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Energy Level Engineering in Transition-Metal Doped Spinel-Structured Nanosheets for Efficient Overall Water Splitting
摘要： Unraveling the role of transition-metal doping on affecting the native spinel-structured nanosheets’ water splitting remains a grand challenge. In this work, a series of spinel-structured nanosheets wrapped hollow nitrogen-doped carbon polyhedrons was constructed, and doped transition-metal domains were deliberately introduced on the surface. Theoretical investigations show that their energy level can be finely tuned via direct transition-metal doping engineering. As a prototype, Fe-doped NiCo2O4 nanosheets wrapped hollow nitrogen-doped carbon polyhedron (Fe-NiCo2O4@HNCP) exhibits outstanding bifunctional electrocatalytic performances with low overpotentials (η = 270 mV for OER, η = 84 mV for HER), low Tafel slopes (b = 42 mV dec-1 for OER, b = 47 mV dec-1 for HER), and high durability. The enhanced performance is attributed to the synergistic effects of energy level matching for electron transfer, and partial charge delocalization-induced rich active sites for reactant adsorption via thermodynamic and kinetic acceleration. This work may open a new pathway to design highly active and stable transtion-metal doped electrocatalysts by manipulated energy levels for efficient overall water splitting.
关键词： energy level engineering,water splitting,electrocatalysts,spinel-structured nanosheets,transition-metal doping
更新于2025-09-04 15:30:14
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To the Problem of Optimization of Parameters of a Double Heterostructure Based on Direct-Gap Semiconductors for Avalanche Photodiodes
摘要： A double heterostructure based on direct-gap semiconductors with a photoabsorption middle layer at the avalanche breakdown voltage is considered. Such structures are used in the development of avalanche photodiodes with separate absorption and multiplication regions (APD with SAMR). It is shown that impact generation of electron–hole pairs should be considered in calculating the maximum possible characteristics of APDs with SAMR even in the absorption layer; therewith, this can be performed analytically.
关键词： avalanche photodiode,avalanche breakdown,multiplication,tunneling current,double heterostructure,doping,absorption
更新于2025-09-04 15:30:14
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[Springer Theses] Electrical Properties of Indium Arsenide Nanowires and Their Field-Effect Transistors || Influence of Different Growth Methods on the Electrical Properties of InAs Nanowires
摘要： In this chapter, we have studied the similarity and difference between the electrical properties of InAs nanowires grown by two commonly used material growth systems, MBE and MOCVD. Bases on the statistical data of more than 70 InAs nanowires back-gated FETs whose diameter range from 16 nm to more than 100 nm, we ?nd that when the diameter of InAs nanowires is relatively small, most of the MOCVD-grown InAs nanowires have similar electron mobility, threshold voltage, ON-state current, and OFF-state current with MBE-grown InAs nanowires. However, the dispersion of these electrical properties within the MOCVD-grown InAs nanowires is much larger than that within the MBE-grown nanowires. On the other hand, when the diameter of InAs nanowires is relatively large, the ON-state properties of MBE- and MOCVD-grown nanowires does not show obvious difference, but their OFF-state properties have apparently different features. The MOCVD-grown nanowires have smaller OFF-state resistance than the MBE-grown nanowires, and some of the large-diameter nanowires even show metallic behavior. By simulating the distribution of electrons under ON-state and OFF-state in the nanowires with various doping levels through the ?nite element model, we attribute the background carbon doping induced by the organic sources used in the growing procedures of MOCVD to be the main cause for the above differences. Our work has deepened the understanding of the relation between nanowire growth and device performance, and may be instructive for controlling the growth of InAs nanowires.
关键词： OFF-state current,Growth methods,Simulation of the distribution of electrons,Background carbon doping,ON-state current
更新于2025-09-04 15:30:14
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High-performance GaAs nanowire cathode for photon-enhanced thermionic emission solar converters
摘要： GaAs nanowire cathodes with exponential doping and graded Al composition structures are proposed for photon-enhanced thermionic emission (PETE) devices. The conversion ef?ciency models with these two nanowire cathodes are deduced on the basis of one-dimensional continuity equations. The conversion ef?ciency as a function of wire length, wire width, Al composition distribution, cathode temperature, emissive surface and back interface recombination velocity are also simulated, respectively. Results show that exponential doping and graded Al composition cathode structures can obviously improve the conversion ef?ciency of devices through introducing a built-in electric ?eld along the growth direction of nanowire. Besides, the optimum wire length and wire width range are 300–340 nm and 5.9–6.4 lm, respectively. Moreover, wider Al composition range is bene?cial to achieve higher conversion ef?ciency. These simulations provide an interesting attempt to explore the working mechanism of GaAs nano-based PETE devices and are expected to be veri?ed by the experimental results in the future.
关键词： exponential doping,graded Al composition,photon-enhanced thermionic emission,GaAs nanowire,conversion efficiency
更新于2025-09-04 15:30:14
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Junction-less optical phase shifter loaded silicon Mach Zehnder modulator
摘要： In this paper, we design and numerically analyze the performance of electrostatic doping (ED) assisted junction-less optical phase shifter loaded silicon Mach-Zehnder (MZM), which is realizable on the 220 nm SOI platform. The proposed phase shifter contains a vertical metal–insulator–semiconductor (MIS) junction and a lateral metal-semiconductor (MS) junction. Change in the refractive index profile inside the rib waveguide, which supports the phase shifter, is achieved by altering the concentration of free carriers via the plasma dispersion effect. Numerical simulation using commercially available TCAD tool and mode solver are used to estimate the performance of the proposed modulator. Two different sets of materials are used as electrodes to realize the MIS-MS charge plasma diode. In one design gold (Au) and silver (Ag) is used as electrode material while the other design utilizes palladium (Pd) and aluminum (Al) as electrode material. The performance of the proposed modulator(s) is extensively studied both in steady state and transient state. A complete analysis of chirp and nonlinear distortion for the proposed modulator are also presented in the paper. Results predict that a maximum of 15.4 dB dynamic extinction ratio (ER) is achievable with a minimum of 3.2 dB insertion loss (IL). The proposed modulator is expected to provide a maximum of 30.3 Gbps operating speed with 22.2 GHz of 3-dB electro-optical bandwidth. Simulation result predicts that the worst case dynamic energy per bit for the proposed ED assisted MZM is approximately 54.4 fJ/bit.
关键词： work-function,intensity modulator,IMD3,electrostatic doping,plasma dispersion effect,Mach-Zehnder modulator
更新于2025-09-04 15:30:14
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Nitrogen-Doping Chemical Behavior of Graphene Materials with Assistance of Defluorination
摘要： Heteroatom-doping reactions are essential to achieve advanced graphene-based materials for energy and biological areas. Unfortunately, considerably less is known regarding the detailed reaction pathways up to now. Here, we focus on investigating the nitrogen (N) doping process of fluorinated graphene (FG) under the assistance of defluorination based on modified in situ fourier transform infrared spectroscopy. It was demonstrated FG possesses a higher and more effective reactivity with ammonia in comparison with other graphene derivatives, which enable N-doping to proceed efficiently with assistance of defluorination even at a lower temperature (16.8 at % of N at 300 °C, 19.9 at % of N at 400 °C). Combining with Density functional theory, it was proved that, at the initial reaction step of N-doping, ammonia molecule attacked and substituted the C-F of FG by the new C-NH2. Sequentially, amino group was cyclized to the three-membered ring of ethylenimine. More importantly, the dissociation and migration of C-F bonds facilitates the dissociating of C-C bonds and the recombining of C-N bonds, thus significantly promoting the N atom in ethylenimine ring to transform to the pyridinic-N or graphitic-N in graphene skeleton.
关键词： Fluorinated graphene,Reaction pathway,Defluorination,Nitrogen doping,Two-dimensional chemistry
更新于2025-09-04 15:30:14
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Phase diagram of Bi2Sr2CaCu2O8+δ revisited
摘要： In cuprate superconductors, the doping of carriers into the parent Mott insulator induces superconductivity and various other phases whose characteristic temperatures are typically plotted versus the doping level p. In most materials, p cannot be determined from the chemical composition, but it is derived from the superconducting transition temperature, Tc, using the assumption that the Tc dependence on doping is universal. Here, we present angle-resolved photoemission studies of Bi2Sr2CaCu2O8+δ, cleaved and annealed in vacuum or in ozone to reduce or increase the doping from the initial value corresponding to Tc = 91 K. We show that p can be determined from the underlying Fermi surfaces and that in-situ annealing allows mapping of a wide doping regime, covering the superconducting dome and the non-superconducting phase on the overdoped side. Our results show a surprisingly smooth dependence of the inferred Fermi surface with doping. In the highly overdoped regime, the superconducting gap approaches the value of 2Δ0 = (4 ± 1)kBTc.
关键词： cuprate superconductors,Fermi surfaces,superconducting gap,doping,angle-resolved photoemission spectroscopy
更新于2025-09-04 15:30:14
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First Principle Calculations of Optical Properties of CdS:Al system (A DFT+U study)
摘要： In current research, we perform a computational study to calculate optical properties of Al doped CdS system for 1 × 1 × 2, 2 × 2 × 1, 2 × 2 × 2 supercell configurations and for DFT+U (1 × 2 × 2). Cd atoms are substituted with Al atoms and the result for optical properties shows significant changes in the case of 2 × 2 × 1 supercell configuration. This study has been executed with PBE-GGA and GGA+U approaches, used in Wien2K code employed within the framework of DFT. In comparison to 1 × 1 × 2 supercell configuration, optical absorption for 2 × 2 × 1 supercell configuration and DFT+U shows blueshift while for 2 × 2 × 2 redshift is observed. Study explore that optical properties are enhanced and absorption increases in visible region. Hence, Al doping into host CdS lattice suggest that opto-electrical properties are enhanced which advocate candidacy of this material for nanotechnology and optoelectronic devices.
关键词： DFT calculations,Density of states,Al-doping,Cadmium sulfide,Optical properties
更新于2025-09-04 15:30:14
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[IEEE 48th European Solid-State Device Research Conference (ESSDERC 2018) - Dresden (2018.9.3-2018.9.6)] 2018 48th European Solid-State Device Research Conference (ESSDERC) - Effect of Electron-phonon Scattering on the Thermal Conductivity of Si Nanowires
摘要： Even the effect of electron-phonon scattering on the electronic properties of Si nanowires has been widely studied, its impact on phonon transport has received much less attention. Recent experiments gave the first evidence of a doping-induced reduction of the thermal conductivity in highly B-doped (~5?×?1019?cm-3) Si nanowires with a diameter of 31?nm. Here, we present a model that can fully explain these data. We also simulated the thermal conductivity of P-doped Si nanowires and found a smaller reduction compared to the B-doped samples. Our model includes the effect of incomplete ionization due to interface states, trapped charges, and the dielectric mismatch between nanowire and its surrounding. This effect is most pronounced close to a doping level of 1018?cm-3 for B- and P-doped Si nanowires with an electronic diameter of 31?nm at room temperature. In mitigating the dielectric mismatch, both an increasing diameter and coating the nanowire by an oxide reduce the effect of incomplete ionization. At high doping concentration (~5?×?1019?cm-3) it can be neglected.
关键词： electron-phonon scattering,incomplete ionization,Si nanowires,thermal conductivity,doping
更新于2025-09-04 15:30:14
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Study of anharmonicity in pure and doped InSe by Raman scattering
摘要： With the help of temperature dependence, Raman scattering anharmonic effect of various modes of layered semiconductor InSe over temperature range of 20–650 K has been studied. It was found that with an increase in temperature, anharmonicity will increase. Two and three phonons coupling with optical phonon, are used to describe temperature-induced anharmonicity in the linewidth of Raman modes. It was found that the temperature variation of the phonon parameter can be accounted for well by the cubic term in anharmonic model. To describe line-center shift of Raman modes, a model not considering independently cubic and quartic anharmonicity was used. A similar study has been done for InSe doped with different concentration of GaS dopant. The result of temperature study of InSe doped with GaS revealed that in this case anharmonicity increases with an increase in dopant and an increase in temperature.
关键词： GaS,doping,Raman scattering,Semiconductor,InSe
更新于2025-09-04 15:30:14