Equivalent Band Gap Research Articles

A study on low-frequency vibration mitigation by using the metamaterial-tailored composite concrete-filled steel tube column

The bandgap properties exhibited by local resonant metamaterials provide a potential approach for structural vibration reduction. In this work, we introduce the local resonance mechanism into the composite structure for the first time and propose a novel metamaterial column with 33.8–47.2 Hz low-frequency vibration mitigation based on practical engineering materials and utilizing material shear deformation. By vertically arranging metamaterials, the metamaterial concrete-filled steel tube column with low-frequency vibration reduction bandgap is designed. Its equivalent bandgap model is proposed by combining the Timoshenko beam and Bloch theorem. The bandgap formation mechanism and vibration mitigation effect of the metamaterial are clarified by finite element analysis. It is revealed that the bandgap generation depends on the contrary motion between the resonator and the substrate, thus the reaction force from the relative motion can cancel the external excitation. Then, the bandgap vibration mitigation effect of the metamaterial column is proved by shaking table tests at different amplitudes. This also supplies a feasible solution for vibration mitigation control and even earthquake protection for buildings, bridges, and major infrastructures. Finally, the theoretical, numerical, and experimental results are discussed to verify the validity of the theoretical approach and numerical model, and the rubber damping is found to widen the bandgap but weaken the vibration reduction capacity.

Synthesis, characterization, and thermoluminescence‐based high‐dose neutron and gamma dosimetry study of Al5BO9: Mn, Li nanophosphor

AbstractA near tissue equivalent (Zeff = 10.8) and wide bandgap (Eg = 5.95 eV) Al5BO9: Mn, Li nanophosphor was synthesized by facile gel‐combustion (GC) method, and structural characterizations were performed by XRD, infra‐red, transmission electron microscopy, energy‐dispersive spectra, diffuse reflectance UV–visible spectra, and PL studies. Thermoluminescence (TL) study of Al5BO9: Mn, Li revealed the dosimetry glow peak at 542 K, which was absent in undoped Al5BO9 indicating the importance of Mn dopant. The highest TL response was obtained for the lowest studied dopant concentration (0.1 mol% Mn) that was attributed to the concentration quenching phenomenon. The material is highly reusable with low fading (<10%) up to 110 days. TL response for both thermal neutron and gamma radiations showed excellent linearity within 5 × 109–3 × 1011 n/cm2 and 30–5000 Gy, respectively. These studies suggested promising potential of Al5BO9: Mn, Li nanophosphor in clinical neutron dosimetry and food irradiation dosimetry applications. Based on the variation of calcination temperature, strategy toward dual application, namely, radiation dosimeter and red‐light emitting phosphor of the material was established. For a better understanding of the TL process, various kinetic parameters like activation energy (E), order of kinetics (b), and frequency factor (s) were evaluated using different methodologies, and the results were found to be in good agreement.

Structure and enhanced antimicrobial activity of mechanically activated nano TiO2

AbstractTitanium dioxide is a photocatalyst, known not only for its ability to oxidize organic contaminants, but also for its antimicrobial properties. In this article, significant enhancement of the antimicrobial activity of TiO2 (up to 32 times) was demonstrated after its activation by ball milling. The antimicrobial activity was analyzed for one fungal and 13 bacterial ATCC strains using the microdilution method and recording the minimum inhibitory concentration (MIC) values. In order to further investigate the correlation between the mechanical activation of TiO2 and its antimicrobial activity, the structure, morphology and phase composition of the material were studied by means of Electron Microscopy, X‐ray diffraction and nitrogen adsorption‐desorption measurements. UV‐Vis diffuse reflectance spectra were recorded and the Kubelka‐Munk function was applied to convert reflectance into the equivalent band gap energy (Eg) and, consequently, to investigate changes in the Eg value. X‐ray photoelectron spectroscopy was used to analyze the influence of mechanical activation on the Ti 2p and O 1s spectra. The presented results are expected to enable the development of more sustainable and effective advanced TiO2‐based materials with antimicrobial properties that could be used in numerous green technology applications.

Numerical calculation of visible light absorption enhancement of CdSe-quantum dot-sensitized TiO2 nanorod periodic array as photoanode

Light absorption enhancement in a CdSe-quantum dot (QD)-sensitized TiO2 nanorod periodic array-based photoanode is calculated by the finite differential time domain (FDTD) model through optimizing the height, diameter, and periodic space between TiO2 nanorods. Results show that light absorption in the CdSe-QD-sensitized TiO2 nanorods is enhanced at the visible wavelength range and the absorption edge is shifted toward higher wavelengths as a result of decreasing the height and increasing the diameter of the TiO2 nanorods. Consequently, the equivalent bandgap of the CdSe-QD-sensitized TiO2 nanorod photoanode was decreased. Also, absorption spectra indicate that the position of the absorption peak related to TiO2 has a redshift with increasing periodic space between the TiO2 nanorods, suggesting a decrease in the bandgap of TiO2. In addition, results show that for TiO2 nanorod heights lower than 300 nm, light absorption in the visible region is considerably enhanced as the periodic space is reduced from 400 nm to 100 nm. In comparison, for TiO2 nanorod heights larger than 300 nm, light absorption is considerably enhanced. Finally, it is found from absorption spectra that coupling optical modes of TiO2 nanorods and CdSe QDs are enhanced by increasing the diameter and decreasing the height and periodic space between the TiO2 nanorods. As a result, the light absorption is increased in the photoanodes at the visible region, leading to an improvement in the performance of the photoanode at visible light.

Morphological and electrical properties of SrTiO3/TiO2/SrTiO3 sandwich structures prepared by plasma sputtering**Project supported by the City University of Hong Kong Applied Research Grant (ARG) of China (Grant No. 9667122). One of the authors, Mr. Saqib Jabbar, is grateful to the Higher Education Commission (HEC) of Pakistan for financial support under IRSIP.

SrTiO3 (STO) and TiO2 are insulating materials with large dielectric constants and opposite signs of the quadratic coefficient of voltage (. Insertion of a TiO2 thin film between STO layers increases the linearity of the capacitance in response to an applied voltage, to meet the increasing demand of large-capacitance-density dynamic random access memory capacitors. Both STO and TiO2 suffer from the problem of high leakage current owing to their almost equivalent and low bandgap energies. To overcome this, the thickness of the thin TiO2 film sandwiched between the STO films was varied. A magnetron sputtering system equipped with radio frequency and direct current power supply was employed for depositing the thin films. TiN was deposited as the top and bottom metal electrodes to form a metal–insulator metal (MIM) structure, which exhibited a very large linear capacitance density of 21 fF/um2 that decreased by increasing the thickness of the TiO2 film. The leakage current decreased with an increase in the thickness of TiO2, and for a 27-nm-thick film, the measured leakage current was A. X-ray diffraction and Raman spectroscopy revealed that TiN, STO, and TiO2 films are crystalline and TiO2 has a dominant anatese phase structure.

Laser synthesis of 2D heterostructures of transitional metal oxides for photo sensors with high sensitivity

Photons of a KrF laser (248 nm) were used for the synthesis of Cr3−XO3−Y/Fe2O3−X two dimensional (2D) multilayer heterostructures by reactive pulsed laser deposition. Each nanometric multilayer heterostructure with a definite number of layers of iron and chromium oxides was deposited in 2D form on ⟨100⟩ Si substrate at its temperature 293 or 800 K resulted in changing of 2D multilayer heterostructure thickness in the range of 25–85 nm. X-ray diffractometer analysis confirmed polycrystalline structure of these deposits. Element analysis was carried out by an energy dispersive x-ray spectroscopy. All synthesized 2D multilayer heterostructures demonstrated semiconductor temperature trend with variable equivalent energy band gap (Eg) in the range of 0.36–0.87 eV. The more substrate temperature was the more Eg value, and the more 2D multilayer heterostructure photosensitivity. Optimum experimental parameters were found out to obtain the highest photosensitivity of 2D multilayer heterostructure. Highest obtained photosensitivity was high as 420 VC/W at white light power density ∼6 × 10−3 W/cm2. VC is “chemical” photo electromotive force induced in the deposited 2D multilayer heterostructure while it irradiating with a white light, W is white light power. High photosensitivity nature of the 2D multilayer heterostructure synthesized on a heated substrate was explained. Therefore, such 2D multilayer heterostructures of iron and chromium oxides exhibiting high photosensitivity are exceptionally a strong candidate for effective photo sensors of white light.

Experimental observation of low threshold optical bistability in exfoliated graphene with low oxidation degree

We have experimentally investigated low threshold Optical Bistability (OB) and multi-stability in exfoliated graphene ink with low oxidation degree. Theoretical predictions of N-layer problem and the resonator feedback problem show good agreement with the experimental observation. In contrary to the other graphene oxide samples, we have indicated that the absorbance does not restrict OB process. We have concluded from the experimental results and Nonlinear Schrödinger Equation (NLSE) that the nonlinear dispersion – rather than absorption – is the main nonlinear mechanism of OB. In addition to the enhanced nonlinearity, exfoliated graphene with low oxidation degree possesses semiconductors group III–V equivalent band gap energy, high charge carrier mobility and thus, ultra-fast optical response which makes it a unique optical material for application in all optical switching, especially in THz frequency range.

Band gap analysis of star-shaped honeycombs with varied Poisson’s ratio

In this paper, star-shaped honeycombs are analyzed in terms of their equivalent mechanical behaviors and band gap properties. Firstly, by applying Castigliano’s second theorem, the effective Young’s modulus and Poisson’s ratio are derived by an analytical method used in structural mechanics. On the basis of Bloch’s theorem, the dispersion characteristics are then analyzed by the dynamic matrix in conjunction with the Wittrick–Williams (W–W) algorithm. It should be noted that the presented method can form a more simple stiffness and mass matrices of the proposed structures, compared with the traditional finite element (FE) method. Thereafter, the effects of the geometrical parameters on the effective constants and band gaps are investigated and discussed. Numerical results demonstrate that the negative Poisson’s ratio provides an enhanced effective Young’s modulus of the considered honeycombs. Furthermore, the band gap exists in a much lower frequency region with an unchanged summing band gap width when the Poisson’s ratio is in negative values. In general, the work can serve as a guide for the optimal design of cellular structures.

Modeling and Analysis of Bandwidth-Enhanced Multilayer 1-D EBG With Bandgap Aggregation for Power Noise Suppression

A circuit model of multilayer electromagnetic bandgap (EBG) structure with application on bandgap aggregation design is investigated in this paper. A design concept for bandgap aggregation is merging the lowest two bandgaps into an equivalent wide bandgap by narrowing central passband. This goal could be achieved by optimizing pitch and arrangement of power/ground vias. The theoretical circuit model which only focuses on cutoff frequencies is proposed for efficient bandgap prediction. The accuracy of the proposed model is validated by comparison with full-wave simulation and measurement results. By using the circuit model, mechanism of bandgap aggregation can be explained well, and the influence of structural parameters can also be studied easily. Furthermore, effect on limiting excitation of propagation modes by narrowing central passband is also validated for merging adjacent bandgaps. Test boards with unit cell size 2.03 mm × 3.94 mm are fabricated and measured to validate the design concepts. Both simulation and measurement show the wide bandgap in insertion loss results, which ranges from 1.27 GHz to above 10 GHz by merging even higher bandgaps.

Excitation wavelength dependent photoluminescence intensity of six faceted prismatic ZnO microrods

This article presents the investigation on the large-scale synthesis of ZnO microrods with a simple low temperature hydrothermal method without using surfactants, organic solvents, or catalytic reagents. The synthesized ZnO powder is characterized with different techniques. The X-ray diffraction study reveals the excellent crystal quality of the ZnO product possessing the hexagonal (wurtzite-type) crystal structure. The scanning electron microscope observation confirms the formation of six faceted prismatic hexagonal ZnO microrods with the aspect ratio of 10. It also reveals that the ZnO microrods grow along the (0001) direction and finally emerge with a sharp tip because of the existence of polar faces. The UV–vis spectrum shows a sharp absorption peak centered at 370nm, which is in a good agreement with the equivalent bulk band gap value. The strong UV absorption peak implies the excellent crystal quality of the synthesized ZnO microrods. Room temperature photoluminescence spectroscopic study of the ZnO microrods with different excitation wavelengths reveals a strong band edge emission peak centered at 398nm and a defect related visible blue emission peak at 460nm. The decrease in photoluminescence intensity with negligible red shift in peak position is observed with increasing excitation wavelength.

Enhanced photocatalytic oxidation of arsenite to arsenate in water solutions by a new catalyst based on MoOx supported on TiO2

Photocatalytic oxidation of As(III) to As(V) was investigated using a new catalyst based on molybdenum oxide supported on titania (MoOx/TiO2), under different irradiation intensities and catalyst dosages. Photocatalysts were prepared by incipient wet impregnation of anatase titania with ammonium heptamolybdate solutions. The obtained samples were characterized by thermogravimetric analysis, N2 adsorption at −196°C, X-ray diffraction, Laser Raman spectra and UV–vis reflectance spectra. UV–vis DRS spectra of the photocatalysts evidenced that the surface coverage with MoOx did not significantly decrease the equivalent band gap energies. X-ray diffraction analysis showed that up to 8.4wt% Mo-loading, molybdenum oxide remains on the surface of titania support as amorphous phases. Raman spectra showed the presence of hydrated octahedrally molybdate anchored species interacting with TiO2 surface and a molybdenum oxide monolayer coverage of corresponding to about 9.8wt% of MoO3. Photocatalytic oxidation tests showed that TiO2 alone is not able to oxidize all As(III) present in solution, while the complete conversion of As(III) to As(V) was achieved in the presence of MoOx/TiO2 catalyst. In particular, the best conversion was observed within 60min of exposure to UV light irradiation with a Mo-loading corresponding to a monolayer coverage. As(V) produced during the photoreaction was completely released into solution, thus not occupying stably the active sites which results in a photocatalyst with high stability over the time.

1-eV InGaAsN/GaAs quantum well structure for high efficiency solar application grown by MOVPE

In this article, we have demonstrated 1-eV energy band gap In0.22GaAsNy/GaAs multi-quantum well (MQW) solar cells grown by a metal organic vapor phase epitaxy (MOVPE) system. With nitrogen incorporation, the equivalent band gap energy of quantum well structure will decrease and reach near 1eV. The structures of In0.22GaAsNy/GaAs MQWs were inserted into an intrinsic absorption layer for absorbing the incident light in the longer wavelength region. From the measurement results, the absorption band edge of In0.22GaAsNy/GaAs MQW solar cells is extended over 1300nm. On the other hand, in order to improve the device performance pre-deteriorated by nitrogen incorporation, a hybrid structure which consists of In0.22GaAs/GaAs and In0.22GaAsN0.043/GaAs quantum wells is adopted; with this hybrid quantum well structure as the absorption layer, consequently the short circuit current is enhanced from 10.85 to 15.29mA/cm2.

Variable-color poly(3,4-propylenedioxythiophene) electrochromics from precursor polymers

We have developed two approaches to processable precursors to conjugated polymers: main-chain and side-chain. Upon oxidative conversion to the conjugated polymer, a main-chain precursor yielded a nearly perfect spectral match, an identical λ max, and an equivalent band gap to that of electrodeposited chromophore, resulting in a color match. This precursor method has the potential to incorporate any chromophore and achieve spectral and color matching with relative ease, as opposed to extensive synthetic monomer design. We describe the synthesis and characterization of a new side-chain and two new main-chain precursor polymers, each of which contains a derivative of 3,4-propylenedioxythiophene, ProDOT-Me 2. The side-chain precursor tethers one ProDOT-Me 2 molecule to a poly(norbornene) backbone; the main-chain systems are perfectly alternating copolymers of ProDOT-Me 2, one with dimethylsilane and one with tetramethyldisiloxane. Electronic and optical properties for these converted precursors were described and compared to electrodeposited PProDOT-Me 2.

Properties of Sr7Nb13O36/Nb2O5/Sr7Nb13O36 Laminated Films for Gigabit Memory Capacitors

Properties of Sr7Nb13O36/Nb2O5/Sr7Nb13O36 laminated films for gigabit memory capacitors were investigated. The equivalent oxide thicknesses (EOT), dielectric constant, band gap and leakage current for a single layer Sr7Nb13O36 having 10 nm film thickness were 1.12 nm, 34.8, 4.45 eV and 3×10-9 A/cm2 at 1 V, respectively. Those properties for a single layer Nb2O5 having 20 nm thickness were 0.72 nm, 108, 4.25 eV, and 2×10-8 A/cm2, respectively. The Sr7Nb13O36/Nb2O5/Sr7Nb13O36 laminated films satisfied the EOT of 0.77 nm, effective dielectric constant of 51, effective band gap of 4.35 eV and leakage current density of 6.4×10-9 A/cm2 at 1 V. The fraction of applied voltage across the Sr7Nb13O36 film was dominant so that the voltage across the high dielectric constant Nb2O5 film could be reduced. The Sr7Nb13O36/Nb2O5/Sr7Nb13O36 laminated film is a solution for gigabit memory capacitors.

A step forwards in ethanol selective photo-oxidation

This work focuses on the optimization of a photocatalyst formulation for the selective oxidation of ethanol to acetaldehyde. VO(x)/TiO(2) catalysts at different vanadium loading were studied in a gas-solid photocatalytic fluidized bed reactor at high illumination efficiency, in which the bed is constituted by photocatalyst diluted with alpha-Al(2)O(3) or silica gel. Photocatalytic tests showed the selective formation of acetaldehyde, with ethylene and carbon dioxide as by-products. Selectivity is influenced by the vanadium loading. For ethanol inlet concentration of 0.2 vol%, maximum conversion and acetaldehyde selectivity of 73% and 97%, respectively, were obtained at 100 degrees C on catalyst at nominal 5 wt% V(2)O(5) content (53% of surface monolayer) mixed with alpha-Al(2)O(3). Selective sites were related to surface polymeric vanadates possessing Ti-O-V and V-O-V functionalities while the photoactivity appeared correlated with the catalyst equivalent band gap energy. Increasing the ethanol inlet concentration to 1 vol% and diluting the catalyst with silica gel, total ethanol conversion with about 97% selectivity to acetaldehyde was achieved with a photoreactivity of 0.34 mol m(irradiated)(-3) s(-1). This is three times higher than reported for other photoreactors.

Photocatalytic cyclohexane oxidehydrogenation on sulphated MoO x/γ-Al 2O 3 catalysts

The photocatalytic oxidative dehydrogenation of cyclohexane on sulphated MoO x /γ-Al 2O 3 catalysts has been studied in a two-dimensional fluidized bed photoreactor. The influence of Mo loading at similar sulphate content and the effect of catalyst preparation method have been investigated. Considering the influence of Mo loading at similar sulphate content, the highest photoactivity at 2.4 SO 4 wt% was found at MoO 3 loading of 8 wt%. Selectivity to cyclohexene was 100%, irrespective of the Mo content. At fixed MoO x content, in particular at 50% of theoretical monolayer coverage, the preparation method of catalysts strongly affected the photocatalysts performances, showing in addition a slight decrease in selectivity to cyclohexene due to side-production of benzene. All the catalysts showed a similar equivalent band gap energy. Thermogravimetric analysis evidenced the presence of surface sulphate species of different thermal stabilities. A linear correlation of photoactivity with the surface sulphates amount of lower thermal stability has been found for all sub-monolayer MoO x sulphated catalysts. The neighboring of surface sulphates to octahedral polymolybdate species appears to be a key parameter for the photoactivity of the catalysts. The catalyst selectivity was related to surface acidity. Higher acidity resulted in increased cyclohexene dark adsorption and consequently in enhanced benzene formation.

Quantum confinement in amorphousTiO2 films studied via atomic layer deposition

Despite the significant recent increase in quantum-based optoelectronics deviceresearch, few deposition techniques can reliably create the required functionalnanoscale systems. Atomic layer deposition (ALD) was used here to study thequantum effects attainable through the use of this ångström-level controlled growthprocess. Size-dependent quantum confinement has been demonstrated usingTiO2 layers of nanoscale thickness applied to the surfaces of silicon wafers.TiO2 films weredeposited at 100 °C using TiCl4 andH2O2 in a viscous flow ALDreactor, at a rate of 0.61 Å/cycle. The low-temperature process was utilized to guarantee the amorphous deposition ofTiO2 layers and post-deposition thermal annealing was employed to promote crystallite-size modification.Hydrogen peroxide significantly reduced the residual chlorine that remained from a typicalTiCl4–H2O ALD process at this temperature, down to 1.6%. Spectroscopic ellipsometry was used toquantify the optical properties both below and above the bandgap energy. A central compositedesign was employed to map the surface response of the film thickness-dependent bandgapshift for the as-deposited case and up to a thermal annealing temperature of550 °C. The Brus model was used to develop a correlation between the amorphousTiO2 film thickness and the quantum length to promote equivalent bandgap shifts.

MBE growth of wide band gap wurtzite MgZnO quasi-alloys with MgO/ZnO superlattices for deep ultraviolet optical functions

Wurtzite quasi-alloys of MgZnO with MgO/ZnO superlattices have been grown by molecular beam epitaxy on sapphire substrates on high-quality ZnO buffer layers. The equivalent band gap energy of the quasi-ternary MgZnO was successfully tuned from 3.3 to 4.65 eV by changing the thicknesses of the MgO and ZnO layers. The near-band-edge cathodoluminescence was obtained from the MgO/ZnO superlattice without noticeable deep-level emissions and the multiple quantum well structures with MgO/ZnO superlattice quasi-ternary alloys were definitely fabricated, being capable of emitting ultraviolet (UV) luminescence from the well layers. These results suggest the promising potential of their optical functions for deep UV light emission and/or detection applications.

Determination of the substitutional nitrogen content and the electron effective mass in InNxSb1−x (001) epitaxial layers

The electronic properties of epitaxial layers of InNxSb1−x grown on GaAs (001) substrates have been investigated using high-resolution electron-energy-loss spectroscopy (HREELS), Hall measurements and band structure modelled by a modified k·p Hamiltonian. The chemical composition of the epitaxial layers was found to be InN0.02Sb0.98 from secondary ion mass spectrometry (SIMS). However, electrical measurements and band structure calculations indicate a band gap of 135 meV, thus entailing an epilayer composition of InN0.0015Sb0.9985 , indicating that approximately 7.5% of the nitrogen present is electrically active, being located substitutionally on antimony lattice sites. Hall measurements and simulations of HREEL spectra imply a much larger effective mass at the Fermi level than a conventional Kane band structure material with an equivalent band gap.

Auger recombination in long-wavelength infrared InNxSb1−x alloys

Dilute nitrogen alloys of InSb exhibit strong band gap bowing with increasing nitrogen composition, shifting the absorption edge to longer wavelengths. The conduction band dispersion also has an enhanced nonparabolicity, which suppresses Auger recombination. We have measured Auger lifetimes in alloys with 11 and 15 μm absorption edges using a time-resolved pump-probe technique. We find the lifetimes to be longer at room temperature than equivalent band gap Hg1−yCdyTe alloys at the same quasi-Fermi level separation. The results are explained using a modified k⋅p Hamiltonian which explicitly includes interactions between the conduction band and a higher lying nitrogen-related resonant band.