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Semiconductor nanoparticles (NPs) of high structural and optical quality are now produced by means of wet chemistry in application-sufficient quantity and variety of composition and morphology. Development of composite (hetero-) NPs further extends their application range and improves the relevant properties. For a thorough understanding and precise manipulation of properties of composite (hetero-) nanoparticles, the knowledge about their interface structure is needed. Besides, new information about charge and energy transfer at nanointerfaces is also of big fundamental importance.
This communication focuses on capabilities of vibrational Raman spectroscopy in probing the local structure and elemental excitations in semiconductor NPs and hetero-NPs prepared by means of colloidal synthesis. The results of Raman spectroscopy are supplemented by photoluminescence (PL), optical absorption, electron microscopy, X-ray and atomic emission spectroscopy.
Two kinds of compounds are considered: II-VI and I-III-VI.
For II-VI core-shell NPs, of particular importance is comparison of the coupling of photoexcited exciton to the core- and shell-localized phonons. Actually, the degree of their localization in the nm-sized counterparts is the matter of discussion itself, in view of the smoothing the interface by interdiffusion. As the interdiffusion at the interface is critical for the properties of core-shell NPs [1], the effect of the shell parameters, such as thickness and shape, onto the strain distribution over the heterostructure and structure of the interface are studied here. The common dot-in-dot structures are compared to novel dot-in-plate ones, with predominantly hydrostatic and biaxial stress, correspondingly.
For I-III-VI compounds, particularly CuInS2 (CIS), numerous studies exist for
bulk samples and thin films, for which Raman spectroscopy proved to be
efficient in determination of chemical composition, defects, secondary phases
and other imperfections abundant in I-III-VI compounds. At the same time, only
a few studies reported recently the phonon Raman spectra of CIS nanoparticles
and no studies - for hetero-NPs. In present communication we discuss our recent results on CIS-based NPs (CuInS2, CuInS2:Zn) and heteronanoparticles such as Cu2S/CuInS2, CuInS2/ZnS. The current progress and challenges in separation of the size effects and structural imperfections in this kind of nanostructures are discussed.
The work was partly supported by Ukrainian State Fund for Fundamental Researches (Φ40.2/068, 41.1/017), and Alexander von Humboldt Foundation (Research Group Linkage Programme). [1] F. Garcia-Santamaria, S. Brovelli, R. Viswanatha, J.A. Hollingsworth, H. Htoon, S.A. Crooker, and V.I. Klimov. Breakdown of Volume Scaling in Auger Recombination in CdSe/CdS Heteronanocrystals: The Role of the Core-Shell Interface. Nano Lett. 11 (2011) 687-693. |
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