Bio-inspired 3D funnel structures made by grayscale electron-beam patterning and selective topography equilibration

Display Omitted Discrete, multi-step polymer features were realized by electron beam lithography.Self-optimization based on thermoplastic, surface-energy driven reflow was used.This transformed polymer features into ultra-smooth two-directional gradients.Large-area, bio-mimetic master structures for ceramic powder injection molding were made. Electron beam grayscale lithography and selective thermal polymer reflow were combined to realize replication master having a bio-inspired surface topography. It consists of an array of asymmetric denticles with two-directional gradients on different length-scales. Each denticle has a sharp pin of 2µm height on one and a smooth taper on the other side. In contrast to funnel-like structures having only vertical sidewalls, master with a sidewall angle smoothly changing between 15¿ and 70¿ were prepared. Discrete patterns, predefined by electron beam lithography, were transformed by reflow into well-defined, continuous, final device structures. Starting from stepped structures with only a few levels, this new approach of tapering allowed a very smooth transition from steep, sub-500nm regions with aspect ratios up to four towards very broad and shallow regions within the same structure. This enabled the origination of master structures to be used for replication as low-frictional, durable, bio-inspired surfaces by ceramic powder injection molding.