Variation Of Band Gap Research Articles

Sequentially evaporated layer deposition stack of CuxS thin films for photonics applications

CuxS(x;1,2) layers were grown on thermal annealing of the sequentially evaporated layer deposition (SELD) stack of Cu/S from 373 to 573 K. The thicknesses of the deposited stacks were fixed at 200 and 600 nm. The 300 K deposited layers possess a CuS (covellite) phase and a few impurity peaks of Sulphur (S). The as-deposited films of both thicknesses provided the CuS (covellite) phase with impurity peaks of Sulphur (S). The CuS single phase was observed at 373 and 473 K. The CuS transformed into a copper-rich Cu2S (chalcocite) phase at 523 K, and the same phase continued at 573 K. The Cu2S phase was obtained on re-evaporation of S from CuS at 523 K. An intermediary digenite phase was also spotted at 523 K. The CuS and Cu2S phases were confirmed from the Raman spectra. The oxidation states of Cu and S of the CuS films were also determined from XPS analysis. The Cu 2p and S 2p levels of CuS (covellite) were established using high-resolution XPS spectra. The phase transformation from CuS to Cu2S and change in stoichiometry at higher temperatures give rise to bandgap variation from 2.30 to 1.20 eV for direct and 2.10–1.34 eV for indirect allowed bandgaps. The absorption coefficient (α) for both thickness values is > 1 × 105 cm-1. Further, the 600 nm films provided higher absorption coefficient (α) values than the 200 nm layers. The unique electrical and optical properties and bandgap tuning make CuS and Cu2S thin films suitable for gas sensors, photodetectors, absorber layers in low-cost PV solar cells, and energy storage applications.

Lead-Free Cs2BB′X6 (B: Ag/Au/Cu, B′: Bi/Sb/Tl, and X: Br/Cl/I) Double Perovskites and Their Potential in Energy Conversion Applications

A mere decade-long research focused on perovskites for photovoltaics (PVs) has unearthed their exciting promise. However, as an alternative to the inaugural class of single perovskites, which suffer from instability and toxicity, an interesting class of halide double perovskites (DPs) have recently been in the hot list of photovolatic (PV) researchers. This article presents 27 Cs2BB′X6 halide DPs using different exchange–correlation approximations and reports investigations based on factors such as the Goldschmidt tolerance factor (t) and modified tolerance factor (t′) and thermodynamical investigations considering mixed decomposition pathways for assessing their stability. The spin–orbit coupling (SOC) is explored to understand the role of the heavy element as an alternative to Pb. A wide range of band gaps (0.2 eV to 2.35 eV) are noticed for the 27 DPs. As a single exception, a halide DP with a trivalent thallium cation exhibits metallic characteristics. Further, an insight into the mechanism behind band gap variation is correlated with different B/B′/X combinations and understood from molecular orbital alignment analysis. Such a broad band gap spectrum has the potential to provide the possibility of integrating them in single- or multiple-junction solar cells or thermoelectric applications. This article, on the whole, hopefully provides insights into the potential of DPs for various applications befitting their particular material properties.

TeO2 for enhancing structural, mechanical, optical, gamma and neutron radiation shielding performance of bismuth borosilicate glasses

The synthesized 12Bi2O3– 8BaO–12ZnO-0.5CeO2-17.5SiO2- (50-x) B2O3- xTeO2 glasses with x = 0, 10, 20, 30 and 40 mol% (coded BiTe-0 to BiTe-40) were investigated in terms of physical, structural, optical and mechanical properties to examine the influence of CeO2 and TeO2 on the heavy metal oxide (HMO) borosilicate network. Density values increased continuously with increasing TeO2 concentration with BiTe-40 glass exhibiting maximum value of 5.0875 gcm−3. This property helped in enhancement of refractive index values from 1.769 for BiTe-0 to 1.942 for BiTe-40. Fourier transform infrared (FTIR) analysis of studied glasses revealed the presence of additional small peak at 683 cm−1 in BiTe-30 and BiTe-40 which confirmed the formation of stable TeO4 units in the glass network. The deep brown colour of the glass existing due to bismuth's presence was nullified by CeO2 and TeO2 additives which improved transparency of the glass. Urbach analysis of these glasses led to optical bandgap variation between 3.27 eV and 2.73 eV for 0–40 mol% TeO2 concentration. Makishima and Mackenzie model was utilized for evaluation of elastic property of the glasses, and Poisson's ratio ranging between 1.935 and 1.953 was obtained. Vickers micro-indentation test on the current glasses revealed decreasing microhardness from 4.116 to 4.076 GPa with TeO2 variation from 0 to 40 mol% at 9.8 N load. Gamma radiation shielding parameters were determined using Phy-X/PSD software and it was found that BiTe-40 glass produce maximum MAC (mass attenuation co-efficient) values in high photon energy region 3.5–15 MeV. The present article also contains a detailed emphasis on behaviour of gamma radiation build-up factors at different incident photon energy and TeO2 concentration. The increasing trend of exposure build up factor (EBF) was seen with increasing penetration depth inside the samples at all energies, indicating that glasses of larger thickness improve the escape probability of photons. Meanwhile, fast neutron removal cross-section (FNRCS) was highest for BiTe-10 sample (0.10118 cm−1) which also surpassed the value of ordinary concrete (0.093 cm−1). Overall, the present glass system bested other conventional shields available commercially in terms of gamma and neutron radiation shielding effectiveness.

The tunable electronic structure and optical properties of vacancy-ordered double perovskites Tl2PdBrxCl6-x (x = 0, 2, 4, 6)

Double perovskites show excellent stability and suitable band gaps, which are superior materials for solar cell applications. In this work, the structure, electronic, and optical properties of vacancy-ordered double perovskites Tl2PdBrxCl6-x (x = 0, 2, 4, 6) are explored by first-principles calculations. The tunable band gaps of the studied compounds are in the range of 1.3–2.2 eV. The band gap is narrowed from Tl2PdCl6 to Tl2PdBr6. Moreover, the band gap of Tl2PdCl6 can be adjusted to the appropriate band gap value through minor Br doping. High concentration of Br doping results in a small band gap variation. The visible light absorption capacity is significantly enhanced from Tl2PdCl6 to Tl2PdBr6. The results show that three compounds including Tl2PdBr2Cl4, Tl2PdBr4Cl2, and Tl2PdBr6 are promising materials for potential optoelectronic applications.

Comparative analysis of strain engineering on the electronic properties of homogenous and heterostructure bilayers of MoX2 (X = S, Se, Te)

In this work, for the first time, the comparative electronic properties of homogenous and van der Waals (vdW) heterostructure bilayers of Molybdenum Dichalcogenides, MoX2 (X = S, Se, Te) is investigated using first-principle calculations with the emphasis on their response to applied biaxial mechanical strain. The dynamical, thermal, and energetical stability of the vdW bilayers are assessed in detail. Next, a comprehensive analysis of energy band structure with the atomic orbital projections of band edges has been performed for individual bilayers. In this context, the energy of different conduction and valence band edges are studied within a range of 5% biaxial compressive (BC) to 5% biaxial tensile (BT) strain. The applied strain-dependent band edge energy modulations are extensively analysed based on the change in structural properties and thereby the strength of in-plane and interlayer atomic orbital couplings. The analysis is further extended to correlate the variations in energy bandgaps and density of states (DOS) in different bilayers with applied strain. The results indicate that, unlike homogenous bilayers, the vdW bilayers demonstrate distinct electronic properties in their relaxed configuration. Specifically, the MoSe2/MoTe2, MoS2/MoSe2, and MoS2/MoTe2 exhibit small direct bandgap, moderate indirect bandgap, and metallic/semimetallic nature, respectively. Furthermore, distinctly different modulations in conduction band minima (CBM) and valence band maxima (VBM) positions in the Brillouin zone are observed with applied strain for individual vdW bilayers in contrast to almost similar nature of variations in CBM/VBM positions of homogenous bilayers. This leads to characteristic nonlinear variations in energy bandgap and distinct DOS modulations for individual vdW bilayers under applied strain. The key findings indicate that the suitably strained VdW bilayer MoX2 are highly promising materials for a plethora of electronic and optoelectronic applications.

Optimization of electrodeposition time on the properties of Cu2ZnSnS4 thin films for thin film solar cell applications

The Electrochemical deposition was used to create a quaternary CZTS (Cu2ZnSnS4) kesterite thin layer. An aqueous solution of CZTS was used to deposit a thin layer over Indium Tin Oxide. The effects of deposition time (variation) on CZTS thin films under ambient conditions were investigated in this study. Several available characterization systems were used to study the samples as they were produced. The polycrystalline description of the layer is investigated by X-ray diffraction. The SEM as well as AFM study show that the deposition time improved surface morphology and topography of CZTS thin films which increase several nm in grain size. Furthermore, depending upon the deposition duration that affect the thickness and crystallinity of the films prepared, the optical study reveals an acceptable band gap in a range of 1.71–1.42 eV. Characteristics of high-quality CZTS absorber layers for solar cell applications are determined by deposition time variation. To check the effect of this band gap variation (1.71–1.42 eV, depending upon the deposition time) on the performance of a CZTS based thin film solar cell, a simulation software SCAPS-1D is being used.

Electric field and strain-induced band-gap engineering and manipulation of the Rashba spin splitting in Janus van der Waals heterostructures

The compositional as well as structural asymmetries in Janus transition metal dichalcogenides (J-TMDs) and their van der Waals heterostructures (vdW HSs) induce an intrinsic Rashba spin-splitting. We investigate the variation of band-gaps and the Rashba parameter in three different Janus heterostructures having AB-stacked Mo$XY$/W$XY$ ($X$, $Y$ = S, Se, Te; $X\neq Y$) geometry with a $Y-Y$ interface, using first-principles calculations. We consider the effect of external electric field and in-plane biaxial strain in tuning the strength of the intrinsic electric field, which leads to remarkable modifications of the band-gap and the Rashba spin-splitting. In particular, it is found that the positive applied field and compressive in-plane biaxial strain can lead to a notable increase in the Rashba spin-splitting of the valence bands about the $\Gamma$-point. Moreover, our \textit{ab-initio} density functional theory (DFT) calculations reveal the existence of a type-II band alignment in these heterostructures, which remains robust under positive external field and biaxial strain. These suggest novel ways of engineering the electronic, optical, and spin properties of J-TMD van der Waals heterostructures holding a huge promise in spintronic and optoelectronic devices. Detailed $\mathbf{k\cdot p}$ model analyses have been performed to investigate the electronic and spin properties near the $\Gamma$ and K points of the Brillouin zone.

Acetophenone and benzophenone adsorption studies on θ-phosphorene nanosheets – A DFT investigation

In the proposed research work, we utilised θ-phosphorene nanosheet as a superior sensing element to detect acetophenone and benzophenone at room temperature. Firstly, the structural firmness and dynamical stability of θ-phosphorene are confirmed with the support of cohesive formation energy (-5.198 eV/atom) and phonon bands spectrum. With the support of band structure and projected density of states spectrum, the electronic properties of θ-phosphorene are explored. The energy band gap of θ-phosphorene is obtained as 1.414 eV. Besides, the adsorption features of target volatiles on the base substrate are studied by the deciding parameters, namely relative band gap variation, Bader charge transfer, and adsorption energy. Furthermore, the range of adsorption energy (-0.060 eV to −0.546 eV) proves that acetophenone and benzophenone are physisorbed on θ-phosphorene. The present result suggested that the θ-phosphorene can be utilised as an excellent chemical sensor to sense the acetophenone and benzophenone evolved from the cosmetics and perfume industries.

Synthesis of nano-sized lead sulfide thin films from Avocado (Glycosmis cochinchinensis) Leaf extracts to empower pollution remediation

The translucent and nano-crystalline PbS films were equipped with the CBD techniques on metal substrates by the temperature of 90 °C through aqueous solutions of Lead Nitrate and Thiourea. The XRD phases verify the crystalline property of synthesized thin films that the shape falls in the cubic structures with favourite orientations. It revealed that the prepared material is cubic crystal oriented as (111), (110), (100) and (101) crystal planes. The crystalline size varied between 0.4 and 0.7 nm. The band gap was assessed using UV–vis captivation spectra and Tau relations. The average energy band gap was found to be 2.43 eV which is greater than bulk materials of PbS; because of quantum confinements of Lead Sulfide Nano Crystalline thin films, and PL also confirms this result. The variation in band gap with Leaf extracts and particle sizes displayed blue shifts characteristic of electrons quantum confinements. SEM micrograph shows extremely uniform and adherent PbS films are found at higher PH values. It was evidently observed that the viscosity of the synthesized thin films reduced from 563 to 111 nm with a rise in pH value. The sample prepared at pH 4 shows good performance, and thin films deposited from Avocado (Glycosmis cochinchinensis) leaf extracts are a promising method to empower pollution remediation and future energy.

The effect of deposition time on the growth and properties of cupper doped zinc sulfide thin films deposited via spray pyrolysis

A high transparent Cu doped ZnS thin films were successfully deposited by the spray pyrolysis method at different deposition times. X-ray diffraction (XRD) patterns showed that all films were monocrystalline with the wurtzite crystal structure. A small variation in the optical band gap for all films was observed, indicating that the variation of deposition time doesn't affect strongly the bandgap. The average crystallite size of prepared thin films was calculated using Scherrer's formula and found to be in the range 29–33 nm. The crystallite size and microstrain of samples were investigated. Raman scattering spectra indicate the presence of different phonon modes and different peaks of Photoluminescence spectra for all samples which confirmed the presence of the elements Zn, S, and Cu with a comparison to the previous reported work. Using scanning electron microscope (SEM) images of elaborated thin films show a spherical with agglomeration. UV–visible measurements revealed height transmittance in the visible range for all growth time.

Acoustic three-terminal controller with amplitude control for nonlinear seismic metamaterials

To design and optimize seismic metamaterials, the impacts of nonlinearity in different locations of locally resonant acoustic metamaterials on the dispersions and the variation of amplitude-dependent bandgaps are investigated in this paper. The research used theoretical calculations, namely, Lindstedt–Poincaré perturbation method and prediction method, and combined finite-element simulation. Summarizing from our research, the lower bandgap is sensitive when exposed to amplitude stimulation, when there arise nonlinear characteristics between matrices; while nonlinearity appears within the interior oscillator, amplitudes obtain a more intense influence on the bandgap, introducing an enormous magnitude of deviation between the upper bandgap and the lower bandgap. Based on the peculiar frequency-shift characteristics, an acoustic three-terminal controller is proposed as a conventional subsize acoustical device and nonlinear seismic metamaterials component. This controller enables the realization of modulating the value of output signals by adjusting the quantitative loading on the control port, without changing the input signals and the parameters of the apparatus validated with the finite-element simulation. The work may offer potential applications in low-frequency vibration reduction and external-controllable multi-functional acoustical devices.

Determination of Al occupancy and local structure for β-(AlxGa1−x)2O3 alloys across nearly full composition range from Rietveld analysis

Al occupancy and local structure (bond lengths and bond angles) for monoclinic β-(AlxGa1−x)2O3 alloys, with Al compositions (x) up to 90%, have been determined from Rietveld refinement of x-ray diffraction data. An Al atom preferentially occupies an octahedron (Oh) atomic site in comparison with a tetrahedron (Td) atomic site. However, a sizable number of Td atomic sites, i.e., 20% for Al composition of 5%, remain occupied by Al atoms, which is found to increase sharply with Al composition. The Oh atomic sites are not fully occupied by Al atoms even for the Al composition of 90%. The lattice parameters (bandgap) of the β-(AlxGa1−x)2O3 alloy decrease (increase) linearly with Al composition, but a change in slope of the variation of both lattice parameters and bandgap is observed at around Al composition of 50%. The lattice is found to be distorted for Al compositions more than 50% as indicated by a large change in the bond angles. The lattice distortion is determined to be the origin for the observed change in slope of the variation of both lattice parameters and bandgap for a monoclinic β-(AlxGa1−x)2O3 alloy system. Our results provide an insight into the local structure of β-(AlxGa1−x)2O3 alloys, which are required to have better understanding of their physical properties.

Structure induced modification on thermoelectric and optical properties by Mg doping in CuCrO2 nanocrystals

P-type semiconductors draw special attention because of its application in high-temperature thermoelectric devices and sensors. Oxide materials showing a negative temperature coefficient of resistance at high-temperatures make them good substitutes as one leg of the devices. Proper doping makes CuCrO2 a potential P-type semiconductor for TE application. The study incorporate Mg2+ for Cr3+ site in delafossite CuCrO2 crystal lattice. High-temperature solid-state reaction route has been chosen for the synthesis CuCrMgO2, by taking appropriate proportion of Cu2O, Cr2O3, and MgO. The structural studies were done by XRD, Raman analysis, FTIR, and SEM. CuCrMgO2 pellets with a thickness of 2 mm and a diameter of 13 mm were prepared for thermoelectric studies. By varying doping percentages, considerable changes in conductivity were observed. The highest conductivity of 1149.42 S/m was obtained for 1.5 wt% sample at 600 °C. It was observed that the electrical conductivity increased with the increase of doping percentages while the Seebeck coefficient decreased, which led to a maximum increase of 1.95 times in the power factor of CuCrO2. The maximum power factor of 1.2153 × 10−4 W/mK2 was calculated for 0.5 wt% doped sample at 600 °C. The electronic spectroscopic studies at ambient conditions reveal weak absorbance in the wavelength range of 300–400 nm for all samples. It is also found that increased absorbance, and direct optical band gap variation between 3.35 and 3.44 eV with doping.

Defective and doped MgO monolayer as promising 2D materials for optoelectronic and spintronic applications

On the basis of first-principles projector augmented wave method, the effects of point defects and doping on the MgO monolayer electronic and magnetic properties are studied. Pristine monolayer is an insulator two-dimensional (2D) material with a band gap of 3.37 eV. Various defect types including single vacancy of Mg (VMg) and O (VO), Mg+O divacancy (VMgO), and antisites formed by replacing one Mg atom by one O atom (OMg), one O atom by one Mg atom (MgO) and exchanging position of one Mg-O pair (Mg↔O) have been considered. Material becomes ferromagnetic semiconductor upon creating a Mg single vacancy, whose magnetic properties are produced mainly by O atoms closest to the defect site. Meanwhile, the non-magnetic nature is preserved in other cases with a significant variation of the electronic band gap. Similarly, non-magnetic features are obtained when substituting one Mg atom by one Si or Ge atom (SiMg and GeMg). In contrast, the feature-rich half-metallicity (semiconductor spin-up state and metallic spin-down state) is induced when doping at O site (SiO and GeO). In these cases, magnetism is generated mainly by dopants with a small contribution from their neighbor O atoms. This work provides important insights on the MgO monolayer purposing efficient approaches to widen its working region for optoelectronic applications, as well as make it prospective to be applied as spin-filter and generate spin current in spintronic devices.

Efficient magnetic and antibacterial properties of CdO/ZnO nanocomposites prepared via facile hydrothermal method

The effect of molar composition on the efficiency of antibacterial and magnetic properties of binary transition metal oxide nanocomposites synthesized using pH optimized hydrothermal method is reported. Its response to X-ray diffraction confirmed the crystallinity of nanocomposites. The average crystallite size is observed to be 27.37 nm, 30.21 nm and 32.3 nm for 1:1, 2:1 and 1:2 molar ratioed CdO/ZnO nanocomposites respectively. FT-IR spectroscopy revealed the presence of moisture and other functional groups, which is further confirmed the Thermogravimetric analysis showing approximately 1.5% of thermal decomposition within 200 °C in all composition. The synthesized composites are characterized for surface morphology using High-resolution scanning electron microscopy and Energy dispersive X-ray analysis showed mixed nanorods, nanotubes and spheroid structures. The optical band gap of proposed nanocomposites is characterized by UV-diffused reflectance spectroscopy showing the variation of optical band gap confirming the change in a molar proportion of CdO/ZnO nanocomposites particles. Investigation on magnetic properties displayed its paramagnetic behavior by illustrating the hysteresis curves of all nanocomposites. The antibacterial activities of proposed nanocomposites investigated for both Gram-positive and Gram-negative bacteria showed its efficiency towards antibacterial application.

A Numerical Simulation for Efficiency Enhancement of CZTS Based Thin Film Solar Cell Using SCAPS-1D

In this paper we proposed a solar cell having model “Back Contact/CZTS/ZnCdS/ZnO/Front Contact”. CZTS is working as an absorber layer, ZnCdS as a buffer layer and ZnO as a window layer with back and front contacts. The Zn content was varied from 0% to 10% and bad gap was changed from 2.42 to 2.90 eV as described in the literature. The impact of this band gap variation has been observed on the performance of solar cell by using SCAPS-1D software. The efficiency was varied due to variation in bandgap of ZnCdS thin film layer. The simulation was carried out at 300K under A.M 1.5 G 1 Sun illumination. The energy bandgap diagram has been taken from SCAPS to explain the different parameters of solar cell. The effect of ZnCdS having different bandgap values was observed. Then the thickness of CZTS layer was varied to check its effect and hence at 3.0 um gave the imporved efficiency of 13.83% roundabout. After optimization of CZTS layer thickness, the effect of working temperature was examined on the performance of solar cell. The absorption coefficient variation from 1E+4 to 1E+9 cm-1 caused major effects on the characteristics parameters of solar cell along with on J-V characteristics and Quantum Efficiency curve. At 1E+9 cm-1 absorption coefficient the efficiency of solar cell boost up to 16.24%. This is the remarkable improvement in the efficiency of solar cell from 13.82% to 16.24%. After optimization of all parameters, simulation was run at 280K, having CZTS thickness of 3.5 um, with 10% content Zn in ZnCdS (2.90 eV), and absoption coefficient of 1E+9, the model efficiency reached up to 17.6% with Voc of 0.994 V, Jsc 26.1 mA/cm2 and Fill factor was 71.4%.

Influence of annealing process on structural, optical and electronic properties of nano-structured ZnO films synthesized by hydrothermal technique: Supported by DFT study

The annealing temperature effect on the physical properties of zinc oxide (ZnO) nanorods is experimentally and theoretically investigated. Different diagnostics techniques such as XRD, UV–Vis, SEM, and Hall effect measurements were employed to analyze the influence of annealing temperature on the structural, optical, and electrical properties of ZnO nanorods films. Additionally, Density Functional Theory (DFT) was also applied to calculate ZnO’s lattice parameters, energy gap, and optical properties depending on annealing temperature.Experimental results show that the variation of the optical band gap of the fabricated samples has the same behavior within the theoretical calculation. X-ray diffraction (XRD) results reveal that the pure film is crystallized in the hexagonal phase of ZnO with the miller plane (002).The crystallite size is affected by annealing temperature.The field emission scanning electron microscopy (FESEM) shows nanorods formation on the surface of the films. The transmittance properties of the studied films are dependent on the annealing temperature in the ZnO films from UV–Vis data, confirming the band gap’s widening effect with annealing. Overall, the experimental and theoretical findings support each other.

Effect of liquidlike cations on electronic and defect properties of solid solutions of Cu2Te and Ag2Te

${\mathrm{Cu}}_{2}\mathrm{Te}$ was recently shown to be an excellent thermoelectric material with a figure of merit approaching 2. Ag alloying was found to be effective for tuning the electrical conductivity of ${\mathrm{Cu}}_{2}\mathrm{Te}$ toward high thermoelectric performance. The liquidlike behavior of cations is well-known to yield ultralow thermal conductivity in the cuprous chalcogenide materials. Here, we study the effect of the liquidlike behavior on the electronic and defect properties of the solid solutions ${\mathrm{Cu}}_{2\ensuremath{-}x}{\mathrm{Ag}}_{x}\mathrm{Te}$. Using first-principles molecular dynamics (MD) simulation, we found that the band-gap variation with increasing $x$ as obtained from MD ensemble averages is much slower than that from direct calculation using the high-symmetry ordered structures. The solid solutions within the whole range of $x$ exhibit significant band gaps. The liquidlike behavior also results in flattened top valence bands, which reduce the Seebeck coefficient and electrical conductivity. Regarding the defect properties, we found that the liquidlike behavior can fail the standard defect models employing the high-symmetry ordered structure. Again, MD simulation would be necessary for sampling the configuration space in defect calculations. However, converging the defect formation energy for the diffusive system would require much longer simulation time than converging the band gap. Our present results suggest that Ag alloying could slightly increase the formation energy of Cu vacancy.

A novel auxetic acoustic metamaterial plate with tunable bandgap

Two-dimensional phononic metamaterials, consisting of plates with resonant cylinders, can significantly attenuate waves by opening a subwavelength bandgap, though their characteristic unit cell size is small. To realize the real-time adjustment of the bandgap, external excitations including mechanical load, temperature field, electric field and magnetic field could be introduced, of which applying mechanical load is the most practical way. In this work, an acoustic metamaterial plate based on the negative Poisson's ratio structure (NP-AMP) is proposed and feasible to achieve lower frequency, wider bandgap, and tunable bandgap compared with traditional ones (T-AMP). A counterpart based on the positive Poisson's ratio structure (PP-AMP) is also introduced for comparison. Studies have indicated that the newly designed structure has a lower frequency bandgap and wider bandwidth. With the increase of compression strain, the initial bandgap of PP-AMP gradually moves to a higher-frequency range. In contrast to PP-AMP, the NP-AMP exhibits lower frequency, which is beneficial for the further research of low-frequency bandgap. Moreover, the bandgap variation range can be enlarged by the enhancement of the auxetic behavior. Finally, the variation range of the NP-AMP initial bandgap frequency increased by 62%. The findings in this work will broaden the design of low-frequency broadband acoustic devices used in a dynamic environment, while providing new ideas and methodologies for real-time adjustment of bandgaps.

Influence of KI salt concentration on the hydroxypropyl methylcellulose films: Optical study

Herein the optical properties of Hydroxypropyl methylcellulose/Potassium iodide (HPMC/KI) composite films were determined. The casting technique was introduced to make HPMC/KI films with different KI salt concentrations (0.1–1) wt%. The absorbance model was used to determine parameters like absorption edge, refractive index, real and imaginary sections of the optical dielectric function, extinction coefficient, Urbach energy, band gap, and optical conductivity in the spectral range 200–800 nm. As shown by the study, KI salt doping affects the optical properties of HPMC. The absorption edge (Ee) was widely displaced towards a region of lower photonic energy. The direct and indirect optical bandwidth gaps were lowered from 5.6 to 2.56 eV and 5.86 to 2.5 eV for the 1 wt % HPMC/KI film, respectively. The optical dielectric loss method was effectively employed as an alternate method for estimating the optical band gap. In addition, Tauc's extrapolation method identified the kind of electronic transition. The variation of the optical energy band gap and optical dielectric constant (ε1) based on KI salt concentration was used to investigate the credibility of Penn's model. In KI salt-composite films, an increase in Urbach energy and optical conductivity was observed which may be evidence of a large shift from tail-to-tail and band-to-tail transitions. Meanwhile, X-ray diffraction (XRD) examination revealed that the KI salts damaged the HPMC polymer's crystalline phase. Lastly, the films were subjected to Fourier Transform Infrared Spectroscopy (FTIR). The considerable variation in transmittance and band change was observed for doped films in FTIR spectra.