, which is not possible for planar systems. Furthermore, this new structure is kinetically stabilized against alloying by the large size difference between the Cd2+ ion and Zn2+ ions. We suggest that all of these factors contribute to the formation of quantum-dot quantum-well ZnS/CdS/ZnS heteronanostructures. (C) 2001 American Institute of Physics.},
	isbn = {0021-9606},
	doi = {10.1063/1.1333758},
	author = {Little, Reginald and El-Sayed, Mostafa A and Bryant, G. W. and Burke, S.}
}
@article {1234,
	title = {Effect of different capping environments on the optical properties of CdS nanoparticles in reverse micelles},
	journal = {International Journal of Quantum Chemistry},
	volume = {72},
	number = {4},
	year = {1999},
	note = {Zou, BS Little, RB Wang, JP El-Sayed, MA},
	month = {Apr},
	pages = {439-450},
	abstract = {CdS(E = 2.5 eV) nanoparticles were synthesized in reversed micelles and capped with materials of different band gaps and charge compensation ability: Cd(OH)(2) (4.0 eV), ZnS (3.2 eV), and CdO (2.3 eV). The preparations allowed the examination and comparison of the efficiencies of confinement of the electron and hole by the various capping materials. The absorption and emission spectra of the capped CdS nanoparticles suggest the following: (1) Efficient capping and strong quantum confinement are observed for CdS particles of small size (< 3.8 nm), showing well-resolved photoexcitation spectra; (2) the confinement efficiency improves with capping thickness; (3) although ZnS has smaller band gap than Cd(OH)(2), it was more efficient in surface-charge compensation and it is the best capping agent of the three materials; and (4) the similar band gaps of CdO and CdS resulted spectroscopically in strong mixing between the excited states of these materials. (C) 1999 John Wiley \& Sons, Inc.},
	isbn = {0020-7608},
	doi = {10.1002/(sici)1097-461x(1999)72:4<439::aid-qua27>3.0.co;2-q},
	author = {Zou, Bingsuo and Little, Reginald and Wang, Jianping and El-Sayed, Mostafa A}
}
@article {1257,
	title = {Charge separation effects on the rate of nonradiative relaxation processes in quantum dots quantum well heteronanostructures},
	journal = {Journal of Physical Chemistry A},
	volume = {102},
	number = {33},
	year = {1998},
	note = {Little, RB Burda, C Link, S Logunov, S El-Sayed, MA},
	month = {Aug},
	pages = {6581-6584},
	abstract = {Using time-resolved optical hole (oh)-burning techniques with femtosecond lasers, the time dependence of the spectral diffusion of the oh is examined for both the CdS quantum dot (QD) and the CdS/HgS/CdS quantum dot quantum well (QDQW) nanoparticles. It is found that the nonradiative relaxation of the optical hole is at least 3 orders of magnitude slower in the QDQW than in the QD system. Analysis of the second derivative of the broad transient bleach spectrum of the QDQW system in the 1.6-2.5 eV energy region at 50 fs delay time is found to have a minimum at 2.1 eV, corresponding to a minimum in the radiative probability. Around this energy, the rise and decay times of the transient bleach in the spectrum an found to change greatly. These results suggest that spectral diffusion in the QDQW is a result of relaxation from high- to low-energy exciton states, involving an intervening dark state at an energy of similar to 2.0 eV. The energies of the maxima and minimum of the second-derivative curve are found to be in good agreement with recent theoretical calculations by Jaskolski and Bryant(1) of the energies of the radiative and dark charge-separated state, respectively. In the latter, the hole is in the CdS clad and the electron is in the HgS well. The slow nonradiative relaxation processes involving this state are expected to be slow owing to the large change in the charge carrier effective masses as they cross from the CdS clad to the HgS well.},
	isbn = {1089-5639},
	doi = {10.1021/jp9822687},
	author = {Little, Reginald and Burda, Clemens and Link, Stephan and Logunov, Stephan L. and El-Sayed, Mostafa A}
}
@article {873,
	title = {Picosecond Electronic Relaxation in CdS/HgS/CdS Quantum Dot Quantum Well Semiconductor Nanoparticles},
	journal = {The Journal of Physical Chemistry },
	volume = {100},
	year = {1996},
	note = {doi: 10.1021/jp953708m},
	month = {1996},
	pages = {6381 - 6384},
	publisher = {American Chemical Society},
	abstract = {Subpicosecond photoexcitation of CdS/HgS/CdS quantum dot quantum well nanoparticles at wavelengths shorter than their interband absorption (390 nm) leads to a photobleach spectrum at longer wavelengths (440?740 nm). The photobleach spectrum changes and its maximum red-shifts with delay time. These results are explained by the rapid quenching of the initially formed laser-excited excitons by two types of energy acceptors (traps); one is proposed to be due to CdS molecules at the CdS/HgS interface, and the other trap is that present in the CdS/HgS/CdS well. The results of the excitation at longer wavelengths as well as the formation and decay of the bleach spectrum at different wavelengths support this description.Subpicosecond photoexcitation of CdS/HgS/CdS quantum dot quantum well nanoparticles at wavelengths shorter than their interband absorption (390 nm) leads to a photobleach spectrum at longer wavelengths (440?740 nm). The photobleach spectrum changes and its maximum red-shifts with delay time. These results are explained by the rapid quenching of the initially formed laser-excited excitons by two types of energy acceptors (traps); one is proposed to be due to CdS molecules at the CdS/HgS interface, and the other trap is that present in the CdS/HgS/CdS well. The results of the excitation at longer wavelengths as well as the formation and decay of the bleach spectrum at different wavelengths support this description.},
	isbn = {0022-3654},
	url = {http://dx.doi.org/10.1021/jp953708m},
	author = {Kamalov, Valey F. and Little, Reginald and Logunov, Stephan L. and El-Sayed, Mostafa A}
}
