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Molecular dynamics simulation of the response of bi-disperse polyelectrolyte brushes to external electric fields 下载免费PDF全文
Langevin dynamics simulations have been performed to investigate the response of bi-disperse and strong polyacid chains grafted on an electrode to electric fields generated by opposite surface charges on the polyelectrolyte(PE)-grafted electrode and a second parallel electrode. Simulation results clearly show that, under a negative external electric field, the longer grafted PE chains are more strongly stretched than the shorter ones in terms of the relative change in their respective brush heights. Whereas under a positive external electric field, the grafted shorter chains collapse more significantly than the longer ones. It was found that, under a positive external electric field, the magnitude of the total electric force acting on one shorter PE chain is larger than that on one longer PE chain, or vice versa. The effects of smeared and discrete charge distributions of grafted PE chains on the response of PE brushes to external electric fields were also examined. 相似文献
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Based to the first-principles calculations, we study the electronic properties of graphene/MoS2 heterostructure by modulating the vertical strains and applying external electric field. Graphene/MoS2 heterostructure is a van der Waals heterostructure (vdWH) with the interlayer spacing is 3.2 Å for the equilibrium state, and the contact property of the interface is n-type Schottky contact. The Schottky barrier height (SBH) changes with vertical strains which induces a change of charge transfer between graphene and MoS2 layer. In addition, with strain or without strain, the applied positive electric field can effectively promote the charge transfer from graphene to MoS2, while the negative electric field has the opposite effect. These findings support for the design of field effect transistors based on graphene vdWHs. 相似文献
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基于SSH(Su-Schrieffer-Heeger)模型,采用静态及动力学自洽算法模拟了有机高分子链内激子在光激发及外电场作用下的形成与解离过程。结果表明,受光激发后,有机高分子链内激子的生成与解离密切依赖于施加外电场的时机,当外电场与光激发同时发生时,激子能否生成完全取决于电场强度的大小;而当外电场在光激发后的一段时间(通常为皮秒量级)之后被引入,则在有机高分子链内能够形成稳定的激子,且该激子只有在强外电场(超过1MV/cm)的作用下,才会发生解离,临界场强量级与实验结果相符合。 相似文献
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Photoinduced charge transfer of positive and negative charges across the interface between a single-crystal organic semiconductor and a polymeric insulator is observed in electric field-effect experiments. Immobilization of the transferred charge by deep traps in the polymer results in a shift of the threshold of field-induced conductivity along the semiconductor-polymer interface, which allows for direct measurements of the charge transfer rate. The transfer occurs when the photon energy exceeds the absorption edge of the semiconductor. The direction of the transverse electric field at the interface determines the sign of the transferred charge; the transfer rate is controlled by the field magnitude and light intensity. 相似文献
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本文研究外加电场对离子交联聚乙烯的微观结构和能量特性的影响,使用分子模拟法建立PbO作硫化剂的交联聚乙烯分子模型,通过半经验法对模型进行几何优化同时施加沿X轴方向的外电场,计算离子交联聚乙烯的分子总能量、偶极矩、极化率、分子轨道能量、能隙、红外光谱、电荷分布并进行分析.得出结论:随着外加电场的上升,交联聚乙烯分子结构会发生变化,当外加电场过大时本文所建交联聚乙烯分子离子盐桥的S-Pb-S键将会发生断裂形成自由基.外加电场会使分子内部的电荷从交联聚乙烯碳链端部向离子盐桥转移,盐桥处Pb原子电荷量不断积累,到达临界点时将会断裂形成电荷量较大的Pb自由基,在外加电场的作用下进一步影响交联聚乙烯分子的稳定性导致其性能下降,研究结果对交联聚乙烯的电树枝老化生成提供参考. 相似文献
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基于Su-Schrieffer-Heeger(SSH)模型并考虑到Brazovskii-Kirova对称破缺项,研究了共轭聚合物中注入极化子和激子在外电场下的散射过程.研究发现在外场作用下极化子总是能通过激子,而激子的运动行为则密切依赖于电场的强度.如果电场大于临界电场3.0×10~5V/cm,那么激子与极化子散射后并不发生任何运动;然而当电场小于此临界值时,激子将在极化子运动的相反方向上有一个明显的位移.激子在弱电场下所发生的这种迁移运动,是由于同极化子发生了慢散射作用. 相似文献
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采用紧束缚的Su-Schrieffer-Heeger模型,利用非绝热动力学方法研究了载流子在金属/聚对苯乙炔(poly(p-phenylene vinylene,简记为PPV))/金属三明治结构中注入与输运的动力学过程.发现由于强的电子-晶格相互作用,注入的电荷在PPV链中形成波包,波包的形成与施加在金属电极上的偏压、PPV链上的电场强度及金属电极与PPV之间的界面耦合强度密切相关.在无外电场的情况下,当偏压达到临界值时电荷能够从金属电极注入到PPV链中并形成波包.随着电场强度的增大,波包能
关键词:
金属/聚对苯乙炔/金属结构
载流子输运
波包 相似文献
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高分子的一维特性使电子激发产生显著的自陷(self-trapping)效应,两个单激子(exciton)会复合形成双激子(biexciton),这是形成双激子的重要通道,其效率高于双光子过程.这种复合过程伴随着晶格畸变,需要了解其演变过程并确定其弛豫时间.本文利用动力学方程研究了激子-激子复合的弛豫过程,确定了它的弛豫时间为160fs,同时还研究了外电场E对复合过程的影响,结果表明,当E大于0.5MV/cm时,两个单激子不能复合成双激子,而是解离成正负双极化子.
关键词: 相似文献
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采用第一性原理计算方法,通过在单层GeSe上施加双轴向应变、外加电场、掺Ag等途径来探索提高单层GeSe对H2O分子传感性能的有效方法,并从微观角度阐明内在机理.计算结果表明,-1.0 V/?的外加电场能有效降低H2O分子在单层GeSe的吸附能并使二者之间的电荷转移量增加11倍,显著提高了单层GeSe对H2O分子的响应速度和敏感性.研究结果为进一步设计并制成二维GeSe基湿度传感器提供了理论依据. 相似文献
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The influence of a static external electric field on surface‐enhanced Raman scattering is investigated by calculating the Raman spectra and excited state properties of pyridine–Au20 complex with the density functional theory and time‐dependent density functional theory method. The external electric field with orientation parallel (positive) or antiparallel (negative) to the permanent dipole moment is respectively applied on the complex. This field slightly changes the equilibrium geometry and polarizabilities, which results in shifted vibration frequencies and selectively enhanced Raman intensities. The changes of charge transfer (CT) excited states in response to the electric field are visualized by employing the charge difference densities. Further, the energy of charge transfer transition is tuned by electric field to be resonant or not with the incident light, leading to the Raman intensities are enhanced or not enhanced. At the same time, the intensities of vibration modes are sensitive to the orientation of the field. The positive electric field enhances the totally symmetric ring breathing mode (~1009 cm−1) but suppresses the trigonal ring breathing mode (~1051 cm−1). On the contrary, the mode at 1051 cm−1 is more enhanced than the mode at 1009 cm−1 when the negative electric field is applied on the complex. The Raman spectra could be modulated by tuning the strength and direction of the electric field. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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V. L. Bychkov S. A. Volkov I. V. Kochetov 《Russian Journal of Physical Chemistry B, Focus on Physics》2011,5(6):940-945
This paper analyzes the local processes of ionization and electron loss in the early stages of an electric discharge in humid
air at altitudes of 0–12 km. The processes of ionization in an external electric field, background ionization, attachment
and detachment of electrons from atomic and molecular oxygen, charge transfer, and the conversion of negative ions are considered.
The dependences of the rate constants on the pressure are taken into account. It is shown that the electric field strength
at which the effective ionization of air begins decreases with increasing altitude. 相似文献
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N. A. Davidenko N. A. Derevyanko A. A. Ishchenko V. A. Pavlov 《Optics and Spectroscopy》2001,91(4):586-592
The effect of a permanent electric field on the absorption spectra of ionic (cationic and anionic) and intraionic symmetric and asymmetric polymethine dyes in poly-N-epoxypropylcarbazole, polyvinylbutyral, and polystyrene polymer films is studied. It is found that the electric field causes an increase in absorption of symmetric dyes in the short-wavelength region and a decrease in their absorption in the long-wavelength region. Asymmetric dyes exhibit opposite properties. These properties are common for these groups of dyes irrespective of their chemical structure and ionic nature. They are retained both in photoconducting polymers and in polymers that are incapable of charge photogeneration. These effects also take place in liquid solutions, although in this case they are much weaker. Various mechanisms of the influence of an electric field on the spectra, such as the electron transfer, Stark and Kerr effects, intermolecular interactions, and dye isomerization, are discussed. It is shown that the spectral effects are caused by the redistribution of the electron density in a chromophore of the dye in the ground state resulting in a change in the probability of vibronic transitions. 相似文献
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Charge injection process from metal electrode to a
nondegenerate polymer in a metal/ polymer/ metal structure has been
investigated by using a nonadiabatic dynamic method. We
demonstrate that the dynamical formation of a bipolaron
sensitively depends on the strength of applied electric field, the
work function of metal electrode, and the contact between the
polymer and the electrode. For a given bias applied to one of the
electrode (V0) and coupling between the electrode and the
polymer (t′), such as V0=0.79 eV and t′=1 eV,
the charge injection process depending on the electric field can
be divided into the following three cases: (1) in the absence of
the electric field, only one electron tunnels into the polymer to
form a polaron near the middle of the polymer chain; (2) at low
electric fields, two electrons transfer into the polymer chain to
form a bipolaron; (3) at higher electric fields, bipolaron can not
be formed in the polymer chain, electrons are transferred from the
left electrode to right electrode through the polymer one by one
accompanying with small irregular lattice deformations. 相似文献
17.
Viorel P. Paun 《Central European Journal of Physics》2009,7(3):607-613
In this paper the driven transport of linear polymers through a nanopore is presented. Biopolymer physical behavior in an
external electric field is modeled and its motion is simulated using the Langevin impulse integrator method. Within fairly
large limits, the polymer translocation time is inversely proportional with the electric field intensity and directly proportional
with the polymer chain length.
相似文献
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基于Su-Schrieffer-Heeger(SSH)模型,考虑电子-电子相互作用,以及在哈密顿量中引入Brazovskii-Kivova对称破缺项,采用动力学演化的方法研究了在外电场作用下共轭高聚物分子链中大极化子与小极化子之间的弹性散射过程.研究发现,载流子的载荷性质不但决定大小极化子之间的相互作用性质,也深刻地影响了其发生散射后的载流子输运性质.在较低电场的作用下,当两载流子电性相同时,发生碰撞后,小极化子将推动着大极化子一起运动;而当两者电性相反时,碰撞后,大极化子将拖曳着小极化子一起运动.当电场强度超过临界值时,将产生量子隧穿效应,即,大小极化子相互迅速穿透,且不受载流子的载荷影响. 相似文献
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By using a multi-configurational time-dependent Hartree–Fock(MCTDHF) method for the time-dependent Schr ?dinger equation and a Newtonian equation of motion for lattice, we investigate the disorder effects on the dissociation process of excitons in conjugated polymer chains. The simulations are performed within the framework of an extended version of the Su–Schrieffer–Heeger model modified to include on-site disorder, off-diagonal, electron–electron interaction, and an external electric field. Our results show that Coulomb correlation effects play an important role in determining the exciton dissociation process. The electric field required to dissociate an exciton can practically impossibly occur in a pure polymer chain, especially in the case of triplet exciton. However, when the on-site disorder effects are taken into account, this leads to a reduction in mean dissociation electric fields. As the disorder strength increases, the dissociation field decreases effectively. On the contrary, the effects of off-diagonal disorder are negative in most cases. Moreover, the dependence of exciton dissociation on the conjugated length is also discussed. 相似文献
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利用第一性原理的离散变分局域密度泛函方法,采用团簇模型(Si34H36-W11)来模拟STM操纵Si(111)-7×7表面顶角吸附原子的过程.通过分析在进行原子操纵过程中体系的能量与电子云密度分布来研究针尖和外电场的作用.结果表明,当针尖与样品间距离较近时,利用两者间有较强的相互作用,能有效地降低脱出能的能垒高度.外电场对体系脱出能的影响与其大小及极性有关,当样品上所加正偏压增强时,脱出能曲线高度单调下降,而外电场极性为负时,反而稍有增高.仅考虑针尖和样品之间的静态电子相互作用及静电场的作用,尚不能使被操纵原子脱离样品表面.最后讨论了在Si(111)-7×7表面上进行原子操纵的其他机理. 相似文献