ID-12-P-3004 Real time observations of collector droplet oscillations in scanning electron microscope

Semiconductor nanowires (NW) are intensively studied for their promising properties in nanoelectronics, photonics, gas and bio-sensing etc. The nanowire shape (cross-section, sidewalls’ orientation etc.) plays a major role in determining electrical transport or sensing properties of nanowire-based devices. The ability to fully control the nanowire morphology is, of course, based on our understanding of the growth process. In this respect, in-situ Transmission Electron Microscopy (TEM) studies have provided vital information [1] on this issue.
In our contribution, we will present our results on the vapor-liquid-solid (VLS) germanium nanowire growth by evaporation inside a SEM vacuum chamber. Compared to TEM, scanning electron microscopy (SEM) can give three-dimensional information of the growth scenario. As the group IV nanowires grown by evaporation are highly faceted, we will focus on effects where SEM can give substantial information. In particular, the initial formation of the growth interface between the droplet and the substrate is decisive on the nanowire orientation (see Figure 1). We will show that it is dependent on the evaporation rate and, hence, by this parameter one can control the growth orientation [2.3]. In another example, we will demonstrate that the droplet on top of a nanowire is not necessarily pinned to the growth interface. Instead, under certain growth conditions it slides down the sidewalls and then climbs up again to the top. Therefore, the growth interface is not planar, but dynamically changes (Figure 2), which results in very complex nanowire morphology [4].

References
[1] Ross F. M., Rep. Prog. Phys. 73 (2010) 114501.
[2] Kolíbal M., Vystavěl T., Novák L. et al., Applied Physics Letters 99 (2011) 143113.
[3] Kolíbal M., Kalousek R., Vystavěl T. et. al., Applied Physics Letters 100 (2012) 203102.
[4] Kolíbal M., Vystavěl T., Varga P., Šikola T., Nanoletters, accepted.