Effect of Microstructures on Superhydrophobic and Slippery Lubricant-Infused Porous Surfaces During Condensation Phase-Change

Superhydrophobic surfaces (SHSs) and slippery lubricant-infused porous surfaces (SLIPSs) are receiving increasing attention for their excellent anti-icing, anti-fogging, self-cleaning and condensation heat transfer properties. The ability of such surfaces to passively shed and repel water is mainly due to the low-adhesion between the liquid and the solid surface, i.e., low contact angle hysteresis, when compared to hydrophilic or to hydrophobic surfaces. In this work we investigated the effect of surface structure on the condensation performance on SHSs and SLIPSs. Three different SHSs with structures varying from the micro- to the nano-scale were fabricated following easy and scalable etching and oxidation growth procedures. The condensation performance on such surfaces was evaluated by optical microscopy in a temperature and humidity controlled environmental chamber. On SHSs important differences on the size and on the number of the coalescing droplets required for the jump to ensue were found when varying the surface structure underneath the condensing droplets. A surface energy analysis is proposed to account for the suppression of the droplet-jumping performance in the presence of microstructures. On other hand, by impregnating the same SHSs with a low surface tension oil, i.e., SLIPSs, the adhesion between the condensate and the SLIPSs can be further reduced. On SLIPSs slight differences on the droplet density over time and shedding performance upon the inclusion of microstructures were observed. Droplets were found to shed faster and with smaller diameters on SLIPSs in the presence of microstructures when compared to solely nanostructured SLIPSs. We conclude that on SHSs the droplet-jumping performance of micrometer droplets is deteriorated in the presence of microstructures with the consequent decrease in the heat transfer performance, whereas on SLIPSs the droplet self-removal is actually improved in the presence of microstructures.

Isotropic Oxidation by Plasma Oxidation and Investigation of RIE Induced Effects for Development of 4H-SiC Trench MOSFETs

In this work, we examined the oxidation growth rates of the (0001) Si-face and (11−20) a-faces of 4H-SiC by carrying out oxidation in the 850°C-950 °C temperature range in a plasma afterglow furnace for application to trench MOSFETs. At 900 °C, this method results in almost equal oxide thickness on the Si-face and a-face which would nominally correspond to trench bottom and sidewalls in trench devices. Our results indicate that after NO annealing, the electronic properties of the plasma oxidized SiO2/SiC interface is comparable to control samples with gate oxides formed by dry oxidation at 1150 °C followed by NO annealing. Next, the effect of reactive ion etching (RIE) of 4H-SiC surfaces prior to gate oxidation was investigated using planar 4H-SiC MOS capacitors. Our experiments show that oxidation followed by NO annealing of surfaces with smooth morphology following the RIE step, results in similar interface charge and trap densities as MOS capacitors which did not undergo the RIE etching.