Direct Energy Gap Research Articles

Effects of Ni doping on the structural, photoelectric, and antibacterial properties of ZnCo2O4 thin films

This study addresses improving the electrical properties and demonstrating the antibacterial capability of spinel ZnCo2O4 films. We used sol–gel and spin-coating techniques to prepare samples and analyzed their crystal structures, microstructures, as well as their photoelectric and antibacterial properties, in relation to Ni doping. Single-phase spinel oxide is maintained in all of the Zn(Co1-xNix)2O4 films. The replacement of cobalt by nickel causes a decrease in the average grain size and surface roughness. Both the grain size and the surface roughness affect the optical properties of the film translucence. The transmittances of all films at a wavelength of 600 nm is ~31.3–48.6%. The characteristic absorption peak of the photon-excited electron is about 400 nm. A higher doping content ratio (Nix = 0.15–0.30) causes the absorption characteristic peak to gradually disappear. The direct energy gap of all spinel oxides ranges from 2.45 to 2.57 eV. All films are p-type semiconductors, and nickel can replace cobalt to increase the carrier concentration, resulting in a decrease in the resistivity of Zn(Co1-xNix)2O4 from 312.5 Ω-cm (Nix = 0) to 15.8 Ω-cm (Nix = 0.30). The antibacterial rate for Escherichia coli and Staphylococcus aureus associated of the material can reach more than 99.9%, and no photocatalysis is necessary. Therefore, Ni-doped ZnCo2O4 possesses excellent properties for potential applications.

Characterization of zinc lead-borate glasses doped with Fe3+ ions: optical, dielectric, and ac-conductivity investigations

The optical, dielectric response, and ac-conductivity properties for six glasses of zinc lead-borate doped with different contents of Fe3+ (Fe2O3 = 0 to 10 wt%) have been investigated. UV–Vis spectra in 190–1100 nm wavelength have been carried out. Band gaps for optical energy (EOptical), Urbach’s energy (EU), index of refraction (n), steepness parameter (S), energy dispersion parameter of refractive index (Ed), single-oscillator energy (Eo), the dispersion refractive index (no), minimum reflectance wavelength (λo), and oscillator strength (So) were evaluated. Results reveal that the indirect energy gap varies from 2.57 to 1.01 eV, while the direct energy gap takes values from 2.80 to 1.45 eV. The EU values change from 0.232 to 0.966 eV for glasses with Fe2O3 = 0 and 10 wt%, respectively. Also, S and λo decrease with the enhancement of Fe2O3 content. The dielectric response and ac-conductivity of the prepared glasses were investigated by broadband dielectric spectroscopy, BDS, in the frequency range from 0.1 Hz to 10 MHz and at temperatures ranging between 300 and 430 K. Two trends of activation plot have been observed in the conductivity of the samples with low content of Fe2O3. Although these samples show a perfect insulation features, they obey an anomalous behavior at higher temperatures. Therefore, the investigated glasses can be applied in several optical and optoelectronic devices.

Novel synthesis, structure characterization, DFT and investigation of the optical properties of cyanine dye/zinc oxide [4-CHMQI/ZnO]C nanocomposite thin film

A novel synthesis of (E)-4-(4-carboxy-3-hydroxystyryl)-1-methylquinolin-1-ium iodide nanostructure thin film has been doped with zinc oxide nanoparticles to study the optical properties of nanocomposite films. Different characterization techniques for nanocomposite film such as Fourier-transform infrared spectroscopy, ultraviolet–visible spectroscopy, x-ray diffraction, scanning electron microscopy and optical properties have been used. The scanning electron microscopy showed a good dispersion of zinc oxide nanoparticles on nanocomposite film surface. The dielectric constant and optical conductivity increased and demonstrated wave-like performance with increasing zinc oxide nanoparticles ratio at hν range of 0.7eV – 5.0 eV. zinc oxide nanoparticles content increases lead to the formation of a wide variety of three dimension-semiconductor networks within nanocomposite film matrix which increase optical conductivity. The density functional theory by thee dimension molecular simulation software and Cambridge serial total energy package was used for optimization of novel cyanine dye and nanocomposite as isolated molecule. From the ultraviolet–visible spectrum of nanocomposite thin film, the direct and indirect optical energy gap values are 2.041 eV and 1938 eV by using Tauc`s equation, respectively, related to direct and indirect transitions of electrons. By using thee dimension molecular simulation software mothed with density functional theory simulation, the highest occupied molecular orbital and lowest unoccupied molecular orbital values for nanocomposite as isolated molecule are 4.735 eV and 3.531 eV, respectively. The simulated Fourier-transform infrared spectroscopy, ultraviolet–visible spectroscopy, x-ray diffraction and optical properties by Gaussian software and Cambridge serial total energy package are in great agreement with the experimental study. A successful choice for optoelectronics and solar cell applications are the novel cyanine dye thin film and its nanocomposite.

SYNTHESIS, CHARACTERIZATION, AND APPLICATION OF Fe3O4 NANOPARTICLES AS A SIGNAL AMPLIFIER ELEMENT IN SURFACE PLASMON RESONANCE BIOSENSING

The Fe3O4 nanoparticle has potential applications to be active materials for biosensor. This research was aimed at synthesizing and applying Fe3O4 nanoparticles for signal amplification of Surface Plasmon Resonance (SPR)-based biosensor. The synthesis was carried out by using the coprecipitation method at a temperature of 80oC for 60 minutes. NaOH of 5 molars was used as a precipitating agent. The Fe3O4 nanoparticles were characterized for their microstructure by using X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM) techniques. The crystallinity of nanoparticles is 87% and the crystallite size is 15.70 nm. The shape of Fe3O4 is nearly spherical. The optical properties were characterized by using Fourier Transform Infrared Spectroscopy (FTIR) and Specular Reflection UV-Vis Spectroscopy (SR UV-Vis). There were vibrations of Fe3+-O and Fe2+-O bonds at characteristic frequencies of 586.86 cm-1 and 422.64 cm-1. The direct and indirect optical gap energies were 3.43 eV and 3.10 eV. The magnetic properties measured by Vibrating Sample Magnetometer (VSM) confirmed that Fe3O4 was ferrimagnetic. The Fe3O4 was successful to be applied as a signal amplifier for SPR-based biosensors due to their optical and magnetic properties. The SPR angle shifted to a higher value and the change was 3.57o.

Thickness Effect of CuAlTe2 Thin Films on Morphological, Structural and Visual Properties

CuAlTe2 thin films were evaporation on glass substrates using the technique of thermal evaporation at different range of thickness (200,300,400and500) ±2nm. The structures of these films were investigated by X-ray diffraction method; showing that films possess a good crystalline in tetragonal structure. AFM showed that the grain size increased from (70.55-99.40) nm and the roughness increased from (2.08-3.65) nm by increasing the thickness from (200-500) nm. The optical properties measurements, such as absorbance, transmtance, reflectance, and optical constant as a function of wavelength showed that the direct energy gap decreased from (2.4-2.34) eV by the gain of the thickness.

Electronic structure, phonons, and high-temperature phonon-mediated superconductivity in lithium-intercalated diamond-like boron compounds

We present the first-principles calculations of lithium-intercalated diamond-like boron compounds LiB and LiB2. Although the pristine diamond structure of boron is dynamically unstable, LiB has no imaginary phonon mode after lithium intercalation. Our calculations show that LiB is an insulator with a direct energy gap of 1.45 eV. By removing a face-centered cubic sublattice of lithium from LiB, a metallic compound LiB2 is obtained. Based on Wannier interpolation, the electron–phonon coupling in LiB2 is accurately determined. We find that LiB2 is stable above 12 GPa, with superconducting transition temperature close to 60 K.

Synthesis and Characterization of a New Solid Solution, Ba5.47Sr0.53Al4B14O33

A new solid solution, Ba5.47Sr0.53Al4B14O33, has been synthesized by a high-temperature solution reaction at 770 °C. The compound crystallizes in the space group P1 with a = 6.86873 (13) A, b = 6.96992 (13) A, c = 14.5370 (3) A, α =88.8075 (15)°, β =86.5809(15)°, γ =83.2613 (14)°, V = 689.84 (2) A3, and Z = 1. It features a three-dimensional (3D) [Al4(B6O14)(B6O13)(BO3)2]n12n− framework with intersecting channels occupied by Ba2+ and (Ba/Sr)2+ cations. The framework is constructed by 1D [Al2(B6O14)(B6O13)(BO3)2]n18n− chains and 1D [Al2O7]n8n− chains interconnected via B–O–Al bridges. The compound melts incongruently at 844 °C. The existence of BO3 and BO4 groups in the structure was indicated by vibrational spectroscopy. A high degree of transparency in the visible wavelength range and a band gap of 3.37 eV were revealed by UV–VIS diffuse reflectance spectra. The band structure and bonding properties have been investigated and the insulating nature with a direct energy gap was confirmed. The manuscript describes the synthesis, crystal structure, vibrational spectroscopy, UV-vis spectrum, thermal stability, and theoretical electronic structure of a new solid solution Ba5.47Sr0.53Al4B14O33.

Investigate the Structural and Optical Properties of Nickel Phthalocyanine (NiPc)Thin Films Prepared by Chemical Spray Pyrolysis Method.

The technique of the chemical spray pyrolysis has been employed to deposit Nickel Phthalocyanine (NiPc) on different substrate types at temperatures 150 °C to investigate their structural, Scanning Electron Micrographs, X-ray diffractograms and optical properties. The results of X-ray diffraction show that structure of the powder is polycrystalline with monoclinic structure, and the results of XRD for a thin film of NiPc shows polycrystalline with a fairly weak degree of crystallization, SEM revealed that the surface of the film is usually homogeneous, the roughness of NiPc films was evaluated by AFM technique and the results showed that the grain size increases with increasing of concentration. The optical measurement using UV-Visible Spectra showed that the NiPc thin films have an optical constant like the absorption coefficient and have a direct energy gap for all samples.

Impact of Se doping on optical and third-order nonlinear optical properties of spray pyrolysis fabricated CdS thin films for optoelectronics

Cadmium sulphide is known to have tremendous applications towards optoelectronic and nonlinear devices. Hence, here we have facilely casted the CdS films with diverse Se contents through low-cost spray pyrolysis technique. XRD study defends mono-phase formation of CdS having hexagonal system at all Se doping contents. Scherrer equation was employed to evaluate crystallite size in range of 15–25 nm. Vibrational study reveals the presence of fundamental modes of vibration of hexagonal CdS. EDX and SEM mapping studies approve the existence of Se and its homogeneous distribution all over the film. SEM micrographs shows the nanoscale grains formation on film surface and the size is increasing with Se doping. Optical study revealed that the grown films are of optimal quality with transparency in range of 60–75% with low absorbance and reflectance values. The refractive index values are noted to varied from 1 to 2.7 with wavelength and noticed to be reduced on Se content in UV–Vis region. The reduction in direct and indirect energy gap was found from 2.46 to 2.34 eV and 2.21 to 1.96 eV, correspondingly due to Se. PL emission profile contains an emission band at 528, 529, 529, 530 and 546 nm for 0.0, 0.5, 1.0, 2.5, 5.0 wt% Se:CdS films. Dielectric constant and loss were estimated. The nonlinear refraction (n2) and absorption coefficient (β) and third-order nonlinear susceptibility $$(\chi^{3} )$$ values were determined using Z-scan and observed in order of 10–8 cm2/W, 10–4 cm/W and 10–3 esu, correspondingly. The high values of $$\chi^{3}$$ propose the films for nonlinear applications.

Growth and vibrational spectroscopy of [formula omitted] crystals

The mixed crystals of the Tutton’s salt doped with Li following the empirical formula K2LiyNixCo1-x (SO4)2.6H2O, were synthesized from the slow evaporation of the solvent at constant temperature. The presence of K, S, Ni, Co and O elements in the studied crystalline structure was confirmed by EDS spectroscopy using a scanning electron microscope and their quantification including Li was carried out with the help of ICP-OES technique. Raman spectroscopy in the range 100−3600 cm−1, confirmed the presence of tetrahedral (SO4), octahedral complexes Ni(H2O)6, Co(H2O)6, and H2O molecules in the crystal structure. Our UV–vis studies have shown that the mixed crystals have good optical transparency in the ultraviolet (200−350 nm) and infrared (750−1000 nm) region. The direct and indirect optical energy gap of the synthesized crystals were determined from the Tauc’s plot. XRD diffractograms of the sample crystals do not show any specific changes due to the presence of Li ion in the crystalline network.

The effect of annealing temperature thin films indium doped SnO2 to optics properties and material composition

This study aims to analyze the effect of annealing of tin oxide thin film doped with Indium. SnO2 thin film has many benefits as electronic devices, solar cells, LPG sensors, etc. Preparation of SnO2: In a thin film using a sol-gel spin coating technique that produces a thin film of high quality. The transmittance of the thin film experienced decreases with increasing ripening temperature with the transmittance of 96.6, 94.7, 89.6, 87.1, and 78.2% at a wavelength of 350 nm with annealing temperature increase, respectively. Thin-film absorbance has increased with higher heating temperatures i.e 3.01, 3.34, 3.41, 3.62, and 3.77, respectively. SnO2 thin film gap energy: In decreases due to increased ripening temperature at room temperature (35), 50, 100, 150, and 200 °C ie 3.65, 3.61, 3.59, 3.58, and 3.56 eV for direct energy gap and 3.96, 3.94, 3.93, 3.91, and 3.89 eV for indirect energy gap, respectively. The decreasing value of the gap energy makes the SnO2: In thin-film material faster in carrying current. The activation energy are decreased by increasing annealing temperature with value 2.91, 2.73, 2.15, 2.11 and 2.09 eV, respectively for increase temperature which makes electrons flow faster. Furthermore, thin-films composition with mass percentage Sn are 16.97% with atomic 2.77% and In are 1.46% with atomic 0.25%.

Synthesis, charaterization and optical properties of nanostructured silica hybrid materials obtained by soft chemistry from perhydropolysilazane/1,2,4-triazole precursors

Nanostructured silica hybrid materials have been synthesized via soft chemistry way, by the incorporation of functional 1,2,4-triazole components into a silica network, using a perhydropolysilazane (PHPS) as a silica source and 1,2,4-triazole components as templates. The compositions, morphological and textural properties of the as-synthesized samples have been studied by 13C and 29Si CP MAS NMR, FTIR and SEM. The spectroscopy results suggest that the organic moieties have been chemically linked to the silica skeleton leading to hybrid materials in which Si–N, Si–O and Si–S bridges are created. Nitrogen adsorption-desorption analysis (BET) shows that the surface area varied between 385 and 425 m2 g−1. The 29Si CP-MAS NMR displays signals between -70 and -120 ppm corresponding to Q2, Q3 and Q4 units. The optical properties have been studied also by UV–visible diffuse reflection spectroscopy and photoluminescence (PL). This study reveals that the direct gap energies varied between 0.71 and 2.53 eV. Photoluminescence shows that the silica nanohybrids are suitable to the emission of blue light with wavelength (λem) values of about 470-480 nm. The PL emission results also from some silicon/oxygen-related defect species.

Facilely fabricated Sr@NiO/FTO films and their characterizations for opto-nonlinear applications

Nickel oxide (NiO) is found to have several fascinating applications in optoelectronics and spintronic devices. Hence, herein we facilely fabricated the NiO thin films with 0.0, 1.0, 2.5 and 5.0 wt.% Sr doping by low-cost spin coater at RT. The single-phase confirmation of Sr@NiO films was done by X-ray diffraction and FT-Raman analyses. The crystallite size was estimated through Scherrer rule and noted to lie between 13 to 31 nm. The broad Raman peaks indicate low dimension nanostructured films formation. Sr doping in NiO was detected by EDX spectra and its homogeneity in final film by SEM e-mapping. AFM analysis revealed nano-spherical grains in all films. The grown films were tested for optical transparency and noticed that the films are transparent viz. ~ 45 to 65% over 500 to 1400 nm wavelength region. The direct energy gap and refractive index was determined and lies between 3.74 to 3.84 eV and 1.6 and 2.2 in the visible, correspondingly. The values of dielectric constant were calculated in range from 2 to 60. The linear, third order nonlinear and nonlinear refractive index values are noted to be enhanced by Sr content in energy range from 1 to 4 eV. The enhanced energy gap and nonlinear activities signify the importance of the grown Sr@NiO films for optoelectronics.

Band structure and infrared optical transitions in ErN

Erbium nitride (ErN) is a rare-earth metal mononitride with desirable electronic, magnetic, and optical properties. ErN can be incorporated into III-nitride semiconductors to develop new functional materials for optoelectronic and spintronic devices. Here, we report on the optical properties of ErN crystals, grown by sublimation and probed by photoluminescence (PL) spectroscopy. Three transition lines were observed near 1 eV. Theoretically, ErN has a small indirect energy gap of around 0.2 eV with a conduction band minimum at the X-point of the Brillouin zone and a valence band maximum at the Γ-point. The predicted smallest direct energy gap is around 1 eV, with two valence bands at the X-point. Using the PL results together with the reported calculations, a coherent picture for the band structure at the X-point for ErN crystals has been derived. Experimental results revealed that ErN has a minimum direct bandgap of 0.98 eV and a total of two valence bands separated by about 0.37 eV at the X-point.

Synthesis and characterization of silver oxide nanoparticles prepared by chemical bath deposition for NH3 gas sensing applications

Nano-silver oxide thin films with high sensitivity for NH3 gas were deposited on glass substrates by the chemical bath deposition technique. The preparations were made under different values of pH and deposition time at 70ᵒ C, using silver nitrate AgNO3 and triethanolamine. XRD analysis showed that all thin films werepolycrystalline with several peaks of silver oxides such as Ag2O, AgO and Ag3O4, with an average crystallite size that ranged between 31.7 nm and 45.8 nm, depending on the deposition parameters. Atomic force microscope (AFM) technique illustrated that the films were homogenous with different surface roughness and thegrain size ranged between 55.69 nm and 86.23 nm. The UV-Vis spectrophotometer showed that the optical direct energy gap ranged between 1.66 eV to 2.12 eV. The silver oxide thin film gives a high sensitivity of 70.12 for NH3 gas at 75°C operating temperature. This study shows that different types of silver oxides can beprepared by the CBD techniques, with the nanostructure to be used in gas sensors and optoelectronic applications.

Profound optical analysis for novel amorphous Cu2FeSnS4 thin films as an absorber layer for thin film solar cells

In this study, quaternary kesterite Cu2FeSnS4 (CFTS4) has been selected due to its interesting optical and electrical characteristics. The CFTS4 films were prepared by exploiting the chemical bath deposition process at room temperature. The films were prepared at different deposition periods (1, 3, 5 and 7 h). The EDAX technique was helped in evaluating the compositional element ratio which near to 2:1:1:4. The morphology and structure of CFTS4 films have been examined by utilizing X-ray diffraction, and field emission scanning electron microscope techniques. XRD charts revealed the absence of sharp peaks and approved the amorphous nature of films under investigations. The transmittance and reflectance data were employed to compute the linear and nonlinear optical constants of the as-deposited CFTS4 films. The energy gap calculations for the CFTS4 films grown on glass substrate displayed a direct energy gap and by increasing the deposition time, a reduction in energy gap values from 1.41 to 1.19 eV was obtained. The deep analysis of linear/nonlinear optical properties as a function of deposition time has revealed many characteristics of the investigated films. Moreover, the nonlinear parameters (refractive index n2, nonlinear absorption coefficient βc and the third-order nonlinear optical susceptibility χ(3)) of the CFTS4 films were boosted with rising up the film thickness and their high values imply the possibility of utilizing these films in various optoelectronic applications.

Development and characterization of TlGaSe2 thin film-based photodetector for visible-light photodetector applications

In current work a thermal evaporation technique has been employed to fabricate the thin films from the grown TlGaSe2 single crystal and investigated. X-ray diffraction study revealed the formation of polycrystalline films of monoclinic crystal system. The crystallite size was estimated to be 11 nm. Atomic force and scanning electron microscopy studies shows the nanocrystalline film fabrication and the size of grain was estimated. Optical study shows that the grown film is about 55% transparent in 800–1500 nm region and possess a sharp absorption edge. The direct energy gap of TlGaSe2 films was estimated around 2.31 eV. The photo current of the fabricated TlGaSe2 photodetector increases about 6 times compare to dark when exposed under 5 mW/cm2 illumination. The fabricated detector possesses high external quantum efficiency of 158% and also the detectivity reached to 5.16 × 1010 at V = 10 V. The on/off behaviour of the device was also studied and found that the response time for growth and decay is 88 ms and 90 ms, respectively.

Cd12O12 cage cluster-assembled nanowires and band gap regulation: A first-principles investigation

Based on the first-principle calculation, the stability and electronic properties of Cd12O12 cluster-assembled nanowires and Na-doped Cd12O12 nanowire are studied. The results show that both Cd12O12 nanowire and Na-doped Cd12O12 nanowire are thermodynamically stable (at least at room temperature). The most stable Cd12O12 nanowire exhibits semiconducting properties with a direct energy gap. After doping Na atoms into the nanowire, the electronic properties of the Cd12O12-based nanowire present dramatic changes, and the system transforms from semiconducting to metallic. It can provide a theoretical guidance for the potential application of Cd12O12-based semiconductor devices.

Influence of post-deposition annealing temperature on the growth of chemically deposited Sb2S3 thin films

Abstract Sb2S3 is a potential material for solar cells because of the suitable optoelectronic properties as well as earth-abundant constituent elements. Post-deposition annealing treatment is a crucial step in the fabrication of high-quality crystalline Sb2S3 thin films. Herein, we analyzed the impact of annealing temperature on grain growth and morphology of Sb2S3 films by annealing them in an Ar atmosphere for 30 min. The as-grown Sb2S3 films were amorphous. On annealing the films at 250–350 ∘ C, crystallization of orthorhombic Sb2S3 occurred and its crystal size increased from 43 to 100nm. The surface morphology and grain growth were improved at an annealing temperature of 300 ∘ C when compared with those at temperatures 250 ∘ C and 350 ∘ C. The annealed Sb2S3 films exhibited direct energy gap values of 1.6–1.7 eV. The films exhibited p-type electrical conductivity. The electrical resistivity of the films decreases and hole mobility increases with increasing annealing temperature from 250 to 350 ∘ C. This study is vital for the optimization of the annealing temperature for growth of good-quality Sb2S3 films, which are necessary for solar cell applications.

Fabrication and growth of linear and nonlinear optical behaviour of Cu2FeSnS4 spherical nanostructured thin films

For cost-effective synthesis of Cu2FeSnS4 (CFTS) thin films, a chemical bath deposition technique was carried out at temperature of 343 K. The formation of tetragonal phase and highly oriented CFTS thin films was confirmed by XRD technique. The morphology and composition of the CFTS thin films were characterized by field emission scanning electron microscopy and EDX techniques. Linear and nonlinear optical studies of the CFTS thin films were executed to determine a future device application. The chemically prepared CFTS thin films reveal a direct energy gap which decreased from 1.54 to 1.31 eV with increasing the thickness. The nonlinear optical constants of the chemically prepared CFTS thin films such as the nonlinear absorption coefficient βc, the nonlinear refractive index n2 and the third-order susceptibility χ(3) were evaluated and analysed.