Understanding the generation of silicide nanowires by CVD in situ in a TEM
Metallic nanowires (NWs) may be of interest in many nano-electronics or plasmonics applications. Nanowires based on silicon are of particular interest as they are naturally compatible with Si technology. Among the latter, nickel silicide NWs are very conductive and could replace copper connections or transparent conductive oxides.1 Regarding fundamental materials science, their growth occurs in absence of a catalyst and, so far, has not received a sound explanation. The aim of the project is to understand this mechanism, by observing it in situ in the NanoMAX environmental transmission electron microscope, in real time, and at the atomic scale.
Figure 1 (left) shows a low-magnification image of the NWs grown in situ between 400°C and 450°C, using a mixture of SiH4:H2 1:250 at 4 Pa. Diffraction patterns of these wires generally correspond to the Ni3Si2 bulk structure but, quite interestingly, energy-dispersive X-ray spectroscopy gives in contrast a composition close to Ni:Si 50:50.
When looking at the NWs during growth, and analysing their structural phase thanks to a running FFT of the real-time lattice image, that phase is clearly not the one which is characterised after growth. At some stage at the end of growth, a phase boundary passes by, switching the growing phase to the final one. This switching stops the growth. Let us note here that this information would have remained hidden without in situ observation. The phase during NW growth is still under investigation. Figure 1 (right) shows the passing of the phase boundary at the growth temperature.
1 T. Le Duc, E. Moyen, M. R. Zamfir, Y. W. Kim, J. Joe, Y. H. Lee and D. Pribat, Connecting wire-based solar cells without any transparent conducting electrode, CrystEngComm 18, 207-212 (2016).
Main collaborators: Didier Pribat (firstname.lastname@example.org), Le Duc Toan (email@example.com); Ileana Florea (firstname.lastname@example.org).
This work has been possible thanks to the TEMPOS EquipEx, pole NanoMAX (ANR-10-EQPX-50).