Extra Absorption Peak Research Articles

Effects of NaCl and sucrose on the structure and thermal properties of microcrystalline starch‐glycerol monostearate complex

SummaryThe crystal structure and type, short‐range ordered structure, as well as thermal properties of microcrystalline starch‐glycerol monostearate complexes treated with different NaCl and sucrose concentrations, were investigated. The complexing index indicated that NaCl and sucrose are beneficial for the formation of starch complexes. Furthermore, starch complexes treated with NaCl and sucrose retained their V‐shaped crystal structures on the X‐ray diffraction patterns. Fourier transform infrared spectroscopy suggested that there were no extra absorption peaks, whilst Raman spectroscopy exhibited a more short‐range ordered structure with increasing NaCl and sucrose concentrations. Similarly, differential scanning calorimetry demonstrated an increase in the ΔH values from 8.67 J g−1 to 16.46 J g−1 (NaCl) and 14.88 J g−1 (sucrose). The results indicated that NaCl and sucrose at low concentrations could modulate the physicochemical properties of the complex. Consequently, there are many articles on starch complex, but my research focuses on the effect of small molecules such as salt and sugar on starch complex, which is conducive to expanding the application of starch and bringing inspiration to other scholars.

Acoustical performance of a wavy micro-perforated panel absorber

In this study, the sound absorption performance of a wavy micro-perforated panel absorber (WMPPA) is investigated. First, a numerical model is established to calculate the sound absorption coefficients of micro-perforated panel absorbers (MPPAs) under normal, oblique, and random incidences. Subsequently, the proposed model is validated using an existing theoretical formula. After that, the acoustical properties of a WMPPA are explored and then compared with those of flat and corrugated micro-perforated panel absorbers (FMPPAs, CMPPAs). It is observed that the normal sound absorption curve of the WMPPA shifts to a lower frequency range compared with those of CMPPA and FMPPA, which is promising for the control of low-frequency noise. Besides, the sound absorption performance of the WMPPA at the dips is considerably improved, which is favourable for the reduction of broadband noise. Modal analysis shows that, apart from the resonant mode, the adjacent non-resonating modes are also excited, which enhances the performance. Moreover, the WMPPA exhibits the properties of a multiple-layered MPPA, and extra sound absorption peaks are observed within the middle- to high-frequency range. In addition, a parametric study is conducted to explore the influence of the corrugation depth and offset distance on the sound absorption performance of the WMPPA. The calculated results demonstrate that the proposed WMPPA is suitable for low-frequency and broadband noise control. Furthermore, a compact WMPPA with a high random sound absorption coefficient is obtained following an optimization scheme. Finally, the sound absorption coefficients of the MPPAs under normal plane-wave incidence are obtained experimentally using an impedance tube. The measurement results agree well with the simulation results, validating the proposed model and verifying some of the numerical findings.

Ex vivo sensing and imaging of corneal scar tissues using terahertz time domain spectroscopy

Pulsed terahertz (THz) broadband spectroscopy and imaging were applied to investigate ex vivo rabbit corneal scar tissues. Scars with different depths and densities were created by laser ablation on four corneal samples while two corneal samples untouched were used as control. The THz time-domain spectroscopy and reconstructed images illustrated the scar tissue density and gave out depth variation distribution profiles. Calculated absorption coefficient spectra displayed extra absorption peaks compared with control corneas and refractive index spectra showed the optical properties changed at the corneal scar locations. THz spectroscopy and imaging demonstrated adequate contrast in reviewing the scar densities and locations and showed potential applications in depicting spatial distribution and composition changes of corneal scars.

Two-photon resonances, ac Stark splittings, and shifts of the resonance peaks in Doppler free absorptive lineshapes of a double-lambda type four level system

Under Doppler free condition and by using semiclassical approach, a double-lambda type four-level system coupled to two electromagnetic fields are investigated. The coupled optical Bloch equations involving the density matrix elements in steady state are solved numerically to investigate the signal lineshapes as the function of signal detuning and pump Rabi-frequencies. The on-resonant pump leads to dynamic Stark splitting. The dent in the absorption lineshape is exhibited for off-resonant pump and is a signature of two-photon resonances. The appearance of extra absorption and emission peaks in the computed lineshapes are attributed by the nonlinear polarizations and hence the spontaneously generated coherences.

Simple Way to Detect Trp to Tb3+ Resonance Energy Transfer in Calcium-Binding Peptides Using Excitation Spectrum.

The sensitized phosphorescence of Tb3+ is often used for the assessment of the ion binding to various chelating agents or natural Ca2+-binding proteins. The detailed structure of the Tb3+ excitation spectrum gives a special advantage for analysis; any extra absorption peak can be easily detected which provides simple and direct evidence that resonance energy transfer occurs. By employing the Tb3+ phosphorescence, we characterized the Ca2+-binding sites of two related peptides - self-processing module of the FrpC protein produced by bacterium Neisseria meningitidis and the shorter peptide derived from FrpC. Here we show that while the increase of direct Tb3+ excitation at 243nm generally corresponds to Tb3+ association with various binding sites, the excitation enhancement in the 250-300nm band signifies Tb3+-binding in the close proximity of aromatic residues. We demonstrate that the presence of resonance energy transfer could be easily detected by inspecting Tb3+ excitation spectra. Additionally, we show that the high level of specificity of Tb3+ steady state detection on the spectral level could be reached at very low Tb3+ concentrations by taking advantage of its narrow phosphorescence emission maximum at 545nm and subtracting the averaged autofluorescence intensities outside this peak, namely at 525 and 565nm.

Characterizing polymorphism and crystal transformation of polylactide by terahertz time-domain spectroscopy

Terahertz time-domain spectroscopy (THz-TDS), which has been proved to show promising application in complex polymer systems, was employed to investigate the polymorphism phenomenon and crystal transformation of polylactide (PLA) in this study. The THz-TDS shows sensitive response on the crystal structure. The α'-form, α-form and stereocomplex crystals exhibit absorption peaks of lattice vibration at 1.82, 2.01 and 2.09 THz, respectively. THz-TDS has no direct chirality identification on the difference between poly (d-lactide) (PDLA) and poly(l-lactide) (PLLA). However, the PLA stereocomplex shows an extra and distinctive absorption peak at 1.43 THz compared with homo-PLA, and the peak was proved to be stemmed from the collective vibration of L-lactic unit and D-lactic unit pairs connecting by hydrogen bonds. This is the first time that THz-TDS has been proved to be of great potential in identification of polymer stereocomplex crystal. Also, the α'→α crystal transformation of PLA were intuitively investigated at 120 °C using THz-TDS, while the transformation rate was quite slow.

Microwave properties of ferromagnetic nanowire arrays patterned with periodic and quasi-periodic structures

Microwave properties of ferromagnetic nanowire arrays patterned with periodic and quasi-periodic structures were investigated in this study. The periodic and quasi-periodic structures were designed based on Fibonacci sequence and golden ratio. Ni nanowires arrays were electrodeposited in anodic aluminum oxide (AAO) templates with patterned Cu electrodes, and then the AAO templates were attached to the coplanar waveguide lines fabricated on quartz substrate for measurement. The S21 of both periodic and quasi-periodic structure-patterned Ni nanowire arrays showed an extra absorption peak besides the absorption peak due to the ferromagnetic resonance of Ni nanowires. The frequency of the absorption peak caused by the patterned structure could be higher than 40 GHz when the length and arrangement of the structural units were modified. In addition, the frequency of the absorption peak due to the quasi-periodic structure was calculated based on a simple analytical model, and the calculated value was consistent with the measured one. The experimental data showed that it could be a feasible approach to tune the performance of microwave devices by patterning ferromagnetic nanowires.

Equally efficient interlayer exciton relaxation and improved absorption in epitaxial and nonepitaxial MoS2/WS2 heterostructures.

Semiconductor heterostructures provide a powerful platform to engineer the dynamics of excitons for fundamental and applied interests. However, the functionality of conventional semiconductor heterostructures is often limited by inefficient charge transfer across interfaces due to the interfacial imperfection caused by lattice mismatch. Here we demonstrate that MoS(2)/WS(2) heterostructures consisting of monolayer MoS(2) and WS(2) stacked in the vertical direction can enable equally efficient interlayer exciton relaxation regardless the epitaxy and orientation of the stacking. This is manifested by a similar 2 orders of magnitude decrease of photoluminescence intensity in both epitaxial and nonepitaxial MoS(2)/WS(2) heterostructures. Both heterostructures also show similarly improved absorption beyond the simple superimposition of the absorptions of monolayer MoS(2) and WS(2). Our result indicates that 2D heterostructures bear significant implications for the development of photonic devices, in particular those requesting efficient exciton separation and strong light absorption, such as solar cells, photodetectors, modulators, and photocatalysts. It also suggests that the simple stacking of dissimilar 2D materials with random orientations is a viable strategy to fabricate complex functional 2D heterostructures, which would show similar optical functionality as the counterpart with perfect epitaxy.

Characterization of cocrystals formed by grinding amino acids through terahertz time-domain spectroscopy

In this paper, we used terahertz time-domain spectroscopy (THz-TDS) over a range of 0.3–2.5 THz to investigate the formation of solid-state cocrystals of amino acids, formed by grinding mixtures of two different kinds of amino acids. For comparison, we prepared dual-layer samples, combined by pressing two single-component pellets together without grinding. In the ground-mixture samples, some extra absorption peaks appeared, different from the characteristic peaks of the pure components, but these peaks did not appear in the dual-layer samples. Thus, these extra absorption peaks in the THz range are unique features of cocrystals. From our results, we believe that THz-TDS is a promising technique to characterize cocrystals.

Vibroacoustic properties of thin micro-perforated panel absorbers

This paper presents theoretical and experimental results on the influence of panel vibrations on the sound absorption properties of thin micro-perforated panel absorbers (MPPA). Measurements show that the absorption performance of thin MPPAs generates extra absorption peaks or dips that cannot be understood assuming a rigid MPPA. A theoretical model is established that accounts for structural-acoustic interaction between the micro-perforated panel and the backing cavity, assuming uniform conservative boundary conditions for the panel and separable coordinates for the cavity cross-section. This model is verified experimentally against impedance tube measurements and laser vibrometric scans of the cavity-backed panel response. It is shown analytically and experimentally that the air-frame relative velocity is a key factor that alters the input acoustic impedance of thin MPPAs. Coupled mode analysis reveals that the two first resonances of an elastic MPPA are either panel-cavity, hole-cavity, or panel-controlled resonances, depending on whether the effective air mass of the perforations is greater or lower than the first panel modal mass. A critical value of the perforation ratio is found through which the MPPA resonances experience a frequency "jump" and that determines two absorption mechanisms operating out of the transitional region.

Coupled mode analysis of thin micro-perforated panel absorbers

The prediction of the isolating properties of lightweight Micro Perforated Panels (MPP) is a subject that has been intensively studied due to their important applications in a wide range of areas such as building acoustics and the aeronautic, astronautic and automotive industries. MPPs have been mostly considered as rigid structures, accounting only for inertia and neglecting any vibrating effects. However, simulation and experimental studies on thin MPPs have found that the absorbing performance can experience variations in the low frequency range from the results expected assuming a rigid structure. The work presented here is a theoretical and experimental study on the influence of panel vibrations on the sound absorption properties of thin MPP absorbers. Measurements show that the absorption performance generates extra absorption peaks or dips that cannot be understood assuming a rigid MPP. A theoretical model is established that exactly accounts for structural-acoustic interaction between the micro-perforated panel and the backing cavity without restriction on the absorber cross-sectional shape or on the panel boundary conditions. This model is verified experimentally against impedance tube measurements and laser vibrometric scans of the cavity-backed panel response. The effect of micro-perforations on panel-cavity or hole-cavity resonances is revealed through coupled mode analysis.

Interacting double dark resonances in a hot atomic vapor of helium

We experimentally and theoretically study two different tripod configurations using metastable helium ($^4$He*), with the probe field polarization perpendicular and parallel to the quantization axis, defined by an applied weak magnetic field. In the first case, the two dark resonances interact incoherently and merge together into a single EIT peak with increasing coupling power. In the second case, we observe destructive interference between the two dark resonances inducing an extra absorption peak at the line center.

Comparative Studies on Degradation of Methyl Orange by Nanostructured Zinc and Zinc Oxide Films

Nanostructured zinc and zinc oxide films were prepared by magnetron sputtering processes and succeeded air annealing treatments. Comparison of reductive degradation rate of methyl orange (MO) by zinc films and photocatalytic degradation rate of MO by zinc oxide films was carried out. Both reductive degradation and photocatalytic degradation process of MO by zinc and zinc oxide films can be described by first order kinetic model. It was found that although MO liquid was most quickly decolorized by metallic zinc films, the mineralization of MO was not thorough. Observation of extra ultraviolet absorption peaks indicated the formation of aromatic intermediates. On the other hand, although the photocatalytic degradation rate of MO liquid by ZnO films was only as about 1/4 large as the reductive degradation rate by zinc films, no signs of aromatic intermediates were found. Moreover, it was found that partially oxidized zinc oxide film showed higher photocatalytic efficiency than the totally oxidized ZnO films. Synergy effect between zinc and zinc oxide phase in the partially oxidized films was considered to be responsible for the higher photocatalytic efficiency.

EPR of Cu2+ Prion Protein Constructs at 2 GHz Using the g⊥ Region to Characterize Nitrogen Ligation

A double octarepeat prion protein construct, which has two histidines, mixed with copper sulfate in a 3:2 molar ratio provides at most three imidazole ligands to each copper ion to form a square-planar Cu2+ complex. This work is concerned with identification of the fourth ligand. A new (to our knowledge) electron paramagnetic resonance method based on analysis of the intense features of the electron paramagnetic resonance spectrum in the g⊥ region at 2 GHz is introduced to distinguish between three and four nitrogen ligands. The methodology was established by studies of a model system consisting of histidine imidazole ligation to Cu2+. In this spectral region at 2 GHz (S-band), g-strain and broadening from the possible rhombic character of the Zeeman interaction are small. The most intense line is identified with the MI = +1/2 extra absorption peak. Spectral simulation demonstrated that this peak is insensitive to cupric Ax and Ay hyperfine interaction. The spectral region to the high-field side of this peak is uncluttered and suitable for analysis of nitrogen superhyperfine couplings to determine the number of nitrogens. The spectral region to the low-field side of the intense extra absorption peak in the g⊥ part of the spectrum is sensitive to the rhombic distortion parameters Ax and Ay. Application of the method to the prion protein system indicates that two species are present and that the dominant species contains four nitrogen ligands. A new loop-gap microwave resonator is described that contains ∼1 mL of frozen sample.

Switching from “absorption within transparency” to “transparency within transparency” in an electromagnetically induced absorption dominated transition

The absorption of a resonant coupling laser driving a closed degenerate two-level system in an atomic cesium beam was investigated as a function of the detuning of a second laser probing the same transition. The measurements were performed for four different polarization combinations of the two laser beams. Except for the beams of counterrotating polarizations all coupling-laser absorption profiles showed "absorption within transparency," i.e., the absorption in the region around the two-photon resonance was smaller than the absorption corresponding to the one-photon transition induced by the coupling laser, and an extra absorption peak was observed on this curve at the two-photon resonance. With regard to the beams of counterrotating polarizations we observed a switch from absorption within transparency to "transparency within transparency" when the probe-laser power exceeded the constant coupling-laser power. In other words, the cesium ensemble became mostly transparent to the coupling-laser beam at the two-photon resonance.

Observation of bulk HfO2 defects by spectroscopic ellipsometry

Spectroscopic ellipsometry was used to investigate the oxidation of pure Hf films on silicon for the formation of HfO2 (hafnium oxide) gate-dielectric films in advanced complementary metal-oxide-semiconductor field-effect transistors. Absorption coefficients near the absorption edge were extracted using the data inversion method, in which the optical constants for short wavelengths were calculated using the film thickness determined from long-wavelength data. The extracted optical band gap of 5.7 eV matches well with published data, and a curve shift due to crystallization was detected. In addition, an extra absorption peak corresponding to electron transition from the valence band to a defect energy level was observed in the range 4.5–5.0 eV above the valence-band edge. The 1.2 eV energy difference between the conduction-band edge and the edge of this extra peak is close to the electron trap energy level reported elsewhere. The intensity of the detected peak was clearly correlated with leakage current and near-interface trap densities. Based on the annealing condition dependence of the extra absorption peak, the defects are likely oxygen vacancies within the HfO2 film.

Process Optimization and Integration of HFO2 and HF-Silicates

ABSTRACTWe have established in-line characterization techniques for analyzing the bulk and interface-charge properties of dielectric films, for process optimization. Surface charge analysis (SCA) is used to determine the densities of interface states, fixed charge, and near-interface traps in ultra-thin dielectrics, and is useful for tracking the influence of post-deposition processing on interface-charge properties. Spectroscopic ellipsometry (SE) is used to obtain the absorption spectra in the conduction band-tail region. The intensity of an extra absorption peak inside the bandgap of HfO2 is clearly correlated with leakage current density and near-interface trap density. Based on the observed process dependencies, defects within the HfO2 films are likely to be oxygen vacancies. The relative scalability of HfO2 and Hf-silicate films of various compositions is examined using a figure of merit based on the direct-tunneling leakage current model. Pure HfO2 is expected to be more scalable than Hf-silicates. However, it is typically accompanied by an interfacial layer which significantly increases the equivalent oxide thickness (EOT). A 20% Hf silicate with relative permittivity of 11 or higher can be more scalable than HfO2 with an interfacial layer. Alternatively, an ultra-thin interfacial Si3N4 diffusion barrier can be used with HfO2, to allow for more aggressive EOT scaling. The dependencies of interface-charge properties and surface roughness on the nitride barrier formation process are presented.

Growth, structural and optical properties of Cu 3N films

Thin films of Cu 3N were grown on (0 0 1) MgO and (0 0 1) Cu substrates by molecular beam epitaxy of copper in the presence of nitrogen obtained from a radio frequency atomic source. The different aspects of the growth and the properties of the copper nitride films were investigated in relation with growth parameters such as: substrate temperature, growth rate and flux of nitrogen. On MgO substrates, despite a mismatch as high as ∼10%, the Cu 3N films grow as epitaxial layers even at room temperature. The upper temperature limit for growth was found to be ∼250 °C. It is likely that the growth mechanism proceeds in a layer-by-layer fashion similar to the growth of γ ′-Fe 4N layers on MgO substrates using the same growth method. This results in the growth of smooth layers of Cu 3N. The films, grown as a pure phase, have a behavior typical for an insulator with an optical gap of 1.65 eV. If a low amount of Cu impurities is present in the Cu 3N insulating matrix, the films still have the overall behavior of an insulator, but with a reduced optical band gap. For higher amounts of metal impurities, seen as Cu crystallites in the epitaxial Cu 3N phase, the optical band gap reduces even further, and additionally, an extra absorption peak due to Cu appears. The films grown on (0 0 1) Cu substrates, despite the better lattice match, did not show a striking improvement of the crystal quality.

Electron-Zeeman Resolved Electron Paramagnetic Resonance Spectroscopy

Abstract Electron-Zeeman (EZ) resolved electron paramagnetic resonance (EPR) spectroscopy is introduced. In this two-dimensional pulse EPR technique a sinusoidal external field Δ B 0 ( t ) of variable amplitude is applied during the pulse sequence, resulting in a field-swept EPR spectrum that is spread into a second dimension, representing the g values of the paramagnetic species. The method can be used to improve the resolution of polycrystalline and single-crystal EPR spectra. For polycrystalline systems, simplified EPR spectra are obtained for fixed g values. For axial symmetry, these spectra allow direct access to coupling constants, also at orientations that differ from the principal axes orientations. Furthermore, overlapping resonances can be disentangled, extra-absorption peaks identified and unresolved hyperfine splittings observed. The sum projection onto the g -value axis corresponds in a g -value spectrum, which is free of hyperfine interactions. A detailed theoretical description of the EZ-EPR experiment is given. Several model calculations for systems with different symmetry of the magnetic interaction tensors are presented, and the versatility of EZ-EPR is demonstrated for different paramagnetic systems with g anisotropy.

Formation of gold nanoclusters in MgO by ion implantation at elevated temperatures

Gold nanoclusters were formed in (100) MgO containing nanosize cavities. Nanocavities were created by a combination of 30 keV 3He implantation and subsequent annealing. Au was introduced inside the cavities by 30 keV Au ion implantation. The implantation dose varied from 1016 to 3×1016 cm−2 and the implantation temperature varied from room temperature (RT) to 1270 K. In the case of the RT implantations the samples were subsequently annealed stepwise in air up to 1370 K. The evolution of the implantation defects and the formation of nanoclusters was monitored by positron beam analysis (PBA), optical absorption spectrometry and Rutherford backscattering spectroscopy (RBS)/channeling. Optical absorption resonance peaks were observed at 570–610 nm for the RT implantations and at 525–550 nm for the implantations carried out at elevated temperatures. In the case of 1270 K implantation an extra absorption peak at 818 nm was observed. The influence of the implantation temperature on shape and position of the absorption band ascribed to nanoclusters is discussed.