Specular Reflectance Spectroscopy Research Articles

Synthesis and Optical/Electronic Properties of Imitation-copper Crystals Based on Low-molecular Azobenzene Derivatives

Abstract Three imitation-copper compounds were synthesized from low-molecular azobenzene derivatives: 4-(3-methylbutoxy)-4′-cyanoazobenzene (NC-azo-DC), 4-(3-methylbutoxy)-4′-nitroazobenzene (NO2-azo-DC), and 1,4-bis[4′-(3-methylbutoxy)phenylazo]benzene (Bis-DCazo). Each compound crystallized with large plate-like planar faces. Copper-colored luster was attained using filtration to accumulate the planar crystals. Specular reflection spectroscopy and calculations indicate the reddish color was enhanced by extending π-conjugation of the azobenzene phenyl rings. These imitation-copper compounds were facilely synthesized and metal free, and did not exhibit electronic conductivity, making them promising substitutes for conventional metal-based lustrous pigments and dyes.

A photonic crystal material for the online detection of nonpolar hydrocarbon vapors.

A modern level of nanotechnology allows us to create conceptually new test systems for chemical analyses and to develop sensitive and compact sensors for various types of substances. However, at present, there are very few commercially available compact sensors for the determination of toxic and carcinogenic substances, such as organic solvents that are used in some construction materials. This article contains an overview of how 3D photonic crystals are used for the creation of a new test system for nonpolar organic solvents. The morphology and structural parameters of the photonic crystals, based upon a crystalline colloidal array with a sensing matrix of polydimethylsiloxane, have been determined by using scanning electron microscopy and by the results of specular reflectance spectroscopy based on the Bragg–Snell law. A new approach has been proposed for the application of this sensor in chemical analysis for the qualitative detection of saturated vapors of volatile organic compounds due to configuration changes of the photonic bandgap, recorded by diffuse reflectance spectroscopy. The exposure of the sensor to aromatic (benzene, toluene and p-xylene) and aliphatic (n-pentane, n-heptane, n-octane and n-decane) hydrocarbons has been analyzed. The reconstitution of spectral parameters of the sensor during the periodic detection of saturated vapors of toluene has been evaluated.

Remazol Black Decontamination Study Using a Novel One-Pot Synthesized S and Co Co-Doped TiO2 Photocatalyst

This study investigated the decolorization of Remazol Black (RBB) using a TiO2 photocatalyst modified by S and Co co-doped TiO2 (S-Co-TiO2) from a single precursor. X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and UV–Vis specular reflectance spectroscopy were used to characterize the photocatalysts. The results revealed that the band-gap energy of the doped and co-doped TiO2 decreased, with the S-Co-TiO2 8% showing the greatest one, and was found to be 2.78 eV while undoped TiO2 was 3.20 eV. The presence of S and Co was also identified through SEM-EDX. An activity study on RBB removal revealed that the S-Co-TiO2 photocatalyst showed the best result compared to undoped TiO2, S-TiO2, and Co-TiO2. The S-Co-TiO2 8% photocatalyst reduced RBB concentration (20 mg L−1) up to 96% after 90 min of visible light irradiation, whereas S-TiO2, Co-TiO2, and undoped TiO2 reduced it to 89%, 56%, and 39%, respectively. A pH optimization study showed that the optimum pH of RBB decolorization by S-Co-TiO2 was 3.0, the optimum mass was 0.6 g L−1, and reuse studies show that S-Co-TiO2 8% has the potential to be used repeatedly to remove colored pollutants. The results obtained indicate that the modification of S, Co co-doped titania synthesized using a single precursor has been successfully carried out and showed excellent characteristics and activity compared to undoped or doped TiO2.

Enhanced photocatalytic degradation of Remazol Black under visible light illumination through S doped TiO2 (S-TiO2) nanoparticles: Operational factors and kinetic study

<p>The degradation of Remazol Black (RBB) by S-TiO2 photocatalyst was investigated. X-ray diffraction, fourier-transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, and UV-vis specular reflectance spectroscopy has been used to characterize S-TiO2. The results suggested that the optical absorption edge of TiO2 was red-shifted by the addition of S dopants and the bandgap energy was 3.02 eV. The sulfur species were found to be evenly dispersed on the TiO2 crystal lattice as cationic sulfur (S6+) which corresponds to the cationic substitution on TiO2. The particle size decreased to 4-14 nm after S doping, which indicates that the addition of S dopants has contributed to an improvement in the photocatalyst surface area. The degradation of RBB was achieved 94% after 120 min visible light irradiation, a remarkable increase compared to bare TiO2 which was only able to degrade 48% of RBB at the same time. Optimization of the pH showed that the optimum pH for RBB degradation was 3.0, and the photocatalyst dose was 0.8 g L-1. Kinetic study showed that S-TiO2 photocatalytic degradation of RBB followed the pseudo-second-order kinetics model. Reducing the bandgap has been found to increase the activity of photodegradation in the visible light region.</p>

Double-Sided, Omnidirectional γ-AlOOH Hierarchical Nanostructures: Imparting Enhanced Antireflective Properties with Self-Cleaning Capacity for Optical Devices.

Herein, we have successfully developed an integrated strategy to develop antireflective coatings with self-cleaning capabilities based on periodic double-sided photonic γ-AlOOH nanostructures to transmit maximum incident light photons. Interfacial reflections are instinctive and one of the fundamental phenomena occurring at interfaces owing to refractive index mismatch. The eradication of such undesirable light reflection is of significant consideration in many optical devices. A systematic approach was carried out to eradicate surface reflection and enhance optical transmission by tailored γ-AlOOH nanostructures. The γ-AlOOH photonic nanostructures with subwavelength features exhibited a gradient index, which almost eliminated the refractive index mismatch at the interface. Optical transmittance of 97% was achieved in the range of 350-800 nm at normal incidence compared to uncoated glass (89%). A multilayer model approach was adopted to extract the effective refractive index of the coating, which showed a graded index from the top to the bottom surface. Further, to fully comprehend the optics of these nanostructures, the omnidirectional (20-70°) antireflective property has been explored using variable-angle specular reflectance spectroscopy. The hierarchical γ-AlOOH nanostructures exhibited only ∼1.3% reflectance at the lower incident angle in the visible spectra and an average reflectance of ∼7.6% up to an incident angle of 70°. Moreover, the hierarchical nanostructures manifested contact angle (CA) >172° and roll-off angle (RA) <1° with excellent self-cleaning performance. Furthermore, the abrasion resistance of the coating is discussed in detail, which displayed a good resistance against sand erosion. Significantly, the photovoltaic performance of the coated modules exhibited a relative enhancement of ∼17% in efficiency, which is attributed to the efficient coupling of light rays. Thus, the integration of the antireflection (AR) property with self-cleaning ability can provide a cost-effective energy solution for optoelectronic devices, display devices, and thin-film optics.

Silicon-Oxygen Region Infrared and Raman Analysis of Opals: The Effect of Sample Preparation and Measurement Type

An extensive infrared (IR) spectroscopy study using transmission, specular and diffuse reflectance, and attenuated total reflection (ATR) was undertaken to characterise opal-AG, opal-AN (hyalite), opal-CT and opal-C, focussing on the Si-O fingerprint region (200–1600 cm−1). We show that IR spectroscopy is a viable alternative to X-ray powder diffraction (XRD) as a primary means of classification of opals even when minor levels of impurities are present. Variable angle specular reflectance spectroscopy shows that the three major IR bands of opal are split into transverse optical (TO) and longitudinal optical (LO) components. Previously observed variability in powder ATR is probably linked to the very high refractive index of opals at infrared wavelengths, rather than heterogeneity or particle size effects. An alternative use of ATR using unpowdered samples provides a potential means of non-destructive delineation of play of colour opals into opal-AG or opal-CT gems. We find that there are no special structural features in the infrared spectrum that differentiate opal from silica glasses. Evidence is presented that suggests silanol environments may be responsible for the structural differences between opal-AG, opal-AN and other forms of opaline silica. Complementary studies with Raman spectroscopy, XRD and scanning electron microscopy (SEM) provide evidence of structural trends within the opal-CT type.

Crystal growth, IR specular reflectance and polarized Raman studies of LiNa5Mo9O30 polar single crystal.

A non-centrosymmetric, polar LiNa5Mo9O30 single crystal was grown using Kyropoulos technique and characterized by polarized Raman scattering and polarized infrared specular reflection spectroscopy at room temperature. The comparison to the polycrystalline spectra has been made and assignment of all observed modes to the respective vibrations and their symmetry has been proposed. Based on the four parameter model the infrared reflection spectra were analyzed and the LO-TO splitting has been determined for the observed modes. Stronger anharmonicity of bands assigned to stretching vibrations of the Mo-O⋯Mo bridges has been evidenced. Our results show that this crystal is attractive and promising SRS-active nonlinear optical material for up- and down-Raman laser-frequency converters with the most intense lasing lines at 947 and 884cm-1. Dielectric permittivity studies in the frequency domain exhibit two anomalies that are assigned to thermally activated relaxation and conductivity processes. The observed increase in electrical conductivity above 400K is dominated by ionic contribution and change of the conductivity mechanism.

Optical and structural properties of amorphous silicon-nitrides and silicon-oxycarbides: Application of multilayer structures for the coupling of Bloch Surface Waves

Hydrogenated amorphous silicon nitrides (a-SiNx:H) and oxycarbides (a-SiOxCy:H) have been grown by means of plasma enhanced chemical vapor deposition (PECVD) at a low power density (40–60mW/cm2) using silane, ammonia, methane and carbon dioxide as silicon, nitrogen, carbon and oxygen precursors, respectively. Their refractive index dispersion curves have been analyzed by means of specular reflectance spectroscopy and their structural properties by FTIR spectroscopy. Taking advantage of their optical properties, the alloys have been fruitfully applied in dielectric stratified structures, optimized for the propagation of surface electromagnetic waves.

Tuning the composition of BixWyO nanorods towards zero bias PEC water splitting

A unique co-oblique angle deposition method was used to create nanorod arrays of mixed phase Bi2O3/WO3/Bi2WO6 with varying atomic ratios of Bi to W. The effect of the tuning on the resulting nanostructures was characterized by EDX, SEM, XRD, optical transmission, specular reflection, and diffuse reflection spectroscopy. Samples with different Bi:W atomic ratio had a wide range of morphology and composition due to the surface mobility of deposited bismuth and its volume expansion during oxidation. Their photocatalytic and photoelectrochemical properties were investigated by methylene blue degradation and photo-generated current respectively. The sample with 38 at.% Bi showed the highest photodecay rates as well as the maximum photocurrent density, 4.3 μA cm−2, at a bias potential of 600 mV versus Ag/AgCl (3M KCl); while the sample with 50 at.% Bi exhibited a high photocurrent density of 0.35 μA cm−2 at zero bias potential, which indicates that varying the composition and mixed crystal phases of different oxides with appropriate band gaps and locations could hold the key to a visible light driven, zero bias potential, photoelectrochemical cell.

Real-Time Monitoring of Morphology and Optical Properties during Sputter Deposition for Tailoring Metal-Polymer Interfaces.

The reproducible low-cost fabrication of functional metal-polymer nanocomposites with tailored optoelectronic properties for advanced applications remains a major challenge in applied nanotechnology. To obtain full control over the nanostructural evolution at the metal-polymer interface and its impact on optoelectronic properties, we employed combined in situ time-resolved microfocus grazing incidence small angle X-ray scattering (μGISAXS) with in situ UV/vis specular reflectance spectroscopy (SRS) during sputter deposition of gold on thin polystyrene films. On the basis of the temporal evolution of the key scattering features in the real-time μGISAXS experiment, we directly observed four different growth regimes: nucleation, isolated island growth, growth of larger aggregates via partial coalescence, and continuous layer growth. Moreover, their individual thresholds were identified with subnanometer resolution and correlated to the changes in optical properties. During sputter deposition, a change in optical reflectivity of the pristine gray-blue PS film was observed ranging from dark blue color due to the presence of isolated nanoclusters at the interface to bright red color from larger Au aggregates. We used simplified geometrical assumptions to model the evolution of average real space parameters (distance, size, density, contact angle) in excellent agreement with the qualitative observation of key scattering features. A decrease of contact angles was observed during the island-to-percolation transition and confirmed by simulations. Furthermore, a surface diffusion coefficient according to the kinetic freezing model and interfacial energy of Au on PS at room temperature were calculated based on a real-time experiment. The morphological characterization is complemented by X-ray reflectivity, optical, and electron microscopy. Our study permits a better understanding of the growth kinetics of gold clusters and their self-organization into complex nanostructures on polymer substrates. It opens up the opportunity to improve nanofabrication and tailoring of metal-polymer nanostructures for optoelectronic applications, organic photovoltaics, and plasmonic-enhanced technologies.

Characterization of buried metal-molecule-metal junctions using Fourier transform infrared microspectroscopy.

We have devised an infrared spectromicroscopy based experimental configuration to enable structural characterization of buried molecular junctions. Our design utilizes a small mercury drop at the focal point of an infrared microscope to act as a mirror in studying metal-molecule-metal (MmM) junctions. An organic molecular monolayer is formed either directly on the mercury drop or on a thin, infrared (IR) semi-transparent layer of Au deposited onto an IR transparent, undoped silicon substrate. Following the formation of the monolayer, films on either metal can be examined independently using specular reflection spectroscopy. Furthermore, by bringing together the two monolayers, a buried molecular bilayer within the MmM junction can be characterized. Independent examination of each half of the junction prior to junction formation also allows probing any structural and/or conformational changes that occur as a result of forming the bilayer. Because our approach allows assembling and disassembling microscopic junctions by forming and withdrawing Hg drops onto the monolayer covered metal, spatial mapping of junctions can be performed simply by translating the location of the derivatized silicon wafer. Finally, the applicability of this technique for the longer-term studies of changes in molecular structure in the presence of electrical bias is discussed.

Hybrid Porous Silicon- Rhodamine B Derivative Nanostructures as Chemical Sensor for Hg(II) Detection

In this work we propose a new method to produce a fluorescent chemical sensor for mercury detection (Hg(II)). This device is mainly based on the optical properties of porous silicon nanostructures (PSi) [1] coupled with the fluorescent properties of Rhodamine B [2] (Rh-urea-Ph-urea-Si) ligand derivative, which is covalently linked to PSi acting as receptor of metal ions. The Rh-urea-Ph-urea-Si (Ph=Phenil) compound was synthesized and its complexing ability was studied in liquid phase and solid by fluorescence spectrometry. The results showed that the fluorescence response of the metallic complex is metal concentration dependent. If the Hg(II) concentration increases, the florescence intensity also increases to reach the saturation point of the fluorophore. The electrochemical etching of crystalline silicon wafer [3] produced the PSi transducers, which in turn were functionalized with the organic receptors. The ligand infiltration into the PSi matrix and the metal coordination on the hybrid substrate were evaluated by specular reflectance, infrared and fluorescence spectroscopy, and SEM. Fluorescence microscopy confirmed the qualitative detection of Hg(II) ions due to the increase of the fluorescence observed after metal capture. The changes in electrical impedance upon porous silicon samples before and after the chemical modification, allowed us to obtain the approximate surface area of the porous devices. During the presentation of this work, the Hg (II) detection through voltammetric techniques will be discussed. Acknowledgements. This work was supported by the CONACYT, Project No. CB-153161 and 169634. P Mayela De la Cruz thanks the CONACYT Scholarship: 237466. We acknowledge to Olga Dávalos Montoya for FTIR support and Prof. Jaime Ruiz for the facilities provided for the use of the fluorescent microscope. References.[1] A. Melek, D. Wissem, M. Ghrib, C. Radhouane, Ezzaouia. Journal of Luminescence. 132 (2012) 277-281.[2] Zhisheng Wu, Xuanjun Wu, Yuhui Yang, Ting-bin Wen, Shoufa Han, Bioorganic & Medicinal Chemistry Letters. 22 (2012) 6358–6361.[3] G. Palestino, M. Martin, V. Agarwal, R. Legros, T. Cloitre, László Zimanyi, C. Gergely, Phys. Status Solidi C. 6(7) (2009) 1624-1628

Measuring the dependence of reflectivity on the incidence angle: a technical note

A simple and easy to implement setup is proposed to be used in undergraduate laboratory classes to study the reflectivity of a material as a function of the incidence angle and, in particular, to investigate Brewster’s law. The apparatus is based on the method used in standard relative specular reflectance spectroscopy measurements: it enables us to place the sample and a reference mirror exactly in the same position of the optical path, thus involving only rough alignments and avoiding slow measurements. The setup is tested by measuring the dependence of reflectivity on the incidence angle of a glass plate for s- and p-polarized light.

High frequency linear rheology of complex fluids measured from their surface thermal fluctuations

We characterize the linear viscoelastic properties of complex fluids using a new technique, based on the measurement of surface fluctuations: surface fluctuation specular reflection (SFSR) spectroscopy. The thermally excited waves propagating on a free surface are measured through the deflection of a laser beam specularly reflected from that surface. Elastic and loss moduli of the complex fluids are inferred from the measured power spectrum density of thermal noise, with the implicit use of Kramers–Kronig relations. The technique, besides being noninvasive, provides rheological data in a large frequency range and at vanishing strains. It is therefore especially well suited for the rheological characterization of complex fluids. We present measurements of the viscoelastic modulus of supramolecular polymer solutions in a frequency range extending up to six decades. We compare the SFSR measurements with rheometric data at low and high frequencies, and show that they are in good agreement. Using supramolecular polymer solutions of different natures, exhibiting or not surface viscoelasticity, we furthermore show that SFSR provides a characterization of the bulk properties of the fluids. In addition, we discuss the accuracy of the measurements.

A sputtered-silica defect layer between two artificial silica opals: an efficient way to engineer well-ordered sandwich structures

We demonstrate a low cost and efficient method to engineer deterministically a defect between two well-ordered silica opals by sputtering silica on the top of the first one. The optical response of these sandwich structures is studied in terms of specular reflection and transmission spectroscopy. For a given thickness of sputtered silica, tailored highly transmitted and reflected optical modes are evidenced. The very good agreement between the experimental results and the simulations, run without fitting parameters, demonstrates the good control of the geometry of our structures. The macroscopic realization of well-controlled 3D photonic crystals with planar defects, presented in this paper, opens the way for an efficient manipulation of embedded nano-emitter fluorescence with applications in the fields of light-emitting devices and high-sensitivity pollutant optical detection.

Far-Ultraviolet Spectroscopy in the Solid and Liquid States: A Review

Ultraviolet (UV) spectroscopy has long been used together with visible (Vis) spectroscopy to investigate electronic transitions of a molecule. Most studies of the electronic structure of molecules using UV spectroscopy have been carried out in the 190–380 nm region because commercial UV-Vis spectrometers are available only for that region. The wavelength region shorter than 190 nm is also very rich in information about the electronic states and structure of a molecule, but the absorptivity is very high in this region, and thus, this region has been employed to investigate mainly the electronic states and structure of gas molecules. Because condensed-phase materials with high molecular density do not transmit much light in the shorter wavelength region of the UV, reflection spectroscopy has been used to observe spectra of solid samples in the wavelength region shorter than 190 nm. However, for liquid samples one cannot generally use either absorption spectroscopy or specular reflection spectroscopy. Accordingly, UV spectroscopy in this region for liquid samples has been a relatively undeveloped research area. To solve the above difficulties of UV spectroscopy in the wavelength region shorter than 190 nm we have recently developed a totally new UV spectrometer based on attenuated total reflection (ATR) that enables us to measure spectra of liquid and solid samples in the 140–280 nm region. We will show that spectroscopy in the wavelength region shorter than 190 nm holds considerable promise not only in basic science but also in applications such as qualitative and quantitative analysis, on-line monitoring, environmental geochemical analysis, and surface analysis. The purpose of the present review paper is to report recent progress in UV spectroscopy of solid and liquid phases in the 140–280 nm region. In this review, we refer to the 120–200 nm region to as the far-UV (FUV) region. The term “vacuum UV region” is no longer appropriate for the 120–200 nm region because most recent spectrometers used in this region are not evacuated but instead incorporate a nitrogen purge. This review consists of eight parts: (1) introduction to FUV spectroscopy, (2) brief history of FUV spectroscopy, (3) development of new FUV spectrometers, (4) FUV studies of liquid water and aqueous solutions, (5) FUV spectra of organic molecules in the liquid states, (6) band assignments by quantum chemical calculations, (7) potential applications of FUV spectroscopy in liquid and solid states; and (8) future prospects of FUV spectroscopy.

Two beam surface fluctuation specular reflection spectroscopy

In surface fluctuation specular reflection spectroscopy (SFSRS) deflections of a specularly reflected laser beam are used to characterize thermally excited surface waves. Here we report on a new two beam version of SFSRS in which the deflections of two reflected laser beams from separate locations on a surface are correlated. We demonstrate that this new two beam SFSRS technique can be used to determine directly the power spectrum of height fluctuation of thermally excited surface waves over a large range of both frequencies and wavevectors. In addition, we show that the technique is well suited for materials ranging from simple liquids to complex liquids and soft solids, including turbid materials.

Fixed‐point and stratified analysis of the fine structure and composition of five gallstones with Fourier transform infrared (FT‐IR) specular reflection spectroscopy

By investigating the identities, amounts, and distributions of the major components of human gallstones, the formation mechanism of calculi may be elucidated. Using FT-IR specular reflection spectroscopy, the compositions of five common types of gallstones, including cholesterol calculus, bile pigment calculus, cholesterol-bilirubin calculus, mixed calculus, and black stones, were positionally, qualitatively, and quantitatively analyzed. Several organic and inorganic substances were found in human gallstones, including cholesterol, calcium bilirubinate, calcium carbonate, calcium phosphate, and calcium stearate. Among them, cholesterol and calcium bilirubinate were the main components. The amounts of these substances varied in different types of gallstone. The distributions of cholesterol and calcium salts (with the exception of calcium bilirubinate) were also closely associated with location. In the various calculi, the amounts of cholesterol and calcium bilirubinate in the cores, the layered structures outside the cores, and the outer shells were higher than those of other substances. The identities of the major components of calculi were similar in different types of gallstones, but their amounts and distributions were significantly different. The analytical method used in this study, which was able to accurately determine the location, quality, and quantity of the major components of gallstones, would be an effective tool to study the formation mechanism of calculi.

Photo-fixation of SO 2 in nanocrystalline TiO 2 films prepared by reactive DC magnetron sputtering

We report on photo-fixation of SO 2 onto nanostructured TiO 2 thin films prepared by reactive DC magnetron sputtering. The films were exposed to 50 ppm SO 2 gas mixed in synthetic air and illuminated with UV light at 298 and 473 K. The evolution of the adsorbed SO x species was monitored by in situ Fourier transform infrared specular reflection spectroscopy. Significant photo-fixation occurred only in the presence of UV illumination. The SO 2 uptake was dramatically enhanced at elevated temperatures and then produced strongly bonded surface-coordinated SO x complexes. The total SO x uptake is consistent with Langmuir adsorption kinetics. The sulfur doping at saturation was estimated from X-ray photoelectron spectroscopy to be ~ 2.2 at.% at 473 K. These films were pale yellowish and had an optical absorption coefficient being ~ 3 times higher than in undoped film. The S-doped films exhibit interesting oleophobic properties, exemplified by the poor adherence of stearic acid. Our results suggest a new method for sulfur doping of TiO 2 to achieve combined anti-grease and photocatalytic properties.

Probing thermal waves on the free surface of various media: Surface fluctuation specular reflection spectroscopy

Thermal motion gives rise to fluctuations in free surfaces; measurement of the thermally excited waves on such surfaces provides information on the mechanical properties of the medium. We have developed an optical tool to probe the thermally excited waves on free surfaces: surface fluctuation specular reflection (SFSR) spectroscopy. It consists in measuring the fluctuations in the position of a laser beam that is specularly reflected onto the free surface of a medium. The position of the reflected beam is sensitive to the roughness of the probed surface; the thermal waves are detected by subtracting the light intensities collected on the two quadrants of a photodiode, on which the beam is centered. We show how the measured signal is related to the medium properties. We also present measurements performed on Newtonian liquids as well as on a viscoelastic solid; we show that in all cases, there is a very good agreement between experimental and computed spectra. SFSR thus applies to a broad range of materials. It moreover offers a very good temporal resolution and should provide a useful tool for dynamical measurements on complex fluids.