Fabrication of nanowires on orthogonal surfaces of microchannels and their effect on pool boiling

A novel microfabrication technique was developed to create silicon nanowires (SiNWs) on orthogonal surfaces of microchannels machined on top of a silicon wafer. Using a two-step metal-assisted etching process, the SiNW for the first time could be selectively fabricated on two different crystalline directions—the channel top and bottom surfaces oriented in the (1 0 0) direction while the sidewall surfaces in the (1 1 0) direction. Different SiNW etching conditions were investigated to get the optimal height, density, morphology and orientation for the SiNWs on the microchannels. The resulting samples were tested as heat sinks with water for their pool boiling applications. The sidewall SiNWs affected bubble behaviors and played important roles during the boiling process. The critical heat flux and the heat transfer coefficient both were thus improved compared to a plain silicon surface and a silicon chip with only microchannels. (Some figures may appear in colour only in the online journal)