Supporting information

Influence of sulphide precursor on crystal phase of ternary I-III-VI2 semiconductors

Milica V. Beloš1, Nadica D. Abazović1*, Jadranka Kuljanin Jakovljević1, Ivana Janković1, ScottP. Ahrenkiel2, Miodrag Mitrić1, Mirjana I. Čomor1

1Vinča Institute of Nuclear Sciences, University of Belgrade, P.O.Box 522, 11001 Belgrade, Serbia

2Nanoscience and Nanoengineering Department, South Dakota School of Mines and Technology, 501 E. Saint Joseph St., Rapid City, SD 57701, United States

Fig 1. Cu-myristic acid complex solutions in OLAM: a) at the beginning of reaction and b) when all Cu+ ion is oxidized to Cu2+ state

In order to evaluate quantity of DT which is needed for formation of AIS2, quick control experiments were done. We have used slightly changed procedure previously published by Zhong et al. (Zhong et al. 2008). Namely, 0.2 mmol of Ag(Ac), 0.2 mmol of In(Ac)3, 5 ml of 1- octadecene and a) 0.4 mmol, b) 0.8 mmol and c) 1.0 mmol 1-dodecanethiol (DT) were loaded in the flask and heated at 240°C under Ar flow. Mixtures were kept at this temperature for 2h. Obtained precipitates were washed few times with toluene/acetone mixture (1/3,v/v), until all excess of ODE is removed. X-ray diffractograms of obtained samples are presented in Fig. A. ODE is non-coordinating solvent, so it has no influence on growth and shape, or crystal structure of obtained crystals. Like this, it is ideal media in which influence of amount of some coordinating solvents, (such as DT) on formation, growth, shape and crystal phase of synthesized material can be tracked. On the other hand, DT is strong reducing agent and due to its –SH group it easily form bonds with surface metal ions of semiconductor. Besides, at such high temperatures it degrades to release S ions that are used, later, in formation of binary or ternary sulphides. Equilibrium between these two “roles” determines quantity of DT needed for certain reaction. It is obvious that stoichiometric amount of DT (0.4 mmol) is not enough for formation of AIS2 (Fig 2a). There are no traces of this material in diffractogram, only two sharp peaks that originate from pure Ag. Even when this amount is doubled to 0.8 mmol (Fig 2b), there are no clear peaks that can be assigned to AIS2-phase. Only when it is raised to 1.0mmol (Fig 2c), clear peaks (*) that originate from AIS2 are observed.

Fig 2. X-ray diffractogram of AIS2 control samples synthesized with different amounts of DT: a)0.4 mmol; b) 0.8 mmol and c) 1.0 mmol

Even though our synthetic procedure (proposed in the article) is different, we have decided that amount of DT can be fixed to 1 mmol, and that it doesn’t need to be enlarged, bearing in mind that OLAM (another coordinating solvent) will be present in the system.

Fig 3Diffraction patterns of S1 and S3
Fig 4Diffraction pattern of S2 and S4

Reference:

Zhong H, Zhou Y, Ye M, He Y, Ye J, He C, Yang C, and Li Y (2008) Controlled Synthesis and Optical Properties of Colloidal Ternary Chalcogenide CuInS2 Nanocrystals. Chem Mater 20 (20): 6434–6443. doi: 10.1021/cm8006827