Infrared Reflectivity Measurements Research Articles

Towards non-invasive Wilson’s disease progression monitoring based on corneal copper content

Abstract Patients suffering from Wilson’s disease accumulate copper in their body. Copper load may become visible as Kayser-Fleischer (KF) rings - colorful copper-sulfur granules in the base of the cornea. Reoccurrence of KF rings in patients under anti-copper medication may be a sign for ineffective treatment. This work proposes a hand-held sensing system based on infrared reflectivity measurement of the cornea as a potential method for regular at-home progression monitoring. The intensity of the LEDs used is safe for operation on the human eye. As proof of concept, reflectivity was measured when placing the sensor onto samples of white paper that had copper tape of different sizes centered within the sensitive area. Further, reflectivity was determined for different solutions of copper sulfate in saline that were poured into adapter bowels fitting the sensor head, with Cu2+ concentrations of the samples deducted from literature. While the prototype system can be used to differentiate between two copper strips of 6 and 12 mm2 or larger, a different measuring principle would be needed to also determine the concentration of copper sulfate solutions. Since these two in-vitro models cannot fully represent the complex in-vivo molecular conditions of patients’ corneas, additional measurements on patients’ eyes are necessary to evaluate the potential of the proposed sensing system.

Revealing intermolecular coupling effects on vibrational spectra with infrared-reflectance absorbance analysis of perylene diimide thin films

Intermolecular interactions govern the optical and electronic properties of organic semiconductor thin films. Optimizing the function of molecular devices such as organic solar cells and light emitting diodes relies on understanding structural effects in a heterogeneous film environment. Because organic thin films are typically more disordered than inorganic crystalline semiconductors, advanced techniques are often needed to sufficiently characterize these materials. However, polarized infrared reflectance measurements are a benchtop method that can provide well-resolved vibrational spectra with specificity in their molecular orientation. By using infrared reflectance-absorbance spectroscopy (IRRAS) we relate the effects of intermolecular packing geometry on thin film vibrational spectra of perylene diimide (PDI), a prototypical molecular semiconductor. We analyze a suite of PDIs with differing sidechain substitutions, which adopt distinct crystal packing arrangements in thin films, by comparison of the reflectance spectra to isotropic KBr mixtures. We observe differences in the degree of Davydov splitting as a function of displacement along the short and long molecular axes and the π-π stacking distance that are evident in either the symmetric or anti-symmetric CO stretching frequencies of the solid. The four PDIs also display changes in relative intensity between the two modes that indicate different average molecular orientations.

One-Way Optical Waveguide Realized by Edge Modes of Topological Photonic Crystals

A one-way optical waveguide was realized on the boundary between two types of photonic crystals with different topological properties, which were demonstrated by high-resolution infrared reflection measurements.

Body composition of female office workers compared with infrared reflection measurement, bioimpedance analysis and calipermetry

There are currently many different anthropometric methods for determining the individual body fat percentage, as well as almost as many variants of bioelectric impedance analysis (BIA) and only a single method of infrared reflection measurement (IR) as easily available methods of field research.
 The present study aims at a simultaneous comparison between calipermetry, IR and BIA. In particular, the question which measurement method could be used as an equivalent method in the event of failure of BIA or IR is investigated.
 The sample group consisted of 121 female office workers (average age 32.5 ± 9.4 years, average height 164.5 ± 6.3 cm and average weight 60.3 ± 6.8 kg), from the Rhine-Main area.
 The measurements were previously scheduled and mostly carried out during the lunch break. For anthropometry, 13 skin fat folds were measured with the Accu® Measure Caliper, thigh circumference with a measuring tape, the height with a height measuring device and the body mass on the weight scale. Subsequently, an IR measurement (Futrex®) and a BIA (InBody®) were performed on the same subjects.
 The parameters of body fat percentage and total body water (in L) were examined.
 Statistical methods were correlation coefficients, Bland-Altman comparison and paired t-test for equivalence.
 For the women studied, the highest correlation coefficients were in the comparisons between the formulas according to Parízková and Brožek et al. (r = 0.82), as well as for Parízková and Siri (r = 0.82).
 The correlation coefficient for the IR vs. BIA comparison was r = 0.92.
 A key result of the present study was the finding that the investigated methods in a female study group could not be substituted in an equivalent way.

Characterization of starch structures isolated from the grains of waxy, sweet, and hybrid sorghum (Sorghum bicolor L. Moench).

In this study, starches were isolated from inbred (sweet and waxy) and hybrid (sweet and waxy) sorghum grains. Structural and property differences between (inbred and hybrid) sweet and waxy sorghum starches were evaluated and discussed. The intermediate fraction and amylose content present in hybrid sweet starch were lower than those in inbred sweet starch, while the opposite trend occurred with waxy starch. Furthermore, there was a higher A chain (30.93-35.73% waxy, 13.73-31.81% sweet) and lower B2 + B3 chain (18.04-16.56% waxy, 24.07-17.43% sweet) of amylopectin in hybrid sorghum starch. X-ray diffraction (XRD) and Fourier transform infrared reflection measurements affirm the relative crystalline and ordered structures of both varieties as follows: inbred waxy > hybrid waxy > hybrid sweet > inbred sweet. Small angle X-ray scattering and 13C CP/MAS nuclear magnetic resonance proved that the amylopectin content of waxy starch was positively correlated with lamellar ordering. In contrast, an opposite trend was observed in sweet sorghum starch due to its long B2 + B3 chain content. Furthermore, the relationship between starch granule structure and function was also concluded. These findings could provide a basic theory for the accurate application of existing sorghum varieties precisely.

Design and characterization of a pyroelectric detector based on three-dimensional structured hafnium oxide thin films

Pyroelectric detectors are used for gas analysis and flame detection because of their fast response and excellent performance. Most pyroelectric devices are based on monocrystalline lithium tantalate or pyroelectric lead zirconate titanate thin films deposited on a silicon (Si) substrate. In comparison, recently discovered pyroelectric-doped hafnium oxide (HfO2) offers the possibility of manufacturing completely complementary metal-oxide-semiconductor (CMOS)-compatible devices on large Si wafers. This is a promising approach to simplifying mass production of the sensor element and realizing new sensor structures with a high performance. Si substrates were structured with trenches and filled with thin-doped HfO2 layers by atomic layer deposition to multiply the pyroelectric current responsivity. An effective pyroelectric coefficient of up to 1300 μC / m2 / K was measured. Micromechanical structuring of the 6-in Si wafers was used to improve the thermal conversion of the sensor element. The applied plasmonic absorbers increase the infrared light absorption to >80 % for the spectral range of 3 to 5 μm, which was determined using Fourier transform infrared reflection measurements. In the first step, the performance of the sensor element was evaluated with an analog transimpedance amplifier with a feedback resistance of 5 GΩ. A specific detectivity D * > 1 · 107 cm√Hz / W was measured for the frequency range of 1 to 10 Hz. In addition, an application-specific integrated circuit was designed for the electrical signal conditioning to build a fully CMOS-compatible pyroelectric detector. It offers a simple to manufacture, flexible configuration, and digital communication interface with a signal-to-noise performance close to analog detectors. We present the measurement results of different sensor elements and detector types.

Evolution of the optical response of the magnetic topological insulators Mn( Bi1−xSbx)2Te4 with Sb content

MnBi$_2$Te$_4$ is a promising representative of intrinsic antiferromagnetic topological insulators, which could enable rare quantum mechanical effects like the quantum anomalous Hall effect. Especially at low temperatures, numerous studies have been reported, demonstrating the great potential of this compound in the magnetically ordered state below $T_{\mathrm{N}}$. Among recent findings, the alloy compound Mn(Bi$_{1-x}$Sb$_x$)$_2$Te$_4$ has been suggested to be an interesting candidate for the realization of an ideal Weyl semimetal state. By exchanging Bi by Sb, the electronic structure is influenced in terms of a shift of the Fermi energy, and a decrease in the energy gap has been predicted. In this work, we investigate and compare the optical conductivity of Mn(Bi$_{1-x}$Sb$_x$)$_2$Te$_4$ single crystals with various Sb doping levels $x$ by infrared reflectivity measurements. We observe a big impact of the Sb content on the low-energy excitations characterizing the metallic state of our samples. Different $x$=0.26 crystals show significant differences in their optical response and also a strong position dependence. The findings are compared to the recently reported optical conductivity spectrum of the pure compound MnBi$_2$Te$_4$.

Strong modulation of carrier effective mass in WTe2 via coherent lattice manipulation

The layered transition-metal dichalcogenide WTe2 is characterized by distinctive transport and topological properties. These properties are largely determined by electronic states close to the Fermi level, specifically to electron and hole pockets in the Fermi sea. In principle, these states can be manipulated by changes to the crystal structure. The precise impact of particular structural changes on the electronic properties is a strong function of the specific nature of the atomic displacements. Here, we report on time-resolved X-ray diffraction and infrared reflectivity measurements of the coherent structural dynamics in WTe2 induced by femtosecond laser pulses excitation (central wavelength 800 nm), with emphasis on a quantitative description of both in-plane and out-of-plane vibrational modes. We estimate the magnitude of these motions, and calculate via density functional theory their effect on the electronic structure. Based on these results, we predict that phonons periodically modulate the effective mass of carriers in the electron and hole pockets up to 20%. This work opens up new opportunities for modulating the peculiar transport properties of WTe2 on short time scales.

Concomitant formation of a pseudogap with the β−to−β′ structural phase transition in melt-quenched As2Te3

${\mathrm{As}}_{2}{\mathrm{Te}}_{3}$ is a chalcogenide with many polymorphic phases. Of current interest are the $\ensuremath{\beta}$ and ${\ensuremath{\beta}}^{\ensuremath{'}}$ phases which have been investigated primarily in the context of their close relationship to the isostructural topological insulator ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$. The $\ensuremath{\beta}$-to-${\ensuremath{\beta}}^{\ensuremath{'}}$ phase transition of ${\mathrm{As}}_{2}{\mathrm{Te}}_{3}$ exhibits a large anomaly in the resistivity that has remained unexplained. In this work we have measured the electronic transport properties of this phase transition in melt-quenched ${\mathrm{As}}_{2}{\mathrm{Te}}_{3}$ via dc resistivity and infrared reflectivity measurements. A sigmoidal fit has been used to describe the general behavior of the resistivity curves over a wide temperature range in order to characterize how hysteresis affects the phase transition anomaly. The optical measurements have identified the formation of a concomitant pseudogap of magnitude $\ensuremath{\approx}100\phantom{\rule{4pt}{0ex}}\mathrm{meV}$ affecting approximately $25%$ of the carriers. Charge density wave order is compatible with the formation of a partial gap as well as the observation of thermal hysteresis, suggesting it could be responsible for the $\ensuremath{\beta}\text{\ensuremath{-}}{\ensuremath{\beta}}^{\ensuremath{'}}$ transition in melt-quenched ${\mathrm{As}}_{2}{\mathrm{Te}}_{3}$.

VO2 sprayed cementitious materials for thermochromic building envelopes

The research on smart building envelopes is urgently needed to respond the requirements of energy efficient buildings. For that purpose, this paper studies the development of innovative thermochromic cementitious materials based on VO2. The VO2 powder is added on the surface of cement based materials at early hydration stages by spraying an aqueous VO2 dispersion. The spraying was done on cement paste surfaces after different times since the paste compaction (between 0 and 120 min). The suitability of this method has been positively proven by microstructural characterization (X-ray diffraction and scanning electron microscopy analyses) and near infrared reflectance measurements. This has been indicated by the proper integration of the VO2 powder in the cementitious matrix and the structural and chemical stability of the thermochromic VO2(M) phase. The results have also indicated that the optimal time to perform the spraying should be lower than 1 h since the compaction. Moreover, the reflectance modulation of the samples was shown to be maximized with the increasing VO2 concentration at the sample’s surfaces, and it was limited by the reflectance modulation of the powder to a 3.5 %. Finally, preliminary durability tests have proven that the thermochromic properties remain unchanged after exposure to outdoor conditions. These results open a field of research to optimize the thermochromic modulation by controlling the powder properties and concentration to achieve a significant impact of this smart optical behavior on the solar energy management in building envelopes.

Structural Analysis of Injection-Molded Polyoxymethylene Treated Below a Melting Point Using Field-Emission Scanning Electron Microscopy and Infrared Spectroscopy.

The heat treatment of an injection-molded polyoxymethylene slightly below the melting point and subsequent isothermal treatment at 130°C were performed. The polyoxymethylene structure was examined using field-emission scanning electron microscopy and polarization infrared reflection measurements. After the heat treatment, a significant change in the surface morphology was observed, and the reflection spectrum derived from the polariton in the injection direction also changed dramatically. Since the reflection spectrum in the injection direction contains the reflection component of the perpendicular direction and vice versa, the polarization spectra of both directions can be calculated consistently. The mixing ratio of each crossed component and the pure relative permittivity both parallel and perpendicular to the main-chain direction were determined using the oscillator model. The heat treatment reduced the ratio of the perpendicular component and increased the order structure until just before melting. The structural changes characterized by the two techniques, along with Raman spectroscopy and differential scanning calorimetry, are discussed.

Tuning of Reciprocal Plasmonic Metasurface Resonances by Ultra-Thin Conformal Coatings

Metamaterials, in the form of perfect absorbers, have recently received attention for sensing and light-harvesting applications. The fabrication of such metamaterials involves several process steps and can often lead to nonidealities, which limit the performance of the metamaterial. A novel reciprocal plasmonic metasurface geometry composed of two plasmonic metasurfaces separated by a dielectric spacer was developed and investigated here. This geometry avoids many common fabrication-induced nonidealities by design and is synthesized by a combination of two-photon polymerization and electron-beam-based metallization. Infrared reflection measurements revealed that the reciprocal plasmonic metasurface is very sensitive to ultra-thin, conformal dielectric coatings. This is shown here by using Al2O3 grown by atomic layer deposition. It was observed experimentally that incremental conformal coatings of amorphous Al2O3 result in a spectral red shift of the absorption band of the reciprocal plasmonic metasurface. The experimental observations were corroborated by finite element model calculations, which also demonstrated a strong sensitivity of the reciprocal plasmonic metasurface geometry to conformal dielectric coatings. These coatings therefore offer the possibility for post-fabrication tuning of the reciprocal plasmonic metasurface resonances, thus rendering this novel geometry as an ideal candidate for narrow-band absorbers, which allow for cost-effective fabrication and tuning.

Piezoelectric lattice vibrations in GaN at optical frequencies

At optical frequency range, lattice vibrations in piezoelectric crystal are associated with ionic polarizations. A relationship is formulated, based on classical dispersion theory, involving the dielectric constant (εjj) and the piezoelectric coefficient (djj) of wurtzite GaN. The relation is utilized to investigate the piezoelectric lattice vibrations in GaN at optical frequency, and a close agreement between the computed and the experimental value of djj is found. The study reveals that applications of piezoelectric nature of GaN could be extended to optical frequencies to generate phase coherent acoustic phonons to modulate thermal conduction. At optical frequencies there are no direct experimental methods exist at present for measurement of djj; however, the proposed relation can help to determine djj from infrared reflection measurements.

Body composition of male office workers compared by means of infrared reflection measurement, bioimpedance analysis and calipermetry

There are currently many different anthropometric methods to determine individual body fat percentage, as well as almost as many variants of bioelectric impedance analysis (BIA) and only a single method of infrared reflection measurement (IR) as easily feasible methods of field research. The present study aims at a simultaneous comparison between calipermetry, IR and BIA. In particular, the question which measurement method could be used as an equivalent method in the event of failure of the BIA or IR is investigated. The sample group consisted of 250 male office workers from the Rhine-Main area (average age 31.75 ± 9.16 years, average height 178.5 ± 6.93 cm and average weight 80.61 ± 9.42 kg). The measurements were previously scheduled and mostly carried out during the lunch break. For anthropometry, 13 skin fat folds were measured with the help of the Accu® Measure Caliper, thigh circumference with the help of a measuring tape, height with a height measuring device and body mass on the weight scale. Subsequently, an IR measurement (Futrex®) and a BIA (InBody®) were performed on the same subject. The parameters of body fat percentage and total body water (in litres) were examined. The statistical methods were correlation coefficients, Bland-Altman comparison and paired t-test for equivalence. For the men studied, the highest correlation coefficients were in the comparisons between the formulas according to Parízkova & Buzkova 1 and Parízkova & Buzkova 3 (r = 0.93), as well as for Parízkova & Buzkova 3 and Parízkova & Buzkova 4 (r = 0.96). The correlation coefficient for the IR vs. BIA comparison was only r = 0.56. A key result of the present study was the finding that certain methods cannot be substituted in an equivalent way, in fact only some calipermetric regression equations.

Photonic Crystals with a Defect Fabricated by Two-Photon Polymerization for the Infrared Spectral Range

One-dimensional photonic crystals composed of alternating layers with high- and low-density were fabricated using two-photon polymerization from a single photosensitive polymer for the infrared spectral range. By introducing single high-density layers to break the periodicity of the photonic crystals, a narrow-band defect mode is induced. The defect mode is located in the center of the photonic bandgap of the one-dimensional photonic crystal. The fabricated photonic crystals were investigated using infrared reflection measurements. Stratified-layer optical models were employed in the design and characterization of the spectral response of the photonic crystals. A very good agreement was found between the model-calculated and measured reflection spectra. The geometric parameters of the photonic crystals obtained as a result of the optical model analysis were found to be in good agreement with the nominal dimensions of the photonic crystal constituents. This is supported by complimentary scanning electron microscope imaging, which verified the model-calculated, nominal layer thicknesses. Conventionally, the accurate fabrication of such structures would require layer-independent print parameters, which are difficult to obtain with high precision. In this study an alternative approach is employed, using density-dependent scaling factors, introduced here for the first time. Using these scaling factors a fast and true-to-design method for the fabrication of layers with significantly different surface-to-volume ratios. The reported observations furthermore demonstrate that the location and amplitude of defect modes is extremely sensitive to any layer thickness non-uniformities in the photonic crystal structure. Considering these capabilities, one-dimensional photonic crystals engineered with defect modes can be employed as narrow band filters, for instance, while also providing a method to quantify important fabrication parameters.

Anomalous temperature dependence of the effective mass in p -type Bi2Te3

Infrared reflectance measurements have been carried on highly $p$-type ${\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ crystals over the broad temperature range from 10 to 650 K and their response function investigated. An anomalous nonmonotonous temperature dependence of the plasma edge frequency is observed---with a pronounced redshift and blueshift that appear above and below room temperature, respectively. Such behavior is explained in terms of the temperature evolution of the free carrier optical weight $N/{m}^{*}$ given by particular temperature dependence of the total carrier concentration $N$ (determined by transport measurements) and characteristic (optical) mass ${m}^{*}$. The effective mass strongly varies from ${m}^{*}=0.1{m}_{0}$ (${m}_{0}$ electron rest mass) at 10 K to ${m}^{*}=0.5{m}_{0}$ respective ${m}^{*}=0.9{m}_{0}$ at 650 K depending on the evaluating procedure. The interpretation is corroborated by complementary magnetotransport and magnetoreflectivity experiments.

Thickness-dependent optical properties of aluminum nitride films for mid-infrared wavelengths

We present a comparative study of optical properties of aluminum nitride (AlN) thin films with different thicknesses. The films with thicknesses ranging from 66 to 303 nm were deposited by reactive sputtering and plasma enhanced atomic layer deposition (PEALD). Permittivity was extracted from an ellipsometry and Fourier-transform infrared (FTIR) spectroscopy reflection measurements. Our particular focus is on the influence of the deposition method and the film thickness on the AlN dielectric function. Here, we show that both PEALD-deposited and sputtered AlN films exhibit a monotonic dependence of negative permittivity on their thickness for vast mid-IR wavelengths including the reststrahlen band around 11.5–15 μm (∼870–667cm−1). By structural analysis, it was shown that PEALD-deposited layers contain a lower amount of oxygen and have smoother surfaces than deposited by the sputtering technique. On the other hand, sputtered films have higher densities and crystallinity, which results in the higher background permittivity (ε∞). In FTIR spectra of the PEALD-deposited layers, two specific features are observed, which can be explained by a higher concentration of nitrogen due to nitrogen-rich plasma in the ALD process. Such peculiarities of the optical properties of AlN films should be taken into account in potential applications of this material for metamaterials and nanostructured systems.

Investigation of the metal-to-insulator transition of N-doped VO2(M1) thin films

This work reports the effect of nitrogen doping on the electrical and optical properties of VO2 thin films. An innovative method based on a VN target and an O2 ambient gas was used to synthesize N:VO2 films on quartz substrates using reactive pulsed laser deposition (RPLD). The doping percentage was determined by elastic recoil distribution (ERD) measurements, while temperature-dependent Raman spectroscopy as well as electrical resistivity and infrared reflectance measurements were performed to investigate the effect of N-doping on the insulator monoclinic-to-metallic tetragonal phase transition (IMT) of VO2. A small doping percentage around 0.7 at.% was achieved, inducing a decrease of the transition temperature TIMT from 68 °C to 50 °C, with slightly reduced electrical contrast ΔR and optical contrast ΔA. By comparing the volume fraction of monoclinic phase, obtained from Raman data to the volume fraction of metallic phase deduced concurrently from both electrical and optical measurements, the IMT in our nitrogen-doped VO2 films occurs through a percolation process.

Limits of the quasiharmonic approximation in MgO: Volume dependence of optical modes investigated by infrared reflectivity and ab initio calculations

Experimental and numerical investigation of phonon optical modes of MgO as a function of temperature (from 300 to 1400 K) and pressure (from 0 to 21 GPa) are here presented. Infrared reflectivity measurements were performed to probe energies and widths of the optical phonons, as well as of the multiphonon processes affecting the spectral shape, over a variation of the unit-cell volume exceeding 20%. Calculations within quasiharmonic approximation (QHA) account well for the volume dependence of the optical phonon energies observed in high-pressure experiments, while they fail at larger volumes, corresponding to the highest investigated temperatures. Moreover, QHA calculations more closely predict energies of transverse optical (TO) modes than those of longitudinal optical (LO) ones. This can be ascribed to known limitations in the modeling of the effective charges (${Z}^{*}$) and dielectric constant (${\ensuremath{\varepsilon}}_{\ensuremath{\infty}}$) that lead to an underestimation of the LO-TO splitting. Based on the comparison of our experimental and theoretical results, we propose an empirical analytical expression for ${{Z}^{*}}^{2}/{\ensuremath{\varepsilon}}_{\ensuremath{\infty}}$ as a function of the atomic cell volume. Density-functional perturbation theory including phonon-phonon scattering up to the third order of the lattice potential expansion is used to calculate phonon widths. These calculations reproduce and explain remarkably well the nontrivial volume dependence of both TO and LO phonons linewidths determined by the experiments.

Garnet Characteristics Associated with Jiama Porphyry-Skarn Cu Deposit 1# Skarn Orebody, Tibet, Using Thermal Infrared Spectroscopy

Field measurements of the thermal infrared (TIR) reflectance from drill hole samples proved to be an effective method to map variations in garnet species associated with hydrothermal alteration zonation of the Jiama porphyry-skarn Cu deposit 1# skarn orebody, Tibetan Plateau, China. The TIR mineral spectral information was combined with electron probe micro-analysis (EPMA) measurements to provide geological insights on effectively determining (a) garnet end components and providing a format for further research on the type and genesis of the deposit; (b) the significance of the characteristic spectrum of garnet to the variation of mineralization environment; (c) the relationship between the characteristic spectrum of garnet and Fe/Al content; (d) the garnet characteristic spectrum to the economic mineralization. The results suggest that garnet characteristics of the thermal infrared spectrum can be used as an indicator for skarn deposit prospecting.