表面修饰调控单层ZnS电子结构和光学性质

为了研究H,F修饰单层ZnS对其电子结构和光学性质的影响,建立了H修饰、F修饰以及H-F共同修饰单层ZnS晶体结构。采用基于密度泛函理论(DFT)的第一性原理平面波超软赝势方法,计算了各二维材料的晶体结构、稳定性、电子结构和光学性质。计算结果表明,单层ZnS是一种准平面结构,经过修饰后则转变为褶皱六元环结构,且修饰后的ZnS具有很好的稳定性。电子结构表明,单层ZnS是一种直接带隙半导体,其计算能隙为2.625eV,H修饰ZnS会导致其能隙增大,且转变为间接带隙半导体,F修饰和H-F共修饰则使得ZnS能隙不同程度减小。载流子有效质量结果显示,单层ZnS为轻空穴重电子型半导体,H或F修饰会导致半导体的空穴有效质量显著增大,电子有效质量的变化则相对较小。光学性质表明,H,F修饰会导致ZnS的吸收边发生蓝移,其中F修饰,H-F共修饰(H与Zn同侧,F与S同侧)ZnS对短中波紫外线的吸收效果明显增强,表明其在未来光电子领域有着广阔的应用前景。     

硅基半导体光电子材料的第一性原理设计

具有特定功能的半导体材料的计算设计，是计算材料科学的一个重要研究领域．由于半导体的诸多性质取决于价带顶和导带底的电子态及其中的载流子分布，因此带隙的大小和能带极值的对称性便成为半导体材料设计最受关注的问题．为了进一步解决硅基光电子集成（OEIC）技术发展的瓶颈．设计具有直接带隙特性的硅基新材料并使其成为有效的光发射体，是一项富有挑战性的工作．本文在分析大量半导体能带结构的基础上，给出类sp系列半导体由间接带隙过渡到直接带隙的主要物理机制，并以对称性概念、芯态效应和电负性差效应为基础，提出一种新的直接带隙半导体材料设计方案．根据这个方案所表达的设计思想，我们对当前十分受关注的硅基光发射材料进行了计算设计．结果发现，用VI族元素在硅生长时进行周期性插层的、具有正交和四角点群对称性的人工微结构材料VIA／Sim／VIB／Sim／VIA具有直接带隙特性．其中当m=5或奇数时，材料有四角结构对称性，而m=6或偶数时是正交结构对称性．VI“。。是在〈001〉生长方向生长的单层VI族元素．这类材料的优点在于可自然地与硅实现晶格匹配，与微电子技术相兼容，并可较容易的用现行的MBE、MOCVD或UHV-CVD生长方法实现．预期这类新材料及其相应器件的研制开发．将大大开拓全硅OEIC和硅光子集成（PIC）技术的进一步发展．     

孔雀绿对电子辐照响应研究

一种以聚乙烯醇缩聚物为基质,以多芳氨基甲烷类化合物(隐色孔雀绿)为染色物质和卤代物为协同剂制成的辐射变色膜.经电子辐照后其颜色由无色透明变为绿色.辐照后吸收光谱显示其最强吸收峰出现在629 nm附近.研究表明：吸光度响应与电子注量成线性关系,电子能量和分次辐照对其有明显影响,在某注量率范围内吸光度存在辐照后效应,24 h后趋于稳定,且膜厚与响应成正相关性.该体系辐射变色膜可作为电子束的辐照变色薄膜剂量计.     

Zn-Ti-O/FTO复合薄膜的选择降解

采用溶胶-凝胶法在氟掺杂氧化锡(fluorine-doped tin oxide,FTO)导电玻璃上制备Zn-Ti-O/FTO复合薄膜,并通过X射线衍射(X-ray diffraction,XRD)分析样品的物相结构,利用紫外可见(ultra-violet and visible,UV-Vis)分光光度计测试样品的吸收...     

Low-voltage organic transistors with an amorphous molecular gate dielectric

Organic thin film transistors (TFTs) are of interest for a variety of large-area electronic applications, such as displays, sensors and electronic barcodes. One of the key problems with existing organic TFTs is their large operating voltage, which often exceeds 20 V. This is due to poor capacitive coupling through relatively thick gate dielectric layers: these dielectrics are usually either inorganic oxides or nitrides, or insulating polymers, and are often thicker than 100 nm to minimize gate leakage currents. Here we demonstrate a manufacturing process for TFTs with a 2.5-nm-thick molecular self-assembled monolayer (SAM) gate dielectric and a high-mobility organic semiconductor (pentacene). These TFTs operate with supply voltages of less than 2 V, yet have gate currents that are lower than those of advanced silicon field-effect transistors with SiO2 dielectrics. These results should therefore increase the prospects of using organic TFTs in low-power applications (such as portable devices). Moreover, molecular SAMs may even be of interest for advanced silicon transistors where the continued reduction in dielectric thickness leads to ever greater gate leakage and power dissipation.     

全相对论下的离域作用以及质量与电荷的相对论效应

基于全对称群的Dirac方程,通过计算硼、碳、氮、氧和氟原子的性质,研究全相对论下的离域作用以及质量与电荷的相对论效应。在单群的非相对论、双群的相对论和全对称群的相对论这三种不同水平的理论下,电子状态的表述是不同的。对于相对论和非相对论都存在离域作用,而相对论的离域作用要满足＂全对称群的最大几率原则＂。同一周期的原子,其质量相对论效应相当显著。对于正离子电荷的差别,不会出现新的相对论效应。     

ZnO薄膜的椭圆偏振光谱研究

采用椭圆偏振光谱法,在1.50～4.50eV光谱范围内,研究了在蓝宝石衬底上使用分子束外延方法制备的纤锌矿结构ZnO薄膜的光学性质.对椭圆偏振光谱拟合结果表明,坦吉扩展(Tanguy extend)色散公式能更准确、方便地描述ZnO薄膜带边附近的折射率和消光系数的色散关系.提供了ZnO薄膜在1.50～4.50eV光谱范围内的寻常光(o光)和非常光(e光)折射率和消光系数色散关系,为定量分析ZnO薄膜带边附近各向异性的光学性质提供了依据.     

Electroluminescence from single monolayers of nanocrystals in molecular organic devices

The integration of organic and inorganic materials at the nanometre scale into hybrid optoelectronic structures enables active devices that combine the diversity of organic materials with the high-performance electronic and optical properties of inorganic nanocrystals. The optimization of such hybrid devices ultimately depends upon the precise positioning of the functionally distinct materials. Previous studies have already emphasized that this is a challenge, owing to the lack of well-developed nanometre-scale fabrication techniques. Here we demonstrate a hybrid light-emitting diode (LED) that combines the ease of processability of organic materials with the narrow-band, efficient luminescence of colloidal quantum dots (QDs). To isolate the luminescence processes from charge conduction, we fabricate a quantum-dot LED (QD-LED) that contains only a single monolayer of QDs, sandwiched between two organic thin films. This is achieved by a method that uses material phase segregation between the QD aliphatic capping groups and the aromatic organic materials. In our devices, where QDs function exclusively as lumophores, we observe a 25-fold improvement in luminescence efficiency (1.6 cd A(-1) at 2,000 cd m(-2)) over the best previous QD-LED results. The reproducibility and precision of our phase-segregation approach suggests that this technique could be widely applicable to the fabrication of other hybrid organic/inorganic devices.     

Measurement of the conductance of single conjugated molecules

Electrical conduction through molecules depends critically on the delocalization of the molecular electronic orbitals and their connection to the metallic contacts. Thiolated (- SH) conjugated organic molecules are therefore considered good candidates for molecular conductors: in such molecules, the orbitals are delocalized throughout the molecular backbone, with substantial weight on the sulphur-metal bonds. However, their relatively small size, typically approximately 1 nm, calls for innovative approaches to realize a functioning single-molecule device. Here we report an approach for contacting a single molecule, and use it to study the effect of localizing groups within a conjugated molecule on the electrical conduction. Our method is based on synthesizing a dimer structure, consisting of two colloidal gold particles connected by a dithiolated short organic molecule, and electrostatically trapping it between two metal electrodes. We study the electrical conduction through three short organic molecules: 4,4'-biphenyldithiol (BPD), a fully conjugated molecule; bis-(4-mercaptophenyl)-ether (BPE), in which the conjugation is broken at the centre by an oxygen atom; and 1,4-benzenedimethanethiol (BDMT), in which the conjugation is broken near the contacts by a methylene group. We find that the oxygen in BPE and the methylene groups in BDMT both suppress the electrical conduction relative to that in BPD.     

Ⅲ-Ⅴ族半导体化合物(311)A表面的电子结构特征

在考虑最近邻、次近邻相互作用的SP3模型基础上,采用形式散射理论的格林函数方法计算了Ⅲ-Ⅴ族半导体化合物GaAs、InSb、InAs和GaP的(311)A表面的电子结构,给出了以上半导体材料体能带的表面投影能带结构,并给出了GaAs的(311)A表面的层态密度函数,分析了各表面态沿表面布里渊区高对称线的色散特性和(311)A表面的共同电子结构特征,计算结果与实验结果基本一致.     

Effective adjustment of the optoelectronic properties of organic conjugated materials by synthesizing <Emphasis Type="Italic">p</Emphasis>-<Emphasis Type="Italic">n</Emphasis> diblock molecules

Because organic conjugated materials offer several advantages relative to their inorganic counterparts,the development of organic conjugated materials has been one of the most active research areas in optoelectronic materials.For almost two decades,the search for organic conjugated materials has represented a major driving force for research concerned with controlling the band gap of extended π-conjugated molecules.In particular,among the parameters affecting the performance of organic light-emitting diodes (OLEDs),the energy levels of organic conjugated materials play an important role because they can affect the driving voltage,wavelength,efficiency,and lifetime of the final device.Balanced injection and transport of electrons and holes are therefore crucial for achieving OLEDs with high quantum efficiency.In this regard,research into adjusting the energy levels of organic conjugated materials is very meaningful for the development of OLEDs.To adjust the energy levels of the organic conjugated materials,Huang et al.have presented a new molecular design and synthesis route that yields p-n diblock conjugated copolymers and oligomers.The present review summarizes and analyzes the progress on adjusting the optoelectronic properties of organic conjugated materials that is due to synthesizing p-n diblock molecules.We discusses primarily work done by Huang et al.,but also discusses work done elsewhere over the past few years.We also point out issues that require attention,and highlight hot spots that require further investigation.     

THE RELATION BETWEEN BAND STRUCTURE AND SUPERCONDUCTING TRANSITION TEMPERATURE IN SOME MIXED ALKALI-METAL DOPED C_(60)

The electronic band stucturec of crystalline N Na2RbC60 and Na2CsC60are examined using the three-dimensional crystal orbital method. Our calculation results reveal that ground states of all these three alkali-metal doped fulle.rides from a metalic conducting phase with a rather narrow molecular crystal-like band-stucture and a high density of state near the. fermi-level, which indicate a very high Tc for this newly found molecular superconductors. A monotonic relationship is found between our calculated band dispersion,Fermi-level density of state, and the experimental transition temperature Tc,which is in exceuentt agre.emet with the prediction of the. BCS model.     

二茂铁基非线性光学材料研究进展

二茂铁衍生物由于具有独特的双环夹心结构和高度的电子离域特点,使其具有优良的非线性光学效应、氧化还原可逆性和特殊稳定性等.文中从结构和性能等方面介绍二茂铁基新型金属有机材料的研究现状,着重介绍电化学和非线性光学活性的二茂铁衍生物的研究进展.引用二茂铁在电化学和非线性光学发展史上具有代表性的论文,旨在帮助读者了解二茂铁功能材料的研究进展,把握其前沿动态.     

Experimental observation of the quantum Hall effect and Berry's phase in graphene

When electrons are confined in two-dimensional materials, quantum-mechanically enhanced transport phenomena such as the quantum Hall effect can be observed. Graphene, consisting of an isolated single atomic layer of graphite, is an ideal realization of such a two-dimensional system. However, its behaviour is expected to differ markedly from the well-studied case of quantum wells in conventional semiconductor interfaces. This difference arises from the unique electronic properties of graphene, which exhibits electron-hole degeneracy and vanishing carrier mass near the point of charge neutrality. Indeed, a distinctive half-integer quantum Hall effect has been predicted theoretically, as has the existence of a non-zero Berry's phase (a geometric quantum phase) of the electron wavefunction--a consequence of the exceptional topology of the graphene band structure. Recent advances in micromechanical extraction and fabrication techniques for graphite structures now permit such exotic two-dimensional electron systems to be probed experimentally. Here we report an experimental investigation of magneto-transport in a high-mobility single layer of graphene. Adjusting the chemical potential with the use of the electric field effect, we observe an unusual half-integer quantum Hall effect for both electron and hole carriers in graphene. The relevance of Berry's phase to these experiments is confirmed by magneto-oscillations. In addition to their purely scientific interest, these unusual quantum transport phenomena may lead to new applications in carbon-based electronic and magneto-electronic devices.     

有机小分子及金属有机配合物电子传输材料的研究进展

概述了有机小分子及金属有机配合物电子传输材料的研究进展,对由小分子电子传输材料构成的有机电致发光器件的发光性能、发光效率等方面进行了比较,并对小分子材料的研究前景进行了展望.     

二维V型AlP半导体及其可调直接带隙

一种新型单分子层V型结构磷化铝(V-AlP)二维半导体材料被理论预测,且通过第一性原理计算,它的稳定性和电学性质也得到详细考察.在外加应力和电场作用下,其电子结构被有效地调控.计算结果表明它有很好的稳定性,且具有宽的直接带隙(2.6 eV).在双轴应力下,其带隙可以在(1～2.6 eV)范围内调控.在外加张力的作用下,...     

Tuning charge transport in solution-sheared organic semiconductors using lattice strain

Circuits based on organic semiconductors are being actively explored for flexible, transparent and low-cost electronic applications. But to realize such applications, the charge carrier mobilities of solution-processed organic semiconductors must be improved. For inorganic semiconductors, a general method of increasing charge carrier mobility is to introduce strain within the crystal lattice. Here we describe a solution-processing technique for organic semiconductors in which lattice strain is used to increase charge carrier mobilities by introducing greater electron orbital overlap between the component molecules. For organic semiconductors, the spacing between cofacially stacked, conjugated backbones (the π-π stacking distance) greatly influences electron orbital overlap and therefore mobility. Using our method to incrementally introduce lattice strain, we alter the π-π stacking distance of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) from 3.33?? to 3.08??. We believe that 3.08?? is the shortest π-π stacking distance that has been achieved in an organic semiconductor crystal lattice (although a π-π distance of 3.04?? has been achieved through intramolecular bonding). The positive charge carrier (hole) mobility in TIPS-pentacene transistors increased from 0.8?cm(2)?V(-1)?s(-1) for unstrained films to a high mobility of 4.6?cm(2)?V(-1)?s(-1) for a strained film. Using solution processing to modify molecular packing through lattice strain should aid the development of high-performance, low-cost organic semiconducting devices.     

不同分散剂对水热法制备氧化锆颗粒分散性的影响

研究利用氯氧化锆和氨水作为原料水热法制备氧化锆微粉的方法。对分散剂种类及分散剂量对氧化锆微粉分散性影响进行了讨论,应用扫描电子显微镜和粒度分布仪对获得的氧化锆粉体进行分析。结果显示：加入聚乙二醇6000时,二氧化锆在水中分散性最好;采用1.150%聚乙二醇作为分散剂时,可获得在水中分散性较好的氧化锆粉末;相同质量分数的分散剂,分散效果较好的排序是：有机高聚物〉无机电解质〉阴离子表面活性剂〉有机物异丙醇。     

Ultralow-power organic complementary circuits

The prospect of using low-temperature processable organic semiconductors to implement transistors, circuits, displays and sensors on arbitrary substrates, such as glass or plastics, offers enormous potential for a wide range of electronic products. Of particular interest are portable devices that can be powered by small batteries or by near-field radio-frequency coupling. The main problem with existing approaches is the large power consumption of conventional organic circuits, which makes battery-powered applications problematic, if not impossible. Here we demonstrate an organic circuit with very low power consumption that uses a self-assembled monolayer gate dielectric and two different air-stable molecular semiconductors (pentacene and hexadecafluorocopperphthalocyanine, F16CuPc). The monolayer dielectric is grown on patterned metal gates at room temperature and is optimized to provide a large gate capacitance and low gate leakage currents. By combining low-voltage p-channel and n-channel organic thin-film transistors in a complementary circuit design, the static currents are reduced to below 100 pA per logic gate. We have fabricated complementary inverters, NAND gates, and ring oscillators that operate with supply voltages between 1.5 and 3 V and have a static power consumption of less than 1 nW per logic gate. These organic circuits are thus well suited for battery-powered systems such as portable display devices and large-surface sensor networks as well as for radio-frequency identification tags with extended operating range.     

二芳基芴类有机/聚合物半导体材料研究进展

在众多构建有机半导体材料分子结构中,二芳基芴类半导体凭借其特殊的电子、空间、位阻以及构象结构展现出良好的商业化前景.国内外研究学者致力于二芳基芴类电致发光小分子与聚合物半导体材料的研究,大量二芳基芴类电致发光小分子与聚合物半导体材料,包括电致发光材料、载流子传输材料、磷光器件的主体材料和电存储材料等已经得到了报道.文中以作者课题组的工作为主线系统总结了二芳基芴类有机/聚合物光电材料的分子结构、性质、及其应用等方面的进展,并展望了二芳基芴类有机/聚合物半导体材料未来发展的趋势与脉络.