Papers by Keyword: Band Gap

Abstract: In this work, the co-precipitation method is used for the synthesis of copper sulfide (CuS) nanoparticles for use in solar cells. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive x-ray analysis (EDX), UV-Visible spectroscopy (UV-Vis), photoluminescence spectroscopy (PL), and Fourier transform infrared spectroscopy (FTIR) are used to analyse the synthesized CuS nanoparticles. CuS nanoparticles with hexagonal phases and crystallite sizes ranging from 19 nm to 24 nm are identified by X-ray. The morphology of the SEM images changes from being asymmetrical to spherical. UV-Vis spectroscopy was carried out for the optical analysis of the synthesized powder. The band gap of the samples is determined using a tauc plot, and it is found to be decreasing with an increase in sulfur concentration, going from 2.01 eV to 1.88 eV. Surface imperfections and green emission bands related to electro-hole recombination are visible in PL spectra. Cu-S stretching vibrations are present at 618 cm^-1, according to FTIR spectra.

Abstract: The structural and electrical adsorption performance of carbon monoxide (CO), nitrous oxide (NO), nitrous dioxide (NO₂), and sulphur dioxide (SO₂) are explored using density functional theory calculations on Ni-doped atoms in the crystal structure of bismuth ferrite oxide (BFO). DFT+U+V offers a more complete description than either DFT or DFT+U alone. Good agreement with the experiments is obtained for both the band gap and the crystal field splitting. Ni-doped BFO (010) has adsorption energies of -0.35443 Ry for CO, -0.056076 Ry for NO, -5.64867 Ry for NO₂, and -55.5483 Ry for SO₂. Also, it was found that the energy of the band gap in pure BFO (010) can be lowered by adding Ni atoms. Further evidence from the DOS plot that Ni-doped BFO (010) may be considered as an emerging doped perovskite in high temperature gas sensing system for SO₂ detection.

Abstract: ZnO has attractive and great properties especially in the fields of photonics, electronics and optics and it is widely used in the manufacturing industry of photodetectors, laser diodes and gas detectors. Therefore, various methods have been carried out to produce ZnO crystals and one of them is the Electric Current Heating method. Electric Current Heating (ECH) method is a fabrication technique applied in researches to grow ZnO crystal on a ceramic bar. This method is preferred because of it is easy to operate in laboratory, low growth temperature and also low cost. In this research, by using powder metallurgy process, Graphene Oxide/GO (in various weight percentage) added into ZnO was pelletized in a compaction die with dimension of 14.95 mm x 30 mm x 40 mm and pressure of 4 bar. The pellet green body was then sintered at 1100 °C with rate 10.0 °C/min for 3 hours. The sintered GO added ZnO ceramic was cut into ceramic bar with dimensio of 13mm x 2mm x 2mm. ECH with current 3 A and applied voltage of 30 V was used to heat the ceramic bar to produce crystals. Under scanning electron observation, it was found different crystal-like structures for each percentage GO addition. UV-Vis measurement has shown that each crystal-like structure of a GO added ZnO has own degree of energy absorbsion because of different band gap. Addition GO into ZnO would increase band gap of pure ZnO.

Abstract: ZnS quantum dots were synthesized using green synthesis route which are cost effective and eco-friendly. X-ray diffraction study revealed the formation of single phase ZnS. Crystallite size and strain in the as synthesized material were calculated through Williamson-Hall and Size-Strain plot. UV-Vis spectroscopy investigations revealed the absorption region and optical band gap for the ZnS with refractive index analysis. Microstructural analysis of material was done using high resolution transmission electron microscope (HRTEM) which confirms the presence of quantum dots. Selected area electron diffraction pattern (SAEDP) of the corresponding area revealed the polycrystalline nature of as synthesized ZnS with fine crystallites oriented along (111) and (022) planes. Results of analysis of lattice fringe spacing’s of fine crystallites are found to be in good agreement with SAEDP data. Elemental compositional analysis was carried by using EDS as an attachment of TEM which showed the presence of Zinc and Sulphur only. Nyquist plot reported Warburg impedance which suggests the material for solar cell applications.

Abstract: Photoelectrochemical cell (PEC) has the same working principle as solar cell which convert solar energy into electricity. PEC consists of photoanode, electrolyte, and counter electrode, where electrolyte plays an important role in determining PEC performance. Yttria-stabilized zirconia (YSZ) is the most suitable electrolyte used due to its high ionic conductivity and chemically stable. In this study, YSZ was deposited to ZnO Nanorods (NRs) by doctor blade method with thickness variation of 100 μm (PEC10) and 120 μm (PEC12). X-ray diffraction (XRD), scanning electron microscope (SEM), and UV-Vis spectroscopy were used to distinguish the phase, morphology, and band gap of the formed materials, respectively. Moreover, I-V test was also conducted to evaluate the performance of the fabricated PEC with different YSZ thickness. SEM image confirmed the deposition thickness of YSZ layer on NRs which formed rough and irregular interface due to grain boundary fusion of YSZ and NRs. In addition, there is little difference XRD pattern from PEC10 and PEC12 which shows ZnO and YSZ peaks with peak shifting observed. Meanwhile, slightly difference noticed on band gap value where PEC10 has 3.25 eV and PEC12 has 3.58 eV. Even though, the characteristic of PEC10 and PEC12 is similar, the I-V test shown a significant difference of solar efficiency where PEC10 has higher efficiency of about 0.328% than PEC12. This difference is contributed by smaller grain size which has higher specific surface area and porosity. Based on this study, the thickness of electrolyte layer YSZ doesn’t affect the basic characteristic of PEC but affect the efficiency of PEC significantly.

Abstract: Copper sulphide quantum dots were synthesized by a simple chemical route using ammonia (aq.) as a complexing agent in PVA matrix. Copper acetate monohydrate and thiourea were used as precursors. The particle sizes as obtained from XRD results were found to be in good agreement with those of HRTEM. The UV-Vis. absorption and PL emission spectra exhibited a systematic blue shift of absorption and emission respectively confirming quantum confinement effect in the synthesized quantum dots. The band gap as estimated from Tauc-plot increased from 3.26eV to 3.92eV with change of concentration of complexing agent. The FTIR spectra exhibited Cu-S stretching peaks characteristic of CuS. Ionic contributions of the electrolytic ionic CuS solution as measured by a standard conductivity cell clearly showed the semiconducting behavior of the product material. The synthesized material may be exploited in fabrication of an optoelectronic device in UV-blue region.

Abstract: In the present investigation Co doped Sm₂O₃ nanostructures (NS) with different concentrations (1%, 3% and 8%) synthesized by thermal decomposition and surface reduction methods using sodium hydroxide as precipitating agent. Flake-like shaped semiconductor crystal features, morphology, optical absorptivity, chemical composition determined by XRD (X-ray diffraction), SEM (scanning electron microscopy) and UV-Visible. Flake-like morphology of the NS observed in SEM analysis having grain size varies in between 80 and 96 nm. XRD pattern depicted mixed phase of cubic crystal structure with crystallite size lying between 36.8 and 29.9 nm. Red shift in the optical absorptivity was observed in the spectrum, and spectral shift from ultraviolet to visible region with optical band gap (Eg) value decreases from 4.33 to 2.01 eV. Upon excitation with ultraviolet radiation (excitation = 300 nm), NS showed red emission in all concentrations of Co dopant and maximal emission intensity appeared at 485.5 nm for 8% of Co dopant concentration. The NS finds prominent utility in the field of optoelectronics and photoelectronic applications.

Abstract: The synthesized MOF with copper metal dopant has shown band gap around 1.5 eV which falls in the UV region of electromagnetic spectrum. This MOF with copper turns into nano/MOF composite with addition of Ag₂O and rGO to it. The results of band gap of MOF/ Ag₂O and MOF/rGO showed 1.904 eV and 1.639 eV respectively. This shift in band gap supports to use them as a UV and near visible light harvest catalyst and also assist in enhancing mechanical, thermal and structural behaviour of compounds. The enhancement of band gap of MOF/nanoMO is attributed to the quantum size effect.

Abstract: We study in this work, the occurrence of defects modes in the transmission spectrum and the band structure of a perfect photonic asymmetric serial loops structure (ASLS) utilized for narrow-band filtering. The perfect structure presents large photonic bandgaps that result from the modes of the loops resonances and the system periodicity. Besides that, the existence of defects within this perfect ASLS, whether at the segment or loop level, or both of them, causes the appearance of two, three, or four defect modes within gaps with good transmission rates and high-quality factors. These defects modes are extremely sensitive to changes in structural parameters. This system can be used to filter or guide the incoming electromagnetic waves. The interface response theory has been used to accomplish the analytical calculation. Green's function of the full system is determinated using this method. It allows us to calculate the dispersion relation and the transmission rate. Therefore, this paper can provide ideas for the design of multi-channel tunable filter using for frequency division multiplexing and microwave and signal processing.

Abstract: Semiconducting single-wall carbon nanotubes (SWCNTs) have already emerged as a promising candidate for molecular electronics and photovoltaic applications including solar cells. Any application of semiconducting SWCNTs is primarily related to proper information about its bandgap. In this work, the impact of the chirality indices and diameters of a series of armchair and zigzag SWCNTs on the electronic properties (band gap, electronic band structure and density of states (DOS)) are investigated using semi-empirical π orbitals tight-binding (TB) method. The results indicate that the electronic behaviour of the nanotubes changes according to chirality, the total number of electronic sub-bands gets increased when the chirality increases and Van Hove singularities (VHs) appear in its electronic DOS. We have found that for small diameter tubes (less than 0.8 nm), the calculated band gaps don’t agree with DFT calculations based on ab-initio (LDA and GGA) methods, which shows that the semi-empirical TB method including π orbitals only is not sufficient to give a reasonable description of small nanotubes. All Obtained results are in good agreement with previous studies. Semiconducting SWCNTs used in this study are particularly well-suited for the nanoelectronic devices and optoelectronic applications with their direct bandgap and optical transitions, while metallic SWCNTs are considered to be ideal candidates for variety of future nanoelectronic applications such as nanocircuit interconnects and power transmission cables.