Nanostructured porous silicon (PS) can be used as a template for the growth of noble metal nanoparticles for the subsequent development of metal/semiconductor hybrid structures with application in several fields. The current work reports on the electrodeposition of silver nanoparticles (AgNPs) into columnar PS layers. In particular, the size, morphology, and surface density of the AgNPs grown into PS were studied as a function of the electrolyte pH value and the infiltration current density. Furthermore, the optical properties of the hybrid PS + AgNPs structures were analyzed. The experimental results show a remarkable reduction in the size of AgNPs and increased growth rate upon reducing the acidity of the electrolyte and upon increasing the current density. In addition, a remarkable reduction of the average reflectance is observed under specific fabrication conditions. In particular, as the pH values of the electrolyte increase, the optical reflectance decreases. This relation is attributed to the reduction in the AgNPs size. On the other hand, increasing the infiltration current density increases the average reflectance due to increasing surface density of the AgNPs. These results demonstrate that the size and shape of AgNPs can be controlled by adjusting the applied infiltration current density and the pH value of the electrolyte depending on the intended application.

Nanoscale noble metal particles have great potential as optical-limiting materials, whereas the size effect of silver nanoparticles on the optical limiting has been seldom reported before now. Silver nanoparticles with different sizes are synthesized by a seed growth method, and their optical-limiting properties to nanosecond laser at 532 nm are investigated. The results showed that, under the involved conditions, the silver nanoparticles with relatively small particle size behave better for optical limiting, and the nonlinear absorption accounts for the optical-limiting behavior.

Vitamin D₃ acts as a crucial biomarker for various diseases. Current methods for vitamin D₃ detection are time-consuming, expensive, and require trained personnel. We report a simple and cheap photodetector (PD)-based vitamin D₃ detection technique for the first time using Ag nanoparticles-covered Er-doped TiO₂ nanowires. The operational stability of the device was tested under the dark as well as the UV light illumination. Vitamin D₃ solution produced absorption bands at 222 and 280 nm, respectively. The PD current density varied from 1.29  ×  10^−  4  A  /  cm² to 1.74  ×  ^{10  −  4} at −4  V for pure ethanol solution and 20  pg  /  ml D₃ solution, respectively (under 220 nm illumination). The average absolute current values were reduced from 3.25 nA (220 nm) and 2.9 nA (340 nm) for 5  pg  /  ml to 2.95 nA (220 nm) and 2.54 nA (340 nm) for 30  pg  /  ml D₃ solution, respectively. The current gradually increased up to 3.34 nA (220 nm) and 2.7 nA (340 nm) as the concentration was increased up to 80  pg  /  ml. The PD current/vitamin D₃ concentration decreases exponentially from 0.58 to 0.03  nA  /  g  /  ml) for 5 and 80  pg  /  ml, respectively, under 220 nm excitation, from which an unknown concentration of vitamin D₃ can be obtained.

Schottky barrier photodetector (PD) (tungsten/nickel/aluminum nitride) based on stacked tungsten gratings is reported in our work. The absorbance of the grating-based structure is obtained using rigorous coupled-wave analysis method. In addition, a responsivity value of 6.164  mA  /  W is calculated at λ  =  559.38  nm based on Fowler’s model. More than three times enhancement in responsivity is achieved as compared with that of bulk structure (without grating) based Schottky barrier PD. In addition, a detectivity value of 33.11  ×  10¹¹  cm Hz^1/2  /  W is obtained. Furthermore, the effect of grating variables and incident angle on responsivity are also demonstrated. In future, the proposed structure can also be used as a plasmonic sensor, absorber, or spectral filter.

Polydimethylsiloxane/multi-walled carbon nanotube (PDMS/MWCNT) composite had high photoacoustic transduction efficiency owing to its high light absorption coefficient and low interfacial thermal resistance. The high expansion coefficient and light absorption ability of PDMS/MWCNT nanocomposite films have significant positive effects when it is used as a laser ultrasonic transducer. We introduce an ultrasonic-assisted forced impregnation method for the preparation of PDMS/MWCNT nanocomposite films. PDMS was used as the matrix phase, and MWCNTs were used as the nano-supporting framework. PDMS matrix was introduced into the MWCNT framework by the forced impregnation method. The morphology, thermal, and mechanical properties of the nanocomposite film were analyzed systematically. The photoacoustic conversion efficiency was researched through both experiment and simulation methods. The output sound pressure of our PDMS/MWCNT nanocomposite film reached 7.59 MPa when applied as an ultrasonic transducer under the pulsed laser excitation of 1  mJ  /  pulse energy. The photoacoustic conversion efficiency of our sample was 9.98  ×  10^−  4, three times higher than similar products reported before, which offered the possibility to greatly enhance the photoacoustic signals.

Zinc oxide nanoparticles (ZnO-NPs) were fabricated using carbon quantum dots (CQD) solution using a laser ablation technique to investigate the photoluminescence properties and applications for the interaction of mercury and lead ions. The ablation times were 5, 7, 10, and 13 min. The prepared samples were characterized using UV–visible spectroscopy, Fourier transform infrared spectroscopy, and high-resolution transmission electron microscopy, which verified the formation of ZnO-NPs in the CQD solution and the capping of the spherical nanoparticles by the functional group of the CQD. Spherical ZnO-NPs were formed in the CQD solution with a particle size in the range of 7.5 to 14.03 nm. The prepared samples were then used to detect mercury and lead ions in aqueous solution using photoluminescence spectroscopy. The photoluminescence peak shift in the presence of mercury was greater than that in the presence of lead. Thus, the interaction of zinc oxide–nanoparticles/CQD with mercury is stronger than that of the CQD with lead.

Metasurface silicon-based optical devices are highly integrated and high-performance, meeting the requirements of photonics integrated circuits. We present a design method for metasurface silicon-based gradient index (GRIN) optical lens. With easy calculation, this method supports large-area GRIN elements design. The Luneburg lens and integrated coupler are shown as examples. Such devices show good performances in simulations. The simulations show that the Luneburg lens can focus light from all directions equally well. The optical 1-dB bandwidth of the integrated coupler is about 100 nm. Our method provides a convenient and feasible approach for designing silicon-based GRIN lenses.

We have designed and numerically analyzed gap-enhanced toroidal dipole (TD) and magnetic Fano resonances with high Q-factors and large modulation depths simultaneously in an all-dielectric metamaterial for sensing. By introducing a gap in the cylinder, we achieved a significant enhancement in Q-factor and electromagnetic field compared to the cylinder with no gap in near-IR regime. In addition, TD and magnetic Fano resonances can be tailored through varying width and position of gap and can be achieved without symmetry breaking, showing polarization-independent characteristics. Further, we theoretically demonstrated a multichannel refractive index (RI) sensor with bulk RI sensitivity exceeding 100  nm  /  RIU and figure of merit reaching 260. With high structural symmetry of the proposed metamaterial, it may find applications in lasing, nonlinear devices, and multiwavelength biomedical sensing.

Tunable fluorescent silica nanoparticles (SiO₂ NPs) with variable sizes based on fluorescence resonance energy transfer were synthesized. The SiO₂ NPs were obtained by the Störber method by varying tetraethyl orthosilicate (TEOS) concentrations and with the incorporation of different concentrations of fluorescein (Fl) and rhodamine B (RhB) conjugated with 3-(aminopropyl)triethoxysilane. We thus recorded homogeneous SiO₂ NPs of different sizes. By transmission electron microscopy imaging, the sizes of 200, 280, and 380 nm were determined. The Fl and RhB fluorescent dyes showed well-overlapped emission from the fluorescent energy donor to the energy acceptor with the optimal ratio of quantum yields. By static fluorescence, varied emissions were recorded according to the concentration ratio of the donor–acceptor pair. Increasing intensity values were collected with the addition of higher concentrations of the fluorescent energy donor and decreased fluorescent lifetime decays. By laser fluorescence microscopy, higher enhanced surfaces were produced in the presence of both emitters, as compared with those in the presence of mono-colored SiO₂ NPs with optimal excitation with the fluorescent energy donor only. These NPs were well dispersed in polar solvents; however, due to their polar surface and size, higher interactions produced dimeric nanoaggregates. In addition, to evaluate their applications, their depositions were evaluated over modified glass slide substrates for smart light-responsive materials and over Cyanobacteria and Escherichia coli for the development of nanobiostructures with varied optical activities.

A transmission matrix method (TMM) commonly used for modeling the electromagnetic properties of multilayered biopolymer/conductive nanoparticle composites is presented, which predicts the behavior of the experimental results of the electromagnetic shielding effectiveness of a deoxyribonucleic acid-silver nanoparticle composite but falls short for accurately predicting the absolute shielding effectiveness. The versatility of the model can handle metamaterials, various incident angles, both TE and TM polarizations, and single and multilayer structures with complex and dispersive permittivity and permeability. We present the simulated results for a single-layer slab using the TMM along with the experimental results. Parametric studies are conducted with the model to investigate the reflection and transmission performance for single-layer slabs by varying the loss tangent, dielectric constant, incident angle, and thickness parameters.

The higher-order harmonic generation process in the nonperturbative regime at the interaction of coherent electromagnetic radiation with the AB-stacked bilayer graphene at high Fermi energies is considered. The applied coherent low-frequency radiation field in the high Fermi energy zone of electrons excludes the interband transitions enhancing high harmonic rates. The developed microscopic nonlinear quantum theory for charged carriers interaction with a strong pump wave is valid near the Dirac points of the Brillouin zone. The Liouville–von Neumann equation for the density matrix in the multiphoton excitation regime is solved both analytically and numerically. Based on the numerical solutions, we examine the rates of higher-order harmonics of the pump wave of arbitrary polarization. Obtained results show that bilayer graphene serves as an effective material for the generation of higher-order harmonics from THz to the mid-IR domain of frequencies at moderate pump wave intensities.

Nanocrystalline copper oxide (CuO) powder was synthesized through solid-state co-precipitation technique using copper sulfate pentahydrate and sodium hydroxide pellets as a source materials. Crystalline nature and surface morphology of the sample are studied through x-ray diffraction, field emission scanning electron microscopy, energy dispersive x-ray, and Fourier transform infrared spectroscopy. Optical properties of synthesized CuO nanopowder were investigated by UV–Vis absorption and photoluminescence spectroscopy. X-ray diffraction study reveals that CuO nanoparticles are in monoclinic structure and crystalline size is found to be around 15 nm as estimated from Debye-Scherrer formula. FESEM measurement confirms that the particles are in almost irregular shape, and some nanorod-like structures are noticed. FTIR spectrum confirms the formation of high-quality and pure CuO nanoparticles. The effect of various solvents on optical properties of CuO nanoparticles is studied. From UV–Vis absorption measurement, a strong quantization along with varying band edges in different solvents was observed. It is seen from photoluminescence spectra that the intensity of emission as well as emission peak wavelength changes with solvents.

To reduce the effects of global warming, visible and near-infrared light must be used more efficiently. Deep ultraviolet light (8 eV) is required for the direct dissociation of CO₂ by light; however, the introduction of a metal complex has made it possible to realize CO₂ reduction with visible light. We demonstrate that the optical near field (ONF) can increase the CO₂ reduction rate. For this, we used gold clusters, because they can be a suitable source for ONFs, as their size and density can be controlled by the number of gold atoms. By attaching a metal complex near gold clusters with diameters of 1.0 to 1.3 nm, we confirm that the reduction rate of CO₂ to CO increased by 1.5 to 2.1 times. The gold clusters were sufficiently small; therefore, there was no plasmonic resonant peak or heat generation. Because the near-field effect is based on a photochemical reaction, it can be applied to other metal complexes used in CO₂ reduction, and it has other applications such as water splitting and water purification.

A 2D hot spot diffusion model for describing the superconducting nanowire response to a single photon is presented. Compared to the 1D hot belt model, the 2D hot spot model can capture the initial stage of the hot spot evolution after photon absorption, which is beneficial for achieving a more comprehensive understanding of the origins and underlying physics of the timing jitter in superconducting nanowire-based single-photon detectors. Based on the established 2D diffusion model, the cross-section effect induced by the random radial position of the photon absorption is investigated, which can qualitatively explain the asymmetry and non-Gaussian shape of the probability density function (PDF) distributions of the time delay. Furthermore, the shift of the right half of the PDF distributions with increasing photon wavelength can also be clarified in the framework of the innovative 2D diffusion model. Considering the spatial inhomogeneity along the nanowire, the calculated results of the timing jitter based on the Monte Carlo methods are in good agreement with the experimental observations. The proposed 2D hot spot diffusion model will not only shed light on the origin and influence of the timing jitter but also reveal the working principle of superconducting nanowire devices.

A compact all-fiber temperature sensor based on a gold nanoparticle (GNP)-coated macrobent standard single-mode fiber (SMF) has been proposed and experimentally demonstrated. It can be easily constructed by just bending an SMF into a suitable bending radius to constitute a Mach–Zehnder modal interferometer. The sensing area of the bent SMF was coated with GNP utilizing the magnetron sputtering technique. Different tuned GNP thicknesses of ∼10, 20, and 30 nm were deposited on different bent fibers and the temperature-sensing performance was examined experimentally. Throughout the experiments, the wavelengths of the monitored interference dips decreased gradually and were blueshifted with an increase in temperature in the range of 35°C to 47°C. Among the three coated sensing heads, the proposed sensor coated by an ∼20-nm layer thickness of GNP showed the best performance with excellent sensitivity, fast rise time, and an excellent resolution of −2.56  nm  /  °C, 1.73 ms, and 1.82  ×  10^−  4°C, respectively. Benefiting from its excellent advantages of simple configuration, easy fabrication, and high mechanical strength, this high-sensitivity temperature sensor could be a competitive candidate for precise temperature measurement of the human body.

An ultra-broadband perfect absorber for visible to near-infrared light utilizing a metamaterial nanostructure is theoretically proposed and numerically analyzed. The absorber consists of a square and plus shape layer of Ti-Al₂O₃ (top layer) and a thin layer of Cr located on a SiO₂ layer over a TiN substrate. By ameliorating the dimensions of the design, an average absorption of 95.4% is attained for wavelengths from 400 to 1800 nm, with a peak absorption of about 100%. Also, the bandwidths corresponding to the absorption above 90% and 99% are 1317 and 773 nm, respectively. The cooperative effects of the corresponding localized plasmonic resonances and the propagating surface plasmons of Ti resonators subsidize to the absorption response. Furthermore, the spectral response of the proposed nanostructure is insensitive to incident angle and independent of polarization angle. The proposed absorber has application prospects in photovoltaic devices, solar energy harvesting, and light trapping.

The design of an ultrasensitive surface plasmon resonance (SPR) sensor for the detection of deoxyribose nucleic acid (DNA) hybridization is highly desirable for biomedical applications. We have proposed an SPR sensor architecture (Prism-SF10/Al/Si/BP/Antimonene/phosphate buffer saline solution) and performed its numerical analysis for DNA hybridization using angular interrogation at 633 nm. Antimonene is used as a biorecognition element layer for better attachment of single stranded (ss), i.e., ss probe DNA on its surface, due to its higher binding energy for ssDNA (even greater than graphene). Silicon and black phosphorous are utilized to enhance the electromagnetic field at the sensing layer interface. Aluminum is used as an surface plasmon active metal and it also improves the quality factor. Remarkable sensitivity (202.37  deg  /  refractive index unit) is attained for this work, which is greater than any other SF10 prism-based SPR sensor proposed to date. The performance of the SPR biosensor is meticulously evaluated as limit-of-detection (0.0028 nM) and figure-of-merit (0.037  nM^−  1) with respect to the concentration of complementary target ssDNA in the sensing medium. This versatile biosensor shows great application to detect deadly diseases via DNA hybridization in the biomedical field if developed as an SPR chip for experimental verification.

Cd_{1  −  x}Ag_xS nanoparticles were synthesized by a simple cost-effective chemical method in air atmosphere. We have achieved novel hybrid ternary nanoparticles of high quality. The prepared samples were characterized by x-ray diffraction, Fourier transform-Raman, field emission scanning electron microscopy, transmission electron microscopy, and UV–visible absorption spectroscopy. The results revealed that Ag₂S nanoparticles were well dispersed on CdS nanoparticles demonstrating gradual structural change in Cd_{1  −  x}Ag_xS from cubic CdS to monoclinic Ag₂S nanoparticles with the increase in x value. The interesting feature is that the visible-light absorption of CdS was enhanced by Ag giving rise to significant bandgap thereby forming the key aspect in solar cell and photocatalytic applications

In the framework of effective mass envelope function approximation, the impurity states in GaN  /  Al_xGa_{1  −  x}N spherical quantum dot (QD) are calculated by plane-wave expansion method. The binding energies of the impurity in 1s and 2p± states and the transition energy between 1s state and 2p± state are calculated and analyzed in detail. Several critical influencing factors of impurity states, including geometry, impurity position, material composition, and applied electric field, are considered in the calculation. The effects of QD radius, the impurity position, and the electric field strength on binding energies of 1s state and 2p± state are different. However, the effect of Al component on binding energies of 1s state and 2p± state is consistent. The transition energy is strongly dependent on the QD radius, impurity position, Al composition, and electric field strength. The change trend of transition energy is similar to that of binding energy in 1s state.

We present a method to passively edge couple multiple optical fibers with silicon nitride waveguides in the visible wavelengths. We efficiently convert the fiber mode to the waveguide mode using an inverse taper mode size converter and support passive alignment using a U-groove that centers the optical fiber to the inverse taper. In our prototypes, we measure a coupling efficiency of −4.2  dB per facet. To reduce light leakage to the silicon substrate, we use a 6-μm oxide layer, which also eliminates the additional processes of undercutting the silicon substrate underneath the waveguide. Furthermore, the U-groove structure has a polished edge surface for coupling, reducing the steps of edge polishing the die. Fabrication of this visible-range edge coupler is complementary metal–oxide–semiconductor-compatible, making it a highly scalable method for passively packaging multiple visible-range integrated photonics devices.