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ACS Nano. 2009 Jun 23;3(6):1518-24. doi: 10.1021/nn9001616.

Size-dependent composition and molar extinction coefficient of PbSe semiconductor nanocrystals.

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Department of Chemistry and Biochemistry, Worcester Polytechnic Institute, Worcester, MA 01609, USA.


Atomic compositions and molar extinction coefficients of PbSe semiconductor nanocrystals were determined by atomic absorption spectrometry, UV-vis-NIR spectrophotometry, and transmission electron microscopy. The Pb/Se atomic ratio was found to be size-dependent with a systematic excess of Pb atoms in the PbSe nanocrystal system. Experimental results indicated that the individual PbSe nanocrystal was nonstoichiometric, consisting of a PbSe core and an extra layer of Pb atoms. For these nonstoichiometric PbSe semiconductor nanocrystals, we proposed a new computational approach to calculate the total number of Pb and Se atoms in different sized particles. This calculation played a key role on the accurate determination of the strongly size-dependent extinction coefficient, which followed a power law with an exponent of approximately 2.5.


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