JSA Vol.11 No.2 Pages 62-70
English contents ｜ Japanese contents
Chemical Structure Changes in TOPO Capped CdSe Nanocrystals Thin Films by Comparable ToF-SIMS and XPS Study
*,***Y.Abe, *H.Asami, *H.Yamauchi, *T.Ohtsu, *I.Kamiya, **H.Okuhira and ***K.Edamoto
*Mitsubishi Chemical Group Science and Technology Research Center, Inc. 1000, Kamoshida-cho, Aoba-ku, Yokohama 227-8502
**Hitachi Science Systems, Ltd. 260-1 Komiya-machi, Hachiouji-shi, Tokyo 192-0031
***Department of Chemistry and Materials Science, Tokyo Institute of Technology 2-12-1, Ookayama, Meguro-ku, Tokyo 152-0033
(Received: February 5, 2004; Accepted: April 16, 2004 )
Abstract
Comparable characterization of trioctylphosphine oxide (TOPO) capped CdSe nacocrystals by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) are demonstrated. Quantitative analysis of surface elemental composition and chemical state for CdSe nanocrystals surface was performed with XPS. Qualitative information about the surface complex formed on the CdSe was extracted from the ToF-SIMS spectra. Based on the results obtained, the mechanism of the photon-induced changes in TOPO capped CdSe surface was proposed as follows: In the initial state, organic ligand TOPO bound to Cd site on the CdSe surface, which was deduced from the detection of (TOPO+Cd) cluster ions. In the photo-brightening state, where photoluminescence (PL) intensity increased after some amount of illumination, a part of TOPO migrated from Cd site to Se site forming TOPO-Se complex. In the photo-darkening state, where the PL intensity gradually decreased after the photo-brightening, oxidation of surface Se and decomposition of TOPO-Se complex occurred, which was followed by the desorption of TOP and SeO2 from the surface. It is proved that XPS and ToF-SIMS can be used for surface chemical structure analysis as complementary techniques.