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51.
Using the finite element method, this paper investigates lateral
stress-induced propagation characteristics in a photonic crystal
fibre of hexagonal symmetry. The results of simulation show the
strong stress dependence of effective index of the fundamental
guided mode, phase modal birefringence and confinement loss. It also
finds that the contribution of the geometrical effect that is
related only to deformation of the photonic crystal fibre and the
stress-related contribution to phase modal birefringence and
confinement loss are entirely different. Furthermore,
polarization-dependent stress sensitivity of confinement loss is
proposed in this paper. 相似文献
52.
The influence of strain-reducing layer on strain distribution and ground state energy levels of GaN/AlN quantum dot 下载免费PDF全文
This article deals with the strain distributions around GaN/AlN
quantum dots by using the finite element method. Special attention
is paid to the influence of Al0.2Ga0.8N strain-reducing
layer on strain distribution and electronic structure. The numerical
results show that the horizontal and the vertical strain components
are reinforced in the GaN quantum dot due to the presence of the
strain-reducing layer, but the hydrostatic strain in the quantum dot
is not influenced. According to the deformation potential theory, we
study the band edge modifications and the piezoelectric effects.
The result demonstrates that with the increase of the strain reducing layer,
the transition energy between the ground state electron and the heavy hole
increases. This result is consistent with the emission wavelength
blue shift phenomenon observed in the experiment and confirms that the
wavelength shifts toward the short wavelength range is realizable by
adjusting the structure-dependent parameters of GaN/AlN quantum dot. 相似文献
53.
1-烷基-3-甲基咪唑系列室温离子液体表面张力的研究 总被引:5,自引:0,他引:5
合成了系列1-烷基-3-甲基咪唑四氟硼酸盐([C2~7mim]BF4)及六氟磷酸盐([C4~7mim]PF6)室温离子液体, 并通过核磁氢谱、红外光谱、质谱等手段对其进行了结构表征; 采用Wilhelmy白金板法, 在293~338 K范围内测定了离子液体的表面张力, 测试结果显示, 同类离子液体表面张力γ随温度的升高而线性下降, 同种离子液体的表面张力呈现出较宽的变化范围, 如293 K下, 表面张力值从[C2mim]BF4的50.4 mJ/m2到[C7mim]BF4的36.1 mJ/m2. 最后对离子液体的表面性能进行了讨论. 相似文献
54.
多工序制造过程通常包含串联和并联两种结构,具有串并联混合结构的多工序制造过程是实践中最为常见的形式,而不同模式的并联结构其上游工序质量波动对下游工序及总过程能力的影响不同。针对多工序制造过程并联结构特点,本文从波动减少的角度重点对多工序并联制造过程中并行、分散和收敛三种基本模式进行过程能力分析,研究多工序制造过程中各子过程波动对整体过程能力的影响,并根据各子过程质量波动减少的“困难度”和“效用比”评价质量改进的效果,给出多工序并联过程能力改进策略选择依据。通过实例表明,本方法能较好地识别各工序质量波动减少对本工序过程能力和总过程能力的不同影响,确定质量改进的优先顺序,实现多工序制造过程的经济性质量改进和优化。 相似文献
55.
We theoretically analyze the steady state emission spectrum and transient temporal dynamics in a coupled biexciton quantum dot(QD)–cavity system. For steady state, a phonon-assisted biexciton–exciton cascade model under continuous wave(CW) excitation is presented to explain the asymmetric QD–cavity emission spectrum intensities(intensities of cavity,exciton, and biexciton emission peak) in off-resonance condition. Results demonstrate that the electron–phonon process is crucial to the asymmetry of emission spectrum intensity. Moreover the transient characteristics of the biexciton–exciton cascade system under pulse excitation show abundant nonlinear temporal dynamic behaviors, including complicated oscillations which are caused by the four-level structure of QD model. We also reveal that under off-resonance condition the cavity outputs are slightly reduced due to the electron–phonon interaction. 相似文献
56.
57.
Influence of disorder and deformation on the optical properties of a two-dimensional photonic crystal waveguide 下载免费PDF全文
We investigate the effect of disorder and mechanical deformation on a two-dimensional photonic crystal waveguide. The dispersion characteristics and transmittance of the waveguide are studied using the finite element method. Results show that the geometric change of the dielectric material perpendicular to the light propagation direction has a larger influence on the waveguide characteristics than that parallel to the light propagation direction. Mechanical deformation has an obvious influence on the performance of the waveguide. In particular, longitudinal deformed structure exhibits distinct optical characteristics from the ideal one. Studies on this work will provide useful guideline to the fabrication and practical applications based on photonic crystal waveguides. 相似文献
58.
Kinetic Monte Carlo simulations of optimization of self-assembly quantum rings growth strategy based on substrate engineering 下载免费PDF全文
In this paper, the kinetic Monte Carlo simulations of the self-assembly quantum rings (QRs) based on the substrate engineering, which is related to the eventual shape of the formed quantum ring, are implemented. According to the simulation results, the availability of the QR with tunable size and the formation of smooth shape on the ideal flat substrate are checked. Through designing the substrate engineering, i.e., changing the depth, the separation and the ratio between the radius and the height of the embedded inclusions, the position and size of QR can be controlled and eventually the growth strategy of optimizing the self-assembly QRs is accomplished. 相似文献
59.
We present equilibrium composition maps in InGaAs/GaAs conic strained quantum dots, using the finite element method and quadratic programming optimization method. The axis-symmetric model is adopted. We compare the steep islands with the shallow islands and determine the influence of entropie energy. The difference of equilibrium composition maps between the single dot and the quantum dot stacks is also discussed. 相似文献
60.
Surface diffusion of Si,Ge and C adatoms on Si (001) substrate studied the molecular dynamics simulation 下载免费PDF全文
Depositions of Si, Ge and C atoms onto a preliminary Si (001) substrate at different temperatures are investigated by using the molecular dynamics method. The mechanism of atomic self-assembling occurring locally on the flat terraces between steps is suggested. Diffusion and arrangement patterns of adatoms at different temperatures are observed. At 900 K, the deposited atoms are more likely to form dimers in the perpendicular [110] direction due to the more favourable movement along the perpendicular [110] direction. C adatoms are more likely to break or reconstruct the dimers on the substrate surface and have larger diffusion distances than Ge and Si adatoms. Exchange between C adatoms and substrate atoms are obvious and the epitaxial thickness is small. Total potential energies of adatoms and substrate atoms involved in the simulation cell are computed. When a newly arrived adatom reaches the stable position, the potential energy of the system will decrease and the curves turns into a ladder-like shape. It is found that C adatoms can lead to more reduction of the system energy and the potential energy of the system will increase as temperature increases. 相似文献