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Effects of vacancy defects location on thermal conductivity of silicon nanowire: a molecular dynamics study
摘要： The improvement of thermoelectric ?gure of merit of silicon nanowire (SiNW) can be achieved by lowering its thermal conductivity. In this work, non-equilibrium molecular dynamics method was used to demonstrate that the thermal conductivity of bulk silicon crystal is drastically reduced when it is crafted as SiNW and that it can be reduced remarkably by including vacancy defects. It has been found that ‘centre vacancy defect’ contributes much more in reducing the thermal conductance than ‘surface vacancy defect’. The lowest thermal conductivity that occurs is about 52.1% of that of pristine SiNW, when 2% vacancy defect is introduced in the nanowire. The vibrational density of states analysis was performed to understand the nature of this reduction and it has been found that the various boundary scatterings of phonon signi?cantly reduce the thermal conductivity. Also, larger mass difference due to voids induces smaller thermal conductivity values. These results indicate that the inclusion of vacancy defects can enhance the thermoelectric performance of SiNWs.
关键词： molecular dynamics,silicon nanowire,thermoelectric performance,thermal conductivity,vacancy defects
更新于2025-09-23 15:21:21
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Incorporation of Nickel Ions to Enhance Integrity and Stability of Perovskite Crystal Lattice for High-Performance Planar Heterojunction Solar Cells
摘要： Enhancement of integrity and stability of crystal lattice are highly challenging for poly-crystalline perovskite films. In this work, a nickel (Ni) ions incorporation strategy is presented to modulate the crystal structure of CH3NH3PbI3 perovskite film. A broad range of experimental characterizations reveal that the incorporation of Ni ions can substantially eliminate the intrinsic halide vacancy defects since Ni ions have a strong preference for octahedral coordination with halide ions, resulting in improved integrity and short-range order of crystal lattice significantly. Moreover, it is also demonstrated that the stronger chemical bonding interaction between Ni ions and halide ions as well as organic group can improve the stability of perovskite material. Simultaneously, the surface morphology of perovskite thin film is also improved by incorporation of nickel ions. As a result, the 1.5% Ni-incorporated planar heterojunction perovskite solar cell exhibits a power conversion efficiency of 18.82%, which is improved by 25% compared with 14.92% for the pristine device. Simultaneously, the 1.5% Ni- incorporated device shows remarkable stability with 90% of the initial efficiency after storage in air environment for 800 h. The studies provide a new insight for metal-incorporated perovskite materials for various optoelectronic applications.
关键词： Ni ions,crystal lattice,Perovskite Solar Cells,MAPbI3,iodine vacancy defects
更新于2025-09-11 14:15:04
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Low-frequency noise in irradiated graphene FETs
摘要： We present a quantitative analysis of the low-frequency noise in irradiated monolayer graphene. In this study, we repeatedly irradiate a back-gated graphene transistor with argon ions at 90 eV and measure its low-frequency noise and channel conductivity after each irradiation. Our results indicate that the noise amplitude decreases monotonically with the increasing density of vacancy defects. The combination of our low-frequency noise measurements and carrier transport studies reveals that the mobility fluctuation model can explain this observation and that the density of vacancy defects, the density of charged impurities, and the mean free path of charge carriers determine the noise amplitude.
关键词： mobility fluctuation model,low-frequency noise,charged impurities,irradiated graphene,vacancy defects,mean free path
更新于2025-09-10 09:29:36
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[IEEE 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Paris, France (2018.7.8-2018.7.13)] 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Electron Paramagnetic Resonance Study on a 28Si Single Crystal for the Future Realization of the Kilogram
摘要： In the future realization of the kilogram using the x-ray crystal density method, isotopically enriched silicon crystals grown by the floating zone method are employed. In this paper, we present the electron paramagnetic resonance study on 28Si single crystal AVO28. We revealed that the concentrations of various kinds of vacancy defects in the crystal are less than 1 × 1012 cm–3. Consequently, the necessary mass deficit correction due to these vacancy defects is estimated to be less than 0.4 μg for 1 kg AVO28 spheres.
关键词： electron paramagnetic resonance,silicon crystal,measurement uncertainty,kilogram,vacancy defects
更新于2025-09-10 09:29:36
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Electronic structures and spectroscopic signatures of silicon-vacancy containing nanodiamonds
摘要： The presence of midgap states introduced by localized defects in wide-band-gap-doped semiconductors can strongly affect the electronic structure and optical properties of materials, generating a wide range of applications. Silicon-divacancy defects in diamond have been recently proposed for probing high-resolution pressure changes and performing quantum cryptography, making them good candidates to substitute for the more common nitrogen-vacancy centers. Using group-theory and ab initio electronic structure methods, the molecular origin of midgap states, zero-phonon line splitting, and size dependence of the electronic transitions involving the silicon-vacancy center is investigated in this paper. The effects of localized defects on the Raman vibrational and carbon K-edge x-ray absorption spectra are also explored for nanodiamonds. This paper presents an important analysis of the electronic and vibrational structures of nanosized semiconductors in the presence of midgap states due to localized defects, providing insight into possible mechanisms for modulating their optical properties.
关键词： midgap states,electronic structure,optical properties,nanodiamonds,Raman vibrational spectra,quantum cryptography,x-ray absorption spectra,silicon-vacancy defects
更新于2025-09-10 09:29:36
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Interaction Between Hydrogen and Vacancy Defects in Crystalline Silicon
摘要： Hydrogen is one of the most important impurities in silicon. It is a mobile and highly reactive species that can passivate dangling bonds at dislocations, surfaces, and interfaces, which has been widely used in the microelectronics and solar cell industry for improving device performance. Vacancy defects are elementary complexes containing dangling bonds, and the study of their interaction with hydrogen is of significant importance. In this work, the interactions of hydrogen with the vacancy-oxygen complex (VO) and the divacancy (V2) are discussed, which are the most dominant and fundamental vacancy defects stable at room temperature. It is shown that VO and V2 can interact with both atomic and diatomic hydrogen species. This complicates the interpretation of experimental data and results in different reaction paths in differently prepared samples. Besides, some of important electronic properties, particularly electronic levels for V2Hn with n > 1, are not experimentally established.
关键词： silicon,vacancy defects,vacancy-oxygen,hydrogen,divacancy
更新于2025-09-04 15:30:14
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[IEEE 2018 International Conference on Simulation of Semiconductor Processes and Devices (SISPAD) - Austin, TX, USA (2018.9.24-2018.9.26)] 2018 International Conference on Simulation of Semiconductor Processes and Devices (SISPAD) - Carrier Transport in a Two-Dimensional Topological Insulator Nanoribbon in the Presence of Vacancy Defects.
摘要： We model transport through two-dimensional topological insulator (TI) nanoribbons. To model the quantum transport, we employ the non-equilibrium Green’s function approach. With the presented approach, we study the effect of lattice imperfections on the carrier transport. We observe that the topologically protected edge states of TIs are robust against a high percentage (2%) of vacancy defects. We also investigate tunneling of the edge states in two decoupled TI nanoribbons.
关键词： nanoribbon,vacancy defects,non-equilibrium Green’s function,carrier transport,two-dimensional topological insulator
更新于2025-09-04 15:30:14