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Efficient Photocatalytic Hydrogen Production Achieved by WO3 Coupled with NiP2 Over ZIF-8
摘要： The photo-catalyst WO3/NiP2@ZIF-8 was synthesized by modifying the WO3 with NiP2@MOFs structure. High H2 production was achieved (341.2 μmol and 11.3 times than pure WO3 after 5 h) and the catalytic property of WO3 was improved. The XRD, FESEM and TEM were used to characterize and analyze the crystalline phase structure, namely, WO3 has nanowire structure and good crystalline phase, meanwhlie, ZIF-8 exhibits regular dodecahedron morphology. The catalysts were characterized and analyzed by electrochemical, steady-state and transient state, those results show that the composite has more efficient charge separation effect and better electrical performance than single catalyst, which provides a reliable basis for relative higher H2 production activity. The band gap structure and elemental valence of the composite catalysts were calculated and analyzed by UV–Vis DR and XPS, respectively. The possible reaction equation and H2 production mechanism of WO3/NiP2@ZIF-8 in HER were proposed.
关键词： NiP2@ZIF-8,Photocatalytic H2 production,WO3,Band gap structure
更新于2025-09-11 14:15:04
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Reference Module in Materials Science and Materials Engineering || Excitonic Model versus Band Gap Model in Organic Materials
摘要： The binding energy Eb of an optical excitation is a key parameter for the understanding of the opto-electronic properties of organic solids in general and of conjugated polymers in particular. It controls the dissociation of an electronic excitation of either singlet or triplet character into a pair of free charges as well as the reverse process, i.e., the recombination of an electron–hole (eh) pair yielding an excitation that can decay radiatively or nonradiatively. If Eb is large, photogeneration of charge carriers is an endothermic, inefficient process. It is obvious that in an organic solar cell (OSC) one would like Eb to be as small as possible, while in a light emitting diode (LED) it is the opposite because charge recombination requires a driving force. In this article an outline of the problem of defining the exciton binding in a molecular solid will be presented followed by experimental and theoretical advances and a critical review of relevant conceptual frameworks with particular emphasis on conjugated polymers.
关键词： Organic Materials,Conjugated Polymers,Band Gap Model,Opto-electronic Properties,Exciton Binding Energy
更新于2025-09-11 14:15:04
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Effect of Annealing on Optical Properties of Zinc Oxide Thin Films Prepared by Homemade Spin Coater
摘要： Zinc oxide (ZnO) thin films were deposited on the ordinary glass substrates by spin coating method. The precursor solution was prepared by mixing zinc acetate dihydrate in appropriate proportions with ethanol and diethanolamine (DEA). The obtained thin films were dried at 200oC for 15 minutes in hot air oven. Crystalline ZnO thin films were achieved following annealing process at temperatures 300o, 400o and 500oC for 2 hours. Thin films as- prepared were studied by X-ray diffraction and UV-visible spectroscopy. The films were transparent from near ultraviolet to infrared region. Optical band gap energy of ZnO was obtained 3.22 eV at 300oC. On annealing at 400o and 500oC, band gap energy was shifted at 3.14 eV and 3.05 eV respectively.
关键词： annealing,absorption spectra,sol-gel method,zinc oxide,band gap energy
更新于2025-09-11 14:15:04
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Interface States in Bilayer Graphene Encapsulated by Hexagonal Boron Nitride
摘要： The threshold voltages at the onset of conduction for electron and hole branches can provide information on band gap values or the interface states in a gap. We measured conductivity of bilayer graphene encapsulated by hexagonal boron nitride as a function of back and top gates, where another bilayer graphene is used as a top gate. From the measured conductivity the transport gap values were extracted assuming zero interface trap states, and they are close to the theoretically expected gap values. From a little discrepancy an average density of interface states per energy within a band gap (Dit) is also estimated. The data clearly show that Dit decreases as a bilayer graphene band gap increases rather than being constant. Despite the decreasing trend of Dit, interestingly the total interface states within a gap increases linearly as a band gap increases. This is because of ~ 2 × 1010 cm-2 interface states localized at band edges even without a band gap, and other gap states are equally spread over the gap.
关键词： band gap,hexagonal boron nitride,bilayer graphene,transport gap,interface states
更新于2025-09-10 09:29:36
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An Experimental Demonstration of Short Circuit Protection of SiC Devices
摘要： An experimental demonstration of an effective short circuit protection scheme for SiC MOSFETs is presented in this paper. Measurements of the static characteristics of the SiC device before and after the short circuit events were obtained to evince that the device remained in good health. An ultra-fast short circuit protection scheme is implemented given the observed lower short-circuit withstand of present SiC devices. It is shown that the integrity of the SiC device was protected after one-hundred short circuit events.
关键词： Short-Circuit,MOSFET,Silicon Carbide,Protection,SiC,Wide band-gap
更新于2025-09-10 09:29:36
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Width dependent structural and electrical properties of zigzag ZnTe nanoribbons
摘要： We carry out density functional theory based investigation to understand the structural and electrical properties such as atomic structure, edge energy, band gap, and work function of zigzag ZnTe nanoribbons. It is found that the zigzag nanoribbons may be stabilized by passivating the edge atoms with Hydrogen, Oxygen or Fluorine atoms. Our study reflects that zigzag ZnTe nanoribbons with smaller width behave like semiconductor. However, they exhibit a transition from semiconducting phase to a metallic phase as width increases. A wide variation of band gap is obtained with respect to the choice of edge passivating elements. Work functions of all the nanoribbons are also estimated in order to assess the utility of these nanoribbons in various field emission devices.
关键词： Density functional theory,Work function,Band gap,Nanoribbon
更新于2025-09-10 09:29:36
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Conductive and photoactive nature of conjugated polymer based on thiophene functionalized thiazole or benzothiadiazole
摘要： New poly (thiophene vinyl thiazole) (PTVT) and poly (thiophene vinyl benzothiadiazole) (PTVBT) was synthesized by Wittig condensation route. The absorption maximum of PTVT and PTVBT appeared at 376 and 410 nm in a solution state, and it was red-shifted to 417 and 510 nm in a thin film state. The optical band gaps were 1.7 and 1.5 eV calculated from thin film absorption edges of the polymer. The photoluminescence spectra of PTVT and PTVBT have an emission peak at 457 nm with bluish green and 487 nm with greenish-yellow fluorescence in THF solution. Both polymers showed a short fluorescence decay time (τ1) of 2.31 and 0.73 ns respectively. Furthermore, the aggregation-caused quenching (ACQ) phenomenon observed in both polymers in decreased fluorescence intensity with different water fractions. The lower electrochemical band gaps were achieved for both polymers (1.4, and 1.3 eV) from cyclic voltammetry. Both polymers have a granular shaped morphology with good surface roughness was observed using AFM. High thermal stability was observed with 8% weight loss at 400 °C for PTVT and 6% weight loss at 460°C for PTVBT. The highest electrical conductivity was observed from electrochemical impedance measurement which was 7.68·10–6 Ω–1·cm–1 for PTVBT.
关键词： poly(p-phenylenevinylene),thermal properties,band gap,photoluminescence,impedance
更新于2025-09-10 09:29:36
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Hot carrier transfer processes in nonstoichiometric titanium hydride
摘要： The absorber of the hot carrier solar cell (HCSC) needs to have a considerably reduced hot carrier thermalisation rate, in order to maintain the photo-generated hot carriers for enough time such that they can be extracted. The slow carrier cooling effect is predicted in materials in which the phononic band gap is sufficiently large to block the Klemens decay. Binary compounds with a large mass ratio between the constituent elements are likely to have large phononic band gap. Titanium hydride is one of these binary compounds that has the potential to become an absorber of the HCSC. Whilst a large phononic gap has been observed in stoichiometric TiH2, it has not been experimentally confirmed for hydrogen deficient TiHx (where x < 2). In this article, we report the phonon density of states of TiH1.65 measured using inelastic neutron scattering and presented to clearly show the phononic band gap. We also present the carrier thermalisation process of a TiHx (1< x <2) thin film by transient absorption, and estimate the carrier cooling time in this material.
关键词： titanium hydride,hot carrier solar cell,inelastic neutron scattering,transient absorption,phononic band gap
更新于2025-09-10 09:29:36
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Preparation and optical characterization of PbWO4 nanocrystals from mechanical alloying process
摘要： This study presents the fabrication of PbWO4 nanoparticles using PbO and WO3 of designed molar ratio as the starting materials by mechanical alloying in atmospheric conditions. The impact energy of the SPEX ball milling machine provided the energy difference to form the PbWO4 through the mechanochemical process. The milled nanocrystals showcase single-phase product with particle sizes in the range of 3–10 nm. The UV–Vis-NIR spectra provide the direct band gap of 3.82 eV.
关键词： mechanical alloying,band gap,optical characterization,PbWO4 nanocrystals
更新于2025-09-10 09:29:36
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Flakes Size-Dependent Optical and Electrochemical Properties of MoS2
摘要： Background: Molybdenum disulfide (MoS2) is a transition metal dichalcogenides and has some interesting and promising properties. MoS2 has direct and indirect band gaps depending on its crystalline structure. In addition, its sheets morphology makes it a good candidate for supercapacitor applications. Objective: The aim of this work is to study the effect of MoS2 flakes size on its optical and electrochemical properties. Method: MoS2 with different flakes sizes were prepared by exfoliation method. The exfoliation was performed by sonication of MoS2 powder in N,N-Dimethylformamide followed by different centrifugation speeds. UV-Vis spectra illustrated the optical energy gap was inversely proportional to the MoS2 flakes size. Results: Absorption coefficient values indicated that the exfoliation reduced the number of layers. Symmetric supercapacitor was made from two MoS2 electrodes and tested in 6 M KOH electrolyte. The specific capacitance was found to be dramatically increased with decreasing flakes size (9.5 and 4.5 mF/cm2 for 0.26 and 0.98 μm flakes size, respectively). Conclusion: These findings recommend that MoS2 can be the excellent electrode material for supercapacitor.
关键词： nanoflakes,cyclic voltammetry,supercapacitors,Transition Metal Dichalcogenides (TMDs),optical band gap,Molybdenum disulfide
更新于2025-09-10 09:29:36