Distance-controlled surface-enhanced Raman spectroscopy of nanoparticles.

Biological particles, e.g., viruses, lipid particles, and extracellular vesicles, are attracting significant research interest due to their role in biological processes and potential in practical applications, such as vaccines, diagnostics, and therapies. Their surface and interior contain many different molecules including lipids, nucleic acids, proteins, and carbohydrates. In this Letter, we show how distance-controlled surface-enhanced Raman spectroscopy (SERS) is a promising method to extract essential information from the spatial origin of the signal. This is a highly important parameter in the analysis of these biological particles. The principle of the method is demonstrated by using polystyrene (PS) beads as a biological particle model conjugated with gold nanospheres (AuNSs) functioning as distance-controlled SERS probes via biotin-streptavidin binding. By tuning the size of AuNSs, the Raman signal from the PS beads can be weakened while the signal from the biotin-streptavidin complex is enhanced.

Tuning temperature gradients in subwavelength plasmonic nanocones with tilted illumination.

Inducing and controlling temperature gradients in illuminated subwavelength plasmonic structures is a challenging task. Here, we present a strategy to remotely induce and tune temperature gradients in a subwavelength metallic nanocone by adjusting the angle of incidence of linearly polarized continuous-wave illumination. We demonstrate, through rigorous three-dimensional numerical simulations, that properly tilting the incident illumination angle can increase or decrease the photoinduced temperature gradients within the nanostructure. We analyze the apex-base photoinduced temperature gradient for different illumination directions, resembling typical illumination schemes utilized in surface or tip-enhanced Raman spectroscopy.

Dielectric Cavity-Insulator-Metal (DCIM) Metamaterial Absorber in Visible Range.

For many years, metamaterial absorbers have received much attention in a wide range of application fields. There is an increasing need to search for new design approaches that fulfill more and more complex tasks. According to the specific application requirements, design strategy can vary from structure configurations to material selections. A new combination of a dielectric cavity array, dielectric spacer, and gold reflector as a metamaterial absorber is proposed and theoretically studied in this work. The complexity of the dielectric cavities leads to a more flexible optical response than traditional metamaterial absorbers. It gives a new dimension of freedom for a real three-dimensional metamaterial absorber design.

Bloch Surface Waves in Open Fabry-Perot Microcavities.

Thanks to the increasing availability of technologies for thin film deposition, all-dielectric structures are becoming more and more attractive for integrated photonics. As light-matter interactions are involved, Bloch Surface Waves (BSWs) may represent a viable alternative to plasmonic platforms, allowing easy wavelength and polarization manipulation and reduced absorption losses. However, plasmon-based devices operating at an optical and near-infrared frequency have been demonstrated to reach extraordinary field confinement capabilities, with localized mode volumes of down to a few nanometers. Although such levels of energy localization are substantially unattainable with dielectrics, it is possible to operate subwavelength field confinement by employing high-refractive index materials with proper patterning such as, e.g., photonic crystals and metasurfaces. Here, we propose a computational study on the transverse localization of BSWs by means of quasi-flat Fabry-Perot microcavities, which have the advantage of being fully exposed toward the outer environment. These structures are constituted by defected periodic corrugations of a dielectric multilayer top surface. The dispersion and spatial distribution of BSWs' cavity mode are presented. In addition, the hybridization of BSWs with an A exciton in a 2D flake of tungsten disulfide (WS2) is also addressed. We show evidence of strong coupling involving not only propagating BSWs but also localized BSWs, namely, band-edge and cavity modes.

Bottom-Gate Approach for All Basic Logic Gates Implementation by a Single-Type IGZO-Based MOS Transistor with Reduced Footprint.

Logic functions are the key backbone in electronic circuits for computing applications. Complementary metal-oxide-semiconductor (CMOS) logic gates, with both n-type and p-type channel transistors, have been to date the dominant building blocks of logic circuitry as they carry obvious advantages over other technologies. Important physical limits are however starting to arise, as the transistor-processing technology has begun to meet scaling-down difficulties. To address this issue, there is the crucial need for a next-generation electronics era based on new concepts and designs. In this respect, a single-type channel multigate MOS transistor (SMG-MOS) is introduced holding the two important aspects of processing adaptability and low static dissipation of CMOS. Furthermore, the SMG-MOS approach strongly reduces the footprint down to 40% or even less area needed for current CMOS logic function in the same processing technology node. Logic NAND, NOT, AND, NOR, and OR gates, which typically require a large number of CMOS transistors, can be realized by a single SMG-MOS transistor. Two functional examples of SMG-MOS are reported here with their analysis based both on simulations and experiments. The results strongly suggest that SMG-MOS can represent a facile approach to scale down complex integrated circuits, enabling design flexibility and production rates ramp-up.

Improved galvanic replacement growth of Ag microstructures on Cu micro-grid for enhanced SERS detection of organic molecules.

Galvanic growth of Ag nano/micro-structures on Cu micro-grid was systematically studied for surface-enhanced Raman scattering (SERS) applications. Detailed characterizations via FE-SEM and HR-TEM showed that processing parameters, (reaction time, Ag(+) concentration, and PVP addition) all substantially affect thermodynamics/kinetics of the replacement reaction to yield substrates of significantly different microstructures/homogeneities and thus varied SERS performances (sensitivity, enhancement factor, and reproducibility) of the Ag substrates in the detection of R6G analyte. PVP as an additive was shown to notably alter nucleation/growth behaviors of the Ag crystals and promote the deposition of dense and uniform Ag films of nearly monodisperse polyhedrons/nanoplates through suppressing dendrites crystallization. Under optimized synthesis (50mM of Ag(+), 30s of reaction, and 700 wt.% of PVP), Ag substrates exhibiting a high Raman signal enhancement factor of ~1.1 × 10(6) and a low relative standard deviation of ~0.13 in the repeated detection of 10 µM R6G were obtained. The facile deposition and excellent performance reported in this work may allow the Ag microstructures to find wider SERS applications. Moreover, growth mechanisms of the different Ag nano/micro-structures were discussed based on extensive FE-SEM and HR-TEM analysis.

Controlled photocatalytic growth of Ag nanocrystals on brookite and rutile and their SERS performance.

Ag nanocrystals (NCs) were photocatalytically grown on the surfaces of brookite and rutile nanocrystals, respectively, and their surface-enhanced Raman scattering (SERS) performance was evaluated. The resultant Ag NCs exhibit different morphologies owing to the different photocatalytic capabilities of the two types of TiO2 under otherwise identical synthetic conditions. The effects of AgNO3 concentration, UV irradiation time, and UV light power on the morphology evolution and growth kinetics of the Ag NCs were systematically investigated. Moreover, PVP was found to serve as both a reductant and a capping agent in the photocatalytic reaction systems, and its presence allows morphological control of the Ag NCs. A proper amount of PVP was confirmed to favor Ag nanoplates of larger sizes and to produce SERS substrates of substantially better performance.