Transition Band Research Articles

Manganese(II) Bromide Compound with Diprotonated 1-Hydroxy-2-(pyridin-2-yl)-4,5,6,7-tetrahydrobenzimidazole: Dual Emission and the Effect of Proton Transfers

An organic–inorganic cation–anion manganese(II) tetrabromide compound with diprotonated 1-hydroxy-2-(pyridin-2-yl)-4,5,6,7-tetrahydrobenzimidazole, [H3L][MnBr4][H2O], has been synthesized and investigated. The compound has a few possible pathways for proton transfers, which play an important role in the observed luminescence, optical, and magnetic properties. The proton transfers result in the appearance of two-band luminescence. One band is caused by the Mn(II) d-d transitions. The other band is caused by the transition from the triplet state of organic cation and the d-d transition of manganese(II) coupled through {[H3L]}-{[MnBr4]}-{[H2O]} vibrations. The optical absorption spectra of [H3L][MnBr4][H2O] indicate the presence of two direct and one indirect band transitions. The reason for the two-band luminescence and complex optical absorption in [H3L][MnBr4][H2O] were additionally considered using the DFT calculations.

Cathodoluminescence and optical absorption spectroscopy of plasmonic modes in chromium micro-rods

Manipulating light at the sub-wavelength level is a crucial feature of surface plasmon resonance (SPR) properties for a wide range of nanostructures. Noble metals like Au and Ag are most commonly used as SPR materials. Significant attention is being devoted to identify and develop non-noble metal plasmonic materials whose optical properties can be reconfigured for plasmonic response by structural phase changes. Chromium (Cr) which supports plasmon resonance, is a transition metal with shiny finished, highly non-corrosive, and bio-compatible alloys, making it an alternative plasmonic material. We have synthesized Cr micro-rods from a bi-layer of Cr/Au thin films, which evolves from face centered cubic to hexagonal close packed (HCP) phase by thermal activation in a forming gas ambient. We employed optical absorption spectroscopy and cathodoluminescence (CL) imaging spectroscopy to observe the plasmonic modes from the Cr micro-rod. The origin of three emission bands that spread over the UV–Vis-IR energy range is established theoretically by considering the critical points of the second-order derivative of the macroscopic dielectric function obtained from density functional theory (DFT) matches with interband/intraband transition of electrons observed in density of states versus energy graph. The experimentally observed CL emission peaks closely match the s–d and d–d band transition obtained from DFT calculations. Our findings on plasmonic modes in Cr(HCP) phase can expand the range of plasmonic material beyond noble metal with tunable plasmonic emissions for plasmonic-based optical technology.

Investigations on the role of doped 3d transition ions in Li2B4O7 glasses: Local structures, spectroscopic properties and optical basicities

Glasses with doped transition metal ions (TMs) have shown specific spectroscopic properties, but the micro-mechanism is hard to be obtained due to the amorphous structure. Based on the high order perturbation formulae of electron paramagnetic resonance (EPR) parameters, the local environment of 3d ions (V4+, Cr3+, Mn2+ and Cu2+) in Li2B4O7 glasses is studied to explain the experimental EPR spectra. The spectroscopic properties of Li2B4O7 glasses are closely correlated with the doped 3d ions, which can be reasonably predicted from the transition bands of divided energy orbitals. The crucial optical basicities of Li2B4O7 glasses doped with different TMs are also investigated, which are consistent with the above calculation results with respect to the local environment. The results show that TMs doping can be an effective way to modify the intrinsic properties of glasses.

The Design and Simulation of a Fifth-order Chebyshev Low-Pass Filter

Chebyshev filter is a design classification of filters. It uses the Chebyshev transfer function, and has many filter types, such as high-pass, low-pass, band-pass, high-resistance, band-stop and so on. Compared with the Butterworth filter, the transition band of the Chebyshev filter is very narrow, but the internal amplitude-frequency characteristics are unstable [1][2]. Chebyshev filter achieves complex transmission zeros to improve the group delay characteristics in the pass band and reduce the signal distortion. In the process of designing a five-order Chebyshev filter, an active filter network needs to be established, and each stage of the low-pass filter composed of an amplifier is connected in the same cascade to form a multi-order Chebyshev low-pass filter. To design a Chebyshev filter, a Sallen-key structure is needed, and the transfer function is determined according to the position and size of the different resistors and capacitors placed, and a Chebyshev filter with different functions is constructed. The Multisim Simulation software is used to simulate the design results, and the frequency response amplitude curve in the image is found to be fluctuating with equal ripple in the pass or stop band.

Development of novel flexible photodetectors based on 0.5PVA/0.5PVP/Fe:NiO nanocomposite system with enhanced optoelectronic properties

Ordinary casting technique has been used to fabricate the intrinsic films of polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP) polymer blend matrix incorporated with dissimilar weight percent contents of Fe:NiO nanocomposite (NC). X-ray diffraction (XRD) and infrared (IR) spectroscopy has been implemented to analyze NC structure of these films. Significant interaction and tuning of PVA/PVP blend matrix due to Fe:NiO NC is detected. XRD pattern reflects the structural modification and partial crystalline nature of the pristine blend matrix. The corresponding peaks of Fourier transform IR identifies the vibrational group of the synthesized samples. Atomic force microscope images indicate that a change in the Fe:NiO concentration in a pristine blend leads to an increase in the roughness and clusters. Numerous optical factors such as E g (transition band gap), refractive index (n), and E ed (absorption edge) of pure blend and blend films with different concentrations of Fe:NiO were assessed via UV–Vis optical absorption spectra. As we increased the doping concentration in pristine blends, the value of E g goes to decrease. The dispersion (E d) and oscillator (E o) energies were calculated from Wemple and Di. Domenico of a single oscillator. Although, optical susceptibilities and nonlinear refractive index were enhanced by doping with Fe:NiO NC. The change in doping content leads to modifications in the optical limiting. The photocurrent density–voltage properties of the present polymers were studied at different values of white light intensity. It was found that the photoconductivity of the PVA/PVP blend is 1.03275 × 10−8 (Ω cm)−1, while NC films varied in the range (1.03–10.6954) × 10−8 (Ω cm)−1 at 8600 lux. In addition, the photosensitivity increased from 13.82 to 24.08. The recombination process was found monomolecular process for pure and doped polymers. The present films assume the possibility of their uses in optical and photo-electric devices.

Highly crystalline In2S3 thin films epitaxially grown on sapphire substrates

Indium sulfide (In2S3) thin films were deposited on glass and sapphire substrates by physical co-evaporation of the elements. The deposition parameters were varied to optimize the structural properties of the thin films. The sample epitaxially grown on a-sapphire substrate shows the smoothest surface and the highest crystallinity. The optical absorption properties were found to be independent on the deposition parameters and substrate material. We found for In2S3 a weakly pronounced absorption onset at 1.7 eV and a strong one at 2.5 eV, which can be attributed to direct band–band transitions located at 2.1 and 2.7 eV, respectively. Electrical characterization reveals photovoltaic activity with p-ZnCo2O4/ n-In2S3 heterodiodes but low performance due to non-ideal heterojunction properties. We further find a strong, persistent photoconductivity, which manifests itself in a strong time-dependence of the dark resistivity after the samples were exposed to light.

Growth of MoS2 Thin Films Using the Two-step Approach

In this study, MoS2 thin films were grown using two-step approach, which is based on employing both PVD and CVD techniques. The films were obtained initially by sputtering 1nm Mo film in the PVD system and followed by sulphurization of the film in CVD at 700 oC. The grown films were optimized employing different sulphurization times. The main difference in our study from the current literature is using preheated CVD furnace (700 oC) ahead of sulphurization. The films quality are then investigated using Raman and Photoluminance spectrometer as well as AFM measurements. The Raman spectrums indicate that two characteristic vibration modes of 2H-MoS2 phase were observed in all samples, however, vibration modes of 1T-MoS2 phase were also observed in some films at low sulphurization time. These results were also in line with PL measurements that confirm the direct band transition of the MoS2 films. The surface topography of the films were investigated by AFM for MoS2 films obtained by the sulfurization of 1 nm-thick Mo film in 15 minutes at 700 oC which shows MoS2 crystals in triangle shape

Saturation spectroscopy of R(0), R(2) and P(2) lines in the (2-0) band of HD

Lamb-dips of R(0), R(2) and P(2) rovibrational transitions in the (2-0) overtone band of the HD molecule are measured at cryogenic temperatures using the technique of NICE-OHMS spectroscopy. Resulting transition frequencies are 214,905,335,240,(100) kHz for R(0), 219,042,856,794,(150) kHz for R(2) and 206 ,898 ,802,150 ,(150) kHz for P(2). Small, but systematic deviations (at 1.7sigma level) are found from advanced ab initio calculations, supporting results from previous studies probing other lines in the (2-0) band. From a combination difference between the R(0) and P(2) lines, an accurate value for rotational-level spacing in the v=0 ground state is determined, of Delta _{(J=2)-(J=0)}= 8,006,533,168,(26) kHz, well in agreement with theory (at 0.6sigma ). Based on the observation of the dispersive line shape of R(0), the status of proposed models for the elusive line shapes of saturated transitions in HD is discussed.

CONSTRUCTION AND VERIFICATION OF A DIGITAL EQUALIZER MODEL

An approach to the development of an equalizer by building its mathematical model based on a microcontroller is proposed. All operations, including signal processing and equalizer kernel calculation, are performed by a single microcontroller. Thanks to the created mathematical model of the equalizer, the calculation of the kernel is reduced to multiple uses of relatively simple operations, which saves time and memory of the program. The equalizer provides satisfactory processing quality at a small filter order which is selected as a digital filter with final impulse response (FIR) because of its linear phase-frequency response, a guarantee of stability at the complex amplitude-frequency response, and also its associativity and linearity allowing it easily reproduce a complex amplitude-frequency response. Schematic implementation is based on parallel bandpass filters and a low-pass filter followed by adding filtered and amplified signals. It is the distributive property of the FIR filter that makes it possible to obtain a new kernel that includes all the amplified ranges by the sum of the corresponding kernel elements, instead of adding amplified ranges. The associativity and linearity of the FIR filter gives the opportunity to easily implement different types of filters on the basis of a low-pass filter, for the calculation of which the cardinal sine function is used together with the window function, which in combination gives qualitative frequency characteristics. The low-pass filter kernel and equalizer model are verified in the GNU Octave environment, which is an open-source analogue of Matlab. The model is checked by setting the frequency response of the test equalizer, and for individual filters the allowable width of the transition band and the maximum value of pulsation in the suppression band are set. The low-pass filter kernel is created with an arbitrary cutoff frequency, and the filter consists of 129 elements, which were multiplied by the Kaiser window with a value of parameter equal to 4.5. As a result of verification of the mathematical model in the GNU Octave environment, the width of the transition band and the maximum value of pulsation in the suppression band meet the specified conditions. The simulated equalizer kernel fully corresponds to the specified frequency response. Verification of the mathematical model confirmed its efficiency and compliance of the obtained characteristics of the equalizer with the specified requirements.

Towards commonality between shear banding and glass-liquid transition in metallic glasses

Despite the high attendance of shear banding in metallic glasses and other disordered materials, the nature of the emergence of shear band is still mysterious. Using molecular dynamics simulations, a set of detailed characterizations of shear band in a typical ${\mathrm{Cu}}_{50}{\mathrm{Zr}}_{50}$ metallic glass is obtained. Then we uncover a large number of robust and intriguing commonalities between the emergence of shear bands and the glass-to-liquid transition, including strong similarities on viscosity drop, enthalpy discontinuity, breakdown of hard backbone network, as well as relaxation process. Such observations indicate that shear banding in metallic glasses is a consequence of deformation-controlled glass transition, as further quantitatively validated via the compelling overlap between the venerable Vogel-Fulcher-Tammann law (and Adam-Gibbs relation) and the evolving glass state of shear band controlled by configurational temperature. These results provide a direct bridge between shear banding and glass-to-liquid transition and are instrumental to build the unified framework of flow behavior induced either by thermal or stressed stimuli in disordered materials.

Unveiling quaternary GeSbSeEr chalcogenides as photocatalyst: Degradation of cationic and anionic pollutant in visible light

This article presents the photo-catalytic dye-degradation from pure and doped multi-component Ge17Sb8Se75-xErx(x = 0, 0.2, 0.4, 0.6, 0.8, 1) chalcogenides system has been established in visible light (orange ∼590 nm) for the first time. Band-gap shifting, suitable band position and higher absorption of visible range radiation have been accounted for Er doping to realize the improvement in electron-hole pair production. The improvement in the photo-catalytic activity dye degradation efficiency of 89% in 90 min for methylene blue and 76% for methyl orange has been achieved for certain compositions of chalcogenides glass which were synthesized by traditional melt quench approach. Further, SEM-EDX Photoluminescence and Raman spectroscopy measurements of these samples are supplemented to deliberate the composition, band edge transitions and chemical signatures of Ge17Sb8Se75-xErx. Overall, the presence of Er ions as well as the band to band transition (∼664 nm) in the chalcogenides system is found to play a decisive role in the photo catalytically process involved for competitive dye degradation to replace conventional dyes working in the UV range.

First principles investigation on the boron-oxygen complexes in diamond

The co-doping mechanism of boron and oxygen substitutional complexes in diamond are investigated since the B-O co-doping seems to be a solution for preparing n-type diamond in some experiments. We use first-principles calculations to predict the geometry of a range of B-O complexes in diamond. Three possibly stable configurations are confirmed through the formation energy and binding energy. We also find that B-rich complexes are more stable when O sits in the centre position, whereas O tends to be closer to another O in the case of O-rich complexes. Electrically, the former shows a shallow acceptor property while the latter is a neutral impurity by analysing the transition levels, band structures and partial density of states. Our calculation suggests that the B-O scheme may not be a feasible way for effective n-type diamond, but it might be a good method to prepare high-quality p-type diamonds.

Influence of Ar gas pressure on the structural and optical properties and surface topography of Al-doped ZnO thin films sputtered by DC-Magnetron sputtering method

In this work, Aluminum doped Zinc oxide thin films were sputtered on glass substrate by the direct current (DC) magnetron sputtering method. The influence of Ar gas pressure on the structural and optical properties was measured. The optical parameters were calculated by UV–Visible spectroscopy, the nature of transition reveals direct allowed transition for the prepared films. Also, some physical quantities such as the strength of electron–phonon interaction, dissipation factor (tanδ) in the visible region and the lattice dielectric constant were presented for these thin films. The AFM analysis extracts surface parameters of the AZO thin films that help us to quantitively investigate the surface analysis. The band gap energy and transition index without any presumption about transition natural were calculated from Derivation Ineffective Thickness Method (DITM) and it was found that the reaction of Ar gas pressure plays an essential part in controlling the physical quantities of AZO thin films.

Novel Scintillating Nanoparticles for Potential Application in Photodynamic Cancer Therapy.

The development of X-ray-absorbing scintillating nanoparticles is of high interest for solving the short penetration depth problem of visible and infrared light in photodynamic therapy (PDT). Thus, these nanoparticles are considered a promising treatment for several types of cancer. Herein, gadolinium oxide nanoparticles doped with europium ions (Gd2O3:Eu3+) were obtained by using polyvinyl alcohol as a capping agent. Hybrid silica nanoparticles decorated with europium-doped gadolinium oxide (SiO2-Gd2O3:Eu3+) were also prepared through the impregnation method. The synthesized nanoparticles were structurally characterized and tested to analyze their biocompatibility. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy confirmed the high crystallinity and purity of the Gd2O3:Eu3+ particles and the homogeneous distribution of nanostructured rare earth oxides throughout the fumed silica matrix for SiO2-Gd2O3:Eu3+. Both nanoparticles displayed stable negative ζ-potentials. The photoluminescence properties of the materials were obtained using a Xe lamp as an excitation source, and they exhibited characteristic Eu3+ bands, including at 610 nm, which is the most intense transition band of this ion. Cytotoxicity studies on mouse glioblastoma GL261 cells indicated that these materials appear to be nontoxic from 10 to 500 μg·mL-1 and show a small reduction in viability in non-tumor cell lines. All these findings demonstrate their possible use as alternative materials in PDT.

Synthesis, crystal structure, Hirshfeld surface analysis, thermal, luminescent properties, and computational studies of the new triazole derivative 1-(5-methyl-1-(pyridin-2-ylmethyl)-1H-1,2,3-triazol-4-yl)ethan-1-one

The title compound, 1-(5-methyl-1-(pyridin-2-ylmethyl)-1H-1,2,3-triazol-4-yl)ethan-1-one, a new triazole derivative with formulae C11H12N4O, which has been synthesized and structurally characterized by MS, elemental analysis, FT-IR, and single-crystal X-ray diffraction. Spectroscopic results are consistent with the proposed structure and XRD experiments. Single-crystal X-ray diffraction analysis indicated that the compound crystallizes in the monoclinic space group P21/n (N°14), Z = 4, and unit cell parameters a = 12.987(2) Å, b = 4.4539(5) Å, c = 19.060(2) Å, β = 93.993(3) °, V = 1099.8(2) Å3. The molecular structure and crystal packing are stabilized by hydrogen-bond-like-interactions CH···O, and weak π ··· π interactions. Thermal studies show a stable phase at 240 °C. Luminescent properties show a benzenoid band pattern, which was assigned to π*- π transition bands and the less energetic band assigned to intramolecular CT transitions and agrees with emission experiments in solution. DFT molecular and crystal calculations show a molecular behavior in the solid state, which agrees with thermal and luminescent properties.

Electrical and optical properties of Nd3+-doped rhombohedral Pb(Mg1/3Nb2/3)O3–PbTiO3 ferroelectric single crystal

Lead Magnesium Niobate Titanate 0.74 Pb(Mg1/3Nb2/3)O3-0.26PbTiO3 (0.74PMN-0.26 PT) single crystal doped with 1 mol% Nd3+ was grown by a modified Bridgman approach. Powder X-ray diffraction exhibited perovskite structure containing rhombohedral phase. The dielectric constants of various orientations with temperature were determined. We observed that the polarization process increases the crystal optical performances. The transmittance is significantly increased after poled along [011] direction. Optical properties changes were interpreted by electric domain structure. Energy band gaps were obtained by Tauc equation. Nd3+ has a strong emission transition band near 1062 nm; the long radiation lifetime of 148 μs indicates a low quenching effect. For the Nd-doped PMN-PT single crystals, their optical and electrical performances have been explored to extend the applications in medical, military and practical industrial production.

Investigation of Band Structure in Strained Single Crystalline Si1-X Sn X

1. Background and purpose Silicon tin (SiSn) alloys are attractive candidate for the next-generation group-IV semiconductors. It is well known that Si and Ge change from indirect to direct transition types with the addition of Sn. Among them, SiSn alloys are expected to be applied for the near-infrared optical devices because it is predicted to become a direct band-gap appropriate for the optical communication with sufficient Sn content [1]. Although the Sn composition that changes from indirect to direct band-gap has been reported using several calculations, there are few reports of experimental results. In addition, the optical properties of single crystalline Si1-x Sn x have not been sufficiently clarified owing to the difficulty of crystal growth. In this study, we evaluated the optical properties to clarify the band structure of single crystalline Si1-x Sn x . 2. Experimental method Strained 30 nm-thick Si1-x Sn x films were grown on Si substrate by molecular beam epitaxy (MBE), and epitaxial growth was confirmed by X-ray diffraction (XRD) two-dimensional reciprocal space mapping (2DRSM) [2]. The Sn composition was determined by 2DRSM. The Sn fraction x of Si1-x Sn x samples used in this study were 0.005, 0.009, 0.018, 0.022, and 0.06. The spectroscopic ellipsometry measurements were performed with an incident angle of 70°, using a 70 W xenon lamp with a wavelength range of 200 to 1600 nm for the light source. The functions used in the analysis are the Tauc-Lorentz and Lorentz function. 3. Results and Discussion Figure 1(a) and (b) show real part and imaginary part of the complex dielectric functions for Si1-x Sn x (x=0.005 - 0.06) and pure-Si, respectively. From Fig. 1, it can be confirmed that the spectra shift with increasing Sn composition and the peaks appear around 1.8 eV and 2.8 eV for the samples with high Sn composition (2.2% and 6.0%). The peak shift characteristic with the addition of Sn is similar to the results of germanium tin (GeSn) [3].The complex dielectric functions of the semiconductor include much information about the electronic band structure. In Fig. 1, the sharp peaks that are due to direct band transitions show what is known as critical points (CPs). In the case of Si, E'0 CP (Γ) and E 1 CP (L) energy are around 3.2 eV [4]. Therefore, it can be considered that the peak at 2.8 eV indicates the separation of the E'0 and E 1 CP energies due to the change in the band gap at the Γ point with the addition of Sn. The peak at 1.8 eV is unique to Si1-x Sn x , which is not found in Si. We consider that this peak is due to the split-off valence band caused by the Sn addition. The behavior of the valence band is strongly affected by strain. These results suggest a reduction of the band gap at the Γ point and the formation of an optical transition region due to the Sn addition, and reveal important findings for the application of SiSn for the near-infrared devices. Acknowledgment This work was partly supported by the Japan Society for the Promotion of Science (JSPS) (17J08240, 19K21971, and 21H01366).

E/Z reversible photoisomerization of methyl orange doped polyacrylic acid‐based polyelectrolyte brush films

AbstractThe photoswitching behavior of the polyacrylic acid (PAA) doped by methyl orange (MO) brush film was investigated using spectral analysis of UV‐Vis absorbance, Fourier Transformation Infrared spectroscopy, 2D electrical conductivity mapping and Atomic Force Microscopy. The kinetics and time evolution of the photoisomerization of the PAA‐MO PEBs film from E‐state to Z‐state by UV‐light irradiation, and reverse thermal relaxation to E‐state was explored. The results confirm that the photoisomerization kinetics of the overall peak is the superposition of the photoisomerization kinetics of transition, low‐ and high‐frequency of the transition bands. The E–Z transformation led to transforming the azobenzene from flat with no dipole moment to 3.0 D dipole moment. Hence, the electrical conductivity escalated accordingly. The transformation of E‐state to Z‐state led to the collapse of the formed brushes because of the angular rotational momentum consequent to E–Z isomerization.

Design of high‐efficiency , multi‐octave hybrid continuous mode power amplifier with novel low‐pass filtering matching network

This paper presents a design method for a multi-octave, high-efficiency power amplifier (PA) with a novel low-pass filtering matching network. Both extended continuous Class-F and continuous Class-F−1 are engaged to expand the design space for the ultra-broad operating band. A wideband vertex coupled radial stubs (VCRS) low-pass filter alongside a transmission line network (TLN) is proposed as an output impedance matching network of the PA. The wide rejection band and sharp transition band of this filter make it suitable for harmonic tuning PAs. To verify the feasibility of the proposed structure, the PA is fabricated and its performance is measured. The fractional bandwidth of 155% across 150 to 1200 MHz with a drain efficiency of 61%–73% and output power of 38.9–39.5 dBm is achieved.

Eco-friendly poly(aniline boronic acid)/gum tragacanth stabilized silver nanoparticles nanocomposite for selective sensing of Hg2+

The stable and dispersed aqueous nanocomposite of poly(aniline boronic acid)/gum tragacanth stabilized silver nanoparticles (PABA/GT@AgNPs) was synthesized and applied as a colorimetric nanoprobe for Hg2+. Aniline boronic acid was used as the only reducing agent of silver nitrate and equally oxidized to PABA based on in situ chemical oxidative polymerization. In the presence of gum tragacanth (GT), hydroxyl groups of GT will bind to PABA at boronic groups to generate the PABA/GT matrix, on which AgNPs are anchored. At the optimal synthesis, absorption spectra at 285 and 421 nm correspond to π -π* transitions of PABA and plasmon resonance band of small sized AgNPs (10–15 nm). Based on the FTIR spectrum, GT is the major constituent of nanocomposite. Under optimal conditions (40 mM phosphate buffer pH 6.0, 150 mM sodium chloride, reaction time of 8 min at room temperature), the PABA/GT@AgNPs was used as a sensing of Hg2+ based on Hg2+ induced transmetalation on arylboronic acid group and redox reaction with Ag0. In the presence of Hg2+, the aggregation of PABA/GT@AgNPs can be seen by a color change from pale yellow to colorless and a blue shift from 407 nm to 370 nm. Good linear ranges in the concentrations of 0.005–1.0 μM and 1.0–40.0 μM were achieved, with a detection limit of 0.85 nM. The practicality of the detection was demonstrated on tap and lake water samples, with no effects of other interfering ions, and satisfactory recoveries of 97–101 % and precisions of 2.9–5.6 %.