The continuous demand for miniaturization is reaching the technological limits of the conventional lithographic patterning approach. Thus, the use of nanocrystals is a very promising solution due to their original optical and electrical properties. It is particularly true for silicon- and germanium-based nano-objects which can be directly introduced in electrical devices. Si and Ge nanocrystals (NCs) have been prepared using a variety of techniques but solution based synthesis hold the promise as they allow with relative ease the modification of surface chemistry. Surface state control is of critical importance for the control of the size, the morphology, the stability of NCs and thus for tuning their conducting and optoelectronic properties. Currently, the most successful strategies reported for solution-based synthesis of Si and Ge NCs rely on the oxidation of silicides or direct reduction of Si(IV) and Ge(IV) precursors. The presence of strong reducing agents or salt by-products represents a major drawback since separation and purification processes may perturb significantly the control of the NCs surface. Moreover, none of these techniques have been able to achieve simultaneously well-passivated NCs with controlled size and low polydispersity, mainly due to the limited precursor reactivity. Thus, despite many academic and applied studies, the synthesis of size and shape controlled NCs is still an important synthetic challenge. The objective of this project is to develop a novel synthetic approach to nanocrystals of Si, Ge and of their binary SiGe, SiSn or GeSn and ternary SiGeSn alloys. The main feature of our approach relies on the design of high energy precursors of group 14 elements to overcome the synthetic problem of known preparation routes. Relevant features of these precursors are i) the presence of low coordinate and multiple bonded group 14 elements or strained heterocycles which provides an easier access to elements at oxidation state of 0 and ii) labile substituents to facilitate their removal to produce naked atoms. Three families of group 14 precursors designed specifically for this purpose will focus our attention: divalent species (mainly various types of germylenes such as aminogermylenes and hydrogermylenes), doubly bonded derivatives (heavier analogues of alkenes, and cumulenes such as germenes, phosphasilaallenes, dimetallaallenes) and three- or four-membered group 14 element heterocycles. The envisioned procedure for the synthesis of NCs of group 14 elements and alloys from these precursors consists in removing their susbtituents under the mildest conditions with the minimum of potentially pollutant reactant. Two solution routes will be explored: thermolysis and seeded growth (growth catalyzed by cluster). Both methods involve as stabilizers ligands which will coordinate firmly or loosely according to the chemical affinity for the NC. The reaction conditions together with the nature and the amount of stabilizer are critical for the control of the nucleation and growth processes and thus for the control of the characteristics (size, shape and surface state) of NCs. According to the precursors used, various types of nanoparticles should be obtained: monoelements from divalent species, from heteroalkenes M=C and heteroallenes M=C=P, M=C=C or M=C=M (M = Si, Ge, Sn) and bi- or tri-elements from mixed dimetallallenes M=M' and small heterocycles with two or three different metal atoms. Moreover, the method used should allow the synthesis of nanocrystals with a controlled ratio of every group 14 element. Monitoring of thermolysis (or photolysis) reactions by photoelectron spectroscopy should allow to determine the best leaving groups, the structure of intermediates and the reaction mechanisms involved in the decomposition of the precursors. A joint experiment/theory approach by DFT should give information about the structure and the electronic bonding situation of the precursors which are essential to better understand their chemical behaviour. Calculations should also predict the type of substituents (electron donor or releasing by inductive or mesomeric effect, with large or small steric effect able to modify the bonding) which is extremely important for the easy or not decomposition of precursors. Depending on these results and on the size and morphology of nanocrystals obtained in every decomposition experiment, a continuous optimization will be realized in order to obtain the most suitable precursors and in fine the mono-, bi- and tri-element nanocrystals under the mildest conditions. Thus, the cooperation between the three groups involved (LHFA, LPCNO and IPREM) will be essential for the success of this project.