P2.4.11 Growth and H2S Gas Sensing Properties of CuO Functionalized ZnO Nanotetrapod
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We report gas-sensing properties of thick films prepared using ZnO Nanotetrapods and CuOfunctionalized ZnO Nanotetrapods. Gas sensors based on ZnO nanostructure have been widely reported, but they have some limitations, such as low sensitivity, specificity and high working temperature. ZnO is a n-type semiconductor and CuO, a well-known sensitizer for H2S is a p-type semiconductor. The use of heterojunctions between p-type and n-type material has been previously reported in literature to increase the sensitivity. As expected sensitivity and selectivity of the CuO coated ZnO Nanotetrapods films towards H2S increased as compared to pure ZnO Nanotetrapods films. It was also observed ZnO Nanotetrapods film senses H2S at higher temperatures, whereas CuO-functionalized ZnO Nanotetrapods show a high sensitivity at very low temperatures.Charge carrier
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Based on first-principles calculations, the structure, electronic and optical properties of g-C3N4/HfSSe heterojunctions have been systematically explored. We prove the stability of two heterojunctions by comparing the binding energies from six different stacking heterojunctions, which name are g-C3N4/SHfSe heterojunction and g-C3N4/SeHfS heterojunction, respectively. It is shown that both heterojunctions behave direct band gaps with type II band alignment. The charge is rearranged at the interface after the heterojunctions are formed, which results in the formation of the built-in electric field. In the ultraviolet, visible and near-infrared regions, excellent light absorption is found in g-C3N4/HfSSe heterojunctions.
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This chapter contains sections titled: Amperemetric selectivity Time-graded selectivity Logic selectivity Directional selectivity Selectivity by differential protection Selectivity between fuses and circuit-breakers
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This chapter demonstrates an investigation into the electronic characteristics of CuPc/F16CuPc, BP2T/F16CuPc, ZnPc/C60, VOPc/Ph3, and SnCl2Pc/F16CuPc organic heterojunctions. Organic heterojunctions are categorized according to their interface electronic structure, including accumulation heterojunctions, depletion heterojunctions, and accumulation/depletion heterojunctions. The formation of an organic heterojunction is explained by the mechanism of thermal emission of electrons and an energy band model. A unique law covering organic heterojunctions and inorganic heterojunctions is revealed, which extends the theory of semiconductor heterojunctions.
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We calculate spatiotemporal distributions of dopant in an implanted-heterojunction rectifier. We analyzed the influence of inhomogeneity of heterostructure on dopant distribution. The influence of radiation processing of materials of the heterostructure, which has been done during ion implantation, on properties of the heterostructure has been also analyzed. It has been shown that radiation processing of materials of heterostructure leads to a decrease in mechanical stress in heterostructure. Our calculations have been done by using analytical approach, which gives us the possibility to obtain all results without joining solutions on all interfaces of heterostructure.
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Semiconductor heterojunctions offer unique electrical and optical properties not otherwise found in nature. Growth methods are now available to create new novel heterojunction structures with state-of-the-art physical properties for next generation electronics. This chapter covers the unique interface features of semiconductor heterojunctions in terms of their geometrical, chemical, and electronic structure. For a particular application, one chooses semiconductors or semiconductor alloys based on both their energy gaps and their good lattice match. The lattice mismatch between heterojunction constituents leads to strain and ultimately the formation of lattice dislocations. Semiconductor-semiconductor heterojunctions can exhibit a variety of chemical structures including interdiffusion, chemical reactions, and interlayer effects. The chapter reviews both experimental and theoretical work to understand the nature of heterojunction band offsets as well as atomic-scale methods to control them. One approach to describe band offsets involves the alignment of charge neutrality levels in the two semiconductors.
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Photocarrier recombination remains a big barrier for the improvement of solar energy conversion efficiency. For 2D materials, construction of heterostructures represents an efficient strategy to promote photoexcited carrier separation via an internal electric field at the heterointerface. However, due to the difficulty in seeking two components with suitable crystal lattice mismatch, most of the current 2D heterostructures are vertical heterostructures and the exploration of 2D lateral heterostructures is scarce and limited. Here, lateral epitaxial heterostructures of BiOCl @ Bi2 O3 at the atomic level are fabricated via sonicating-assisted etching of Cl in BiOCl. This unique lateral heterostructure expedites photoexcited charge separation and transportation through the internal electric field induced by chemical bonding at the lateral interface. As a result, the lateral BiOCl @ Bi2 O3 heterostructure demonstrates superior CO2 photoreduction properties with a CO yield rate of about 30 µmol g-1 h-1 under visible light illumination. The strategy to fabricate lateral epitaxial heterostructures in this work is expected to provide inspiration for preparing other 2D lateral heterostructures used in optoelectronic devices, energy conversion, and storage fields.
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Abstract : A technique based on the use of x-ray photoelectron spectroscopy was developed to measure heterojunction band discontinuities with an uncertainty of + or - 0.04 eV and changes in band discontinuities for a specific heterojunction interface with an uncertainty of + or - 0.01 eV. This technique was used to investigate Ge-GaAs, GaAs-A1As, ZnSe-GaAs, and ZnSe-Ge heterojunctions. It was discovered that microscopic dipoles present at abrupt heterojunction interfaces can substantially affect observed band discontinuities. Variations in heterojunction band discontinuities as functions of crystallographic orientation, growth sequence, and growth conditions were observed. It was established that heterojunction band discontinuities depend on microscopic properties of the interface and cannot be predicted from individual semiconductor properties alone. Based on electrostatic considerations, it was shown that polar heterojunction interfaces cannot be atomically abrupt but must require at least two interfacial transition planes to be consistent with experimental observations.
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Two-dimensional transition-metal dichalcogenides are not only promising optoelectronic materials but also can improve the optoelectronic performances of perovskites by forming heterostructures. Here, the structural, electronic, and optical properties of four kinds of CsPbI3/MS2 (M = Mo, W) heterostructures have been comprehensively investigated by density functional theory. No matter what the heterostructure structures, the electronic structure and excellent transport properties of both CsPbI3 surface and monolayer MS2 can be preserved in the CsPbI3/MS2 heterostructures. Moreover, CsPbI3/MS2 heterostructures show type-II band alignment with indirect band gaps and charge transfers, which separate electrons and holes spontaneously. The light absorptions of CsPbI3 surfaces in the infrared, visible, and ultraviolet regions are enhanced upon forming heterostructures. Note that the performances of heterostructures are strongly dependent on the heterostructure structure. Pb–I-terminated CsPbI3/MS2 heterostructures exhibit lower tunneling barriers and larger band offsets, which may lead to higher circuit voltages and lower dark currents, but they show lower stabilities compared with Cs–I-terminated CsPbI3/MS2 heterostructures. Moreover, CsPbI3/MoS2 heterostructures demonstrate higher electric and optical performances than those of CsPbI3/WS2 heterostructures. Our findings provide a deep understanding of CsPbI3/MS2 heterostructures and suggest an effective way to improve the performance of perovskite optoelectronic devices, such as radiation detection.
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