UV-visible Reflectance Research Articles

Effect of porosity on structural, optical, thermal, and electrical properties of nickel-foam coated graphene sheets

Nickel foam of various pore-size coated graphene thin film of 200 nm thickness was investigated as a function of the pore size. The structural properties were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared (FTIR) analysis. The optical properties were analyzed through the UV–Visible reflectance and Photoluminescence spectra. Hall Effect and Electrochemical impedance spectroscopy techniques were used to study the electrical and dielectric properties. The thermal properties were measured through the photothermal deflection technique. By decreasing the pore size, the electrical conductivity was increased from 9.42 × 10 7 to 33.26 × 10 7 S m −1 , volume and surface carrier densities were decreased from −8.66 × 10 21 to −2.05 × 10 21 cm −3 and from −1.13 × 10 14 cm −2 to −0.41 × 10 14 cm −2 ; respectively, the specific capacitance was increased from 15.52 × 10 6 F to 19.65 × 10 6 F and the dielectric permittivity of value in the order of 1.5 × 10 3 F m −1 was decreased with the frequency. It was developed the photothermal deflection technique and discussed its sensitivity to the determination of thermal properties which show that the thermal conductivity decreased from 4.12 to 3.58 W m −1 K −1 and the thermal diffusivity decreased from 0.146 to 0.109 cm 2 s −1 . It was established semi-empirical relationships which allow to deduce the thermal properties and optical band gap without needing to measure them. These results introduce the graphene coated on Nickel foam sheets as good candidate for potential use in photoelectric and thermoelectric devices.

Chiral {Ni6PW9} Cluster-Organic Framework: Synthesis, Structure, and Properties.

A chiral three-dimensional polyoxometalate cluster-organic framework (POMCOF) H3[(btc)Ni6(μ3-OH)3(H2O)5(B-α-PW9O34)]·17H2O (1, btc = 1,2,4-benzenetricarboxylate) has been made under hydrothermal conditions in the absence of amine or chiral starting reagents. 1 shows high stability in CH3CN/DMF (1:3), acidic, and basic solutions with the pH ranging from 2 to 12 for 5 days. The UV-vis reflectance spectra and Mott-Schottky measurements reveal that 1 could be a suitable catalyst for photocatalysis. Visible-light-driven H2 evolution studies have demonstrated that 1 is an ecofriendly, efficient, and recyclable catalyst with a H2 evolution rate of 1058.24 μmol h-1g-1. Nonlinear optical (NLO) measurement reveals that 1 exhibits a second-harmonic generation (SHG) response of about 1.4 times that of KH2PO4 (KDP), indicating that 1 is a potential NLO material as well.

Facile Synthesis, Physicochemical Properties, and Photocatalytic Activity ofIn SituGr@WO3⋅H2O Nanoplate Nanocomposite

In situ nanocomposites of graphene (Gr) and tungsten oxide hydrate (WO[Formula: see text]O) nanoplates were synthesized via facile and energy-saving acid precipitation method at room temperature. The effect of the in situ composition on the physicochemical properties of WO[Formula: see text]O platform material in nanocomposites was examined with X-ray diffraction, Raman scattering, UV–Vis reflectance spectra. Gr helped reduce microstrain, reduce the average crystalline size, increase the distance between (111) planes in WO[Formula: see text]O platform nanoplates, and abnormally increase the optical bandgap. All samples showed a moderate photocatalytic activity in methylene blue (MB) removing efficiency under visible light irradiation, which was remarkably enhanced by adding 0.1[Formula: see text]mL H2O2. In comparison with both pristine and nanocomposite samples, the sample having 0.1[Formula: see text]wt.% of Gr in nanocomposite showed the highest MB removing efficiency of 47% and 99% in corresponding to without and with 0.1[Formula: see text]mL H2O2. The photocatalytic activity was assigned to the key role of the photogenerated holes, which was enhanced by compositing with Gr and/or the appearance of H2O2. The results of this work were a contribution to studying the photocatalytic mechanism of tungsten oxide hydrate-based nanocomposite and also proposed a facile method for preparing WO[Formula: see text]O-based nanocomposite.

Effect of Films Thickness on Structural and Optical Properties of Gold (Au) Thin Films Prepared by DC Magnetron Sputtering

In this paper, the effect of films thickness on the structural and optical properties of gold (Au) thin films prepared by the DC sputtering method was studied. At three different deposition times, three samples of gold thin films of three different thicknesses (200,400, and 600 nm) were prepared. X-ray diffraction patterns, scanning electron microscopy (SEM), and atomic force microscopy (AFM) images, as well as optical spectroscopy, were used to characterize thin films. The crystalline structure of gold thin films was determined by the XRD pattern which showed to be cubic phase and polycrystalline in nature. The preferred orientation was (111) at 2Ѳ equal 37.4. The effect of deposition time on the morphology of the deposited films was visualized with a scanning electron microscope (SEM) which showed a homogenous surface with nanoparticles with a diameter size of 50-100 nm. Changes in deposition time caused variations in roughness, thickness, and surface quality, as shown by AFM results. UV-Vis reflection spectroscopy was also used to investigate the optical properties of thin films.

Graphene-based deep-ultraviolet photodetectors with ultrahigh responsivity using chemical vapor deposition of hexagonal boron nitride to achieve photogating

This study presents high-responsivity graphene-based deep-ultraviolet (DUV) photodetectors using chemical vapor deposition (CVD)-hexagonal boron nitride (h-BN) photogating. To improve the DUV photoresponse, h-BN was used as a photosensitizer in graphene field-effect transistors (GFETs). The h-BN photosensitizers were synthesized using CVD and then transferred onto a SiO2/Si substrate. The behavior of h-BN irradiated with DUV light was investigated using cathodoluminescence and UV–VIS reflectance. Under 260 nm light, it exhibited a clear photoresponse with an ultrahigh responsivity of 19600 AW-1, which was 460% higher than a GFET device without h-BN photosensitizers. A noise equivalent power of 3.09×10−13 W/Hz1/2 was achieved.

Hybrid Surface-Enhanced Raman Scattering Substrates for the Trace Detection of Ammonium Nitrate, Thiram, and Nile Blue.

We report the fabrication and performance evaluation of hybrid surface-enhanced Raman scattering (SERS) substrates involving laser ablation and chemical routes for the trace-level detection of various analyte molecules. Initially, picosecond laser ablation experiments under ambient conditions were performed on pure silver (Ag) and gold (Au) substrates to achieve distinct nanosized features on the surface. The properties of the generated surface features on laser-processed portions of Ag/Au targets were systematically analyzed using UV–visible reflection and field emission scanning electron microscopy studies. Later, hybrid-SERS substrates were achieved by grafting the chemically synthesized Au nanostars on the plain and laser-processed plasmonic targets. Subsequently, we employed these as SERS platforms for the detection of a pesticide (thiram), a molecule used in explosive compositions [ammonium nitrate (AN)], and a dye molecule [Nile blue (NB)]. A comparative SERS study between the Au nanostar-decorated bare glass, silicon, Ag, Au, and laser-processed Ag and Au targets has been established. Our studies and the obtained data have unambiguously determined that laser-processed Ag structures have demonstrated reasonably good enhancements in the Raman signal intensities for distinct analytes among other substrates. Importantly, the fabricated hybrid SERS substrate of “Au nanostar-decorated laser-processed Ag” exhibited up to eight times enhancement in the SERS intensity compared to laser-processed Ag (without nanostars), as well as up to three times enhancement than the Au nanostar-loaded plain Ag substrates. Additionally, the achieved detection limits from the Au nanostar-decorated laser-processed Ag SERS substrate were ∼50 pM, ∼5 nM, and ∼5 μM for NB, thiram, and AN, respectively. The estimated enhancement factors accomplished from the Au nanostar-decorated laser-processed Ag substrate were ∼106, ∼106, and ∼104 for NB, thiram, and AN, respectively.

Tailoring the Properties of Polyurethane Coatings with Epoxidized Bio-Polyol Spin-Coated onto Glass and P-Type Si(100) Substrates

High-performance plastics or engineering polymers have been actively studied for various microelectronic applications as the demand for faster processing speeds increases. Taking advantage of its high Young’s modulus ideal for inter-layer dielectric applications, polyurethane (PU), a class of linearly-segmented polymer primarily made by reacting isocyanate and polyol, were deposited on borosilicate glass and p-type Si (100) substrates via spin coating method utilizing epoxidized soybean oil as a bio-polyol replacement. Optical micrographs showed that 100% ESBO-based PU coatings exhibited homogeneous and superior quality coatings in contrast to 50% ESBO-and 100% petroleum-based PU coatings as confirmed by scanning electron micrographs and EDX analysis. Based on the surface profilometry data, we found out that PU coatings with film thickness ranging from 6 μm to 28.5 μm can be achieved. FTIR-ATR analysis revealed that maintaining the stoichiometric ratio between O–H and N–C–O vibrational modes closer to unity is a vital factor to produce a high-quality PU coating regardless of the choice of substrate. The average bandgap energy of 4.35 ± 0.03 eV was estimated from the UV-vis reflectance spectra, and the electrical resistance of 107–1010 orders of magnitude was measured using a two-probe method which are typical for dielectric materials. Preliminary insights about the dielectric response of the fabricated PU coatings were investigated using electrochemical impedance spectroscopy and a low κ-value of 2.749 was calculated from the Nyquist plot of the 7.9-μm thick 100% ESBO-based PU coating deposited at 6000 rpm for 45 seconds. These promising results proved that PU coatings from bio-polyols can be tailored to achieve desired coating properties that are amenable for next-generation microelectronic packaging and curable photoresists.

Insights into Della Robbia’s Terracotta Monument to Cardinal Federighi: Raw Materials and Technologies

The present work comprises the application of a multi-analytical strategy based on the combination of several non-destructive and micro-invasive methodologies for the examination of the glazed tiles from the tomb of Benozzo Federighi made by Luca della Robbia. The marble tomb is framed by flat glazed terracotta tiles, each ornamented with naturalistically depicted flowers. The tiles are assembled like an “opus sectile” and their background is gilded. The leaf is incorporated on the top of the glaze, differently by traditional gilding technique as in previous glazed works of della Robbia. The identification methodology integrates the results from spot analyses such as UV-vis reflectance spectroscopy and X-ray fluorescence, with those obtained on tiny samples by X-ray diffraction, electron microscopic observations, laser ablation inductively coupled plasma mass spectrometry and firing temperature analysis. The adopted analytical protocol allowed us to clarify peculiarities of the artist’s technique and of the manufacturing technology used to create the terracotta and gilded glazed tiles. The terracotta body shows main phases related with Ca-rich ceramic body and the glaze results Pb-based and additioned with Sn as an opacifier. Co, Pb-Sb and Cu were identified as glazes colouring agents. The hypothesis on the use of the “third firing” technique for gilding tiles is explored in the text.

Diffuse reflectance spectroscopy of γ-irradiated UHMWPE: A novel fractional order based filters approach for accessing the radiation modification

Spectral data pre-processing is a very effective method to improve the accuracy of constructing hyper spectral models, and differential spectroscopy is a valuable analysis method for the pre-processing of hyper spectral signals. It is usually used to increase the intensity of spectral signals and makes the researcher able to figure out hidden inflection points along with the minimum and maximum bands. In this particular study, fractional derivatives have been employed for the analysis of UV-VIS spectra of PE (ultra-high, MW) samples. The fractional order derivatives of UV-VIS (reflectance) spectra of un-irradiated and irradiated samples are simulated, and radiation modifications in UHMWPE are assessing. The classic definition of Riemann-Liouville (RL) integral is used for the calculation fractional order derivatives. For this the rule given by Lagrange operator (differential) is used i.e., taking the n th derivative over the ( n − α ) th order integral gives the derivative of α th order. It is of particular importance to mention here that n is the neighboring integer satisfying the condition n > α . Staring from following definition of RL integral (fractional) with 0 < α < 1 and initial value a = 0 . J a + α f ( x ) = 1 Γ ( α ) ∫ a x ( x − τ ) α − 1 f ( τ ) d τ It is observed that the fractional order differential transformation gives better estimates regarding spectral pre-processing and accessing the radiation modification of UHMWPE while minimizing the loss of original data. • Reflectance spectra of irradiated PE are processed with fractional derivatives. • Correlation coefficient index model is used for modification quantification. • Concept of radius of curvature is used for assessing the radiation damage.

Photonic Crystal-Enhanced Photodynamic Antibacterial Therapy

Photonic Crystal-Enhanced Photodynamic Antibacterial Therapy

Selective preparation of samarium phosphates from transition metal mixed solution by two-step precipitation

ABSTRACT Samarium-cobalt alloys are used as materials for powerful magnets with relatively high Curie temperatures. Samarium is a valuable and expensive material because it is one of a group of rare earth elements. In order to utilize this rare earth resource in a sustainable society, it is necessary to recover, reuse, and recycle rare earth elements. With this in mind, a new process for recovering neodymium phosphate from neodymium-iron mixed aqueous solutions has recently been reported, avoiding the difficulties reported with conventional methods. Given that rare earth phosphates are a major component of rare earth ores, this new process was proposed to recover them as phosphates. In this method, neodymium phosphate was selectively precipitated from a neodymium-iron mixture in a two-step process with an adjusted pH value. In this study, we attempted to selectively precipitate samarium phosphate from a mixed solution of transition metals using this two-step precipitation method. The advantage of this method is that the samarium compound can be separated from other metal salts without the use of high temperatures or special equipment. Optimal conditions were determined by evaluating the precipitates by molar ratio, color hue, UV-visible reflectance spectra, X-ray diffraction, and infrared spectroscopy of the precipitates obtained. In Step 1, the pH was adjusted using sodium hydroxide to remove cobalt, iron, and copper hydroxides other than samarium. In Step 2, after adding phosphoric acid, the pH was adjusted so that a precipitate of samarium phosphate was formed.

Synthesize Fe&lt;sub&gt;3&lt;/sub&gt;O&lt;sub&gt;4&lt;/sub&gt;-TiO&lt;sub&gt;2 &lt;/sub&gt;Composite for Methyl Orange Photocatalytic Degradation

The effect of Fe3O4 percentage on Fe3O4-TiO2 composite for methyl orange photocatalytic degradation has been investigated. Hydrothermal was carried out on TiO2 before being combined with Fe3O4 by precipitation method. The composites were characterized by means of Scanning Electron Microscope (SEM), X-ray diffraction (XRD) and UV-Vis diffuse and reflectance spectroscopy (UV-Vis DRS). The photocatalytic activity of Fe3O4-TiO2 composites were evaluated for methyl orange degradation. The addition of Fe3O4 to TiO2 could reduce the bandgap energy. The lowest bandgap energy was obtained at 20% Fe3O4-TiO2 composite. By using this composited, the degradation of methyl orange was 90%.

Hydrogen Production from MeOH /H2O Using MWCNT/UV100-TiO2 Catalysts

The current work deals with the synthesis of binary composites MWCNT/UV100 - TiO2 nanoparticles by simple mix method and compares their photocatalytic activates for the pristine and impregnated two ratios of MWCNTs using hydrogen production process under UV- light irradiation. X-ray diffraction, UV-visible reflectance and surface area BET were used to characterize binary synthesized Nano composites. The results in this work were related to two causes; the abilities of MWCNTs towards creating more active species with TiO2-UV100 when dispersion in all the surface, which causing reduce in bandgap, leading to a slight shift in the absorption. The second; the XRD has shown that two samples were did not change in crystallized the anatase phase. According to the results MWCNTs can be used to enhance the activates of UV100 for produce high quantiles of H2 as compare with pristine case without impregnated.

An approach towards modification of UiO-type MOFs with phosphonate-substituted porphyrins

The post-modification of UiO-66 with a porphyrin bearing phosphonic acid moieties is reported. The preservation of thermal stability and crystallinity of the material is revealed. The binding motif is investigated by FT-IR and UV–vis. The specific surface area of the material is decreased in comparison with the starting UiO-66 , proving the surface localization of the porphyrin. The post-modification of UiO-type materials with a porphyrin bearing phosphonic acid moieties is reported for the first time. The prolonged interaction of UiO-66 and tetrakis(4-phosphonatophenyl)porphyrinato nickel(II) Ni ( H 8 - TPPP ) resulted in the formation of a hybrid material with the preservation of the crystallinity of the material. The measured specific surface area of Ni ( H 8 - TPPP@UiO-66 ) showed considerable decrease of the corresponding value in comparison with the starting UiO-66 (from 1181 to 619 m 2 /g), providing indirect proof of the localization of the porphyrin at the surface of the material crystallites. The prepared hybrid material was excessively characterized with a set of physical–chemical methods. The preservation of the thermal stability up to 400 °C is revealed, moreover the thermogravimetric data allowed to evaluate the ratio of the grafted porphyrin as ca . 18% by weight. UV–vis reflectance data of the hybrid material were found to be in consistency with the spectra of the starting porphyrin allowing to assume the absence of its intermolecular interactions at the surface of UiO. The analysis of the FT-IR spectra of the obtained material and its precursors allowed assuming the binding motifs of the phosphonic acid residues.

Radiation damage in ion-irradiated CeO2 and (Ce, Gd)O2 sinters: Effect of the Gd content

The radiation damage induced in cerium dioxide CeO 2 and cerium-gadolinium mixed oxides (Ce, Gd)O 2-x was studied by micro-Raman spectroscopy and diffuse UV-visible reflectance spectroscopy. Sintered samples of undoped CeO 2 and (Ce, Gd)O 2-x for 1 mol% and 5 mol% of Gd 2 O 3 were irradiated at room temperature with 2.5-MeV Ar 2+ and 12-MeV Ar 4+ ions up to high fluences (i.e. 5 × 10 14 cm −2 and 2.1 × 10 14 cm −2 respectively). The Raman spectra show that no amorphization of those oxides occurs whatsoever, regardless of the Gd content. No clear change of the damage cross section with the Gd 3+ content is deduced from the decay of F 2g peak intensity versus fluence. Moreover, the reflectivity spectra show a clear decrease of the band-gap energy and increase of the Urbach energy arising from point defect accumulation. Similar effects are found for 1 mol% and 5 mol% Gd 2 O 3 , whereas a larger effect on band tailing is seen for undoped ceria. The respective roles of nuclear collisions and electronic excitations are discussed for both ion energies knowing that the two kinds of measurements do not probe the same sample depth. The substitution of Gd 3+ ions for Ce 4+ ions is likely reducing the damage and the formation of band tails related to the formation of Ce 3+ ions by electronic excitation processes.

Synthesis, Crystal Structure, and Broadband Emission of (CH3)3SSnCl3.

We report here on the synthesis, crystal structure, optoelectronic and vibrational properties, as well as the DFT calculations of the novel trimethylsulfonium tin trichloride (CH3)3SSnCl3. The air-stable compound is prepared by reacting the (CH3)3SCl and SnCl2 solid precursors in evacuated silica tubes at 100 °C. According to powder X-ray diffraction and Rietveld refinement, it crystallizes at room temperature in the orthorhombic space group Pbca (No. 61) with isolated pyramids of [SnCl3]- and (CH3)3S+ units. UV-vis reflectance and photoluminescence spectroscopies reveal a direct energy band gap of 3.85 eV, accompanied by a broad Stokes-shifted luminescence signal. Photoexcitation of the compound at room temperature and at -196 °C results in broadband luminescence with weak magenta emission centered at 400 nm using an excitation at 250 nm. First principal calculations provide insight into the physical properties through the electron and phonon density of states. Multitemperature Raman spectroscopy and differential scanning calorimetry reveal a reversible phase transition at ca. 70 °C that affects the vibrational modes of the [SnCl3]-. By dissolving (CH3)3SSnCl3 in dimethylformamide in ambient air for a week, oxidation of tin occurs in the "defect" perovskite ((CH3)3S)2SnCl6. The crystal structure of ((CH3)3S)2SnCl6 is also determined with high accuracy via single-crystal X-ray diffraction (cubic space group Pa-3 (No. 205)) and compared with (CH3)3SSnCl3 via Hirshfeld surface analysis.

Poly(vinyl pyridine) and Its Quaternized Derivatives: Understanding Their Solvation and Solid State Properties

A series of N-methyl quaternized derivatives of poly(4-vinylpyridine) (PVP) were synthesized in high yields with different degrees of quaternization, obtained by varying the methyl iodide molar ratio and affording products with unexplored optical and solvation properties. The impact of quaternization on the physicochemical properties of the copolymers, and notably the solvation properties, was further studied. The structure of the synthesized polymers and the quaternization degrees were determined by infrared and nuclear magnetic spectroscopies, while their thermal characteristics were studied by differential scanning calorimetry and their thermal stability and degradation by thermogravimetric analysis (TG-DTA). Attention was given to their optical properties, where UV-Vis and diffuse reflectance spectroscopy (DRS) measurements were carried out. The optical band gap of the polymers was calculated and correlated with the degree of quaternization. The study was further orientated towards the solvation properties of the polymers in binary solvent mixtures that strongly depend on the degree of quaternization, enabling a better understanding of the key polymer (solute)-solvent interactions. The assessment of the underlying solvation phenomena was performed in a system of different ratios of DMSO/H2O and the solvatochromic indicator used was Reichardt’s dye. Solvent polarity parameters have a significant effect on the visible spectra of the nitrogen quaternization of PVP studied in this work and a detailed path towards this assessment is presented.

Effects of some extracted oxides on silica fume waste for mullite preparation: Physical, mechanical, optical, magnetic, and dielectric properties

In this study, Ceramic pigments on the base waste silica-containing material were obtained. Extracted corundum from alum sludge is mixed with silica fume to prepare mullite. The ions of iron, in the form of hematite (α-Fe2O3), magnetite (Fe3O4), and maghemite (γ-Fe2O3), which were extracted from alum sludge are embedded, from 2 to 15 wt%, in the prepared mixtures. The samples are sintered at 1300, 1400, 1500, and 1550 °C to follow the phase compositions. The phase composition, microstructure, physical properties, mechanical properties, magnetic properties, and dielectric properties as well as UV–visible reflectance spectra are determined for the sintered samples. A decrease in apparent porosities (The minimum apparent porosity is about 2%) and an increase in the bulk density (maximum bulk density reaches 2.77 g/cm3) are observed with increasing iron ions and sintering. The strength of the resulting samples increases with an increase in iron ions that enhance the in situ mullite formations, which act as the reinforcement agent of the matrix and form enough liquid phase at 1550 °C. The compressive strength becomes 278 MPa for samples containing high iron ions. Thus, the liquid phase helps in holding a crystalline mass together. The highest saturation magnetization is 2.26 emu/g after sintering at 1500 °C, obtained for the sample containing high amount of iron ions. The presence of high amount of iron oxide enhances the formation of the glassy phase that facilitates the mobile ions to find an easy path to move, thus, increasing the dielectric constant to 16. The pale browns to dark brown pigments are obtained to be recommended for ceramic paints and colored glazes for building materials.

Angular-Independent Structural Colors of Clay Dispersions.

Clay mineral nanosheet colloids were found to show angular-independent structural colors after desalting. Naked-eye observation and UV–visible reflectance spectra showed that the color is tuned by varying the average nanosheet size and nanosheet concentration. The low angular-dependence of the structural color was also clarified by these observations, which is the first case for a nanosheet system. The present system is expected as an environmentally benign and low-cost structural color material for various applications.

Crystallographic studies and optical analysis on nanocrystalline CrxFe2−xO3 (0.0 ≤ x ≤ 2.0) synthesized through hesperidin mediation

CrxFe2−xO3 (0.0 ≤ x ≤ 2.0) nanoparticles were synthesized through phytochemical mediated reduction method using hesperidin and the samples were annealed at 600 °C for 4 hrs for ageing. The data obtained after characteristic measurements such as X-ray diffraction, Uv–visible spectroscopy and photoluminescence were systematically studied. The crystallographic plane reflections corresponding to the formation of rhombohedral rhomb-centered lattice of Fe2O3 phase and Cr2O3 phase under the space group R¯3c (1 6 7) were confirmed for x = 0.0 and x = 2.0 samples. Both Fe2O3 and Cr2O3 phases were coexisted in intermediate compositions between x = 0.0 and 2.0 with considerable intensity variations and shift in peak positions. Crystallite size, strain and dislocation density were estimated from the crystallographic data obtained from X- ray diffraction pattern. The doping with chromium resulted greater defects or dislocation density in the intermediate compositions (0.0 < x < 2.0), owing to the difference in ionic radii of iron and chromium. The optical band gap assessments were obtained from Uv–visible reflection data using Tauc’s plot employing Kubelka Munk function. The band gap estimations show considerable red shift on gradual addition of chromium and then at x > 1.1, found undergoing blue shift. The optical emission resulted from photo excitation was observed at wavelengths 303 nm, 546 nm and 783 nm, respectively for different samples.