No abstract

Functional nanostructures are exploited for a variety of cutting-edge fields including plasmonics, metasurfaces, and biosensors, just to name a few. Some applications require nanostructures with uniform feature sizes while others rely on spatially varying morphologies. However, fine manipulation of the feature size over a large area remains a substantial challenge because mainstream approaches to precise nanopatterning are based on low-throughput pixel-by-pixel processing, such as those utilizing focused beams of photons, electrons, or ions. In this work, we provide a solution toward wafer-scale, arbitrary modulation of feature size distribution by introducing a lithographic portfolio combining interference lithography (IL) and grayscale-patterned secondary exposure (SE). Employed after the high-throughput IL, a SE with patterned intensity distribution spatially modulates the dimensions of photoresist nanostructures. Based on this approach, we successfully fabricated 4-inch wafer-scale nanogratings with uniform linewidths of <5% variation, using grayscale-patterned SE to compensate for the linewidth difference caused by the Gaussian distribution of the laser beams in the IL. Besides, we also demonstrated a wafer-scale structural color painting by spatially modulating the filling ratio to achieve gradient grayscale color using SE.

Metallic nanostructures are becoming increasingly important for both fundamental research and practical devices. Many emerging applications employing metallic nanostructures often involve unconventional substrates that are flexible or nonplanar, making direct lithographic fabrication very difficult. An alternative approach is to transfer prefabricated structures from a conventional substrate; however, it is still challenging to maintain high fidelity and a high yield in the transfer process. In this paper, we propose a high-fidelity, clean nanotransfer lithography method that addresses the above challenges by employing a polyvinyl acetate (PVA) film as the transferring carrier and promoting electrostatic adhesion through triboelectric charging. The PVA film embeds the transferred metallic nanostructures and maintains their spacing with a remarkably low variation of <1%. When separating the PVA film from the donor substrate, electrostatic charges are generated due to triboelectric charging and facilitate adhesion to the receiver substrate, resulting in a high large-area transfer yield of up to 99.93%. We successfully transferred the metallic structures of a variety of materials (Au, Cu, Pd, etc.) with different geometries with a <50-nm spacing, high aspect ratio (>2), and complex 3D structures. Moreover, the thin and flexible carrier film enables transfer on highly curved surfaces, such as a single-mode optical fiber with a curvature radius of 62.5 μm. With this strategy, we demonstrate the transfer of metallic nanostructures for a compact spectrometer with Cu nanogratings transferred on a convex lens and for surface-enhanced Raman spectroscopy (SERS) characterization on graphene with reliable responsiveness.

Spectrally selective narrowband photodetection is critical for near‐infrared (NIR) imaging applications, such as for communicationand night‐vision utilities. It is a long‐standing challenge for detectors based on silicon, to achieve narrowband photodetection without integrating any optical filters. Here, this work demonstrates a NIR nanograting Si/organic (PBDBT‐DTBT:BTP‐4F) heterojunction photodetector (PD), which for the first time obtains the full‐width‐at‐half‐maximum (FWHM) of only 26 nm and fast response of 74 µs at 895 nm. The response peak can be successfully tailored from 895 to 977 nm. The sharp and narrow response NIR peak is inherently attributed to the coherent overlapping between the NIR transmission spectrum of organic layer and diffraction enhanced absorption peak of patterned nanograting Si substrates. The finite difference time domain (FDTD) physics calculation confirms the resonant enhancement peaks, which is well consistent with the experiment results. Meanwhile, the relative characterization indicates that the introduction of the organic film can promote carrier transfer and charge collection, facilitating efficient photocurrent generation. This new device design strategy opens up a new window in developing low‐cost sensitive NIR narrowband detection.

Spectrally selective narrowband Si photodetection is critical for near-infrared (NIR) medical imaging, optical communication, light detection and autonomous mobiles. For conventional inorganic semiconductors such as silicon with broadband absorption from visible until 1.1 µm, it remains challenging to achieve narrowband photodetection without integrating optical filters. We demonstrate the very first narrowest NIR silicon photodetectors without any bandpass filter, reaching the full-width-at-half-maximum of only 26 nm at 912 nm. The narrowband response is inherently attributed to the resonant enhancement effect of optical microcavities formed by patterned Si nanograting combined with the organic D18:Y6 blend film. The Conductive-Atomic Force Microscope (C-AFM), Kelvin Probe Force Microscope (KPFM) and transient absorption (TA) spectroscopy characterization indicate effective charge transfer between Si and organic layers, significantly contributing to ultrafast photoresponse of 74 \(\mu s\). Therefore, this design concept opens up the new possibility of developing filter-less and effective low-cost NIR detection, enabling entirely new configurations of optical imaging devices with narrowband tunability for telecommunications and imaging applications.