Energy Band Gap Narrowing Research Articles

Magnetically separable Nd and Mn co-doped SrFe12O19 hexa-ferrites nanostructures for the evaluation of structural, magnetic and photo-catalytic studies under solar irradiation for the crystal violet dye removal from the industrial wastes

In the current research study, Nd & Mn co-doped strontium hexa-ferrite Sr1-xNdxFe12-yMnyO19 nanoparticles (NPs) were fabricated using facile micro-emulsion approach. The as-fabricated bare and co-doped materials were characterized for the structural X-ray diffraction (XRD), Raman and Fourier Transform of Infrared (FTIR), magnetic and photo-catalytic activities (PCA). The structural characterization confirms the synthesis of single phase M-type Sr-hexa-ferrite, along with successful doping of Nd and Mn ions at tetrahedral/octahedral site. The crystallite/grain size was observed to increase from 18 to 27 nm. The vibrating sample magnetometer (VSM) analysis revealed that the saturation magnetization (Ms), coersivity (Hc) and remanence increases on co-doping. Optical and band gap studies revealed the narrowing of energy band-gap (Eg) which decreases from (2.18 eV–1.98 eV) on Nd and Mn doping which might be attributed to the new energy level generation in the co-doped materials. BET surface analysis shows well porous nature of the Nd and Mn co-doped materials with pore size 74 m2/g in comparison to 56 m2/g of un-doped material. The PCA was determined by solar-light degradation of crystal violet (CV) dye as industrial model contaminant. The results revealed that Nd and Mn co-doped Sr1-xNdxFe12-yMnyO19 NPs efficiently degraded CV dye (90.7%) when compared with (36.8%) of un-doped SrFe12O19 NPs in the 90 min of solar-light exposure. This increase in the PCA was ascribed because of the narrow band gap and defected structure of Nd and Mn co-doped Sr1-xNdxFe12-yMnyO19 NPs. The stability and reusability tests revealed the excellent stability of the photo-catalyst which is only 1.10% loss observed after 5 repeated rounds which indicate its potential stability and reuse. The results of the application studies of Nd and Mn co-doped Sr1-xNdxFe12-yMnyO19 NPs revealed the potential uses for various electrical, as magnetic materials and for the remediation of toxic contaminants from the various industrial units and environment.

Optimization of structural and optical properties of sputter deposited TiO2 thin films by controlling deposition parameters

Titanium oxide (TiO2) thin films have been deposited onto highly cleaned soda lime glass substrates by DC magnetron reactive sputtering system. The Ti target with purity 99.99% is sputtered by argon gas in the sputtering chamber. Oxygen gas with purity 99.99% is introduced during the deposition process into the sputtering chamber as reactive gas for the synthesis of titanium oxide. Structural and optical properties of TiO2 thin films have been characterized by X-ray diffraction (XRD), Raman spectroscopy and UV-Vis. spectroscopy. The effect of substrate temperature and sputtering power on the optical properties of TiO2 thin films has been studied. The XRD and Raman spectroscopy of as-deposited films are used to study the structural properties of TiO2 as a function of substrate temperature and sputtered power. The structural studies show the crystalline nature of TiO2 thin films. The narrowing of energy band gap of sputtered deposited TiO2thin films was studied using UV-Vis. spectroscopy.

Removal of naphthalene from aqueous solutions by phosphorus doped- titanium dioxide coated on silica phosphoric acid under visible light

In this research, titanium dioxide-phosphorus (TiO2-P) immobilized on silica phosphoric acid (SPA) was prepared by a simple modified sol-gel method with SPA as a precursor instead of phosphoric acid. TiO2-P thin film photocatalyst immobilized on SPA as a novel high-efficiency photocatalyst was investigated to remove naphthalene as a toxic compound from wastewater. The novel resulting photocatalyst were characterized by energy-dispersive X-ray (EDX) and X-ray diffraction pattern revealed nano-photocatalyst TiO2-P with the average size of 15-20 nm. EDX analysis showed the presence of phosphorus elements in the crystalline structure of TiO2 and diffuse reflectance spectroscopy showed the energy bandgap narrowing and transfer of photocatalytic activity of TiO2-P to the visible region. The excellent photocatalytic activity of TiO2-P/SPA compared with TiO2-N,S as thin films coated on glass microspheres. The results showed that the optimal pH, time, concentration, and efficiency removal of naphthalene for TiO2-P were 5, 50 min, 25 mg/L, and 92.12% and TiO2-N,S catalyst were 5, 60 min, 25 mg/L, and 88.47%, respectively (P < 0.05). The removal of chemical oxygen demand in pH 5 for TiO2-N,S was obtained 79.26% and for TiO2-P was obtained 81.64%. In this research, the ability to use immobilized TiO2-P in SPA can be used as a new, effective and practical method in the treatment of water and industrial wastewater containing naphthalene in the presence of visible light.

150 KeV Cu− ion- implantation in SrVO3 thin films: A study of Cu induced defect states

Investigations on the extrinsic defects induced alteration in B–O6 octahedra, energy band-structure amendments and physical assets of ABO3 perovskites are technologically important and require modest approaches for the defect creation and their investigations. In this study, Cu defects have been assimilated in SrVO3 films using 150 KeV Cu ion-implantation with two different ion fluences; 1.63 × 1015 ion/cm2 and 8.15 × 1015 ion/cm2. The implanted Cu ions do not make metallic/oxide clusters in SrVO3 films, as confirmed by XRD studies, but have facilitated the lattice parameter enlargement and energy band-gap narrowing by creating their defect states and V–O6 octahedra distortion. NEXAFS spectra at Cu L-edge have confirmed the Cu2+ ions in low/high Cu doses implanted SrVO3 films. Cu defects induced V–O6 octahedra distortion has manifested a diverse ligand field interaction between V 3 d and O 2p orbitals and has narrowed the; (i) energy gap of V 2p3/2 and V 2p1/2 transitions and (ii) energy gap between t2g/eg and the O 2p and metal (n+1)sp hybridized orbitals, leading to the band-structure alteration of SrVO3 films. Mechanistic understanding of band-structure perturbation is discussed in the light of ion-solid interaction induced defect formation in SrVO3 thin films.

Sulfur and nitrogen doped-titanium dioxide coated on glass microspheres as a high performance catalyst for removal of naphthalene (C10H8) from aqueous environments using photo oxidation in the presence of visible and sunlight

Naphthalene is a toxic aromatic compound whose presence in aqueous environments is very hazardous. In this research, naphthalene removal from wastewater using titanium dioxide-nitrogen-sulfur (TiO2-N-S) photocatalyst immobilized on glass microspheres was investigated. Additionally, the effect of visible and sunlight, radiation time, pH, and initial concentration of naphthalene on photocatalytic removal of naphthalene were studied. Scanning electron microscope images revealed nanoparticles with an average size between 10 and 15 nm, and X-ray diffraction pattern revealed nano-photocatalyst with an average size of 11 nm. Energy-dispersive X-ray showed the presence of two elements, that is, sulfur and nitrogen in the crystalline structure of TiO2 powder, and diffuse reflectance spectroscopy showed the energy bandgap narrowing and transfer of photocatalytic activity of TiO2-N-S to the visible region. Chemical kinetic equation of naphthalene removal was second-order kinetic. The maximum level of naphthalene removal in the presence of visible and sunlight was obtained at a concentration of 25 mg/L (94.29%) and 40 mg/L (93.24%), respectively. Therefore, the immobilized TiO2-N-S on glass microspheres can be used as a new, effective, and functional method in treating water and industrial wastewater containing naphthalene in the presence of visible and sunlight.

In situ observations of the permanent structural modifications, phase transformations and band gap narrowing upon heating of Cu2Se/Yb/Cu2Se films

In this study, we have investigated the temperature dependent structural, optical and dielectric properties of Cu2Se thin films that are nanosandwiched with 50 nm thick ytterbium slab (CYC). The X-ray diffraction monitoring of the films during the heating process in the temperature range of 293–473 K has shown that the CYC films which contain both of the cubic and orthorhombic phases in its structure exhibits lattice expansion that increases the grain size and decreases the defect density, stacking faults and microstrain by 12.5% and by 28.9%, 12.8% and 11.3%, respectively. The CYC films show enhanced permanent crystallinity presented by high degree of orientation with reduction of the weight of the orthorhombic phase after cooling. On the other hand, a red shift in the energy band gap value is observed during the heating process. The analysis of the temperature dependent optical properties has shown a good correlation between the lattice expansion and energy band gap narrowing. In additions, the CYC samples are observed to exhibit negative capacitance effect that nominates the material for use in electronic circuits. The negativity of the capacitance decreased with increasing temperature due to the reduction in the defect density.

The influence of photointercalaction and photochromism effects on the photocatalytic properties of electrochemically obtained maze-like MoO3 microstructures

Molybdenum oxide (α-MoO3) thin films with oriented crystalline facets were synthesised by anodization of Mo foils. The obtained samples were exposed to UV–Vis illumination in aqueous electrolytes providing different cations. The morphology and structure of modified samples were investigated. The effect of photointercalated alkali metal cations (Li+, Na+, K+) on optical and structural properties was studied using UV–vis and Raman spectroscopies, respectively. The observed energy band gap narrowing caused by the photochromic effect is found to affect the photocatalytic properties of the intercalated oxide. The photoactivity of obtained samples was tested during the photocatalytic process of methylene blue decomposition in the presence of 0.1 M Li2SO4, Na2SO4, K2SO4. After 2 h of continuous illumination, the photodecomposition efficiency of MB in the presence of K2SO4, Na2SO4 and Li2SO4 was 67%, 69% and 76%, respectively, whereas when no inorganic salt had been dissolved it reached only 57%.

Temperature effects on the structural and optical properties of the TlInSe2xS2(1−x) mixed crystals ([formula omitted

In this work, we have studied the temperature effects on the recrystallization process and on the energy band gap of the TlInSe2xS2(1−x) mixed crystals at the critical composition (x=0.3) where structural phase transition from tetragonal to monoclinic takes place. Remarkable effect which included permanent recrystallization process, enlargements in the monoclinic crystallite size, decreases in the compressing strain and in the dislocation density as well as in the stacking faults and in the energy band gap with increasing temperature were observed. In addition, the temperature dependent energy band gap of the crystal which is investigated in the same temperature range that was used for the recrystallization process revealed that the recrystallization process is associated with energy band gap narrowing.

Efficient visible light-induced degradation of rhodamine B by W(NxS1\u2212x)2 nanoflowers

Here, W(NxS1−x)2 nanoflowers were fabricated by simple sintering process. Photocatalytic activity results indicated our fabricated N-doped WS2 nanoflowers shown outstanding photoactivity of degradating of rhodamine B with visible light. Which is attributed to the high separation efficiency of photoinduced electron–hole pairs, the broadening of the valence band (VB), and the narrowing of energy band gap. Meanwhile, our work provided a novel method to induce surface sulfur vacancies in crystals by introduing impurities atoms for enhancing their photodegradation.

Photocatalytic performance enhanced via surface bismuth vacancy of Bi6S2O15 core/shell nanowires

Core/shell structured Bi6S2O15 nanowires with surface bismuth defects are fabricated via a one-step hydrothermal method. The UV photocatalytic activity of the defective Bi6S2O15 nanowires is about 4 times as high as that of pure Bi6S2O15 nanowires. The light response range of Bi6S2O15 nanowires is greatly expanded from 370nm to 450nm via surface bismuth-vacancy. The main oxidative species transform from holes (h+) to the superoxide radical (O2−) and hydroxyl radicals (OH) owing to the great changes of the electronic structure of vacancy Bi6S2O15. Surface bismuth vacancies elevate the conduction band (CB) and introduce impurity states above the valence band (VB) of Bi6S2O15. The higher potential of CB benefits for the production of superoxide radical (O2−) and the hydroxyl radicals is result from the surface hydroxide radical defects formed with the introduction of surface bismuth-vacancy. The enhancement in photocatalytic performance is attributed to the high separation efficiency of photoinduced electron–hole pairs due to the broadening of the valence band (VB), and the extending of photoresponse is result from the narrowing of energy band gap owing to the rise of the valence band maximum (VBM).

Empirical determination of the energy band gap narrowing in p+ silicon heavily doped with boron

In the analysis of highly doped silicon, energy band gap narrowing (BGN) and degeneracy effects may be accounted for separately, as a net BGN in conjunction with Fermi-Dirac statistics, or lumped together in an apparent BGN used with Boltzmann statistics. This paper presents an experimental study of silicon highly doped with boron, with the aim of evaluating the applicability of previously reported BGN models. Different boron diffusions covering a broad range of dopant densities were prepared, and their characteristic recombination current parameters J0 were measured using a contactless photoconductance technique. The BGN was subsequently extracted by matching theoretical simulations of carrier transport and recombination in each of the boron diffused regions and the measured J0 values. An evaluation of two different minority carrier mobility models indicates that their impact on the extraction of the BGN is relatively small. After considering possible uncertainties, it can be concluded that the BGN is slightly larger in p+ silicon than in n+ silicon, in qualitative agreement with theoretical predictions by Schenk. Nevertheless, in quantitative terms that theoretical model is found to slightly underestimate the BGN in p+ silicon. With the two different parameterizations derived in this paper for the BGN in p+ silicon, both statistical approaches, Boltzmann and Fermi-Dirac, provide a good agreement with the experimental data.

Enhanced Photocatalytic Performance for the BiPO4–x Nanorod Induced by Surface Oxygen Vacancy

The BiPO4–x nanorod with surface oxygen vacancy was fabricated via vacuum deoxidation. The concentration and kind of oxygen vacancy could be controlled by tuning the deoxidation temperature and time in vacuum. The photocatalytic activity depended on the concentration and kind of surface oxygen vacancy, and the optimum photocatalytic activity and photocurrent of the BiPO4–x nanorod was about 1.5 and 2.5 times as high as that of pure BiPO4, respectively. Besides, the photocatalytic response wave range of the BiPO4–x nanorod has been expanded to more than 365 nm. The enhancement of photocatalytic activity is attributed to the high separation efficiency of photoinduced electron–hole pairs due to the broadening of the valence band (VB) induced by surface oxygen-vacancy states, and the extending of photoresponse is considered to be the narrowing of energy band gap resulting from the rise of the valence band maximum (VBM).

Empirical determination of the energy band gap narrowing in highly doped n+ silicon

Highly doped regions in silicon devices should be analyzed using Fermi-Dirac statistics, taking into account energy band gap narrowing (BGN). An empirical expression for the BGN as a function of dopant concentration is derived here by matching the modeled and measured thermal recombination current densities J0 of a broad range of n+ dopant concentration profiles prepared by phosphorus diffusion. The analysis is repeated with Boltzmann statistics in order to determine a second empirical expression for the apparent energy band gap narrowing, which is found to be in good agreement with previous work.

Preparation and Photocatalytic Performance of Iodine-Doped NaTaO3 Nanoparticles

Iodine-doped NaTaO3 nanoparticles were prepared by hydrothermal conditions and explored as the visible-light-driven photocatalysts for photodegradation of methylene blue in water. It is found that I-doped NaTaO3 showed photodegradation efficiency superior over the un-doped NaTaO3. UV-Vis diffuse reflectance spectra indicate that the absorption edges shifted towards longer wavelength with increasing the iodine concentration. The energy band structure and the transient behavior of the photogenerated charge carriers for both un-doped and doped NaTaO3 powders were investigated using density functional theory. The improved photocatalytic activity under visible light for I-doped NaTaO3 may be caused by both the broadening of valence band that inhibited the recombination of e-h+ pairs and the narrowing of energy band gap due to the much negative energy levels in the bottom of conduction bands.

Enhancement of CMOSFETs Performance by Utilizing SACVD-Based Shallow Trench Isolation for the 40-nm Node and Beyond

This paper reports an improved densification anneal process for sub-atmospheric chemical vapor deposition (SACVD)-based shallow trench isolation (STI) to enhance CMOSFETs performance for 40-nm node and beyond. The improved STI densification process is demonstrated to generate a lower compressive stress in the active area as compared to the Standard STI process used in 40 nm technology. For nMOS devices with the improved densification process, the reduction of STI compressive stress is beneficial to the electron mobility and leads to an enhancement of on-current (ION ). In addition, the ION enhancements would significantly increase with shrinking the device dimensions (gate width and source/drain length). On the other hand, the improved densification process would not degrade the pMOSFET's performance resulting from the very small piezoresistance coefficients for 〈1 0 0〉 channel direction. The superior junction leakage characteristics for the junction diodes with the improved anneal process can further verify the lower STI-induced compressive stress due to the less energy bandgap narrowing. Hence, the improved STI process can be adopted in 40-nm CMOS technology and beyond, where device structures have very small active areas.

Optical Properties of InAsSb Single Crystals with Cutoff Wavelengths of 8–12 µm Grown by Melt-Epitaxy

The transmittance spectra of melt epitaxiy (ME)-grown InAsSb single crystals with cutoff wavelengths of 8–12 µm were measured and calculated under the assumption of a microscopic composition distribution function. A good agreement between the experimental and theoretical transmittance spectra was obtained. The results indicate that a microscopic composition distribution inhomogeneity exists in long-wavelength InAsSb epilayers with different compositions, which may be related to the energy band gap narrowing of this InAsSb.

Band gap narrowing effect in Be-doped Al xGa 1− xAs studied by photoluminescence spectroscopy

The energy band gap narrowing (BGN) as a function of doping concentration in Be-doped Al 0.33Ga 0.67As is investigated using photoluminescence (PL) measurements on samples grown by molecular beam epitaxy (MBE). An expression for theoretically predicting the band gap narrowing has been deduced for p-type doping in Al xGa 1−xAs (0≤x≤0.45). The experimental results obtained from the PL spectra are in good agreement with this expression. A simple empirical relation for the PL peak energy of Be-doped Al 0.33Ga 0.67As as a function of carrier concentration is also presented. This provides a convenient way of determining the carrier concentration in Be-doped Al 0.33Ga 0.67As samples nondestructively.

Effects of epitaxial strain and ordering direction on the electronic properties of GaSb/InSb and InAs/InSb superlattices.

The structural and electronic properties in common-anion GaSb/InSb and common-cation InAs/InSb [111] ordered superlattices have been determined using the local-density total-energy full-potential linearized augmented plane-wave method. The influence of the ordering direction, strain conditions, and atomic substitution on the electronic properties of technological and experimental interest (such as energy band gaps and charge carrier localization in the different sublattices) were determined. The results show an appreciable energy band-gap narrowing compared to the band gap averaged over the constituent binaries, either in [001] ordered structures or (more markedly) in the [111] systems; moreover energy band gaps show an increasing trend as the substrate lattice parameter is decreased. Finally, the systems examined offer interesting opportunities for band-gap tuning as a function of the growth condition (about 0.7 eV in GaSb/InSb and 0.3 eV in InAs/InSb).

Determination of band gap narrowing and hole density for heavily C-doped GaAs by photoluminescence spectroscopy

The energy band gap narrowing effect in heavily C-doped GaAs was investigated using photoluminescence spectroscopy. The band gap was determined over the hole density range 1017–4×1020 cm−3 at 10 and 300 K. The band gap data at low temperatures confirm the available theoretical calculations up to 1020 cm−3. An unexpected temperature dependence of the observed band gap at high doping levels is discussed on the basis of carrier-phonon interactions. We present an analysis of the band gap narrowing effect that can be used for nondestructive measurement of hole densities in the range 1017–4×1020 cm−3.

Band-gap narrowing in semi-insulating gallium arsenide

A model of energy band-gap narrowing in SI GaAs crystals doped by chromium is proposed in order to explain the higher values of intrinsic carrier densities deduced from galvanomagnetic measurements in some Cr-doped SI GaAs crystals by various authors. This model is based on the screening of electron-hole interaction due to the chromium Cr2⇄Cr3+ state transitions. Also some other possible reasons for band-gap narrowing in SI GaAs are discussed.