Colloidal Synthesis and Properties of InAs/InP and InAs/CdSe Core/Shell Nanocrystals
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sis and Properties of InAs/InP and InAs/CdSe Core/Shell Nanocrystals YunWei Cao, Julia Aksenton, Victor Soloviev and Uri Banin MRS Proceedings / Volume 571 / 1999 DOI: 10.1557/PROC57175
Link to this article: http://journals.cambridge.org/ abstract_S1946427400166904 How to cite this article: YunWei Cao, Julia Aksenton, Victor Soloviev and Uri Banin (1999). Colloidal Synthesis and Properties of InAs/InP and InAs/CdSe Core/Shell Nanocrystals. MRS Proceedings,571, 75 doi:10.1557/PROC57175 Request Permissions : Click here
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COLLOIDAL SYNTHESIS AND PROPERTIES OF InAs/InP AND InAs/CdSe CORE/SHELL NANOCRYSTALS Yun-Wei Cao, Julia Aksenton, Victor Soloviev, Uri Banin* Department of Physical Chemistry and the Farkas Center for Light Induced Processes, The Hebrew University, Jerusalem 91904, Israel. [email protected]
ABSTRACT High-temperature colloidal synthesis of InAs/InP and InAs/CdSe core/shell nanocrystal quantum dots is reported. InP and CdSe shells with several thicknesses were grown on InAs cores ranging in diameter between 20 to 50 A. Optical spectra, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and X-ray diffraction (XRD) were used to analyze the core/shell quantum dots and determine their chemical composition, average size, size distributions, and structures. The experimental results indicate that shell growth is uniform, expitaxial, and controllable. For both InP and CdSe shells, growth is accompanied by a red shift of the band gap energy as a result of the extension of the electron wavefunction into the shell region. An increase of the room temperature photoluminescence quantum yield by a factor of-4 is observed with CdSe shell growth on InAs Cores. The growth of InP shells, however, quenches the photoluminescence quantum yield. The difference is assigned to outer surface effects in core/shell nanocrystals. INTRODUCTION Room temperature fluorescence quantum yields on the order of several percent have been observed for InAs nanocrystal quantum dots capped by organic ligands [1]. Similar quantum yields have been reported for CdSe nanocrystals [2]. Nanocrystals are characterized by very large surface to volume ratios and the organic surfactants can not passivate all the surface atoms due to the steric hindrance effect. In addition, the phosphine ligands typically used, are electron donors and only bind to Lewis-acid sites on the nanocrystal surface. This results in incomplete passivation and trapping of charge on the surface, which competes with the fluorescence and limits the emission quantum yield. A successful strategy to increase substantially the quantum yields and the photostability of the CdSe nanocrystals is the growth of an outer shell of a higher band gap semiconductor [3-5]. We apply a similar strategy to III-V semiconductor nanocrystals. Previously, a low temperature route to synthesis of InAs/CdS core/shell nanocrystals in pyridine and benzylamine has been devel
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