Photoreduction-Insensitive GO/rGO Patterning Based on Multistep Femtosecond Laser Writing for Implementing Fresnel Zone Plates

As boosting the degree of photoreduction widens a patterning linewidth, devices comprising femtosecond laser (fs-laser)-induced reduced graphene oxide (rGO) present the dilemma of a choice between optimum performance and miniaturization. Here, by exploiting multistep fs-laser writing with a low repetition rate, photoreduction-insensitive GO/rGO patterning is realized, which exhibits a photoreduction-insensitive and constant patterning linewidth at arbitrary stages of the evolving photoreduction process. During a photo-reductioninsensitive patterning, a GO film is exposed iteratively to the same fs-laser beam to achieve targeted photoreduction levels, while the minimum patterning linewidth is preserved under a fixed pulse energy. The proposed patterning approach that results from preventing a thermal accumulation and roughening a GO/rGO surface achieves an optimizable device performance, without compromising on the feature size. In particular, a photoreduction-insensitive patterning provides a high optical transmission contrast while preserving a minimum linewidth. When two Fresnel zone plates that involve binary zones comprising GO/rGO are fabricated via single-exposure and multistep fs-laser-writing methods, respectively, the latter patterning approach provides a 3.9-fold enhancement of focusing efficiency compared with the former. Consequently, the demonstrated photoreduction-insensitive patterning approach confirms the feasibility of maintaining a patterning linewidth while tailoring the photoreduction levels of GO/rGO, thus promoting the development of GO/rGO-related micro/nanodevices.

Automated summary

By utilizing multistep fs-laser writing with a low repetition rate, photoreduction-insensitive GO/rGO patterning is achieved, maintaining a minimum linewidth and optimizing device performance without compromising feature size.