Fabrication and Characterization of the Capillary Performance of Superhydrophilic Cu Micropost Arrays

We report the fabrication of dense arrays of super-hydrophilic Cu microposts at solid fractions as high as 58% and aspect ratios as high as four using electrochemical deposition and chemical oxidation techniques. Oxygen surface plasma treatments of photoresist molds and a precise control of the initial electrodeposition current are found to be critical in creating arrays of nearly defect-free Cu posts. The capillary performance of the micropost arrays is characterized using capillary rate of rise experiments and numerical simulations that account for the finite curvatures of liquid menisci. For the given wick morphology, the capillary performance generally decreases with increasing solid fraction and is enhanced by almost an order of magnitude when thin nanostructured copper oxide layers are formed on the post surface. The present work provides a useful starting point to achieve optimal balance between the capillary performance and the effective thermal conductivity of advanced wicks for micro heat pipes.