High-pressure single-crystal growth of NaSi6 precursor for synthesis of (quasi) direct-bandgap silicon allotrope.

Axe 5 - Matériaux en conditions extrêmes

Post-doctorat de Carlos Renero-Lecuna

Projet de recherche mené du 15/06/2016 au 14/12/2017

Cotutelles

• Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie (IMPMC)
  Porteur de projet : Oleksandr Kurakevych
  Co-encadrant : Yann Le Godec
• Laboratoire Chimie de la Matière Condensée de Paris (LCMCP)
  Co-encadrant : David Portehault

Key words

Silicon allotropes - High pressure - Crystal growth - Silicon chemistry

Résumé

The aim of this MATISSE project was to study the crystallization of a suitable precursor NaSi6 for synthesis of novel silicon allotrope Si24 with advanced optoelectronic properties.

Crystallization of NaSi6 and other compounds between Na and Si has been studied. The mechanism of formation of NaSi6 and other clathrates has been probed by in situ methods (electrical resistivity probing at IMPMC, XRD probing at ESRF). The phase diagram of Na-Si system has been constructed based on data obtained in situ (probing the reaction volume during transformation) and ex situ (study of recovered samples). The results have been approved at 2017 AIRAPT international conference in Bejing (China), the paper is under preparation.

The formation of silicon forms from different high-pressure Na-Si clathrates has been observed in situ while heating in primary vacuum (XRD probing at IMPMC). Depending on the heating protocol, the formation of a number of different silicon forms have been observed (Si24 and Si136 with clathrate structures, nano-Si), among them one new crystalline form of silicon never observed so far. These results show a big potential for future studies of silicon clathrates formed at high pressure and their employment as precursors for soft chemistry. 

The optimized large-volume synthesis of NaSi6 and, consequently, of Si24 allowed to perform detailed characterization by a large variety of methods (especially by those that require large volume) accessible at CMCP (NMR), IMPMC (XRD, Raman) and to develop new collaborations for PL measurements (INSP of SU, LSPM à Villetaneuse, RSE at Canberra, Australia).

Publications

• Silvia Pandolfi, Carlos Renero-Lecuna, Yann Le Godec, Benoit Baptiste, Nicolas Menguy, Michele Lazzeri, Christel Gervais, Kristina Spektor, Wilson A. Crichton and Oleksandr O. Kurakevych
  Nature of Hexagonal Silicon Forming via High-Pressure Synthesis: Nanostructured Hexagonal 4H Polytype
  Nano Lett., 2018, 18 (9), pp 5989–5995
  DOI : 10.1021/acs.nanolett.8b02816