A Semitransparent and Flexible Single Crystal Si Thin Film: Silicon on Nothing (SON) Revisited

Ultrathin single crystal Si films offer a versatile vehicle for high performance flexible and semitransparent electric devices due to their outstanding optoelectric and mechanical properties. Here, we demonstrate the formation of an ultrathin (100) single crystal Si film based on morphological evolution of nanoporous Si during high temperature annealing. Square arrays of cylindrical Si pores are formed by nanoimprint lithography and deep reactive etching and then subjected to annealing in hydrogen ambient. By controlling the aspect ratio of nanoporous Si, defect-free single crystal Si membranes with controlled thicknesses from 330 to 470 nm are formed on a platelike void after the annealing. In addition, we investigate the role of oxygen impurities in a hydrogen atmosphere on defect formation on a Si surface and eliminate the oxygen-related defects on Si by controlling gas phase diffusion of oxygen impurities during annealing in a conventional tube furnace. Finally, we demonstrate the transfer of a defect-free, flexible, and wafer scale Si membrane with thickness of 470 nm onto a PDMS substrate, utilizing the platelike void under the membrane as a releaser. The ultrathin flexible Si film on PDMS shows optical transmittance of about 30–70% in visible and near-infrared light

Supplementary document for Easy-to-make-and-use gold nanotrench arrays for surface-enhanced Raman scattering - 5367773.pdf

Experimental details of microRNA measurement

Supplementary document for Easy-to-make-and-use gold nanotrench arrays for surface-enhanced Raman scattering - 5427738.pdf

Details of SERS measurement

Analyte-Induced Desert Rose-like Ag Nanostructures for Surface-Enhanced Raman Scattering-Based Biomolecule Detection and Imaging

Biomolecule detection based on surface-enhanced Raman scattering (SERS) for application to biosensors and bio-imaging requires the fabrication of SERS nanoprobes that can generate strong Raman signals as well as surface modifications for analyte-specific recognition and binding. Such requirements lead to disadvantages in terms of reproducibility and practicality, and thus, it has been difficult to apply biomolecule detection utilizing the advantages of the SERS phenomenon to actual clinically relevant analysis. To achieve reproducible and practical SERS signal generation in a biomolecule-specific manner without requiring the synthesis of nanostructures and their related surface modification to introduce molecules for specific recognition, we developed a new type of SERS probe formed by enzyme reactions in the presence of Raman reporters. By forming unique plasmonic structures, our method achieves the detection of biomolecules on chips with uniform and stable signals over long periods. To test the proposed approach, we applied it to a SERS-based immunohistochemistry assay and found successful multiplexed protein detection in brain tissue from transgenic mice

Dual-Function Janus Nanozymes for Performance Evaluation and Application in a Surrogate Virus Neutralization Test with Vaccinated Samples

The need exists for biosensing technologies capable of sensitively and accurately detecting various biomarkers. In response, the development of nanozymes is actively underway; they have advantages in stability, cost, performance, and functionalization over natural enzymes commonly used for signal amplification in sensing technologies. However, the performance of nanozymes is interdependent with factors such as shape, size, and surface functional moiety, making it challenging to perform quantitative performance comparisons based on the nanozyme material. In this study, we propose a physical synthetic approach to fabricate double-layered bimetallic nanozymes with identical shapes, sizes, and surfaces but different material compositions. These Janus nanozymes consist of a nanozymatic layer responsible for catalytic activity and a gold layer responsible for quantification and efficient surface modification. Based on their identical physicochemical properties, the synthesized double-layered bimetallic nanozymes allow, for the first time, a quantitative comparison of nanozymatic activities in terms of various kinetic parameters. We compared several candidates and found that the Ir–Au nanozyme exhibited the best performance. Subsequently, we applied this nanozyme to detect neutralizing antibodies against SARS-CoV-2 based on a surrogate virus neutralization test. The results demonstrated a limit of detection as low as 2 pg/mL and selectivity specifically toward MERS-CoV. The performance of this assay was further validated using vaccinated samples, demonstrating the potential of our approach as a cost-effective, rapid, and sensitive diagnostic tool for neutralizing antibody detection against viruses such as SARS-CoV-2

Sombrero-Shaped Plasmonic Nanoparticles with Molecular-Level Sensitivity and Multifunctionality

We demonstrate top-down synthesis of monodisperse plasmonic nanoparticles designed to contain internal Raman hot spots. Our Raman-active nanoparticles are fabricated using nanoimprint lithography and thin-film deposition and are composed of novel internal structures with sublithographic dimensions: a disk-shaped Ag core, a Petri-dish-shaped SiO₂ base whose inner surface is coated with Ag film, and a sub-10 nm scale circular gap between the core and the base. Confocal Raman measurements and electromagnetic simulations show that Raman hot spots appear at the inside perimeter of individual nanoparticles and serve as the source of a 1000-fold improvement of minimum molecular detection level that enables detection of signals from a few molecules near hot spots. A multimodality version of these nanoparticles, which includes the functionality offered by magnetic multilayers, is also demonstrated. These results illustrate the potential of direct fabrication for creating exotic monodisperse nanoparticles, which combine engineered internal nanostructures and multilayer composite materials, for use in nanoparticle-based molecular imaging and detection

Hierarchical Silver Network Transparent Conducting Electrodes for Thin-Film Solar Cells

Flexible metal network transparent conducting electrodes (TCEs) are expected to be the most promising candidates to replace indium tin oxide (ITO) due to their excellent electro-optical performance and mechanical flexibility. However, to successfully replace ITO with the metal network TCEs, more studies on their suitability for integration with real devices are needed. In this study, we developed a hierarchical silver network simultaneously meeting the requirements of (i) low sheet resistance, (ii) high optical transmittance, (iii) excellent mechanical flexibility, and (iv) good integration into a thin-film solar cell. The hierarchical silver network consists of a silver micromesh as the main framework and silver nanowires as the secondary framework. The hierarchical network provides a figure of merit similar to that of the individual micromesh and much higher than those of silver nanowires and ITO. When applied to Cu­(In, Ga)­Se2 thin-film solar cells, the hierarchical network achieved better device performance than the micromesh. In the hierarchical network, the micromesh enables low sheet resistance and the silver nanowires enable excellent integration with the device while maintaining high optical transmittance. Thus, considering the aforementioned requirements, the hierarchical network could be one of the best candidates as a TCE for Cu­(In, Ga)­Se2 thin-film solar cells

Hierarchical Silver Network Transparent Conducting Electrodes for Thin-Film Solar Cells

Flexible metal network transparent conducting electrodes (TCEs) are expected to be the most promising candidates to replace indium tin oxide (ITO) due to their excellent electro-optical performance and mechanical flexibility. However, to successfully replace ITO with the metal network TCEs, more studies on their suitability for integration with real devices are needed. In this study, we developed a hierarchical silver network simultaneously meeting the requirements of (i) low sheet resistance, (ii) high optical transmittance, (iii) excellent mechanical flexibility, and (iv) good integration into a thin-film solar cell. The hierarchical silver network consists of a silver micromesh as the main framework and silver nanowires as the secondary framework. The hierarchical network provides a figure of merit similar to that of the individual micromesh and much higher than those of silver nanowires and ITO. When applied to Cu­(In, Ga)­Se2 thin-film solar cells, the hierarchical network achieved better device performance than the micromesh. In the hierarchical network, the micromesh enables low sheet resistance and the silver nanowires enable excellent integration with the device while maintaining high optical transmittance. Thus, considering the aforementioned requirements, the hierarchical network could be one of the best candidates as a TCE for Cu­(In, Ga)­Se2 thin-film solar cells