Full spin and spatial symmetry adapted technique for correlated electronic hamiltonians: Application to an icosahedral cluster

One of the long standing problems in quantum chemistry had been the inability to exploit full spatial and spin symmetry of an electronic Hamiltonian belonging to a non-Abelian point group. Here, we present a general technique which can utilize all the symmetries of an electronic (magnetic) Hamiltonian to obtain its full eigenvalue spectrum. This is a hybrid method based on Valence Bond basis and the basis of constant z-component of the total spin. This technique is applicable to systems with any point group symmetry and is easy to implement on a computer. We illustrate the power of the method by applying it to a model icosahedral half-filled electronic system. This model spans a huge Hilbert space (dimension 1,778,966) and in the largest non-Abelian point group. The C60 molecule has this symmetry and hence our calculation throw light on the higher energy excited states of the bucky ball. This method can also be utilized to study finite temperature properties of strongly correlated systems within an exact diagonalization approach. (C) 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012

Investigation of phase separation in bulk heterojunction solar cells via supramolecular chemistry

In this work, we have prepared two donor-acceptor-donor (D-A-D) pi-conjugated oligomers to investigate the effect of phase separation on the performance of bulk heterojunction (BHJ) solar cells. These charge transfer low band gap pi-conjugated oligomers (TTB and NMeTTB) were synthesized by Knoevenagel condensation of terthiophenecarbaldehyde and barbiturate appended pyran derivative. The thin film morphology of both the oligomers and along with electron acceptor 6,6]-phenyl-C60-butyric acid methyl ester (PC61BM) was investigated by atomic force microscopy (AFM) and transmission electron microscopy (TEM). The blend of NMeTTB and PC61BM thin film yield highly ordered thin film, whereas there was clear phase separation between TTB and PC61BM in thin film. The BHJ solar cell was fabricated using a blend of NMeTTB and TTB with PC61BM acceptor in 1:1 ratio as active layer, and a power conversion efficiency of 1.8% was obtained. This device characteristic was compared with device having TTB:PC61BM as active layer, and large difference is observed in photocurrents. This poor performance of TTB in BHJ devices was attributed to the difference in the nanoscale morphology of the corresponding derivatives. We rationalize our findings based on the low charge carrier mobility in organic field-effect transistors and miscibility/phase separation parameter of binary components (oligomers and PC61BM) in the active layer of bulk heterojunction solar cells.

Synthesis of carbon 'onions' in water.

The fabrication of carbon nanomaterials usually calls for expensive vacuum systems to generate plasmas and yields are disappointingly low. Here we describe a simple method for producing high-quality spherical carbon nano-'onions' in large quantities without the use of vacuum equipment. The nanoparticles, which have C60 cores surrounded by onion-like nested particles, are generated by an arc discharge between two graphite electrodes submerged in water. This technique is economical and environmentally benign, and produces uncontaminated nanoparticles which may be useful in many applications.

C_(60)自组装单分子膜的制备及其摩擦特性

利用胺基与C60 分子的加成反应 ,在 3 胺基丙基 三乙氧基硅烷 (APS)的自组装单分子膜 (SAMs)表面上成功的制备了与基底化学键结合的C60 SAMs。其表面水接触角约为 76° ,膜厚约为 1.15nm ,AFM形貌像显示其表面光滑、均匀 ,基本不含缺陷。摩擦学结果表明 ,APS自组装单分子膜由于其分子链短 ,膜的有序性差 ,表面颗粒聚集物及“针孔”等缺陷多 ,而不具有润滑作用。当在其上形成C60 单分子层膜后 ,表现出优异的摩擦学性能 ,摩擦系数约为 0 .0 9～ 0 .13,在给定实验条件下抗磨损寿命大于 10 0 0 0次 ,有望作为微型机械的边界润滑材料使用。

Charge and spin transport in graphene devices

170 p.

Dieta hiperlipídica compromete a morfologia e alguns parâmetros funcionais de testículo e tireóide de ratos jovens

Estudos demonstram que o sobrepeso e a obesidade podem afetar a fertilidade masculina. Além disso, a função tireóidea também esta associada à alteração da função testicular, entretanto, o papel fisiológico dos hormônios tireoideanos na regulação do sistema reprodutor masculino ainda não esta claro. Aos 21 dias de idade, ratos machos receberam uma dieta manipulada contendo diferentes concentrações de óleo de soja até a idade de 30 e 60 dias, os grupos controle (C30, n=6 e C60, n=6), receberam dieta contendo 7% e os grupos hiperlipídicos (HL30, n=6 e HL60, n=6), receberam dieta contendo 19% deste óleo. Ao final de cada período, os animais foram avaliados por DXA (Absorciometria de Raios-x em Duas Energias) e sacrificados por exsanguinação. Para avaliar alterações na estrutura dos tecidos testicular e tireóideo, foram realizados a morfologia e a estereologia. No plasma, para determinar os perfis bioquímico e hormonal, foram avaliados, triglicerídeos, colesterol total, HDL-colesterol, VLDL, glicose e albumina, por métodos colorimétricos e leptina, insulina, T4, T3, TSH e testosterona por radioimunoensaio (RIE). Para evidenciar a expressão de receptor androgênico (AR) em testículos, foi realizado imunomarcação, com anti-AR. Durante todo o período experimental, foram analisados a massa corporal, a ingestão alimentar e o comprimento corporal, os quais permaneceram inalterados. No grupo HL, a massa magra foi menor aos 30 dias, já a gordura corporal total foi maior no mesmo grupo, aos 60 dias nenhuma diferença foi notada entre os grupos. No grupo HL30 não houve diferença quanto à massa dos tecidos, já no grupo HL60, o peso do epidídimo, fígado e gordura visceral mantiveram-se aumentados. No grupo HL30 não houve diferença em relação ao perfil bioquímico, já no grupo HL60, os níveis de glicose, mantiveram-se altos. Quanto às dosagens hormonais no grupo HL30, TSH e leptina estiveram aumentados e T3 reduzido, e no grupo HL60, T3 e leptina estiveram aumentados. Os dados morfométricos e estereológicos de testículo no grupo HL30 mostram aumento no número de túbulos seminíferos e da densidade de comprimento (Lv), já no grupo HL60, há redução no número de túbulos seminíferos e no diâmetro do mesmo. Quanto à expressão de receptor androgênico nas células testiculares, não parece haver diferença entre os grupos independente da idade de consumo da dieta. A dieta hiperlipídica promoveu alterações metabólicas aos 30 dias e modificações na morfologia do tecido tireoidiano e testicular em ambas as idades, o que indica reflexos na função reprodutora.

Calculation of the electronic structure of carbon films using electron energy loss spectroscopy.

The detailed understanding of the electronic properties of carbon-based materials requires the determination of their electronic structure and more precisely the calculation of their joint density of states (JDOS) and dielectric constant. Low electron energy loss spectroscopy (EELS) provides a continuous spectrum which represents all the excitations of the electrons within the material with energies ranging between zero and about 100 eV. Therefore, EELS is potentially more powerful than conventional optical spectroscopy which has an intrinsic upper information limit of about 6 eV due to absorption of light from the optical components of the system or the ambient. However, when analysing EELS data, the extraction of the single scattered data needed for Kramers Kronig calculations is subject to the deconvolution of the zero loss peak from the raw data. This procedure is particularly critical when attempting to study the near-bandgap region of materials with a bandgap below 1.5 eV. In this paper, we have calculated the electronic properties of three widely studied carbon materials; namely amorphous carbon (a-C), tetrahedral amorphous carbon (ta-C) and C60 fullerite crystal. The JDOS curve starts from zero for energy values below the bandgap and then starts to rise with a rate depending on whether the material has a direct or an indirect bandgap. Extrapolating a fit to the data immediately above the bandgap in the stronger energy loss region was used to get an accurate value for the bandgap energy and to determine whether the bandgap is direct or indirect in character. Particular problems relating to the extraction of the single scattered data for these materials are also addressed. The ta-C and C60 fullerite materials are found to be direct bandgap-like semiconductors having a bandgaps of 2.63 and 1.59eV, respectively. On the other hand, the electronic structure of a-C was unobtainable because it had such a small bandgap that most of the information is contained in the first 1.2 eV of the spectrum, which is a region removed during the zero loss deconvolution.

生命体能量代谢过程中的电子传递与光合作用中电子传递反应的化学模拟的ESR研究

本文采用电子自旋共振ESR方法，结合运用自旋捕捉技术（Spin Trapping-ESR）和时间分辨手段(TRESR)，针对某些与生命能量代谢体系电子传递及其化学模拟反应的研究相关的几个重要问题(包括高等植物光系统II颗粒内超氧阴离子自由基(O2-)的产生机制、光合作用模型体系电子传递和跨膜电子传递反应动力学、传统中药有效成分提取物抗氧化分子机理与构效关系），从分子设计、实验方法、分子结构理论、反应机理与动力学分析等几个角度进行了较为系统的探索性研究，并获得以下几点新颖的研究成果： 1．光系统II颗粒内光抑制过程中O2-生成的分子机制 (1)．首先，发展了新Spin Trapping-ESR技术，研制一系列性能优良的新型磷酰基取代的吡咯啉类活性氧自旋捕捉剂，并通过对比研究其捕捉性能，证明磷酰基取代的吡咯啉类捕捉剂比常用的DMPO捕捉剂的捕捉能力强、速度快，自由基加合物稳定性高，适合于光系统II体系中活性氧的研究。 (2)．在PSII颗粒的光抑制过程中成功地检测到了O2-，并探讨了影响O2-产生的诸多因素。包括氧分子的浓度、1O2增强剂与淬灭剂、pH值效应、电子传递链阻断剂的影响。首次提出了O2-生成的分子机制：PSII颗粒中产生的O2-是光系统II中反应中心产生的1O2与次级电子受体QA形成的质子化半醌自由基反应的产物。此外，设计了一套化学模拟体系，进一步证明了02-的生成的分子机制。 2. 中国传统性中药的酚类提取物抗氧化剂的抗氧化分子机理与构效关系研究 用理论计算与实验结合的手段，研究了酚类抗氧化剂与02的反应。探讨了酚类抗氧化物的分子结构与其抗氧化活性的构效关系，为评价抗氧化剂的抗氧化能力提供了一定的依据。 3．有关光合作用模型体系电子传递和跨膜电子传递反应动力学的探索性基础研究 (1)．对原有的电子自旋共振谱仪进行改造，自行设计并研制一套时间分辨ESR装置，时间分辨率达到准微秒级。 (2)．利用时间分辨ESR装置，对C60及其环加成衍生物分子间和分子内光诱导电子转移反应的自由基复合过程动力学进行了研究，从分子结构角度分析了影响电荷分离态稳定性的因素。 (3)．初步探讨了TPP／DODAC与HA／DODAC两种单层囊泡间的光诱导电子转移反应，获得了长寿命的电荷分离态，为光合作用模拟提供有价值的模型。 (4)．通过对比研究mes-卟啉Ⅱ／苯醌／CH。OH的化学诱导动态核自旋态极化( CIDNP)和ESR波谱，提出一个激发态苯醌与质子给体间的光诱导氢转移自由基反应新机理。

环糊精富勒烯－富勒烯衍生物的电化学及电催化研究

在本工作中，首次研究了β-环糊精/C60以及富勒烯衍生物在有机溶剂中的电催化性能，成功地实现了α-、β-环糊精/C60以及富勒烯衍生物在水溶液中的电化学，并探讨了催化反应的机理以及α-、β-和γ-环糊精/C60的电化学行为产生差异的原因，主要的研究结果如下： 1．α-、β-和γ-环糊精/C60超分子包合物在DMF中的电化学行为很相似，可以显示出三对可逆的氧化还原峰，其半波电位在-0.27, -0.73, -1.31V vs. SCE左右, 这与C60本身在DMF中的半波电位近乎相同(-0.26, -0.72, -1.31 V vs. SCE)，说明环糊精对于C60在DMF中的电化学影响不大。γ-环糊精/C60在水溶液中可以给出可逆的电化学信号，但是α-、β-环糊精/C60在水溶液中却没有电化学响应，这说明α-、β-环糊精/C60在水溶液发生了聚集，且聚集的程度要大于γ-环糊精/C60。 2．β-环糊精/C60以及富勒烯的衍生物都可以在DMF中显示出电催化还原1,2-二碘乙烷的作用，这说明包和以及衍生化之后C60同样还具有电催化脱卤的作用。 3．借助于表面活性剂的作用，成功的实现了α-、β-环糊精/C60以及富勒烯衍生物在水溶液中的电化学，这为其在电分析化学方面的应用提供了可能。

具有负微分电阻和存储特性的有机二极管研究

作为有机电子器件中的重要组成部分，具有负微分电阻和存储特性的有机二极管吸引了越来越多的关注。虽然目前这方面的研究已经取得了一定进展，但产生负微分电阻和存储特性的机制以及器件的存储稳定性等问题仍亟待解决。因此深入开展具有负微分电阻和存储特性的有机二极管的研究具有重要意义。 本论文研究了一系列具有负微分电阻和存储特性的有机二极管，并对其工作机制进行了深入探讨，为具有负微分电阻和存储特性的有机二极管的进一步研究奠定了基础。 1、制备出了一系列具有负微分电阻特性的有机小分子二极管。研究发现，基于CuPc 有机半导体的有机二极管表现了可重复的负微分电阻特性，而这种负微分电阻特性易受所用电极、有机膜蒸镀速率、测试速率和所加负向电压等因素的影 响。机理研究表明，该器件的负微分电阻特性是由于CuPc 内存在的深能级陷阱对电荷的捕获和释放的结果。而基于Alq3 等多种有机半导体的有机二极管也表现了良好的可重复的负微分电阻特性。机理研究表明，该类器件的负微分电阻特性是由于在有机层内少数载流子的注入和积累引起的纳米导电丝的结果，电荷的大量积累导致了导电丝通道的形成，使器件表现了高的导电态；而大的电压又及易使导电丝通道消失，使器件表现了低的导电态，电流降低。 2、开发出了一系列具有可重复负微分电阻和存储特性的掺杂聚合物有机二极管。研究发现，合适的共掺杂可显著提高器件的存储性能，基于1,4-dibenzyl C60和ZnPc 掺杂PS 的器件可循环上百万次，开关电流比超过了两个数量级，电流维 持时间超过了三个小时，其负微分电阻和存储特性可以用ZnPc 的氧化及1,4-dibenzyl C60 和ZnPc 之间的电荷转移很好地给予解释。而金纳米粒子掺杂PVK的器件也表现了很好的存储特性，循环次数超过了25 万次，开关电流比超过了100 倍，其存储过程被认为是由于金纳米粒子电荷俘获的结果。 3、通过控制有机/金属界面层处有机分子的蒸镀速率，制备出了基于并五苯有机半导体的写一次读多次存储有机二极管。该器件表现出了高的开关电流比（最大可达5000）和良好的数据维持时间（超过了240 小时），界面偶极层的形成和破坏所导致的注入势垒的改变很好地解释了该器件写一次读多次的开关电流转变过程。通过热退火控制PVK 聚合物薄膜的表面形态也制备出了具有写一次读多次存储特性的聚合物二极管，该器件同样表现了良好的开关存储特性，而且该器件可以用更简单的旋涂方法制备，进一步简化了器件制备工艺。

Raman Spectroscopy of Irradiation Effect in Three Carbon Allotropes Induced by Low Energy B Ions

Irradiation efect in three carbon allotropes C60, diamond and highly oriented pyrolytic graphite (HOPG) induced by 170 keV B ions, mainly including the process of the damage creation, is investigated by means of Raman spectroscopy technique. The diferences on irradiation sensitivity and structural stability for C60, HOPG and diamond are compared. The analysis results indicate that C60 is the most sensitive for B ions irradiation,diamond is the second one and the structure of HOPG is the most stable under B ion irradiation. The damage cross sections ? of C60, diamond and HOPG deduced from the Raman spectra are 7.78×10−15 , 6.38×10−15 and1.31 × 10−15cm2, respectively.

纳秒激光诱导C_(60)分子碎裂中轻碎片离子C_n~+(n<30)的产生机理研究

采用飞行时间质谱计测量了纳秒激光诱导C60分子碎裂中轻碎片离子Cn+(n≤11)的初始平均动能,结果显示轻碎片离子具有相同的初始平均动能(约为0.34 eV),并且该动能在一定范围内不随激光通量的变化而明显改变.结合前人的实验结果,对纳秒激光诱导C60分子碎裂中轻碎片离子Cn+(n<30)的主要产生模式作了新的阐述,即C60分子级联发射15个C2分子和一个电子形成自身不稳定的C3+0离子,在皮秒时间尺度内C3+0离子的笼形结构塌陷,进而轻碎片离子产生.

GeV能量的Fe离子在C_(60)薄膜中的辐照效应研究

利用傅立叶转换红外光谱和Raman谱仪分析了0.98GeV的Fe离子在电子能损Se为3.5keV/nm时,不同辐照剂量(5×1010—8×1013ions/cm2)下,在C60薄膜中引起的辐照损伤效应。分析表明,Fe离子辐照引起了C60分子的聚合与损伤。在辐照剂量达到一中间值1×1012ions/cm2,C60分子的损伤得到部分恢复,归因于电子激发引起的退火效应。通过对Raman数据的拟合分析,演绎出Fe离子辐照在C60材料中形成的潜径迹截面或引起损伤的截面约为1.32×10-14cm2。

C_(60)薄膜在快重离子辐照下的结构稳定性研究

用傅立叶变换红外光谱、X射线衍射谱、X射线光电子谱和拉曼散射技术分析了能量为GeV量级的S、Fe、Xe、和U离子,以及120keV的H离子在室温下辐照多层堆积C60薄膜的结构稳定性,即快重离子在C60薄膜中由高密度电子激发引起的效应,主要包括C60分子的聚合、分子结构的损伤、新的高温-高压相的形成和晶态向非晶态的转变。

高能重离子辐照制备碳氮化合物材料研究

室温下,先用100—120keV的N离子注入类金刚石薄膜和石墨中,注入剂量5×1017至5×1018 cm-2,再用高能Xe、U、C60离子分别辐照注氮后的样品,然后用显微FTIR和Raman、XRD/XPS等手段进行分析表征,研究了实验样品中由辐照引起的新化学键和新相的产生。实验结果显示,高能重离子辐照可在所有样品中产生大量的CN键,高N浓度和大密度能量沉积导致sp3/sp2键比率的增加以及形成α-和β-C3N4必需的N-sp3C键的量的增加。C60离子辐照在注氮石墨样品中引起了ta-C、N=sp2C和N-sp3C键的形成;而高能离子辐照在注氮类金刚石薄膜样品中产生了α-和β-C3N4晶态夹杂物,其尺寸在1.4—3.6nm之间。