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Wang Z.,Fudan University | Shen B.,Fudan University | Dong F.,Fudan University | Wang S.,Fudan University | And 3 more authors.
Physical Chemistry Chemical Physics | Year: 2015

The mechanical properties, electronic structures and optical properties of CaAlSiN3 were investigated using the first-principles calculations. The elastic constants, bulk moduli, shear moduli, Young's moduli, and Poisson's ratio were obtained. These results indicate that CaAlSiN3 is mechanically stable and a relatively hard material. Moreover, this compound has an indirect band gap of ∼3.4 eV according to its band structure and density of states. The linear photon energy dependent dielectric functions and related optical properties including the refractive index, extinction coefficient, absorption spectrum, reflectivity, and energy loss spectrum were computed and discussed. It is shown that no sizable anisotropy is found in the optical properties of CaAlSiN3. The obtained structural estimation and some other results are in agreement with available experimental and theoretical data. This investigation is not only helpful for better understanding the electronic, mechanical and optical properties of CaAlSiN3, but also will open up the possibility of its use in device applications. © the Owner Societies 2015.

Wang Z.,Fudan University | Dong F.,Fudan University | Shen B.,Fudan University | Zhang R.J.,Fudan University | And 11 more authors.
Carbon | Year: 2016

The vibrational properties, electronic structures and optical properties of novel carbon allotropes, such as monolayer penta-graphene (PG), double-layer PG and T12-carbon, were studied by first-principles calculations. Results of phonon calculations demonstrate that these exotic carbon allotropes are dynamically stable. The bulk T12 phase is an indirect-gap semiconductor having a quasiparticle (QP) bandgap of ∼5.19 eV. When the bulk material transforms to a two-dimensional (2D) phase, the monolayer and double-layer PG become quasi-direct gap semiconductors with smaller QP bandgaps of ∼4.48 eV and ∼3.67 eV, respectively. Furthermore, the partial charge density analysis indicates that the 2D phases retain part of the electronic characteristics of the T12 phase. The linear photon energy-dependent dielectric functions and related optical properties including refractive index, extinction coefficient, absorption spectrum, reflectivity, and energy-loss spectrum were also computed and discussed. Additionally, the chemical stability of monolayer PG and the electronic and optical properties of double-side hydrogenated monolayer PG were also investigated. The results obtained from our calculations are beneficial to practical applications of these exotic carbon allotropes in optoelectronics and electronics. © 2016 Elsevier Ltd. All rights reserved.

Chen M.,Rensselaer Polytechnic Institute | Chen M.,Zte United States Inc. | Chen M.,Hunan Normal University | Xiao X.,Zte United States Inc. | And 6 more authors.
Journal of Lightwave Technology | Year: 2016

We experimentally demonstrate an IFFT/FFT size efficient discrete Fourier transform (DFT)-spread orthogonal frequency-division multiplexing (OFDM) based on complex-valued IFFT/FFT operations without Hermitian symmetry constraint at the input, for short-reach intensity-modulated and directly-detected optical fiber transmission systems. The only complex-valued IFFT-based OFDM has the similar peak-to-average power ratio (PAPR) and bit error rate (BER) performance, but with only half of the IFFT/FFT size as the conventional real IFFT-based OFDM. In this paper, the complex IFFT-based OFDM combined with DFT-spread technique is proposed and applied to reduce PAPR and IFFT/FFT size, and improve BER performance at the same time. The experimental results show that, with the help of PAPR reduction enabled by DFT-spread, more than 2-dB improvement in receiver sensitivity has been achieved after 20.62 km of single mode fiber transmission at a BER of 3.8 × 10-3 (7% hard-decision forward error correction threshold). In addition, by using the DFT-spread technique, the BER performance comparison between complex IFFT-based OFDM and real IFFT-based OFDM is also performed. The results show that, the BER performance of the former is slightly worse than the latter, but has lower hardware complexity and less power consumption due to the reduced IFFT/FFT size. © 2016 IEEE.

Zhang J.,Fudan University | Zhang J.,Yangzhou University | Zheng Y.,Fudan University | Wang Z.,Fudan University | And 8 more authors.
Journal of Physical Chemistry C | Year: 2016

In1-xSnx (x = 0.06-0.51) alloy films were deposited on Si substrates by electron beam evaporation and characterized by X-ray diffraction, field-emission scanning electron microscopy, atomic force microscopy, and spectroscopic ellipsometry. The dielectric functions of the In1-xSnx alloy films were obtained in the energy range from 1.55 to 4.13 eV based on the spectroscopic ellipsometry measurements, and it is believed that a solid-solid phase transitions led to changes in ϵ. The phase diagram of nanometer-sized particles is different from that of the bulk material, and this phenomenon can be explained by the surface stress of the particles. The effects of alloying on the electronic band structure were studied from the perspective of first-principles calculations. © 2016 American Chemical Society.

Qiao C.,Zhengzhou University | Zhou Y.,Henan Industry and Trade Vocational College | Cai X.,Zhengzhou University | Cai X.,Henan Polytechnic University | And 7 more authors.
RSC Advances | Year: 2016

The plastic deformation mechanism of iron (Fe) nanowires under torsion is studied using the molecular dynamics (MD) method by applying an external driving force at a constant torsion speed. We find that the deformation behavior depends on the orientation of the wire. The dislocations in <100> and <111> oriented nanowires propagate through the nanowires under torsion, whereas those in <110> oriented nanowires divide the wire into two parts. The situation that there is a low angle twist grain boundary (GB) in the nanowires is also under consideration. The results reveal that the dislocations are concentrated on the GB in the initial state, presenting different patterns of dislocation network. The networks change depending on the twist direction. They shrink with increase in twist angle but expand with the decreasing twist angle, presenting an asymmetric phenomenon. Our findings can help us more thoroughly understand the plastic deformation mechanism of Fe nanowires under torsion. © The Royal Society of Chemistry 2016.

Yue G.Q.,Fudan University | Wu S.,Fudan University | Wu S.,Iowa State University | Shen B.,Fudan University | And 7 more authors.
Journal of Physics Condensed Matter | Year: 2013

The effects of strontium modification on the structure and dynamics of Al88Si12 liquid are studied by means of ab initio molecular dynamics simulations. By replacing 0.5% and 4.0% of Al with Sr, we show that the addition of Sr lowers the self-diffusion of Al and Si of the liquid and reduces the nearest-neighbor correlation between Si atoms. The simulation provides an explanation for the change in morphology of the eutectic phases observed in rapidly solidified Al-Si alloys modified with Sr. © 2013 IOP Publishing Ltd.

Hu E.T.,Fudan University | Yue G.Q.,Fudan University | Zhang R.J.,Fudan University | Zheng Y.X.,Fudan University | And 3 more authors.
Renewable Energy | Year: 2015

The multilevel impurity photovoltaic effect (IPV) of the sulfur doped crystalline silicon (c-Si) is studied by using the SCAPS program. The effects of impurity concentration (Nt) of two and four defect levels on the performance of sulfur doping c-Si solar cell are investigated, respectively. Then, the quantum efficiencies (QE) of different cases (without impurity, two and four defect levels) are considered. The results show that after the doping of sulfur, the infrared response of the c-Si solar cell is enhanced. Moreover, the infrared response wavelength range of the case considering two defect levels may be wider than that of four defect levels. In order to get the highest photovoltaic conversion efficiency (PCE), the number and the type of defect levels should be controlled. In the end, with four defect levels considered, the thickness and background doping concentration (ND for the n-type layer and Na for the p-type layer) of each layer of the n+-p-p+ structure are optimized. Our results suggest that higher PCE could be achieved than that without impurity by choosing a suitable doping concentration. The efficiency of 25.32% attained in the four-defect case improved the PCE by 2% more than the value of 23.22% without sulfur doping. © 2014 Elsevier Ltd.

Zhang D.X.,Fudan University | Shen B.,Fudan University | Zheng Y.X.,Fudan University | Wang S.Y.,Fudan University | And 8 more authors.
Applied Physics Letters | Year: 2014

The temperature dependent optical properties of tin film from solid to liquid were studied by spectroscopic ellipsometry and ab initio molecular dynamics simulations. The dielectric function of liquid Sn was different from solid, and an interband transition near 1.5 eV was easily observed in solid while it apparently disappeared upon melting. From the evolution of optical properties with temperature, an optical measurement to acquire the melting point by ellipsometry was presented. From first principles calculation, we show that the local structure difference in solid and liquid is responsible for this difference in the optical properties observed in experiment. © 2014 AIP Publishing LLC.

Shen B.,Fudan University | Liu C.Y.,Zhengzhou University | Jia Y.,Zhengzhou University | Yue G.Q.,Fudan University | And 8 more authors.
Journal of Non-Crystalline Solids | Year: 2014

The structural and dynamical properties of rapidly quenched Al are studied by molecular dynamics simulations. The pair-correlation function of high temperature liquid Al agrees well with the experimental results. Different cooling rates are applied with high cooling rates leading to glass formation, while low cooling rates leading to crystallization. The local structures are characterized by Honeycutt-Andersen indices and Voronoi tessellation analysis. The results show that for high cooling rates, the local structures of the liquid and glassy Al are predominated by icosahedral clusters, together with considerable amount of face-centered cubic and hexagonal close packed short-range orders. These short-range order results are further confirmed using the recently developed atomic cluster alignment method. Moreover, the atomic cluster alignment clearly shows the crystal nucleation process in supercooled liquid of Al. Finally, the mean square displacement for the liquid is also analyzed, and the corresponding diffusion coefficient as a function of temperature is calculated. © 2013 Elsevier B.V.

Ke F.S.,Fudan University | Yue G.Q.,Fudan University | Yue G.Q.,Iowa State University | Shen B.,Fudan University | And 8 more authors.
Acta Materialia | Year: 2014

The structure of liquid and rapidly quenched amorphous Ag0.74Ge0.26 alloy at the eutectic composition was studied by ab initio molecular dynamics (MD) simulations. The local structural properties were systematically investigated from the liquid at 1123 K to amorphous solid at 300 K. The pair-correlation function at 976 K from the MD simulations agrees well with the experimental data. The local structures were also analyzed using Honeycutt-Andersen (HA) indices, Voronoi tessellation and the atomic cluster alignment (ACA) method. The HA indices analysis reveals that there is a high population of pentagonal bipyramid structure which become more predominant upon solidification. Voronoi tessellation analysis indicates strong icosahedral short-range order (SRO) in the liquid and amorphous samples generated by the MD simulations. Using the ACA method, the development of icosahedral SRO upon cooling is further confirmed and a Bergman medium-range order is also observed. The analysis of structural properties and chemical short-range order suggests that Ag atoms tend to have a Bergman-like packing, while the dispersed Ge atoms prevent the alloy from forming a long-range order upon cooling. The Bergman medium-range order is also confirmed by the constrained reversed Monte Carlo results. © 2014 Acta Materialia Inc.

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Loading Key Laboratory for Information Science of Electromagnetic Waves MoE collaborators