Broad Wavelength Range Research Articles

Interface properties study of black silicon solar cells with front surface a-Si:H/c-Si heterojunction

Abstract The exceptionally low reflectance of black silicon across a broad wavelength range makes it an intriguing surface texture for solar cell applications. Silicon heterojunction (SHJ) solar cells fabricated on black silicon (Si) formed by dry reactive ion etching (RIE) using inductive coupled plasma (ICP) on n-type Si are explored. The study is focused on the properties of the a-Si:H/c-Si interface, being a key issue for the photovoltaic performance of SHJ. Deep-level transient spectroscopy (DLTS) detected no radiation defect in Si after the etching. The surface of black Si was passivated with an intrinsic a-Si:H layer, followed by the deposition of p-type and n-type a-Si:H on the front and back sides, respectively. The SHJ solar cell photovoltaic performance based on black Si is strongly influenced by defect density at the a-Si:H/Si interface. Admittance spectroscopy and effective charge carrier lifetime measurements demonstrate that interface defect density decreases with the increase of (i)a-Si:H thickness. The value of 0.75 ms effective charge carrier lifetime was reached for single (i) a-Si:H layer passivation and 0.25 ms when (p)a-Si:H was deposited over the intrinsic a-Si:H layer. The measured open circuit voltage (VOC) values for the SHJ solar cells increase with the (i)a-Si:H layer thickness reaching 658 mV. However, the fill factor decreases with increasing (i) a-Si:H layer thickness, limiting the efficiency at the maximum value below 14% due to the thickness uniformity of the a-Si:H layer. The development of conformal growth of a-Si:H is a key issue for further improvement of black Si heterojunction solar cell photovoltaic performance. 

Achiral and chiral ligands synergistically harness chiral self-assembly of inorganics.

Chiral structures and functions are essential natural components in biominerals and biological crystals. Chiral molecules direct inorganics through chiral growth of facets or screw dislocation of crystal clusters. As chirality promoters, they initiate an asymmetric hierarchical self-assembly in a quasi-thermodynamic steady state. However, achieving chiral assembly requires a delicate balance between intricate interactions. This complexity causes the roles of achiral-chiral and inorganic components in crystallization to remain ambiguous. Here, we elucidate a definitive mechanism using an achiral-chiral ligand strategy to assemble inorganics into hierarchical, self-organized superstructures. Achiral ligands cluster inorganic building blocks, while chiral ligands impart chiral rotation. Achiral and chiral ligands can flexibly modulate the chirality of superstructures by fully using their competition in coordination chemistry. This dual-ligand strategy offers a versatile framework for engineering chiroptical nanomaterials tailored to optical devices and metamaterials with optical activities across a broad wavelength range, with applications in imaging, detection, catalysis, and sensing.

Enhanced solar interfacial evaporation through lignin-polyaniline composite coatings on Balsa wood substrates

Solar interfacial evaporation employing wood-derived substrates is increasingly acknowledged as a viable desalination and wastewater treatment technique. This study presents an optimized method that enhances the efficiency of solar interfacial evaporation by applying a coating of lignin-polyaniline composites (EHL-PANI) onto balsa wood substrates. Initial assessments involved comparing evaporators made from various kinds of wood, identifying balsa wood-based photothermal evaporators as the most effective, with an evaporation rate of 1.63 kg·m−2·h−1 and an efficiency of 72.7 %. Photothermal properties were further improved through the chemical oxidation of enzymatic hydrolysis lignin (EHL) with polyaniline, producing a composite with notably high dispersion stability and uniform particle distribution. This modification resulted in reduced particle size and enhanced stability of the polyaniline, which is crucial for boosting photothermal activity. Additionally, the EHL-PANI composites demonstrated exceptional light absorption, exceeding 95 %, and significant photothermal conversion efficiency across a broad wavelength range, attributable to polyaniline's broadband light absorption characteristics. A prototype evaporator, featuring the EHL-PANI coated on a balsa wood substrate, was constructed to assess performance, achieving a water evaporation rate of 2.10 kg·m−2·h−1 and an efficiency of 80.7 % under solar illumination of 1 kW·m−2.

Planar waveguide to vertical mode couplers covering the visible to IR spectral range

Planar 45o turning mirrors with metal coating embedded in SU8 polymer waveguides enable waveguide to vertical mode coupling across a broad range of wavelengths from the visible to IR. The fabrication of these 2.5D structures is achieved using relatively simple grayscale lithography in thin film resists, compatible with standard planar lithography methods. Mirror losses of <1 dB are measured from 516 -1630 nm, and direct coupling to single mode fibre is achieved.

Fabrication of Low-Cost Porous Carbon Polypropylene Composite Sheets with High Photothermal Conversion Performance for Solar Steam Generation.

The development of absorber materials with strong light absorption properties and low-cost fabrication processes is highly significant for the application of photothermal conversion technology. In this work, a mixed powder consisting of NaCl, polypropylene (PP), and scale-like carbon flakes was ultrasonically pressed into sheets, and the NaCl was then removed by salt dissolution to obtain porous carbon polypropylene composite sheets (P-CPCS). This process is simple, green, and suitable for the low-cost, large-area fabrication of P-CPCS. P-CPCS has a well-distributed porous structure containing internal and external connected water paths. Under the dual effects of the carbon flakes and porous structure, P-CPCS shows excellent photothermal conversion performance in a broad wavelength range. P-CPCS-40 achieves a high temperature of 128 °C and a rapid heating rate of 12.4 °C/s under laser irradiation (808 nm wavelength, 1.2 W/cm2 power). When utilized for solar steam generation under 1 sun irradiation, P-CPCS-40 achieves 98.2% evaporation efficiency and a 1.81 kg m-2 h-1 evaporation rate. This performance means that P-CPCS-40 outperforms most other previously reported absorbers in terms of evaporation efficiency. The combination of carbon flakes, which provide a photothermal effect, and a porous polymer structure, which provides light-capturing properties, opens up a new strategy for desalination, sewage treatment, and other related fields.

Why does distilled liquor (Baijiu) have a yellowish color: A comprehensive analysis

Elucidating the mechanisms underlying Baijiu production is a shared aspiration among academic groups specializing in the field of Baijiu research. This study comprehensively examined the mechanisms underlying the yellowish coloration of Baijiu through a synergistic application of chromatographic, spectroscopic, and physical methodologies. Aging of Baijiu in earthenware pots involves the infiltration of mineral ions such as iron, aluminum, and calcium; however, these ions are detected at extremely low concentrations and are therefore not linked to the development of Baijiu's yellowish color. Instead, the yellowish coloration is attributed to the diverse colorants generated during the high-temperature fermentation of small-molecule sugars derived from the saccharification of grain materials. Although these colorants exist in minimal quantities and exhibit spectral absorption peaks ranging from 300 to 450 nm, their overlapping spectra collectively contribute to the light-absorbing properties of Baijiu across a broad wavelength range, ultimately accounting for its characteristic yellowish color.

Metasurface-enabled broadband multidimensional photodetectors

Light encodes multidimensional information, such as intensity, polarization, and spectrum. Traditional extraction of this light information requires discrete optical components by subdividing the detection area into many “one-to-one” functional pixels. The broadband photodetection of high-dimensional optical information with a single integrated on-chip detector is highly sought after, yet it poses significant challenges. In this study, we employ a metasurface-assisted graphene photodetector, enabling to simultaneously detect and differentiate various polarization states and wavelengths of broadband light (1-8 μm) at the wavelength prediction accuracy of 0.5 μm. The bipolar polarizability empowered by this design allows to decouple multidimensional information (encompassing polarization and wavelength), which can be achieved by encoding vectorial photocurrents with varying polarities and amplitudes. Furthermore, cooperative multiport metasurfaces are adopted and boosted by machine learning techniques. It enables precise spin-wavelength differentiation over an extremely broad wavelength range (1-8 μm). Our innovation offers a recipe for highly compact and high-dimensional spectral-polarization co-detection.

Broadband Unidirectional Thermal Emission

AbstractDirectional control of far‐field thermal emission plays a key role in effective heat and energy transfer. However, conventional photonic strategies are challenging to concurrently control the polar and azimuthal angle of thermal emission over broadband. Here both polar and azimuthal angles of thermal emission are constrained to narrow ranges over broadband by introducing in‐plane anisotropy combined with magneto‐optical materials in the epsilon‐near‐zero (ENZ) wavelength range. The physical mechanism of tunable perfect absorption/emission is explored by investigating the evolution of multiple topological phase singularity pairs (TPSPs). The structure consisting of a magnetized gradient‐ENZ emitter and anisotropic spacer that exhibits high (>0.8) unidirectional emissivity (θ: 55°–79°, φ: 163.5°–196.5°) in the p‐polarization for a broad range of wavelength (22–26 µm) is demonstrated. The unveiled physics synergizing ENZ, anisotropy, and magneto‐optical properties that support broadband unidirectional thermal emission will bring new opportunities in applications such as thermal camouflaging, thermal photovoltaics, and infrared light sources.

Hyperspectral imaging and artificial intelligence enhance remote phenotyping of grapevine rootstock influence on whole vine photosynthesis.

Rootstocks are gaining importance in viticulture as a strategy to combat abiotic challenges, as well as enhancing scion physiology. Photosynthetic parameters such as maximum rate of carboxylation of RuBP (Vcmax) and the maximum rate of electron transport driving RuBP regeneration (Jmax) have been identified as ideal targets for potential influence by rootstock and breeding. However, leaf specific direct measurement of these photosynthetic parameters is time consuming, limiting the information scope and the number of individuals that can be screened. This study aims to overcome these limitations by employing hyperspectral imaging combined with artificial intelligence (AI) to predict these key photosynthetic traits at the canopy level. Hyperspectral imaging captures detailed optical properties across a broad range of wavelengths (400 to 1000 nm), enabling use of all wavelengths in a comprehensive analysis of the entire vine's photosynthetic performance (Vcmax and Jmax). Artificial intelligence-based prediction models that blend the strength of deep learning and machine learning were developed using two growing seasons data measured post-solstice at 15 h, 14 h, 13 h and 12 h daylengths for Vitis hybrid 'Marquette' grafted to five commercial rootstocks and 'Marquette' grafted to 'Marquette'. Significant differences in photosynthetic efficiency (Vcmax and Jmax) were noted for both direct and indirect measurements for the six rootstocks, indicating that rootstock genotype and daylength have a significant influence on scion photosynthesis. Evaluation of multiple feature-extraction algorithms indicated the proposed Vitis base model incorporating a 1D-Convolutional neural Network (CNN) had the best prediction performance with a R2 of 0.60 for Vcmax and Jmax. Inclusion of weather and chlorophyll parameters slightly improved model performance for both photosynthetic parameters. Integrating AI with hyperspectral remote phenotyping provides potential for high-throughput whole vine assessment of photosynthetic performance and selection of rootstock genotypes that confer improved photosynthetic performance potential in the scion.

In Vivo Optical Clearing of Mammalian Brain.

Established methods for imaging the living mammalian brain have, to date, taken optical properties of the tissue as fixed; we here demonstrate that it is possible to modify the optical properties of the brain itself to significantly enhance at-depth imaging while preserving native physiology. Using a small amount of any of several biocompatible materials to raise the refractive index of solutions superfusing the brain prior to imaging, we could increase several-fold the signals from the deepest cells normally visible and, under both one-photon and two-photon imaging, visualize cells previously too dim to see. The enhancement was observed for both anatomical and functional fluorescent reporters across a broad range of emission wavelengths. Importantly, visual tuning properties of cortical neurons in awake mice, and electrophysiological properties of neurons assessed ex vivo, were not altered by this procedure.

Highly coherent mid-infrared wideband supercontinuum generation by a silica cladded silicon nitride core buried waveguide

Abstract Optical waveguides with semiconductor cores are drawing considerable research interest in the domain of supercontinuum (SC) generation in recent times. In this work, we design a square-core silicon nitride buried waveguide with a silica-clad, aiming for a wideband spectrum generation in the mid-IR region when operated at the standard telecommunication wavelength of 1550 nm. Among different such silicon nitride square-core buried waveguides, we propose a typical design with dimensions of 400 nm × 400 nm along its height and width, capable of producing a highly coherent broadband intensity spectrum ranging from 810 nm to 5441 nm after propagating through just a few millimeters of the waveguide. The group velocity dispersion maintains minimal value over a broad wavelength range in the mid-IR region, while the nonlinear coefficient is estimated to be sufficiently high. The nonlinear pulse propagation through such a waveguide leads to achieving an SC spanning over 2.76 octaves, sufficiently broader than previously reported silicon nitride-based waveguides. Furthermore, our calculations confirm the highly coherent nature of the generated SC. To the best of our knowledge, this is the first report of SC generation maintaining a high degree of coherence over such a wide wavelength range in the mid-IR zone using a square-core silicon nitride buried waveguide.

Carbon Dots in Photodynamic Therapy: The Role of Dopant and Solvent on Optical and Photo-Responsive Properties.

Carbon dots (CDs) are novel carbon-based luminescent materials with wide-ranging applications in biosensing, bioimaging, drug transportation, optical devices, and beyond. Their advantageous attributes, including biocompatibility, biodegradability, antioxidant activity, photostability, small particle size (<10 nm), and strong light absorption and excitation across a broad range of wavelengths, making them promising candidates in the field of photodynamic therapy (PDT) as photosensitizers (PSs). Further enhancements in functionality are imperative to enhance the effectiveness of CDs in PDT applications, notwithstanding their inherent benefits. Recently, doping agents and solvents have been demonstrated to improve CDs' optical properties, solubility, cytotoxicity, and organelle targeting efficiency. These improvements result from modifications to the CDs' carbon skeleton matrices, functional groups on the surface state, and chemical structures. This review discusses the modification of CDs with heteroatom dopants, dye dopants, and solvents to improve their physicochemical and optical properties for PDT applications. The correlations between the surface chemistry, functional groups, the structure of the CDs, and their optical characteristics toward quantum yield, redshift feature, and reactive oxygen species (ROS) generation, have also been discussed. Finally, the progressive trends for the use of CDs in PDT applications are also addressed in this review.

Design and optimization of broadband near-perfect absorber based on transition metal nitrides thin-films for solar energy harvesting

Broadband metamaterial absorbers hold promise for solar energy harvesting, but their complex designs and use of expensive noble metals hinder scalability and thermal stability. Additionally, traditional design methods are time-consuming. We propose a novel approach that combines a genetic algorithm with the transfer matrix method to optimize both material composition and layer structure for large-scale, cost-effective, and thermally stable solar absorbers. This method enables the design of near-perfect absorbers with an average absorptance exceeding 90 % and over 80 % across a broad wavelength range (0.3–2.5 μm) within the key solar spectrum. By optimizing the arrangement of metal and insulator layers using nitride materials (e.g., vanadium nitride), we achieve superior performance compared to traditional metal–insulator and insulator–metal structures. This optimization utilizes resonant absorption and the inherent absorption of metal layers. Our work paves the way for efficient and scalable solar energy harvesting devices.

Distributed semiconductor heterojunctions of ZnO–Cu2O for ultraviolet photodetection

Semiconductor heterojunctions, because of their unique optoelectronic properties, have gained significant attention for integrated photonic devices. UV photodetectors based on semiconductor heterojunctions are promising due to their enhanced light absorption, efficient charge separation, and tunable electronic properties, which collectively lead to superior sensitivity and performance. An inter-band transition-based UV photodetector utilizing Cu2O/ZnO distributed heterojunctions has been demonstrated. We propose an integrated photonic structure based on semiconductor heterojunctions in the form of Cu2O–ZnO grating for ultraviolet photodetection yielding a low dark current and improved efficiency. The Cu2O–ZnO grating heterostructure, in comparison to individual planar heterojunction, boosts light-matter interaction enabling higher absorption and enhanced responsivity. The device depicts a responsivity of 0.7A/W at 360nm wavelength. The device exhibits a broadband absorption which remains good over a broad wavelength range from 250nm to 450nm. The reported UV photodetector may find applications in environmental monitoring, UV light communication, biomedical diagnostics, and industrial safety.

The n-MoO3/p-Si heterojunction photodiode: Influence of the MoO3 film thickness on the ultraviolet and infrared photodetector performance

Here, we studied the effect of the MoO3 thin film thickness on the ultraviolet (UV) and infrared (IR) photodiode properties of the n-MoO3/p-Si heterojunction structure. Initially, the metal molybdenum (Mo) thin films with different thicknesses (50,150, and 250 nm) were created via DC magnetron sputtering on a p-type Si substrate. Then, the MoO3 thin films were synthesized using a thermal oxidation method with an optimal oxygen flow rate of 60sccm. XRD and Raman analysis showed that the structure of prepared thin films has converted from an amorphous to an orthorhombic (α-MoO3) crystalline phase with increasing thickness. The optical transmittance of the layers was tuned by controlling the thickness, and the maximum transmittance for the 50 nm-thick film was achieved in the broad wavelength range of 300–1100 nm. The current density–voltage (J–V) characteristics indicate the prepared samples' rectifying behavior under dark conditions. The heterojunction photodiode with a 50 nm-thick MoO3 layer shows the best performance. This sample had a maximum amount of transmittance in the UV–visible and IR regions, compared to other samples, which leads to efficient electron-hole separation and transportation. This sample demonstrates a significant photoresponse ratio (ILight/IDark) of about 55 and 52.5 in the ultraviolet (UV) and infrared (IR) regions, respectively.

High-speed measurement method for diffraction efficiency of gratings in broad range wavelength based on AOTF

High-speed measurement method for diffraction efficiency of gratings in broad range wavelength based on AOTF

Green-synthesized Ag hierarchical assemblies for SERS detection of rhodamine dye

This study presents a simple benchtop synthetic protocol for the fabrication of silver (Ag) hierarchical structures in aqueous media using environmentally friendly and inexpensive reagents under mild experimental conditions. Natural organic acids that are known to be present in plants were employed as reducing and morphology-directing reagents. SEM and TEM imaging revealed that the products are three-dimensional hierarchical structures that were formed from self-assembly of smaller nanoparticles. They are generally spherical in shape, measure around 1.5 to 5 μm in size, and possess highly roughened surfaces due to the interstitial gaps between their nanoparticle subunits. Their hierarchical architecture allows for strong absorption of light in a broad range of wavelengths that extends to the near-infrared region. In addition, their surface morphology has an abundance of hot spot regions, which are capable of inducing strong SERS enhancement effects. The green-synthesized Ag nanostructures showed remarkable SERS activity when used as substrates for the detection of rhodamine 6G dye, a highly toxic water contaminant, even at a concentration as low as 10–8 M. Overall, this study does not only provide a greener approach to Ag hierarchical structures, but also demonstrates the immense potential of these nano-assembled architectures in the sensitive detection of organic dye pollutants.

On the glow of cremated remains: long-lived green photo-luminescence of heat-treated human bones.

The long-lived green luminescence of human bone (that has been heated to 600°C for a short duration) is attributed to a carbon quantum dot material (derived from collagen) encapsulated and protected by an inorganic matrix (derived from bone apatite) and is more intense in dense rigid and crystalline parts of (healthy) human bones. The strong collagen-apatite interaction results (upon decomposition) in a protective inorganic environment of the luminescent centers allowing long-lived triplet-based emission of a carbon (quantum) dot-like material at room temperature, as well as resilience against oxidation between 550 and 650°C. The graphitic black phase (obtained upon heating around 400°C) is a precursor to the luminescent carbon-based material, that is strongly interacting with the crystalline inorganic matrix. Human bone samples that have been heated to 600°C were subjected to steady-state and time-resolved spectroscopy. Excitation-emission matrix (EEM) luminescence spectroscopy revealed a broad range of excitation and emission wavelengths, indicating a heterogeneous system with a broad density of emissive states. The effect of low temperature on the heat-treated bone was studied with Cryogenic Steady State Luminescence Spectroscopy. Cooling the bone to 80K leads to a slight increase in total emission intensity as well as an intensity increase towards to red part of the spectrum, incompatible with a defect state model displaying luminescent charge recombination in the inorganic matrix. Time-resolved spectroscopy with an Optical Multichannel Analyzer (OMA) and Time Correlated Single Photon Counting (TCSPC) of these samples showed that the decay could be fitted with a multi-exponential decay model as well as with second-order decay kinetics. Confocal Microscopy revealed distinct (plywood type) structures in the bone and high intensity-fast decay areas as well as a spatially heterogeneous distribution of green and (fewer) red emissive species. The use of the ATTO 565 dye aided in bone-structure visualization by chemical adsorption. Conceptually our data interpretation corresponds to previous reports from the material science field on luminescent powders.

Pop-cosmos: A Comprehensive Picture of the Galaxy Population from COSMOS Data

We present pop-cosmos: a comprehensive model characterizing the galaxy population, calibrated to 140,938 (r < 25 selected) galaxies from the Cosmic Evolution Survey (COSMOS) with photometry in 26 bands from the ultraviolet to the infrared. We construct a detailed forward model for the COSMOS data, comprising: a population model describing the joint distribution of galaxy characteristics and its evolution (parameterized by a flexible score-based diffusion model); a state-of-the-art stellar population synthesis model connecting galaxies’ intrinsic properties to their photometry; and a data model for the observation, calibration, and selection processes. By minimizing the optimal transport distance between synthetic and real data, we are able to jointly fit the population and data models, leading to robustly calibrated population-level inferences that account for parameter degeneracies, photometric noise and calibration, and selection. We present a number of key predictions from our model of interest for cosmology and galaxy evolution, including the mass function and redshift distribution; the mass–metallicity-redshift and fundamental metallicity relations; the star-forming sequence; the relation between dust attenuation and stellar mass, star formation rate, and attenuation-law index; and the relation between gas-ionization and star formation. Our model encodes a comprehensive picture of galaxy evolution that faithfully predicts galaxy colors across a broad redshift (z < 4) and wavelength range.

Shielding development for the spallation neutron source VENUS instrument

VENUS is a neutron imaging instrument that will use a broad range of neutron wavelengths, from epithermal to cold energies, and will include enhanced contrast mechanisms. It will offer novel energy-selective imaging techniques directly connecting complex engineering materials and systems’ structures, properties, and functions to reveal practical and fundamental answers about their real-world performance. The instrument will be built at SNS beamline 10, facing the decoupled poisoned hydrogen moderator. The driving cost for the instrument is the beamline and instrument cave shielding. Final analyses were performed to evaluate the thickness and composition of shielding materials for the instrument cave and beamline to meet radiation safety criteria for the instrument to start up in 2024 after completing the SNS proton power upgrade.