Electronic Band Gap Structure Research Articles

Stable novel silicon allotropes in space group P2/m with various band gap structures by high-throughput screening

Silicon is the fundamental material for the semiconductor and microelectronics industries, but controlling the electronic band gap structure of diamond-type silicon remains a huge challenge to adapt to growing applications. Here, we have predicated 23 new silicon allotropes in space group P2/m from 279 possible structures by high-throughput screening accompanied by graph and group theory based on random strategy (RG2) code. The mechanical, electronic and optical properties of these structures were studied in detail. These novel silicon allotropes demonstrate various electronic structures, including metal, direct/quasi direct bandgap structure, and indirect bandgap structures. These new silicon allotropes demonstrate various electronic structures, including metal, direct/quasi direct bandgap structure, and indirect bandgap structures. Besides different electronic bandgap structures, all 23 structures exhibit strong absorption in the visible light region and P2/m-15 demonstrates the excellent mechanical properties (Bulk modulus beyond 80 GPa). Based on their nice stability, good mechanical, electronic and optical properties validated by the ab inito molecular dynamics simulation, phonon spectra and density functional theoretical calculations, these predicted silicon allotropes provide not only ideas for the synthesis of new silicon allotropes but also dawn for expanding the application of semiconductor materials.

Impact of Sn-doping on the optoelectronic properties of zinc oxide crystal: DFT approach.

This study aims to provide a concise overview of the behavior exhibited by Sn-doped ZnO crystals using a computational technique known as density functional theory (DFT). The influence of Sn doping on the electronic, structural, and optical properties of ZnO have been explored. Specifically, the wavelength dependent refractive index, extinction coefficient, reflectance, and absorption coefficient, along with electronic band gap structure of the Sn doped ZnO has been examined and analyzed. In addition, X-ray diffraction (XRD) patterns have been obtained to investigate the structural characteristics of Sn-doped ZnO crystals with varying concentrations of Sn dopant atoms. The incorporation of tin (Sn) into zinc oxide (ZnO) has been observed to significantly impact the opto-electronic properties of the material. This effect can be attributed to the improved electronic band structure and optical characteristics resulting from the tin doping. Furthermore, the controllable structural and optical characteristics of tin-doped zinc oxide will facilitate the development of various light-sensitive devices. Moreover, the impact of Sn doping on the optoelectronic properties of ZnO is thoroughly investigated and documented.

High-throughput calculation screening for new silicon allotropes with monoclinic symmetry.

A total of 87 new monoclinic silicon allotropes are systematically scanned by a random strategy combined with group and graph theory and high-throughput calculations. The new allotropes include 13 with a direct or quasi-direct band gap and 12 with metallic characteristics, and the rest are indirect band gap semiconductors. More than 30 of these novel monoclinic Si allotropes show bulk moduli greater than or equal to 80 GPa, and three of them show even greater bulk moduli than diamond Si. Only two of the new Si allotropes show a greater shear modulus than diamond Si. The crystal structures, stability (elastic constants, phonon spectra), mechanical properties, electronic properties, effective carrier masses and optical properties of all 87 Si monoclinic allotropes are studied in detail. The electron effective masses ml of five of the new allotropes are smaller than that of diamond Si. All of these novel monoclinic Si allotropes show strong absorption in the visible spectral region. Taken together with their electronic band gap structures, this makes them promising materials for photovoltaic applications. These investigations greatly enrich the current knowledge of the structure and electronic properties of silicon allotropes.

A triband EBG loaded microstrip fractal antenna for THz application

Future wireless communication needs antenna with multifunctional operation. This paper focuses on Terahertz Antenna that could be easily integrated with micro and nano devices. In this paper, an octagonal shaped Microstrip Fractal Antenna loaded with the EBG structure is designed for tri-band terahertz application. Triple band characteristic achieved by fractal radiating patch is loaded with Electronic Band Gap (EBG). The antenna is working on triple band characteristics at 948 GHz, 984GHz and, 1040 GHz with overall dimensions of 700x900 µm2. The result and performance show that the recommended antenna will be compatible with compact wireless devices and Monolithic Microwave Integrated Circuit (MMIC). All simulation work has been done using electromagnetic software Ansoft High Frequency Structure Simulator (HFSS) and CST studio suite. The electromagnetic features like S11 parameters, VSWR, gain, efficiency and the radiation characteristics of such antenna are also explored. The simulation results show that this antenna has 9 dB realized gain at 0.948 THz resonating frequency.

Synthesis, crystals structures and theoretical studies of novel alkali copper indium orthophosphates ACuIn(PO4)2 (A = Na, K and Rb)

ACuIn(PO4)2 compounds (A ​= ​K and Rb) have been prepared by the flux method and solid-state reaction. They were characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) with Energy Dispersive X-Ray analysis (EDX), Fourier Transform Infra-Red (FTIR), Raman and optical spectroscopies, as well as a Density Functional Theory (DFT) study has been performed. Single XRD analysis shows that the compounds were isostructural and crystallize in the monoclinic centrosymmetric P21/n space group. There are one A (Na, K or Rb), one Cu, one In, two P and eight O sites in the asymmetric unit of the ACuIn(PO4)2 structure. Its structure is made up from corners-sharing between InO6 octahedra and Cu2O8 units, built up from edge-sharing of two CuO5 polyhedra, to form zigzag chains ranging infinitely along the b axis. The inter-connection between these chains is assured by the PO4 tetrahedra creating a 3D framework with six-sided tunnels parallel to the [101] direction, where the A+ ions are located. XRD diagrams of the powder samples reveal the formation of single purity phases with monoclinic symmetry. FTIR and Raman spectroscopies revealed the presence of two isolated PO4 groups in the analyzed phosphates. The SEM-EDX verifies the morphology and the chemical composition of the synthesized samples. The diffuse reflectance spectroscopy (DRS) has proven an indirect bandgap of 3.34 ​eV, 3.33 and 2.82 ​eV for NaCuIn(PO4)2, KCuIn(PO4)2 and RbCuIn(PO4)2, respectively. The electronic bandgap structure and bonding character analysis of important atom pairs in the ACuIn(PO4)2 structure are also studied in details.

Oxygen doping facilitated N-vacancies in g-C3N4 regulates electronic band gap structure for trimethoprim and Cr (VI) mitigation: Simulation studies and photocatalytic degradation pathways

The strategic designing of graphitic carbon nitride (CN)by elemental doping is likely to generate nitrogen vacancies which benefit by serving as electron trapping sites or by introducing additional energy levels (mid-gap states). In this work, uracil-assisted oxygen doped graphitic carbon nitride (OCNv-Ux) was synthesized by the hydrothermal method. The OCNv-U40 exhibited vigorous photocatalytic efficiency for 98% trimethoprim (TMP) antibiotic degradation and 90.8% Cr (VI) reduction under visible light irradiations. A combined inference from experimental results and simulation studies indicates band gap reduction from 2.7 to 2.34 eV for extended visible light absorption up to 620 nm. In particular, the density of states comprehends band structure regulation by the electron redistribution resulting in valence band up shifting and downshift of the conduction band, as validated by Mott-Schottky spectra. The synergistic outcomes of nitrogen vacancies and oxygen doping sites restrain the recombination of electron-hole pairs by mid-gap state formation and also promote high oxygen molecule adsorption on the nitrogen vacancies. The pioneering advantage of highly adsorbed oxygen molecule leads to the generation of plentiful superoxide anion radicals along with indirect production of hydroxyl radicals via in-situ produced H2O2, evident by radical scavenging and electron paramagnetic resonance experiments. The effect of chloride and nitrate anions showed inhibitory effect on the TMP degradation efficiency. The identification of formed intermediates and TMP degradation mechanism involving oxidation, hydroxylation, and cleavage was proposed, as investigated by TMP DFT studies. This research accomplishes significant enhancement in pristine CN photocatalytic activity by the virtue of increased specific surface area, fully exposed N-vacancies active sites, optimized electronic, structure and visible light active band gap.

Multidimensional Perovskites for High Detectivity Photodiodes.

Low-dimensional perovskites attract increasing interest due to tunable optoelectronic properties and high stability. Here, it is shown that perovskite thin films with a vertical gradient in dimensionality result in graded electronic bandgap structures that are ideal for photodiode applications. Positioning low-dimensional, vertically-oriented perovskite phases at the interface with the electron blocking layer increases the activation energy for thermal charge generation and thereby effectively lowers the dark current density to a record-low value of 5 × 10-9 mA cm-2 without compromising responsivity, resulting in a noise-current-based specific detectivity exceeding 7 × 1012 Jones at 600nm. These multidimensional perovskite photodiodes show promising air stability and a dynamic range over ten orders of magnitude, and thus represent a new generation of high-performance low-cost photodiodes.

DESIGN OF SQUARE MICROSTRIP PATCH MULTI BAND ANTENNA FOR WIRELESS COMMUNICATION USING EBG STRUCTURE

Application of electromagnetic band-gap (EBG) structure and its use in the design of antenna and microwave integrated circuits is becoming more attractive. The recent electromagnetic band-gap structure method is capturing more importance in antenna design due to its uniqueness properties to suppress the propagation of surface waves in microstrip patch antenna. In this paper a square microstrip antenna is designed and its performance parameters are compared with geometry designed on EBG structure. The square antenna of 29 mm x29 mm size is designed at 2.455 GHz and analysis is done using IE3D simulation software. The proposed work mainly focuses on modification of antenna using electronic band gap structure (EBG). The antenna parameters such as Return loss, VSWR, Gain and Bandwidth, with and without EBG are obtained using IE3D simulation tool. The Electromagnetic band-gap structures have been used to improve the performance of the gain of the antennas and radiation patterns. One of the main advantages of electromagnetic band-gap structure is its ability to suppress the surface wave current present on the microstrip antenna. Combining the square patch with EBG structure, the bandwidth of the antenna has been increased by 34.66%, and attained gain of 44.44% at resonant frequency around 2.4 GHz as compared to the antenna without EBG..

Electronic bandgap miniaturized UWB antenna for near-field microwave investigation of skin

Near-field microwave investigation and tomography has many practical applications, especially where the trend of fields and signals in different environments is vital. This article shows an elliptical patch ultra-wideband antenna fed by a transmission line for the near-field characterization of cancerous cells in the skin. The antenna comprises an elliptical patch, stub loading to shift the band to lower bands, and an electronic bandgap structure on the ground side. Even though the antenna has a low profile of 15 × 15 mm2, the proposed antenna has more promising results than recent studies. Furthermore, both simulated near-field and far-field results show a broad bandwidth of 3.9–30 GHz and a resonance at 2.4 GHz applicable for industrial, scientific, and medical band applications. The proposed antenna also illustrates a peak gain of 6.48 dBi and a peak directivity of 7.09 dBi. Free space and skin (on a layer of breast fat and a tumor with a diameter of 4 mm at the boundary of skin and breast) are used as test environments during the simulation and measurement of near-field and far-field investigations while considering a phantom breast shape. Both far-field and near-field microwave investigations are performed in Computer Simulation Technology studio, and results are then compared with the measured data. The simulated and measured results are in good agreement, and the focused energy around the tumor is completely reconstructed. Therefore, the proposed antenna can be an adequate candidate for the differentiation of breast skin and tumor to reconstruct the tumor’s image.

Giant Enhancement of Fluorescence Emission by Fluorination of Porous Graphene with High Defect Density and Subsequent Application as Fe3+ Ion Sensors.

Defect-mediated nonradiative recombination in traditional semiconductors, such as porous graphene, tremendously lowers the fluorescence emission, thus greatly restricting their applications in more extensive fields. Here, we report that the fluorescence emission of porous graphene with a high defect density has a giant enhancement (about two orders of magnitude) by a direct and simple fluorination strategy, showing a fine defect-tolerance characteristic. Meanwhile, the corresponding fluorocarbon bonds with excellent thermostability (over 500 °C in N2 even air) also bring about good stability. The photophysical origins during the whole photoluminescence evolution are further investigated. In the excitation process, the coexistence of fluorine and aromatic regions in fluorinated porous graphene (FPG) contributes to producing a new electronic band gap structure to match the maximum excitation wavelength, then numerous excitons generate, which is a precondition for strong fluorescence emission. In the emission process, weak electron-phonon interactions, large rigidity, and constrained electron at the defects in FPG greatly reduce nonradiative recombination loss. Moreover, fluorine at the defects also reduces interlayer interactions among FPG nanosheets and resists the influence of absorbed impurities, thereby further restricting nonradiative recombination pathway. Highly fluorescent FPG has been utilized as a fascinating tool to achieve sensitive and naked-eye detection of Fe3+ ions with a high selectivity. The fluorescence quenching efficiency reaches 24% even with an ultralow concentration of Fe3+ (0.06 μM), and that increases to 84% when the concentration of Fe3+ is 396 μM.

Toward high-efficiency photoluminescence emission by fluorination of graphene oxide: Investigations from excitation to emission evolution

Graphene oxide (GO) alters zero bandgap of graphene to achieve photoluminescence (PL), while the low quantum yield (generally: PLQY < 1%) seriously restricts its further development in practical applications. Here we employ two-step fluorination strategy to controllably modify GO, achieving island structure of aromatic regions in continuous phase of fluorine regions. The fluorinated product (FGO) presents a high PLQY of 66%, far exceeding the largest value (21.2%) reported for modifications of GO. We systematically and meticulously investigate fluorine effect of FGO during whole PL evolution. In excitation process, the coexistence of fluorine and aromatic regions in FGO is responsible for new electronic bandgap structure then multitudinous excited electrons produce, thus providing foundation for strong PL. In emission process, Raman measurements show that the weaker electron-phonon interactions in FGO result in slower nonradiative decay. It is attributed to that FGO possesses larger rigidity, as demonstrated by temperature-dependent fluorescence spectra, broadband dielectric measurements, density functional theory calculations and infrared spectra. Interestingly, different types of fluorine-related groups in FGO play different roles. That is, unoriented CF2 and CF3 groups realize passivation of defects, and C–F bonds perpendicular to graphene plane contribute to weakening interlayer interactions, both greatly enhancing PL.

Integrated-EBG Ridge Waveguide and Its Application to an E-Band Waveguide 32×32 Slot Array Antenna

A methodology of designing an E-band waveguide 32×32 slot array antenna with high-efficiency and low-cost manufacturing characteristics is proposed in this article, which is based on an integrated electronic bandgap (EBG) ridge waveguide designed by integrating a cross rectangle-hollow EBG structures in the conventional ridge waveguide. The integrated EBG structure intercepts the leakage from the unconnected gap in between the two metallic plates of the waveguide, and then it decreases the manufacturing cost without using the diffusion bonding technology and multi-layer welding assembly process. The design guideline is discussed, and then the antenna is fabricated. The measured radiation characteristics are in good agreement with predicted ones, which confirms that the proposed cross rectangle-hollow EBG structures is an attractive candidate of high-performance millimeter wave antenna.

Performance Analysis of a Defected Ground-Structured Antenna Loaded with Stub-Slot for 5G Communication.

In this paper, a defected ground-structured antenna with a stub-slot configuration is proposed for future 5G wireless applications. A simple stub-slot configuration is used in the patch antenna to get the dual band frequency response in the 5G mid-band and the upper unlicensed frequency region. Further, a 2-D double period Electronic band gap (EBG) structure has been implemented as a defect in the metallic ground plane to get a wider impedance bandwidth. The size of the slots and their positions are optimized to get a considerably high impedance bandwidth of 12.49% and 4.49% at a passband frequency of 3.532 GHz and 6.835 GHz, respectively. The simulated and measured realized gain and reflection coefficients are in good agreement for both operating bandwidths. The overall antenna structure size is 33.5 mm × 33.5 mm. The antenna is fabricated and compared with experimental results. The proposed antenna shows a stable radiation pattern and high realized gain with wide impedance bandwidth using the EBG structure, which are necessary for the requirements of IoT applications offered by 5G technology.

Photocatalytic disinfection efficiency of 2D structure graphitic carbon nitride-based nanocomposites: a review

Nanostructured carbon-based photocatalysts have gained attention in photocatalytic disinfection of microbial species. With distinctive features of possessing appropriate electronic band gap structure and high chemical and thermal stability, metal-free polymeric 2D stacked structure graphitic carbon nitride (g-C3N4) is an important photocatalytic material for environmental and energy applications. Besides, it has the potential for inactivation of harmful pathogens. Disinfection of microbial species is mainly ascribed to the formation of reactive oxidative species. Further, surface modification of g-C3N4 can remarkably improves photocatalytic disinfection efficiency. In this review, we have discussed the recent advances in photocatalytic disinfection using g-C3N4-based nanocomposites. An overview of metal-free nanostructure g-C3N4, metal (anions) and nonmetal (cations)-doped g-C3N4 and g-C3N4 hybridized with low band gap semiconductor is also presented. Moreover, we have emphasized on the photocatalytic disinfection mechanism associated with g-C3N4-modified composites. Nitrogen-rich g-C3N4 polymeric material can serve as an alternative to metal oxide (TiO2 and ZnO) photocatalysts for photocatalytic disinfection technology. Other applications such as CO2 photoreduction, H2 generation, organic pollutant degradation, and sensing using g-C3N4-based nanocomposites are also summarized.

Reduced mutual coupling MIMO antenna

In this paper, a reduced mutual coupling 1 × 2 inset feed rectangular patch antenna is presented. The antenna elements are separated by a distance of λ0/4 exhibiting excellent isolation of −55 dB at 5 GHz band. To improve the isolation between closely placed antennas, a compact planar meander line based electronic Bandgap structure (EBG) behaves like a double negative (DNG) material is placed between them. The proposed EBG structure is implemented on the MIMO antenna with continuous as well as discontinuous ground plane. It is found that the EBG structure with discontinuous ground plane improves at least 6 dB isolation between antenna elements than continuous ground. The proposed antenna structures are fabricated showing good agreement between simulated and measured results.

Postillumination Activity in a Single-Phase Photocatalyst of Mo-Doped TiO2 Nanotube Array from Its Photocatalytic “Memory”

Several composite photocatalysts with photocatalytic “memory” effect had recently been developed, which could possess postillumination activity for an extended period of time in the dark for many potential applications. Here, a single-phase photocatalyst of Mo-doped TiO2 nanotube array was developed for the first time with the postillumination photocatalytic memory effect, which could eliminate the requirement of building composite photocatalysts with heterojunctions and largely broaden the material selection for this interesting photocatalytic memory effect. Because of the proper electronic band gap structure and variable valences of Mo dopants, photogenerated electrons could transfer from TiO2 to Mo dopants and be trapped there by reducing Mo6+ to Mo5+ under UV irradiation. When UV irradiation was switched off, these trapped electrons could be released from Mo dopants and react with O2 through the two-electron O2 reduction process to produce H2O2 in the dark. Thus, Mo-doped TiO2 nanotube array could remain active in the dark as demonstrated by its effective disinfection of Escherichia coli cells when UV irradiation was turned off. This work demonstrated that photocatalysts with postillumination photocatalytic memory effect were not limited to composite photocatalysts with heterojunctions. Various single-phase photocatalysts could also possess this interesting photocatalytic memory effect through doping metal elements with variable valences.

Investigations of electronic and thermoelectric properties of half-Heusler alloys XMgN (X = Li, Na, K) by first-principles calculations

The rapid depletion of the fossil fuels and their environment repercussion can be resolved wisely by exploring the efficient and sustainable materials which have the ability to convert waste heat into electricity. Half-Heusler materials are also considered one of the promising class for the thermoelectric applications. In this paper, the investigations on the thermoelectric properties of half-Heusler compounds, XMgN (X=Li, Na, K) are reported. The study is carried out within full potential linearised augmented plane wave plus local orbital approach (FP-LAPW+lo) in conjunction with the semi-empirical Boltzmann theory. To incorporate exchange-correlation energy/potential part, Perdew and Wang (PW) suggested local density approximation (LDA), parameterized generalized gradient approximation (GGA) by Perdew-Berke-Ernzerhof (PBE) and the modified Becke-Johnson (mBJ) exchange potential by Trans-Blaha are used. Our electronic band structure calculations show that the KMgN is indirect band gap material, whereas LiMgN and NaMgN demonstrate their direct electronic band gap structure. To comprehend their thermoelectric character, the calculations of the Seebeck coefficient, electrical conductivity, thermal conductivity, power factor and figure of merit (ZT) are carried out at temperatures of values 300K, 600K, and 900K. From our calculations, the optimal value of Seebeck coefficient for the all three materials although was found at 300K, the results of the Seebeck coefficient for the LiMgN were found more good as compared to NaMgN and KMgN and in coordination with the Lee et al. study as well. Similarly, electrical conductivity results endorse the Wiedemann-Franz law. The calculated results of the ZT parameter (ZT~1) for the all three materials (LiMgN, NaMgN, and KMgN) revealing that the investigated materials have a potential to be used for thermoelectric applications.

Single-Nanoparticle Plasmonic Electro-optic Modulator Based on MoS2 Monolayers.

The manipulation of light in an integrated circuit is crucial for the development of high-speed electro-optic devices. Recently, molybdenum disulfide (MoS2) monolayers generated broad interest for the optoelectronics because of their huge exciton binding energy, tunable optical emission, direct electronic band-gap structure, etc. Miniaturization and multifunctionality of electro-optic devices further require the manipulation of light-matter interaction at the single-nanoparticle level. The strong exciton-plasmon interaction that is generated between the MoS2 monolayers and metallic nanostructures may be a possible solution for compact electro-optic devices at the nanoscale. Here, we demonstrate a nanoplasmonic modulator in the visible spectral region by combining the MoS2 monolayers with a single Au nanodisk. The narrow MoS2 excitons coupled with broad Au plasmons result in a deep Fano resonance, which can be switched on and off by applying different gate voltages on the MoS2 monolayers. A reversible display device that is based on this single-nanoparticle modulator is demonstrated with a heptamer pattern that is actively controlled by the external gates. Our work provides a potential application for electro-optic modulation on the nanoscale and promotes the development of gate-tunable nanoplasmonic devices in the future.

Industrial liquid characterization enhancement using microwave sensor equipped with electronic band gap structure

In this paper, we present a novel sensor for permittivity measurement of the industrial liquids to achieve more sensitivity. An electronic band gap (EBG) structure is used. The simulation results show that applying EBG scheme enhances the electric field strength at the measuring part. This issue causes a significant shift in resonant frequency and therefore an increased sensitivity of the designed sensor. The proposed sensor is tested for characterization of liquids with various permittivity and loss tangent values, and the results show the proposed sensor can precisely classify a wide range of liquids in terms of electromagnetic properties. Measurement results indicate that the presented sensor is well suited for transformer oil aging applications.

Fast analysis and optimal design of metasurface for wideband monostatic and multistatic radar stealth

In this paper, a metasurface (MS) is designed based on the hybrid array pattern synthesis and particle swarm optimization method for wideband monostatic and multistatic radar stealth. The non-absorptive MS is composed of two kinds of electronic band gap structures with the reflection phase difference of 180° (±37°) over a wide frequency range. Far field scattering pattern of the MS can be quickly and accurately synthetized by the method of moments and array pattern synthesis. A new strategy is proposed for realizing the diffusion reflection of electromagnetic waves by redirecting electromagnetic energies to more directions through optimizing the reflected phase arrangement for the MS by hybrid array pattern synthesis and particle swarm optimization algorithm. Due to the non-uniform distributions of phase gradient between neighboring lattices, numerous scattering lobes are produced in the upper half-space, leading to a great reduction of bistatic radar cross section (RCS). The −10 dB RCS reduction bandwidth of 80.2% is achieved for both monostatic and bistatic at normal incidence. The specular reflection and bistatic scattering for oblique incidence with TE and TM polarizations are also considered in detail. The measured results are in good agreement with the corresponding simulations.