Effect of field enhancement on inorganic powder electroluminescence using short carbon nanotubes

Inorganic powder electroluminescence (IPEL) devices with the insertion of a carbon nanotube (CNT) layer were investigated to verify the effect of the increased local field produced by CNTs on electroluminescence (EL). To increase the field strength effectively, the CNTs were shortened using the cryogenic crushing method. IPEL devices with the insertion of a short CNT layer exhibited an increase in brightness and efficiency with increasing amount of CNTs. The local field enhancement by CNTs, further enlarged by the triple-junction, could increase the field strength applied to the phosphor, resulting in improved EL performance. In addition, short CNTs in an EL device can lead to field enhancement without an unintentional current flowing into the device.     

Simple and Fast Organic Device Encapsulation Using Polyisobutene

Summary: We demonstrate the use of polyisobutene (PIB) in a glass encapsulation method suitable for organic devices. The PIB viscosity at environmental temperatures provides a fast and non‐aggressive passivant layer formation method for device protection with glass. Due to its fully aliphatic character, PIB is suitable for passivating organic light‐emitting and photovoltaic devices. The observed preservation of encapsulated Ca films demonstrates the PIB suitability for air‐unstable metals passivation. Stable I(V) characteristics and increased operational lifetime were observed in PIB‐encapsulated organic devices. This encapsulation method is cheap, simple, and dispenses intensive equipment use, so that it is appropriate even for laboratories with restricted experimental facilities.

Setup used for Ca samples testing. The right Ca contact was encapsulated with PIB and a glass cover plate (dashed square). The electrical diagram of the apparatus used to obtain the resistance behavior is also shown.     

Enhancing the electroluminescence performances of blue polymer light emitting devices via carriers transporting materials incorporation

A series of polymer light emitting devices (PLEDs) based on the composite films of N‐arylbenzimidazoles trimer (TPBI), poly (n‐vinylcarbazole) (PVK), and a triarylaminooxadiazole‐containing tetraphenylsilane light emitting polymer (PTOA) were investigated. Electroluminescence (EL) performance is enhanced with doped TPBI into the light‐emitting layer for the PTOA‐based devices. A deep blue emission (Commission Internationale de L'Eclairage (CIE_x,y) corodinates (0.16,0.06)) is obtained for the TPBI‐PTOA‐based device. Brightness and current efficiency of the TPBI‐PTOA‐based device can be as high as 961 cd/m² and 1.85 cd/A, respectively. The EL performances of TPBI‐PTOA composite film‐based devices are further enhanced by inserting a TPBI layer into the light emitting layer and cathode interface for a better electron and hole charge balance. Doping TPBI into the light‐emitting layer of PVK‐PTOA is not favorable for enhanced EL performances. Brightness and current efficiency reduced with increasing TPBI content for the TPBI‐PVK‐PTOA‐based devices. Similar results are obtained for devices based on the TPBI‐PVK‐PTOA/TPBI bi‐layer composite solid film. Morphology and charge balance effects on EL performances of TPBI‐PTOA and TPBI‐PVK‐PTOA composite films based PLEDs are discussed in detail. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Electroluminescence from porous silicon formed by photoetching in an HF/I<Subscript>2</Subscript> solution

We demonstrate the formation of a light-emitting porous silicon (PSi) layer by photoetching in an HF/I₂ solution. The use of a Xe lamp makes possible a large and homogeneous PSi layer on an n-type Si(100) wafer. An insulating layer has been formed on the PSi layer by chemical oxidation in an acidic solution. These techniques are used to fabricate electroluminescent (EL) devices of metal/insulator/semiconductor (MIS) type. It is shown that the present device is superior with respect to emission efficiency to the conventional Schottky- or metal/semiconductor-type device.     

吡唑啉衍生物作为空穴传输层在电致发光材料中的应用

我们曾报道过有关１，３二苯基吡唑啉衍生物的光谱和光物理行为［１，２］，并详细地研究了它们在受激发后的辐射和非辐射衰变过程．该类化合物作为一种良好的光致发光材料，由于存在着分子内共轭的电荷转移结构，因此表现出较强的光诱导分子极化能力，可用作为有机非线性光学材料［３］、光折变材料等．此外，还发现该类化合物在组合型光导器件中可用作空穴传输层材料．既然这类化合物兼具光致发光和空穴传输功能，很自然的会考虑到，它是否也能用作为一种有机的电致发光（ＥＬ）材料．有机电致发光材料的重要性自不待言，特别近年来许多…     

Synthesis and light‐emitting properties of new poly(p‐phenylenevinylene) derivatives containing oxadiazole moiety

Two new poly(p‐phenylenevinylene) (PPV) derivatives containing the oxadiazole moiety (OXA–PPV1 and OXA–PPV2) were synthesized by the Wittig condensation polymerization reaction and their thermal and light‐emitting properties were investigated. The single‐layer and triple‐layer electroluminescent (EL) devices with configurations of ITO/OXA–PPV1/Al and ITO/OXA–PPV1/OXD/Alq₃/Al were fabricated. They both exhibited blue emission at 460 nm. For comparison, the PPV derivative containing the oxadiazole moiety only in the side chains (OXA–PPV2) was also synthesized. Both single‐layer and triple‐layer EL devices with OXA–PPV2 as the emissive layer emitted green‐light at 560 nm. The turn‐on voltages of the triple‐layer device was 11 V for OXA–PPV1 and 8 V for OXA–PPV2. The triple‐layer EL devices showed much better performance than that of the single‐layer devices. The spectra indicated that energy or electron transfer occurred from the side‐chain oxadiazole to the main‐chain styrene unit. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2424–2428, 2002     

电解制氟与石墨阳极表面氟化石墨钝化层的研究

合成氟化石墨的关键原料是单质氟气。利用自制的电解装置,通过电解熔盐KF·2HF成功地制取了氟气。采用特制的“阳极罩”使电解制得的F2与H2隔离,提高了安全性。用石墨材料作阳极,表面易生成不利于电解电流通过的“钝化层”,经红外光谱测试分析,其组成为富含F-C健的氟化石墨,而用无定型炭材料作电解阳极,不易生成该钝化层,且使用寿命较长。     

Syntheses and properties of electroluminescent polyfluorene-based conjugated polymers, containing oxadiazole and carbazole units as pendants, for LEDs

New polyfluorenes (PF)-based conjugated copolymers, containing oxadiazole and carbazole units as pendants, were prepared as the electroluminescent (EL) layer in light-emitting diodes (LEDs) to show that most of them have higher maximum brightness and EL efficiency as compared to poly(2,7-(9,9-bis(2-ethylhexyl)fluorene)) (PF2/6). The prepared polymers, poly[(9-(6-(N-carbazolyl)-hexyl)-9-hexyl)-fluorene-2,7-diyl]-co-[(9-hexyl-9-(6-(4-(5-phenyl-1,3,4-oxadiazolyl)-phenoxy)-hexyl)-fluorene-2,7-diyl)] (Oxd-PF-co-Cz-PF), were soluble in common organic solvents and used as the EL layer in double layer light-emitting diodes (LEDs) (ITO/PEDOT/polymer/Al). All polymers show photoluminescence around λ_max=430 nm (exciting wavelength, 370 nm) and blue EL around λ_max=426 nm. The current–voltage–luminance (I–V–L) characteristics of the polymers show turn-on voltages of 3.5–5.5 V which are lower than that of PF2/6. The maximum brightness and EL efficiency of the device with the configuration of ITO/PEDOT/polymer/Al were 3000 cd/m² at 10 V and 2.13 cd/A at 10.6 mA/cm², respectively, which are all higher than those of PF2/6.     

Synthesis and light‐emitting properties of new poly(p‐phenylenevinylene) derivatives containing oxadiazole moiety

Two new poly(p‐phenylenevinylene) (PPV) derivatives containing oxadiazole moiety (OXA‐PPV1 and OXA‐PPV2) were synthesized by the Wittig condensation polymerization reaction. Their thermal and light‐emitting properties were investigated. The single‐ and triple‐layer electroluminescent (EL) devices with configurations of ITO/polymer/Al and ITO/polymer/OXD‐7/Alq₃/Al were fabricated. They exhibited blue emission at 470 nm for OXA‐PPV1 and green emission at 560 nm for OXA‐PPV2. The turn‐on voltages of triple‐layer device were 11 V for OXA‐PPV1 and 8 V for OXA‐PPV2. The triple‐layer EL devices showed much better performance than did the single‐layer devices. The spectra indicated energy transfer occurred from segments of side chain to polymer backbone. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 422–428, 2002     

Remarks on the passivation of reduced Cu-, Ni-, Fe-, Co-based catalysts

Catalysts containing metals such as Cu, Ni, Fe, Co in their reduced state are often subjected to passivation procedures prior to characterization. Passivation with N₂O or O₂ to create a protective oxide layer also results in a certain degree of sub-surface oxidation. The heat released during oxidation is a critical parameter. The extent of bulk oxidation depends on the type of oxidant as well as on the size of the metal particles, as shown for copper catalysts. The final, meta-stable passivation layer requires a certain thickness to sustain exposure to ambient atmosphere. The encapsulation of metal particles in carbon is an efficient method for preserving the metallic state, as demonstrated for metallic nickel and iron with carbon nanofibers. The use of passivated samples for characterization of the active, i.e., reduced, catalyst has limited value.     

The production of a flexible electroluminescent device on polyethylene terephthalate films using transparent conducting carbon nanotube electrode

An inorganic electroluminescent (EL) device on a flexible polyethylene terephthalate (PET) substrate and its properties were investigated. The transparent conducting film (TCF) made from carbon nanotubes (CNTs) (CNT-TCF) was employed in the flexible EL device. CNT-TCF was formed by filtration of CNT solution and was transferred to the PET film. It was found that the brightness of the inorganic EL device was strongly dependent on the quality of the CNT composite films. After a 3-aminopropyltriethoxysilane treatment of the PET substrate, CNTs uniformly were dispersed and showed a good adhesion to the substrate, and the resulting EL device showed better performance. The flexible EL device showed the brightness of 96.8 cd/m² at 28 kHz and 50 V.     

Effects of moisture and electrode material on AlN-based resistive random access memory

Resistive random access memory (RRAM) has been developed as a next-generation nonvolatile memory because of its fast operation speed, low power consumption, high density, and simple structure. Non-oxide materials such as AlN-based RRAM also exhibit low operation energy and large on/off ratios. However, AlN-based RRAM may deteriorate upon oxidation when exposed to air/moisture. In addition, chemical reactivity between the electrode and the switching layer material affects device stability. In this study, four kinds of top electrode materials (Al, Ti, TiN, and Pt) were used in an AlN/TiN stack and a water-resistant encapsulation layer was used to prevent the degradation of AlN-based RRAM. The electrical properties of the device were measured at weekly intervals for 7 weeks. The devices containing Al and Ti top electrodes showed degradation of resistance states despite being encapsulated in a thin Al2O3 layer. In contrast, the devices with TiN and Pt electrodes maintained their resistance states and switching properties regardless of the encapsulation layer. These trends in degradation can be explained by the electrode and AlN reactivity with moisture based on fundamental thermodynamics.     

Injection molding electroluminescent components

This article explores the feasibility of using mass manufacture, namely injection molding, as a route to produce cost effective electroluminescent (EL) components straight from the mold tool. EL screen printing pastes were adapted and introduced into the injection molding environment as a multilayer structure. Four‐layer systems were investigated using a spray deposition method to apply individual layer components directly in‐mold. Finally, the substrate was back injected to produce a three‐dimensional illuminating device straight from the mold tool. Materials, methods, and outcomes are described, the implication being that electronic manufacture could be moved upstream and performed in‐mold with resultant cost and energy savings. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

开路电位测量法评价镀锌层三价铬钝化膜的耐蚀性

用钝化剂TRI-V 120、TRI-V 121和SpectraMATETM 25分别对碱性无氰镀锌层进行钝化,考察了钝化层在不同pH的1%(质量分数)NaCl溶液中的开路电位随时间的变化.结果表明,开路电位变化受溶液pH的影响.在pH=3时,镀锌钝化层的开路电位随时间呈规律性变化:开始电位较高,反映了完整钝化层的电极电位;随后逐渐变负,反映了钝化膜的溶解过程;最后处在锌的电极电位范围,反映了钝化膜已经完全溶解.对比盐雾试验结果后发现,从钝化膜电位变化到锌电极电位所需的时间能够反映钝化膜的稳定性,即时间越长,耐蚀性能越好.因此,开路电位测量法能够快速评价镀锌钝化层的耐蚀性.     

Synthesis of copolyfluorenes with high fluorenone contents and its application in electroluminescent device by simple blending

Poly(fluorene‐co‐fluorenone)s containing high contents of fluorenone chromophore were synthesized by the Suzuki coupling reaction to study their electroluminescent (EL) properties. The copolymers are thermally stable below 430°C (T_d) in nitrogen atmosphere. In film state, their absorption and photoluminescence spectra (peaked at 373–382 nm and 562–564 nm, respectively) are mainly originated from fluorenone units, because of its efficient energy transfer. Both LUMO and HOMO energy levels, estimated from their cyclic voltammograms, are lowered slightly (−3.17→−3.23 eV, −5.84→−5.89 eV) with increasing contents of electron‐withdrawing fluorenone units. Double‐layer EL devices, using the copolyfluorenes or their blends with poly(9,9‐dihexylfluorene) ( PF ) as emitting layer, show exclusive emission originated from fluorenone chromophore (565 nm) when its content is high. Blending 0.02–5 wt % of PF‐33 (fluorenone fraction: 0.37) with PF greatly enhances device performance (610 cd m⁻² → 4400 cd m⁻² and 0.45 cd A⁻¹ → 1.52 cd A⁻¹). Our results demonstrate that the copolyfluorenes are promising emitting materials for EL devices by simple blending. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Mechanism of the effects of low temperature Al2O3 passivation on graphene field effect transistors

The origin of the device instability of chemical vapor deposited graphene metal oxide semiconductor field effect transistor has been investigated while varying the characterization time scale from milliseconds to a few tens of seconds. When oxygen diffusion to the graphene interface was suppressed with Al₂O₃ passivation layer, the hysteresis activated with a time scale over a few tens of seconds was reduced significantly at both electron and hole branches of current–voltage curves. However, a fast charge trapping process occurring within a few milliseconds was not affected by the passivation and became a dominant mechanism of hysteresis.     

Synthesis and optoelectronic properties of luminescent copolyfluorenes slightly doped with thiophene chromophore

This paper describes the synthesis of new copolyfluorenes (P05-P5) slightly doped with 2,5-bis(2-phenyl-2-cyanovinyl)thiophene (GM, <3.4 mol%) and their application in electroluminescent (EL) devices. In film state, EL spectra of the copolyfluorenes are very different from photoluminescence (PL) spectra, which have been ascribed to charge trapping in GM and energy transfer from fluorene segments to GM chromophores. The maximum brightness and current efficiency of EL device from P05 (5230 cd/m², 0.65 cd/A) are significantly enhanced when compared with those from poly(9,9-dihexylfluorene) (PF) (1310 cd/m², 0.18 cd/A). The EL device using blend of P5 and PF (w/w = 10/1) as emitting layer exhibits near-white emission with CIE coordinate being (0.26, 0.32). The results demonstrate that the copolyfluorenes slightly doped with GM chromophore are promising emitting materials for optoelectronic devices.     

Air-stable all inorganic green perovskite light emitting diodes based on ZnO/CsPbBr3/NiO heterojunction structure

Perovskite light emitting diodes (PeLEDs) now emerge as a promising new optoelectronic application field for these amazing semiconductors. However, most PeLEDs contain organic components, which make them unstable in the air. For fabricating the air-stable all inorganic green PeLEDs, we have designed green PeLEDs based on the ZnO/CsPbBr₃/NiO heterojunction structure. The emission layer inorganic perovskite CsPbBr₃ film with small grain sizes was prepared using a two-step method. The device exhibits a typical rectification behavior with turn-on voltage of ~ 3 V. The working mechanism of the device is discussed. The EL emission bands are narrow with small FWHM values. The continuous working air-stability was also monitored. The results reveal our PeLED can maintain a good color purity and a stable EL intensity when it works continuously in the air. Our present work suggests great potential for the development and practical commercial application of PeLEDs.     

Green electroluminescent diode from poly(2-trimethylsilyl-1,4-phenylene vinylene)

Summary Poly(2-trimethylsilyl-1,4-phenylenevinylene) (TMS-PPV) was synthesized through a organic-soluble precursor polymer, and its properties were characterized by UV-visible, FT-IR spectroscopy and thermal anaylsis. The EL devices were fabricated with TMS-PPV as an emitting layer, and ITO and aluminum as positive and negative electrodes, respectively. Threshold voltage of the device was about 15 V and the emission maximum was at about 540 nm with quantum efficiency of 3.5x10^-4% photons per electron in air and room temperature condition.     

Adhesion of underfill and components in flip chip encapsulation

The underfill material is a polymeric adhesive used in flip chip packaging. It encapsulates the solder joints by filling the gap between a silicon die and an organic substrate or board. Within a typical flip chip structure, there are interfaces between the various components, namely, substrate, solder mask, flux residue, underfill encapsulant and die passivation layer, etc. Maintaining a good adhesion condition, both as-made and after temperature/humidity aging, is vital for these interfaces because of the expected performance of the flip chip device, where the underfill material is employed to enhance the reliability of the flip chip interconnect. We have studied the adhesion strength between the various components for different process variables as measured with the lap shear and die shear test configurations. The effects of the assembly factors, i.e. solder mask, flux residue, underfill, and die passivation, etc., were evaluated and the adhesion strength was found to depend greatly on these factors. The die shear strength of a passivated die assembled onto an organic board coated with a solder mask was much higher after using a no-clean flux on the solder mask than for the assembly without such a no-clean flux. The influence of some accelerated aging tests on the adhesion durability was also investigated. A die passivation layer of benzocyclobutene exhibited better capability in retaining the die shear strength than a passivation layer of silicon nitride or polyimide, especially for the initial aging period. The knowledge obtained in this study should provide insights into the interfacial adhesion in the flip chip assembly structure.