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As the demand for energy in world is increasing rapidly and there is pursuit for renewable energy sources which is cheap, easy to generate and requires low maintenance, solar energy is a top contender. The world is in dire need of photovoltaic solar cells that can aid in keeping up with the hiking energy demands. However, thin film solar cells (TFSCs) which are developed for cost effectivity, suffer in performance due to reduced thickness. Therefore, this computational study uses Finite-Difference Time-Domain (FDTD) and delves into the scope of using a 1-D nano-grating structure embedded into absorbing layer of cadmium telluride TFSC to enhance the optoelectronic performance. A unique nano-grating structure with SiO2 at its core and aluminium coating aims to enhance the performance of CdTe TFSC with cost effectivity and ease of fabricability as the main motifs. Additionally, an evolutionary computational technique, Particle Swarm Optimization (PSO), was used to determine the optimal parameters of nano-gratings on CdTe TFSCs, i.e., nano-grating height, angle, duty cycle, aluminium coating thickness and grating substrate thickness. The PSO algorithm resulted in a nano-grating structure that yielded an efficiency increase of 52.86% and increase in short-circuit current density of 25.45% with respect to bare CdTe TFSCs. Subsequently, the performance of the optimal nano-grating structure was also observed to be insensitive to variation of wide range of incidence angle of light, a key feature preferred for versatile application of TFSCs.

The scientific community has been looking for novel approaches to develop nanostructures inspired by nature. However, due to the complicated processes involved, controlling the height of these nanostructures is challenging. Nanoscale capillary force lithography (CFL) is one way to use a photopolymer and alter its properties by exposing it to ultraviolet radiation. Nonetheless, the working mechanism of CFL is not fully understood due to a lack of enough information and first principles. One of these obscure behaviors is the sudden jump phenomenon—the sudden change in the height of the photopolymer depending on the UV exposure time and height of nano-grating (based on experimental data). This paper uses known physical principles alongside artificial intelligence to uncover the unknown physical principles responsible for the sudden jump phenomenon. The results showed promising results in identifying air diffusivity, dynamic viscosity, surface tension, and electric potential as the previously unknown physical principles that collectively explain the sudden jump phenomenon. [ABSTRACT FROM AUTHOR]

• Non-harmonic triangle and trapezoidal vibration trajectories are generated and control. • Effect of 2D tool vibration trajectory on the nano-grating formation is revealed. • Triangle tool vibration trajectory can fabricate nano-gratings with typical sawtooth profile. • Trapezoidal tool vibration trajectory can fabricate nano-gratings with specific duty cycle. • Structural color attributes are flexibly manipulated via innovative tool trajectory designs. Nano-gratings induced structural color is of great value in various anti-counterfeiting and decoration applications. Despite the attractive rendering performances, the manipulation strategy for vibration-assisted diamond-cutting structural color is far from complete due to the intrinsically limited tool trajectory designs. The novelty of this paper lies in the precise generation and control of non-harmonic triangle and trapezoidal two-dimensional vibration trajectories to shape typical blazed nano-gratings and nano-grating with specific duty cycles. A two-degree-of-freedom non-resonant vibration tool with closed-loop control was employed to reveal the effect of tool vibration trajectory on the machined nano-grating topography, and establish a sound framework for diamond-cutting structural-color to manipulate color attributes through innovative tool trajectory designs. Triangle and trapezoidal vibration trajectories are utilized for the first time to generate nano-gratings, which will be systematically compared to the common utilization of elliptical vibration trajectory throughout the trajectory generation, kinematical modelling and finite element analysis. Then, various vibration-assisted diamond cutting experiments were carried out to validate the identified differences of nano-grating topography induced by different tool vibration trajectories. The results show that smooth triangle and trapezoidal trajectories can be accurately generated for texturing nano-gratings with typical sawtooth topography and specific duty cycle, which can hardly be achieved using conventional elliptical trajectory. Ultimately, the manipulation of structural color effect via varying tool vibration trajectory was successfully demonstrated using the comparisons of color palette and diffractive spectrum. The revealed effects of tool vibration trajectory are beneficial to guide the process parameter designs for deterministically manipulating the vibration-assisted diamond-cutting structural color effect. [Display omitted] [ABSTRACT FROM AUTHOR]

The scientific community has been looking for novel approaches to develop nanostructures inspired by nature. However, due to the complicated processes involved, controlling the height of these nanostructures is challenging. Nanoscale capillary force lithography (CFL) is one way to use a photopolymer and alter its properties by exposing it to ultraviolet radiation. Nonetheless, the working mechanism of CFL is not fully understood due to a lack of enough information and first principles. One of these obscure behaviors is the sudden jump phenomenon—the sudden change in the height of the photopolymer depending on the UV exposure time and height of nano-grating (based on experimental data). This paper uses known physical principles alongside artificial intelligence to uncover the unknown physical principles responsible for the sudden jump phenomenon. The results showed promising results in identifying air diffusivity, dynamic viscosity, surface tension, and electric potential as the previously unknown physical principles that collectively explain the sudden jump phenomenon.

As the demand for energy in world is increasing rapidly and there is pursuit for renewable energy sources which is cheap, easy to generate and requires low maintenance, solar energy is a top contender. The world is in dire need of photovoltaic solar cells that can aid in keeping up with the hiking energy demands. However, thin film solar cells (TFSCs) which are developed for cost effectivity, suffer in performance due to reduced thickness. Therefore, this computational study uses Finite-Difference Time-Domain (FDTD) and delves into the scope of using a 1-D nano-grating structure embedded into absorbing layer of cadmium telluride TFSC to enhance the optoelectronic performance. A unique nano-grating structure with SiO 2 at its core and aluminium coating aims to enhance the performance of CdTe TFSC with cost effectivity and ease of fabricability as the main motifs. Additionally, an evolutionary computational technique, Particle Swarm Optimization (PSO), was used to determine the optimal parameters of nano-gratings on CdTe TFSCs, i.e., nano-grating height, angle, duty cycle, aluminium coating thickness and grating substrate thickness. The PSO algorithm resulted in a nano-grating structure that yielded an efficiency increase of 52.86% and increase in short-circuit current density of 25.45% with respect to bare CdTe TFSCs. Subsequently, the performance of the optimal nano-grating structure was also observed to be insensitive to variation of wide range of incidence angle of light, a key feature preferred for versatile application of TFSCs., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 The Author(s).)

A self-referencing plasmonic platform is proposed and analyzed. By introducing a thin gold layer below a periodic two-dimensional nano-grating, the structure supports multiple modes including localized surface plasmon resonance (LSPR), surface plasmon resonance (SPR), and Fabry-Perot resonances. These modes get coupled to each other creating multiple Fano resonances. A coupled mode between the LSPR and SPR responses is spatially separated from the sensor surface and is not sensitive to refractive index changes in the surrounding materials or surface attachments. This mode can be used for self-referencing the measurements. In contrast, the LSPR dominant mode shifts in wavelength when the refractive index of the surrounding medium is changed. The proposed structure is easy to fabricate using conventional lithography and electron beam deposition methods. A bulk sensitivity of 429 nm/RIU is achieved. The sensor also has the ability to detect nanometer thick surface attachments on the top of the grating. [ABSTRACT FROM AUTHOR]

The primary focus of this review article mainly emphasizes the light absorption enhancement for various nanostructured gratings assisted metal-semiconductor-metal photodetectors (MSM-PDs) that are so far proposed and developed for the improvement of light capturing performance. The MSM-PDs are considered as one of the key elements in the optical and high-speed communication systems for applications such as faster optical fiber communication systems, sensor networks, high-speed chip-to-chip interconnects, and high-speed sampling. The light absorption enhancement makes the MSM-PDs an ideal candidate due to their excellent performances in detection, especially in satisfying the high-speed or high-performance device requirements. The nano-grating assisted MSM-PDs are preordained to be decorous for many emerging and existing communication device applications. There have been a significant number of research works conducted on the implementation of nano-gratings, and still, more researches are ongoing to raise the performance of MSM-PDs particularly, in terms of enhancing the light absorption potentialities. This review article aims to provide the latest update on the exertion of nano-grating structures suitable for further developments in the light absorption enhancement of the MSM-PDs.

An ultra-compact broadband silicon polarizing beam splitter is proposed based on a tilted nano-grating structure. A light cross coupling can be realized for transverse-magnetic mode, while the transverse-electric light can almost completely output from the through port. The length of the coupling region is only 6.8 μm, while an extinction ratio of 23.76 dB can be realized at a wavelength of 1550 nm. As a proof of concept, the device was fabricated by a commercial silicon photonic foundry. It can realize a 19.84 dB extinction ratio and an 80 nm working bandwidth with an extinction ratio of larger than 10 dB. The presented device also shows a good fabrication tolerance to the structure deviations, which is favorable for its practical applications in silicon photonics.

[Display omitted] • An innovative diffraction prediction model is firstly proposed and validated to describe the diffractive spectrum of atypical gratings in UPC processes. • The deterministic rendering of structural color is demonstrated by texturing three groups of blazed gratings with controllable topography. • The optimal grating topography design is given for maximizing the region size of color gamut using the novel concept of average saturation. • The sound framework for UPC-induced structural color is established by linking the cutting process parameters to final optical performance. Ultra-precision diamond cutting (UPC) has been recently proposed for fast generation of nano-gratings to render diffractive structural color on various metallic surfaces. However, the complex nanoscale generation mechanism and atypical grating topography provide the significant challenges for deterministic rendering of structural color with standard representations. In this paper, an innovative diffraction prediction model is firstly proposed to describe the diffractive spectrum of atypical gratings under the full considerations of cutting process parameters, double working facets, material optical properties and environmental conditions. The standard CIE 1931 chromaticity diagram for grating-induced structural color is released for color gamut determination and optimization, where the color gamut range is defined by a novel concept of average saturation. The experimental results demonstrate the deterministic generation of three groups of nano-gratings with desired 3D topography, of which the measured angle-dependent diffractive spectrum and rendering color attributes show good agreements with theoretical results. Moreover, the new topography-modulation based strategies for achieving maximal color gamut and manipulating the ternary color attributes are clarified. The outcome of this paper lays the scientific foundations for deterministic rendering and performance enhancement of structural color enabled by UPC processes. [ABSTRACT FROM AUTHOR]

Infections with antimicrobial resistant bacteria are a rising threat for global healthcare as more and more antibiotics lose their effectiveness against bacterial pathogens. To guarantee the long-term effectiveness of broad-spectrum antibiotics, they may only be prescribed when inevitably required. In order to make a reliable assessment of which antibiotics are effective, rapid point-of-care tests are needed. This can be achieved with fast phenotypic microfluidic tests, which can cope with low bacterial concentrations and work label-free. Here, we present a novel optofluidic chip with a cross-flow immobilization principle using a regular array of nanogaps to concentrate bacteria and detect their growth label-free under the influence of antibiotics. The interferometric measuring principle enabled the detection of the growth of Escherichia coli in under 4 h with a sample volume of 187.2 µL and a doubling time of 79 min. In proof-of-concept experiments, we could show that the method can distinguish between bacterial growth and its inhibition by antibiotics. The results indicate that the nanofluidic chip approach provides a very promising concept for future rapid and label-free antimicrobial susceptibility tests.

A novel lateral dual-axis a-Si/SiO2 waveguide Bragg grating based quad-beam accelerometer with high-resolution and large linear range has been presented in this paper. The sensor consists of silicon bulk micromachined proof mass suspended by silica beams. Three ridge gratings are positioned on the suspending beam and proof mass to maximize sensitivity and reduce noise. Impact of external acceleration in the sensing direction on the Bragg wavelength of gratings and MEMS structure has been modelled including the effects of strain, stress and temperature variation. Acceleration induces stress in the beam thus modifying the grating period and introducing chirp. The differential wavelength shift with respect to reference grating on the proof mass is the measure of acceleration. To compensate for the effect of the weight of the proof mass and increase the sensitivity of the sensor, electrostatic force of repulsion is applied to the proof mass. For the chosen parameters, the designed sensor has a linear response over a large range and a sensitivity of 30 pm/g. The temperature of surroundings, which acts as noise in sensor performance is compensated by taking differential wavelength shift with respect to reference grating. By design and choice of material, low cross-axis sensitivity is achieved. The proposed design enables a high-resolution well below 1 μ g/ Hz and is suitable for inertial navigation and seismometry applications.

Based on our recent work, this paper reviews our theoretical study on gallium nitride (GaN) light-emitting-diode (LED). The focus of the paper is to improve LED light extraction efficiency through various nano-grating designs. The gratings can be designed at different locations, such as at the top, the middle, and the bottom, on the LED. They also can be made of different materials. In this study, we first present a GaN LED error-grating simulation model. Second, nano Indium Tin Oxide (ITO) top gratings are studied and compared with conventional LED (CLED) using standing wave analysis. Third, we present results related to a patterned sapphire substrate (PSS), SiO2 Nanorod array (NR), and Ag bottom reflection layer. Finally, we investigate the nano-top ITO grating performance over different wavelengths to validate our design simulation, which focusing on a single wavelength of 460 nm.

A new method for simple and low-cost fabrication of nano-grating structures is reported in this paper. First, microscale grating structures on the master mold are replicated into Polydimethylsiloxane(PDMS), which serves as an intermediate, negative mold, by a conventional soft lithography process. The PDMS negative mold was then stretched along the direction of the grating lines to reduce the period of grating. Last, transfer the grating pattern from the PDMS membrane to PMMA. Nano-grating can be fabricated on polymethylmethacrylate(PMMA) by repeating the steps for several times. The grating has been tested and performs the width of 820 nm. The technology, utilizing the high elasticity of PDMS and the nano-molding technology, can be used to fabricate nano-gratings in low-cost and no expensive or high precision equipment. Because of the excellent replication property of PDMS molds, a large number of gratings can be made with a single master mold. The nano-gratings can be widely used in the optical measurement, integrated optics, optical information processing and other fields. [ABSTRACT FROM AUTHOR]

We fabricate Si nano-grating layers and measure their electrical characteristics to monitor geometry induced doping. SOI device layer was thinned down by thermal oxidizing and subsequent wet etching of the oxide. Grating was fabricated using laser interference lithography (375 nm laser) followed by reactive ion etching of Si. Next, large square island (0.5x0.5 mm) was shaped in the device layer and four Si\Ti\Ag ohmic contacts were formed to measure electrical characteristics. The I-V characteristics were recorded using both 4 wire and 2 wire methods. Resistance-temperature dependences (T= 4-300 K) were recorded as well. For all 12 samples, nano-grating layers show 2-3 order reduction of resistivity. Resistivity anisotropy was in the range 0.2-1 at 300 K. Obtained geometry induced doping level corresponds to “effective impurity” concentration of 3x10 18 cm -3 . The dependence is in agreement with G-doping theory only below T=150K. [ABSTRACT FROM AUTHOR]

Optical absorption enhancements of graphene by exciting graphene surface plasmon waves using nano-gratings are studied. Based on temporal coupled mode theory, we show that the electron relaxation time of graphene and the geometry of the device play crucial roles in determine the absorption rate, and complete optical absorption is possible by adjusting the geometric parameters of the device to match the electron relaxation time of graphene. Moreover, the absorption spectrums can be dynamically tuned by varying the Fermi energy of graphene. Our study could benefit the development of graphene based photonic and optoelectronic devices, such as infrared photodetectors and bolometers. [ABSTRACT FROM AUTHOR]

In this paper, a low-cost one-step nano-grating fabrication has been described which is applied in the grating-coupled excitation of Surface Plasmon Polaritons (SPPs). This technique is based on a kind of physical vapor deposition technique that is so called oblique angle deposition (OAD). Our nano-gratings fabricated at angles of deposition of 60°, 70° and 80° have been investigated by the aid of atomic force microscopy, surface plasmon resonance and measurement of optical reflectance at low incidence angle. Our results show the surface plasmon resonance coupling at different azimuth angle and the sensing ability of oblique angle deposited Cr- nano-grating to the groove distance in low angle measurement system. [ABSTRACT FROM AUTHOR]

This paper presents the light transmission efficiency of metal-semiconductor-metal photo-detectors (MSM-PDs) using finite difference time-domain method. The absorption of MSM PDs can be enhanced with the aid of nano-grating coupled surface plasmon resonances at the design wavelength. The simulated results show that the light absorption enhancement of nano-grating assisted MSM-PD is $$\sim $$ 9-times better than the conventional MSM-PD. [ABSTRACT FROM AUTHOR]

Highlights: [•] A novel metal–semiconductor–metal (MSM) photodetector light-capture performance analysis. [•] Plasmonic interaction enhanced transmission in nano-grating based MSM photodetector. [•] Theoretical agreement of E field configuration in subwavelength area of MSM photodetector. [•] A 12-fold enhancement in light transmission of plasmonic MSM photodetector structures. [Copyright &y& Elsevier]

We demonstrate the formation of nanostructures inside the microholes on soda-lime glass surface by irradiation with femtosecond laser pulses. Self-organized periodic nanogratings, oriented perpendicular to the laser polarization, are observed at the bottom of the microholes. The period of the nanogratings are ranging from 170 nm to 200 nm. We also report the formation of nano-ripples on the side walls of the microholes, the period of which are independent of the laser fluence and the number of laser pulses. Nano-cones, with a diameter varied from 100 nm to 250 nm, are also discovered on the sidewalls of the microholes. Randomly distributed spherical-shaped nanostructures with a diameter ranging from 10 nm to 60 nm are also evident inside the microholes, especially, on the top of the nano-ripples and nano-cones. We also describe, briefly, the dependence of various micro/nano-structures on the laser fluence and the number of applied laser pulses in each spot. Finally, we explain the formation mechanism of all of the micro/nano-scale features, produced during our experiment. [ABSTRACT FROM AUTHOR]

Abstract: We have successfully demonstrated a series of results that push the limits of optical sensing, acceleration sensing and lithography. Previously, we built some of the most sensitive displacement sensors with displacement sensitivities as low as at 1kHz. Using reference detection circuitry in conjunction with correlated double sampling methods, we lowered the 1/f noise floor to 10mHz, hence improving the detection limit at low frequencies (10mHz) by 77dB to . We converted these highly sensitive displacement sensors to highly sensitive acceleration sensors through a direct mass integration processes. Our accelerometers have resonant frequencies as low as 36Hz and thermal noise floors as low as (where 1G=9.8m/s2). We have pushed the limits of shaker table experiments to independently verify acceleration measurements as low as . Direct measurements with our integrated sub-wavelength optical nano-grating accelerometers have shown device sensitivities of 590V/G and noise floors corresponding to (at 1Hz). [Copyright &y& Elsevier]

High-frequency nano-gratings were fabricated using focused ion beam (FIB) and the Moiré fringes were then demonstrated using scanning electron microscope (SEM). A customized silicon-on-insulator (SOI) process was developed to fabricate the micro-cantilever used for the nano-grating patterned by FIB. The nano-gratings were precisely fabricated on SOI-based cantilever by controlling the milling current and the milling time of FIB under certain magnification and contrast. A theoretical analysis of the Moiré fringe is introduced and then demonstrated by the experimental results using FIB and SEM. The measurement is discussed by changing the pitch of the nano-grating, the raster scanning lines, magnification, contrast and the rotation angles of SEM. The currently patterned high frequency nano-gratings using focused ion beam can be adjusted to serve as a calibration tool of NEMS and MEMS fabrication which can also be extended to broad categories of engineering applications. [Copyright &y& Elsevier]

An ultra-compact broadband silicon polarizing beam splitter is proposed based on a tilted nano-grating structure. A light cross coupling can be realized for transverse-magnetic mode, while the transverse-electric light can almost completely output from the through port. The length of the coupling region is only 6.8 μm, while an extinction ratio of 23.76 dB can be realized at a wavelength of 1550 nm. As a proof of concept, the device was fabricated by a commercial silicon photonic foundry. It can realize a 19.84 dB extinction ratio and an 80 nm working bandwidth with an extinction ratio of larger than 10 dB. The presented device also shows a good fabrication tolerance to the structure deviations, which is favorable for its practical applications in silicon photonics. [ABSTRACT FROM AUTHOR]

Infections with antimicrobial resistant bacteria are a rising threat for global healthcare as more and more antibiotics lose their effectiveness against bacterial pathogens. To guarantee the long-term effectiveness of broad-spectrum antibiotics, they may only be prescribed when inevitably required. In order to make a reliable assessment of which antibiotics are effective, rapid point-of-care tests are needed. This can be achieved with fast phenotypic microfluidic tests, which can cope with low bacterial concentrations and work label-free. Here, we present a novel optofluidic chip with a cross-flow immobilization principle using a regular array of nanogaps to concentrate bacteria and detect their growth label-free under the influence of antibiotics. The interferometric measuring principle enabled the detection of the growth of Escherichia coli in under 4 h with a sample volume of 187.2 µL and a doubling time of 79 min. In proof-of-concept experiments, we could show that the method can distinguish between bacterial growth and its inhibition by antibiotics. The results indicate that the nanofluidic chip approach provides a very promising concept for future rapid and label-free antimicrobial susceptibility tests. [ABSTRACT FROM AUTHOR]

A novel lateral dual-axis a-Si/SiO2 waveguide Bragg grating based quad-beam accelerometer with high-resolution and large linear range has been presented in this paper. The sensor consists of silicon bulk micromachined proof mass suspended by silica beams. Three ridge gratings are positioned on the suspending beam and proof mass to maximize sensitivity and reduce noise. Impact of external acceleration in the sensing direction on the Bragg wavelength of gratings and MEMS structure has been modelled including the effects of strain, stress and temperature variation. Acceleration induces stress in the beam thus modifying the grating period and introducing chirp. The differential wavelength shift with respect to reference grating on the proof mass is the measure of acceleration. To compensate for the effect of the weight of the proof mass and increase the sensitivity of the sensor, electrostatic force of repulsion is applied to the proof mass. For the chosen parameters, the designed sensor has a linear response over a large range and a sensitivity of 30 pm/g. The temperature of surroundings, which acts as noise in sensor performance is compensated by taking differential wavelength shift with respect to reference grating. By design and choice of material, low cross-axis sensitivity is achieved. The proposed design enables a high-resolution well below 1 μ g/ Hz and is suitable for inertial navigation and seismometry applications. [ABSTRACT FROM AUTHOR]

Based on our recent work, this paper reviews our theoretical study on gallium nitride (GaN) light-emitting-diode (LED). The focus of the paper is to improve LED light extraction efficiency through various nano-grating designs. The gratings can be designed at different locations, such as at the top, the middle, and the bottom, on the LED. They also can be made of different materials. In this study, we first present a GaN LED error-grating simulation model. Second, nano Indium Tin Oxide (ITO) top gratings are studied and compared with conventional LED (CLED) using standing wave analysis. Third, we present results related to a patterned sapphire substrate (PSS), SiO2 Nanorod array (NR), and Ag bottom reflection layer. Finally, we investigate the nano-top ITO grating performance over different wavelengths to validate our design simulation, which focusing on a single wavelength of 460 nm. [ABSTRACT FROM AUTHOR]