掺杂剂对聚乙炔中孤子的影响

本文用半经验CNDO/2量子化学计算方法研究了各种掺杂剂对聚乙炔中孤子性质的影响。掺杂剂的存在使孤子的宽度变小, 且p型掺杂剂比n型掺杂剂的影响更大, 这主要是由于掺杂剂与聚乙炔链之间的电荷转移量不同造成的。     

聚乙炔掺杂导电的双向机制

提出了一种掺杂聚乙炔的双向导电机理。垂直聚乙炔分子链方向的电荷输运是通过掺杂原子(或分子)在链间振动实现的;平行分子链方向的电荷输运是通过电荷密度波的传播实现的。掺杂聚乙炔的电导率随掺杂剂与聚乙炔链之间电荷转移量的增大而增大。     

掺杂剂对聚乙炔中电荷密度波的影响

用CNDO／2方法研究了各种掺杂剂对聚乙炔中电荷密度波的影响，在掺杂剂附近的碳原子上出现较大的电荷密度，且p型比n型掺杂剂的影响更大，讨论了电荷波与导电性的关系。     

掺杂剂锂链间迁移在聚乙炔纵向导电机制中的作用

聚乙炔(PA)的电导率X(Ω~(-1).cm~(-1))经掺杂可以在十二个数量级内变化。PA导电机理与一般的无机导体或半导体不同,PA通过荷电孤子与中性孤子之间的电子跃迁导电,而掺杂剂参与可增大这种跃迁的几率。掺杂剂与PA之间存在着相互作用,并由此而引起PA多种性质的变化。深入研究PA链间通过掺杂原子(或分子)进行的相互作用以及电荷传递过程,对于进一步揭示PA的垂直电导率产生的本质有着十分重要的意义。     

n-型掺杂反式聚乙炔导电性能各向异性研究

根据固体能带理论，用量子化学ＥＨＭＯ／ ＣＯ 方法，计算了高取向反式聚乙炔及其ｎ－ 型掺杂态（掺杂Ｌｉ，Ｎａ，Ｋ） 的二维能带结构，首次从能隙与带宽角度讨论了聚乙炔经ｎ－ 型掺杂呈现的导电性能的各向异性．研究表明：平行和垂直于分子链方向的电导率之比（σ∥／σ⊥） 取决于这两个方向上能隙和带宽的大小；掺杂后σ∥／σ⊥下降，其原因是掺杂剂在聚乙炔链间架起了一个“浮桥”，使链间耦合作用增强．理论计算与实验结果一致     

导电高聚物的EXAFS研究(Ⅱ)FeCl_3掺杂的聚噻吩

聚噻吩是一种共轭有机高聚物,其结构如图1所示。类似于聚乙炔,经电子受体掺杂后的聚噻吩,呈现出较高的电导率。为了阐明导电高聚物的电导机制,必须搞清掺杂后掺杂剂的化学结构和高分子链与掺杂剂之间的相互作用。前文我们报道了用扩展X射线吸收精细结构(EXAFS)谱对H_2PtCl_6·6H_2O掺杂聚乙炔的研究,本文报道对FeCl_3掺杂聚噻吩的研究结果。     

MF~5(M=P,As,Sb)掺杂聚乙炔的能带结构和导电性能

本文采用EHMO晶体轨道方法计算了第五主族氟化物高掺杂聚乙炔的能带结构参数,肯定了六氟化物为聚乙炔的有效导电掺杂剂.在进一步比较PF~6,AsF~6和SbF~6掺杂聚乙炔能带结构的基础上,满意地解释了掺杂物电导率实验测定的次序:AsF~6>SbF~6～PF~6.最后,本文又从P,As,Sb 的电负性和原子半径的角度讨论了这一次序的起因     

从二聚体到长链体系II:含二重螺轴或滑移面的体系

本文考虑了含二重螺轴或滑移面的体系由二聚体构造长链体系定性能带的方法, 讨论了一些有代表性的体系如顺式聚乙炔、扭角不为零的聚对苯撑、聚吡咯及其类似物的导电性问题, 与孤子理论进行了联系, 进一步说明从二聚体可以获得长链体系的信息。     

从二聚体到长链体系II:含二重螺轴或滑移面的体系

本文考虑了含二重螺轴或滑移面的体系由二聚体构造长链体系定性能带的方法, 讨论了一些有代表性的体系如顺式聚乙炔、扭角不为零的聚对苯撑、聚吡咯及其类似物的导电性问题, 与孤子理论进行了联系, 进一步说明从二聚体可以获得长链体系的信息。     

氧化和硫化对聚乙炔导电性能的影响

本文采用量子化学CNDO/2晶体轨道方法,对硫化聚乙炔和氧化聚乙炔的分子结构及电子质进行了了理论计算和分析,探讨了氧化和硫化对聚乙炔导电性能的影响,揭示了硫化抑制聚乙炔氧化,从而在空气中稳定的本质。     

Effects of Various Dopants on Solitons in Polyacetylene

The effects of various dopants on solitons in polyacetylene were studied by using CNDO/2 level semiempirical quantum chemical method. The width of solitons is reduced when dopant is present, and the charge density wave(CDW) is further gathered on the carbon atom in soliton center. The effects of p-type of dopants are greater than those of n-type of ones. The charge transfer in doped polyacetylene can be achieved by the propagation of CDW along the chain. The conductivity of doped polyacetylene is proportional to the quantity of charge transfer between dopant and polyacetylene chain.     

XPS法对聚乙炔化学掺杂机制的研究

用XPS(X射线光电子能谱法)研究了十余种掺杂聚乙炔的电荷转移过程, 发现对大部分掺杂剂, 由Cls谱裂分所计算的电荷转移量与掺杂剂的氧化电位直接相关. 一些强氧化性或过渡金属质子酸也符合这一规律, 同时观察到掺杂后这些氧化性质子酸本身发生价态变化. 因此这些质子酸的掺杂不是文南中所报道的质子酸机制而是氧化还原机制.所研究的若干种非氧化性或弱氧化性质子酸掺杂后电导率均较低, 这进一步表明掺杂过程中的电荷转移过程是产生高导聚乙炔的必要条件.     

Highly twisted helical polyacetylene with morphology free from the bundle of fibrils synthesized in chiral nematic liquid crystal reaction field

We synthesized novel axially chiral binaphthyl derivatives with highly twisting powers by substituting phenylcyclohexyl (PCH) mesogenic moieties into 2,2' positions or 2,2',6,6' positions of binaphthyl rings. The di- and tetrasubstituted binaphthyl derivatives, abbreviated as D-1 and D-2, respectively, were adopted as chiral dopants to induce chiral nematic liquid crystals (N*-LCs) available for synthesis of helical polyacetylene. The helical twisting power (betaM) of D-2 was 449 microm(-1), which was ca. 2.6 times larger than that of D-1 (171 microm(-1)). We prepared two kinds of induced N*-LCs with 5 microm and 270 nm in helical pitch by adding the chiral dopants D-1 and D-2 into the host N-LCs, respectively. The helical polyacetylene synthesized in the N*-LC containing D-2 exhibited highly screwed fibrils, but not a bundle of fibrils. This result is in quite contrast to the usual fibril morphology, where the screwed fibrils are gathered to form the bundle of fibrils, as observed in the helical polyacetylene synthesized in the N*-LC containing a chiral dopant with moderate helical twisting power, such as D-1. It is of keen interest that the helical pitch (270 nm) of the N*-LC including D-2 is much smaller than the diameter (ca. 1 microm) of the bundle of fibrils, which should depress the formation of the bundle of fibrils. The morphology free from the bundle of fibrils might enable us to evaluate more precisely intrinsic electromagnetic properties of a single screwed fibril of helical polyacetylene.     

Study of a bisquaternary ammonium salt by atmospheric pressure photoionization mass spectrometry

A comprehensive atmospheric pressure photoionization (APPI) mass spectrometry investigation of hexamethonium bromide is reported. This bisquaternary ammonium salt is a model system for the investigation of multiply charged species and elucidation of ion formation processes. It has been used to elucidate the physicochemical phenomenon occurring when photoionization is carried out at atmospheric pressure. First, the in-source fragmentations were studied for aqueous solutions of the salt with the photoionization lamp switched off, i.e. under thermospray conditions. It is shown that, in this mode of operation, fragmentations are minor and may be classified into two classes, namely dequaternization and charge separation, arising from the two precursors, M2+ and [M+Br]+. Second, the fragmentation patterns have been monitored in dopant- assisted APPI for different dopants (toluene, toluene-d8, anisole and hexafluorobenzene) at various amounts. At low dopant flow rates, the [M+Br]+ and M2+ ions are still observed. As the flow rate is increased, these precursor ions lose intensity and are finally suppressed for all three dopants. Comparison of toluene and toluene-d8 reveals that H atoms may be transferred from the dopant to the molecular ions, very likely mediated by the solvent. The role of the solvent (water) was also investigated by using heavy water. Apart from the thermospray fragmentations, which are also observed in APPI, several fragmentation pathways appear to be specific to the photoionization process. Photoionization efficiencies are measured by determination of the relative photoionization cross sections with respect to toluene. It is found that, when the ionization efficiencies are taken into account, the depletion of the precursors as a function of the dopant flow rates is the same for all three dopant molecules. This result shows that the precursor ions are depleted by reactions with the photoelectrons released from the dopant. Three additional mechanisms are proposed to account for this effect: electron transfer or H atom transfer from negatively charged water nanodroplets and H atom transfer from the dopant.     

Periodic Hartree-Fock and density functional theory calculations for Li-doped polyacetylene chains

We have performed periodic restricted Hartree-Fock/6-31G** and B3LYP6-31G** density functional theory calculations on Li-doped trans-polyacetylene at various dopant concentrations, using C(2m)H(2m)Li2 unit cells (m = 7-14). Except for maintaining P1 rod symmetry the geometry was completely optimized for both uniform and nonuniform doping structures. In addition to geometry we obtain atomic charges, along with soliton formation and dopant binding energies, as well as band structures and densities of states. A thorough analysis of the band structure and density of states, as a function of dopant concentration, is presented. We also characterize the complex nature of the binding interaction between Li and the polyacetylene chain.     

Depth-dependent imaging of individual dopant atoms in silicon.

We have achieved atomic-resolution imaging of single dopant atoms buried inside a crystal, a key goal for microelectronic device characterization, in Sb-doped Si using annular dark-field scanning transmission electron microscopy. In an amorphous material, the dopant signal is largely independent of depth, but in a crystal, channeling of the electron probe causes the image intensity of the atomic columns to vary with the depths of the dopants in each column. We can determine the average dopant concentration in small volumes, and, at low concentrations, the depth in a column of a single dopant. Dopant atoms can also serve as tags for experimental measurements of probe spreading and channeling. Both effects remain crucial even with spherical aberration correction of the probe. Parameters are given for a corrected Bloch-wave model that qualitatively describes the channeling at thicknesses 20 nm, but does not account for probe spreading at larger thicknesses. In thick samples, column-to-column coupling of the probe can make a dopant atom appear in the image in a different atom column than its physical position.     

The origin of the enhanced oxygen storage capacity of Ce(1-x)(Pd/Pt)(x)O2

Doping CeO(2) with Pd or Pt increases the oxygen storage capacity (OSC) and catalytic activity of this environmentally important material. To date, however, an understanding of the mechanism underlying this improvement has been lacking. We present a density functional theory analysis of Pd- and Pt-doped CeO(2), and demonstrate that the increased OSC is due to a large displacement of the dopant ions from the Ce lattice site. Pd(II)/Pt(II) (in a d(8) configuration) moves by ～1.2 ? to adopt a square-planar coordination due to crystal field effects. This leaves three three-coordinate oxygen atoms that are easier to remove, and which are the source of the increased OSC. These results highlight the importance of rationalizing the preferred coordination environments of both dopants and host cations when choosing suitable dopants for next generation catalysts.     

XPS Studies of PtCl4 and H2PtCl6·6H20 doped polyacetylene

The PtCl₄ and H₂PtCl₆-6H₂O doped polyacetylene were studied by X-ray photoelection spectroscopy and transmission electron microscopy. We found that both Pt 4f and Cl 2p peaks could be resolved into two components both with a splitting of ca. 1.5 eV. The higher binding energy components of Pt 4f peak is attributed to Pt⁴⁺ and the lower binding energy one to Pt²⁺ species. From quantitative analysis of the results of decomposition of both Pt 4f and Cl 2p peaks it was found that an atomic ratio of chlorine to platinum for Pt²⁺ species is (Cl) / (Pt) = 2 and that for Pt⁴⁺ species is (Cl) / (Pt) = 6 for both PtCl₄ and H₂PtCl₆·6H₂O doped polyacetylene. The C 1s peaks could be decomposed into two components separated by ca. 1 eV. The intensity of the higher binding energy component increased with increasing dopant concentration. These indicate that the platinum salt doping proceeds through charge transfer from polyacetylene chain to platinum atom resulting in a partial reduction from Pt⁴⁺ to Pt²⁺ state. The existence of PtCl₂ cluster on the surface of the doped polyacetylene film was supported by transmission electron microscopy and electron diffraction observations. These results indicate that a random distribution of the dopant along the macromolecular chain, and the charge per carbon atom in the metallic region of doped polyacetylene has been estimated to be 0.2 |e|. From these results the mechanism of the PtCl₃ and H₂PtCl₆·6H₂O doping process in polyacetylene is clarified as follows: Thus the dopant anion in polyacetylene is PtCl,^2? for both PtCl₄ and H₂PtCl₆·6H₂O doping.