Shift Of Energy Gap Research Articles

Electronic properties of heterometallic zeolitic imidazolate framework and its encapsulation with Ni, Pd and Pt

The electronic properties of heterometallic zeolitic imidazolate frameworks (ZIF-8) containing Cd and Zn metal centres have been examined using density functional theory to reveal the nature of metal to ligand interaction, band gap, density of states and charge distribution. The band gap energy of mixed-metal ZIF-8(Zn/Cd) has been calculated for each ratio of Cd and Zn in the mixed-metals showing a small window of possible alternating the electronic states of this material. The band gap energy shifts from 4.84 eV in pristine ZIF-8(Zn) to 4.33 eV when all the Zn2+ metal centres were replaced by Cd2+ ions. Increasing the ratio of Cd to Zn decreases the band gap energy due to the shifting of the electronic states of Cd at the edge of the conductance band. Modification of the electronic structure was also examined when several metals of Ni, Pd, and Pt were dopped in the mixed-metal ZIF-8(Zn/Cd) to give band gap energies of 2.19, 3.35, and 3.41 eV, respectively. The presence of mixed-metal seems to fine tune the band gap energy than doping the metals in ZIF-8(Zn) only. Density of states have been evaluated to reveal the coordination nature in the mixed-metal ZIF-8(Zn/Cd) as well as after doping with the metals. Additional electronic parameter of the net atomic charge distribution based on the repeating electrostatic potential extracted atomic method was also determined in a range of van der Waals (vdW) radius to see the effect of mixed metals in ZIF-8(Zn/Cd). The net atomic charge of each metal centre is observed to be convergence when the vdW radius scale was set to 0.8, 0.9 and 1.0.

DFT exploration of sensor performances of pristine and metal-doped graphdiyne monolayer to acetaminophen drug in terms of charge transfer and bandgap changes

In order to study the electronic identity of pristine graphdiyne (GDY) as well as Zinc-doped graphdiyne (ZnGDY), first-principles calculations were done. Main parameters were investigated to analyze the adsorption behavior of acetaminophen (ACE) on the GDY and Zn GDY substrates, including the energy of adsorption, charge transfer along with the shift in the energy gap. The pristine DY sheet showed a weak attraction toward the ACE adsorbate. Additionally, the ACE adsorption onto GDY resulted in a negligible band gap energy shift of about 5.65%. On the contrary, in the gas phase, ZnGDY is mainly affected by the ACE adsorption with the adsorption energy of about 13.65. In addition, the ACE adsorption energy over the Zn-doped sheet was obtained to be 26.76 kcal/mol in the aqueous medium. A mild water solubility of ACE was reported regarding the moderate value of the calculated solvation energy. Noticeable charge transfer occurred during the ACE adsorption onto the ZnGDY substrate compared to the pristine GDY. Finally, the Zn addition resulted in an enhanced tendency toward ACE and the electrical conductivity was shifted by 13.92%, which is required for the sensory role of an adsorbent toward the ACE drug species.

Energy gaps of Si nanoparticles using size-dependent Debye-Waller factors

A model of size-dependent Debye-Waller screening of effective potential is proposed. The calculated effective potential of silicon nanoparticles (SiNPs) is used to predict the dependence of energy bands on diameter. The empirical pseudopotential method is implemented to calculate the band structure. SiNPs having diameters of 3.753–15.744 nm are studied. The results show that the fundamental (indirect) energy gap increases and shifts toward the center of the Brillouin zone as the diameter decreases. The direct energy gap at point Γ increases slowly as the diameter is reduced to ~5.75 nm and decreases rapidly for diameters below this value. Variations of indirect and direct energy gaps at point Γ are fitted to model equations. The results indicate a conversion to a direct energy gap when the diameter becomes ~1.6 nm. The calculated behavior of the energy gaps and the predicted transition to a direct energy gap are in good agreement with other experimental and theoretical results.

Structural, energy gap tuning, photoluminescence and magnetic properties of Sn-doped Zn0.96Ni0.04O nanostructures

Ni (4%) doped ZnO and Ni, Sn (Ni = 4% and Sn = 1 and 2%) dual doped ZnO nanostructures have been synthesized by sol-gel route. The hexagonal ZnO structure of Ni/Sn doped ZnO was not disturbed by Sn addition and no secondary or impurity phases of Ni/Sn were identified in the XRD pattern. The continuous suppression of nucleation and hence the growth rate by Sn doping reduce the grain size and the replacement of Sn4+ ions with lower ionic radius instead of Zn2+ in Zn–Ni–O lattice is also accelerate the size decrement. Hexagonal wurtzite structure was not affected by Sn substitution. The reduced size and higher transmittance at Zn0.94Ni0.04Sn0.02O is recommended for the industrial application like transparent electrode. The continuous blue shift of energy gap from 3.53 eV (Sn = 0%) to 3.75 eV (Sn = 2%) is clarified by Burstein-Moss (BM) band filling effect with the help of energy level diagram. The existence of Zn–O–Ni/Sn bonding is verified by Fourier transform infra-red examination. The improved visible PL emissions like near violet, blue and green emissions by Sn doping is due to the existence of higher oxygen vacancies and oxygen related defects in Zn–Ni–Sn–O lattice. The room temperature ferromagnetism (RTFM) with elevated saturation magnetization by Ni/Sn doping in ZnO is stimulated by the intrinsic exchange interaction between Zn/Ni/Sn ions through the defects induced by Sn.

Antimicrobial Hybrid Coatings Combining Enhanced Biocidal Activity under Visible-Light Irradiation with Stimuli-Renewable Properties.

Hybrid, organic-inorganic, biocidal films exhibiting polishing properties were developed as effective long-lasting antimicrobial surface coatings. The films were prepared using cationically modified chitosan, synthesized by the reaction with 3-bromo-N,N,N-trimethylpropan-1-aminium bromide, to introduce permanent biocidal quaternary ammonium salt (QAS) groups along the polymer backbone and were cross-linked by a novel, pH-cleavable acetal cross-linker, which allowed polishing the hybrid coatings with the solution pH. TiO2 nanoparticles, modified with reduced graphene oxide (rGO) sheets, to narrow their band gap energy value and shift their photocatalytic activity in the visible light regime, were introduced within the polymer film to enhance its antibacterial activity. The hybrid coatings exhibited an effective biocidal activity in the dark (∼2 Log and ∼3 Log reduction for Gram-negative and Gram-positive bacteria, respectively), when only the QAS sites interacted with the bacteria membrane, and an excellent biocidal action upon visible-light irradiation (∼5 Log and ∼6 Log reduction for Gram-negative and Gram-positive bacteria, respectively) due to the synergistic antimicrobial effect of the QAS moieties and the rGO-modified TiO2 nanoparticles. The gradual decrease in the film thickness, upon immersion of the coatings in mildly basic (pH 8), neutral (pH 7), and acidic (pH 6) media, reaching 10, 20, and 70% reduction, respectively, after 60 days of immersion time, confirmed the polishing behavior of the films, whereas their effective antimicrobial action was retained. The biocompatibility of the hybrid films was verified in human cell culture studies. The proposed approach enables the facile development of highly functional coatings, combining biocompatibility and bactericidal action with a "kill and self-clean" mechanism that allows the regeneration of the outer surface of the coating leading to a strong and prolonged antimicrobial action.

Band Gap Energy and Near Band Edge Emission Blue Shifts of ZnO Nanorods Prepared by Electrodeposition

Band Gap Energy and Near Band Edge Emission Blue Shifts of ZnO Nanorods Prepared by Electrodeposition

Physical properties of heteroatom doped graphene monolayers in relation to supercapacitive performance

Electrodes fabricated using graphene are quite promising for electric double layer capacitors. However graphene has the limitations of low ‘Quantum Capacitance (QC)’ near fermi level due to the presence of Dirac point that can be modified by doping graphenewith suitable dopant. The density functional theory DFT calculations are performed for doped graphene using Boron, Sulphur and phosphorus as dopants to improve the quantum capacitance of electrodes fabricated using graphene. The calculations are performed at temperatures of 233, 300 and 353 °K. From present calculations no significant temperature dependence of quantum capacitance is observed, however a marked increase in QC of value above 58μFcm -2 is seen. Forphosphorus and Sulphur doped graphene a significant energy gap shift of ~ 1.5 eV from the Fermi level is observed that significantly increases the QC at Fermi level to a high value of ~ 35 μFcm -2 . With boron dopant as well, a shift of energy gap ~ 1.25eV from the Fermi level is observed. The shift in Dirac point increases quantum capacitance at Fermi level that in turn can increase the energy density of supercapacitor remarkably. The effect of increasing doping concentration on quantum capacitance is also investigated. These results suggest that doping of graphene may result in significant increase in QC near Fermi level, if the dopants are selected carefully depending upon the use of graphene as a positive or negative electrode. The results of these calculations reveal that the problem of low QC of graphene in the range of interest can be addressed by modifying itssurface and structure chemistry which may increase energy density in supercapacitors.

Oxygen vacancies mediated cooperative magnetism in ZnO nanocrystals: A d0 ferromagnetic case study

This article reports on the oxygen vacancies and defects induced cooperative magnetism of 28nm (as prepared) and 74nm (annealed) sized nanocrystals of ZnO synthesized through sol- gel auto-combustion route. UV–Vis–NIR optical absorption and photoluminescence (PL) spectroscopic measurements showed marginal red shifting in the band gap energy and characteristic blue shift in the UV absorption peak position with the size reduction of ZnO nanocrystallites. PL analysis revealed that 28nm sized ZnO nanocrystals have higher number of oxygen vacancies and lower interstitial defects in comparison to 74nm (annealed) nanocrystals of ZnO. Both the sample display oxygen vacancy and defect mediated ferromagnetic behaviour at 300K but 28nm ZnO nanocrystals are better ferromagnetic in comparison to annealed ZnO nanocrystals. The annealed ZnO nanocrystals also showed considerable diamagnetic character. High field (±7 Tesla) magnetization measurements down to 5K and PL analysis establish presence, inter-conversion of oxygen vacancies and valence fluctuations in neutral, mono and divalent oxygen vacancies. The monovalent oxygen and zinc vacancies play important role in the mediation of d0 type cooperative magnetism in the ZnO nanocrystals.

An impact of La doping content on key physical properties of PbS spherical nanoparticles facilely synthesized via low temperature chemical route

Herein, we are reporting a facile chemical process to attain high-grade PbS spherical nanoparticles with diverse La doping contents at low temperature and named it as La@PbS SNPs. All the prepared La@PbS SNPs samples are of single-cubic phase with good crystalline nature confirmed from XRD and Rietveld refinement. Along with lattice constants several other structure-related parameters like size, dislocations, strain, stacking fault, density and specific surface area were calculated. EDX and SEM-e-mapping analyses confirm the presence of La in PbS with homogeneous distribution throughout the samples. For morphological investigation FESEM was employed, which approved the synthesis of SNPs of low dimensions at all La contents. FT-Raman analysis shows characteristics vibrational modes related to cubic-PbS and that is in good accordance with XRD outcomes. Energy gap values were determined through Kubelka–Munk procedure and noticed to lie between 1.01 to 1.103 eV ( $$ \Delta E = 0.093 \;{\text{eV}}) $$ , this shows a very minute shift in energy gap with La doping in PbS. Dielectric constant ( $$ \varepsilon ' $$ ), loss tangent, dielectric loss and impedance values were assessed and stable values of $$ \varepsilon ' $$ were noticed in 20–50 range and 5.0 wt % La@PbS SNPs possesses highest value. The ac electrical conductivity analysis revealed enhancement with La content in PbS. The correlated barrier hoping mechanism was involved in the prepared La@PbS SNPs. Furthermore, the DC electrical properties were studied and discussed the impact of La content.

Monocrystalline InP Thin Films with Tunable Surface Morphology and Energy Band gap.

InP is currently being used in various (opto)electronic and energy device applications. However, the high cost of InP substrates and associated epitaxial growth techniques has been huge impediments for its widespread use. Here, large-area monocrystalline InP thin films are demonstrated via a convenient cracking method, and the InP thin films show material properties identical to their bulk counterparts. Furthermore, the same substrate can be reused for the production of additional InP thin films. This cracking technique is also shown to be a versatile tool to form an ultrasmooth surface or a microscale periodic triangular grating structure on the surface, depending on the orientation of the donor substrate used. Strain-induced band gap energy shift is also observed in localized regions of the thin film with a grating structure. The simplicity of this technique, which does not require any sophisticated equipment and complex fabrication process, is promising to reduce the cost of InP thin-film devices.

A DFT study of influence of dichloromethane solvent and electric field on light absorption and electronic properties of two Quinoxaline-based solar cells

Geometric structure, molecular vibration, electronic and spectroscopic properties including frontier molecular orbitals, energy gap and global reactivity descriptors, Uv–vis absorption spectrum, charge separation degree, driving force of electron injection and generation and fluorescence lifetime of two D-A-π-A Quinoxaline-based indoline dyes, IQ4 and IQ22, were investigated theoretically in vacuum and dichloromethane (DCM) solvent by methods of density functional theory and time-dependent density functional theory, so as to gain more insight into the influence of DCM solvent and substitution of cyclopentadithiophene (CPDT) conjugated bridge for thiophene on photoelectric properties of the targets. Comparing IQ22 with IQ4, the larger dipole moment, narrower HOMO-LUMO energy gap and bathochromic shift in absorption benefit IQ22 optoelectric performance while weaker driving force of regeneration, smaller charge transfer rate, lower charge separation degree and shorter fluorescence lifetime are unfavorable to its photoelectric conversion properties. There are no significant differences of Jsc and Voc between title dyes based on the previous experiment, mainly due to the positive role and negative impact induced by substitution of CDPT into thiophene. Solvent effect caused by DCM makes the parameters more favorable to be applied in solar cells device.

Investigation of the band gap energy shift and photocatalytic properties of Bi3+-doped ceria

A series of Bi3+-doped CeO2 photocatalysts have been prepared using simple coprecipitation method. The effect of Bi3+ doping on structural surface morphology and optical properties of the prepared photocatalysts was characterized using diffuse reflectance spectroscopy (DRS), powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) for determination of the specific surface area and porosity. All prepared photocatalysts exhibit fluorite-type structure with no phase change up to 10 mol percent Bi3+ doping when calcinated at 973 K for 1 h. A red shift in optical band gap measurements was observed with increasing Bi3+ ion percent doping. Photocatalytic performance of prepared photocatalysts were examined using visible-light-induced photocatalytic reduction of 4-nitroaniline to p-phenylenediamine. The highest photocatalytic efficiency was achieved using CeO2 photocatalyst with 5 mol percent Bi3+ doping.

Novel cis-[PdCl2(NHC)(PPh3)] complex: synthesis, crystal structure, spectral investigations, DFT and NCI studies, prediction of biological activity

This study contains the synthesis of a heteroleptic Pd(II) cis–[PdCl2(NHC)(PPh3)] complex containing an N-heterocyclic carbene (NHC) and a triphenylphosphine (PPh3) ligand. The complex was prepared from the related [PdCl2(NHC)(3–Clpy)] complex (PEPPSI), replacing the 3-chloropyridine ligand (3-Clpy) by the PPh3 ligand, and characterized by using 1H NMR, 31P NMR, 13C NMR, FT-IR, UV-vis spectroscopies and elemental analysis. The molecular and crystal structure of the complex was determined by single-crystal X-ray diffraction analysis. Comprehensive theoretical calculations including the optimized structural parameters, the HOMO–LUMO energy gap, vibrational frequencies, and chemical shifts were calculated using density functional theory (DFT) with the B3LYP/LanL2DZ//6–31G* level and compared with the experimental data. Natural population analysis (NPA), charge decomposition analysis (CDA) and natural bond analysis (NBO) were carried out. Non-covalent interaction (NCI) calculations were also performed to identify the weak non-covalent interactions from the topological analysis and the reduced gradient of the electron density of complex. Predictive study for the biological activities using PASS (prediction of activity spectra for biologically active substances) online software showed optimistic activities for the complex as an antineoplastic (melanoma) and nicotinic α6β3β4α5 receptor antagonist.

Energy level tuning of CdSe colloidal quantum dots in ternary 0D-2D-2D CdSe QD/B-rGO/O-gC3N4 as photocatalysts for enhanced hydrogen generation

Colloidal quantum dots (QD) electronic properties are tailorable via modifications of its quantum confinement environment. Herein, surface-chemistry-mediated approach through the application of unique surface thiol ligands (thioglycolic acid, glutathione, 3-mercaptopropioninc acid and N-Acetylcysteine) exhibited energy level and gap shifts in aqueous CdSe QDs. Trends in the photocatalytic performance employing ligand-specific CdSe QDs are consistent with their respective measured energy and gap level. Results underscore that a still underutilized mean of surface-chemistry-mediated modification of colloidal CdSe QDs can be employed as a versatile parameter in the performance optimizations of QD photocatalysts for photocatalytic hydrogen (H2) reactions. This optimized CdSe QD is further utilized as sensitizers to bolster and facilitate effective charge transfer across the ternary, multi-level heterointerfaces of 0D-2D-2D CdSe QD/B-rGO/O-gC3N4. Upon loading, the ternary composite achieved a maximum H2 evolution of 1435 μmol h−1 g−1 even without the help of precious metal co-catalyst which is otherwise required when used as individual unit. This augmented photoactivity is attributed to the synergetic effect of CdSe sensitization and p-n junction administered by the p-type B-rGO and n-type O-gC3N4.

Synthesis and Characterization of a Polystyrene (Cork) Doped by Aluminium Oxide (Al<sub>2</sub>O<sub>3</sub>) to Improve Its Optical Properties Using the (UV-VIS) Techniques

Cork is considered one of the polymers of very low industrial value and is used only for secondary purposes such as packaging, and it is possible to have any other uses of high value by doping the cork with materials that can change its physical properties, this paper aimed to synthesize and characterize the optical properties of pure Polystyrene (200 grams) Cork, and Polystyrene (200 grams) Cork doped by Aluminum oxide in ratios (0.1 to 0.9) molar, for the preparation of Aluminum oxide, aluminum nitrate (Al(NO₃)39H₂O)) was used (as a source of Aluminum oxide, provided by (LOBA CHEMIE) company, with a molecular weight of 375.13 and a concentration of 98%, which is a white powder that is soluble in water, it was prepared at a temperature of (80) degrees Celsius for each Samples with different concentrations ranging from (0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9) morality by adding N, N-Dimethylformamide for HPLC and Spectroscopy as an oxidizing agent and precipitant, then by Sol-Gel method at a temperature of 80°C for 60 minutes, samples of doped cork were deposited on glass slides. By using the ultraviolet technique (UV-VIS), the transmittance and absorption spectra were recorded within the wavelength range of (200-800) nm. The results showed that the transmittance decreased with increasing the cork doping percentage. The basic absorption peaks of the cork tends towards the low photon energy (red shift) when increasing the doping rates of Aluminum oxide, while it was tending towards the high energy (blue shift) photon at the cork before doping, and that is through the absorption coefficient values that were calculated from the absorbance spectrum, which is greater than Likewise, the optical parameters of reflectivity, extinction coefficient, and refractive index were calculated. The energy gap of the cork doped by Aluminum oxide is small compared to the energy gap of the pure polystyrene cork. It has been concluded that the Aluminum oxide ratios with different molar values confirm the cause of the energy gap shifts.

Trans influence and substituent effects on the HOMO-LUMO energy gap and Stokes shift in Ru mono-diimine derivatives

The ground (S0) and excited triplet (T1) electronic states and corresponding optical spectra of a series of cationic complexes [RuH(CO)L(PPh3)2]+ (L = 2,2′-bipyridyl) (Rubpy), 4,4′-dicarboxylic-2,2′-bipyridyl(Rudcbpy),bis-4,4′-(N-methylamide)-2,2′-bipyridyl(Rudamidebpy),bis-4,4′-(methyl)-2,2′-bipyridyl(RudMebpy),[Ru(CO)2dcbpy(PPh3)2]2+(Ru(2CO)dcbpy),and [Ru(H)2dcbpy(PPh3)2] (Ru(2H)dcbpy) have been studied by combined Density Functional/Time-Dependent Density Functional (DFT/TDDFT) techniques using different combinations of DFT exchange-correlation functionals and basis sets. PBE0/LANL2DZ provided more accurate geometries to describe S0 whereas B3LYP/LANL2DZ predicted spectral energies that correlated better with the available experiment data. The Ru (II) complexes with different substituents emit photons ranging from 560 to 610 nm in the series RudMebpy, Rubpy, Rudamidebpy, Rudcbpy. The calculations predicted a maximum emission at about 540 nm for the complex constructed from two carbonyl π-acceptors ligands trans to the dcbpy, while an emission in the far infrared region is calculated when two H σ-donor ligands trans to the dcbpy. Our calculation results show correlations between HOMO-LUMO energy gap, Stokes shift, and T1 distortion, which reflect the different effects of electron-withdrawing and donating groups. We proposed that these correlations can be used to predict the photophysical properties for new complexes.

Tuning of structural and optical properties and defect induced photoluminescence on Ni-doped Cd0.9Zn0.1S nanoparticles

Ni-doped Cd0.9Zn0.1S nanoparticles with Ni = 0, 1 and 3% have been prepared by co-precipitation route. Cubic structure was authenticated by XRD pattern in the entire Ni range without any impurities and secondary phase formation. The size variation between 42 and 63 Å, lattice parameters and micro-strain was discussed by Ni-doping and defects induced by Ni. The lattice disorder and more number of defect states by Ni addition is expressed by scanning electron microscope images. The Ni-modified CdS functional groups and their chemical bonding were confirmed by Fourier transform infrared studies. The strong red shift of energy gap from 3.81 eV (Ni = 0%) to 3.38 eV (Ni = 1%) can be linked with defect encouraged energy gap tailoring owing to the manufacturing of localized states and confirmed that Ni2+ ions were actually included into the Cd–Zn–S lattice. The synthesis of Zn, Ni dual doped CdS nanoparticles is expected to be green solid-state lighting materials.

Correlation between Nucleon-Nucleon Interaction, Pairing Energy Gap and Phase Shift for Identical Nucleons in Nuclear Systems

Assuming some known nucleon-nucleon interactions, and using the relations between phase shift δ and nucleon-nucleon interaction potential V (r) ; the relation between nucleon-nucleon interaction and scattering length a; the relation between energy gap Δ, and scattering length a; an equation is obtained between energy gap Δ and Fermi momentum kF via the phase shift δ (kF). Assuming 1s0 (singlet) pairing between the nucleons, the energy gap Δ has been calculated and it is found that Δ = 3.0 MeV at Fermi momentum kF = 0.8 fm-1.

Nonreciprocal spin waves in a chiral antiferromagnet without the Dzyaloshinskii-Moriya interaction

Non-reciprocal spin wave can facilitate the realization of spin wave logic devices. It has been demonstrated that the non-reciprocity can emerge when an external magnetic field is applied to chiral magnets, of which spin structures depend crucially on an asymmetric exchange interaction, that is, the Dzyaloshinskii-Moriya interaction (DMI). Here we demonstrate that the non-reciprocity can arise even without the DMI. We demonstrate this idea for the chiral antiferromagnet Ba$_2$NbFe$_3$Si$_2$O$_{14}$, of which DMI is very small and chiral spin structure arises mainly from the competition between symmetric exchange interactions. We show that when an external magnetic field is applied, asymmetric energy gap shift occurs and the spin wave becomes non-reciprocal from the competition between symmetric exchange interactions and the external magnetic field.

Theoretical study on electronic and absorption characters of p-type D-A-π-A triaryamine sensitizer

The structural and electronic properties of well-known 4,4′-(4-(5-(2,2-dicyanovinyl)thiophen-2-yl)phenylazanediyl)dibenzoic acid (O2) and its hypothetical dyes O3–O7 were investigated by computational techniques. The absorption properties were probed. By replacing the 2-methylidenepropanedinitrile acceptor with 1,3-diethyl-5-methylene-2-thioxo-dihydropyrimidine-4,6(1H,5H)-dione, the molecular orbital energy levels were well tuned. The modified dyes meet the basic requirements of both –ΔGinj and –ΔGreg being over 0.2 eV for an efficient hole injection and dye regeneration, respectively. All the designed p-type dyes O3–O7 have smaller energy gap and significant red shift in absorption spectra than that of the reference O2. Finally, our results suggested that O3–O7 have larger light-harvesting efficiencies (LHE) in the visible spectral regions of 400 nm to 700 nm than O2. Among all the dyes, O5 is expected to have an excellent performance as a p-type sensitized dye in solar cells due to its great LHE and sufficient hole injection efficiency.