Physico-Chemical nanomaterials science

In situ aberration-corrected STEM studies of metal-induced crystallization of amorphous semiconductor films
Kryshtal A.P. 1, Bogatyrenko S.I. 2
1 Faculty of Metals Engineering and Industrial Computer Science & International Centre of Electron Microscopy for Material Science, AGH University of Science and Technology, al. A. Mickiewicza 30, 30-059 Kraków, Poland. 
E-mail: kryshtal@agh.edu.pl
2 Department of Physics and Technology, Karazin National University, 4 Svobody sq., Kharkiv 61022, Ukraine.

Thin crystalline Ge and Si films are a key material for high-efficient solar cells, optical and spintronic devices. However, Si or Ge films grown from the vapor phase are usually amorphous, and their crystallization requires annealing at temperatures above 500°C. On the other hand, the crystallization temperature of the amorphous film is reduced significantly when the semiconductor film is in contact with the metal, e.g. Au, Ag, Al, Bi, Pd [1]. This effect is commonly known as a metal-induced crystallization (MIC), and it was discovered almost 50 years ago. However, a fundamental mechanism of the reaction is still an issue.
In this work, we have applied state-of-the-art electron microscopy techniques for studies of the initial stages of the reaction in Ag/Ge films. The nucleation and growth of crystalline Ge phase were observed in real time with HAADF- and monochromated EELS-STEM imaging by heating the system in a probe-corrected FEI Titan G2 60-300 transmission electron microscope equipped with Wildfire D6 heating holder (DENSsolutions). Ag and Ge surface and volume plasmon resonances were used for nanoscale mapping of the interphase boundaries and chemical elements in an individual nanoparticle at different stages of the reaction without substantial radiation damage. HAADF-STEM tomography was applied for 3D reconstruction of post-annealed Ag/Ge film morphology.
A new insight into the mechanism of the MIC effect will be presented and discussed.
Financial support from the National Science Centre, Poland under Grant No. 2016/23/B/ST8/00537 and EU Horizon 2020 research and innovation program under grant agreement No. 823717_ESTEEM3 is gratefully acknowledged.

1.	Kryshtal A., Minenkov A., Bogatyrenko S., Gruszczyński A., Melting process and the size depression of the eutectic temperature in Ag/Ge and Ge/Ag/Ge layered films // J. Alloys Compd.-2019.-786.-P. 817-825.