C_(60)富勒稀分子的电子传输特性

采用扩展的Hückel方法与格林函数方法,分析了双Au电极作用下C60富勒稀分子的电子结构与电子输运特性。结果表明,C60富勒稀分子与Au电极“接触”后,其分子轨道能级发生了较大的变化,HOMO,LUMO间的能隙显著减小;C60与Au电极之间的结合既有共价键的成分,又有离子键的成分;C60富勒稀分子的电压-电导率曲线以及伏安曲线表现出了微妙的量子特性。     

富勒烯C74分子的电子传导特性

采用密度泛函理论和非平衡Green函数的Tight-Binding方法,对C74富勒烯分子及其连接Au电极构成的C74分子器件的电子结构和电子传导特性进行了理论研究.得出了电子通过C74分子器件的传输谱、态密度及C74分子的分子轨道能级,结果显示C74分子的传输谱和态密度有明显的对应性,且电子的传导概率随电子的入射能量...     

钴酞菁分子结中电子输运性质的理论研究

利用半经验Extended Hueckel分子轨道方法和格林函数方法来研究钴酞菁(CoPc)分子结的电子输运性质。计算结果表明分子结(器件)电子输运性质对分子本身的电子结构、电极不同晶向表面、分子与电极间耦合强度、其界面的几何构型，对电极表面接触分子的末端原子的种类等诸多方面都有不同程度的依赖关系。对于CoPc这类弱耦合分子结而言，可以通过测量其I-V曲线来研究分子本身的电子结构。本文的理论方法不仅可以用来描述分子器件的电子输运行为，还能用来研究扫描探针显微镜体系的伏安特性和扫描隧道谱。     

C20富勒烯分子及C±20富勒烯离子特性分析与比较

以C1对称C20富勒烯分子为模型,在Gussion03上做了结构优化、频率计算以及自然键轨道理论(NBO)计算,并在同样的方法和基组下分别对C20分子得失一个电子的情况做了计算,并进行了分析和比较.结果表明:C1对称C20富勒烯分子不稳定,易于得失电子而以离子形式存在.C20,C+20,C-20三者的能量关系为:EC20＞EC+20＞EC-20,C20更容易得到电子,成为C-20.三种分子的能隙关系为:ΔEC20＞ΔEC+20＞ΔEC-20,说明C20分子带电后电子性质更活泼.C+20富勒烯离子的杂化方式最接近sp2杂化     

C20富勒烯分子及C±20富勒烯离子特性分析与比较

以C1对称C20富勒烯分子为模型,在Gussion03上做了结构优化、频率计算以及自然键轨道理论(NBO)计算,并在同样的方法和基组下分别对C20分子得失一个电子的情况做了计算,并进行了分析和比较.结果表明:C1对称C20富勒烯分子不稳定,易于得失电子而以离子形式存在.C20,C+20,C-20三者的能量关系为:EC2...     

缺陷富勒烯C20分子器件的电子输运研究

运用基于第一性原理密度泛函理论（DFT）的非平衡格林函数（NEGF）方法,对正十二面体富勒烯C20分子及其有缺陷的C20分子进行了电子输运性质的研究。通过计算得出了模拟的电子透射谱线。通过比较不同缺陷的分子的传导特性,获得了C20的电子输运特点。通过比较发现,几乎所有情况下缺陷器件的传输概率在电子能量大于0．52eV时都大约是10^-10,几乎没有电子透过,所以这种器件可以作为一种响应很好的电子开关;而器件中原子的缺失并没有造成电子传输路径的中断,在大多数情况下,在原子缺失处反而产生更多的传输路径,通路的增多使得器件传输能力得到提高。     

缺陷富勒烯C_20分子器件的电子输运研究

运用基于第一性原理密度泛函理论(DFT)的非平衡格林函数(NEGF)方法,对正十二面体富勒烯C20分子及其有缺陷的C20分子进行了电子输运性质的研究。通过计算得出了模拟的电子透射谱线。通过比较不同缺陷的分子的传导特性,获得了C20的电子输运特点。通过比较发现,几乎所有情况下缺陷器件的传输概率在电子能量大于0.52eV时都大约是10-10,几乎没有电子透过,所以这种器件可以作为一种响应很好的电子开关;而器件中原子的缺失并没有造成电子传输路径的中断,在大多数情况下,在原子缺失处反而产生更多的传输路径,通路的增多使得器件传输能力得到提高。     

C_(20)富勒烯分子及异构体的密度泛函方法研究

为更好地研究小富勒烯分子的形成机理和存在方式以及更好地了解它们的各种物理化学性质,利用密度泛函理论,在B3LYP/6-31G*方法和基组水平下对分属D2h、C2h、C2、Ci和D3d对称群的C20富勒烯分子及异构体进行了结构优化、频率计算和自然键轨道分析,得到了它们的能量、能隙、振动光谱、电子结构特性。结果表明:C20分子具有明显的离域特征,这是它虽然违反五元环隔离规则却能够稳定存在的原因;所讨论的C20异构体的能量和能隙差别微小,属于等能体,其稳定性顺序为C2>D2h>D3d>Ci>C2h;各异构体的轨道杂化特征和电子转移特征也基本一致。研究发现红外光谱不适宜用来鉴别C20富勒烯分子的对称性,而喇曼光谱可能将D3d对称群的C20分子辨认出来。     

PVK/C_(60)组合薄膜荧光的光辐照效应

富勒烯分子具有较高的电子亲和势，因而易于接收电子，而一些有机材料及高分子材料分子则易于失去电子，当这两种材料组合在一起时，在其中可以产生激发传递及电行转移效应，通过吸收、荧光、光谱等测量，可以研究这种电行转移（D－A）体系的有关过程。我们采用物理喷束淀积（PJD）方法制备了纯C60纯PVK（聚乙烯咔唑）、PVK／C60的混合膜及多层膜。这种方法具有设备简单、成膜性能好及控制简易等优点，特别适宜于蒸镀量少的稀有样品。当激光照射在PJD法制备得的薄膜上时，可以探测到薄膜中分子所发射的荧光，而采用锁模皮秒激光及条…     

C_(20)分子与C_(20)~±离子的电子及光谱特性分析比较

利用Gaussion98对C20分子及C2±0离子进行了结构优化、频率计算,得到了没有虚频的稳定结构。在此基础上对C20分子及C20±离子的电子结构和振动光谱进行了比较分析。自然键轨道理论(NBO)分析表明:三者都具有离域特性,C20分子及C20-离子的电子都向部分原子转移,它们的共价键是带有部分离子性质的共价键。对三者的光谱计算显示C20+离子几乎没有红外吸收特性,而喇曼光谱较容易将C20分子和C20±离子分辨开来。红外光谱可以将C20-离子与C20+离子区分开。     

An amphiphilic C60 penta-addition derivative as a new U-type molecular rectifier

Unimolecular rectification behavior of a known amphiphilic fullerene derivative, 1,4,11,15,30-pentakis(4-hydroxyphenyl)-2H-1,2,4,11,15,30-hexahydro-[60]fullerene, (4-HOC₆H₄)₅HC₆₀ (referred to here as the fullerene pentapod), is reported. The HOMO and LUMO energy levels of the pentapod were determined by density functional theory calculations (B3LYP/6-31G⁷). It was found that the HOMO of the donor moiety and the LUMO of the acceptor are in the same fullerene cage, quite unlike the fullerene derivatives so far reported as molecular rectifiers. The molecule formed a stable Langmuir-Blodgett film at the air–water interface. Characterization of the film indicated that it constitutes mostly a monolayer of molecules with the hydrophobic C₆₀ moiety pointing upwards. The LB film was transferred over Au(1 1 1) substrate and electrical conductivity of the film was measured by conducting atomic force microscopy. An asymmetric electrical rectification behavior was observed in the voltage range of ±1.0 V to ±2.0 V. Beyond a bias voltage of ±2.0 V, rectification ratio decreased steadily, until at ±2.5 V the current–voltage curve became symmetric. The observed electrical rectification behavior was ascribed to resonant electron tunneling between the Fermi level of the electrode and the molecular orbital levels of the fullerene pentapod. Charge transport in the preferred direction under a suitable applied bias was facilitated due to efficient electronic interactions of the molecular orbitals through a combined effect of homo- and peri-conjugation. This constitutes a new class of donor–acceptor system and a step forward in the field of molecular electronics.     

弯曲锯齿型单壁碳纳米管的电子学特性研究

采用密度泛函数的B3LYP和非平衡格林函数方法分别对锯齿型单壁(5.0)碳纳米管(SWCNT)及外接Au电极后的电子结构和电子传输特性进行了理论研究。另外用同样的方法,对弯曲的SWCNT和外接Au电极的器件的电子结构、电子传输特性进行了研究。比较发现,两个模型在HOMO状态下的电子分布主要集中在两端,总的传输性能比LUMO状态下要弱。虽然两种模型具有相似的能带结构,但弯曲SWCNT的能隙较未弯曲SWCNT的能隙要小。另外两种模型的传输谱与态密度有着明显的对应性,但弯曲的碳纳米管的传输谱较未弯曲碳纳米管的传输谱峰值大很多,说明弯曲过后SWCNT的电子输运性能要远优于未弯曲SWCNT。     

Mixed C60/C70 based fullerene acceptors in polymer bulk-heterojunction solar cells

Different mixtures of identically substituted C60 and C70 based fullerens have been used as acceptors in three polymer:fullerene systems that strongly express various performance limiting aspects of bulk heterojunction solar cells. Results are correlated with, and discussed in terms of e.g. morphology, charge separation, and charge transport. In these systems, there appears to be no relevant differences in either mobility or energy level positions between the identically substituted C60 and C70 based fullerenes tested. Examples of how fullerene mixtures influence the nano-morphology of the active layer are given. An upper limit to the open circuit voltage that can be obtained with fullerenes is also suggested.     

Dark current and photovoltage models on the formation of depletion region in C60/NPB organic heterojunctions

We establish quantitative models on the formation of depletion regions in organic photodiodes (OPD) based on fullerene/N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′-biphenyl-4,4′-diamine (C₆₀/NPB) heterojunctions. The models describe the relation of dark current and open-circuit voltage to the deposited thickness of C₆₀ or NPB. Interfacial electronic structures, such as built-in potential, the charge density, the minimized thicknesses of completely developed depletion regions and the energy level bending on each side of the heterojunction were derived from the fitting model. Also, we observed a shift of depletion region from NPB to C₆₀ due to the relative change of charge density under illumination. The device performance proved the reasonability of the models. This paper provides a universally applicable method to probe the interfacial information of organic semiconductors.     

Non-conventional metallic electrodes for organic field-effect transistors

We study micrometer-sized organic field-effect transistors with either Pd or NiFe metallic electrodes. Neither of these materials is commonly used in organic electronics applications, but they could prove to be particularly advantageous in certain niche applications such as organic spintronics. Using organic semiconductors with different carrier transport characteristics as active layer, namely n-type C60 fullerene and p-type Pentacene, we prove that Pd (NiFe) is a very suitable electrode for p- (n-) type semiconductors. In particular, we characterized devices with channel lengths in the order of the micrometer, a distance which has allowed us to evaluate the electronic behavior in a regime where the interfacial problems become predominant and it is possible to reach elevated longitudinal electric fields. Our experimental results agree well with a simple model based on rigid energy levels.     

Structure and optical properties of C60 films on polymer substrates

The results of investigations of the structure and optical properties of films of fullerene C₆₀ are reported. The films were obtained by vacuum thermal evaporation on substrates from heat-resistant polymers (polyacrylonitrile and cyclized polyacrylonitrile in composition with polyimide). The structure of C₆₀ films was determined by X-ray diffractometry. In all diffraction patterns of fullerene films, their structure manifests itself through reflections from the (111), (220), and (311) planes. Cubic C₆₀ films were obtained by fullerene deposition at substrate temperatures as high as 200°C. Atomic force microscopy of the film surface revealed the existence of a laminated structure. The infrared (IR) transmission spectra are indicative of the presence and constancy of the position of characteristic bands of C₆₀ (527, 576, 1183, and 1428 cm^?1) for all fullerene films. The investigation of photoluminescence of fullerene films revealed bands whose energy position both exceeded typical values for molecular C₆₀ or fell below these values. This circumstance is caused by the interaction between the electron π systems of C₆₀ and the polymer substrate at the heterointerface, as well as by the photopolymerization reaction of fullerene under the effect of high-energy laser radiation and by the emergence of trap centers in the films.     

A label-free biosensor based on organic transistors by using the interaction of mercapto DNA and gold electrodes

Organic thin-film transistors (OTFTs) with Au electrodes were successfully used as transducers for label-free deoxyribonucleic acid (DNA) sensors. Single-strand DNA (ssDNA), perfectly-matched double-strand DNA (dsDNA) and mis-matched DNA were immobilized on the surface of the source/drain electrodes of three OTFT devices respectively. The ssDNA molecules with mercapto group (–SH) can be well immobilized on the surface of Au electrode by chemical bond between –SH and Au atom. According to the significant difference in channel current, which was attributed to the changed contact resistances by introducing different DNA molecules on Au electrode, ssDNA, matched-dsDNA and mismatched-dsDNA were differentiated successfully in the experiments. The results may provide a promising approach for detecting DNA specificity and hybridization with label-free.     

A Novel Three-Dimensional Packaging Method for Al-Metalized SiC Power Devices

A novel three-dimensional packaging method for Al-metalized SiC power devices has been developed by means of Au stud bumping technology and a subsequent vacuum reflow soldering process with Au-20Sn solder paste. Al-metalized electrodes of a SiC power chip can be robustly assembled to a direct bonded copper (DBC) substrate with this method. The bump shear strength of a Au stud bump on an Al electrode of a SiC chip increased with bonding temperature. The die shear strength of a SiC chip on the DBC substrate increased with the number of Au stud bumps which were preformed on the Al electrode. The bonded SiC-SBD chips on a DBC substrate were aged at 250 ${^circ}{rm C}$ in a vacuum furnace and the morphologies, die shear strength and electrical properties were investigated after a certain aging time. After 1000 h aging at 250 ${^circ}{rm C}$, the electrical resistance of the bonded SiC-SBD chips only increased about 0.4%, the residual die shear strength was much higher than that of the IEC749 (or JEITA) standard value, and little morphological change was observed by a micro-focus X-ray TV system. Very little diffusion between Au stud bumps and Au-20Sn solder was observed by scanning electron microscope (SEM) equipped with an energy dispersed X-ray analyzer (EDX). Intermetallic compounds (IMC) evolved at the interface of chip/solder and chip/Au stud bumps after 1000 h aging at 250 ${^circ}{rm C}$. With this method, power devices with Al bond pads can be three-dimensionally packaged.