Maskless fabrication of plasmonic metasurfaces in polymer film using a spatial light modulator

We demonstrate a high-speed optical technique to fabricate plasmonic metasurfaces in a polymer film. The technique is based on a programmable spatial light modulator, which is used to spatially control the photoreduction sites of gold ions in a polyvinyl alcohol film doped with a gold precursor. After irradiation, annealing was used to induce the growth of nanoparticles, producing plasmonic microstructures. Using a 473 nm excitation wavelength, microscopic plasmonic gratings, and meta-atom arrays with arbitrary orientations, an effective nanostructure size of ∼700 nm and constituent nanoparticles with average size of ∼37 nm were created. The technique enables a cost-effective and straightforward light-based approach to fabricate plasmonic metasurfaces with tunable properties.acceptedVersionPeer reviewe

Surface and optical properties of phase-pure silver iodobismuthate nanocrystals

The study of surface defects is one of the forefronts of halide perovskite research. In the nanoscale regime, where the surface-to-volume ratio is high, the surface plays a key role in determining the electronic properties of perovskites. Perovskite-inspired silver iodobismuthates are promising photovoltaic absorbers. Herein, we demonstrate the colloidal synthesis of phase pure and highly crystalline AgBiI4 nanocrystals (NCs). Surface-sensitive spectroscopic techniques reveal the rich surface features of the NCs that enable their impressive long-term environmental and thermal stabilities. Notably, the surface termination and its passivation effects on the electronic properties of AgBiI4 are investigated. Our atomistic simulations suggest that a bismuth iodide-rich surface, as in the case of AgBiI4 NCs, does not introduce surface trap states within the band gap region of AgBiI4, unlike a silver iodide-rich surface. These findings may encourage the investigation of surfaces of other lead-free perovskite-inspired materials.publishedVersionPeer reviewe

Third-harmonic generation microscopy of undeveloped photopolymerized structures

Third-harmonic generation (THG) microscopy is demonstrated as a powerful technique to visualize undeveloped photopolymerized microstructures within a negative photoresist film. By comparing the THG microscopy images of developed and undeveloped single-photon polymerized structures in a SU-8 film, THG was found to provide sufficient contrast for distinguishing polymerized and unpolymerized regions. This also suggests that the technique can be used as a complementary technique to visualize the effect of photoresist development where microstructure shrinkage could occur. In addition, we applied the technique to visualize a three-photon polymerized microstructure that was fabricated in the same microscopy setup. This demonstrates the potential of the technique for in situ microscopy of photopolymerized microstructures in three dimensions.publishedVersionPeer reviewe

Demonstration of the hierarchical arrangement of persistent luminescent microparticles in direct doping-prepared photonic glasses using second-harmonic generation microscopy

Using three-dimensional (3D) second-harmonic generation (SHG) scanning microscopy, we unravel the formation and distribution of distinct and highly localized persistent luminescent (PeL) microparticles of varied hierarchical levels in glasses prepared using the direct doping method. The PeL microparticles were added in the glasses at different doping temperatures and the glasses were quenched after different dwell time. The SHG maps of the PeL microparticles in the glass, prepared with a doping temperature of 975°C and a dwell time of 3 min, reveal grating-like microscopic domains. This suggests that a large arrangement of PeL crystals spanning several micrometers in three dimensions is manifested by the imbued PeL microparticle. In contrast, the SHG maps of the PeL microparticles inside the glass prepared at doping temperature of 1025°C and dwell time of 10 min, show the existence of single, highly localized and most importantly, submicrometer-sized PeL crystals. These findings substantiate well with the expected behavior of the PeL microparticles in glasses and their physical disintegration in the form of nanoparticles at high doping temperatures and dwell times. The SHG microscopy technique is shown to circumvent the fundamental challenges of traditional and usually destructive imaging methods to detect and visualize PeL nanoparticles in a glass matrix and expected to open a new avenue to evidence the presence of crystals in glasses.publishedVersionPeer reviewe

Lead-free cesium titanium bromide double perovskite nanocrystals

Double perovskites are a promising family of lead-free materials that not only replace lead but also enable new optoelectronic applications beyond photovoltaics. Recently, a titanium (Ti)-based vacancy-ordered double perovskite, Cs2 TiBr6, has been reported as an example of truly sustainable and earth-abundant perovskite with controversial results in terms of photoluminescence and environmental stability. Our work looks at this material from a new perspective, i.e., at the nanoscale. We demonstrate the first colloidal synthesis of Cs2 TiX6 nanocrystals (X = Br, Cl) and observe tunable morphology and size of the nanocrystals according to the set reaction temperature. The Cs2 TiBr6 nanocrystals synthesized at 185◦ C show a bandgap of 1.9 eV and are relatively stable up to 8 weeks in suspensions. However, they do not display notable photoluminescence. The centrosymmetric crystal structure of Cs2 TiBr6 suggests that this material could enable third-harmonic generation (THG) responses. Indeed, we provide a clear evidence of THG signals detected by the THG microscopy technique. As only a few THG-active halide perovskite materials are known to date and they are all lead-based, our findings promote future research on Cs2 TiBr6 as well as on other lead-free double perovskites, with stronger focus on currently unexplored nonlinear optical applications.publishedVersionPeer reviewe

Reduced graphene oxide integrated poly(ionic liquid) functionalized nano-fibrillated cellulose composite paper with improved toughness, ductility and hydrophobicity

Reduced graphene oxide (rGO) integrated nano-fibrillated cellulose (NFC) grafted poly(ionic liquid) (PIL) composite paper with enhanced hydrophobicity, ductility and toughness was fabricated by vacuum filtration of an aqueous dispersion of rGO/NFC-graft-PIL (NFC-g-PIL). The NFC-g-PIL was synthesized by growing PIL chains from the NFC surface using free radical polymerization of a pyridinium acrylate-based ionic liquid monomer.Peer reviewe