Yujun Xie1 2 3 Sungwoo Sohn1 2 Jan Schroers1 Judy Cha1 2 3

1, Yale University, New Haven, Connecticut, United States
2, Yale University, New Haven, Connecticut, United States
3, Yale West Campus, West Haven, Connecticut, United States

Crystallization is a dynamic event that involves multiple phenomena and length scales, and many physical phenomena can deviate from classical theories as samples approach relevant length scales. In situ crystallization experiments inside a transmission electron microscope (TEM) using nanostructured metallic glasses (MGs) provide a unique platform to study directly crystallization kinetics and pathways at unprecedented time and spatial resolution [1]. Here, we use Pt-Ni-Cu-P MG nanorods and in situ TEM technique to explore unexpected crystallization phenomena at the nanoscale. We report the previously unknown asymmetry behavior between critical heating and cooling rates in MGs, which disappears when the sample size is below 35 nm [2]. Moreover, in contrast to bulk MG samples that form polymorphic phases, we observe a formation of an unusual single crystalline phase, which has previously never been reported [2]. The metastable phase can be attributed to the lack of nuclei as the samples size approaches the nucleation length scale, resulting in the starvation of nuclei. Our findings provide insights of cluster and nucleation density by controlling the MG nanorod diameter, which can also affect the resulting crystallization phases.
[1] S. W. Sohn, Y. Jung, Y. Xie, C. Osuji, J. Schroers, J. J. Cha, “Nanoscale size effects in crystallization of metallic glass nanorods,” Nature Communications 6:8157 (2015).
[2] S. W. Sohn, Y. Xie, Y. Jung, J. Schroers, J. J. Cha, “Tailoring crystallization phases in metallic glass nanorods via nucleus starvation,” Nature Communications (2017), accepted.