Infrared Reflectance Spectra Research Articles

New Li3Ni2NbO6 microwave dielectric ceramics with the orthorhombic structure for LTCC applications

New Li3Ni2NbO6 (indexed as LNN) microwave dielectric ceramics were prepared by the conventional solid-state method. The phase composition, crystal structure, sintering characteristics, micro-structures, microwave dielectric properties, intrinsic factors and vibrational phonon modes were investigated. XRD results showed that LNN phase exhibit orthorhombic structure with Fddd (No. 70) space group. Rietveld refinement was applied to analyze the crystalline structure and the lattice parameters were obtained. On the basis of the chemical bond theory and lattice parameters, the bond ionicity, lattice energy, bond energy and coefficient of thermal expansion were calculated to evaluate the structural characteristics. NbO bonds played an important role in affecting the microwave dielectric proprieties of LNN ceramics. The results of Infrared reflectivity spectrum indicated that the absorptions of phonon oscillation played an important influence on the dielectric contribution of LNN ceramics. At the sintering temperature of 850 °C, excellent microwave dielectric properties of εr = 15.85, Q·ƒ = 19,860 GHz and τf = −15.45 ppm/°C were obtained for LNN ceramics. The excellent microwave dielectric properties and low sintering temperature of LNN ceramics made it a promising candidate for low temperature co-fired ceramics (indexed as LTCC) applications.

The 2013 FLEX—US Airborne Campaign at the Parker Tract Loblolly Pine Plantation in North Carolina, USA

The first European Space Agency (ESA) and NASA collaboration in an airborne campaign to support ESA’s FLuorescence EXplorer (FLEX) mission was conducted in North Carolina, USA during September–October 2013 (FLEX-US 2013) at the Parker Tract Loblolly Pine (LP) Plantation (Plymouth, NC, USA). This campaign combined two unique airborne instrument packages to obtain simultaneous observations of solar-induced fluorescence (SIF), LiDAR-based canopy structural information, visible through shortwave infrared (VSWIR) reflectance spectra, and surface temperature, to advance vegetation studies of carbon cycle dynamics and ecosystem health. We obtained statistically significant results for fluorescence, canopy temperature, and tower fluxes from data collected at four times of day over two consecutive autumn days across an age class chronosequence. Both the red fluorescence (F685) and far-red fluorescence (F740) radiances had highest values at mid-day, but their fluorescence yields exhibited different diurnal responses across LP age classes. The diurnal trends for F685 varied with forest canopy temperature difference (canopy minus air), having a stronger daily amplitude change for young vs. old canopies. The Photochemical Reflectance Index (PRI) was positively correlated with this temperature variable over the diurnal cycle. Tower measurements from mature loblolly stand showed the red/far-red fluorescence ratio was linearly related to canopy light use efficiency (LUE) over the diurnal cycle, but performed even better for the combined morning/afternoon (without midday) observations. This study demonstrates the importance of diurnal observations for interpretation of fluorescence dynamics, the need for red fluorescence to understand canopy physiological processes, and the benefits of combining fluorescence, reflectance, and structure information to clarify canopy function versus structure characteristics for a coniferous forest.

Temperature-dependent far-infrared reflectance of an epitaxial (BaTiO3)8/(SrTiO3)4 superlattice

Infrared reflectance spectra of the polar optic phonons in a [(BaTiO3)(8)/(SrTiO3)(4)](50) superlattice over the temperature range 8 to 650 K are reported. The spectra exhibit lattice vibration features typical of the perovskite constituents, BaTiO3 and SrTiO3. Using the effective medium approximation for multilayer systems and a fitting procedure, we were able to successfully simulate the infrared reflectivity of the superlattice structures and extract the parameters and dielectric functions of the phonons. When applied at varying temperatures, this approach provides the parameters of the zone-center polar phonons and their temperature dependence. Comparing these results with x-ray diffraction we identified some anomalies in phonon behavior related to the phase transitions that the superlattice undergoes.

A TSS classification study of ‘Rocha’ pear (Pyrus communis L.) based on non-invasive visible/near infra-red reflectance spectra

The study focuses on the application of machine learning techniques for classifying the internal quality of ‘Rocha’ Pear (Pyrus communis L.), i.e., the total soluble solids (TSS), using the non-invasive technique of visible/near infra-red reflectance spectroscopy. Six representative classifiers were evaluated under realistic experimental conditions. The classifiers include representatives of classic parametric (logistic and multiple linear regression), non-parametric distance based methods (K-nearest neighbors), correlation-based (partial least squares), ensemble methods (random forests) and maximum margin classifiers (support vector machines). The classifiers were assessed against metrics such as accuracy, Cohen's Kappa, F-Measure, and the area under the precision-recall curve (AUC) in a 10×10-fold cross-validation plan. For result analysis non-parametric statistical test of hypotheses were employed. A total of 4880 fruit samples from different origins, maturation states, and harvest years were considered. The main conclusion is that the maximum margin classifier outperforms all the others studied ones, including the commonly used partial least squares. The conclusion holds for both a reflectance spectrum with 1024 features and for a 128 subsample of these. An estimate of the out-of-sample performance for the best classifier is also provided.

Определение концентрации свободных электронов в n-InSb по спектрам отражения в дальней инфракрасной области с учетом плазмон-фононного взаимодействия

Определение концентрации свободных электронов в n-InSb по спектрам отражения в дальней инфракрасной области с учетом плазмон-фононного взаимодействия

Dielectric and phonon spectroscopy of Nb-doped Pb(Zr1-yTiy)O3-CoFe2O4 composites

Broad-band dielectric and phonon response of Nb-doped (1-x)Pb(Zr1-yTiy)O3-xCoFe2O4 composites with x = 10%–30% was investigated between 0.1 MHz and 100 THz. At room temperature, a broad distribution of relaxation times causes a constant dielectric loss below 1 GHz. Above room temperature, a strong Maxwell-Wagner relaxation process dominates below 1 GHz due to the conductivity of CoFe2O4 (CF). Two additional relaxation processes are seen between 1 GHz and 1 THz. The lower-frequency one, coming from domain wall motion, disappears above TC ≈ 650 K. The higher-frequency component slows down on heating towards TC, because it is the central mode, which drives the ferroelectric phase transition. Time-domain THz transmission and infrared reflectivity spectra reveal a mixture of polar phonons from both ferroelectric Nb-doped Pb(Zr,Ti)O3 (PZTN) and magnetic CoFe2O4 (CF) components, while the micro-Raman scattering spectra allow to study phonons from both components separately. Similar temperature behavior of phonons as in the pure PZTN and CF was observed. While in CoFe2O4 the Raman-active phonons gradually reduce their intensities on heating due to increasing conductivity and related reduced Raman-scattering volume, some phonons in PZTN disappear above TC due to change of selection rules in the paraelectric phase. Like in the pure Pb(Zr,Ti)O3, the soft phonon and central modes were also observed.

A Comparison Between Three Sparse Unmixing Algorithms Using a Large Library of Shortwave Infrared Mineral Spectra

The comparison described in this paper has been motivated by two things: 1) a “spectral library” of shortwave infrared reflectance spectra that we have built, consisting of the spectra of 60 nominally pure materials (mostly minerals, but also water, dry vegetation, and several man-made materials) and 2) the needs of users in the mining industry for the use of fast and accurate unmixing software to analyze tens to hundreds of thousands of spectra measured from drill core or chips using HyLogging instruments, and other commercial reflectance spectrometers. Individual samples are typically a mixture of only one, two, three, or occasionally four minerals. Therefore, in order to avoid overfitting, a sparse unmixing algorithm is required. We compare three such algorithms using some real world test data sets: full subset selection (FSS), sparse demixing (SD), and L1 regularization. To aid the comparison, we introduce two novel aspects: 1) the simultaneous fitting of the low frequency background with mineral identification (which provides greater model flexibility) and 2) the combined fitting being carried out using a suitably defined Mahalanobis distance; this has certain optimality properties under an idealized model. Together, these two innovations significantly improve the accuracy of the results. FSS and L1 regularization (suitably optimized) produce similar levels of accuracy, and are superior to SD. Discussion includes possible improvements to the algorithms, and their possible use in other domains.

Exploring optoelectronic properties and mechanisms of layered ferroelectric K4Nb6O17 nanocrystalline films and nanolaminas

Two-dimensional layered K4Nb6O17 (KN) was easily formed as a secondary phase caused by the volatilization of alkali metal ions, when preparing ferroelectric KxNa1−xNbO3 based ceramics and films. In this work, it was believed that KN film is with weak ferroelectricity and has a little effect on the ferroelectric properties of KxNa1−xNbO3 based films. Moreover, temperature dependent (77–500 K) dielectric functions of KN film have been firstly extracted by fitting ellipsometric spectra with the Adachi dielectric function model and a four-phase layered model. The high-frequency dielectric constant linearly increases and optical band gap slightly decreases with increasing the temperature. We also research its photoelectrochemical properties and its application in high-efficient light-induced H2 evolution. In addition, X-ray photoelectron spectroscopy, Raman scattering, temperature dependent transmittance and infrared reflectance spectra, and first-principles calculation were conjointly performed to further reveal the intrinsic optoelectronic features and relevant mechanisms of KN.

Visible/shortwave near infrared spectroscopy and hyperspectral scattering for determining bulk density and particle size of wheat flour

Particle size and bulk density are two important fundamental properties of food powder that directly affect processing and final product quality. The objective of this study was to evaluate and compare two optical sensing methods, i.e. visible/shortwave near infrared spectroscopy and hyperspectral scattering, for bulk density determination and particle size classification of wheat flour. Hyperspectral scattering images over the spectral region of 500–1000 nm and visible/shortwave near infrared reflectance spectra covering the spectral region of 400–1000 nm were acquired for 474 wheat flour samples. Partial least squares regression and discriminant analysis models for visible/shortwave near infrared spectra and mean spectra extracted from the hyperspectral scattering profiles were developed for determining the bulk density and classifying the particle size, of wheat flour samples. Hyperspectral scattering gave much better prediction results for bulk density, with the r2 (the coefficient of determination for prediction) value of 0.87 and the root mean squares error of prediction value of 30.20 mg ml−1, compared with the r2 of 0.55 and root mean squares error of prediction of 57.13 mg ml−1 obtained by visible/shortwave near infrared spectroscopy. Moreover, hyperspectral scattering resulted in 98.2% classification accuracy for particle size, versus 96.8% by visible/shortwave near infrared spectroscopy. This research suggested that hyperspectral scattering is more suitable than visible/shortwave near infrared spectroscopy for bulk density determination and particle size classification of food powder.

Raman and infrared spectroscopic studies of LaTaTiO6 polymorphs

Abstract X-ray diffraction, Raman scattering and infrared spectroscopy were used to investigate the orthorhombic-to-monoclinic polymorphic transformation of LaTaTiO 6 ceramics, induced at high temperatures. For sake of comparison, Ln TaTiO 6 ceramics for various lanthanides ( Ln ), including La, were prepared by the solid-state reaction method. Phase-pure orthorhombic ( Pnma space group) and monoclinic ( C 2/ c space group) structures were obtained for LaTaTiO 6 at sintering temperatures of 1300 °C and 1400 °C, respectively. The Raman spectrum of the orthorhombic LaTaTiO 6 appeared to be very close to that of PrTaTiO 6 , which crystallizes within the aeschynite structure. Raman and infrared spectra of monoclinic LaTaTiO 6 ceramics are reported for the first time. Polarized Raman spectroscopy allowed determining (and assigning) all the non-polar modes of the material into the C 2/ c monoclinic phase. Infrared reflectivity spectra revealed the main polar modes that contribute to the dielectric response. The intrinsic dielectric parameters obtained by this procedure match well with those found by microwave techniques in ceramics prepared at relatively high sintering temperatures – which must belong to the described monoclinic structure.

First principles study of the vibrational, dielectric and thermal properties of SrClF

SrClF is an important optical crystal and has many technological applications. In this work, vibrational, dielectric and thermal properties of SrClF were investigated by density functional perturbation calculation. The calculated Born effective charges are close to their nominal ionic charges, revealing the ionic characteristic of SrClF. Group theory analysis indicates that there are two E u and A 2u infrared modes at the Brillouin zone center of SrClF. The LO-TO splitting of these infrared modes were calculated and discussed and their vibrational modes were sketched. Static dielectric constants were studied, which show that SrClF has a larger ionic dielectric contribution than its electrons. Its birefringence was calculated and the infrared reflectance spectra were simulated, which can be used to explain the experimental findings. Based on the computed phonon dispersion curves, the lattice heat capacity, the Gruneisen parameter and the thermal expansion coefficient as functions of temperature were predicted.

Structural and optical properties of silicon-carbide nanowires produced by the high-temperature carbonization of silicon nanostructures

Silicon-carbide (SiC) nanowire structures 40–50 nm in diameter are produced by the high-temperature carbonization of porous silicon and silicon nanowires. The SiC nanowires are studied by scanning electron microscopy, X-ray diffraction analysis, Raman spectroscopy, and infrared reflectance spectroscopy. The X-ray structural and Raman data suggest that the cubic 3C-SiC polytype is dominant in the samples under study. The shape of the infrared reflectance spectrum in the region of the reststrahlen band 800–900 cm–1 is indicative of the presence of free charge carriers. The possibility of using SiC nanowires in microelectronic, photonic, and gas-sensing devices is discussed.

Phase structural transition and microwave dielectric properties in isovalently substituted La1−xLnxTiNbO6 (Ln=Ce, Sm) ceramics

Aeschynite-type La1−xLnxTiNbO6 (Ln=Ce, Sm, x=0–1) ceramics were prepared via a conventional solid state method. Analysis of X-ray diffraction, Raman, infrared reflectivity spectra and the microstructures revealed a series of composition-induced phase evolution in sequence: monoclinic→coexistence of monoclinic and orthorhombic→orthorhombic structure, i.e. M→M+O→O. The critical compositions of distinguishing the dominant M or O phase were x=0.15 in La1−xCexTiNbO6 and x=0.10 in La1−xSmxTiNbO6 ceramics, exactly corresponding to the average ionic radius of rare earth ions (IR) ~1.027Å. The crystal structure and microwave dielectric properties of RETiNbO6 (RE=rare earth) ceramics strongly depended on IR. Near-zero τf was achieved in the Ce-sample with x=0.153 (εr=28.9, Q×f=17,275GHz@6.54GHz) as well as in the Sm-sample with x=0.098 (εr=28.2, Q×f=19,186GHz@6.78GHz). Eventually, RETiNbO6 would form O euxenite (-τf), O aeschynite (+τf), and M aeschynite (-τf), as IR<0.945Å, 0.945Å <IR<1.027Å, and 1.027Å<IR<1.032Å, respectively. The infrared reflectivity study also confirmed that the structural phonon oscillations in the infrared region dominated the dielectric performance in the microwave region for this system.

Spin-phonon coupling in epitaxialSr0.6Ba0.4MnO3thin films

Spin-phonon coupling is investigated in epitaxially strained $\mathrm{S}{\mathrm{r}}_{1\ensuremath{-}x}\mathrm{B}{\mathrm{a}}_{x}\mathrm{Mn}{\mathrm{O}}_{3}$ thin films with perovskite structure by means of microwave (MW) and infrared (IR) spectroscopy. In this work we focus on the $\mathrm{S}{\mathrm{r}}_{0.6}\mathrm{B}{\mathrm{a}}_{0.4}\mathrm{Mn}{\mathrm{O}}_{3}$ composition grown on ${(\mathrm{LaAl}{\mathrm{O}}_{3})}_{0.3}{(\mathrm{S}{\mathrm{r}}_{2}\mathrm{AlTa}{\mathrm{O}}_{6})}_{0.7}$ substrate. The MW complex electromagnetic response shows a decrease in the real part and a clear anomaly in the imaginary part around 150 K. Moreover, it coincides with a $17%$ hardening of the lowest-frequency polar phonon seen in IR reflectance spectra. In order to further elucidate this phenomenon, low-energy muon-spin spectroscopy was carried out, signaling the emergence of antiferromagnetic order with N\'eel temperature (${T}_{N}$) around 150 K. Thus, our results confirm that epitaxial $\mathrm{S}{\mathrm{r}}_{0.6}\mathrm{B}{\mathrm{a}}_{0.4}\mathrm{Mn}{\mathrm{O}}_{3}$ thin films display strong spin-phonon coupling below ${T}_{N}$, which may stimulate further research on tuning the magnetoelectric coupling by controlling the epitaxial strain and chemical pressure in the $\mathrm{S}{\mathrm{r}}_{1\ensuremath{-}x}\mathrm{B}{\mathrm{a}}_{x}\mathrm{Mn}{\mathrm{O}}_{3}$ system.

Infrared phonons as a probe of spin-liquid states in herbertsmithite ZnCu3(OH)6Cl2

We report on temperature dependence of the infrared reflectivity spectra of a single crystalline herbertsmithite in two polarizations—parallel and perpendicular to the kagome plane of Cu atoms. We observe anomalous broadening of the low frequency phonons possibly caused by fluctuations in the exotic dynamical magnetic order of the spin liquid.

Resonance Raman Scattering in TlGaSe2 Crystals

The resonance Raman scattering for geometries Y(YX)Z and Y(ZX)Z at temperature 10 K and infrared reflection spectra in E∥a and E∥b polarizations at 300 K were investigated. The number of Aa (Ba) and Au (Bu) symmetry vibrational modes observed experimentally and calculated theoretically agree better in this case than when TlGa2Se4 crystals belong to D2h symmetry group. The emission of resonance Raman scattering and excitonic levels luminescence spectra overlap. The lines in resonance Raman spectra were identified as a combination of optical phonons in Brillouin zone center.

Conformer of the peroxynitrite ion formed under photolysis of crystalline alkali nitrates – cis or trans?

The optical and infrared reflectance spectra of the crystalline powders prepared by co-crystallization of caesium nitrate, nitrite, and peroxynitrite from alkali solution have been studied. We find that the trans conformer forms under photolysis of crystalline pure caesium nitrate. Under its dissolution the trans conformer transforms to the cis conformer.

Infrared reflection spectroscopy and optical constants of LiNbO3films on crystal substrates

We have measured infrared reflectivity spectra of thin lithium niobate films of nanometer thickness, grown by a pulsed laser deposition technique using KrF-excimer laser (λ=248 nm) on the single crystalline substrates (sapphire, MgO, NdGaO3 and SrTiO3). Using the dispersion analysis technique, we have calculated thicknesses and optical constants of the films. The phonon parameters of the substrates and films are obtained.

Infrared reflection spectra of the films of topological insulator Pb1-xSnxSe on the substrates ZnTe/GaAs

Infrared reflectivity spectra of the 700 nm thick topological insulator Pb 1-x Sn x Se films grown by the molecular beam epitaxy technique on ZnTe/GaAs substrates were studied. Using dispersion analysis of reflectivity spectra plasmon and phonon parameters for the samples under study were obtained.

Highly doped InP as a low loss plasmonic material for mid-IR region.

We study plasmonic properties of highly doped InP in the mid-infrared (IR) range. InP was grown by metal-organic vapor phase epitaxy (MOVPE) with the growth conditions optimized to achieve high free electron concentrations by doping with silicon. The permittivity of the grown material was found by fitting the calculated infrared reflectance spectra to the measured ones. The retrieved permittivity was then used to simulate surface plasmon polaritons (SPPs) propagation on flat and structured surfaces, and the simulation results were verified in direct experiments. SPPs at the top and bottom interfaces of the grown epilayer were excited by the prism coupling. A high-index Ge hemispherical prism provides efficient coupling conditions of SPPs on flat surfaces and facilitates acquiring their dispersion diagrams. We observed diffraction into symmetry-prohibited diffraction orders stimulated by the excitation of surface plasmon-polaritons in a periodically structured epilayer. Characterization shows good agreement between the theory and experimental results and confirms that highly doped InP is an effective plasmonic material aiming it for applications in the mid-IR wavelength range.