Narrow Band Research Articles

Enhancing the properties of Cd-free MgZnS buffer for solar cells by co-sputtering ZnS and Mg targets

The buffer is an essential component that connects the window and absorber layers in thin film solar cells, which has significant impacts on the performance of cell device. CdS is widely used buffer material, but it has drawbacks of toxicity and narrow band gap of 2.4eV. This work explores the fabrication of a novel Cd-free MgZnS buffer layer through co-sputtering ZnS and Mg targets. The grain size, morphology, phase composition, transmittance and band gap of MgZnS films are manipulated by adjusting the substrate temperature, sputtering power of ZnS target and sputtering current of Mg target. The MgZnS film exhibits remarkable characteristics, including high crystallinity with grain size of about 35nm, high transmittance of over 80%, and high band gap of 3.44eV. The process parameters with favorable outcomes include substrate temperature of 300 °C, ZnS sputtering power of 100W, and Mg sputtering current of 0.05A. Furthermore, compared with the CdS buffer, the MgZnS buffer has better compactness and transmittance. This method provides a promising new and effective avenue to fabricate Cd-free buffers for solar cells.

Narrow band imaging-based radiogenomics for predicting radiosensitivity in nasopharyngeal carcinoma

Narrow band imaging-based radiogenomics for predicting radiosensitivity in nasopharyngeal carcinoma

Electronic, thermoelectric and electrical transport properties of single layer γ-graphyne

Recently, graphyne has emerged as the sole two-dimensional carbon material exhibiting both sp and sp2 hybridization. It’s remarkable attributes have ignited considerable interest, particularly in the realm of optoelectronics, driven by its narrow band gap, signifying its vast potential in this field. In this paper we investigated electronic, thermoelectric and electrical transport properties of single layer γ-graphyne systematically and comparatively by using density functional theory (DFT). Our findings reveal that γ-graphyne displays pronounced absorption peaks within both the infrared (IR) and visible regions (VR), indicating its robust optical characteristics. Additionally, γ-graphyne showcases exceptional thermoelectric performance. The insights gained from this study elucidate the properties of γ-graphyne and suggest its applicability across various domains, including optical sensing and thermoelectric energy conversion devices.

Increasing the raw contrast of VLT/SPHERE with the dark hole technique

Context. Imaging exoplanetary systems is essential to characterizing exoplanet atmospheres and orbits as well as circumstellar disks and to studying planet-disk interactions to understand the planet formation processes. Imaging exoplanets or circumstellar disks in the visible and near-infrared is challenging, however, because these objects are very faint relative to their star, even though only fractions of an arcsecond away. Coronagraphic instruments have already allowed the imaging of a few exoplanets, but their performance is limited by wavefront aberrations. Adaptive optics systems partly compensate for the Earth’s atmosphere turbulence, but they cannot fully control the wavefront. Some of the starlight leaks through the coronagraph and forms speckles in the astrophysical image. Focal plane wavefront control, used as a second stage after the adaptive optics system, has been proposed to minimize the speckle intensity within an area called the dark hole. Aims. We previously demonstrated the on-sky performance of dark hole techniques, pairwise probing coupled with electric field conjugation, using the apodized pupil Lyot coronagraph of the VLT/SPHERE instrument. In this paper, we probe their performance using the SPHERE four-quadrant phase mask coronagraph, and we demonstrate the interest of combining dark hole techniques and reference differential imaging. Methods. We used these dark hole techniques on-sky to create a dark hole in the narrow band around 1.7 |j.m observing HR 4796. We then recorded broadband images of HR 4796 and a reference star at the H band. Results. The dark hole techniques improved the H-band detection limit by a factor of three. The dark hole was stable from one star to a nearby star enabling reference differential imaging. Conclusions. This stability offers two new strategies of observation. First, one can quickly create a dark hole observing a bright star before pointing to a faint target star. Furthermore, one can couple dark hole techniques and reference differential imaging. A very interesting point is that the performance of these methods does not depend on the astrophysical signal.

First principles study of structural and electronic properties of Ce substituted Ti2O3 slabs with compositions TixCe4-xO6 where x = 0, 1, 2, 3, 4

This study employs Density-functional theory (DFT) to investigate the structural and electronic properties of Ce2O3–Ti2O3 alloys. We systematically examined the structural and electronic properties of the two dimensional (2D) alloys, thereby exploring the impact of Ce substitution in Ti2O3 in full alloy range. The study of charge transfer and bonding analysis revealed the series of materials have dominant ionic character and it decreases linearly with an increase of Ce percentage. Initially, we observed that the parent material Ti2O3 exhibited semiconducting behavior with a narrow band gap of 0.29 eV. However, upon further incorporating Ce substitution into the pristine crystal structure, all the prepared alloys showed an increase of population of states in the band structure. Notably, the band gap of Ti3CeO6 alloy decreased to 0.13 eV and eventually reduced to zero. This trend was consistent across other metallic alloy systems, including Ti2Ce2O6, TiCe3O6, Ce2O3. Moreover, our results revealed that an increased concentration of Ce atoms led to the emergence of magnetic behaviour in the alloys. The work function of all materials to check the reactivity of the studied alloys is also reported. Further, the DFT + U method is employed to include the Hubbard U correction for electronic properties of materials.

MEMS-actuated terahertz metamaterials driven by phase-transition materials

The non-ionizing and penetrative characteristics of terahertz (THz) radiation have recently led to its adoption across a variety of applications. To effectively utilize THz radiation, modulators with precise control are imperative. While most recent THz modulators manipulate the amplitude, frequency, or phase of incident THz radiation, considerably less progress has been made toward THz polarization modulation. Conventional methods for polarization control suffer from high driving voltages, restricted modulation depth, and narrow band capabilities, which hinder device performance and broader applications. Consequently, an ideal THz modulator that offers high modulation depth along with ease of processing and operation is required. In this paper, we propose and realize a THz metamaterial comprised of microelectromechanical systems (MEMS) actuated by the phase-transition material vanadium dioxide (VO2). Simulation and experimental results of the three-dimensional metamaterials show that by leveraging the unique phase-transition attributes of VO2, our THz polarization modulator offers notable advancements over existing designs, including broad operation spectrum, high modulation depth, ease of fabrication, ease of operation condition, and continuous modulation capabilities. These enhanced features make the system a viable candidate for a range of THz applications, including telecommunications, imaging, and radar systems.Graphical

Structural and photophysical properties of two-dimensional lead bromide hybrid perovskite (C8H17NH3)2PbBr4

The structural versatility of organic compounds imparts manifold properties to hybrid organic−inorganic perovskites, where two-dimensional (2D) halide perovskites are potential future platforms for light-emitting devices because of their unique quantum well configuration and dielectric confinement. Notwithstanding the numerous studies on the organic−inorganic perovskites carried out to date, precisely charactering the structure and photoluminescence mechanism remain considerable challenges. Herein, by applying Rietveld refinement, we have obtained crystal structure and atomic sites of 2D layered OA2PbBr4 perovskite, which undergoes a phase transition at 190 K with activation energies of 29.6 and 3.8 meV for the two phases, respectively. The theoretical analysis based on the crystal structure were performed to understand the nature of vibrations and band structure. Steady-state PL shows a narrow emission and a broad emission located at 409 and 487 nm, respectively. With temperature cooling down to 118 K, narrow emission gradually narrowed and enhanced. Meanwhile, intensity of broad emission first weakens and then increases. The turning point occurs near 198 K. By applying time-resolved PL (TRPL) and transient absorption (TA) spectra experiment, we observed a rapid carrier transfer from the FE to the STE state, and demonstrated the narrow and broad bands originate from free exciton and self-trapped exciton emission, respectively. And the self-trapping depth is proved to be 26.3 meV by low-temperature PL. Our findings indicate the synthesized 2D perovskite has potential applications in optoelectronic and display devices.

Comparative analysis of machine learning frameworks for automatic polyp characterization

Early detection and characterization of adenomatous polyps, the precursors to colorectal cancer is crucial for effective diagnosis and treatment of colorectal cancer. A suitably trained machine learning algorithm can perform automatic real-time optical characterization of polyps during colonoscopy procedures with virtual chromoendoscopy systems, such as Narrow Band Imaging (NBI). This study proposes to perform a detailed comparative analysis between the performances of two popular machine learning frameworks, namely training from scratch and transfer learning, using three state-of-the-art architectures ResNet50, EfficientNetB2, and ViTb_32 with one indigenous dataset and one publicly available dataset. The indigenous dataset was created using 1739 NBI frames extracted from colonoscopy videos of 30 polyp masses from 24 patients [870 hyperplastic polyp frames and 869 adenomatous polyp frames]. The publicly available dataset also consisted of NBI frames. Blurry frames or frames with specular reflections were not excluded to closely resemble real-life polyp characterization in a clinical setting. Among the three models used in two different frameworks, EfficientNetB2 in the training from scratch framework yielded the best accuracy, AUC and NPV of 91.91%, 0.99 and 89.06%. The results show that the training from scratch framework outperformed the transfer learning framework in terms of the evaluation metrics. To the best of our knowledge, this is the first indigenous study to focus on polyp classification using solely Narrow Band Imaging (NBI) polyp images. Our results using only NBI polyp frames outperformed those obtained with a combination of white light and NBI frames, as observed in similar existing studies.

An Ultra-broadband Metallic Plasmonic Antenna for Ultrasensitive Molecular Fingerprint Identification.

Near-field enhanced mid-infrared light-matter interactions via metallic plasmonic antennae (PA) have attracted much attention but are inevitably limited by the detuning between their narrow band and the broad applied spectral range. Here, we develop a new low-temperature incubation synthetic method to acquire uniform Ag microparticles (MPs) with numerous hotspots. Their plasmonic band is remarkably extended by the plasmonic coupling of numerous hotspots and covers the entire mid-infrared range (400-4000 cm-1). Hence, the almost complete molecular fingerprint of 4-mercaptobenzonitrile was successfully probed for the first time via resonant surface-enhanced infrared absorption (rSEIRA), and the rSEIRA spectra of different essential amino acids were further detected and exhibit a high spectral identification degree assisted by machine learning. This work changes the inertia perception of "narrow band and large size but small hotspot area" of mid-infrared metallic PA and paves the way for the ultrasensitive mid-infrared optical sensing.

An Optical Detection Model for Stratospheric Airships

This study proposes a numerical model to simulate the thermal characteristics of stratospheric airships (SA). This model introduces a simple yet accurate method for the selection of the optical bands for target detection based on multispectral features. The key to this model is the selection of the spectral bands in which a significant radiation difference exists between the target and its surrounding background. Using the signal-to-noise ratio (SNR), detection probability, and false alarm rate as model evaluation metrics, and based on the analysis of the radiation differences between the target and atmospheric background, it is found that there are two narrow bands possible for SA detection: one with a central wavelength of 8.83 µm and a bandwidth of 0.35 µm and the other with a central wavelength of 11.51 µm and a bandwidth of 0.34 µm. Further numerical simulations and theoretical analyses under varying space environments demonstrate that considerable detection potential can be achieved; thus, the presented optical detection model is useful for the night detection of SA targets.

Tunable Near-Infrared Transparent Bands Based on Cascaded Fabry–Perot Cavities Containing Phase Change Materials

In this paper, we construct a near-infrared Fabry–Perot cavity composed of two sodium (Na) layers and an antimony trisulfide (Sb2S3) layer. By cascading two Fabry–Perot cavities, the transmittance peak splits into two transmittance peaks due to the coupling between two Fabry–Perot modes. We utilize a coupled oscillator model to describe the mode coupling and obtain a Rabi splitting of 60.0 meV. By cascading four Fabry–Perot cavities, the transmittance peak splits into four transmittance peaks, leading to a near-infrared transparent band. The near-infrared transparent band can be flexibly tuned by the crystalline fraction of the Sb2S3 layers. In addition, the effects of the layer thickness and incident angle on the near-infrared transparent band and the mode coupling are investigated. As the thickness of the Na layer increases, the coupling strength between the Fabry–Perot modes becomes weaker, leading to a narrower transparent band. As the thickness of the Sb2S3 layer increases, the round-trip propagating of the Sb2S3 layer increases, leading to the redshift of the transparent band. As the incident angle increases, the round-trip propagating of the Sb2S3 layer decreases, leading to the blueshift of the transparent band. This work not only provides a viable route to achieving tunable near-infrared transparent bands, but also possesses potential applications in high-performance display, filtering, and sensing.

Estimation and Compensation of the Ionospheric Path Delay Phase in PALSAR-3 and NISAR-L Interferograms

Spatial and temporal variation in the free electron concentration in the ionosphere affects SAR interferograms, in particular at low radar frequencies. In this work, the identification, estimation, and compensation of ionospheric path delay phases in PALSAR-3 and NISAR-L interferograms are discussed. Both of these L-band sensors simultaneously acquire SAR data in a main spectral band and in an additional, spectrally separated, narrower second band to support the mitigation of ionospheric path delays. The methods presented permit separating the dispersive and the non-dispersive phase terms based on the double-difference interferogram between the two available spectral bands and the differential interferogram of the main band. The applicability of the proposed methods is demonstrated using PALSAR-3-like data that were simulated based on PALSAR-2 SM1 mode data.

Are Selenides the Same as Sulfides? Structure, Spectroscopy, and Properties of Narrow-Gap Rare-Earth Semiconductors RE2Sn(S1-xSex)5 (RE = La, Ce; x = 0-0.8).

The ternary rare-earth sulfides RE2SnS5 (RE = La-Nd) and the partial solid solutions RE2Sn(S1-xSex)5 (RE = La, Ce; x = 0-0.8) were prepared in the form of polycrystalline samples by reaction of the elements at 900 °C and as single crystals in the presence of KBr flux. They adopt the La2SnS5-type structure (orthorhombic, space group Pbam, Z = 2) consisting of chains of edge-sharing SnCh6 octahedra separated by RE atoms. Although the cell parameters evolve smoothly in RE2Sn(S1-xSex)5, detailed structural analysis by single-crystal X-ray diffraction revealed a pronounced preference for the Se atoms to occupy two out of the three chalcogen sites, which offers a rationalization for why the all-selenide end-members RE2SnSe5 do not form. Solid-state 119Sn NMR spectra confirmed the nonrandom distribution of SnS6-nSen local environments, which could be resolved into individual resonances. The Raman spectra of RE2SnS5 compounds show an intense peak at 307-320 cm-1 assigned to a symmetric A1g mode, which is dominated by Sn-S bonds; the Raman peak intensities varied with Se substitution in La2Sn(S1-xSex)5. Optical diffuse reflectance spectra, band structure calculations, and electrochemical impedance spectra indicated that these compounds are narrow band gap semiconductors; the optical band gaps are insensitive to RE substitution in RE2SnS5 (0.7 eV) but they gradually decrease with greater Se substitution in RE2Sn(S1-xSex)5 (0.7-0.4 eV).

Accuracy of optical diagnosis with narrow band imaging in the surveillance of ulcerative colitis: a prospective study comparing Kudo, Kudo-IBD and NICE classifications

PurposeThe diagnostic accuracy of Narrow Band Imaging (NBI) in the endoscopic surveillance of ulcerative colitis (UC) has been disappointing in most trials which used the Kudo classification. We aim to compare the performance of NBI in the lesion characterization of UC, when applied according to three different classifications (NICE, Kudo, Kudo-IBD).MethodsIn a prospective, real-life study, all visible lesions found during consecutive surveillance colonoscopies with NBI (Exera-II CV-180) for UC were classified as suspected or non-suspected for neoplasia according to the NICE, Kudo and Kudo-IBD criteria. The sensitivity (SE), specificity (SP), positive (+LR) and negative (-LR) likelihood ratios of the three classifications were calculated, using histology as the reference standard.Results394 lesions (mean size 6 mm, range 2–40 mm) from 84 patients were analysed. Twenty-one neoplastic (5%), 49 hyperplastic (12%), and 324 inflammatory (82%) lesions were found. The diagnostic accuracy of the NICE, Kudo and Kudo-IBD classifications were, respectively: SE 76%-71%-86%; SP 55-69%-79% (p < 0.05 Kudo-IBD vs. both Kudo and NICE); +LR 1.69-2.34-4.15 (p < 0.05 Kudo-IBD vs. both Kudo and NICE); -LR 0.43-0.41-0.18.ConclusionThe diagnostic accuracy of NBI in the differentiation of neoplastic and non-neoplastic lesions in UC is low if used with conventional classifications of the general population, but it is significantly better with the modified Kudo classification specific for UC.

2D–3D heterostructure of PtS2−x /Ga2O3 and their band alignment studies for high performance and broadband photodetector

For deep ultraviolet (UV-C) photodetectors, gallium oxide (Ga2O3) is a suitable candidate owing to its intrinsic ultra-wide band gap and high stability. However, its detection is limited within the UV-C region, which restricts it to cover a broad range, especially in visible and near-infrared (NIR) region. Therefore, constructing a heterostructure of Ga2O3 with an appropriate material having a narrow band gap is a worthwhile approach to compensate for it. In this category, PtS2 group-10 transitional metal dichalcogenide stands at the top owing to its narrow band gap (0.25–1.65 eV), high mobility, and stability for heterostructure synthesis. Moreover, heterostructure with Ga2O3 sensing in UV and PtS2 broad response in visible and IR range can broaden the spectrum from UV to NIR and to build broadband photodetector. In this work, we fabricated a 2D–3D PtS2−x /Ga2O3 heterostructure based broadband photodetector with detection from UV-C to NIR region. In addition, the PtS2−x /Ga2O3 device shows a high responsivity of 38.7 AW−1 and detectivity of 4.8 × 1013 Jones under 1100 nm light illumination at 5 V bias. A fast response of 90 ms/86 ms illustrates the device’s fast speed. An interface study between the PtS2−x and Ga2O3 was conducted using x-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy (UPS) which confirmed type-I band alignment. Finally, based on their band alignment study, a carrier transport mechanism was proposed at the interface. This work offers a new opportunity to fabricate large-area high-performance 2D–3D heterostructures based photodetectors for future optoelectronics devices.

Oxynitride from Oxide vs Nitride: Manifesting Competitive and Synergistic Properties in Titanium Oxynitride for Solar‐Drive Water Splitting and Nitrogen Fixation

The present study investigates the phase formation of the titanium oxynitride (TiOxNy) system by employing the ‘oxide‐to‐oxynitride’ and ‘nitride‐to‐oxynitride’ synthesis strategies. The XRD patterns of both the materials showed peaks corresponding to Ti‐N and Ti‐O lattices, confirming the formation of Ti‐oxynitride system. Accordingly, the presence of Ti3+‐N3‐ and Ti4+‐2O2‐ signals is also confirmed by XPS analysis. The TiOxNy derived from oxide (TO‐TON) exhibits wide visible light absorption with a narrow band gap energy of ∽2.30 eV, while the nitride‐derived‐TiOxNy (TN‐TON) exhibits relatively a wide band gap energy (∽2.92 eV) along with the plasmonic band of TiN. In line with this, an enhanced recombination resistance and charge carriers with extended lifetime is observed for TN‐TON (4.47 ns) and TO‐TON (4.33 ns) systems via PL and TRPL analysis. Consequently, the TN‐TON system demonstrated a superior H2/NH3 production at a rate of ∽1432/646 µmol g‐1 h‐1 under solar irradiation, while it is ∽1136/553 µmol g‐1 h‐1 for the TO‐TON system. These efficiencies are ∽20x and 3x times higher than the bare TiN and TiO2, respectively towards H2/NH3 production. The insights from this study demonstrate that the nitride and oxide‐based precursors likely manifest synergistic and competitive properties, respectively, in the resulting oxynitride system.This article is protected by copyright. All rights reserved.

Theoretical prediction of broadband ambient light optogenetic vision restoration with ChRmine and its mutants

Vision restoration is one of the most promising applications of optogenetics. However, it is limited due to the poor-sensitivity, slow-kinetics and narrow band absorption spectra of opsins. Here, a detailed theoretical study of retinal ganglion neurons (RGNs) expressed with ChRmine, ReaChR, CoChR, CatCh and their mutants, with near monochromatic LEDs, and broadband sunlight, halogen lamp, RGB LED light, and pure white light sources has been presented. All the opsins exhibit improved light sensitivity and larger photocurrent on illuminating with broadband light sources compared to narrow band LEDs. ChRmine allows firing at ambient sunlight (1.5 nW/mm2) and pure white light (1.2 nW/mm2), which is lowest among the opsins considered. The broadband activation spectrum of ChRmine and its mutants is also useful to restore color sensitivity. Although ChRmine exhibits slower turn-off kinetics with broadband light, high-fidelity spikes can be evoked upto 50 Hz. This limit extends upto 80 Hz with the improved hsChRmine mutant although it requires double the irradiance compared to ChRmine. The present study shows that ChRmine and its mutants allow activation of RGNs with ambient light which is useful for goggle-free white light optogenetic retinal prostheses with improved quality of restored vision.

ВОЛНОВОДНО ДИЭЛЕКТРИЧЕСКИЙ МЕТОД И УСТРОЙСТВА ДЛЯ ИЗМЕРЕНИЯ КОНЦЕНТРАЦИИ ВОДНЫХ РАСТВОРОВ И ОБЛУЧЕНИЯ БИОЛОГИЧЕСКИХ ОБЪЕКТОВ

A technique for studying the absorption of microwave radiation of biological objects in a thin dielectric capillary is proposed. The results of experimental studies are presented and the mechanism of the detected effects of the biological action of microwave radiation is proposed. It was found that at a certain ratio between the dimensions of the waveguide, the diameter and thickness of the walls of the capillary, the dielectric parameters of the biological material that fills the capillary and the wavelength of microwave radiation in the waveguide, a significant increase in the absorbed power in a rather narrow frequency band (waveguide-dielectric resonance) is possible. This phenomenon must be taken into account in biotechnological experiments on the irradiation of suspensions. As a result of the work done on the study of the absorption of microwave radiation by hydrocarbon mixtures and models of biological objects in aquatic environments, new designs of measuring devices were created and a technique for hydrocarbon aquametry was developed. The created products are protected by the authors of this work by a patent for an invention.

Hafnium dinitride/poly(9-vinylcarbazole) heterojunction: Structural, electronic, optical and vibrational properties. A DFT and DFPT study

Photosensitivity of semiconducting polymers can be enhanced by blending donor and acceptor polymers to optimize photoinduced charge separation. With a motivation to understand microscopic aspects of HfN2 and PVK relevant to optoelectronic properties of transition metal-dinitride/semiconductor interfaces, we examined their structural, electronic, optical and vibrational properties using first-principles calculations based on density functional theory (DFT) and density functional perturbation theory (DFPT) levels of theory. We computed a large direct energy gap of 3.751 eV for PVK and an indirect narrow band gap of 1.396 eV in HfN2. The gap value computed for the composite structure, HfN2/PVK, was 0.958 eV. The heterojunction displayed an indirect energy gap. The charge transfer between HfN2 and PVK results in a polarized field within the interface region, which will benefit the separation of photogenerated carriers. The calculated density of electronic states, Lowdin charge transfer and charge density difference certify that this proposed layered nanoheterojunction is an excellent light-harvesting semiconductor. These findings indicate that the conjugated polymer PVK is a promising candidate as a non-noble metal co-catalyst for HfN2 photocatalysis. It also provides useful information for understanding the observed enhanced photocatalytic mechanisms in experiments.

Graphene Quantum Dots as Hole Extraction and Transfer Layer Empowering Solar Water Splitting of Catalyst-Coupled Zinc Ferrite Nanorods.

Despite the narrow band gap energy, the performance of zinc ferrite (ZnFe2O4) as a photoharvester for solar-driven water splitting is significantly hindered due to its sluggish charge transfer and severe charge recombination. This work reports the fabrication of a hybrid nanostructured hydrogenated ZnFe2O4 (ZFO) photoanode with enhanced photoelectrochemical water-oxidation activity through coupling N-doped graphene quantum dots (GQDs) as a hole transfer layer and Co-Pi as a catalyst. The GQDs not only reduce the surface-mediated nonradiative electron-hole pair recombination but also induce a built-in interfacial electric field leading to a favorable band alignment at the ZFO/GQDs interface, helping rapid photogenerated hole separation and serving as a conducting hole transfer highway, improve the hole transportation into the Co-Pi catalyst for enhanced water oxidation reaction kinetics. The optimized ZFO/GQD/Co-Pi hybrid photoanode delivers a 23-fold photocurrent enhancement at 1.23 V versus the reversible hydrogen electrode (RHE) and a significant 360 mV reduction in the onset potential, reaching 0.65 VRHE compared with the ZFO photoanode under 1 sun illumination in a neutral electrolytic environment. This investigation underscores the mechanism of synergistic interplay between the hole transport layer and cocatalyst in boosting the solar-illuminated water-splitting activity of the ZFO photoanode.