@article{7215e4d8c31f46c2bdc5901463bd076a,
title = "Mapping the spatial distribution of charge carriers in quantum-confined heterostructures",
abstract = "Quantum-confined nanostructures are considered 'artificial atoms' because the wavefunctions of their charge carriers resemble those of atomic orbitals. For multiple-domain heterostructures, however, carrier wavefunctions are more complex and still not well understood. We have prepared a unique series of cation-exchanged HgxCd1xTe quantum dots (QDs) and seven epitaxial core-shell QDs and measured their first and second exciton peak oscillator strengths as a function of size and chemical composition. A major finding is that carrier locations can be quantitatively mapped and visualized during shell growth or cation exchange simply using absorption transition strengths. These results reveal that a broad range of quantum heterostructures with different internal structures and band alignments exhibit distinct carrier localization patterns that can be used to further improve the performance of optoelectronic devices and enhance the brightness of QD probes for bioimaging.",
author = "Smith, {Andrew M.} and Lane, {Lucas A.} and Shuming Nie",
note = "Funding Information: This work was supported by grants from the National Institutes of Health (R01CA163256, RC2CA148265 and HHSN268201000043C to S.N.). A.M.S. acknowledges the NCI Nano-Alliance Program for a Pathway to Independence Award (K99CA154006 and R00CA153914). We wish to thank Dr Hong Yi of Emory University for electron microscopy imaging, Professor Rohit Bhargava and Dr Prabuddha Mukherjee of the University of Illinois at Urbana-Champaign for Raman spectroscopy measurements, and Professor Z.L. Wang of Georgia Tech for high-resolution TEM studies (supported by NSF grant DMR 0922776). Funding Information: Instrumentation. Absorption spectra were measured using a Shimadzu UV-2401PC scanning spectrophotometer (300–900 nm) or an Ocean Optics NIR-512 spectrometer with tungsten halogen lamp (850–1,700 nm). Room-temperature steady-state fluorescence spectra were obtained at using a Photon Technology International spectrofluorometer with photomultiplier tube for the 400–800 nm spectral range and InGaAs detector for 800–1,700 nm. Photoluminescence excitation spectroscopy was performed using a Horiba Nanolog UV–vis-NIR spectrofluorometer (240–1,550 nm) with internal excitation intensity correction and photomultiplier tube for the 400-to 800-nm spectral range and InGaAs detector for 800–1,550 nm. PLE spectra were obtained at 0 °C using a cell immersed in an ice water bath. Room-temperature Raman spectra were obtained using a Spex Triplemate microscope with Princeton Instruments CCD detector and 532-nm laser excitation. Samples were cast from hexane solutions on aluminum slides. For X-ray diffraction, dried solid nanocrystals from hexane solutions were analysed using a PANalytical X-Pert PRO with Cu X-ray source. For electron microscopy and EDX spectroscopy, samples were prepared from a hexane suspension of purified nanocrystals (5 µl) dropped on formvar/carbon 200 mesh TEM grids. Normal resolution TEM imaging was performed with a Hitachi H-7500 TEM. High-resolution images were obtained using a Tecnai F30 with Oxford EDX 6763 attachment (in the lab of ZL Wang, supported by NSF funding DMR 0922776). For elemental analysis, purified aqueous nanocrystals were dissolved with the addition of a small amount of nitric acid; hydrophobic nanocrystals in nonpolar solvents were purified with acetone precipitations, dried under vacuum, dissolved in aqua regia at 80 °C for B4 h and diluted in deionized water. Solutions were analysed for cadmium, mercury and tellurium using ICP-MS (VG PlasmaQuad 3).",
year = "2014",
month = jul,
day = "31",
doi = "10.1038/ncomms5506",
language = "English (US)",
volume = "5",
journal = "Nature communications",
issn = "2041-1723",
publisher = "Nature Publishing Group",
}