Nanocomposites and nanomaterials

Phonon spectra of small non-stoichiometric Ag-In-S and Cu-In-S nanocrystals
N. Mazur1, B.V. Lopushanska2, V.M. Dzhagan1, Yu. M. Azhniuk2,3, O. Selyshchev4, O. Raievska4,5, O. Stroyuk5,6, D.R.T. Zahn4
1 V. Lashkaryov Institute of Semiconductors Physics, NAS of Ukraine, 03028 Kyiv, Ukraine
2 Uzhhorod National University, Uzhhorod 88000, Ukraine
3 Institute of Electron Physics, Ukr. Nat. Acad. Sci., Uzhhorod 88017, Ukraine
4 Semiconductor Physics, Chemnitz University of Technology, D-09107 Chemnitz, Germany
5 Institute of Physical Chemistry, Nat. Acad. of Science of Ukraine, 03028 Kyiv, Ukraine.
6 Forschungszentrum Jülich GmbH, Helmholtz-Institut Erlangen Nürnberg für Erneuerbare Energien (HI ERN), 91058 Erlangen, Germany.

E-mail: nazarmazur@isp.kiev.ua

Colloidal semiconductor nanocrystals (NCs) are in the focus of a sustainably growing direction of fascinating fundamental research with numerous promising applications. Along with well-developed II-VI NCs, a series of I-III-VI NC compounds have emerged in recent years as a viable alternative for light-emitting, bio-medical, and energy conversion applications1,2. One of the challenges with this sort of NCs is establishing the relation between their typically non-stoichiometric composition and lattice structure. Resonant Raman spectroscopy is an efficient tool of probing not only the phonon spectra of (nano)crystals, but also the lattice structure and local resonances.
We present a detailed analysis of Raman and infrared (IR) phonon spectra of strongly luminescent non-stoichiometric Ag-In-S and Cu-In-S NCs nanocrystals (NCs) of small size (d  2-4 nm), formed by means of aqueous colloidal chemistry under mild conditions. Despite presumably similar factors determining position and broadening of the Raman and X-ray diffraction (XRD) peaks, phonon spectra are shown to be more sensitive to NC composition and crystals structure. The Raman pattern of these NCs is different from that of the corresponding stoichiometric phases, e.g. CuInS2 or AgIn5S8, and is assumed to be characteristic of the specific structure of these highly non-stoichiometric small NCs. 

1 O. Stroyuk, A. Raevskaya, N. Gaponik. Chem. Soc. Rev. 2018, 47, 5354-5422. 
2 M.A. Boles, D. Ling, T. Hyeon, D.V. Talapin. Nature Materials 2016, 15, 141–153.