Peak Absorption Wavelength Research Articles

Single Cell Assessment of Mitochondrial Function

Cellular mitochondrial function can be assessed using high resolution respirometry that measures O2 consumption rate during various conditions that systematically alter the tricarboxylic acid (TCA) cycle or the electron transport chain (ETC). However, current high resolution respirometry does not measure O2 consumption rate at the single cell level, but actually measures average mitochondrial function across a number of cells (either isolated or in tissues). Thus, respirometry assumes physiological homogeneity across cells. However, in many tissues, mitochondrial function varies across cells and this heterogeneity is physiologically important. Therefore, a direct measurement of cellular mitochondrial function will provide valuable novel information and physiological insight. In the present study, we used a quantitative histochemical technique to measure the activity of succinate dehydrogenase (SDH), a key enzyme located in the inner mitochondrial membrane, and the only enzyme to participate in both the TCA cycle and the ETC as Complex II. SDH mediates the oxidation of succinate to fumarate in the TCA cycle, which is coupled to the reduction of ubiquinone to ubiquinol in the ETC. In this study we determined the maximum velocity of the SDH reaction (SDHmax) in isolated human airway smooth muscle (hASM) cells using 1‐methoxyphenazine methosulphate (mPMS), as an exogenous electron carrier, and azide to inhibit cytochrome oxidase. To measure SDHmax, the cells were exposed to a solution containing 80 mM succinate and 1.5 mM nitroblue tetrazolium (NBT) as the reaction indicator. hASM cells were imaged in 3D (Z optical slice of 0.5 μm) using a Nikon Eclipse A1 laser scanning confocal system with a ×60/1.4 NA oil‐immersion lens. In the quantitative histochemical procedure, changes in cell optical density (OD) due to the progressive reduction of NBT to its diformazan (peak absorbance wavelength of 570 nm) were measured every 15 s over a 10 min period. Linearity of the SDH reaction was confirmed across the 10 min period, and SDHmax was expressed as mM fumarate/liter of tissue/min. Validation of this technique included specific ETC inhibitors including oligomycin (ATP synthase inhibitor), FCCP (proton ionophore), antimycin A (Complex III inhibitor) and rotenone (Complex I inhibitor), similar to those used in high resolution respirometry. We observed that FCCP‐mediated disruption of the mitochondrial proton gradient does not affect SDHmax, while SDHmax is decreased by rotenone and antimycin A. In addition, we used MitoTracker Green to label and image mitochondria in hASM cells and determined mitochondrial volume density. The SDHmax was then normalized to mitochondrial content. Our results confirm that this quantitative technique is rigorous and reproducible, and that measurements of cellular SDHmax can serve as a reliable surrogate for the measurement of maximum mitochondrial respiration in single cells.

Ultra-Sensitive Si-Based Optical Sensor for Nanoparticle-Size Traditional Water Pollutant Detection

A low-cost Si-based optical nano-sensor that monitors traditional water pollutants is introduced in this paper. The introduced sensor works in the near-infrared region, 900 nm to 2500 nm spectral range. The proposed structure consists of a Si layer with an optimized thickness of 300 nm on the top of the Al layer acting as a back reflector. On the top of the Si layer, the water pollutants are modeled as nanoparticle materials of different sizes. The finite difference time domain method is utilized to optimize the thicknesses of the Si layer by analyzing the optical light absorption considering different Si layer thicknesses and different pollutant nanoparticles’ sizes. Different interpolation techniques, including polynomials with various degrees and locally weighted smoothing quadratic regression, are used to find the best fitting model representing the simulated data points with goodness of fit analysis. Three features are proposed to identify the water pollutant with its size, peak absorption wavelength, relative amplitude, and a full width at half maximum. The device’s performance in detecting six different pollutants, silver, aluminum, copper, chromium, selenium, and ammonia, is evaluated. Sensitivity, a figure of merit, and a quality factor are used to evaluate the proposed sensor. The obtained maximum sensitivity is 11,300 nm/RIU, FOM of 740, and quality factor of 670.

Using critical coupling to achieve monolayer graphene perfect absorber with high-sensitivity and polarization-independence

In this paper , by using critical coupling theory analysis and the finite-difference time-domain (FDTD) method for simulation calculations, we indicate theoretically that the graphene-cylinder-metal arrays structure is a perfect absorber with high-sensitivity and polarization-independent in the near-infrared region. The results show that the absorber can achieve a perfect absorption of 99.14%, which is more than 43 times the absorption of bare monolayer graphene (2.3%). In the case of the same geometric parameters, whether transverse magnetic (TM) or transverse electric (TE) polarizations, the absorption and resonance peak wavelength of the absorber are equal , because the graphene-cylinder-metal arrays structure is a highly symmetric structure. Furthermore, through numerical simulation and theoretical analysis, on the one hand, the absorber has high sensitivity up to 939.30 nm/RIU. On the other hand, when the incident light source is normally incident, the absorption performance of the arrays structure does not vary with the change of the polarization angle, that is, the system has polarization-independent characteristics. We believe this work provides a good reference for studying the interaction of enhanced light with monolayer graphene, and opens up new possibilities for the practical application of new photons and optoelectronic devices (such as detectors, sensors, etc.). By using critical coupling theory and the finite-difference time-domain (FDTD) method simulations, we indicate theoretically that the graphene-cylinder-metal arrays structure is a monolayer graphene perfect absorber in the near-infrared. Through numerical simulation and theoretical analysis, the absorber has high sensitivity up to 939.30 nm/RIU and the absorption performance of the arrays structure is polarization-independent. • The proposed graphene-cylinder-metal arrays structure can achieve a perfect absorption of 99.14%. • The sensitivity (S) and figure of merits (FOM) of the proposed perfect absorber can reach 939.30 nm/RIU and 161.11, respectively. • In the critical coupling state, the perfect absorber has high-sensitivity and polarization-independent.

Laser dewetting mechanism and antibacterial properties of Cu-Al based medium entropy alloy films

High entropy alloys (HEAs) have attracted significant interest in recent decades due to their unique microstructures and many favorable properties, including high mechanical strength, good thermal stability and excellent corrosion resistance. In the present study, three Cu-Al based medium entropy alloys (MEAs), namely CuAlAg (CAA), CuAlZn (CAZ) and CuAlV (CAV), are deposited on glass substrates using a high-vacuum sputtering system. The as-sputtered MEA films (MEAFs) are processed by Rapid Thermal Annealing (RTA) for 5 min in order to stabilize their microstructures and are then dewetted using a near infrared (NIR) fiber laser system with various repetition rates, pulse powers and scan speeds to produce nanoparticle structures. Finally, the antibacterial properties of the MEAFs and dewetted films are investigated using three bacterial strains, namely Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus. It is shown that the particle size of the dewetted films decreases as the accumulated energy (AE) density increases. The smaller particle size leads to a blue shift of the localized surface plasmon resonance (LSPR) absorption peak wavelength as a result of the greater uniformity of the induced electromagnetic field. In the dewetting process, the Ag and Cu elements of the MEAFs form particles, while the Al atoms are repelled to the bottom or surrounding region of the nanoparticles, and the Zn and V atoms remain on the glass surface. The MEAFs and dewetted films show an antibacterial efficiency of 100% for all three bacterial strains after 24 h. Moreover, the bacterial growth curves indicate that the majority of the bacteria are destroyed within 4–5 h of contact. The antibacterial effect of the MEAFs and dewetted films is attributed to the production of reactive oxygen species (ROS) and the release of metal ions, which collectively destroy the cell membranes and lead to cell shrinkage and death. For all of the MEAFs, the antibacterial performance improves after dewetting as a result of the increased surface contact area provided by the nanoparticles. Overall, the present results confirm the effectiveness of MEAs and dewetted films in realizing thin-film coatings with enhanced antibacterial properties.

Tunable perfect dual-narrowband absorber based on graphene-photonic crystal heterostructure

A dual-narrowband absorber in the terahertz (THz) band is proposed and numerically analyzed, which consists of a sheet of graphene on a photonic crystal (PC) heterostructure. We find a huge enhancement of absorption because optical Tamm states (OTSs) are excited at the interfaces of graphene-PC and PC heterostructure. The full width at half maximum (FWHM) of the absorption peak near the wavelength of 300 μm can be as narrow as 1.25 μm, and narrower FWHM can be obtained by adapting the wavelength and incident angle of the light beam. The wavelengths of absorption peaks and the absorptivities can be tuned by controlling the Fermi energy of graphene and the periods of PCs. In addition, the absorber can maintain high absorptivity over a wide incident angle range for both TE and TM polarization. The proposed optical absorber has potential applications in THz biosensors, filters, and switches.

Localized Plasmon-Based Multicore Fiber Biosensor for Acetylcholine Detection

In this work, tapered/etched multicore fiber (MCF) probes are spliced with multimode fiber (MMF) to fabricate the sensor structure. To improve sensitivity, gold nanoparticles (AuNPs) and molybdenum disulfide nanoparticles (MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -NPs) are used to immobilize both probes. Synthesized AuNPs and molybdenum disulfide (MoS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> )-nanoparticles (NPs) have peak absorption wavelengths of 519 and 330 nm, respectively. High-resolution transmission electron microscopy is used to examine the morphology of the NPs. The scanning electron microscope (SEM) is used to characterize the NP-immobilized optical fiber sensor structures, and SEM-EDX is used to verify the NP-coating over fiber structure. The functionalization of the acetylcholinesterase enzyme over the NP-immobilized probe increases the specificity of the sensor later on. Finally, the developed sensor probes are tested by detecting various acetylcholine concentrations. In addition, performance analyses, such as reusability, reproducibility, and selectivity (in the presence of ascorbic acid, glucose, dopamine, and uric acid), are carried out, and proposed biosensors are experimentally evaluated. The developed tapered fiber sensor with a sensitivity of 0.062 nm/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{M}$ </tex-math></inline-formula> can detect even very low concentrations, such as 14.28 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{M}$ </tex-math></inline-formula> , over a wide detection range of 0–1000 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{M}$ </tex-math></inline-formula> .

Color sensing ability of spin coated poly (3-hexylthiophene-2, 5-diyl) thin films

Photo sensing properties of Poly (3-hexylthiophene-2, 5-diyl) (P3HT) with respect to white light and different colored lights were studied. In photo sensing studies, a decrease in resistance with illumination was observed in P3HT, indicating their sensitivity to light making them to be utilized in photo sensors. In this work, color sensing studies were done by noting down the resistance variation when exposed to a particular-colored light. A stable response was observed for P3HT devices for all the sensing cycles. It was found that P3HT photo response was more for green light compared to other colors, making it useful in color sensors. Structural studies were done on P3HT films to find its fingerprint peak and interplanar distance. Uv–vis characterization was used to study the energy band gap and the peak absorption wavelength for spin coated P3HT thin films.

A Comparison between Silver Nanosquare Arrays and Silver Thin-Films as a Blood Cancer Prognosis Monitoring Electrode Design Using Optical and Electrochemical Characterization.

The development of silver (Ag) thin films and the fabrication of Ag nanosquare arrays with the use of an anodic aluminum oxide (AAO) template and leaf extracts were successfully carried out using the DC sputtering and spin coating deposition methods. Ag thin films and Ag nanosquare arrays are developed to monitor cancer prognosis due to the correlation between serum albumin levels and prognostic factors, as well as the binding of serum albumin to the surface of these electrodes. Nanosquare structures were fabricated using AAO templates with varying diameters and a gap distance between adjacent unit cells of 100 nm. The nanosquare array with a diameter of 250 nm and irradiated with electromagnetic waves with a wavelength of around 800 nm possessed the greatest electric field distribution compared to the other variations of diameters and wavelengths. The results of the absorption measurement and simulation showed a greater shift in absorption peak wavelength when carried out using the Ag nanosquare array. The absorption peak wavelengths of the Ag nanosquare array in normal blood and blood with cancer lymphocytes were 700–774 nm and 800–850 nm, respectively. The electrochemical test showed that the sensitivity values of the Ag thin-film electrode deposited using DC sputtering, the Ag thin-film electrode deposited using spin coating, and the Ag nanosquare array in detecting PBS+BSA concentration in the cyclic voltammetry (CV) experiment were 1.308 µA mM−1cm−2, 0.022 µA mM−1cm−2, and 39.917 µA mM−1cm−2, respectively. Meanwhile, the sensitivity values of the Ag thin film and the Ag nanosquare array in detecting the PBS+BSA concentration in the electrochemical impedance spectroscopy (EIS) measurement were 6593.76 Ohm·cm2/mM and 69,000 Ohm·cm2/mM, respectively. Thus, our analysis of the optical and electrochemical characteristics of Ag thin films and Ag nanosquare arrays showed that both can be used as an alternative biomedical technology to monitor the prognosis of blood cancer based on the concentration of serum albumin in blood.

Deep Learning Proteins using a Triplet-BERT network.

Modern sequencing technology has produced a vast quantity of proteomic data, which has been key to the development of various deep learning models within the field. However, there are still challenges to overcome with regards to modelling the properties of a protein, especially when labelled resources are scarce. Developing interpretable deep learning models is an essential criterion, as proteomics research requires methods to understand the functional properties of proteins. The ability to derive quality information from both the model and the data will play a vital role in the advancement of proteomics research. In this paper, we seek to leverage a BERT model that has been pre-trained on a vast quantity of proteomic data, to model a collection of regression tasks using only a minimal amount of data. We adopt a triplet network structure to fine-tune the BERT model for each dataset and evaluate its performance on a set of downstream task predictions: plasma membrane localisation, thermostability, peak absorption wavelength, and enantioselectivity. Our results significantly improve upon the original BERT baseline as well as the previous state-of-the-art models for each task, demonstrating the benefits of using a triplet network for refining such a large pre-trained model on a limited dataset. As a form of white-box deep learning, we also visualise how the model attends to specific parts of the protein and how the model detects critical modifications that change its overall function.

Sensitive Hemoglobin Concentration Sensor Based on Graphene-Plasmonic Nano-structures.

In this paper, half-cylindrical-shaped rods are arranged in a row in order to form hemoglobin concentration sensors. The proposed structures can effectively detect hemoglobin concentrations in blood samples. Five individual structures based on graphene-plasmonic combinations are proposed and investigated. The proposed structures are made of different layers of Au, Ag, SiO2, and graphene. Different plates and cylindrical-shaped graphene layers are introduced in the structures to improve the functionality (absorption peak value and wavelength) of the absorber (sensor). Adding more Au layers strengthens the confinement of the incident electromagnetic waves and improves the absorption factor. Also, in the proposed structures, for improving the results, the effects of the chemical potential of graphene layers and “G” (graphene layer thicknesses) on the absorption peak and wavelength are considered. The final suggested structure indicates unity absorption peak and thus can be utilized in wide ranges of applications. As a refractive index bio-sensor, the structure is considered for detecting hemoglobin concentrations in blood samples which indicates a reasonable sensitivity factor of 570 nm/RIU.

An Asymmetric Silicon Grating Dual-Narrow-Band Perfect Absorber Based on Dielectric-Metal-Dielectric Structure

With the exhaustion of world energy, new energy has become the most important content of each country’s development strategy. How to efficiently use solar energy has become a research hotspot in current scientific research. Based on surface plasmon resonance and Fabry-Perot (FP) cavity, this paper proposes a design method of asymmetric silicon grating absorber, and uses finite difference time domain (FDTD) method for simulation calculation. By adjusting the geometric parameters, the asymmetric silicon grating absorber realizes two narrow-band absorption peaks with absorption greater than 99% in the optical wavelength range of 3,000–5,000 nm, and the absorption peak wavelengths are λ1 = 3,780 nm and λ2 = 4,135 nm, respectively. When the electromagnetic wave is incident on the surface of the metamaterial, it will excite the plasmon resonance of the metal to form a surface plasmon (SP) wave. When the SP wave propagates along the x axis, the silicon grating can reflect the SP wave back and forth. When the frequency of the SP wave and the incident light are equal, it will cause horizontal FP coupling resonance, resulting in different resonance wavelengths. This paper also discusses the influence of geometric parameters, incident angle and polarization angle on the performance of silicon grating absorbers. Finally, the sensing performance of the structure as a refractive index sensor is studied. The absorber can be used for various spectral applications such as photon detection, optical filtering and spectral sensing.

Optical neural stimulation using the thermoplasmonic effect of gold nano-hexagon.

The use of nanoparticle photothermal effect as adjuvants in neuromodulation has recently received much attention, with many open questions about new nanostructures' effect on the action potential. The photothermal properties of hexagonal gold nanoparticles are investigated in this work, including the absorption peak wavelength and light-heat conversion rate, using both experimental and simulation methods. Furthermore, the ability to use these nanostructures in axonal neural stimulation and cardiac stimulation by measuring temperature changes of gold nano-hexagons under 532 nm laser irradiation is studied. In addition, their thermal effect on neural responses is investigated by modeling small-diameter unmyelinated axons and heart pacemaker cells. The results show that the increase in temperature caused by these nano-hexagons can successfully stimulate the small diameter axon and produce an action potential. Experiments have also demonstrated that the heat created by gold nano-hexagons affects toad cardiac rhythm and increases T wave amplitude. An increase in T wave amplitude on toad heart rhythm shows the thermal effect of nano hexagons heat on heart pacemaker cells and intracellular ion flows. This work demonstrates the feasibility of utilizing these nanostructures to create portable and compact medical devices, such as optical pacemakers or cardiac stimulation.

Biosynthesis of Silver Nanoparticles Using Orange Peel Extract for Application in Catalytic Degradation of Methylene Blue Dye

Interest in the biosynthesis of silver nanoparticles (AgNPs) has been steadily increasing primarily due to their numerous applications in various fields, low-cost, use of non-toxic environmentally-friendly materials and easy implementation. This study focused on the biosynthesis of AgNPs using orange peel extract (OPE), optimization of process conditions, and application in catalytic degradation of methylene blue (MB) dye used in the textile industry. A central composite design in response surface methodology resulted in optimum conditions of 0.0075 g dry peel/mL for OPE concentration, pH of 11 and 1.5 mM silver nitrate concentration. The optimum conditions for the response variables corresponded to the peak absorbance of 0.79 and SPR wavelength of 403.8 nm in UV-vis spectra, and minimum particle size of 12.9 nm. In addition, peak absorbance and SPR wavelength appeared to be related to the size of the AgNPs. A full-factorial design for the catalytic degradation of MB dye by the biosynthesized AgNPs for 1 h indicated the maximum influence of AgNPs compared to the concentrations of MB dye and NaBH4 in decreasing order. The MB dye was reduced rapidly with NaBH4 in the presence of AgNPs due to their catalytic action. The findings of the study show the potential of OPE for the biosynthesis of AgNPs with excellent catalytic activity for the treatment of MB dye in industrial effluent.

Design of novel sensitive terahertz metamaterial absorbers based on graphene-plasmonic nanostructures

In this paper, four different configurations of sensitive metamaterial absorbers based on graphene-plasmonic combinations are designed and proposed. The nanostructures are made of graphene, SiO2, aluminum and gold layers on a silicon substrate. Graphene-ring shaped structures with diagonal strips in vertical and horizontal directions are considered in the structures which greatly affect the absorption characteristics (absorption peak value and wavelength). Aluminum layer is used in the structure to prevent the transmission of light throughout some layers and improve the absorption factor. To promote the functionality of the structures, effects of the structural parameters (R1 and R2) and chemical potentials (Ef1, Ef2, Ef3 and Ef4) on the absorption peak are also studied. The four individual configurations with different layers and strip directions demonstrate distinct and different wavelength ranges; structure-1: 45–60 µm, structure-2: 50–70 µm, structure-3: 70–85 µm, and structure-4: 80–100 µm. Thus, they can be utilized for wide categories of applications. Sensitivities of 1500 nm/RIU, 2250/RIU, 3750 nm/RIU and 4850 nm/RIU are obtained for four types, respectively. The proposed structures can be categorized as refractive index biosensors, which indicate acceptable sensitivities and can be used for detection of different elements like hemoglobin and glucose in blood samples.

The Peak Absorbance Wavelength of Photosynthetic Pigments Around Other Stars From Spectral Optimization

In the search for life on other planets, the presence of photosynthetic surface vegetation may be detectable from the colors of light it reflects. On the modern Earth, this spectral reflectance is characterized by a steep increase in reflectance between the red and near‐infrared wavelengths, a signature known as the “red edge”. This edge-like signature occurs at wavelengths of peak photon absorbance, which are the result of adaptations of the phototroph to their spectral environment. On planets orbiting different stellar types, red edge analogs may occur at other colors than red. Thus, knowing the wavelengths at which photosynthetic organisms preferentially absorb and reflect photons is necessary to detect red edge analogs on other planets. Using a numerical model that predicts the absorbance spectrum of extant photosynthetic pigments on Earth from Marosvölgyi and van Gorkom (2010), we calculate the absorbance spectrum for pigments on an Earth-like planet around F through late M type stars that are adapted for maximal energy production. In this model, cellular energy production is maximized when pigments are tuned to absorb at the wavelength that maximizes energy input from incident photons while minimizing energy losses due to thermal emission and building cellular photosynthetic apparatus. We find that peak photon absorption for photosynthetic organisms around F type stars tends to be in the blue while for G, K, and early M type stars, red or just beyond is preferred. Around the coolest M type stars, these organisms may preferentially absorb in the near-infrared, possibly past one micron. These predictions are consistent with previous, qualitative estimates of pigment absorptance. Our predicted absorbance spectra for photosynthetic surface organisms depend on both the stellar type and planetary atmospheric composition, especially atmospheric water vapor concentrations, which alter the availability of surface photons and thus the predicted pigment absorption. By constraining the absorbance spectra of alien, photosynthetic organisms, future observations may be better equipped to detect the weak spectral signal of red edge analogs.

Effect of pump-induced loss on the spectral dependence of Rhodamine 6G laser efficiency under microsecond coherent pumping

We examine the effect of the pump-induced loss in the gain medium of a Rhodamine 6G laser on the spectral dependence of the laser efficiency under microsecond coherent pumping. It is shown theoretically and experimentally that the pump-induced loss is mainly due to nonlinear refraction and thermo-optic inhomogeneities of the gain medium, which produce a negative thermal lens, whose defocusing effect reduces the laser efficiency. The induced absorption by excited-state singlet and triplet levels of dye molecules is shown to make no significant contribution to changes in laser efficiency. The pump-induced thermal loss at the peak absorption wavelength of Rhodamine 6G plays a more important role well above the threshold pump power density (γ ⩾ 5). We demonstrate that the maximum dye laser efficiency under microsecond coherent pumping can only be achieved at an optimal pump wavelength.

Effect of metal ions on the thermo-optic properties of Rhodamine 6G-gold nanoparticle hybrids

The dye-plasmonic nanoparticle (NP) mixtures were reported to be an efficient probe for heavy metal detection in aqueous solution, particularly metals like Hg2+ ions. However, little is known about the variation in such dye-NP mixtures' thermal properties upon the addition of heavy metals. In this work, using the laser-based dual-beam thermal lens technique, the variation in thermal diffusivity value of Rhodamine6G (Rh6G)-gold nanoparticle (AuNP) mixture upon the addition of various concentrations of Hg2+ ions are investigated. The thermal property measurements are corroborated with optical absorption studies. The analysis reveals that the absorption peak wavelength and the shape of the spectrum are very sensitive to the addition of the Hg2+ ions. The measured thermal diffusivity values found to increase with the Hg2+ ion concentrations range from 0.1 nM to 10 µM and beyond which, the Hg2+ ions cause little variation in the thermal diffusivity value. The variation in the thermal diffusivity value originates from amalgam formation due to heavy metal-NP interaction. The investigation of dye molecules' emission spectral studies using a laser-based fluorescence setup reveal that the fluorescence behavior concurs with the data obtained from thermal lens studies. Additionally, the studies using the monovalent and divalent metal ions to dye-NP mixture elucidate that divalent metals are more efficient in tailoring the thermal and optical properties. The present study elucidates that optical sensor development based on the emission or absorption properties of the dye-plasmonic NP mixture for heavy metals have a concomitant variation in thermal properties.

Raman and photoluminescence spectroscopy analysis of gamma irradiated human hair

Preliminary study has been made of black human hair, carbon concentration of some 53%, a model in examining the potential of hair of the human head in retrospective and emergency biodosimetry applications, also offering effective atomic number near to that of water. The hair samples were exposed to ^{60}Co gamma rays, delivering doses from 0 to 200 Gy. Structural alterations were observed, use being made of Raman and photoluminescence (PL) spectroscopy. Most prominent among the features observed in the first-order Raman spectra are the D and G peaks, appearing at 1370 {{pm }} 18,{hbox {cm}}^{-1} and 1589 {{pm }} 11,{hbox {cm}}^{-1} respectively, the intensity ratio {{{I}}}_{{{D}}}{{/}}{{{I}}}_{{{G}}} indicating dose-dependent defects generation and annealing of structural alterations. The wavelengths of the PL absorption and emission peaks are found to be centred at 592.3 pm 12.5 nm and 1077.4 pm 7.3 nm, respectively. The hair samples mean band gap energy ({{{E}}}_{{{g}}}) post-irradiation was found to be 2.10 pm 0.04 eV, of the order of a semiconductor and approximately two times the {{{E}}}_{{{g}}} of other carbon-rich materials reported via the same methodology.

Reversible Transformations at Room Temperature among Three Types of CdTe Magic-Size Clusters.

We report the first observation of the reversible transformations that occur among three types of CdTe magic-size clusters (MSCs) in dispersion at room temperature and discuss our understanding of the transformation pathway. The reversible transformations were achieved with CdTe prenucleation stage samples, which were prepared with reactions of cadmium oleate [Cd(OA)2] and tri-n-octylphosphine telluride in 1-octadecene and were then dispersed in mixtures of toluene and a primary amine at room temperature. Three types of OA-passivated CdTe MSCs evolved, exhibiting sharp optical absorption singlets peaking at 371, 417, and 448 nm. The MSCs and their immediate precursor compounds (PCs; with no sharp optical absorption) are labeled by the MSC absorption peak wavelengths. The transformation between MSC-371 and MSC-417 has a distinct isosbestic point at ∼385 nm and that between MSC-417 and MSC-448 at ∼430 nm. Our findings suggest that these PC-enabled reversible transformations occur through a process of quasi-isomerization, transforming between PCs and their counterpart MSCs, combined with substitution reactions that cause transformation between the two involved PCs.

Enhanced light absorption in monolayer tungsten disulfide with dielectric Bragg reflector and metallic thin film

A multi-layer structure based on the microcavity effect of a dielectric Bragg reflector (DBR) and metallic thin film to enhance light absorption of monolayer tungsten disulfide (WS2) is proposed. This structure is combined with a cover layer and a spacer layer to adjust the phase-matching condition. The transfer matrix method (TMM) was used to study its optical transport characteristics. It was found that the microcavity effect of DBR and the metallic thin film forms a maximum value of electric field intensity near the monolayer WS2, which effectively promotes the light-matter interaction in monolayer WS2. As the thicknesses of the spacer layer and cover layer were comprehensively optimized, the light absorption of monolayer WS2 at the wavelength of 611 nm reached 94.38 % and the full width at half maximum (FWHM) is only 9 nm. Furthermore, the effect of DBR periodicity and angle of incidence on the light absorption of monolayer WS2 were discussed. The research presented here confirms that changing the above structural parameters can effectively regulate the absorption peak wavelength and maximum value of monolayer WS2. The results of this study provide new ideas for the preparation of high-performance monolayer WS2 photodetectors and other new optoelectronic devices.