This paper describes a self‐regulating system that combines wrinkle‐patterned hydrogels with plasmonic nanoparticle (NP) lattices. In the feedback loop, the wrinkle patterns flatten in response to moisture, which then allows light to reach the NP lattice on the bottom layer. Upon light absorption, the NP lattice produces a photothermal effect that dries the hydrogel, and the system then returns to the initial wrinkled configuration. The timescale of this regulatory cycle can be programmed by tuning the degree of photothermal heating by NP size and substrate material. Time‐dependent finite element analysis reveals the thermal and mechanical mechanisms of wrinkle formation. This self‐regulating system couples morphological, optical, and thermo‐mechanical properties of different materials components and offers promising design principles for future smart systems.
Collecting significant and measurable signals from the typically omnidirectional emission of nanoscale emitters is challenging. To improve the collection efficiency, it is essential to deterministically place the emitters in desired locations and design mode converters to match the modes of emission to those of the collection system. In this Letter, we propose the deterministic placement of nanoscale emitters using a pick-and-place technique called polymer-pen lithography. We demonstrate the concept with upconversion nanoparticles placed deterministically at the focus of three-dimensional-printed ellipsoidal micro-lenses. A significant part of the forward-going emission is collimated leading to increased collection efficiency, even at low numerical apertures of the collecting optics. The proposed approach lends itself to hybrid integration for fiber-to-chip and on-chip applications.
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