Decline In Band Gap Research Articles

Photocatalytic Scheme with External Magnetic Field on Coffee Waste in Hydrogen Production

Photocatalytic is considered a deadlock-breaking technology for renewable energy and lowering environmental pollutants. Photocatalytic efficiency efforts are improved by activating the photocatalyst to introduce an external magnetic field. This review highlights recent breakthroughs by comparing original coffee waste, activation of coffee waste with the addition of catalysts, and manipulation of spin electrons by applying external magnets. Characterization was done with FTIR to look at chemical bonds, UV-Vis with Tauc's Relation approach to measure bandgap, and material morphology using SEM EDX. The increase in photocatalyst activation aligns with the decrease in bandgap value. The rate of decline in bandgap is in line with the rate of acceleration of hydrogen production. Adding an external magnetic increases hydrogen production up to 1.5 times greater than the original photocatalytic.

Mangifera indica mediated biogenic synthesis of undoped and doped TiO2 nanoparticles and evaluation of their structural, morphological, and photocatalytic properties

Biogenic synthesis is a growing trend to synthesize various nanoparticles. In this study, pristine and doped TiO2 nanoparticles were synthesized utilizing mango leaf extract via a cost effective and eco-friendly biogenic route. As a precursor, titanium isopropoxide (TTIP) was used. The transition metals, Cu and Ag, were added as dopant materials in various concentration levels of 0.5%, 1%, 1.5%, and 2%. To assess the morphological, structural, photocatalytic properties of the prepared samples, several characterization techniques such as SEM, EDX, XRD, UV–Vis were implemented. Both Cu- and Ag doped TiO2 samples showed a gradual decline in band gap in comparison to undoped TiO2 with the increasing doping percentage. The result of the photo-degradation of methylene blue (MB) demonstrated that doping of TiO2, whether with Cu/Ag, greatly enhances the photocatalytic performance which is attribute to the “Red-Shift” phenomena along with the reduced photogenerated electron-hole recombination rate. Results obtained suggest that TiO2 nanoparticles (both undoped and doped) synthesized through a greener and more cost-effective approach may have a promising future for water purification and dye remediation owing to better photo-degradation.

Impact of N+ ion implantation on the properties of ZnSe thin films

Ion implantation in II–VI semiconducting nanostructures has proven to be an effective tool in tailoring the properties of nanostructures, thus making them a prominent candidate to be used in solar cells, gas sensing, optoelectronic, catalytic and many more applications. The present study is aimed at N+ ion implantation effects on various properties of ZnSe thin films. First, a two-step synthesis was employed to synthesize ZnSe nanoflakes by solvothermal technique which were then drop casted onto glass substrate. The impact of 80 keV N+ ions on ZnSe thin films was explored for structural, morphological, elemental, optical and electrical analysis using characterization tools. The X-ray diffraction study revealed peak intensity variation without any shift in the reflex positions. However, the texture analysis depicted a relative intensity variation along with change in preferred orientation of planes with fluence. The optical study demonstrated a decrement in band gap. The I–V characteristics exhibited an intensification in the current values with the exposed fluence. This decline in band gap and increment in conduction values may be because of decrease in charge carrier scattering by the grain boundaries along with generation of higher number of electron–hole pairs with increasing fluence. The effects of implantation on sample characteristics are described in this contribution along with feasible reasons for observed changes in properties.

Highly enhanced solar conversion efficiency of novel layer-by-layer PbS:Hg and CdS quantum dots-sensitized ZnO thin films prepared by sol–gel spin coating

Owing to superior optical properties, ZnO thin films have immense potential in solar cell preparation. ZnO thin films were prepared by sol–gel technology. However, this is prolonged technique and it necessitates a complex precursor solution. In the present work, ZnO thin films are prepared by sol–gel spin coating with simple precursor, zinc acetate. A very remarkable feature of the method is that polycrystalline, non-abrasive and translucent films were obtained. Additionally, novel PbS:Hg quantum dots (QDs) and CdS QDs are successfully synthesized. Moreover, both types of QDs are deposited layer-by-layer over pure ZnO and Ag:ZnO thin films. The films are characterized by X-ray diffraction, and crystallinity continuation is observed even after the addition of QDs layer. Presence of synthesized QDs over thin films is also confirmed. The films were also characterized by scanning electron microscopy (SEM) and UV–Vis spectroscopy. Uniform, dense and porous surface morphology is clearly revealed. Sensitized thin films show a huge decline in band gap and large enhancement in efficiency. Superior current density (\(10.87~\hbox {mA}~\hbox {cm}^{-2})\) is achieved with PbS:Hg/CdS/Ag:ZnO, which leads to enhancement in overall solar conversion efficiency by 6.34 times.

Impact of nucleation of carbonaceous clusters on structural, electrical and optical properties of Cr+-implanted PMMA

Specimens of polymethylmethacrylate (PMMA) have been implanted with 400 keV Cr+ ions at different ion fluences ranging from 5 × 1013 to 5 × 1015 ions/cm2. The possible chemical reactions involved in the nucleation of conjugated carbonaceous clusters in implanted PMMA are discussed. Furthermore, impact of formation of carbonaceous clusters on structural, optical, electrical and morphological properties of implanted PMMA has been examined. The structural modifications in implanted PMMA are observed by Raman spectroscopy. The variation in optical band gap and Urbach energy is measured using UV–visible spectroscopic analysis. The effects of Cr+ ion implantation on electrical and morphological properties are investigated by four-probe apparatus and atomic force microscopy, respectively. The Raman spectroscopic analysis confirmed the formation of carbonaceous clusters with the transformation of implanted layer of PMMA into amorphous carbon. Simultaneously, the optical band gap of implanted PMMA has reduced from 3.13 to 0.85 eV. The increase in Urbach energy favors the decline in band gap together with the structural modification in implanted PMMA. As a result of Cr+ ion implantation, the electrical conductivity of PMMA has improved from 2.14 ± 0.06 × 10−10 S/cm (pristine) to 7.20 ± 0.36 × 10−6 S/cm. The AFM images revealed a decrease in surface roughness with an increment in ion fluence up to 5 × 1014 ions/cm2. The modification in the electrical, optical and structural properties makes the PMMA a promising candidate for its future utilization, as a semiconducting and optically active material, in various fields like plastic electronics and optoelectronic devices.

Kr++ Ion Implantation-Induced Changes in Optical Properties of Polycarbonate

Transparent polycarbonate samples were implanted with 200 keV Kr++ ions to various doses ranging from 1 × 1015 to 8.4 × 1016 ions cm−2 with a beam current density of 1 µA cm−2. Modification in the optical and chemical properties of polycarbonate as a function of the implantation fluence was investigated for UV-visible spectroscopy. UV-visible absorption analysis suggests the formation of a carbonaceous layer and a drastic decrease in optical band gap from 4.12 eV for unimplanted polycarbonate to 0.71 eV at an implanted dose of 8.4 × 1016 ions cm−2 has been observed. The width of the tail of localized states in the band gap was evaluated using the Urbach edge method and it increased from 0.10 eV for unimplanted polycarbonate to 2.46 eV for Kr++ implanted polycarbonate at the highest dose of 8.4 × 1016 ions cm−2, indicating an increase in disorder. The decrease in optical band gap points towards the formation of carbonaceous clusters and/or networks of conjugated unsaturated bonds. The number of carbon atoms, N, in a cluster can be calculated from absorption spectra and it increases from a value of 83 at a dose of 1 × 1015 ions cm−2 to 2333 at a dose of 8.4 × 1016 ions cm−2. The correlation between the decline in band gap and change in structure has been discussed.