Nonconfinement growth of edge-curved molecular crystals for self-focused microlasers

Spatially Resolved Organic Whispering-Gallery-Mode Hetero-Microrings for High-Security Photonic Barcodes

Whispering-gallery-mode (WGM) microcavities featuring distinguishable sharp peaks in a broadband exhibit enormous advantages in the field of miniaturized photonic barcodes. However, such kind of barcodes developed hitherto are primarily based on microcavities wherein multiple gain medias were blended into a single matrix, thus resulting in the limited and indistinguishable coding elements. Here, a surface tension assisted heterogeneous assembly strategy is proposed to construct the spatially resolved WGM hetero-microrings with multiple spatial colors along its circular direction. Through precisely regulating the charge-transfer (CT) strength, full-color microrings covering the entire visible range were effectively acquired, which exhibit a series of sharp and recognizable peaks and allow for the effective construction of high-quality photonic barcodes. Notably, the spatially resolved WGM hetero-microrings with multiple coding elements were finally acquired through heterogeneous nucleation and growth controlled by the directional diffusion between the hetero-emulsion droplets, thus remarkably promoting the security strength and coding capacity of the barcodes. The results would be useful to fabricate new types of organic hierarchical hybrid WGM heterostructures for optical information recording and security labels.

Damage protection from focused ion beam process toward nanocavity-implemented compound semiconductor nanowire lasers

A focused ion beam (FIB) can precisely mill samples and freely form any nanostructure even on surfaces with curvature, like a nanowire surface, which are difficult to implement by using conventional fabrication techniques, e.g. electron beam lithography. Thus, this tool is promising for nanofabrication; however, fabrication damage and contamination are critical issues, which deteriorate optical properties. In this work, we investigated the protective performance of Al₂O₃against the FIB process (especially by a gallium ion). Nanowires were coated with Al₂O₃as a hard mask to protect them from damage during FIB nanofabrication. To estimate the protective performance, their emission properties by photoluminescence measurement and time-resolved spectroscopy were compared with and without Al₂O₃coating conditions. From the results, we confirmed that the Al₂O₃coating protects the nanowires. In addition, the nanowires also showed lasing behavior even after FIB processing had been carried out to implement nanostructures. This indicates that their optical properties are well maintained. Thus, our study proves the usefulness of FIBs for future nanofabrication.