In situ observation of droplet nanofluidics for yielding low-dimensional nanomaterials

Droplet based micro/nanofluidics has been demonstrated as a versatile tool in a wide range of fields. In particular, seeded growth of planar low-dimensional nanomaterials often relies on crawling metal droplets as catalytic media where nucleation and crystal growth proceed. However, direct observations of nanomaterials growth led by self-propelled droplet transport remain rare, which leaves many open questions on droplet behavior during growth. Here, we report in situ observations of in-plane Si nanowire growth in a transmission electron microscope, where an indium droplet migrates on a silicon nitride membrane coated by a layer of hydrogenated amorphous silicon (a-Si:H), dissolves the a-Si:H coating film on the membrane, and results in the production of a crystalline Si nanowire in its trail. This in situ observation, combined with the geometric investigation of the nanowires, presents nice consistency with de Gennes' theoretical prediction of reactive wetting induced droplet motion. Interestingly, we recorded a nanoflake-to-nanowire transition when the growth rate was increased by heating the membrane from 350 degrees C to 400 degrees C. This work directly unveils rich transport mechanism of catalytic droplets, which are expected to be a new platform for producing diverse low-dimensional nanomaterials and promote their potential applications in nanoscience and technologies.

Automated summary

This study reports in situ observations of the growth of silicon nanowires in a transmission electron microscope, revealing the behavior and mechanisms of droplets during the growth process. The results show that crystalline silicon nanowires can be grown on a membrane through the movement and dissolution of the droplet. By investigating the geometric properties of the nanowires, the results are consistent with theoretical predictions.