Ring Vibrations to Sense Anionic Ibuprofen in Aqueous Solution as Revealed by Resonance Raman

We unravel the potentialities of resonance Raman spectroscopy to detect ibuprofen in diluted aqueous solutions. In particular, we exploit a fully polarizable quantum mechanics/molecular mechanics (QM/MM) methodology based on fluctuating charges coupled to molecular dynamics (MD) in order to take into account the dynamical aspects of the solvation phenomenon. Our findings, which are discussed in light of a natural bond orbital (NBO) analysis, reveal that a selective enhancement of the Raman signal due to the normal mode associated with the C–C stretching in the ring, νC=C, can be achieved by properly tuning the incident wavelength, thus facilitating the recognition of ibuprofen in water samples.

Use of Recycling-Reflection Color-Purity Enhancement Film to Improve Color Purity of Full-Color Micro-LEDs

A common full-color method involves combining micro-light-emitting diodes (LEDs) chips with color conversion materials such as quantum dots (QDs) to achieve full color. However, during color conversion between micro-LEDs and QDs, QDs cannot completely absorb incident wavelengths cause the emission wavelengths that including incident wavelengths and converted wavelength through QDs, which compromises color purity. The present paper proposes the use of a recycling-reflection color-purity-enhancement film (RCPEF) to reflect the incident wavelength multiple times and, consequently, prevent wavelength mixing after QDs conversion. This RCPEF only allows the light of a specific wavelength to pass through it, exciting blue light is reflected back to the red and green QDs layer. The prototype experiment indicated that with an excitation light source wavelength of 445.5 nm, the use of green QDs and RCPEFs increased color purity from 77.2% to 97.49% and light conversion efficiency by 1.97 times and the use of red QDs and RCPEFs increased color purity to 94.68% and light conversion efficiency by 1.46 times. Thus, high efficiency and color purity were achieved for micro-LEDs displays. Graphical Abstract

Extraordinary optical transmission from a thin microcavity by macroscopic quantum effect

The macroscopic quantum effect is revealed to elaborate the extraordinary optical transmission (EOT) from a subwavelength thin microcavity based on the uncertainty property of the transmitted electromagnetic fields after the aperture. A critical radius is found in the thin microcavity under a certain incident electromagnetic wavelength. With the aperture radius varying, the transmitted field can be divided into three regimes: I. the macroscopic quantum regime when the aperture radius is less than the critical radius, in which the field edge effect occurs and EOT phenomenon is perfectly manifested; II. The wave-particle duality regime in the vicinity of the critical radius, in which the edge effect and diffraction phenomenon exist simultaneously; III. The wave regime when the aperture radius is greater than the critical radius, in which the near-field diffraction emerges. In addition, the influences of incident wavelength and microcavity thickness on EOT are also investigated. Our research have potential applications in advanced optical devices, such as light switch and optical manipulations.

INVESTIGATION OF THE SURFACE PLASMON-POLARITONS EXCITATION EFFICIENCY ON ALUMINUM GRATINGS, TAKING INTO ACCOUNT DIFFRACTED RADIATION

Detailed studies of the efficiency of excitation of surface plasmon-polaritons (SPP) on aluminum gratings with a period a = 694 nm, which exceeds the incident wavelength of λ = 632,8 nm, have been carried out. The gratings relief depth (h) range was 6–135 nm. Research samples were formed on As40S30Se30 chalcogenide photoresist films using interference lithography and vacuum thermal deposition of an opaque aluminum layer about 80 nm thick. An atomic force microscope was used to determine the groove profile shape and the grating relief depth. The study of the SPP excitation features was carried out on a stand mounted on the basis of a G5M goniometer and an FS-5 Fedorov stage by measuring the angular dependences of the intensity of specularly reflected and diffracted p-polarized radiation of He-Ne laser. When determining the SPP excitation efficiency, the resonance values of both specular reflection and reflection in the -1st DO were taken into account. It was found that the dependence of the integral plasmon absorption on the grating modulation depth (h/a) is described by a somewhat asymmetric curve with a wide maximum, the position of which corresponds to an h/a value of about 0.07 and a half-width of about 0.123. This allows to excite SPP with an efficiency ≥ 80% of the maximum value on the gratings with the 0,05-0,105 h/a range. The half-width of the plasmon minimum of the reflection in the -1st DO is less than in the specular reflection, which can increase sensitivity of sensor devices when registering the shift of the minimum from angular measurements. The dependence of the half-width of the SPP reflection minima on the grating modulation depth is close to quadratic. In the investigated h/a range (from 0.009 to 0.194), the maximum dynamic range of the reflection coefficient is two orders of magnitude and is achieved in specular reflection for gratings with h/a ≈ 0.075.

Theoretical and Experimental Investigation on SPR Gas Sensor Based on ZnO/Polypyrrole Interface For Ammonia Sensing Applications

This work includes the exploitation of laboratory-assembled SPR technique for the application of gas sensor at room temperature. The refractive index change at the interface of ZnO/Polypyrrole with adsorption of gases (NO2 and NH3) is the basis of SPR gas sensor. The theoretical simulations were done to find out the optimum thickness of ZnO and Polypyrrole composite films for sharp SPR reflectance values. Theoretical SPR curves obtained by changing the value of thickness of Gold nanoparticles film and incident wavelength are also presented in the manuscript. Experimental studies were done to validate the theoretical studies and discussion were done about the interaction of NH3 gas with prism/Au/ZnO/Polypyrrole system. Here, ZnO/Polypyrrole multilayer structure is the sensing layer to develop highly efficient SPR based NH3 gas sensor. The outcome of these results validate the significance of SPR technique for application of interaction of surface adsorbed analytes, with the interface of dielectrics and sensing material.

A numerical study on the closed packed array of gold discs as an efficient dual mode plasmonic tweezers

In this report, we propose the closed pack array of gold discs on glass, as a dual mode plasmonic tweezers that benefits from two trapping modes. The first trapping mode is based on leaky surface plasmon mode (LSPM) on the gold discs with a longer penetration depth in the water and a longer spatial trapping range, so that target nanoparticles with a radius of 100 nm can be attracted toward the gold surface from a vertical distance of about 2 µm. This trapping mode can help to overcome the inherent short range trapping challenge in the plasmonic tweezers. The second trapping mode is based on the dimer surface plasmonic mode (DSPM) in the nano-slits between the neighboring gold discs, leading to isolated and strong trapping sites for nanoparticles smaller than 34 nm. The proposed plasmonic tweezers can be excited in both LSPM and DSPM modes by switching the incident wavelength, resulting in promising and complementary functionalities. In the proposed plasmonic tweezers, we can attract the target particles towards the gold surface by LSPM gradient force, and trap them within a wide half widthhalfmaximum (HWHM) that allows studying the interactions between the trapped particles, due to their spatial proximity. Then, by switching to the DSPM trapping mode, we can rearrange the particles in a periodic pattern of isolated and stiff traps. The proposed plasmonic structure and the presented study opens a new insight for realizing efficient, dual-mode tweezers with complementary characteristics, suitable for manipulation of nanoparticles. Our thermal simulations demonstrate that the thermal-induced forces does not interefe with the proposed plasmonic tweezing.

Design of Switchable On/Off Subpixels for Primary Color Generation Based on Molybdenum Oxide Gratings

Structural color emerges from the interaction of light with structured matter when its dimension is comparable to the incident wavelength. The reflected color can be switched by controlling such interaction with materials whose properties can be changed through external stimuli such as electrical, optical, or thermal excitation. In this research, a molybdenum oxide (MoOx) reflective grating to get a switchable on/off subpixel is designed and analyzed. The design is based on subpixel on and off states that could be controlled through the oxidation degree of MoOx. A suitable combination of three of these subpixels, optimized to get a control of primary colors, red, green, and blue, can lead to a pixel which can cover a wide range of colors in the color space for reflective display applications.

Nonlinear Optical Properties of Porphyrin, Fullerene and Ferrocene Hybrid Materials

In this research, we investigated the second-order nonlinear optical (NLO) properties of multicomponent hybrid materials formed by meso-tetraphenylporphyrin P (both as free base and ZnII complex), carrying in 2 or 2,12 β-pyrrolic position an electron donor ferrocene (Fc), and/or an electron acceptor fullerene (C60) moiety, connected to the porphyrin core via an ethynyl or an ethynylphenyl spacer. We measured the NLO response by the electric-field-induced second-harmonic generation (EFISH) technique in CH2Cl2 solution with a 1907 nm incident wavelength, recording for all the investigated compounds unexpected negative values of μβ1907. Since density functional theory (DFT) calculations evidenced for P-Fc dyads almost null ground state dipole moments and very low values for P-C60 dyads and Fc-P-C60 triads, our EFISH results suggested a significant contribution to γEFISH of the purely electronic cubic term γ(−2ω; ω, ω, 0), which prevails on the quadratic dipolar orientational one μβ(−2ω; ω, ω)/5kT, as confirmed by computational evidence.

Computational Sub-10 nm Plasmonic Nanogap Patterns by Block Copolymer Self-Assembly

Plasmonic nanoparticle (NP) arrays with narrow gaps have been suggested as an effective light collection solution for plasmonic structures. For an effective low-cost bottom-up strategy, block copolymer (BCP) self-assembly with evaporative metal-deposition is mentioned as one of the best effective ways to produce Au NP arrays with narrow gaps. In this paper, BCP self-assembly for nanopost-template arrays and metal-deposition over the nanotemplate surface for positional arrangement of Au NPs are described using a self-consistent field theory (SCFT) and a level-set method, respectively. According to the of BCP self-assembly simulation results, both the diameter of the cylinder post and gap size become larger due to the increase of polymerization degree (N). However, these parameters become smaller in terms of the increase of the Flory-Huggins interaction parameter χ. For plasmonic phenomena about a top-down incident wavelength of 600-nm, according to a rigorous coupled-wave analysis (RCWA), although the electric field around a single spherical post becomes larger at smaller diameter, there is no top-down plasmonic phenomenon at a gap size of 10-nm between nanoposts.