高分子有机场效应晶体管中退火引起的自组织微观结构变化的研究

为了进一步洞悉高分子薄膜自组织机理和高分子有机场效应晶体管(OFET)载流子迁移率之间的直接关联性,本工作采用先进的同步辐射掠入射X射线衍射(GIXRD)技术,研究了高分子OFET中高分子半导体高度区域规则的聚(3-己基噻吩)(RR-P3HT)工作层薄膜,由不同退火温度所导致的薄膜自组织微观结构的变化.GIXRD测试实验结果显示了,对于不同高分子薄膜制备方法(旋涂法及滴膜法)及不同溶液浓度(RR-P3HT溶液浓度为2.5 mg/ml及3.5 mg/ml)制备的RR-P3HT有机半导体工作层,在氮气气氛下, 关键词： 高分子有机场效应晶体管 同步辐射掠入射X射线衍射 自组织 退火     

非溶剂掺杂完善自组织机理提升高度区域规则的(3-己基噻吩)有机场效应晶体管器件性能的研究

为了保证在低温加工及溶液制备的情况下,能够提升高度区域规则的聚(3-己基噻吩) (RR-P3HT)有机场效应晶体管(OFET)的器件性能,本文研究了室温下乙醇及乙腈非溶剂的掺杂,及其对高分子自组织机理与导致的RR-P3HT OFET电学性能的影响.实验发现,适量进行乙醇及乙腈非溶剂的掺杂,将促进RR-P3HT薄膜形成更多期望的微晶粒薄片结构,完善高分子自组织机理,导致RR-P3HT OFET电学性能的提升.实验表明,在RR-P3HT溶液中进行5 %乙腈添加后,其器件场效应迁移率的值由原来的4.04×10< 关键词： 高度区域规则的聚(3-己基噻吩)有机场效应晶体管 非溶剂掺杂 自组织机理 场效应迁移率     

金衬底调控单层二硫化钼电子性能的第一性原理研究

基于密度泛函的第一性原理研究了金衬底对单层二硫化钼电子性能的调控作用. 从结合能、能带结构、电子态密度和差分电荷密度四个方面进行了深入研究. 结合能计算确定了硫原子层在界面的排布方式, 并指出这种吸附结构并不稳定. 能带结构分析证实了金衬底与单层二硫化钼形成肖特基接触, 并出现钉扎效应. 电子态密度分析表明金衬底并没有影响硫原子和钼原子之间的共价键, 而是通过调控单层二硫化钼的电子态密度增加其导电率. 差分电荷密度分析表明单层二硫化钼的导电通道可能在界面处产生. 研究结果可对单层二硫化钼晶体管的建模和实验制备提供指导.     

石墨烯等二维原子晶体薄片样品的光学衬度计算及其层数表征

本文以鉴别机械剥离法制备的高质量石墨烯样品的层数为例, 阐明了如何利用传输矩阵来计算二维原子晶体薄片样品的光学衬度, 并进一步精确地鉴别其层数. 计算结果表明测试时所选用的显微物镜数值孔径对精确确定薄片样品的层数非常重要, 并为实验所证实. 同时提出了使用两个激光波长可以快速地表征样品尺寸接近物镜衍射极限的薄片样品层数的方法. 本文所采用的传输矩阵形式非常适合于计算二维原子晶体薄片样品的光学衬度, 并可以方便地推广到更复杂的多层衬底结构, 以便快速和准确地鉴别各种衬底上二维原子晶体薄片样品的厚度. 关键词： 二维原子晶体材料 层数 传输矩阵 光学衬度     

金属-氧化物-半导体场效应管辐射效应模型研究

基于氧化层陷阱电荷以及界面陷阱电荷的产生动力学以及辐射应力损伤的微观机理,推导出了金属-氧化物-半导体场效应管(MOSFET)中辐射应力引起的氧化层陷阱电荷、界面陷阱电荷导致的阈值电压漂移量与辐射剂量之间定量关系的模型. 根据模型可以得到:低剂量情况下,氧化层陷阱电荷与界面陷阱电荷导致的阈值电压漂移量与辐射剂量成正比;高剂量情况下,氧化层陷阱电荷导致的阈值电压漂移量发生饱和, 其峰值与辐射剂量无关,界面陷阱电荷导致的阈值电压漂移量与辐射剂量呈指数关系. 另外,模型还表明氧化层陷阱电荷与界面陷阱电荷在不同的辐射剂量点开始产生饱和现象, 其中界面陷阱电荷先于氧化层陷阱电荷产生饱和现象.最后,用实验验证了该模型的正确性. 该模型可以较为准确地预测辐射应力作用下MOSFET的退化情况.     

高度取向的半导体聚合物薄膜的溶液浸涂法生长及其电荷传输特性研究

有效地控制有机半导体分子取向和堆积特性对实现高性能电子器件具有非常重要的意义,而发展简便高效的溶液相成膜技术是实现这一目的的重要途径.本文采用改进的溶液浸涂法,成功地成长出大面积宏观取向的半导体聚合物P(NDI2OD-T2)和PTHBDTP薄膜.偏光显微镜和极化的紫外-可见光吸收谱测量显示,薄膜中聚合物分子主链骨架沿成膜时液面下移方向择优取向.原子力显微镜观察到聚合物薄膜由纳米尺度的取向有序晶畴构成,畴的取向与分子链的取向一致.采用衬底-溶液界面处表面张力和溶剂蒸发诱导的分子自组织过程来解释浸涂法生长聚合物取向薄膜的微观机理.使用取向的P(NDI2OD-T2)薄膜制备场效应晶体管,显著地提高了电子迁移率(可达4倍),并实现高达19的迁移率各向异性度.这可归因于共轭的聚合物主链骨架择优取向引起电荷传导通路的变化.     

Fe/ZnO (0001)体系界面相互作用中薄膜厚度效应的光电子能谱研究

利用同步辐射光电子能谱(SRPES)和X射线光电子能谱(XPS)技术,系统研究了室温下Fe/ZnO界面形成过程中Fe薄膜与氧结尾的ZnO(000 1 )衬底之间的相互作用,结果显示初始沉积的Fe明显被表面氧氧化为Fe²⁺离子,在Fe覆盖度为0—3 nm的范围内,分别观察到与界面电荷传输、化学反应以及薄膜磁性相关的三个有意义的临界厚度,这一结果将有助于基于Fe/ZnO界面的相关器件的设计和研发. 关键词： Fe/ZnO 界面作用 同步辐射光电子能谱 X射线光电子能谱     

氧化锌电阻阀片中ZnO(002)/β-Bi_2O_3(210)界面结构的第一性原理研究

为了从物质微观结构上了解氧化锌避雷器阀片的性能,采用基于密度泛函理论的第一性原理方法对ZnO(002)/β-Bi_2O_3(210)界面结构进行弛豫和电子结构计算.结果表明弛豫后,原子间的键长发生改变.界面区域差分电荷密度图和原子布居分析可得ZnO层片中Zn原子电荷缺失,β-Bi_2O_3层片中O原子电荷富集,ZnO层片向β-Bi_2O_3层片转移电子电荷23.61e.晶界结构的内建电场由ZnO层片指向β-Bi_2O_3层片,内建电场是ZnO电阻阀片具有非线性伏安特性的重要原因.界面附近态密度表明界面的结合主要依靠ZnO层片中Zn原子与β-Bi_2O_3层片中O原子相互作用.计算显示ZnO(002)/β-Bi_2O_3(210)界面结合较强,界面能约为-4.203 J/m~2.本文研究结果对于研制高性能非线性伏安特性氧化锌电阻片提供了机理解释和理论支持.     

SrTiO3金属-绝缘体-半导体结构的介电与界面特性

采用金属有机分解法在p型Si衬底上制备了SiTiO3(STO)薄膜.研究了STO薄膜金属-绝缘体-半导体(MIS)结构的介电和界面特性.结果表明,STO薄膜显示出优异的介电性能,在10kHz处的介电常数约为105,损耗低于0.01,这来源于多晶结构和良好的结晶性;MIS结构中的固定电荷密度Nf和界面态密度Dit分别约为1.5×1012cm-2和(1.4-3.5)×1012 cm-2 eV-1,这主要与Si/STO界面处形成的低介电常数界面层有关.     

Si_3N_4钝化层对横向PNP双极晶体管电离辐射损伤的影响机理

航天器中电子器件在轨服役期间,会遭受到空间带电粒子及各种射线的辐射环境的显著影响,易于造成电离辐射损伤.本文采用60Coγ射线辐照源,针对有/无Si_3N_4钝化层结构的横向PNP型(LPNP)双极晶体管,开展了电离辐射损伤效应及机理研究.利用KEITHLEY 4200-SCS半导体参数测试仪测试了LPNP晶体管电性能参数(包括Gummel特性曲线和电流增益等).采用深能级瞬态谱分析仪(DLTS),对辐照前后有/无Si_3N_4钝化层结构的LPNP晶体管的电离缺陷进行测试.研究结果表明,在相同吸收剂量条件下,与无Si_3N_4钝化层的晶体管相比,具有Si_3N_4钝化层的LPNP晶体管基极电流退化程度大,并且随吸收剂量的增加,电流增益退化更为显著.通过DLTS分析表明,与无Si_3N_4钝化层的晶体管相比,有Si_3N_4钝化层的晶体管辐射诱导的界面态能级位置更接近于禁带中心.这是由于制备Si_3N_4钝化层时引入了大量的氢所导致,而氢的存在会促使辐射诱导的界面态能级位置更接近于禁带中心,复合率增大,从而加剧了晶体管性能的退化.     

摩擦导致的聚合物表层微观结构改变

应用大规模分子动力学方法, 模拟了锥形探头在非晶态聚合物薄膜表面的滑动摩擦过程, 研究了摩擦导致的聚合物薄膜表层微观结构改变, 以及探头与基体间黏着作用、滑动速度和分子链长度对基体表层微观结构改变的影响. 当探头与基体之间为黏着作用时, 摩擦导致基体表面滑痕区域的键取向沿滑动方向重新取向, 导致表层分子链回转半径沿滑动方向伸长, 并且这些表层微观结构的改变程度随滑动速度的减小而增大. 在摩擦导致结构改变的过程中, 链端单体和链中单体的贡献作用不同, 形成了不同的分子链拉伸变形机制. 当样本缠结度较大或探头滑动速度较小时, 相比于链中单体, 探头对链端单体的拖曳作用使更多分子链发生拉伸变形. 研究还发现, 在探头与聚合物薄膜系统中, 使薄膜表层微观结构发生改变是摩擦能量耗散的重要途径.     

Computer simulation of structure and mechanical properties of polymer liquid crystals

In this contribution, we report on a study of the self-organization and mechanical properties of polymer liquid crystals (PLCs). Both processes are computer simulated by the method of molecular dynamics. We investigated two real longitudinal PLCs (thermotropic polyesters) with macromolecules that consist of rigid and flexible parts arranged in a regular way. One rigid and one flexible part form a monomer containing 45 or 47 atoms. The total number of atoms in the macromolecules studied was 4700 (100 monomers) and 5400 (75 monomers). The self-organization was similar to that obtained earlier for a beads-on-a-string model, so compression calculations were done using this simpler model containing 1200 beads (100 monomers). Macroscopic characteristics such as the stress-strain relation, temperature change during deformation, as well as microscopic changes in structure, were investigated.     

Nanostructural self-organization and dynamic adaptation of metal–polymer tribosystems

The results of investigating the effect of nanosize modifiers of a polymer matrix on the nanostructural self-organization of polymer composites and dynamic adaptation of metal–polymer tribosystems, which considerably affect the wear resistance of polymer composite materials, have been analyzed. It has been shown that the physicochemical nanostructural self-organization processes are developed in metal–polymer tribosystems with the formation of thermotropic liquid-crystal structures of the polymer matrix, followed by the transition of the system to the stationary state with a negative feedback that ensures dynamic adaptation of the tribosystem to given operating conditions.     

Self-organization effect in poly（3-hexylthiophene）： methanofullerenes solar cells

This paper studies the self-organization of the polymer in solar cells based on poly（3-hexylthiophene）： [6, 6]-phenyl C61-butyric acid methyl ester by controlling the growth rate of active layer. These blend films are characterized by UV-vis absorption spectroscopy, charge-transport dark J - V curve, x-ray diffraction pattern curve, and atomic force microscopy. The results indicate that slowing down the drying process of the wet films leads to an enhanced selforganization, which causes an increased hole transport. Increased incident light absorption, higher carrier mobility, and balanced carrier transport in the active layer explain the enhancement in the device performance, the power conversion efficiency of 3.43% and fill factor up to 64.6% are achieved under Air Mass 1.5, 100 mW/cm^2.     

Depletion effect on partial organization of atactic polymer chain segments in microcells

Glass transition for atactic poly(methyl methacrylate) (a-PMMA) prepared in nano-cells by microemulsion polymerization was measured at a faster heating rate after slow cooling of the sample from a temperature above T_g. An additional enthalpy relaxation and glass transition were observed at higher temperatures for the a-PMMA sample due to the partial organization of the chain segments which occurred during microemulsion polymerization. The re-precipitated a-PMMA did not show any self-organization under the same thermal conditions, although there are no changes in molecular weight or tacticity of the polymer chains. A depletion-interaction phenomenon was understood to provide entropic force for the self-organization of polymer chains inside the walls of the microemulsion cells.     

Regularities of lamellae ordering in the formation of polypropylene membrane porous structure

The lamellar structure of porous polypropylene membranes prepared by the extrusion of the polymer melt, annealing of extruded films, and their uniaxial extension has been investigated using data of computer analysis of scanning electron microscopy images. It has been shown that the formation of pores at the stage of uniaxial extension is accompanied by an ordering of lamellae or their self-organization controlled by the annealing temperature T _ann. It has been found that the self-organization of lamellae can occur through two mechanisms depending on the spin draw ratio at the stage of extrusion of the polymer melt: in the first case, an increase in the temperature T _ann leads to a gradual transition of the disorder-order type; in the second case, a bifurcation transition occurs with a nonmonotonic change in the order parameter. The conditions of the preparation of regular spatial lattices of lamellae have been discussed.     

Molecular dynamics and strengthening of liquid-crystal polymers

The role of large-scale molecular motion in the self-organization and strengthening of liquid-crystal polymer fibers is discussed. It is shown that, at high temperatures, these objects are oriented liquid-crystal melts in which macromolecules remain extended but execute high-frequency conformational motions without leaving the tube approximately 20 Å in diameter. This large-scale motion is referred to as quasi-segmental motion. During annealing, the chains involved in quasi-segmental motion can accomplish longitudinal displacements (reptate) over considerable distances. It is this reptation that favors spontaneous self-organization and, consequently, strengthening of liquid-crystal polymer fibers upon heat treatment. The role played by the quasi-segmental motion of rigid macromolecules in the strengthening of polymers of different types is compared with the role played by the segmental motion of flexible chains in this process.     

Orientation order and birefringence in nanolayers of polymer films

A model for describing the self-organization of chains with intra- and intermolecular interactions of the dipolar type and the birefringence (BR) effect in surface nanolayers of polymer films obtained by evaporation of a solvent is developed. Calculations of the planar orientation order parameter versus the Kuhn segment length and BR coefficient versus the film thickness are in good agreement with experimental data on investigating ordering with an inclined polarized beam for various polymer homologs.