Exploiting Thin-Film Properties and Guided-Mode Resonance for Designing Ultrahigh-Figure-of-Merit Refractive Index Sensors.

Guided-mode resonance (GMR) gratings have emerged as a promising sensing technology, with a growing number of applications in diverse fields. This study aimed to identify the optimal design parameters of a simple-to-fabricate and high-performance one-dimensional GMR grating. The structural parameters of the GMR grating were optimized, and a high-refractive-index thin film was simulated on the grating surface, resulting in efficient confinement of the electric field energy within the waveguide. Numerical simulations demonstrated that the optimized GMR grating exhibited remarkable sensitivity (252 nm/RIU) and an extremely narrow full width at half maximum (2 × 10-4 nm), resulting in an ultra-high figure of merit (839,666) at an incident angle of 50°. This performance is several orders of magnitude higher than that of conventional GMR sensors. To broaden the scope of the study and to make it more relevant to practical applications, simulations were also conducted at incident angles of 60° and 70°. This holistic approach sought to develop a comprehensive understanding of the performance of the GMR-based sensor under diverse operational conditions.

Facile and Unplugged Surface Plasmon Resonance Biosensor with NIR-Emitting Perovskite Nanocomposites for Fast Detection of SARS-CoV-2.

The emergence of the coronavirus disease 2019 (COVID-19) pandemic prompted researchers to develop portable biosensing platforms, anticipating to detect the analyte in a label-free, direct, and simple manner, for deploying on site to prevent the spread of the infectious disease. Herein, we developed a facile wavelength-based SPR sensor built with the aid of a 3D printing technology and synthesized air-stable NIR-emitting perovskite nanocomposites as the light source. The simple synthesis processes for the perovskite quantum dots enabled low-cost and large-area production and good emission stability. The integration of the two technologies enabled the proposed SPR sensor to exhibit the characteristics of lightweight, compactness, and being without a plug, just fitting the requirements of on-site detection. Experimentally, the detection limit of the proposed NIR SPR biosensor for refractive index change reached the 10-6 RIU level, comparable with that of state-of-the-art portable SPR sensors. In addition, the bio-applicability of the platform was validated by incorporating a homemade high-affinity polyclonal antibody toward the SARS-CoV-2 spike protein. The results demonstrated that the proposed system was capable of discriminating between clinical swab samples collected from COVID-19 patients and healthy subjects because the used polyclonal antibody exhibited high specificity against SARS-CoV-2. Most importantly, the whole measurement process not only took less than 15 min but also needed no complex procedures or multiple reagents. We believe that the findings disclosed in this work can open an avenue in the field of on-site detection for highly pathogenic viruses.

Boosting the detection performance of severe acute respiratory syndrome coronavirus 2 test through a sensitive optical biosensor with new superior antibody.

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus emerged in late 2019 leading to the COVID-19 disease pandemic that triggered socioeconomic turmoil worldwide. A precise, prompt, and affordable diagnostic assay is essential for the detection of SARS-CoV-2 as well as its variants. Antibody against SARS-CoV-2 spike (S) protein was reported as a suitable strategy for therapy and diagnosis of COVID-19. We, therefore, developed a quick and precise phase-sensitive surface plasmon resonance (PS-SPR) biosensor integrated with a novel generated anti-S monoclonal antibody (S-mAb). Our results indicated that the newly generated S-mAb could detect the original SARS-CoV-2 strain along with its variants. In addition, a SARS-CoV-2 pseudovirus, which could be processed in BSL-2 facility was generated for evaluation of sensitivity and specificity of the assays including PS-SPR, homemade target-captured ELISA, spike rapid antigen test (SRAT), and quantitative reverse transcription polymerase chain reaction (qRT-PCR). Experimentally, PS-SPR exerted high sensitivity to detect SARS-CoV-2 pseudovirus at 589 copies/ml, with 7-fold and 70-fold increase in sensitivity when compared with the two conventional immunoassays, including homemade target-captured ELISA (4 × 103 copies/ml) and SRAT (4 × 104 copies/ml), using the identical antibody. Moreover, the PS-SPR was applied in the measurement of mimic clinical samples containing the SARS-CoV-2 pseudovirus mixed with nasal mucosa. The detection limit of PS-SPR is calculated to be 1725 copies/ml, which has higher accuracy than homemade target-captured ELISA (4 × 104 copies/ml) and SRAT (4 × 105 copies/ml) and is comparable with qRT-PCR (1250 copies/ml). Finally, the ability of PS-SPR to detect SARS-CoV-2 in real clinical specimens was further demonstrated, and the assay time was less than 10 min. Taken together, our results indicate that this novel S-mAb integrated into PS-SPR biosensor demonstrates high sensitivity and is time-saving in SARS-CoV-2 virus detection. This study suggests that incorporation of a high specific recognizer in SPR biosensor is an alternative strategy that could be applied in developing other emerging or re-emerging pathogenic detection platforms.

Superhydrophilic Modification of Polycarbonate Substrate Surface by Organic Plasma Polymerization Film.

Superhydrophilicity performs well in anti-fog and self-cleaning applications. In this study, polycarbonate substrate was used as the modification object because of the low surface energy characteristics of plastics. Procedures that employ plasma bombardment, such as etching and high surface free energy coating, are applied to improve the hydrophilicity. An organic amino silane that contains terminal amine group is introduced as the monomer to perform plasma polymerization to ensure that hydrophilic radicals can be efficiently deposited on substrates. Different levels of hydrophilicity can be reached by modulating the parameters of plasma bombardment and polymerization, such as plasma current, voltage of the ion source, and bombardment time. The surface of a substrate that is subjected to plasma bombarding at 150 V, 4 A for 5 min remained superhydrophilic for 17 days. After 40 min of Ar/O2 plasma bombardment, which resulted in a substrate surface roughness of 51.6 nm, the plasma polymerization of organic amino silane was performed by tuning the anode voltage and operating time of the ion source, and a water contact angle < 10° and durability up to 34 days can be obtained.

Design of a High-Efficiency Multilayer Dielectric Diffraction Grating with Enhanced Laser Damage Threshold.

Diffraction gratings are becoming increasingly widespread in optical applications, notably in lasers. This study presents the work on the characterization and evaluation of Multilayer Dielectric Diffraction Gratings (MDG) based on the finite element method using Comsol MultiPhysics software. The optimal multilayer dielectric diffraction grating structure using a rectangular three-layer structure consisting of an aluminum oxide Al2O3 layer sandwiched between two silicon dioxide SiO2 layers on a multilayer dielectric mirror is simulated. Results show that this MDG for non-polarized lasers at 1064 nm with a significantly enhanced -1st diffraction efficiency of 97.4%, reaching 98.3% for transverse-electric (TE) polarization and 96.3% for transverse-magnetic (TM) polarization. This design is also preferable in terms of the laser damage threshold (LDT) because most of the maximum electric field is spread across the high LDT material SiO2 for TE polarization and scattered outside the grating for TM polarization. This function allows the system to perform better and be more stable than normal diffraction grating under a high-intensity laser.

A Simple Phase-Sensitive Surface Plasmon Resonance Sensor Based on Simultaneous Polarization Measurement Strategy.

The SPR phenomenon results in an abrupt change in the optical phase such that one can measure the phase shift of the reflected light as a sensing parameter. Moreover, many studies have demonstrated that the phase changes more acutely than the intensity, leading to a higher sensitivity to the refractive index change. However, currently, the optical phase cannot be measured directly because of its high frequency; therefore, investigators usually have to use complicated techniques for the extraction of phase information. In this study, we propose a simple and effective strategy for measuring the SPR phase shift based on phase-shift interferometry. In this system, the polarization-dependent interference signals are recorded simultaneously by a pixelated polarization camera in a single snapshot. Subsequently, the phase information can be effortlessly acquired by a phase extraction algorithm. Experimentally, the proposed phase-sensitive SPR sensor was successfully applied for the detection of small molecules of glyphosate, which is the most frequently used herbicide worldwide. Additionally, the sensor exhibited a detection limit of 15 ng/mL (0.015 ppm). Regarding its simplicity and effectiveness, we believe that our phase-sensitive SPR system presents a prospective method for acquiring phase signals.

Dissociation of water on atomic oxygen-covered Rh nanoclusters supported on graphene/Ru(0001).

We studied the dissociation of water (H2O*, with * denoting adspecies) on atomic oxygen (O*)-covered Rh nanoclusters (RhO* ) supported on a graphene film grown on a Ru(0001) surface [G/Ru(0001)] under ultrahigh-vacuum conditions and with varied surface-probe techniques and calculations based on density-functional theory. The graphene had a single rotational domain; its lattice expanded by about 5.7% to match the Ru substrate structurally better. The Rh clusters were grown by depositing Rh vapors onto G/Ru(0001); they had an fcc phase and grew in (111) orientation. Water adsorbed on the Rh clusters was dissociated exclusively in the presence of O*, like that on a Rh(111) single-crystal surface. Contrary to the case on Rh(111)O* , excess O* (even at a saturation level) on small RhO* clusters (diameter of 30-34 Å) continued to promote, instead of inhibiting, the dissociation of water; the produced hydroxyl (OH*) increased generally with the concentration of O* on the clusters. The difference results from more reactive O* on the RhO* clusters. O* on RhO* clusters activated the dissociation via both the formation of hydrogen bonds with H2O* and abstraction of H directly from H2O*, whereas O* on Rh(111)O* assisted the dissociation largely via the formation of hydrogen bonds, which was readily obstructed with an increased O* coverage. As the disproportionation (2 OH* → H2O* + O*) is endothermic on the RhO* clusters but exothermic on Rh(111)O* , OH* produced on RhO* clusters showed a thermal stability superior to that on the Rh(111)O* surface-thermally stable up to 400 K.

Engineering an Indium Selenide van der Waals Interface for Multilevel Charge Storage.

As the continuous miniaturization of floating-gate transistors approaches a physical limit, new innovations in device architectures, working principles, and device materials are in high demand. This study demonstrated a nonvolatile memory structure with multilevel data storage that features a van der Waals gate architecture made up of a partially oxidized surface layer/indium selenide (InSe) van der Waals interface. The key functionality of this proof-of-concept device is provided through the generation of charge-trapping sites via an indirect oxygen plasma treatment on the InSe surface layer. In contrast to floating-gate nonvolatile memory, these sites have the ability to retain charge without the help of a gate dielectric. Together with the layered structure, the surface layer with charge-trapping sites facilitates continual electrostatic doping in the underlying InSe layers. The van der Waals gating effect is further supported by trapped charge-induced core-level energy shifts and relative work function variations obtained from operando scanning X-ray photoelectron spectroscopy and Kelvin probe microscopy, respectively. On modulating the amount of electric field-induced trapped electrons by the electrostatic gate potential, eight distinct storage states remained over 3000 s. Moreover, the device exhibits a high current switching ratio of 106 within 11 cycles. The demonstrated characteristics suggest that the engineering of an InSe interface has potential applications for nonvolatile memory.

Admittance analysis of broadband omnidirectional near-perfect absorber in epsilon-near-zero mode.

In this paper, we propose a broadband omnidirectional near-perfect absorber that transforms light energy into heat. In contrast to previous research on structural metamaterials, this study focuses on light absorption in the epsilon-near-zero (ENZ) layers without any structural patterns. Chromium (Cr) thin films were applied as ENZ layers. Using the admittance method, we found the proper thicknesses of SiO2 layers to match the incident medium and achieve perfect absorption. Also, the absorber is angular insensitive up to 60°. The temperature of the absorber increases from room temperature to 42°C, which is 4°C higher than the uncoated substrate at 38°C, after exposure to sunlight for 20 min.

Dipolar magnetism in assembled Co nanoparticles on graphene.

The magnetic properties of the assembled Co nanoparticles on graphene were studied using X-ray magnetic circular dichroism (XMCD), magneto-optical Kerr effects, and a modeling simulation. We demonstrate that the superparamagnetic nanoparticles reveal a ferromagnetic phase when they are assembled on graphene. The moderate increase of the XMCD asymmetry and magnetization with coverage for this assembly indicates a dipolar-mediated magnetism, which is further verified by a model simulation considering the dipolar interaction between neighboring nanoparticles. Furthermore, C K-edge spectra reveal visible dichroism at the π* state of graphene, which indicates the existence of a spin-polarized interface state, while the assembled Co nanoparticles reveal a ferromagnetic phase. These results suggest an efficient route to stabilize the ferromagnetic phase of nanostructures on graphene by tailoring dipolar interactions, which is essential to realize a higher efficiency of spin injection in graphene-based spintronics.

Microscopic evidence for the dissociation of water molecules on cleaved GaN(11[combining macron]00).

The dissociation of water molecules absorbed on a cleaved non-polar GaN(11[combining macron]00) surface was studied primarily with synchrotron-based photoemission spectra and density-functional-theory calculations. The adsorbed water molecules are spontaneously dissociated into hydrogen atoms and hydroxyl groups at either 300 or 130 K, which implies a negligible activation energy (<11 meV) for the dissociation. The produced H and OH were bound to the surface nitrogen and gallium on GaN(11[combining macron]00) respectively. These results highlight the promising applications of the non-polar GaN(11[combining macron]00) surface in water dissociation and hydrogen generation.

An innovative application of time-domain spectroscopy on localized surface plasmon resonance sensing.

White-light scanning interferometry (WLSI) is often used to study the surface profiles and properties of thin films because the strength of the technique lies in its ability to provide fast and high resolution measurements. An innovative attempt is made in this paper to apply WLSI as a time-domain spectroscopic system for localized surface plasmon resonance (LSPR) sensing. A WLSI-based spectrometer is constructed with a breadboard of WLSI in combination with a spectral centroid algorithm for noise reduction and performance improvement. Experimentally, the WLSI-based spectrometer exhibits a limit of detection (LOD) of 1.2 × 10-3 refractive index units (RIU), which is better than that obtained with a conventional UV-Vis spectrometer, by resolving the LSPR peak shift. Finally, the bio-applicability of the proposed spectrometer was investigated using the rs242557 tau gene, an Alzheimer's and Parkinson's disease biomarker. The LOD was calculated as 15 pM. These results demonstrate that the proposed WLSI-based spectrometer could become a sensitive time-domain spectroscopic biosensing platform.

Varying stress of SiOxCy thin films deposited by plasma polymerization.

SiOxCy thin films were deposited by plasma polymerization. The stress of the deposited SiOxCy thin films can be modified by adjusting the beam current, the anode voltage, and the flow rate of hexamethyldisiloxane (HMDSO) gas and oxygen. Reducing the beam current or increasing the flow rate of HMDSO gas increased the linear/cage structure ratio and turned the stress of the SiOxCy thin films from compressive to tensile. The linear/cage structure ratio can be adjusted by changing the composite parameter, W[FM]c/[FM]m, to control the stress of the deposited plasma polymer films. Multilayers of TiO2/SiO2/TiO2 were coated on a SiOxCy plasma polymer film herein, reducing their stress by 70% from 0.06 to 0.018 GPa. The refractive index is 1.55, and the absorption coefficient is less than 10-4 at 550 nm of the SiOxCy films. Superior optical performances of SiOxCy thin films make their use in optical thin films.

A Transparent and Flexible Graphene-Piezoelectric Fiber Generator.

Piezoelectric fiber-based generators are prepared by combining two distinctive materials - poly(vinlyidene fluoride) fibers and monolayer/bilayer graphene. Novelty lies in the replacement of opaque metal electrodes with transparent graphene electrodes which enable the graphene-piezoelectric fiber generator to exhibit high flexibility and transparency as well as a great performance with an achievable output of voltage/current about 2 V/200 nA.

Fourier transform analysis of hexagonal domain for transparent conductive graphene.

In this paper, we applied the Fourier Transformation as a notion to calculate the orientation of hexagonal graphene domains on Cu substrate. We developed that a hexagon function to describe the diffraction pattern of hexagonal graphene. Hexagonal graphene domains grown on Cu (111) has an average value of orientation surrounding 3° in the frequency domain. For transparent conducting electrode applications, optical and electrical properties of large-area graphene film (2cm(2)) was measured. The results demonstrate that graphene grown on Cu (111) was greater than graphene grown on polycrystalline Cu.

The deviation of growth model for transparent conductive graphene.

An approximate growth model was employed to predict the time required to grow a graphene film by chemical vapor deposition (CVD). Monolayer graphene films were synthesized on Cu foil at various hydrogen flow rates from 10 to 50 sccm. The sheet resistance of the graphene film was 310Ω/□ and the optical transmittance was 97.7%. The Raman intensity ratio of the G-peak to the 2D peak of the graphene film was as high as ~4 when the hydrogen flow rate was 30 sccm. The fitting curve obtained by the deviation equation of growth model closely matches the data. We believe that under the same conditions and with the same setup, the presented growth model can help manufacturers and academics to predict graphene growth time more accurately.

Therapeutic effect of dynamic interpersonal group psychotherapy for taiwanese patients with depressive disorder.

This study investigated the therapeutic effects of dynamic interpersonal group psychotherapy (DIGP) for the depressed in Taiwan. A 16-session DIGP was held weekly, and participants were evaluated with the Hamilton Depression Rating Scale, Taiwanese Depression Questionnaire, and World Health Organization Quality of Life-BREF before and after DIGP. Compared with control group, the patients treated with DIGP showed significant improvement in severity of their depression, especially in the somatic subscale and quality of life regarding psychological health. We found that focusing on repairing interpersonal interaction in DIGP would improve the social interaction problems of Chinese with depressive disorder.

FTO films deposited in transition and oxide modes by magnetron sputtering using tin metal target.

Fluorine-doped tin oxide (FTO) films were prepared by pulsed DC magnetron sputtering with a metal Sn target. Two different modes were applied to deposit the FTO films, and their respective optical and electrical properties were evaluated. In the transition mode, the minimum resistivity of the FTO film was 1.63×10(-3) Ω cm with average transmittance of 80.0% in the visible region. Furthermore, FTO films deposited in the oxide mode and mixed simultaneously with H2 could achieve even lower resistivity to 8.42×10(-4) Ω cm and higher average transmittance up to 81.1% in the visible region.

Optical constants of electrochromic films and contrast ratio of reflective electrochromic devices.

This study investigates the optical constants of WO3 electrochromic films and NiO ion-storage films in bleached and colored states and that of a Ta2O5 film used as an ion conductor. These thin films were all prepared by electron-beam evaporation and characterized using a spectroscopic ellipsometer. The spectra obtained using a spectrophotometer and those calculated from the optical constants agreed closely. An all-solid thin-film reflective electrochromic device was fabricated and discussed. Its mean contrast ratio of reflectance in the range of 400-700 nm was 37.91.

Controllable photonic mirror fabricated by the atomic layer deposition on the nanosphere template.

In this study, a controllable photonic mirror was fabricated using the atomic layer deposition (ALD) coating technique on a polystyrene (PS) nanosphere template. PS nanospheres were self-assembled on an Al/glass substrate to form the bottom electrode. A 20 nm ALD Al2O3 film was then coated onto the surface of the reduced PS nanosphere structure. The PS nanospheres were removed in air at 350°C to form hollow Al2O3 nanospheres. Then a 30 nm indium tin oxide film was sputtered on the hollow nanosphere structure to form the top electrode. The results show that the incorporation of the photonic mirror could control the reflectance to a value of 0.3% per 0.1 V of bias voltage.