Nanoengineering coaxial carbon nanotube-dual-polymer heterostructures.

We describe studies of new nanostructured materials consisting of carbon nanotubes wrapped in sequential coatings of two different semiconducting polymers, namely, poly(3-hexylthiophene) (P3HT) and poly(9,9'-dioctylfluorene-co-benzothiadiazole) (F8BT). Using absorption spectroscopy and steady-state and ultrafast photoluminescence measurements, we demonstrate the role of the different layer structures in controlling energy levels and charge transfer in both solution and film samples. By varying the simple solution processing steps, we can control the ordering and proportions of the wrapping polymers in the solid state. The resulting novel coaxial structures open up a variety of new applications for nanotube blends and are particularly promising for implementation into organic photovoltaic devices. The carbon nanotube template can also be used to optimize both the electronic properties and morphology of polymer composites in a much more controlled fashion than achieved previously, offering a route to producing a new generation of polymer nanostructures.

Mechanical and chemical bonding properties of ground state BeH2

The crystal structure, mechanical properties and electronic structure of ground state BeH2 are calculated employing the first-principles methods based on the density functional theory. Our calculated structural parameters at equilibrium volume are well consistent with experimental results. Elastic constants, which well obey the mechanical stability criteria, are firstly theoretically acquired. The bulk modulus B, Shear modulus G, Young's modulus E, and Poisson's ratio upsilon are deduced from the elastic constants. The bonding nature in BeH2 is fully interpreted by combining characteristics in band structure, density of states, and charge distribution. The ionicity in the Be-H bond is mainly featured by charge transfer from Be 2s to H 1s atomic orbitals while its covalency is dominated by the hybridization of H 1s and Be 2p states. The Bader analysis of BeH2 and MgH2 are performed to describe the ionic/covalent character quantitatively and we find that about 1.61 (1.6) electrons transfer from each Be (Mg) atom to H atoms.

Structural, mechanical, thermodynamic, and electronic properties of thorium hydrides from first-principles

We perform first-principles calculations of the structural, electronic, mechanical, and thermodynamic properties of thorium hydrides (ThH2 and Th4H15) based on the density functional theory with generalized gradient approximation. The equilibrium geometries, the total and partial densities of states, charge density, elastic constants, elastic moduli, Poisson's ratio, and phonon dispersion curves for these materials are systematically investigated and analyzed in comparison with experiments and previous calculations. These results show that our calculated equilibrium structural parameters are well consistent with experiments. The Th-H bonds in all thorium hydrides exhibit weak covalent character, but the ionic properties for ThH2 and Th4H15 are different due to their different hydrogen concentration. It is found that while in ThH2 about 1.5 electrons transfer from each Th atom to H, in Th4H15 the charge transfer from each Th atom is around 2.1 electrons. Our calculated phonon spectrum for the stable body-centered tetragonal phase of ThH2 accords well with experiments. In addition we show that ThH2 in the fluorite phase is mechanically and dynamically unstable.

Enhanced photoresponse from the ordered microstructure of naphthalocyanine-carbon nanotube composite film

Naphthalocyanine-sensitized multi-walled carbon nanotube (NaPc-MWNT) composites have been synthesized through the pi-stacking between naphthalocyanine (NaPc) and carbon nanotubes. The resultant nanocomposites were characterized with a scanning electron microscope (SEM), a transmission electron microscope (TEM), and by UV - vis absorption and photocurrent spectra. The long-range ordering was observed in the NaPc - MWNT composites by using a TEM. The enhancement in the absorption intensity and the broadening of the absorption wavelength observed in the composite films, which were due to the attachment of NaPc on the MWNT surface, is discussed based on the measured UV - vis absorption spectra. Furthermore, the photoconductivity of the poly( 3-hexylthiophene)(PAT6) - NaPc - MWNT composite film was found to increase remarkably in the visible region and broaden towards the red regions. These new phenomena were ascribed to the larger donor/acceptor (D/A) interface and the formation of a biconsecutive D/A network structure, as discussed in consideration of the photoinduced charge transfer between PAT6 and NaPc - MWNT.

Electrical transport through individual DNA molecules

A theoretical model is presented to describe electrical transport through individual DNA molecules. By contacting the proposed model with the experimentally measured data, a variety of valuable quantities are identified. The partially decoherent nature on the guanine-cytosine (GC) pairs of DNA is also elaborated in contrast to the completely incoherent hopping mechanism discussed in the context of charge transfer experiments. (C) 2001 American Institute of Physics.

Photostimulated luminescence of AgI clusters in zeolite-Y

AgI clusters in zeolite-Y (AgI/Y) were prepared by Ag+ exchange followed by reaction with NaI in solution. The formation of the clusters was determined by transmission electron microscopy and Auger electron spectroscopy. The clusters were uniform and even in size, 1.0-2.0 nm. The fluorescence spectrum of the clusters consists of two emission bands, which are attributed to AgI and Ag clusters, respectively. Photostimulated luminescence (PSL) is observed by stimulation at 675 or at 840 nm. The PSL spectrum of AgI/Y is consistent with the emission spectrum of Ag clusters and thus the PSL is considered to be caused by the charge transfer or carrier migration from the zeolite framework or from the AgI clusters to the Ag clusters. The appearance of PSL indicates that these materials may find application as a medium for erasable optical memory. (C) 1998 American Institute of Physics. [S0021-8979(98)02407-4].

Highly efficient and stable organic light-emitting diodes employing MoO3-doped perylene-3, 4, 9, 10-tetracarboxylic dianhydride as hole injection layer

We report highly efficient and stable organic light-emitting diodes (OLEDs) with MoO3-doped perylene-3, 4, 9, 10-tetracarboxylic dianhydride (PTCDA) as hole injection layer (HIL). A green OLED with structure of ITO/20 wt% MoO3: PTCDA/NPB/Alq(3)/LiF/Al shows a long lifetime of 1012 h at the initial luminance of 2000 cd/m(2), which is 1.3 times more stable than that of the device with MoO3 as HIL. The current efficiency of 4.7 cd/A and power efficiency of 3.7 lm/W at about 100 cd/m(2) have been obtained. The charge transfer complex between PTCDA and MoO3 plays a decisive role in improving the performance of OLEDs.

Optical properties and electrical bistability of CdS nanoparticles synthesized in dodecanethiol

We reported the synthesis of CdS semiconductor nanoparticles using a simple one-pot reaction by thermolysis of cadmium acetylacetonate in dodecanethiol. Optical measurements of the as-obtained CdS nanoparticles revealed that their optical properties were closely related to surface effects. Based upon the cocktail of poly (N-vinylcarbazole) (PVK) and CdS nanoparticles, a bistable device was fabricated by a simple solution processing technique. Such a device exhibited a remarkable electrical bistability, which was attributed to the electric field-assisted charge transfer between PVK and the CdS nanoparticles capped by dodecaethiol. The conduction mechanism changed from an injection-controlled current to a bulk-controlled one during switching from OFF-state to ON-state.

TCNQ电荷转移配合物薄膜的制备和表征

TCNQ电荷转移配合物作为一种新型有机材料具有很多特殊的物理、化学性质，由于它在材料研究方面的特殊贡献而成为研究热点。本论文在此领域的主要研究内容如下： 1. C18TCNQ和TMB电荷转移配合物LB膜的制备和表征 利用LB技术制备了TMB•C18TCNQ LB膜，与LB-Doping法相比省略了电子给体的液相掺杂步骤，简单、易行。研究结果表明，与TMB•C18TCNQ LB-Doping膜比较，LB膜的结构和表面形貌都发生了很大变化，LB膜中TMB和C18TCNQ的环面分别垂直于基底表面，脂肪烃链有向垂直于基底表面方向变化的趋势，5层LB膜的表面形貌是由许多堆积在一起的六边形片状微晶组成。所以，通过选择制备方法获得具有不同结构的配合物薄膜是可能的。 2. TMB•TCNQ和硬脂酸混合LB膜的制备和表征 利用LB技术组装了TMB•TCNQ和硬脂酸的混合LB膜。研究发现：本身没有两亲性的TMB•TCNQ可以通过硬脂酸的夹带作用转移到基底上。混合LB膜中硬脂酸与TMB•TCNQ是物理混合，很容易被除去，而且，可以根据实际应用需要来决定混合LB膜中硬脂酸的比例。 3. TMB•TCNQ和硬脂酸混合LB膜的热稳定性研究 利用变温红外光谱研究TMB•TCNQ和硬脂酸的混合LB膜的热稳定性。结果显示，混合LB膜中硬脂酸相变发生70-72 oC，TMB•TCNQ在142-144 oC发生反掺杂（分解）。 4. TCNQ和TMB电荷转移配合物自组装膜的制备和表征 利用layer-by-layer法制备了TMB•TCNQ自组装膜。结果表明，通过三氯锗丙酸的中介作用成功地将TMB和TCNQ组装到基底上并形成电荷转移配合物，电荷转移度约为0.48。 5. 利用红外光谱研究硬脂酸镉LB膜的亚晶胞堆积类型 利用红外光谱研究了沉积在CaF2基底上的1，3，5，7-层硬脂酸镉（CdSt）LB膜的亚晶胞堆积形式，以及交替沉积LB膜中氘代硬脂酸镉（d-CdSt）LB膜对1，2，3-层硬脂酸镉LB膜的亚晶胞堆积的影响。结果表明：1-层CdSt LB膜的亚晶胞是六方堆积，而厚度超过3层的CdSt LB膜的亚晶胞是正交堆积。只有相同种类的CdSt LB膜层与层之间的相互作用才会影响碳氢长链的堆积形式，而不同种类的CdSt LB膜和d-CdSt LB膜之间的相互作用不会影响碳氢长链的堆积形式，不论这种作用是亲水头基之间的还是疏水长链之间的。 6. 近红外光谱分辨率对定量分析的影响 利用近红外光谱分析方法建立了多组分混合物中对乙酰氨基苯酚和乙水杨胺的定量分析模型。研究发现，光谱分辨率对定量分析模型有重要影响，针对具体样品的特定组分，需要选择合适的光谱分辨率，进而获得最佳的定量分析结果。

电荷在液/液界面上的转移反应

针对目前液/液界面电分析化学存在的问题,从三方面研究了电荷在液/液界面上的转移反应.主要结果如下：1将含有氧化还原电对的水相支撑在铂盘电极表面,倒置后插入到有机相中,与参比电极和对电子极构成常规的三电极系统,实现了液/液界面上的电荷转移反应.2应用电化学方法详细探讨了中性载体加速离子在微、纳米管支撑的微、纳米级-水/1,2-二氯乙烷界面上转移反应的机理、热力学和动力学.3研究了手性联萘冠醚与手性酪氨酸在微、纳米管支撑的微、纳米级-水/1,2-二氯乙烷界面上的选择性络合过程的势力学和动力学.研究结果表明R型冠醚易于与D-酪氨酸络合.

应用单、双通道微／纳米管研究液／液界面上电荷转移反应

应用单、双通道微／纳米管研究液／液界面上电荷转移反应过程是目前液／液界面电化学和电分析化学领域的研究热点之一。本文简要地回顾了液／液界面电分析化学研究的发展历程，介绍了液／液界面电分析化学的基本理论和最新进展。围绕着单、双通道微／纳米管技术，分别研究了液／液界面上的电子转移、简单离子转移、加速离子转移和电荷祸合转移过程。主要结果如下：1．应用循环伏安法和微、纳米管系统地研究了二苯并十八冠六（DB18C6）加速二十种氨基酸在水／1，2一二氯乙烷（CE）界面上的转移反应，探讨了其反应机理，测量了其配合常数以及动力学常数。这一研究将对人们理解在生命体中氨基酸在载体蛋白的推动作用下越过生物膜的主动运送过程有较重要意义。2．利用循环伏安法研究了在直接支撑在双通道微米管管尖上的单微一液／液界面上的电荷转移反应，包括简单离子（四甲基按离子TMA+）转移、加速离子转移（DB18C6加速K+离子）和电子转移（二茂铁／铁氰化钾＋亚铁氰化钾体系）反应过程。此装置是目前为止最简单的可用于研究液／液界面上的电荷转移反应的装置之一。3．利用双通道微米管支撑双一微液／液界面作为产生／收集装置考察了液／液界面上的电子转移以及电荷祸合转移过程，包括电子一离子、离子一离子祸合 转移反应。该工作丰富了双通道微米管技术，并且可以通过产生／收集实验观察到一些强亲水或强憎水离子的直接转移的伏安曲线，测得它们在W/DCE界面上的转移式电位以及条件吉布斯转移能。4．初步探讨了双通道微米管作为产生／收集装置所涉及的理论及其传质过程，应用边界元法数值拟合了收集效率与管形之间的关系，通过加速离子转移实验对拟合结果进行了验证。该工作将对于今后进一步深入地应用双通道微米管技术研究液／液界面上的电荷转移反应具有一定的指导作用。

ELECTRONIC-STRUCTURES OF THE ALKALI-CONTAINING BUCKMINSTERFULLERENES (A-DELTA-C60) (A=LI,NA,K,RB,CS) AND THE HALOGEN-CONTAINING BUCKMINSTERFULLERENES (H-DELTA-C60) (H=F,CL,BR,I)

The geometrical parameters and electronic structures of C60, (A partial derivative C60) (A = Li, Na, K, Rb, Cs) and (H partial derivative C60) (H = F, Cl, Br, I) have been calculated by the EHMO/ASED (atom superposition and electron delocalization) method. When putting a central atom into the C60 cage, the frontier and subfrontier orbitals of (A partial derivative C60) (A = Li, Na, K, Rb, Cs) and (H partial derivative C60) (H = F, Cl) relative to those of C60 undergo little change and thus, from the viewpoint of charge transfer, A (A = Li, Na, K, Rb, Cs) and H (H = F, Cl) are simply electron donors and acceptors for the C60 cage resPeCtively. Br is an electron acceptor but it does influence the frontier and subfrontier MOs for the C60 cage, and although there is no charge transfer between I and the C60 cage, the frontier and subfrontier MOs for the C60 cage are obviously influenced by I. The stabilities DELTAE(X) (DELTAE(X) = (E(X) + E(C60)) - E(x partial derivative C60)) follow the sequence I < Br < None < Cl < F < Li < Na < K < Rb < Cs while the cage radii r follow the inverse sequence. The stability order and the cage radii order have been explained by means of the (exp-6-1) potential.

Photostimulated luminescence of silver clusters in zeolite-Y

Upon UV-irradiation at 254 nm, the photoluminescence of silver atoms in zeolite-Y decreases, meanwhile an absorption band shows up around 840 nm. By photostimulation at 840 nm, fluorescence of silver atoms is detected, which is called photostimulated luminescence, and the photoluminescence of silver atoms is increased slightly. These phenomena are attributed to the charge-transfer interaction between the zeolite framework and the entrapped silver atoms. (C) 1997 Published by Elsevier Science B.V.

Electrical bistability and negative differential resistance in diodes based on silver nanoparticle-poly(N-vinylcarbazole) composites

An electrically bistable device has been fabricated using nanocomposite films consisting of silver nanoparticles and a semiconducting polymer by a simple spin-coating method. The current-voltage characteristics of the as-fabricated devices exhibit an obvious electrical bistability and negative differential resistance effect. The current ratio between the high-conducting state and low-conducting state can reach more than 103 at room temperature. The electrical bistability of the device is attributed to the electric-filed-induced charge transfer between the silver nanoparticles and the polymer, and the negative differential resistance behavior is related to the charge trapping in the silver nanoparticles. The results open up a simple approach to fabricate high quality electrically bistable devices by doping metal nanoparticles into polymer.

Theoretical investigation on excitation, ionization and capture in H(1s, 2s)+H(1s, 2s) collisions

Cross sections of electron- loss in H( 1s)+ H( 1s) collisions and total collisional destruction of H( 2s) in H( 1s) + H( 2s) collisions are calculated by four- body classical- trajectory Monte Carlo ( CTMC) method and compared with previous theoretical and experimental data over the energy range of 4 - 100 keV. For the former a good agreement is obtained within di. erent four- body CTMC calculations, and for the incident energy Ep > 10 keV, comparison with the experimental data shows a better agreement than the results calculated by the impact parameter approximation. For the latter, our theory predicts the correct experimental behaviour, and the discrepancies between our results and experimental ones are less than 30%. Based on the successive comparison with experiments, the cross sections for excitation to H( 2p), single- and double- ionization and H- formation in H( 2s)+ H( 2s) collisions are calculated in the energy range of 4 - 100 keV for the. rst time, and compared with those in H( 1s)+ H( 1s) and H( 1s)+ H( 2s) collisions.