High performance solution-processed indium oxide thin-film transistors

In2O3 thin-film transistors (TFTs) were fabricated on various dielectrics [SiO2, self-assembled nanodielectrics (SANDs)] by spin-coating In2O3 film precursor solutions consisting of ethanolamine (EAA) and InCl3 in methoxyethanol. Optimized film microstructures are characterized by the high-mobility In2O3 00 L orientation and are obtained only within a well-defined range of base: In3+ molar ratios. Electron mobilities as high as approximately 44 cm2 V(-1) s(-1) are measured for n+-Si/SAND/In2O3/Au devices using an EAA/In3+ molar ratio = 10. This result combined with Ion/Ioff ratios of approximately 10(6) and <5 V operating voltages is encouraging for high-speed applications.In2O3 thin-film transistors (TFTs) were fabricated on various dielectrics [SiO2, self-assembled nanodielectrics (SANDs)] by spin-coating In2O3 film precursor solutions consisting of ethanolamine (EAA) and InCl3 in methoxyethanol. Optimized film microstructures are characterized by the high-mobility In2O3 00 L orientation and are obtained only within a well-defined range of base: In3+ molar ratios. Electron mobilities as high as ~44 cm2 V(-1) s(-1) are measured for n+-Si/SAND/In2O3/Au devices using an EAA/In3+ molar ratio = 10. This result combined with Ion/Ioff ratios of approximately 10(6) and <5 V operating voltages is encouraging for high-speed applications.     

Printable cross-linked polymer blend dielectrics. Design strategies, synthesis, microstructures, and electrical properties, with organic field-effect transistors as testbeds

We report here the synthesis and dielectric properties of optimized, cross-linked polymer blend (CPB) dielectrics for application in organic field-effect transistors (OFETs). Novel silane cross-linking reagents enable the synthesis of CPB films having excellent quality and tunable thickness (from 10 to approximately 500 nm), fabricated both by spin-coating and gravure-printing. Silane reagents of the formula X 3Si-R-SiX 3 (R = -C 6H 12- and X = Cl, OAc, NMe 2, OMe, or R = -C 2H 4-O-C 2H 4- and X = OAc) exhibit tunable reactivity with hydroxyl-containing substrates. Dielectric films fabricated by blending X 3Si-R-SiX 3 with poly(4-vinyl)phenol (PVP) require very low-curing temperatures ( approximately 110 degrees C) and adhere tenaciously to a variety of FET gate contact materials such as n (+)-Si, ITO, and Al. The CPB dielectrics exhibit excellent insulating properties (leakage current densities of 10 (-7) approximately 10 (-8) A cm (-2) at 2.0 MV/cm) and tunable capacitance values (from 5 to approximately 350 nF cm (-2)). CPB film quality is correlated with the PVP-cross-linking reagent reactivity. OFETs are fabricated with both p- and n-type organic semiconductors using the CPB dielectrics function at low operating voltages. The morphology and microstructure of representative semiconductor films grown on the CPB dielectrics is also investigated and is correlated with OFET device performance.     

Achieving high electric energy storage in a polymer nanocomposite at low filling ratios using a highly polarizable phthalocyanine interphase

Polymer nanodielectrics have become attractive for practical applications such as electric energy storage and electromechanical actuation. However, to enhance the apparent dielectric constant of polymer nanodielectrics, a significant amount (>30 vol %) of spherical particles needs to be incorporated into the polymer matrix. As a consequence, melt-processing of polymer nanodielectrics into uniform thin films becomes difficult at such a high filler content, and electric breakdown strength will greatly decrease. In this work, we describe a three-phase composite approach towards high energy density nanodielectrics at low filling ratios. In this approach, a highly polarizable tetrameric metallophthalocyanine (TMPc) initiator is coated onto 68 nm BaTiO₃ nanoparticles, from which poly(methyl methacrylate) (PMMA) brushes are grafted using atom transfer radical polymerization for the nanoparticles to be uniformly dispersed in a poly(vinylidene fluoride-co-hexafluoropropylene) [P(VDF-HFP)] matrix. For comparison, two-phase P(VDF-HFP)/BaTiO₃ composites without the TMPc interfacial layer are also prepared. Owing to the high polarizability of the TMPc interface layer, the three-phase composite films exhibit higher dielectric constant and thus higher energy density than the two-phase composite films at volume-filling ratios below 5 vol %. Therefore, these high energy density three-phase nanodielectrics with a low filling ratio are promising for melt-processing into thin dielectric films. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1669–1680     

Low-voltage organic field-effect transistors and inverters enabled by ultrathin cross-linked polymers as gate dielectrics

The quest for high-performance organic thin-film transistor (OTFT) gate dielectrics is of intense current interest. Beyond having excellent insulating properties, such materials must meet other stringent requirements for optimum OTFT function: efficient low-temperature solution fabrication, mechanical flexibility, and compatibility with diverse gate materials and organic semiconductors. The OTFTs should function at low biases to minimize power consumption, hence the dielectric must exhibit large gate capacitance. We report the realization of new spin-coatable, ultrathin (<20 nm) cross-linked polymer blends exhibiting excellent insulating properties (leakage current densities approximately 10(-)(8) Acm(-)(2)), large capacitances (up to approximately 300 nF cm(-)(2)), and enabling low-voltage OTFT functions. These dielectrics exhibit good uniformity over areas approximately 150 cm(2), are insoluble in common solvents, can be patterned using standard microelectronic etching methodologies, and adhere to/are compatible with n(+)-Si, ITO, and Al gates, and with a wide range of p- and n-type semiconductors. Using these dielectrics, complementary invertors have been fabricated which function at 2 V.     

Solution-deposited organic-inorganic hybrid multilayer gate dielectrics. Design, synthesis, microstructures, and electrical properties with thin-film transistors

We report here on the rational synthesis, processing, and dielectric properties of novel layer-by-layer organic/inorganic hybrid multilayer dielectric films enabled by polarizable π-electron phosphonic acid building blocks and ultrathin ZrO(2) layers. These new zirconia-based self-assembled nanodielectric (Zr-SAND) films (5-12 nm thick) are readily fabricated via solution processes under ambient atmosphere. Attractive Zr-SAND properties include amenability to accurate control of film thickness, large-area uniformity, well-defined nanostructure, exceptionally large electrical capacitance (up to 750 nF/cm(2)), excellent insulating properties (leakage current densities as low as 10(-7) A/cm(2)), and excellent thermal stability. Thin-film transistors (TFTs) fabricated with pentacene and PDIF-CN(2) as representative organic semiconductors and zinc-tin-oxide (Zn-Sn-O) as a representative inorganic semiconductor function well at low voltages (<±4.0 V). Furthermore, the TFT performance parameters of representative organic semiconductors deposited on Zr-SAND films, functionalized on the surface with various alkylphosphonic acid self-assembled monolayers, are investigated and shown to correlate closely with the alkylphosphonic acid chain dimensions.     

A Facile Photo-cross-linking Method for Polymer Gate Dielectrics and Their Applications in Fully Solution Processed Low Voltage Organic Field-effect Transistors on Plastic Substrate

A simple and effective photochemical method was developed for cross-linking of polymer gate dielectrics.Laborious synthetic processes for functionalizing polymer dielectrics with photo-cross-linkable groups were avoided.The photo-cross-linker,BBP-4,was added into host polymers by simple solution blending process,which was capable of abstracting hydrogen atoms from polymers containing active C―H groups upon exposure to ultraviolet(UV) radiation.The cross-linking can be completed with a relatively long wavelength UV light(365 nm).The approach has been applied to methacrylate and styrenic polymers such as commercial poly(methylmethacrylate)(PMMA),poly(iso-butylmethacrylate)(Pi BMA) and poly(4-methylstyrene)(PMS).The cross-linked networks enhanced dielectric properties and solvent resistance of the thin films.The bottom-gate organic field-effect transistors(OFETs) through all solution processes on plastic substrate were fabricated.The OFET devices showed low voltage operation and steep subthreshold swing at relatively small gate dielectric capacitance.     

Averaged local field intensities in composite materials

Averaged local field intensities are calculated for isotropic composites in the Maxwell-Garnett and in the effective medium theories. Exact upper and lower bounds on these intensities are also found. Implications for photophysical properties of molecules embedded in the composites are discussed.     

Polymer electrolyte-gated organic field-effect transistors: low-voltage, high-current switches for organic electronics and testbeds for probing electrical transport at high charge carrier density

We report the fabrication and extensive characterization of solid polymer electrolyte-gated organic field-effect transistors (PEG-FETs) in which a polyethylene oxide (PEO) film containing a dissolved Li salt is used to modulate the hole conductivity of a polymer semiconductor. The large capacitance (approximately 10 microF/cm2) of the solution-processed polymer electrolyte gate dielectric facilitates polymer semiconductor conductivities on the order of 103 S/cm at low gate voltages (<3 V). In PEG-FETs based on regioregular poly(3-hexylthiophene), gate-induced hole densities were 2 x 10(14) charges/cm2 with mobilities >3 cm2/V.s. PEG-FETs fabricated with gate electrodes either aligned or intentionally nonaligned to the channel exhibited dramatically different electrical behavior when tested in vacuum or in air. Large differences in ionic diffusivity can explain the dominance of either electrostatic charging (in vacuum) or bulk electrochemical doping (in air) as the device operational mechanism. The use of a larger anion in the polymer electrolyte, bis(trifluoromethanesulfonyl)imide (TFSI-), yielded transistors that showed clear current saturation and square law behavior in the output characteristics, which also points to electrostatic (field-effect) charging. In addition, negative transconductances were observed using the PEO/LiTFSI electrolyte for all three polymer semiconductors at gate voltages larger than -3 V. Bias stress measurements performed with PEO/LiTFSI-gated bottom contact PEG-FETs showed that polymer semiconductors can sustain high ON currents for greater than 10 min without large losses in conductance. Collectively, the results indicate that PEG-FETs may serve as useful devices for high-current/low-voltage applications and as testbeds for probing electrical transport in polymer semiconductors at high charge density.     

Thermal stability of CR/CSM rubber blends filled with nano- and micro-silica particles

The properties of filled polymers depend on the properties of the matrix and the filler, the concentration of the components and their interactions. In this research we investigated the rheological and mechanical properties and thermal stability of polychloroprene/chlorosulfonated polyethylene (CR/CSM) rubber blends filled with nano- and micro-silica particles. The density of the nano-silica filled CR/CSM rubber blends was lower than that of the micro-silica filled samples but the tensile strength and elongation at break were much higher. The nano-silica filled CR/CSM rubber blend has higher V _r0/V _rf values than micro-silica composites and show better polymer–filler interaction according to Kraus equation. The nano-silica filled CR/CSM rubber blends were transparent at all filler concentration, and have higher glass transition values than micro-silica filled compounds. The higher values of the glass transition temperatures for the nano- than the micro-filled cross-linked systems are indicated by DMA analysis. The nano-filled cross-linked systems have a larger number of SiO–C links than micro-filled cross-linked systems and hence increased stability.     

Preparation and applications of novel fluoroalkyl end-capped oligomers/calcium carbonate nanocomposites

Calcium chloride reacted with sodium carbonate in the presence of a variety of self-assembled molecular aggregates formed by fluoroalkyl end-capped acrylic acid, 2-methacryloyloxyethane sulfonic acid, dimethylacrylamide, and acryloylmorpholine oligomers in aqueous solutions to afford the corresponding fluorinated oligomers/calcium carbonate composites in excellent to moderate isolated yields. These fluorinated calcium carbonate composites thus obtained were shown to have a good dispersibility not only in water but also in traditional organic media including fluorinated solvents. Dynamic light scattering measurements (DLS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that these fluorinated composites are nanometer-size-controlled particles and well dispersed in these media. Cross-linked fluoroalkyl end-capped acrylic acid co-oligomer containing poly(oxyethylene) units was also applied to the preparation of new cross-linked fluorinated calcium carbonate nanocomposites under similar conditions. The obtained cross-linked fluorinated calcium carbonate nanocomposites were found to have an extremely higher dispersibility in aqueous and organic media including fluorinated solvents, compared to that of the corresponding fluoroalkyl end-capped oligomer nanocomposites. In particular, it was verified that these fluorinated calcium carbonate nanocomposites are applicable to the dispersion above poly(methyl methacrylate) (PMMA) film surface. Interestingly, field-emission SEM (FE-SEM) images of the cross-section of the modified PMMA films showed that calcium carbonate particles dispersed into these PMMA films could be arranged regularly above the modified film surface. More interestingly, cross-linked fluorinated oligomeric aggregates were able to provide suitable host moieties for the crystallization of calcium carbonate.     

自组装金团簇电极库仑台阶现象和电化学阻抗谱研究

采用示差脉冲伏安法研究了自组装单层保护金纳米团簇(C8AuMPC)在常温下二氯甲烷溶液中的量子化电容充电效应. 研究结果表明, 该团簇在-0.8~0.8 V 电位范围内有4 对明显的量子化电容充电峰. 同时采用电化学阻抗谱对C8AuMPC修饰金电极体系的界面结构进行了表征, 研究结果表明, MPC自组装层存在两个界面, 即金电极-MPC层界面和MPC层-溶液界面; 这两个界面的界面电容在MPC的零电荷电位(ca.-0.2 V)附近均基本保持不变, 随着电位正移或负移到一定程度, 界面电容发生变化. 进一步利用双隧道结金属岛库仑阻塞效应理论讨论了已有报道中对MPC量子化电容充电的理论分析结果, 并证明电化学阻抗谱也是研究MPC量子化电容充电效应的有效方法. 另外, 用示差脉冲伏安法及循环伏安法研究了电活性物种二茂铁对C8AuMPC量子化电容充电的影响, 发现溶液中的电活性物种对MPC层-溶液界面的电子传递的贡献可以忽略, 表明该界面的电子传递主要发生在纳米粒子之间.     

Multilayered polycarbonate/poly(vinylidene fluoride‐co‐hexafluoropropylene) for high energy density capacitors with enhanced lifetime

The dielectric lifetime and corresponding damage morphology of polycarbonate/poly(vinylidene fluoride‐co‐hexafluoropropylene) (PC/P(VDF‐HFP)) layered systems are studied under constant direct current (DC) field. Melt blends of the two polymers are also considered for comparison. The dielectric lifetimes of the latter are systematically much shorter than the layered systems. The interfaces between the polymers act as flaws that induce up to two orders of magnitude difference between the layered and blend systems. The capacitance values versus time during breakdown progression exhibit an inversed S‐shape pattern. The three regimes in the S‐shape pattern are consecutively attributed to randomly isolated breakdowns, interconnecting breakdowns, and wearing‐out of the capacitor film. The film breakdown images during dielectric lifetime test confirmed the transition from randomly isolated breakdowns to interconnecting breakdowns. This transition was further evidenced by a bimodal distribution in the Weibull analysis. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

自组装单层保护金纳米团簇的量子化电容充电

本文研究自组装单层保护金纳米团簇(C12Au MPC)在常温下二氯甲烷溶液中的量子化电容充电效应.示差脉冲伏安曲线显示金核平均直径为2.0 nm的C12Au MPC在-0.6~0.6 V电位区间内有9个明显的量子化电容充电峰,其双电层电容总的变化趋势为在零电荷电位附近最小,随着电位正移或负移电容变大.而且随着该金核尺寸的增大,MPC双电层电容值也变大.     

Modeling interband transitions in silver nanoparticle-fluoropolymer composites

The interband transition contributions to the optical properties of silver nanoparticles in fluoropolymer matrices are investigated. For the materials in this study, nanoparticle synthesis within the existing polymer matrix is accomplished using an infusion process that consists of diffusing an organometallic precursor gas into the free volume of the fluoropolymer and decomposing the precursor followed by metal nanoparticle nucleation and growth. The resulting polymer matrix nanocomposite has optical properties that are dominated by the response of the nanoparticles owing to the broadbanded transparency of the fluoropolymer matrix. The optical properties of these composites are compared to Maxwell-Garnett and Mie theory with results indicating that interband transitions excited in the silver nanoparticles affect the optical absorption over a range of frequencies including the surface plasmon resonance. It is shown that calculations of the optical absorption spectrum using published data for the silver dielectric function do not accurately describe the measured material response and that a classical model for bound and free electron behavior can best be used to represent the dielectric function of silver.     

Al3+交联聚合物分子构型及其影响因素

The chemical composition, percolation performace, and microscopic configuration of“intramolecular cross鄄linked”gel systems were investigated by changing the contents of Na+, Ca2+, Mg2+ ions and polymer concentration in water solvent. The results show that the viscosity of“intramolecular cross-linked”polymer solution changes not too much with time, but the resistance factor and residual resistance factor are obviously larger than those of the ordinary polymer solution with the same viscosity, and the residual resistance factor is larger than the resistance factor. The contents of Na+, Ca2+ and Mg2+ ions and polymer concentrations will affect the molecular configuration of the cross-linked polymer, in which the effect of Ca2+ and Mg2+ is the largest.     

Recent Progress in Two-dimensional Nanomaterials Following Graphene for Improving Fire Safety of Polymer (Nano)composites

The high fire safety of polymer nanocomposites is being pursued by research institutions around the world. In addition to intrinsic flame retardancy strategy, the additive-type flame retardants have attracted increasing attention due to low commercial cost and easy fabrication craft. However, traditional additive-type flame retardants usually need high addition amount to achieve a desirable effect, which causes many side-effects on the overall performance of polymer materials, such as deteriorated mechanical property and processability. At present, two-dimensional(2 D) nanomaterials have also been applied to reduce the fire hazards of polymer(nano)composites with the coupling of barrier function and catalysis as well as carbonization effect. Even though most research work mainly focus on graphene-based flame retardants, more emerging two-dimensional nanomaterials are taking away research attention, due to their complementary and unique properties, mainly including hexagonal boron nitride(h-BN), molybdenum disulfide(MoS_2), metal organic frameworks(MOF), carbon nitride(CN),titanium carbide(MXene) and black phosphorene(BP). In this review, except for graphene, the flame retardant mechanism involving different layered nanomaterials are also reviewed. Meanwhile, the functionalization method and flame retardancy effect of different layered nanomaterials are emphatically discussed for offering an effective reference to solve the fire hazards of polymer materials. Moreover, this work objectively evaluates the practical significance of polymer/layered nanomaterials composites for industrial application.     

Synthesis of polymer dielectric layers for organic thin film transistors via surface-initiated ring-opening metathesis polymerization

The use of surface-initiated ring-opening metathesis polymerization (SI-ROMP) for producing polymer dielectric layers is reported. Surface tethering of the catalyst to Au or Si/SiO2 surfaces is accomplished via self-assembled monolayers of thiols or silanes containing reactive olefins. Subsequent SI-ROMP of norbornene can be conducted under mild conditions. Pentacene semiconducting layers and gold drain/source electrodes are deposited over these polymer dielectric films. The resulting field effect transistors display promising device characteristics, demonstrating for the first time that SI-ROMP can be used in the construction of organic thin-film electronic devices.     

Amphiphilic self-assembled polymeric copper catalyst to parts per million levels: click chemistry

Self-assembly of copper sulfate and a poly(imidazole-acrylamide) amphiphile provided a highly active, reusable, globular, solid-phase catalyst for click chemistry. The self-assembled polymeric Cu catalyst was readily prepared from poly(N-isopropylacrylamide-co-N-vinylimidazole) and CuSO(4) via coordinative convolution. The surface of the catalyst was covered with globular particles tens of nanometers in diameter, and those sheetlike composites were layered to build an aggregated structure. Moreover, the imidazole units in the polymeric ligand coordinate to CuSO(4) to give a self-assembled, layered, polymeric copper complex. The insoluble amphiphilic polymeric imidazole Cu catalyst with even 4.5-45 mol ppm drove the Huisgen 1,3-dipolar cycloaddition of a variety of alkynes and organic azides, including the three-component cyclization of a variety of alkynes, organic halides, and sodium azide. The catalytic turnover number and frequency were up to 209000 and 6740 h(-1), respectively. The catalyst was readily reused without loss of catalytic activity to give the corresponding triazoles quantitatively.     

超高分子量聚乙烯基导电复合材料的电性能和自发热性能的研究

超高分子量聚乙烯(UHMWPE)具有优异的综合性能,本文采用凝胶结晶溶液方法制备了分别以碳纤维(CF)和镀镍碳纤维(NiCF)为导电填料,UHMWPE为基体的3个系列导电聚合物复合材料—UHMWPE/CF、UHMWPE/NiCF和UHMWPE/EMMA/CF复合体系,并分别对它们进行了室温伽马射线辐射处理,重点研究了这些材料的电性能和自发热性能,利用DSC、SEM、WAXS、DMA和体积膨胀等仪器进行了一系列测试表征。结果表明,NiCF作为导电填料时体系的逾渗阈值最低,为3vol%。伽马射线辐射处理不仅能有效提高材料的PTC效应,而且在合适的辐射剂量时也能有效提高材料的自发热性能。对材料介电性能的研究揭示了材料的交流电阻率与温度、频率的依赖关系。     

Cellulose acetate/poly(methyl methacrylate) interpenetrating networks: synthesis and estimation of thermal and mechanical properties

IPN-type composites consisting of cellulose acetate (CA) and poly(methyl methacrylate; PMMA) were successfully synthesized in film form. In this synthesis, a mercapto group (SH)-containing CA, CA-MA, was prepared in advance by esterification of CA with mercaptoacetic acid, and then intercomponent cross-linking between CA-MA and PMMA was attained by thiol–ene polymerization of methyl methacrylate (MMA) onto the CA-MA substrate. For comparison, polymer synthesis was also attempted to produce a semi-IPN type of composites comprising CA and cross-linked PMMA, via copolymerization of MMA and ethylene glycol dimethacrylate as cross-linker in a homogeneous system containing CA solute. Thermal and mechanical properties of thus obtained polymer composites were investigated by differential scanning calorimetry, dynamic mechanical analysis, and a tensile test, in correlation with the mixing state of the essentially immiscible cellulosic and methacrylate polymer components. It was shown that the specific IPN technique using thiol–ene reactions usually resulted in a much better compatibility-enhanced polymer composite, which exhibited a higher tensile strength and even an outstanding ductility without parallel in any film sample of CA, PMMA, and their physical blends.