Bandgap Tuning and Blue-Green Band Emissions of Sol-Gel Synthesized ZnO Films by High Cu Doping

The present research focuses on the preparation of ZnO thin films both undoped and doped with varying Cu concentrations (0.0%, 0.8%, 3.0%, 5.0%, 10.0% and 20.0%) using sol-gel spin coating technique. The optical bandgap (E_g) for undoped films is recorded as 3.239 eV and shows a little increase to 3.248 eV when it is doped with 0.8% Cu concentration whereas further increase of Cu doping concentration, it is decreased from 3.248 eV to 3.107 eV for 20% Cu. The E_U (Urbach Energy) is improved with the enhancement of Cu doping concentration. Ultraviolet (UV) and bluegreen band emissions are noticed from PL (photoluminescence) spectra. The UV peak intensities are diminished with increasing Cu doping concentration while the blue peaks intensities are amplified. These results illustrate that ZnO films doped with Cu meet the requirement for applications in different blue emission devices.

Investigating the coumarin capability in chalcogenide 20TI2Se-80Pr2Se3 system based photovoltaics

Chalcogenide films containing various contents of coumarin (CO) are deposited on the p-type Si substrates. Al/coumarin doped chalcogenide films/p-Si contact exhibits a rectifying behavior. The electrical and photoresponse properties of the prepared diodes are characterized by current and capacitance measurements under various illumination intensities. The addition of coumarin to TI₂Se-Pr₂Se₃ significantly affects the characteristic parameters of diodes. Kohlrausch function is used as an appropriate way to obtain the photo charge density (ρ_ph) and the relaxation time constant from the photocurrent/capacitance transients. It is shown that coumarin doped chalcogenide films have a potential to obtain the photocarrier generation.

Composite CuFe1-xSnxO2/p-type silicon photodiodes

CuFe_1-xSn_xO₂ composite thin film/p-type silicon diodes were prepared on substrate by sol-gel method (x=0.00, 0.01, 0.03, 0.05, 0.07). The structure of CuFe_1-xSn_xO₂ composite thin films was studied using XRD analysis and films exhibited amorphous behavior. The elemental compositions and surface morphology of the films were characterized using SEM and EDX. EDX results confirmed the presence of the compositional elements. The optical band gap of CuFe_1-xSn_xO₂ composite thin films was determined using the optic spectra. The optical band gaps of the CuFe_1-xSn_xO₂ composite thin films were calculated using optical data and were found to be 3.75, 3.78, 3.80, 3.85 and 3.83eV for x=0.00, 0.01, 0.03, 0.05 and 0.07, respectively. The photoresponse and electrical properties of the Al/CuFe_1-xSn_xO₂/p-Si/Al diode were studied. The barrier height and ideality factor were determined to be averagely 0.67eV and 2.6, respectively. The electrical and photoresponse characteristics of the diodes have been investigated under dark and solar light illuminations, respectively. The interface states were used to explain the results obtained in present study. CuFe_1-xSn_xO₂ photodiodes exhibited a high photoresponsivity to be used in optoelectronic applications.

Microwave-assisted hydrothermal synthesis and characterization of ZnO nanorods

For the purpose of this study, the nanorods of zinc oxide were synthesized by rapid microwave-assisted hydrothermal route. The microstructure and surface morphology of the sensitized nanorods were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM) and transmission electron microscope (TEM). XRD results indicate that synthesized ZnO nanorods have wurtzite phase. The calculated value of the particle size using Debye Scherrer formula and Williamson Hall plot was found to be 20-28 nm and 35.3 nm, respectively. Low uniformity distribution of rod-like morphology (60-80 nm in diameter and average length about 250 nm) are seen in TEM micrographs. The optical parameters of the prepared ZnO nanorods have been calculated using Kubeleka-Munk approach for the UV-vis diffuse reflectance spectrum. It is found that the direct transition optical band gap of the studied sample is 3.17 eV. The direct current electrical conductivity (σ) was increased from 6.7×10(-8) to 3×10(-7) Ω(-1) cm(-1) with increasing the temperature (T) in the range (300-425 K). The obtained variation of σ with T refers that the conductivity mechanism is controlled by thermally activated process.

Novel rapid synthesis of zinc oxide nanotubes via hydrothermal technique and antibacterial properties

ZnO nanotubes with the wurtzite structure have been successfully synthesized via simple hydrothermal solution route using zinc nitrate, urea and KOH for the first time. The structural, compositions and morphology architectures of the as synthesized ZnO nanotubes was performed using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS) and high resolution transmission scanning electron microscopy (HRTEM). TEM showed that ZnO nanotubes exhibited a wall thickness of less than 2 nm, with an average diameter of 17 nm and the length is 2 μm. In addition, the antibacterial activity of ZnO nanotubes was carried out in vitro against two kinds of bacteria: gram - negative bacteria (G -ve) i.e. Escherichia coli (E. coli) and gram - positive bacteria (G +ve) i.e. Staphylococcus aureus. Therefore, this work demonstrates that simply synthesized ZnO nanotubes have excellent potencies, being ideal antibacterial agents for many biomedical applications.

Semiconducting properties of Al doped ZnO thin films

Aluminum doped ZnO (AZO) thin films were successfully deposited via spin coating technique onto glass substrates. Structural properties of the films were analyzed by X-ray diffraction, atomic force microscopy (AFM) and energy dispersive X-ray spectroscopy. X-ray diffraction results reveal that all the films are polycrystalline with a hexagonal wurtzite structure with a preferential orientation according to the direction (002) plane. The crystallite size of ZnO and AZO films was determined from Scherrer's formula and Williamson-Hall analysis. The lattice parameters of the AZO films were found to decrease with increasing Al content. Energy dispersive spectroscopy (EDX) results indicate that Zn, Al and O elements are present in the AZO thin films. The electrical conductivity, mobility carriers and carrier concentration of the films are increased with increasing Al doping concentration. The optical band gap (Eg) of the films is increased with increasing Al concentration. The AZO thin films indicate a high transparency in the visible region with an average value of 86%. These transparent AZO films may be open a new avenue for optoelectronic and photonic devices applications in near future.

Structural and optical properties of nanostructure CdZnO films

CdZnO thin films with different ratio of CdO and ZnO (3:1, 1:1, and 1:3) were grown on glass substrate using sol-gel spin coating method. The morphology of the CdZnO films depends on the amount of ZnO and CdO in the films. The optical band gap of the CdZnO films depends on the compositions of CdO and ZnO. Films having higher amount of CdO shows the presence of grains along with the fiber nature of ZnO, whereas the film with lower percentage of CdO shows fiber nature of the film very similar to pure ZnO film. The optical bandgap of CdZnO (3:1), CdZnO (1:1), and CdZnO (1:3) films was calculated to be 2.80, 2.49, and 2.52 eV, respectively. Other optical properties such as refractive index, extinction coefficient, and dielectric constants were calculated using the optical data. The volume and surface energy loss functions were also calculated and observed to increase with increase in the photon energy.

Optical spectroscopy studies of the interaction between thiophanate methyl and human serum albumin for biosensor applications

Optical properties of the interaction between thiophanate methyl and human serum albumin have been investigated for biosensor applications. The interaction between human serum albumin (HSA) and thiophanate methyl (MT) was investigated by UV-Vis absorption spectra and atomic force microscopy. The optical constants (refractive index, absorption index, band gap and dielectric properties) of HSA, MT and MT+HSA films were determined using absorbance, transmittance and reflectance spectra. The refractive index dispersion curve (>530 nm) exhibits the normal dispersion. The refractive index of the MT+HSA is higher than both HSA and MT alone due to the highest reflectance of the mixture of MT and HSA. This behavior is indicative of the complex formation between the MT and HSA.

The Thermal Decomposition Kinetics of [Co(bipy)(H2O)4](C4H4O4)·4H2O

The thermal decomposition kinetics of [Co(bipy)(H2O)4](C4H4O4) · 4H2O was carried out by thermogravimetry (TG) and derivate thermogravimetry (DTG) analysis at four heating rates of 5, 8, 11 and 14 °C/min in nitrogen atmosphere. TG confirmed that thermal decomposition of the compound takes place in a single step. The kinetic parameters (activation energy, frequency factor, and activation entropy) were calculated using various forms of non-isothermal methods. The activation energy obtained by the Ozawa method is in agreement with the value determined by the Coats–Redfern technique. However, a much lower activation energy was obtained by the Kissinger method.

Photovoltaic properties of Au/beta-carotene/n-Si organic solar cells

Photovoltaic properties of Au/beta-carotene/n-Si organic solar cells characterized by current-voltage and capacitance-voltage measurements have been investigated. The photocurrent in the reverse direction increases with increasing illumination intensity. The I(sc) increases linearly with light intensity. The I(sc) dependence of light intensity follows a power law I(sc) approximately F(alpha). The exponent alpha was found to be 1.38. This indicates a monomolecular recombination in this device. Au/beta-carotene/n-Si organic solar cells give an open-circuit voltage of 0.316 V and a short-circuit current of 2.33 x 10(-4) A at light intensity of 6 W/m(2). The best conversion efficiency for Au/beta-carotene/n-Si solar cells was found to be 23.3% at a light intensity of 6 W/m(2).

Electrical, Optical, Thermoelectric Power, and Dielectrical Properties of Organic Semiconductor Poly(1,12-bis(carbazolyl) Dodecane) Film

Electrical conductivity, optical, thermoelectric, and dielectrical properties of the poly(1,12-bis(carbazolyl) dodecane) film have been investigated. The activation energy for electrical conductivity and room-temperature electrical conductivity (at 25 degrees C) values were found to be 0.25 eV and 2.65 x 10-6 S/cm, respectively. The thermoelectric power results suggest that the conductivity is due to large polarons (i.e., the carriers in polymer move by hopping in the localized states at band gap edges). Electrical conductivity and thermoelectric power results confirm that the polymer is a p-type organic semiconductor. Optical absorption results suggest that the direct allowed transitions are dominant in the fundamental absorption edge in the polymer with optical band gap value of 2.72 eV. The refractive index dispersion of the polymer obeys the single oscillator model with oscillator energy (Eo = 3.06 eV) and dispersion energy (Ed = 17.82 eV) values. Alternating current conductivity results suggest that the hopping conductivity is dominant in the polymer. The dielectrical properties exhibit a non-Debye relaxation.

Dielectric spectroscopy analysis in employing liquid crystal phthalonitrile derivative in nematic liquid crystals

Dielectric anizotropy and relaxation properties of 2,3-dicyano-1,4-di[3,4,5-tri(dodecyloxy)phenylcarbonyloxy] benzene (DCDPB)-doped E7 and E7 liquid crystal have been investigated by the dielectric spectroscopy method. Dielectric anisotropy property of the LCs changes from the positive type to negative type. Dielectric relaxation properties suggest that LCs exhibit a monodispersive dielectric property. The relaxation frequency of E7 and E7/DCDPB liquid crystals was calculated by means of Cole-Cole plots. Consequently, DCDPB dopant changes the dielectric anizotropy and relaxation parameters of E7 LC.

A theoretical study on 1-(thiophen-2-yl-methyl)-2-(thiophen-2-yl)-1H-benzimidazole

The molecular geometry and vibrational frequencies of 1-(thiophen-2-yl-methyl)-2-(thiophen-2-yl)-1H-benzimidazole (C(16)H(12)N(2)S(2)) in the ground state has been calculated using the Hartree-Fock (HF) and density functional method (B3LYP) with 6-31G(d) basis set. The optimized geometric bond lengths and bond angles obtained by using HF and DFT (B3LYP) show the best agreement with the experimental data. Comparison of the observed fundamental vibrational frequencies of 1-(thiophen-2-yl-methyl)-2-(thiophen-2-yl)-1H-benzimidazole (C(16)H(12)N(2)S(2)) and calculated results by density functional B3LYP and Hartree-Fock methods indicate that B3LYP is superior to the scaled Hartree-Fock approach for molecular vibrational problems.

A theoretical study on N-phenyl-N'-(2-thienylmethylene)hydrazine

The molecular geometry and vibrational frequencies of N-phenyl-N'-(2-thienylmethylene)hydrazine (C11H10N2S) have been calculated using Hartree-Fock and density functional method (B3LYP) with 6-31G(d) basis set. The optimized geometric bond lengths and angles obtained using HF and DFT (B3LYP) are in agreement with the experimental data. B3LYP method seems to be appropriate than HF method for the calculation of vibrational frequencies and geometrical parameters of the (C11H10N2S) compound.

Electrical and Optical Properties of an Organic Semiconductor Based on Polyaniline Prepared by Emulsion Polymerization and Fabrication of Ag/Polyaniline/n-Si Schottky Diode

The electrical, optical, and metal-semiconductor contact properties of the polyaniline prepared by emulsion polymerization have been investigated to obtain an organic semiconductor material. The obtained results suggest that the polyaniline (PANI) studied is an organic semiconductor material with optical band gap (E(g) = 2.21 eV) and room electrical conductivity (sigma(25) = 3.12 x 10(-2) S/cm) values. A Schottky diode with configuration Ag/PANI/n-Si was fabricated. The ideality factor and barrier height of Ag/PANI/n-Si diode at room temperature were found to be 4.59 and 0.38 eV, respectively. The obtained diode parameters change with temperature. The Richardson constant A* value for the Ag/PANI/n-Si diode was found to be 3.81 x 10(-4) A/cm(2).K. The Ag/PANI/n-Si diode is a metal-insulator-semiconductor-type device. The standard deviation, which is a measure of the barrier homogeneity, was found to be 0.14, indicating the presence of interface inhomogeneities. It can be concluded that the polyaniline prepared by emulsion polymerization is an organic semiconductor and Ag/PANI/n-Si configuration shows a Schottky contact.

Theoretical studies of molecular structure and vibrational spectra of 2-amino-5-phenyl-1,3,4-thiadiazole

The molecular geometry and vibrational frequencies of 2-amino-5-phenyl-1,3,4-thiadiazole (C8H7N3S) in the ground state has been calculated using the Hartree-Fock and density functional method (B3LYP) with 6-31G(d) basis set. The optimized geometric bond lengths and bond angles obtained by using HF and DFT (B3LYP) show the best agreement with the experimental data. Comparison of the observed fundamental vibrational frequencies of 2-amino-5-phenyl-1,3,4-thiadiazole (C8H7N3S) and calculated results by density functional B3LYP and Hartree-Fock methods indicate that B3LYP is superior to the scaled Hartree-Fock approach for molecular vibrational problems.

Optical Properties of the Poly(N-benzylaniline) Thin Film

The optical properties of the poly(N-benzylaniline) thin film were investigated by optical characterization. The optical constants such as refractive index and dielectric constant were determined from the transmittance and reflectance spectra of the film. The refractive index dispersion was analyzed by the Wemple-DiDomenico model. The n(infinity) values changed from 6.37 to 5.71 and these values did not show any certain trend with annealing temperatures. The average oscillator parameter So value, which is the strength of the individual dipole oscillator, was found to be in the range of 1.15 x 10(13) to 1.03 x 10(13) m(-2). The optical band was determined from the direct optical transitions in K space. The optical band Eg of the film decreases from 2.089 to 2.046 eV with increasing annealing temperatures while the Urbach energy Eu called the width of localized states in the optical band gap increases from 0.544 to 0.598 eV. Consequently, the optical constants and optical band gap of the poly(N-benzylaniline) change with the annealing temperatures.

Dielectric Studies of Tetraethylene Glycol−Bis(3-methylimidazolium) Dichloride (TEGDC) Exhibiting Large Negative Dielectric Anisotropy

A dielectric anisotropy property of a TEGDC (tetraethylene glycol-bis(3-methylimidazolium) dichloride) is investigated as a function of frequency. TEGDC showed an extremely large negative dielectric anisotropy (-10.95 to -4753.73). Variation of dielectric anisotropy (delta epsilon) with respect to the spot frequencies reveals that liquid crystal (LC) orientation has an n-type property at low frequencies and as the frequency increases dielectric anisotropy character shifts from negative dielectric anisotropy type (n-type) to positive dielectric anisotropy type (p-type). Consequently, the TEGDC is a liquid crystal with large negative dielectric anisotropy.