Modified isothermal discharge current theory and its application in the determination of trap level distribution in polyimide films

Modified isothermal discharge current theory (MIDC) was thoroughly investigated in order to obtain the trap level distribution in polymers. In this theory, a new function was defined to weight the contribution of any trap level to the depolarization current at an instant time. The demarcation energy was used to study the trap empty process. Analysis showed that only electrons with trap levels very close to the demarcation energy significantly contribute to the external current. As an application example, this theory was applied to determine the trap level distribution in Kapton 100HN and 100CR (nanodielectrics) PI films before and after corona ageing. Experiments showed that traps in 100CR PI films were about twice as much as that in the 100HN PI films through all trap levels. It's also found that the quantity of traps was increased evidently after corona ageing and lots of deeper traps were produced in 100HN film, whereas for 100CR, changes were not very significant. Since both physical and chemical defects intrinsic or extrinsic can change the trap level distribution and make a significant impact on the dielectric behavior. So modified isothermal current theory may be a useful tool for determining the defect characteristic and investigating the electrical properties of polymer dielectrics.     

Effect of corona ageing on the structure changes of polyimide and polyimide/Al2O3 nanocomposite films

In order to investigate the corona ageing mechanism of polyimide and polyimide/Al₂O₃ nanocomposites, effects of corona ageing on the structure changes of the two polymers were studied. The physical and chemical changes were studied by Atomic Force Microscope (AFM), Scanning Electron Microscope (SEM) and Fourier Transform Infrared Spectroscope (FTIR) respectively. Modified isothermal discharge current method (MIDC) was used to investigate the trap level distribution before and after corona ageing. AFM images showed that there are large amounts of nano-clusters on the surface of polyimide nanocomposite before corona ageing. The surface roughness parameters of the nanocomposite is much larger than that of the pure polyimide, and that is slightly decreased for polyimide nanocomposite and largely increased for pure polyimide after corona ageing. FTIR spectra analysis showed that possible chemical changes due to the decomposition of C–O–C bond and C–N bond occurred during corona ageing for both polyimide and its nanocomposite. Pulse corona ageing can introduce even larger structure changes than the AC corona ageing for 100HN, while 100CR was just the opposite. IDC measurements showed that the trap level density was increased evidently after corona ageing and become larger for longer ageing time in 100HN film, whereas for 100CR, the trap level density was decreased with ageing time extended. Thus conclusions can be drawn that, corona ageing is a combined process leading to physical and chemical degradation of PI film. The more serious ageing the specimen suffers, the more changes of the trap level density and the surface roughness occurs. The deposition of inorganic nanoparticles on the surface of nanocomposite can form a flat block layer for corona ageing, which can decrease both the surface roughness and the physical trap level density.     

Influence of polymer dielectric surface energy on thin‐film transistor performance of solution‐processed triethylsilylethynyl anthradithiophene (TES‐ADT)

This study investigates the correlation between surface energy of polymer dielectrics and the film morphology, microstructure, and thin‐film transistor performance of solution‐processed 5,11‐bis(triethylsilylethynyl) anthradithiophene (TES‐ADT) films. The low surface energy polyimide (PI) dielectric induced large grains with strong X‐ray reflections for spin‐cast TES‐ADT films in comparison to high surface en‐ ergy poly(4‐vinyl phenol) (PVP) dielectric. Furthermore, thin‐film transistors based on spin‐cast TES‐ADT films on PI dielectric exhibited enhanced electrical performance, small hysteresis, and high stability under bias stress with carrier mobility as high as 0.43 cm²/Vs and a current on/off ratio of 10⁷. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Fabrication and structural characterization of nanocomposites consisting of Ni nanoparticles dispersed in polyimide films

Formation and structure of composite layer consisting of polyimide films containing Ni nanoparticles were investigated. The preparation method relies on KOH treatment on polyimide film to form carboxyl acid groups and adsorption of Ni ions by ion exchange followed by hydrogen reduction. The amount of Ni ions adsorbed in polyimide films were found to be systematically controlled by changing initial KOH concentration, subsequent ion exchange time, pH and temperature. Cross-sectional TEM observation revealed that Ni nanoparticles with 3-5 nm in diameter were homogeneously dispersed in the surface modified polyimide layer after heat treatment above 250 ^°C in H₂ atmosphere. The size and distribution of the Ni nanoparticles were strongly dependent on the heat treatment temperature, indicating that this method allows microstructural tuning of metal/polymer nanocomposites.     

气相沉积法制备聚酰亚胺薄膜不同单体配比的表征及其性能影响

聚酰亚胺微球作为惯性约束聚变的重要候选靶丸之一,其力学性能和热学性能的提高对于实现聚变点火有重要意义.本文以均苯四甲酸二酐和二氨基二苯醚为原料,采用气相沉积法制备了不同单体配比的聚酰胺酸薄膜,研究了制备聚酰胺酸薄膜过程中不同单体蒸发温度对薄膜组成的影响,并对聚酰胺酸薄膜进行热环化处理.采用红外光谱仪分析了聚酰胺酸薄膜和聚酰亚胺薄膜的组成,结果表明:随着二酐蒸发温度的增加,聚酰胺酸薄膜中过量二酐单体的红外吸收振动特征峰(1780 cm~(-1),1850 cm~(-1)强度增加,单体配比由二胺过量到二酐二胺配比均衡再到二酐过量.热环化处理的过程中,薄膜中过量单体会再次蒸发,其红外图谱显示最终产物只有聚酰亚胺,但单体配比接近样品聚酰亚胺红外特征振动峰(1380 cm~(-1))强度更大.X射线衍射图谱显示配比接近的样品具有更高的晶化程度,说明过量单体的存在抑制了聚酰胺酸分子链的生长,造成分子量降低.采用纳米压痕仪和热重分析仪分别测量了聚酰亚胺薄膜的弹性模量和硬度以及失重曲线,结果表明分子量的降低会造成聚酰亚胺薄膜的弹性模量和硬度的降低,同时热稳定性也变差.扫描电子显微镜图像显示聚酰亚胺薄膜呈层状结构,单体配比接近的样品表面状况更好,这一点与聚酰亚胺分子的生长规律相符合.     

分层蒸镀制备聚酰亚胺自支撑膜及其特性研究

 采用分层蒸镀法,在玻璃基片上依次蒸镀二氨基二苯醚（ODA）和均苯四甲酸二酐（PMDA）两种单体,然后在空气环境中对样品进行不同温度和时间的热亚胺化处理,使二者在交界面上反应生成聚酰亚胺。经加热150 ℃ 1 h然后经350 ℃ 2 h处理的样品,在脱膜后能制备出直径1.8 cm,厚度为100 nm的聚酰亚胺自支撑薄膜。用FTIR测量了自支撑薄膜的红外光谱,特征吸收峰的分析表明薄膜已基本上完全亚胺化。用原子力显微镜分析了浮法玻璃衬底上聚酰亚胺薄膜的表面形貌,结果表明以ODA作为内层制备的膜层表面更光滑平整。     

从聚酰亚胺单分子链电荷陷阱特性的改变探讨体材料的沿面放电现象

沿面放电是破坏绝缘系统性能的原因之一.聚酰亚胺常用于高频电力设备的气-固绝缘中,为此利用密度泛函理论,从原子分子层面探讨了在外电场下聚酰亚胺及其受极性基团OH~–影响后的单分子链结构、能级与态密度、静电势、激发态等微观参数对陷阱形成以及沿面放电的影响.结果表明,外电场下,聚酰亚胺分子结构卷曲,偶极矩增加,易于积聚电荷形成空间电荷中心,尤属引入极性基团OH~–后变化较明显;聚酰亚胺分子中,苯环区域形成空穴陷阱,酰亚胺环区域形成电子陷阱,且电子陷阱能级的数量较多,其中空间电荷陷阱深度随外电场的增加逐渐变深;聚酰亚胺分子在引入极性基团OH~–后激发能降低,使得分子内部的电子变得容易被激发;电子与空穴的空间分离度随电场增加而降低,利于空穴与电子的复合而发出光子.     

空间多能电子辐照聚合物充电过程的稳态特性

空间同步轨道上多能电子辐照聚合物的充电过程及其稳态特性是研究和抑制通信卫星静电放电的基础.在同步电子散射-输运微观模型的基础上,采用具有10—400 keV积分能谱分布的多能电子辐照聚酰亚胺样品,进行了多能电子辐照聚酰亚胺充电过程的数值模拟,获得了空间电荷密度、空间电位、空间电场分布和聚合物样品参数条件下的表面电位和最大场强.结果表明,多能电子与样品发生散射作用并沉积在样品内形成具有高密度的电荷区域分布,同时在迁移和扩散的作用下输运至样品底部形成样品电流;充电达到稳态、电子迁移率较小时(小于10-10cm2·V-1·s-1),表面电位绝对值和充电强度随电子迁移率的降低明显加强,捕获密度较大时(大于1014cm-3),表面电位绝对值和充电强度随捕获密度的增大明显加强;聚合物样品厚度对表面电位和充电强度的影响大于电子迁移率、捕获密度和相对介电常数的影响.研究结果对于揭示空间多能电子辐照聚合物的充电现象及微观机理、提高航天器故障机理研究水平具有重要科学意义和价值.     

A facile method for preparing highly conductive and reflective surface-silvered polyimide films

A novel method was developed for the preparation of reflective and electrically conductive surface-silvered polyimide (PI) films. The polyimide films were functionalized with poly(dopamine), simply by dipping the PI films into aqueous dopamine solution and mildly stirring at room temperature. Electroless plating of silver was readily carried out on the poly(dopamine) deposited PI (PI-DOPA) surface. The surface compositions of the modified PI films were studied by X-ray photoelectron spectroscopy (XPS). XPS results show that the PI-DOPA surfaces were successfully deposited with ploy(dopamine) and were ready for electroless deposition of silver. The poly(dopamine) layer was used not only as the chemi-sorption sites for silver particles during the electroless plating of silver, but also as an adhesion promotion layer for the electrolessly deposited silver. The as-prepared silvered PI films show high conductivity and reflectivity, with a surface resistance of 1.5 Ω and a reflectivity of 95%, respectively.     

Electrodeposited metals at conducting polymer electrodes: I—Effect of particle size and film thickness on electrochemical response

Conducting polymers are electrochemically polymerized at platinum electrode substrates. The thickness, porosity and surface morphology of the resulting films are controlled by the charge passing during electropolymerization step and the synthesis conditions. The polymer films are modified by electrochemically depositing platinum particles. The technique of deposition depends on applying a programmed potential pulse at the polymer film from a solution containing platinum complex that resulted in the formation of platinum particles of controlled size and distribution. The effect of changing the size of platinum particles and polymer film thickness on the voltammetric behavior of the resulting hybrid material showed noticeable changes in the electro-catalytic current in acid medium. On the other hand, the electrochemical impedance spectroscopy experiments showed that diffusion and charge-transfer rate increased in the order: unmodified polymer films, thin polymer films containing small size/amount of platinum particles and relatively thick polymer films containing larger size/amount of platinum particles. The morphology of polymer films, size and distribution of platinum particles in the film were studied by scanning electron microscopy. The presence of platinum and its distribution over the film surface was confirmed from the X-ray dispersive analysis and surface mapping. The hybrid materials are good candidates for the application in devices for exchange of hydrogen ions.     

基于衬底图形化与链取向技术实现平面光波导

采用喷墨打印的方法对衬底进行图形化, 结合链取向技术, 实现聚合物混合体Poly(9, 9-dioctylfluorene-co-benzothiadiazole)(F8BT, 主体)和Red F(客体)在指定区域链取向. 利用链取向区域内外的折射率差异, 设计出了各种宽度的薄膜光波导, 使光信号在链取向区域传播. 同时, 这一共混体系中主体的荧光光谱与客体的吸收光谱区域重叠, 可以使有效的能量传递发生, 利用主体向客体的能量传递机理, 使链取向处理后的聚合物混合体实现了红光发射.     

Structure formation in UV-laser-ablated polyimide foils

The formation of nap-type and wall-type structures on laser-irradiated polyimide (PI) films is reported for the first time. These investigations demonstrate that such structures can develop on non-melting polymer surfaces.     

退火与极化温度对尼龙11薄膜驻极体内陷阱能级分布的影响

用热释电技术研究了尼龙11薄膜驻极体制备过程中热处理与极化温度对驻极体陷阱能级分布的影响.结果显示，淬火驻极体的热释电流谱上存在四个空间电荷退陷阱电流峰，而在退火处理后则显示两个退陷阱电流峰.采用多点法对热释电流谱进行理论拟合可以将各个退陷阱电流峰分离并得到它们的陷阱深度参数.这些参数进一步表明，淬火尼龙11薄膜驻极体内存在四个空间电荷的陷阱能级，极化温度升高对它们的分布情况影响不大；退火处理后，陷阱能级减少为两个，且随着极化温度的升高，较浅的陷阱能级有明显向较深陷阱能级接近的趋势. 关键词： 尼龙11 薄膜驻极体 热释电 热处理     

聚酰亚胺LB膜上液晶表面锚定的研究

通过测试光延迟研究了聚酰亚胺ＬＢ膜的光学各向异性，分析了在ＬＢ膜成膜过程中成膜分子的流动取向特性，并研究了液晶的表面锚定能，分析了ＬＢ膜上液晶的取向机制．聚酰亚胺ＬＢ膜的链段的取向程度较强摩擦情形的聚酰亚胺表面的链段取向要差．强摩擦的聚酰亚胺会比聚酰亚胺ＬＢ膜具有更好的排列液晶分子的能力．ＬＢ膜的流动取向模式使得聚酰亚胺成膜分子沿拉伸方向形成一定的有序排列，并诱导液晶分子定向排列，液晶和聚合物分子相互作用是液晶表面排列的主要动力 关键词：     

Atomic oxygen erosion resistance of polyimide/ZrO2 hybrid films

A series of polyimide/zirconia (PI/ZrO₂) hybrid films were synthesized based on zirconium n-butoxide, pyromellitic acid dianhydride (PMDA) and 4,4′-oxydianiline (ODA) by a sol-gel process. The atomic oxygen (AO) exposure tests were carried out using a ground-based atomic oxygen effects simulation facility. The effects of ZrO₂ content on the morphology and structure evolvement of PI/ZrO₂ hybrid films were investigated using field emission scanning electron microscopy (FE-SEM) and X-ray photoelectron spectrometer (XPS), respectively. The results indicated that a zirconia-rich layer was formed on the polyimide film sourcing from the zirconium n-butoxide after AO exposure, which decreased the erosion rate and obviously improved the AO resistance of polyimide films.     

基体对应力诱导的纳米晶W膜开裂行为的影响

采用磁控溅射方法同时在Si(100)和聚酰亚胺(PI)基体上沉积W膜,对比研究不同基体约束对纳米晶W膜微观结构及应力诱导的开裂行为的影响.结果发现,在两种基体上W膜的裂纹形态明显不同.在Si基体上W膜的裂纹呈楔形,而在PI基体上W膜的裂纹呈半圆柱形凸起于薄膜表面.这种裂纹形态的差异源于两种基体上W膜的变形机理不同.在刚性Si基体上,W膜的裂纹扩展是通过晶粒平面内的转动实现的,而在柔性PI基体上W膜裂纹扩展是通过排列晶粒在平面内、外的转动协调完成的.分析表明,两种截然不同的开裂行为与不同基体上薄膜内应力的变 关键词： W膜 残余应力 裂纹 晶粒     

AFM investigation of polymer LB films on the alignment of ferroelectric liquid crystal

A kind of newly synthesized polyimide (PI) LB films were fabricated to align ferroelectric liquid crystal (FLC). The topologies of PI LB films treated by different imidization processes were investigated by atomic force microscopy (AFM). It is found that the imidization temperature influences the crystalline structure of the LB films and high-temperature imidized LB films can provide the energy barrier for the realization of excellent bistability, while the ultra-thinness of LB films is helpful for the quick response of the FLC cell.     

快重离子辐照聚酰亚胺潜径迹的电子能损效应

快重离子辐照聚合物材料时，由于密集电离激发在其路径上产生几纳米直径的潜径迹，径迹形貌受离子种类、离子能量等多种因素的影响.为了研究电子能损对径迹形成所起的作用，利用1.158GeV 的Fe⁵⁶离子和 1.755GeV Xe¹³⁶离子在室温真空环境下辐照叠层聚酰亚胺(PI)薄膜，结合傅里叶转换红外光谱(FTIR)分析技术对辐照引起的化学变化进行了测量.聚酰亚胺官能团的降解及炔基的生成是离子辐照聚合物的主要特征，在注量1×10¹¹到6×10¹²/cm²范围及较宽的电子能损(dE/dX)_e范围 (Fe⁵⁶ 离子：2.2 到 5.2 keV/nm， Xe¹³⁶ 离子：8.6 到 11.3 keV/nm)对官能团的断键率及炔基生成率进行了研究. 红外结果显示在实验涉及的能损范围都有炔基生成，应用径迹饱和模型对实验结果进行拟合，不同能损下的平均损伤径迹半径及炔基生成径迹半径被得到，通过热峰模型对实验结果拟合，给出了离子在聚酰亚胺中产生潜径迹的能损阈值，实验给出的径迹形貌的电子能损效应曲线与热峰模型预言走势基本一致. 关键词： 离子辐照 潜径迹 红外光谱 热峰模型     

Physical characteristics of polyimide films for flexible sensors

Physical characteristics of polyimide films, including optical, micro/nano mechanical, and thermophysical characteristics were investigated using a photometric, a nanoindentation, and a thermomechanical analyzer for applications in flexible sensors. Experimental results show that UV light cannot transmit into the polyimide films. The transmittances, with a maximum of about 86%, at VIS and near IR lights decrease with increasing PI film thicknesses. The mechanical characteristics were determined using tensile, bending moment, and nanoindentation testing. The stress–strain curve approximated bilinear characteristics, the load–unload bending moment exhibited hysteresis, and nanoindentation generated elastic energy dissipation in the loading–unloading region. Nanoindentation showed an almost uniform hardness and a reduced Young’s modulus of about 0.181±0.03 and 3.21±0.06 GPa, respectively, when the penetrating depth was more than about 2 μm. Thermophysical characteristics were greatly influenced on 8.3 and 25 μm specimens due to the higher relaxation of thin PI films. The thermal expansion remained steady when the thickness was over 50 μm. The results show that PI films have potential in flexible sensing and higher temperature fabrication.     

Effect of heating treatment on trap level distribution in polyamide 66 film electrets

The effect of heating treatment on the trap level distribution in polyamide 66 film electret is studied by thermally stimulated depolarization current （TSDC） technique. For annealed polyamide 66, there are three trap levels that respectively originate from space charge trapped in amorphous phase, interphase and crystalline phase. There is one peak that originates from space charge trapped in amorphous phase for quenched one. Using multi-point method to fit the experimental curves, the detrapping current peaks can be separated and the trap depth is obtained. The shallower trap levels trapped in amorphous phase and interphase are obviously close to the deeper trap level trapped in crystalline phase for annealed polyamide 66 as the polarization temperature increases, while the trap level distribution remains unaffected by polarization temperature for quenched one.