Increase In Band Gap Energy Research Articles

Annealing temperature-dependent microstructure and optical and electrical properties of solution-derived Gd-doped ZrO2 high-k gate dielectrics

In current work, the microstructure and optical and electrical properties of sol–gel-derived Gd-doped ZrO2 gate dielectric thin films as functions of annealing temperatures were systemically investigated. Analyzes by x-ray diffraction have indicated that the 240 °C-baked sample as well as those samples annealed at lower temperatures keep amorphous state. In the sample annealed at 500 °C, however, the amorphous phase disappears and tetragonal ZrO2 is formed. Measurements from ultraviolet-visible spectroscopy (UV/Vis) have demonstrated that transmittance of all samples in the visible region is approximately 80% and the increase in band gap energy has been found with increasing the annealing temperature. Electrical properties of all samples based on Al/Si/ZrGdOx/Al MOS capacitor have been investigated by using semiconductor device analyzer. Through the analysis and calculation of the electrical characteristic curves, solution-processed Al/ZrGdOx/Si/Al capacitor shows improved performances at a annealing temperature of 400 °C, such as high dielectric constant (k) of 16.56, lowest oxidation charge density (Q ox) of −0.74 × 1012 cm−2, and boundary trap oxidation charge density (N bt) of 3.17 × 1012 cm−2. In addition, the leakage current mechanism for 400 °C-annealed sample has been discussed in detail. solution-processed Gd-doped ZrO2 gate dielectric films were realized. Al/ZrGdOx/Si/Al capacitor shows optimized and improved performances at a annealing temperature of 400 °C.

Structure and optical properties of Fe3O4 nanoparticles synthesized by co-precipitation method with different organic modifiers

Synthesis and modification of magnetite nanoparticles were carried out by co-precipitation method. The influence of different organic modifiers on structure and optical properties of Fe3O4 nanoparticles has been studied in detail. The X-ray diffraction method, transmission electron microscopy, Fourier transform infrared spectroscopy and UV–visible spectroscopy were used to determine crystallite size, structure, morphology and optical band-gap energy. The magnetite nanoparticles with different crystallite size at range of 2.9–12.2nm were obtained by the modified controlled chemical co-precipitation method. The results showed that the Fe3O4 nanoparticles synthesized in solution containing tartaric acid were the smallest and had the highest value of optical band-gap energy (3.01eV). The use of dextrin allowed obtaining nanocomposite, in which magnetite nanoparticles were dispersed in polysaccharide matrix. It was confirmed that with the decrease in the crystallite size the value of the optical band-gap energy increases, which is related to quantum phenomena. Additionally, shift of characteristic peaks from FeO bond in Fourier transform infrared spectra were observed, what is also associated with change of the nanoparticles size.

Wet Chemical Co-precipitation Synthesis of Nickel Ferrite Nanoparticles and Their Characterization

In this study, wet chemical co-precipitation method was employed for the synthesis of pure and doped nickel ferrite nanoparticles at low temperature whereas the concentration of nickel varies from 2, 4, 6 and 8%. Optical absorption and transmission, Surface morphology, and structural properties of material are characterized by Fourier-transform infrared spectrometer, ultra-violet visible spectroscopy, scanning electron microscopy and powder X-ray diffraction respectively. It is observed that the transmission, size and band gap energy increases by increasing the amount of nickel. Red shift of the peaks is observed in the UV–visible spectra which is associated with the increase in size of the nickel ferrite. It can be used to fabricate devices intended to store data, for the classification of inorganic materials which plays a very important role in the different aspects of life due to their outstanding magnetic, electronic and optical properties.

Effect of impurity concentration on optical and magnetic properties in ZnS:Cu nanoparticles

To obtain enhanced room temperature ferromagnetism (RTFM) along with the increase in optical bandgap in the compound semiconductors has been an interesting topic. Here, we report RTFM along with increase in energy bandgap in chemically synthesized Zn1−xCuxS (0 ≤ x ≤ 0.04) DMS nanoparticles. Structural properties of the synthesized samples studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) show the formation of cubic phase Cu doped ZnS nanoparticles of ~3–5nm size. An intrinsic weak ferromagnetic behavior was observed in pure ZnS sample (at 300K) which got increased in Cu doped samples and was understood due to defect induced ferromagnetism. UV–vis measurement showed increase in the energy bandgap with the increase in Cu doping. The PL study suggested the presence of sulfur and zinc vacancies and surface defects which were understood contributing to the intrinsic FM behavior.

Performance of photovoltaic cells in different segments of spatial-spectral distributions

In a single-bandgap solar cell, efficiency is limited by the inability to efficiently convert the broad range of energy that photons possess in the solar spectrum. One of the effective ways of enhancing the efficiency of solar cells is to split the broad solar spectrum into smaller energy ranges and to utilize each range with a photovoltaic (PV) cell of the appropriately tuned bandgap. The conventional approach to implementing this idea is to use stacks of PV cells sequentially placed in the order of increasing bandgap energy, with the highest bandgap cell at the top. Lateral spectrum splitting can avoid many of the disadvantages of this conventional approach. We demonstrate that spectrum splitting with a prism and a lens can achieve enhanced efficiency with a combination of GaAs and c-Si solar cells.

Chemical spray deposition technique of antimony (Sb) doped polycrystalline MnIn2S4 thin films: Preparation and characterization

The Sb-doped Manganese Indium Sulphide (MnIn2S4) films were deposited on glass substrates using spray pyrolysis technique. The thin films were grown at various substrate temperatures ranging from 250 to 400°C with a constant spray time (5mins). The structural, morphological, optical and electrical properties of the thin films were investigated through different techniques such as X-ray diffraction (XRD), Field emission scanning electron microscopy (FE-SEM), Electron diffraction spectroscopy (EDS), and UV–vis spectroscopy. The XRD studies reveal that the Sb-doped MnIn2S4 films were polycrystalline in nature with a cubic spinal structure having (220) plane as the preferred orientation. The EDS spectrum predicts the presence of Mn, In, Sb and S in the film grown at a substrate temperature of 250°C. The FE-SEM photographs indicate the modification in the surface morphology of the films with an increase of substrate temperatures. From the optical studies, it is noted that, the band gap energy increases (1.85–2.75eV) with an increase of substrate temperature (250–400°C). These results reveal that the Sb-doped MnIn2S4 thin film prepared by spray pyrolysis technique is a promising candidate for photovoltaic applications.

Efficient photoelectrochemical water splitting and impedance analysis of WO3−x nanoflake electrodes

Solar-powered water splitting with photoelectrochemical (PEC) devices is considered to be a promising method to simultaneously harvest and store solar energy at a large scale. Nanostructured semiconductors offer potential advantages in PEC application due to their large surface area and size-dependent properties, such as increased absorption coefficient, increased band-gap energy and reduced carrier-scattering rate. In this contribution, self-doped tungsten trioxide (WO3−x) nanoflake arrays were synthesized via a new route which involves the dealloying of Fe–W amorphous alloy, thermal treatment in air and properly cathodic polarization. The effects of different cathodic polarization current leading to different x value in WO3−x on the morphology, phase, and photoelectrochemical performance of the resultant samples were investigated. It was found that WO3−x with the appropriate x value presents a dramatic photoelectrochemical current density of 8.7 mA cm−2 in the presence of methanol as a hole scavenger, five folds larger than that of pristine WO3 nanoflakes. UV–vis reflection spectra suggest that the light absorption spectrum range of WO3−x extends from UV to visible light region. Electrochemical impedance spectroscopy disclosed that the unique nanoflake architecture and the surface defects offer improved light harvesting as well as efficient charge transportation.

Structural and Optical Properties Correlation of Nickel Doped Magnesium–Titanium Alloys with Sorption Kinetics Reaction for Hydrogen Storage Application

In this work, synthesis of Ni doped Mg–Ti nanostructured alloys were made using mechanical alloying method. The structural and optical properties of Mg–Ti alloys were studied by X-Ray diffraction (XRD), UV–Vis spectroscopy and Density Functional theoritical (DFT) studies. The electrochemical performance of Mg–Ti alloys was studied by cyclic voltammetry and impedance studies. The XRD pattern of 20 h milled powders revealed the formation of Mg(Ti) solid solution, Mg2Ni and TiNi compounds. DFT studies confirmed the strong modification of the valence band structure of the Ni doped Mg–Ti alloys which could significantly hasten the hydrogenation and dehydrogenation properties. UV–Vis spectrum revealed increase in band gap energy due to blue shift and hyperchromic shift in both absorption and transmission peaks. Obviously, electrochemical studies revealed high exchange current density and Warburg impedance, as well as decrease in diffusion coefficient and charge transfer resistance. Ultimately, it showed the result of high catalytic activity and faster kinetic reaction rates for the good reversibility of hydrogen ions.

Study on degradation mechanism of perovskite solar cell and their recovering effects by introducing CH3NH3I layers

We demonstrate the degradation mechanism of CH3NH3PbI3 perovskite solar cells (PSCs) and their recovery effects by introduction of CH3NH3I layers. After degradation by exposure to air under a 1-sun condition for 18 h, the absorption of the CH3NH3PbI3 perovskite between 530 and 800 nm decreases, and thereby the energy band gap increases. X-ray diffraction (XRD) patterns indicate that moisture with sunlight corrodes the CH3NH3PbI3 perovskite into PbI2, which generates cracklike voids on the surface of illumination-degraded CH3NH3PbI3 perovskite thin films. As a result, the PSC photovoltaic performance is degraded and the power conversion efficiency (PCE) is reduced from 16.8 to 0.7%. However, the PCE is recovered to 7.6% by spin-coating a CH3NH3I layer into the illumination-degraded CH3NH3PbI3 perovskite thin films. The recovery of the absorption between 530 and 800 nm and the CH3NH3PbI3-perovskite-assigned peaks in the XRD patterns verifies that the illumination-induced PbI2 is recombined with spin-coated CH3NH3I and that the CH3NH3PbI3 perovskite structure is recrystallized.

Chemical functionalization of graphene oxide and its electrochemical potential towards the reduction of triiodide

Among a diverse set of properties, graphene is also noted for its electrochemical and catalytic capabilities. These can also be influenced by functionalization of graphene. This study reports the chemical functionalization of graphene oxide (GO) with an aromatic compound 4-hydroxy-4′-n-pentylbiphenyl, by an esterification reaction. Formation of new coupled product was investigated through scanning electron microscopy, X-rays diffractometer, Fourier-transform infrared, and UV–Vis spectrometry studies. UV–visible spectrometry also indicated an increase in band gap energy, likely due to the Burstein–Moss effect. Electrochemically, the esterified product was found to be better than GO in terms of triiodide reduction, which gives plausible worth to exploring this functionalization strategy further for the development of counter electrode materials for dye-sensitized solar cells.

Composition-tuned band gap energy and refractive index in GaSxSe1−x layered mixed crystals

Transmission and reflection measurements on GaSxSe1−x mixed crystals (0 ≤ x ≤ 1) were carried out in the 400–1000 nm spectral range. Band gap energies of the studied crystals were obtained using the derivative spectra of transmittance and reflectance. The compositional dependence of band gap energy revealed that as sulfur (selenium) composition is increased (decreased) in the mixed crystals, band gap energy increases quadratically from 1.99 eV (GaSe) to 2.55 eV (GaS). Spectral dependencies of refractive indices of the mixed crystals were plotted using the reflectance spectra. It was observed that refractive index decreases nearly in a linear behavior with increasing band gap energy for GaSxSe1−x mixed crystals. Moreover, the composition ratio of the mixed crystals was obtained from the energy dispersive spectroscopy measurements. The atomic compositions of the studied crystals are well-matched with composition x increasing from 0 to 1 by intervals of 0.25.

Preparation and characterization of sphere-like Cu2SnS3 nanoparticles and their dropcasted thin films

Ternary sphere-like Cu2SnS3(CTS) semiconductor and 2D hexagonal sheets were synthesized via a simple solvothermal method using PVP as the surface ligand at two temperatures of 180 and 220 °C. The structural, morphological, and chemical compositions as well as optical properties of as-synthesized CTS particles were characterized using X-ray diffraction (XRD), Raman spectroscopy, energy dispersive X-ray spectrometry (EDS), field emission scanning electron microscopy (FESEM), and UV–Vis spectroscopy. The size of sphere-like particles and the side length of hexagonal sheets were within the range of 120–140 nm and 500 nm–, respectively. FESEM, XRD, and EDS were analyzed to investigate the mechanism of the morphological evolution of CTS particles. CTS particles showed proliferation of Sn atomic ratio, which is strongly sensitive to reaction temperature and, highly affects the increase of band gap energy from 1.36 to 1.53 eV due to generation metal defects and formation SnS2. The optical analysis via the transmittance and reflectance reveals that the band-gap energy of dropcasted CTS thin films decreases after annealing due to grain growth and change of chemical compositions. Photo-responses of CTS nanocrystal thin films indicated a considerable increase in the conductivity of the films under light illumination. All these results showed the potential of these films for solar cell applications.

Effect of temperature on the characteristics of ZnO nanoparticles produced by laser ablation in water

Effect of the water temperature on the characteristics of zinc oxide nanoparticles (NPs) produced by laser ablation process is investigated experimentally. The fundamental wavelength of a Q-switched Nd:YAG laser was employed to irradiate a high-purity zinc plate in distilled water at different temperatures of 0, 20, 40 and 60∘C. The produced NPs were diagnosed by UV–vis–NIR spectroscopy, X-ray diffraction method, transmission electron microscopy and scanning electron microscopy. Results show that with increase in the water temperature from 20 to 60∘C, size of NPs decreases while their bandgap energy increases. Maximum ablation rate occurs at the highest temperature. Crystalinity also increases with increase in the water temperature. The abnormal behaviour of water at 0–4∘C affects the NPs characteristics.

Electronic and optical properties of cubic SrHfO3 at different pressures: A first principles study

The electronic and optical properties of cubic SrHfO3 under the variation of pressures were investigated by first-principles calculation within the framework of generalized gradient approximation (GGA). The calculated equilibrium lattice constant of cubic SrHfO3 is in good agreement with available experimental and theoretical results. The result shows that SrHfO3 is an insulator with an indirect band gap up to 20.00 GPa, along (M−Γ). While the application of pressure above 20.00 GPa the band gap changes to direct band gap, along (Γ−Γ). The band gap increases from 3.80 eV to 4.11 eV with the increase in pressure from 0.00 GPa to 35.00 GPa. In order to understand the optical properties of SrHfO3 perovskite, the dielectric function, optical conductivity and electron energy loss are calculated for photon energy up to 14.00 eV. We have also observed the decrease in static dielectric constant with the increase in energy band gap under pressure.

Impact of the annealing temperature on Pt/g-C3N4 structure, activity and selectivity between photodegradation and water splitting

This work presents a systematic study of the effect of fabrication temperature (450 to 650°C) on the structure and electronic properties of g-C3N4 prepared from melamine. The work is conducted by X-ray diffraction, elemental analysis, BET nitrogen adsorption, UV–vis absorption, and electron paramagnetic resonance (EPR). The photocatalytic activity is tested for hydrogen production in the presence of oxalic acid (OA) as well as triethanolamine (TEOA). A considerable change in the morphology is observed with increasing the synthesis temperature resulting in an increase of the surface area, likely due to thermal etching. The decrease of charge carriers’ concentration, per unit surface area, with increasing annealing temperature may be due to the decrease of the conjugation of the polymer. Probing the activity of in situ reduced Pt/g-C3N4 for hydrogen evolution reinforced this conclusion, the rate of hydrogen evolution per unit area for OA as well as TEOA decreased with increasing annealing temperature. An interesting finding is the correlation between CO2:H2 ratio and the increase in the band gap of g-C3N4 prepared at different temperatures when using oxalic acid as an electron donor. This suggests that water oxidation becomes easier with increasing band gap energy, probably due to a lowering of the valence band edge.

Phenol photocatalytic degradation over mesoporous TUD-1-supported chromium oxide-doped titania photocatalyst

Mesoporous Technische Universiteit Delft (TUD-1)-supported chromium oxide-doped titania (Cr-TiO2) was developed as a promising photocatalyst for phenol photodegradation under visible light irradiation. Low-angle X-ray diffraction and Fourier transform infrared spectroscopy results confirmed the amorphous and mesoporous silicate framework of TUD-1 in TUD-1-supported Cr-TiO2. The mesostructure of TUD-1 was further verified via N2 adsorption–desorption analysis, which showed a type-IV isotherm with a narrow average pore size distribution of 3.9 nm and high surface area of > 490 m2/g. Transmission electron microscopy analysis results indicated that TUD-1-supported Cr-TiO2 contained nanoparticles and porous channels. An increase in band gap energy was observed after loading Cr-TiO2 into TUD-1. Compared with that of unsupported Cr-TiO2, TUD-1-supported Cr-TiO2 showed higher photocatalytic activity for phenol degradation under visible light irradiation. The TUD-1 supported Cr-TiO2 photocatalyst with a Si/Ti molar ratio of 30 exhibited the highest photodegradation of phenol (82%) of the prepared samples. The photodegradation of phenol by the supported catalyst followed the Langmuir adsorption isotherm with first-order kinetics.

Visible-light photoactivity of plasmonic silver supported on mesoporous TiO2 nanoparticles (Ag-MTN) for enhanced degradation of 2-chlorophenol: Limitation of Ag-Ti interaction

Various weight loadings of Ag (1–10 wt.%) were introduced to mesoporous titania nanoparticles (MTN) via a direct in-situ electrochemical method. The catalysts were characterized by XRD, surface area analysis, FTIR, ESR, FESEM-EDX and TEM. Characterization results indicated that the introduction of Ag onto MTN decreased the particles size and band gap of the MTN while increasing the number of oxygen vacancies (OV) and Ti3+ site defects (TSD). The activity performance of Ag-MTN on photodegradation of 2-chlorophenol (2-CP) under visible light irradiation was in the following order: 5wt% Ag-MTN>1wt% Ag-MTN>MTN>10wt% Ag-MTN, with degradation percentages of 97, 88, 80 and 63%, respectively. The synergistic effect between Ag0 and MTN seemed to play an important role in the system. The Ag0 acted as both an electron trap and a plasmonic sensitizer which suppressed the electron-hole recombination, while OV and TSD in the MTN accelerated the production of hydroxyl radicals for enhanced degradation of 2-CP. However, the formation of Ti-O-Ag in 10wt% Ag-MTN was found to decrease the photoactivity due to the decrease in the formation of Ag0, TSD and OV as well as the increase in band gap energy. The photodegradation of 5wt% Ag-MTN followed a pseudo-first-order Langmuir- Hinshelwood model and the catalyst was still stable after five cycles.

Effects of fluorine doping on structural, optical and electrical properties of spray deposited CdO thin films

Fluorine doped cadmium oxide (CdO:F) thin films were deposited onto glass substrates by spray deposition technique. Fluorine concentration dependent structural, optical and electrical properties of the films are reported. X-ray diffraction study confirms the growth of polycrystalline cubic CdO films. Optical absorption analysis of the films shows increase of optical band gap energy from 2.45 to 2.65 eV for the increase of fluorine concentration. The transparency of the films is found to be ≥ 80% and also it is increased with the fluorine concentration. Hall-Effect measurement of the films shows resistivity change between 2.5 × 10−4 and 4.5 × 10−4 Ω cm and carrier concentration in the range of 4 × 1015 cm−3 to 7 × cm−3 depending on doping concentration. Photoresponse study of the fabricated CdO:F/p-Si heterostructure diode is also studied and reported.

Band Gap Engineering of Wurtzite-Type Narrow Band Gap Oxide Semiconductor β-CuGaO2

β-CuGaO2 is an oxide semiconductor possessing wurtzite-derived β-NaFeO2 structure. Its band gap is 1.47 eV in near-infrared region, and the first principles calculation indicates that it is a direct band gap semiconductor. Therefore, this material is expected to be applicable to optoelectronic devices working in near-infrared region. When the band gap of β-CuGaO2 is widened into visible region, the material is expected to be applicable to visible LEDs and lasers, photocatalyst and so on. In the present study, we demonstrated band gap engineering of β-CuGaO2 by alloying with β-CuAlO2 and β-LiGaO2 possessing wurtzite-derived β-NaFeO2 structure in order to widen the band gap. Cu(Ga1-xAlx)O2 alloys were prepared by ion-exchange of Na+ ions in β-Na(Ga1-xAlx)O2 with Cu+ ions in CuCl at 250 °C for 48 h under vacuum. (Cu1-xLix)GaO2 alloys were prepared by ion-exchange of Cu+ ions in β-CuGaO2 with Li+ ions in LiCl at 300 °C for 48 h under vacuum. Wurtzite-type β-phases were obtained in 0≤x≤0.7 for Cu(Ga1-xAlx)O2 system and in 0≤x≤1 for (Cu1-xLix)GaO2 system. In β-Cu(Ga1-xAlx)O2, the optical band gap increased linearly with the increasing alloying level; no band gap bowing appeared in the present system. The band gap of β-CuGaO2 was widened up to 2.1 eV at β-Cu(Ga0.3Al0.7)O2; this energy corresponds to red light. In β-(Cu1-xLix)GaO2, the energy band gap increased almost linearly with the increasing alloying level up to x~0.9; the largest band gap in this composition range was 3.0 eV corresponding to violet light at β-(Cu0.11Li0.89)GaO2. When the alloying level increased further, the band gap steeply increased from 3.0 eV at x=0.89 to 5.6 eV at x=1. The valence band X-ray photoelectron spectra of β-(Cu1-xLix)GaO2 indicated that the steep increase in energy band gap from x~0.9 to 1 is attributed to that the Cu 3d contribution around the top of the valence band electronic states vanishes for the alloys with x>0.9. These results indicate that the energy band gap of β-CuGaO2 is highly controllable in the wavelength region from near-infrared to entire visible lights. Thus, it is expected that β-CuGaO2 opens new applications of oxide semiconductors in devices working in visible region.

Structural, optical and electrical investigations on Nb doped TiO2 radio-frequency sputtered thin films from a powder target

Pure and Nb doped TiO2 (TNO) thin films were deposited onto glass substrates by RF magnetron sputtering technique using a Nb and TiO2 mixture powder target at room temperature to explore the possibility of producing sputtered TNO films by a low cost process. The effect of Nb doping on the structure, morphology, optical and electrical properties of the prepared films was studied by systematically varying the Nb content from 2 to 6 wt%. GXRD results show that the deposited films mainly possess rutile phase with the (110) orientation. Raman spectra confirm that the deposited films are predominantly rutile phase. Surface roughness increases with the increase of Nb doping concentration , which may be attributed to the structural changes in the film due to the incorporation of Nb into the TiO2 lattice. Optical transmittance in the visible range reaches 85 % for the undoped films then it decreases as the doping content increases. Doping by niobium resulted in a slight increase in the optical band gap energy of the films due to the Burstein–Moss effect. The resistivity measurement of TNO films reveals that the Nb doping improves the electrical conductivity of the deposited films compared to the undoped one. The best value was observed for films deposited at 4 wt% Nb.