Controlling Competing Feedback Mechanisms for Programmable Patterns via Nonlinear Laser Lithography

Abstract: Controlling laser-induced pattern formation remains a long-standing challenge. A key advance was recognising the pivotal role of intrinsic feedback mechanisms in self-organisation, which enabled self-similar patterns with long-range order through nonlinear laser lithography. This concept was recently leveraged to surpass the diffraction limit. However, the demonstrated structures are relatively simple and material-specific, as they rely on a single assumed formation mechanism for each material. Here, we reveal the previously unknown coexistence of competing feedback mechanisms that drive distinct chemical and ablative processes, resulting in patterns with different symmetries. We show that one mechanism can be selectively activated, while completely suppressing the other, by tuning the laser parameters independently of the material. The competing mechanisms break surface symmetries in distinct lateral and vertical directions, and the selection can be dynamically inverted in situ, leading to rich surface chemistries and morphologies. We demonstrate the potential for applications through the maskless and ambient-air fabrication of complex composite patterns on diverse materials and substrates. These include seamlessly stitched superhydrophilic and superhydrophobic domains, structural colour, and a holographic temperature sensor. Combining programmable mechanism selection with recent demonstrations of sub-10 nm features could enable the maskless fabrication of composite structures that rival the capabilities of top-down nanofabrication techniques.