Infrared Transmission Spectroscopy Research Articles

Catalytic Properties of Pd Deposited on Polyaniline in the Hydrogenation of Quinoline

A set of Pd-containing composites was prepared by the deposition of Pd on the following carriers: polyaniline (PANI); PANI doped by H2SO4; Norit GSX activated carbon or Aerosil (SiO2) coated by PANI or by H2SO4-doped PANI; PANI after thermal treatment at 300 °C in an atmosphere of H2. One sample was also prepared by the in situ polymerization of aniline in the presence of Pd2+· The decomposition of Pd was carried out via deposition from the solutions of Pd2+ salts or decomposition of Pd0 complex Pd2(dba)3, where dba is dibenzylideneacetone. The composites were studied by powder X-ray diffraction, transmission electron microscopy, IR and Raman spectroscopy. The hydrogenation of quinoline in the presence of composites was carried out; the catalytic performance of the composites was evaluated by the yield of 1,2,3,4-tetrahydroquinoline. It was found that the doping of PANI by H2SO4, inclusion of Norit GSX activated carbon as a component of the carrier or thermal treatment of PANI prior to the deposition of Pd led to significant increase in the catalytic performance of the composites in the hydrogenation of quinoline.

Evidence for Nightside Water Emission Found in Transit of Ultra-hot Jupiter WASP-33 b

To date, the dayside thermal structure of ultra-hot Jupiters (UHJs) is generally considered to be inverted, but their nightside thermal structure has been less explored. Here, we explore the impact of nightside thermal emission on high-resolution infrared transmission spectroscopy, which should not be neglected, especially for UHJs. We present a general equation for the high-resolution transmission spectrum that includes planetary nightside thermal emission. This provides a new way to infer the thermal structure of the planetary nightside with high-resolution transmission spectroscopy. Using the cross-correlation technique, we find evidence for the presence of an H2O emission signature on the UHJ WASP-33 b during the transit, indicating an inverted temperature structure on its nightside. Such a result suggests a stronger heat transport through the circulation than currently expected. An alternative explanation is that the rotating visible hemisphere during transit leads to the potential contribution of the limb and dayside atmospheres to the detected emission signature. In the future, the combination of high-resolution, full-phase-curve spectroscopic observations and general circulation models will hopefully solve this puzzle and provide a complete picture of the three-dimensional nature of the chemistry, circulation, and thermal structure of UHJs.

Spectroscopic Evidence for Doubly Hydrogen-Bonded Cationic Dimers in the Solid, Liquid, and Gaseous Phases of Carboxyl-Functionalized Ionic Liquids.

Intermolecular interactions determine whether matter sticks together, gases condense into liquids, or liquids freeze into solids. The most prominent example is hydrogen bonding in water, responsible for the anomalous properties in the liquid phase and polymorphism in ice. The physical properties are also exceptional for ionic liquids (ILs), wherein a delicate balance of Coulomb interactions, hydrogen bonds, and dispersion interactions results in a broad liquid range and the vaporization of ILs as ion pairs. In this study, we show that strong, local, and directional hydrogen bonds govern the structures and arrangements in the solid, liquid, and gaseous phases of carboxyl-functionalized ILs. For that purpose, we explored the H-bonded motifs by X-ray diffraction and attenuated total reflection (ATR) infrared (IR) spectroscopy in the solid state, by ATR and transmission IR spectroscopy in the liquid phase, and by cryogenic ion vibrational predissociation spectroscopy (CIVPS) in the gaseous phase at low temperature. The analysis of the CO stretching bands reveals doubly hydrogen-bonded cationic dimers (c═c), resembling the archetype H-bond motif known for carboxylic acids. The like-charge doubly hydrogen-bonded ion pairs are present in the crystal structure of the IL, survive phase transition into the liquid state, and are still present in the gaseous phase even in (2,1) complexes wherein one counterion is removed and repulsive Coulomb interaction increased. The interpretation of the vibrational spectra is supported by quantum chemical methods. These observations have implications for the fundamental nature of the hydrogen bond between ions of like charge.

Online Detection of Dry Matter in Potatoes Based on Visible Near-Infrared Transmission Spectroscopy Combined with 1D-CNN

More efficient resource utilization and increased crop utilization rate are needed to address the growing demand for food. The efficient quality testing of key agricultural products such as potatoes, especially the rapid testing of key nutritional indicators, has become an important strategy for ensuring their quality and safety. In this study, visible and near infrared (Vis/NIR) transmittance spectroscopy (600–900 nm) was used for the online analysis of multiple quality parameters in potatoes. The study concentrated on comparing three one-dimensional convolutional neural network (1D-CNN) models, specifically, the fine-tuned DeepSpectra, the fine-tuned 1D-AlexNet, and classic CNN, with UVE-PLS (uninformative variable elimination–partial least squares) models. These models utilized spectral data for the real-time detection of dry matter (DM) content in potatoes. To address the challenges posed by limited data from Vis/NIR, this study strategically implemented data augmentation techniques. This approach significantly enhanced the robustness and generalization capabilities of the models. The 1D-AlexNet and DeepSpectra models achieved 0.934 and 0.913 R2P and 0.0603 and 0.0695 g/100 g RMSEP for DM, respectively. Compared to UVE-PLS, the R2P value improved by 21.31% (0.770 to 0.934) for the 1D-AlexNet model and 18.64% (0.770 to 0.913) for the DeepSpectra model. The RMSEP value was reduced by 47.31% (0.114 to 0.0603) for 1D-AlexNet, and 39.30% (0.114 to 0.0695) for the DeepSpectra model. As a result, this study would be helpful for researching the online Vis/NIR transmission determination of potato DM using deep learning. These results highlighted the immense potential of employing specific spectral features in deep-learning models for a more precise and efficient online assessment of agricultural quality. This advancement provided some insight and reference for further contributing to the evolution of more targeted and efficient quality assessment methods in agricultural products.

Obsidian hydration dating by infrared transmission spectroscopy

AbstractThe obsidian dating method converts the quantity of diffused molecular water within a near‐surface hydration layer to elapsed time using an experimentally derived diffusion coefficient predicted from the structural water content of the glass. Infrared spectroscopic transmission measurements on transparent archaeological samples record vibrational responses of water bands in the near‐infrared region, permitting determination of structural water content (OH), and the amount of diffused ambient water (H2O). In this application, the H2O water band at 5200 cm−1 is measured directly. The accuracy of the approach is assessed by an evaluation of the precision of each contributing variable. The new protocol is evaluated using obsidian artifacts from radiocarbon‐dated deposits at Salamanca Cave in Argentina.

Experimental study on the radiation-induced destruction of organic compounds on the surface of the Moon

Volatile organic molecules and a complex organic refractory material were detected on the Moon and on lunar samples. The Moon’s surface is exposed to a continuous flux of solar UV photons and fast ions, e.g. galactic cosmic rays (GCRs), solar wind (SW), and solar energetic particles (SEPs), that modify the physical and chemical properties of surface materials, thus challenging the survival of organic compounds. With this in mind, the aim of this work is to estimate the lifetime of organic compounds on the Moon’s surface under processing by energetic particles. We performed laboratory experiments to measure the destruction cross section of selected organic compounds, namely methane (CH4), formamide (NH2CHO), and an organic refractory residue, under simulated Moon conditions. Volatile species were deposited at low temperature (17 - 18 K) and irradiated with energetic ions (200 keV) in an ultra-high vacuum chamber. The organic refractory residue was produced after warming up of a CO:CH4 ice mixture irradiated with 200 keV H+ at 18 K. All the samples were analyzed in situ by infrared transmission spectroscopy. We found that destruction cross sections are strongly affected (up to one order of magnitude) by the dilution of a given organic in an inert matrix. Among the selected samples, organic refractory residues are the most resistant to radiation. We estimated the lifetime of organic compounds on the surface of the Moon by calculating the dose rate due to GCRs and SEPs at the Moon’s orbit and by using the experimental cross section values. Taking into account impact gardening, we also estimated the fraction of surviving organic material as a function of depth. Our results are compatible with the detection of CH4 in the LCROSS eject plume originating from layers deeper than about 0.7 m at the Moon’s South Pole and with the identification of complex organic material in lunar samples collected by Apollo 17 mission.

Time intervals between pumping did not affect breastmilk protein produced by mothers of preterm infants.

Few studies investigate factors that might influence the content of expressed breastmilk. This study aims to investigate the influence of the intervals between breastmilk pumping and the time of the day on protein and fat concentration in breastmilk. Mothers of very preterm infants in a neonatal ward who expressed more than 400 mL per day were included. Expressed breastmilk was obtained from each mother over 30 h who were pumping at strictly planned and varying intervals: 2, 3, 4 and 6 h. All samples were analysed using infrared transmission spectroscopy. Ten mothers participated at a median of 22 days postpartum. A total of 176 milk samples were analysed, and the average protein and fat concentrations in g/100 mL were 1.1 ± 0.23 and 4.2 ± 1.3, respectively. The time intervals between breast pumping sessions did not impact protein content, but fat content decreased by longer intervals (p < 0.01). The time of the day for milk pumping did not influence the protein or fat content. A single milk sample collected after any 2-6 h interval, at any time during the day, represents the protein content in the breastmilk, but not the fat content which decreased with longer intervals.

Preparation of bamboo-shaped mesoporous silica using long-chain alcohol cosurfactants

Herein, orderly arranged bamboo-like mesoporous silica materials were prepared using cetyltrimethylammonium bromide (CTAB) as the template and n-hexanol as the long-chain alcohol cosurfactant. The ordered meso-structure was characterized by XRD analysis, field emission scanning electron microscopy (FE-SEM, Hitachi S4800), transmission electron microscopy, BET and IR spectroscopy analysis. The effects of the CTAB/n-hexanol molar ratio(R), length of the hydrophobic chain with a terminating hydroxyl group on the long-chain alcohol cosurfactant, parity of the hydrophobic carbon atoms on the surface topography, specific surface area, and pore size of the powder were investigated. The results showed that when the molar ratio = 1, the mesoporous silica presented neatly arranged bamboo segment lengths of 19.6–23.9 μm, platycodon grandiflorum widths of 2.13–3.32 μm, pore size of 3.04 nm, and surface area of 820.034 m2/g. Increasing or decreasing the amount of n-hexanol directing led to denser or looser lateral molecular interactions between CTAB and the co-structure-directing agents that respectively reduced or increased the pore size, with the latter resulting in the formation of spherical particles. When n-hexanol was replaced by n-heptanol or n-octanol, the pore size and surface area of the mesoporous silica decreased significantly with the increase in the hydrophobic chain length.

Heterogeneous Phosphine-Containing Hydroformylation Catalysts Based on Modified Porous Organic Framework

A series of heterogeneous phosphine-containing rhodium hydroformylation catalysts based on porous aromatic frameworks (PAFs) were prepared. The catalysts PAF30-MDEA-TPPTS-Rh (TPPTS is trisodium triphenylphosphine-3,3',3''-trisulfonate, MDEA is methyldiethanolamine fragment) and PAF-30-Im-TPPTS-Rh (Im is imidazole fragment) showed the highest stability in repeated use in 1-hexene hydroformylation. The catalyst PAF-30-MDEA-TPPTS-Rh before and after use in hydroformylation was characterized by elemental C,N,H,S analysis, inductively coupled plasma atomic absorption spectroscopy, low-temperature nitrogen adsorption–desorption, transmission electron microscopy, IR spectroscopy, and X-ray photoelectron spectroscopy. The effect of temperature, pressure, and solvent on the course of hydroformylation in the presence of PAF-30-MDEA-TPPTS-Rh was studied. The catalyst is active in hydroformylation of a series of unsaturated compounds, including functionalized substrates and olefins with internal double bond.

Nonionic surfactant-templated mesoporous silica as supports for nickel active catalysts in liquid phase organic compounds oxidation

Three surfactants were selected from a series of EOx/POy/EOx triblock copolymers and ethoxylated octylphenol as nonionic templating agents for the synthesis of silica mesoporous materials at room temperature and by hydrothermal treatment. The surfactants were ethylene oxide-propylene oxide-ethylene oxide tri-block copolymers (Pluronic F68) and a polydisperse ethoxylated octylphenol (Triton X-100). The obtained materials were compared with SBA-15 mesoporous silica synthesized with Pluronic P123 surfactant and were used as support to obtain Ni and NiTi-silica catalysts (2.5% NiO, 5% TiO2). The synthesized materials were characterized by X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption-desorption, IR and UV-Vis spectroscopy. Catalytic and photocatalytic activity of Ni and NiTi-silica samples were tested, with and without H2O2, for phenol and Brilliant Blue FCF dye oxidative degradation in the liquid phase. The obtained results showed a significant effect of surfactant on silica structure, morphology and texture, and catalytic and photocatalytic properties.

Development of maintenance-free coatings using composite titania and silica

Atmospheric conditions and the effect of pollutants on the frequently exposed glass furnishings like windows in constructions and windshield in automotive industries often require maintenance due to their extensive usage and heavy exposure. This demanded an additional coating on the conventional glass furnishings to free from the pollutants without additional cleaning cost. Hydrophilicity and hydrophobicity are properties of titania (TiO2) and silica (SiO2) dielectric materials, although when coated as a composite material, they exhibit a larger affinity for water than carbon contamination. Hence, the contamination adsorbed on the surface of the glass can be easily cleaned by water without help of any detergent or cleaning agents. In this work, we report the fabrication and analysis of three TiO2-SiO2 composite coatings (single coated 1C, double coated 2C and triple coated 3C) on glass substrates using the sol-gel spin coating technique. The coatings were subjected to X-ray diffraction (XRD) analysis, which revealed a broad peak at Bragg angle 25 °, confirming the existence of mixed anatase TiO2 and amorphous SiO2. Fourier transform infrared transmission spectroscopy (FT-IR) studies on the coatings demonstrated peaks at 906 cm−1 and 768 cm-1 that corresponds to the characteristic bond of Si-O-Ti, and stretching bond of Ti-O-Ti respectively. The ultraviolet visible and near-infrared spectroscopy (UV-Vis-NIR) studies on the coatings endorsed 40% reflection in the ultraviolet and near-infrared spectral regions and found increasing the composite coating can increase the reflectance further. Finally, water contact angle (WCA) analysis indicated the hydrophilic character of the coatings, with contact angles of 74.8 ° (1C), 83.3 ° (2C), and 112.7 ° (3C) and suggested as a maintenance free coating on the glass furnishings.

SPODUMENE AND BERYL FROM CONȚU LITHIUM - PEGMATITES, CINDREL (CIBIN) MOUNTAINS, CENTRAL GROUP, SOUTH CARPATHIANS, ROMANIA

Spodumene, now in the everyday life, represent a critical source of the chemical element known as lithium. For principle reducing emissions of CO2, now and in the future, we can find an alternative resource like green resources – spodumene. The first step is to identify the field with minerals - prospecting, then the second is exploration, and culminates with exploitation. In Romania, we find probably the only fields with lithium pegmatites in Conțu. Pegmatitic bodies are known as Conțu Superior and Conțu Inferior. Spodumene appears in the form of crystals and massive aggregates, with long habitus – prismatic, sometimes tabular, and with dimensions of 25 cm – 70 cm. Its color varies from white–greenish with vitreous luster, to gray – greenish, color due to the alteration processes, which led to the appearance in green – yellow colors on the spodumene has a good cleavage on the plane (010). Spodumene has monoclinic symmetry and C2/c space group (15), and cell parameters: a = 9.466 Å, b = 8.394 Å, c = 5.221 Å. The analytical method (EPMA) indicated a lithium oxide content between 7.43 % and 7.50 %, these percentages were calculated. Beryl (the emerald variety) macroscopically, has a greasy luster, colors in light green to dark green tones, in the mass of quartz and albite. Beryl crystallizes in the hexagonal system, space group P6/mcc (192), and the cell parameters are a = 9.267 Å, b = 9.187 Å. Infrared transmittance spectroscopy indicated the presence of beryl. BeO4 vibrates at frequencies around 900 cm-1 and 1000 cm-1, we find in sample N118, valence vibrations at: 1094 cm-1, 1039 cm-1, and 957 cm-1.

BP neural network to predict shelf life of channel catfish fillets based on near infrared transmittance (NIT) spectroscopy

The objective of this research was to establish shelf-life prediction model of channel catfish fillets by Back-propagation (BP) neural network technology based on near infrared transmittance (NIT). First, freshness prediction model of channel catfish fillets was established based on the chemical analysis data (total volatile basic nitrogen (TVB-N), K value, thiobarbituric acid reactive substance (TBARS) and trimethylamine (TMA)) and NIT spectra (850–1050 nm). The linear correlation coefficient (R2: 0.667–0.887) showed a good performance of the freshness model prediction. Then, BP neural network was applied to establish the shelf-life prediction model of catfish fillets under temperature fluctuation (−6 to −18 °C). The end effective accumulated temperature of frozen catfish fillets was 10,278.4 h °C. The prediction model showed a great stability (above 93 %) and accuracy (above 90 %) as the structure of BP neural network was 4–7–1. Therefore, this study provided a practical basis and technical supports for the establishment of shelf-life prediction model of freshwater fillets by BP neural network based on NIT spectroscopy.

Ion irradiation triggers the formation of the precursors of complex organics in space

Context. Cosmic rays and solar energetic particles induce changes in the composition of compounds frozen onto dust grains in the interstellar medium (ISM), in comets, and on the surfaces of atmosphere-less small bodies in the outer Solar System. This induces the destruction of pristine compounds and triggers the formation of various species, including the precursors of complex organics. Aims. We investigate the role of energetic ions in the formation of formaldehyde (H2CO) and acetaldehyde (CH3CHO), which are observed in the ISM and in comets, and which are thought to be the precursors of more complex compounds such as hexamethylenete-tramine (HMT), which is found in carbonaceous chondrites and in laboratory samples produced after the irradiation and warm-up of astrophysical ices. Methods. We performed ion irradiation of water, methanol, and ammonia mixtures at 14–18 K. We bombarded frozen films with 40–200 keV H+ that simulate solar energetic particles and low-energy cosmic rays. Samples were analysed by infrared transmission spectroscopy. Results. Among other molecules, we observe the formation of H2CO and CH3CHO, and we find that their abundance depends on the dose and on the stoichiometry of the mixtures. We find that the H2CO abundance reaches the highest value after a dose of 10 eV/16u and then it decreases as the dose increases. Conclusions. The data suggest that surfaces exposed to high doses are depleted in H2CO. This explains why the amount of HMT in organic residues and that formed after irradiation of ices depends on the dose deposited in the ice. Because the H2CO abundance decreases at doses higher than 10 eV/16u, a lower quantity of H2CO is available to form HMT during the subsequent warm-up. The H2CO abundances caused by ion bombardment are insufficient to explain the ISM abundances, but ion bombardment can account for the abundance of CH3CHO towards the ISM and comets.

Concentration of Selected Essential and Toxic Trace Elements in Horse Hair as an Important Tool for the Monitoring of Animal Exposure and Health.

Simple SummaryHeavy metals pose a serious risk to the normal functioning of living organisms. Long-term exposure to heavy metals may lead to many pathologies and various dysfunctions. On the other hand, heavy metals are components of many enzymes, so any anomalies in their concentrations are not desirable. The main purpose of the study was to analyse the concentrations of selected essential and toxic trace elements in the hair of sports and recreational riding horses from studs located in central Poland. We also measured the concentration of heavy metals in oats used as the basic component of the equine diet to investigate the interactions between the elements in the feed and hair. Assessment of essential heavy metals is important for the monitoring of exposure and the health of horses. The study confirmed many significant relationships between the concentrations of elements in the hair and oats, as well as interactions between the content of these xenobiotics in feed and the analytical matrix.The main purpose of the study was to analyse the concentrations of selected essential and toxic trace elements in the hair of sports and recreational riding horses from studs located in central Poland and thus test the usefulness of this matrix for monitoring the exposure of these animals. We also measured the concentration of heavy metals in oats used as a basic component of the equine diet to investigate the interactions between these elements in the feed and hair. The basic chemical composition of oats was analysed. Elemental analysis was performed using an EcaFlow 150 GLP electrochemical analyser with an E-104L electrode and reference to a calibration curve. The chemical composition of oats was investigated by near infrared transmission (NIR) spectroscopy calibrated for an artificial neural network (ANN) using a Foss InfraXact spectrometer. Among all elements, the coefficient of variation was highest for Pb and lowest for Cd, regardless of the study group. The content of elements in horse hair was in the range of 153.56 to 185.79 mg·kg−1 for Zn, 6.10 to 11.99 mg·kg−1 for Cu, 0.578 to 0.813 mg·kg−1 for Pb and 0.011 to 0.015 mg·kg−1 for Cd (in kg of d.w.). For hair, we found a significant negative correlation for Zn-Cu (rxy = −0.539) and Cd-Cu (rxy = −0.676) at p ≤ 0.05. For feed, there was a highly significant positive correlation for Cu-Pb (rxy = 0.723) and Zn-Cd (rxy = 0.714) at p ≤ 0.01. We found significant negative oats–hair interactions for Cu-Zn, Pb-Cu, Cd-Cu and Zn-Pb, and a positive oats–hair interaction for Cu-Cu.

CO2 quantification in silicate glasses using µ-ATR FTIR spectroscopy

Abstract A new method for measurements of high-CO2 concentrations in silicate glasses was established using micro–attenuated total reflectance (µ-ATR) Fourier transform infrared (FTIR) spectroscopy in the mid-IR (MIR) region. We studied two glass/melt compositions, namely leucitite and granite, to cover samples in which CO2 is dissolved as carbonate ions (CO32−) or as CO2 molecules (CO3mol). In the leucitite glasses a carbonate absorption doublet with maxima at 1510 and 1430 cm–1 has shown to clearly separate from aluminosilicate lattice vibrations at lower wavenumbers. Due to the lower sensitivity of the µ-ATR method, we were able to measure high-CO2 contents (cCO2 &amp;gt;0.5 wt%) in experimental silicate glasses that would only be measurable with great difficulties using established transmission MIR measurements due to detector linearity limit effects even with very thin sample wafers. The peak heights of the 1430 cm–1 ATR band (A1430), normalized to the integral of the T-O lattice vibrations (T = Si, Al, Fe) at about 930 cm–1 (Int930) show a linear trend with CO2 contents in the range 0.2–4.3 wt%, yielding a linear correlation with cCO2 (wt%) = 0.4394 ± 0.006·A1430·10000/Int930. The normalization of the CO2 related band to a lattice vibration accounts for variations in the quality of contact between ATR crystal and sample, which has a direct effect on signal intensity. In granitic glasses, where CO2 is dissolved as CO3mol only, the asymmetric stretching vibration at 2350 cm–1 overlaps with the signal of atmospheric, gaseous CO2. As the ATR signal of dissolved CO2 is very weak, the atmospheric signal may dominate the spectrum. Since the absorbance spectrum is calculated by division of the single-channel sample spectrum by a single-channel reference spectrum measured in air, keeping the laboratory and spectrometer atmosphere as constant as possible during spectral acquisition can resolve the problem. Nonetheless, a procedure to subtract the signal of remaining atmospheric CO2 may still be required for the spectral evaluation. We studied a series of 5 granitic glasses with CO3mol contents of 0.08 to 0.27 wt% and found an excellent linear relation between CO2 concentration and lattice vibration normalized ATR intensity of the 2350 cm–1 band: cCO2 (wt%) = 0.2632 ± 0.0016·A2350·10000/Int990. Although the CO3mol concentrations in our granitic glass series can still be analyzed without major difficulties by conventional transmission IR spectroscopy, our data demonstrate the potential of the ATR method for samples with higher CO2 contents or for samples where a high spatial resolution is required (melt inclusions, vesicular or partially crystallized glasses). The lower limits of the ATR method are approximately 0.2 wt% CO2 dissolved as carbonate groups or 0.1 wt% CO2 (or slightly less) dissolved in molecular form.

NATURAL DYE SENSITIZED SOLAR CELLS USING HENNA LEAVES WITH ZnO NANOPARTICLE AT VARIOUS pH VALUES

In this research, ZnO nanoparticles were synthesized at different pH values (3, 6 and 9) by using solvothermal method. To our knowledge, dye sensitized solar cells were fabricated using natural dyes extracted from henna (Lawsonia Inermis) based on ZnO nanoparticle as photoanode at various pH values. Synthesized ZnO samples were characterized using XRay Diffraction (XRD), Field Emission Scanning Electron Microscope (FESEM) with Energy Dispersive X-ray Spectroscopy (EDX), UV-Visible Spectroscopy and Fourier Transmission Infra-Red Spectroscopy (FTIR) and absorbance and transmittance properties of the prepared samples were investigated. The ZnO at pH 9 was obtained highest efficiency extracted from henna (Lawsonia Inermis) of 0.39% better than the other solar cells of pH variations.

Temperature-Dependent Plasmonic Response of Graphene Nanoresonators

Graphene plasmons have attracted enormous research interest due to their dynamic tunability and the extreme field confinement they provide. However, despite their popularity, most studies revolving around graphene plasmons have been restricted to room temperature, leaving unconsidered important tunability knob. In this work, we experimentally investigate the temperature-dependent plasmonic properties of graphene nanoresonators with varying widths on SiO2 substrate by infrared transmission spectroscopy. As temperature drops from 300 to 100 K, the intensity of the graphene plasmon resonance peak increases up to 76%, and the amount of enhancement decreases with increasing carrier concentration and decreasing resonator width. We attribute the enhancement of graphene plasmon resonance to an additional hole doping of Δp = 1.37 × 1012 cm–2 associated with cooling and reduced plasmon damping due to the suppression of phonon-mediated scattering channels. Our results uncover the significance of temperature effects that can be exploited in graphene-based tunable plasmonic devices operating at low temperatures.

Solar-to-supersolar sodium and oxygen absolute abundances for a ‘hot Saturn’ orbiting a metal-rich star

ABSTRACT We present new analysis of infrared transmission spectroscopy of the cloud-free hot-Saturn WASP-96b performed with the Hubble and Spitzer Space Telescopes (HST and Spitzer). The WASP-96b spectrum exhibits the absorption feature from water in excellent agreement with synthetic spectra computed assuming a cloud-free atmosphere. The HST-Spitzer spectrum is coupled with Very Large Telescope (VLT) optical transmission spectroscopy which reveals the full pressure-broadened profile of the sodium absorption feature and enables the derivation of absolute abundances. We confirm and correct for a spectral offset of $\Delta R_{{\rm p}}/R_{\ast }=(-4.29^{+0.31}_{-0.37})\, \times 10^{-3}$ of the VLT data relative to the HST-Spitzer spectrum. This offset can be explained by the assumed radius for the common-mode correction of the VLT spectra, which is a well-known feature of ground-based transmission spectroscopy. We find evidence for a lack of chromospheric and photometric activity of the host star which therefore make a negligible contribution to the offset. We measure abundances for Na and O that are consistent with solar to supersolar, with abundances relative to solar values of $21^{+27}_{-14}$ and $7^{+11}_{-4}$, respectively. We complement the transmission spectrum with new thermal emission constraints from Spitzer observations at 3.6 and 4.5 $\mu$m, which are best explained by the spectrum of an atmosphere with a temperature decreasing with altitude. A fit to the spectrum assuming an isothermal blackbody atmosphere constrains the dayside temperature to be Tp = 1545 ± 90 K.

Rapid determination of ammonia nitrogen concentration in biogas slurry based on NIR transmission spectroscopy with characteristic wavelength selection

As an important intermediate product of the anaerobic digestion (AD) process, ammonia nitrogen (AN) is an essential indicator for analyzing the nitrogen nutrition level in the biogas system. To realize rapid evaluation of ammonia nitrogen concentration (ANC) in biogas slurry during AD, a detection model of ANC was established by combining near infrared (NIR) transmission spectroscopy with partial least squares. The CARS-GSA was constructed based on the competitive adaptive reweighted sampling (CARS) algorithm combined with the genetic simulated annealing algorithm (GSA), which was applied to characteristic wavelength selection of AN for improving the accuracy and efficiency of the spectral detection model. Through the selection of wavelengths by CARS-GSA, the modeling wavelengths decreased to 47 from 1557 of raw spectra, and the performance of the ANC regression model was effectively improved. For the CARS-GSA model, the determination coefficient, root mean squared error and residual predictive deviation of the validation set were 0.989, 12.549 and 9.662, respectively. For the independent test set, the above indexes were 0.990, 21.341 and 9.821, and consistent with those of the calibration set. The results showed that CARS-GSA could effectively reduce modeling wavelength variables and enhance prediction ability of the model. This study provides a theoretical support for the application of NIR transmission spectroscopy in online detection of ANC in biogas slurry.