The Race of Nanowires: Morphological Instabilities and a Control Strategy

The incomplete growth of nanowires that are synthesized by template-assisted electrodeposition presents a major challenge for nanowire-based devices targeting energy and electronic applications. In template-assisted electrodeposition, the growth of nanowires in the pores of the template is complex and unstable. Here we show theoretically and experimentally that the dynamics of this process is diffusion-limited, which results in a morphological instability driven by a race among nanowires. Moreover, we use our findings to devise a method to control the growth instability. By introducing a temperature gradient across the porous template, we manipulate ion diffusion in the pores, so that we can reduce the growth instability. This strategy significantly increases the length of nanowires. In addition to shedding light on a key nanotechnology, our results may provide fundamental insights into a variety of interfacial growth processes in materials science such as crystal growth and tissue growth in scaffolds

Enhancement of Pool Boiling Heat Transfer Using Aligned Silicon Nanowire Arrays

Enhancing the critical heat flux (CHF), which is the capacity of heat dissipation, is important to secure high stability in two-phase cooling systems. Coolant supply to a dry hot spot is a major mechanism to prevent surface burn-out for enhancing the CHF. Here, we demonstrate a more ready supply of coolant using aligned silicon nanowires (A-SiNWs), with a high aspect ratio (>10) compared to that of conventional random silicon nanowires (R-SiNWs), which have a disordered arrangement, for additional CHF improvement. We propose the volumetric wicking rate, which represents the coolant supply properties by considering both the liquid supply velocity and the amount of coolant (i.e., wicking coefficient and wetted volume, respectively). Through experimental approaches, we confirm that the CHF is enhanced as the volumetric wicking rate is increased. In good agreement with the fabrication hypothesis, A-SiNWs demonstrate higher coolant supply abilities than those of R-SiNWs. The longest (7 μm) A-SiNWs have the highest volumetric wicking rate (25.11 × 10^–3 mm³/s) and increase the CHF to 245.6 W/cm², which is the highest value obtained using nanowires among reported data (178 and 26% enhanced vs unmodulated plain surface and R-SiNWs, respectively). These well-aligned SiNWs can increase the CHF significantly with efficient coolant supply, and it can ensure high stability in extremely high thermal load systems. Moreover, our study provides nanoscale interfacial design strategies for further improvement of heat dissipation