Designed molecular sources for the synthesis of metal pnictides nanocrystals

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Despite promising potentialities in many fields of applications such as microelectronics or photovoltaics, the chemistry of metal pnictides (GaAs, InP etc.) nanocrystals (NCs) is lingering far behind that of metal NCs or of chalcogenides NCs such as oxides or sulfides. This situation is essentially due to the lack of reliable and robust methods to synthesize controlled nano-objects.The objective of our proposal is the development of low-cost solution-based strategies for the synthesis of size, surface, shape and composition controlled NCs of groups 12 to 14 pnictides (more precisely, phosphides and arsenides). The target materials for the NCs will be Zn3P2 for group 12-pnictide, InP, InAs and GaAs for the group 13 pnictides and SiPx, GePx and SnP for the group 14-pnictides. They have been chosen on the basis of both the scientific importance for applications and the synthetic challenges.The originality of our approach relies on the design of high energy precursors to provide a reactivity-based, low-temperature method to overcome the synthetic problems and blocking points reported in the literature for pnictide-based nanomaterials. This work will involve the use of either two matched-reactivity precursors (one precursor for each element) or single source precursors (exhibiting preformed M-E bonds for the formation of MxEy NCs; M = Ga, In, Zn, Si, Ge, Sn; E = P, As), all compounds being specifically designed for NCs synthesis. While multi-source precursors are usually easy to obtain, the synthesis of single-source precursors is a challenging approach in this chemistry. Relevant features of these molecular species are (i) halogen-free (or cleanly removable in the gas or solution phase without interacting with NCs) precursors in order to prevent the NCs from potential halide contamination, (ii) labile substituents to facilitate their removal to produce naked atoms and allow synthesis of NCs at low T, and (iii) easy accessibility in large scale. Our strategy relies on the study of the reactivity of the precursor and of the NCs growth mechanism. The understanding of the chemistry behind these processes will be the basis to overcome the scientific barriers and the limitations currently existing for the target materials. We are aiming in particular, at synthesizing NCs in soft conditions (using organometallic approaches), at low temperature (< 150°C). This will allow (i) the development of safer and cost-effective procedures, (ii) the opportunity to realize in situ mechanistic and kinetics studies and most of all, (iii) the avoidance of uncontrolled side-reactions that occur at high temperature and (iv) a better control of the kinetics (and reproducibility) of every synthesis steps (nucleation, growth, ripening) yielding to controlled nano-objects.The preliminary examination of physical (in particular opto-electronic) properties will be performed to provide a first evaluation of the relevancy of theses NCs for applications.