Optical Transmission Measurements Research Articles

Structural and optical properties of a layered ε-GaSe thin film under elastic deformation from flexible PET substrate

The present study focuses on the structural and optical characterizations of a GaSe thin-film consisting of few layers mechanically exfoliated from bulk GaSe on a flexible PET substrate. The XRD and the RAMAN spectroscopies confirm the high crystallinity of our material and show that it belongs to the hexagonal ε-GaSe polytype with a mean crystallite size of about 50 ​nm. The sample’s SEM images exhibit the two-dimensional nature of the layers. The optical transmission measurements clearly show two absorbing edges. They were assigned to an indirect band gap at 1.92 ​eV and to a direct one at 2.2 ​eV. The appreciable difference between the two gaps, of about 0.28 ​eV, is attributed to a compressive biaxial strain. A value, as high as 104 ​cm−1, of the absorption coefficient has been obtained which demonstrates the GaSe material’s great potential for optoelectronic applications.

Visual Assessment of Blood Plasma versus Optical Transmittance and Refractive Index Measurements for Quantifying Lipemia.

Today, visual classification of the degree of lipemia in blood samples is frequently performed in clinical laboratories. However, achieving standardization of this classification at low cost and with fewer resources is an objective that is still under development. In this work, a comparison is made between the visual inspection and optical measurements of blood plasma for quantifying lipemia. The plasma refractive index’s real part was measured using an Abbe refractometer and transmittance measurements were made at a 589 nm wavelength and wavelengths ranging from 320 to 1100 nm in the spectral region, respectively. Taking the slope of the transmittance spectrum at two specific wavelengths, it is possible to establish a more standardized selection criterion and implement it quickly using low-cost optical devices. Furthermore, using the proposed transmittance-spectrum-slope method, statistically significant differences (p < 0.05) were found between healthy blood samples and lipemia 1, 2, 3, and 4. However, there were no statistical differences between lipemia 1 and 2.

A comparison between thermal lens and conventional optical spectroscopy for monitoring of a photocatalytic process

We compare the thermal lens (TLS) and the optical transmission (OT) spectroscopy techniques to monitor the kinetic of a photocatalytic reaction. For this, an OT measurement facility was added to a TLS set-up. The TLS was implemented in a microspatial configuration named thermal lens microscopy (TLM). Methylene blue (MB) in Water solutions were used as test samples within a concentration range in which both techniques show good sensibility. Within this range, the limit of detection obtained by TLM was about one order of magnitude lower than that achieved by OT. The methylene blue concentration evolution with photocatalytic reaction time was measured with both techniques, showing a good agreement between their results. A ZnO thin film deposited on a glass substrate by the spray pyrolysis technique was used as catalyst, and the reaction was induced by UV-violet light.

Plasmonic Strain Sensors Based on Au-TiO2 Thin Films on Flexible Substrates.

This study aimed at introducing thin films exhibiting the localized surface plasmon resonance (LSPR) phenomenon with a reversible optical response to repeated uniaxial strain. The sensing platform was prepared by growing gold (Au) nanoparticles throughout a titanium dioxide dielectric matrix. The thin films were deposited on transparent polymeric substrates, using reactive magnetron sputtering, followed by a low temperature thermal treatment to grow the nanoparticles. The microstructural characterization of the thin films’ surface revealed Au nanoparticle with an average size of 15.9 nm, an aspect ratio of 1.29 and an average nearest neighbor nanoparticle at 16.3 nm distance. The plasmonic response of the flexible nanoplasmonic transducers was characterized with custom-made mechanical testing equipment using simultaneous optical transmittance measurements. The higher sensitivity that was obtained at a maximum strain of 6.7%, reached the values of 420 nm/ε and 110 pp/ε when measured at the wavelength or transmittance coordinates of the transmittance-LSPR band minimum, respectively. The higher transmittance gauge factor of 4.5 was obtained for a strain of 10.1%. Optical modelling, using discrete dipole approximation, seems to correlate the optical response of the strained thin film sensor to a reduction in the refractive index of the matrix surrounding the gold nanoparticles when uniaxial strain is applied.

Pressure and Temperature Transformations of the Molecular Conformation and Crystal Structure of Ferrocene Fe2+(η5-C5H5)2–

X-ray diffraction, optical spectroscopy, and numerical calculations were carried out on pristine ferrocene Fe2+(η5-C5H5)2– single crystals under various pressure/temperature conditions. Structural data were obtained at room temperature and pressures up to 6.5 GPa as well as at ambient pressure and low temperatures up to 100 K. The iron–carbon bond length (l = 2.043 Å under ambient conditions) shows linear temperature dependence and quadratic pressure dependence with the coefficients ∂l/∂T = −2.84 × 10–5 Å K–1, ∂l/∂P = −1.36 × 10–3 Å GPa–1, and ∂2l/∂P2 = −3.04 × 10–4 Å GPa–2, respectively. Jumping of the Fc molecular configuration between D5h and D5d conformations decreases at high pressure/low temperature, leading to complete ordering in low-temperature (LT, <161.3 K) and high-pressure (HP, >3 GPa) phases. The initially large bandwidth of lattice phonon modes increases with pressure to a maximum at 2 GPa and decreases to the common value after molecular ordering at pressures P > 3 GPa. The electronic structure calculations in the HP phase at high pressure show a linear increase in the fundamental gap Eg with the pressure coefficient of 28 meV/GPa. Optical transmission measurements at high pressure demonstrate an almost 2 times smaller pressure coefficient of about 12 meV/GPa and an abrupt decrease in the gap by ∼14.5 meV at P = 2 GPa.

High-Pressure Investigation of 2,4,6-Trinitro-3-bromoanisole (TNBA): Structural Determination and Piezochromism

Understanding phase transitions in energetic materials is crucial for developing predictive models of detonation. 2,4,6-Trinitro-3-bromoanisole (TNBA), an energetic material, was studied in its single-crystal form up to pressures of 45 GPa in a diamond anvil cell. The material was characterized by using X-ray, Raman, and optical transmission measurements. From single-crystal X-ray diffraction, the ambient structure of TNBA was determined which crystallizes in the P21/c space group having four molecular units per unit cell. The X-ray data up to 9.2 GPa were fitted to a third-order Birch–Murnaghan equation of state by using the parameters K0 = 13.2(2.4) GPa and Kp = 5.1(1.4). Between 6.8 and 7.3 GPa, a phase transition was inferred in TNBA from concurrent fading of X-ray diffraction, disappearance of Raman peaks, increase in sample fluorescence, and discontinuous color change. The new phase was consistent with an amorphous state of at least partially intact molecules judging from the presence of higher-order Raman modes and irreversibility of the Raman spectra upon release. Piezochromism was observed with the translucent yellow TNBA gradually darkening and becoming opaque black at ∼25 GPa. This correlated to the absorption edge gradually shifting to the red in the visible spectrum. Signs of two possible additional structural transitions were detected in the 32.4–41.0 GPa range as suggested by a jump in the absorption edge, the irreversible changes in the absorption spectrum upon release to ambient pressure, and by the lack of Raman modes in recovered samples. The crystal and electronic structures of TNBA were also investigated up to 10 GPa by using DFT calculations and crystal structure prediction (CSP) simulations. In agreement with the experimentally observed transition at 7 GPa, the simulations at 10 GPa found a bevy of polymorphs lower in enthalpy and higher in density than P21/c. The lowest calculated enthalpy structure was determined to be P212121, being in a different space group than the ambient experimental result.

Optical characterization of DNA origami-shaped silver nanoparticles created through biotemplated lithography.

Here, we study optically resonant substrates fabricated using the previously reported BLIN (biotemplated lithography of inorganic nanostructures) technique with single triangle and bowtie DNA origami as templates. We present the first optical characterization of BLIN-fabricated origami-shaped silver nanoparticle patterns on glass surfaces, comprising optical transmission measurements and surface-enhanced Raman spectroscopy. The formed nanoparticle patterns are examined by optical transmission measurements and used for surface enhanced Raman spectroscopy (SERS) of Rhodamine 6G (R6G) dye molecules. Polarization-resolved simulations reveal that the higher SERS enhancement observed for the bowties is primarily due to spectral overlap of the optical resonances with the Raman transitions of R6G. The results manifest the applicability of the BLIN method and substantiate its potential in parallel and high-throughput substrate manufacturing with engineered optical properties. While the results demonstrate the crucial role of the formed nanogaps for SERS, the DNA origami may enable even more complex nanopatterns for various optical applications.

Dose rate effects in radiochromic leuco crystal violet dosimeters

Radiochromic dosimeters based on leuco crystal violet (LCV) in aqueous solutions and gelatin hydrogels were evaluated for dose and dose rate performance. Optical transmission measurements were performed on samples in custom 10 cm long cuvettes in order to have measurable signals below 10 Gy. Standard gel formulations with 0.7 mM concentration of anionic surfactant sodium dodecyl sulfate (SDS) had a dose rate effect of increasing sensitivity with increasing dose rate of nearly 15% from 1 to 10 Gy/min at 20 Gy. Solutions of LCV and trichloracetic acid also showed similar dose rate effects. Adding LCV increased dose rate effect. Adding SDS, lowered sensitivity but maintained dose rate effect. Adding 0.4% gelatin also lowered sensitivity but reversed dose rate effect. For gels, lowering the pH reduced both sensitivity and dose rate effect. These trends are consistent with LCV solubility contributing to dose rate effects. These data indicate there are several factors related to dose rate effects in leuco crystal violet dosimeters and formulations designed to maximize sensitivity may not minimize dose rate effects.

Effect of the bottom layer thickness on the structural and optical phase transition properties of V2O5/V/V2O5 thin films

Vanadium dioxide (VO2 (M)) is an intelligence material that undergoes a phase transformation that can be tuned. This material has the potential to be used as an energy-efficient coating. Scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and optical transmittance measurements were used to characterise the multi-layered thin films with a varying bottom layer thickness. Surface morphology reveals irregular shapes, boundary layers, and porous at the nanoscale, and the presence of tiny cracks. For all samples, the root means square (RMS) roughness reveals a smooth film surface. The formation of polycrystalline VO2 (M) thin films is confirmed by XRD patterns. Switching thermochromic properties are demonstrated by temperature-dependent of optical transmittance measurements. Transmittance increases significantly in the infrared region when compared to the visible region. The transmittance in the UV (ultra-violent) ranges between 15 and 25%, while the transmittance in the NIR (near infrared region) ranges between 5 and 40%, depending on the thickness of the bottom layer. We also reduced the phase transition temperature from 48 to 50 °C when compared to pure VO2 (∼68 °C), this reduction in phase transition is attributed to the distinction of nanostructured in VO2. This research could help to advance the use of smart window coatings in the real world.

Effect of the RF-power and annealing on the structural, optical, morphological and electrical properties of RF-sputtered V2O5 thin films

Thin films of vanadium oxide were deposited on glass substrates by the radio frequency reactive sputtering from a high purity metallic vanadium target (99.7%) with a diameter of 10 cm. The reactive sputtering was carried out in an argon-oxygen gas mixture containing 10% of O2 and 90% of Ar. The films were deposited at different RF powers (150 W, 200 W, 250 W and 300 W) for a fixed deposition time of 150 min. X-ray diffractograms showed that the deposited thin films crystallized in an orthorhombic V2O5 phase. It was found that the crystallite size varies with the RF power and is maximized using 300 W as an RF power. Scanning Electron Microscopy and Raman scattering analyzes have confirmed the formation of V2O5 thin films. In addition, optical transmittance measurements were performed using a Shimadzu UV-PC spectrophotometer in the 220–2000 nm range. It was observed that the optical band gap of the films decreases with increasing the RF power. Electrical resistivity was found to decrease with increasing the RF power from 150 to 250 W, and then it increases.

A Portable Device for miRNAs Detection Based on a Gold-Nanoparticle Ratiometric Colorimetric Strategy

MicroRNAs (miRNAs) have recently emerged as a new class of biomarkers for disease diagnosis and play vital roles in physiological and pathological processes. Here, a novel fiber-optic prototype that allows synchronized optical transmittance measurements at different wavelengths has been designed and fabricated for selective and sensitive miRNAs detection based on a ratiometric colorimetric strategy. The proposed measurement method automatically adjusts the output light power through the LEDs, minimizing eventual differences in brightness and potential losses through the optical fiber without the need expensive optical components. The prototype has been validated for the detection of miRNAs identified as biomarkers of bovine mastitis in dairy cattle. Observation of the color changes from red to blue of the AuNP solution, and therefore on the transmittance signal, caused by miRNA-induced gold nanoparticles aggregation has been used for rapid detection of such genetic biomarker. The equipment designed and constructed is portable, being the main parameters of the measurement managed with a smartphone, and it could be potentially employed with any other biosensor whose detection strategy is based on changes in the distance between gold nanoparticles.

Effects of Deposition Time And PH on The Characterization of Chemically Synthesized Composite Nano-Wires of Cu2S Thin Films

&#x0D; The chemical bath deposition technique (CBD) had used for depositing Cu2S thin films on the glass substrates. It found that thickness and deposition rate were significantly dependent on deposition parameters (deposition time and pH value). XRD data indicates that at different deposition times and pH values are given amorphous structure except for the deposited thin film of (8hours) and, pH of (10.4) the structure was crystalline. The morphology of the deposited thin films remarkably changed as the deposition time increased. Optical transmittance measurements illustrate that transmission of the thin films decreases from 93.27% for a deposition time of 4 hours to 81.73 for deposition time of 10 hours and, the maximum transmission rate of the films is 95.21 % with pH=8.4 and decreases to 28.39 % with pH=11.4. Also, optical studies revealed that Cu2S thin film with direct energy bandgap decreased from 3.04 to 2.78 eV as deposition time increased and from 3.09 to 2.32 eV as pH increased.&#x0D;

The role of fluorine in high quantum yield oxyfluoride glasses and glass-ceramics

Oxyfluoride glass-ceramics is considered a great candidate for optical refrigeration. Their ability to form low-phonon fluoride crystals embedded in an oxide glass matrix presents great interest for the development of fluorescent efficient materials with good mechanical and thermal resistance. A better understanding of the material microstructure and its relations on properties is mandatory to achieve the required optical refrigeration values. In the present work, we discuss the effect of fluoride compound evaporations and their impacts on thermal, optical, crystallization, and luminescent properties. Using different melting temperatures, glass samples from the theoretical molar composition 37.6 SiO2 – 22.4 Al2O3 – 19 YF3 – 20 LiF – 1 YbF3 are fabricated by the melt-quenching method. The relation between composition and glass properties is assessed by measurement of glass transition, crystallization temperature, density, refractive index, and optical transmission. A detailed study of the crystallization behavior of the samples is conducted using scanning and transmission electron microscopies, and both classical and temperature in-situ x-ray diffractions. Finally, luminescent properties are measured, including quantum yield, and both steady-state and time-resolved spectroscopies.

Properties of Ti-oxide thin films grown in reactive magnetron sputtering with self-heating target

Titanium dioxide thin films have been synthetized by magnetron sputtering in two configurations: using a classical cooled target (cold configuration) or allowing the target temperature to rise under ion bombardment (hot target configuration). In hot configuration, the heated target emits radiations (especially infrared ones) which affect the thin film growth. The target is pure titanium sputtered in presence of argon and dioxygen gases. The crystalline quality, morphology and structure of thin films have been studied on two substrates: thermally grown SiO2 (500 nm)/Si and c-cut sapphire. X-ray diffraction analyses revealed that anatase phase is mainly obtained in both configurations. Texture factors evidenced different main orientations: in cold target the anatase (004) peak tends to be preferred, whereas when a hot target is used, the (112) family plane is furthered. Microscopy analyses showed that the morphology changed depending on the configuration, which could be attributed to an increase of the adatom mobility at the substrate when the target is hot. Optical transmission measurements performed on titanium dioxide thin films deposited onto sapphire substrates showed that optical band gaps may be tuned depending on the configuration used during deposition.

Study of ergocalciferol and cholecalciferol (Vitamin D): Modeled optical properties and optical detection using absorption and Raman spectroscopy

The task of assembling and calculating spectrally significant lines of Vitamin D2 and D3 is related to a wider goal of establishing if it is possible to develop non-invasive optical sensors for these substances present at concentrations on the order of tens of nmol/L. Such a non-invasive in vivo sensor would be helpful for medical considerations, among others, related to multiple sclerosis prevention, reduced risk of mortality in D3-treated acute in-patients admitted with COVID 19, systemic infection, acute respiratory tract infections, including epidemic influenza, community-acquired pneumonia at concentrations <50nmol/L(<20ng/mL), dental health (90-100nmol/L) of 25(OH) D, general health and others. Currently, to determine the concentration of these substances, it is necessary to draw a sample from a vein in ambulatory settings and analyse the sample with the gold standard of mass spectroscopy or immunoassay. In this article Vitamin D optical properties are studied by density functional theory calculations, compared to reported data, and the new calculated and measured D2 and D3 optical absorption lines are presented, as well as the calculations compared with spectral measurements of optical transmission, FTIR ATR and Raman spectra.

Femtosecond nearly resonant self-focusing in gold nanorod colloids.

We evaluate the threshold power for self-focusing in gold nanorod colloids of varying concentration by a power limiting method in the femtosecond filamentation regime. The pulses are tuned near the longitudinal plasmon peak of the nanorods, leading to saturation of linear absorption and reshaping of the particles. We evaluated the last two effects by optical transmission measurements and spectroscopic analysis and estimated that considerable particle deformation does not occur before the collapse of the beam. We performed numerical simulations based on the experimental results, and evaluated only a subtle, monotonically increasing enhancement of the nonlinear refractive index of the host material (water) as the nanoparticles concentration increases. The role of higher-order contributions is discussed. Our work provides an alternative characterization approach of ultrafast nonlinearities in absorbing media. It further emphasizes that self-focusing of intense femtosecond pulses in gold nanocomposites is hampered by the ultrafast modulation of the susceptibility of the metal.

Field-induced deformation of ferromagnetic soft nanocomposites

Uniaxial ferromagnetic Ni nanorods were prepared by the anodic aluminum oxide (AAO) template method. Reversible magnetization changes, measured perpendicular to the texture axis, were analyzed in terms of the Stoner–Wohlfarth model (SW). Using empirical model parameters, a quantitative and consistent description of the orientation- and field-dependent magnetic torque per particle was achieved. The model was extended (eSW) to take into account the local rotation of the magnetic nanorods in a soft-elastic matrix. The nanorods were characterized regarding their size, using transmission electron microscopy (TEM), their magnetic moment and colloidal volume fraction, determined from static field-dependent optical transmission (SFOT) measurements, and their rotational shape factor, obtained from oscillating field-dependent optical transmission (OFOT). The eSW-model was used in the simulation of simple bending and torsion of thin composite filaments. These simulations were compared with experimental results with the focus on the effect of finite magnetic anisotropy and local elastic rotation on the field-induced deformation of soft nanocomposites. The high sensitivity of thin filaments enabled the investigation of torque-induced deformation at nanorod volume density as low as 10−4 at which particle-particle interactions were negligible. In addition, reprogramming of the magnetic texture by magnetization reversal and the resulting modification in the deformation pattern was investigated.

Wavelength tunable Q-switched Er-doped fiber laser based on ZrSe2

We demonstrated a passively Q-switched Er-doped fiber laser based on the ZrSe2/PVA film. Here, the layer structure ZrSe2 platelets were produced by the liquid-phase exfoliation method. By means of nonlinear optical transmittance measurement, the modulation depth and saturation intensity of the ZrSe2/PVA SA were 31% and 4.75 MW/cm2, respectively. The Q-switched pulses revealed the highest repetition rate and pulse energy around 43.7 kHz and 139.8 nJ with the pump power at 346 mW. Based on the invisible filter, we produced the wavelength-tunable and dual-wavelength Q-switched pulses after insertion of the in-line polarizer inside the cavity. Through the proper adjustment of the polarization controller, a tuning wavelength of from 1544.3 to 1563.5 nm, a tuning range of around 19.2 nm, and the smallest tuning interval of around 1 nm have been achieved.

Influence of nanostructured SnS thin films for visible light photo detection

SnS thin films were deposited onto glass substrates with different substrate temperature of 50 °C, 100 °C, 150 °C and 200 °C by vacuum thermal evaporation at 10 −5 Torr using prepared SnS powder sample as evaporated targets. The structural, electrical and optical properties of substrate temperature influenced SnS films were studied using standard characterization techniques. The X-ray diffraction (XRD) showed that the deposited films are of orthorhombic crystal structure and are polycrystalline in nature. Energy dispersive spectroscopy (EDS) revealed the presence of Sn and S elements in the deposited film and its stoichiometry. Raman studies confirmed the formation of orthorhombic phase SnS films. The optical properties such as film thickness (d), absorption coefficient (α), optical band gap (E g ), refractive index (n) and extinction coefficient (k) of the deposited thin films are estimated from the optical transmittance measurements. The optical band gap values were found to be in the range of (1.843–2.075 eV). The visible photoresponsivity and specific detectivity of the films also increased with increasing the substrate temperature. • Nanostructured SnS thin films were deposited with varying substrate temperature. • Photoresponsivity and specific detectivity increases with substrate temperature. • 200 °C substrate temperature film shown relatively enhanced visible light photodetection than room temperature (RT) film.

Twist-bend nematics and heliconical cholesterics: a physico-chemical analysis of phase transitions and related specific properties

ABSTRACT Certain nematic liquid crystals, for example, those formed by banana-shaped molecules, can exhibit a low-temperature twist-bend nematic (Ntb) phase. Upon addition of chiral dopants, a chiral version of the twist-bend phase (N*tb) can be observed below the conventional chiral nematic (N*) phase, while under electric field the N* phase is transformed into a specific state known as ‘oblique helicoidal cholesteric’. In this work, we have studied the well-known Ntb-forming system CB7CB:CB6OCB with addition of 5CB and chiral dopants (ChDs) using optical microscopy, differential scanning calorimetry (DSC), and measurements of temperature-dependent optical transmission using optical microscopy. Effects of 5CB and different chiral dopants (of steroid or non-steroid nature) upon thermal stability of Ntb phase were analysed, and selective reflection in the visible range could be observed in the N* phase with a sufficiently high ChD content. As a peculiar feature, sharp unwinding of the cholesteric helix was observed at lower temperatures when approaching the N*tb phase, which appears to be similar to the helix unwinding close to the smectic-A transition.