Novel Patterning of Gold Using Spin‐Coatable Gold Electron‐Beam Resist

Conventional lithography methods of gold patterning are based on deposition and lift‐off or deposition and etching. In this letter, we demonstrate a novel method of gold patterning using spin‐coatable gold electron‐beam resist which is functionalized gold nanocrystals with amine ligands. Amine‐stabilized gold electron beam resist exhibits good sensitivity, 3.0 mC/cm², compared to that of thiol‐stabilized gold electron beam resists. The proposed method reduces the number of processing steps and provides greater freedom in the patterning of complex nanostructures.     

Micro‐Nanostructured Interfaces Fabricated by the Use of Inorganic Block Copolymer Micellar Monolayers as Negative Resist for Electron‐Beam Lithography

This paper introduces an approach where the match of two different length scales, i.e., pattern from self‐assembly of block copolymer micelles (< 100 nm) and electron‐beam (e‐beam) writing (> 50 nm), allow the grouping of nanometer‐sized gold clusters in very small numbers in even aperiodic pattern and separation of these groups at length scales that are not accessible by pure self‐assembly. Thus, we could demonstrate the grouping of Au nanoclusters in different geometries such as squares, rings, or spheres.     

n‐Doping of a Low‐Electron‐Affinity Polymer Used as an Electron‐Transport Layer in Organic Light‐Emitting Diodes

n‐Doping electron‐transport layers (ETLs) increases their conductivity and improves electron injection into organic light‐emitting diodes (OLEDs). Because of the low electron affinity and large bandgaps of ETLs used in green and blue OLEDs, n‐doping has been notoriously more difficult for these materials. In this work, n‐doping of the polymer poly[(9,9‐dioctylfluorene‐2,7‐diyl)‐alt‐(benzo[2,1,3]thiadiazol‐4,7‐diyl)] (F8BT) is demonstrated via solution processing, using the air‐stable n‐dopant (pentamethylcyclopentadienyl)(1,3,5‐trimethylbenzene)ruthenium dimer [RuCp*Mes]₂. Undoped and doped F8BT films are characterized using ultraviolet and inverse photoelectron spectroscopy. The ionization energy and electron affinity of the undoped F8BT are found to be 5.8 and 2.8 eV, respectively. Upon doping F8BT with [RuCp*Mes]₂, the Fermi level shifts to within 0.25 eV of the F8BT lowest unoccupied molecular orbital, which is indicative of n‐doping. Conductivity measurements reveal a four orders of magnitude increase in the conductivity upon doping and irradiation with ultraviolet light. The [RuCp*Mes]₂‐doped F8BT films are incorporated as an ETL into phosphorescent green OLEDs, and the luminance is improved by three orders of magnitude when compared to identical devices with an undoped F8BT ETL.     

电子束能量、剂量对固化厚度影响的研究

在电子束液态曝光技术的可行性已被证实的基础上，采用理论和实验相结合的方法，就电子束能量和剂量对固化深度的影响进行了研究，以TMPTA和环氧618两种液体低聚物为抗蚀剂，得出了不同能量、不同剂量下的有效穿透深度曲线，以及两种抗蚀剂在能量为25keV的电子束辐射下的临界剂量，固化出了十字形微结构。     

Electron‐beam crystallized large grained silicon solar cell on glass substrate

Thin film hetero‐emitter solar cells with large‐grained poly‐silicon absorbers of around 10 µm thickness have been prepared on glass. The basis of the cell concept is electron‐beam‐crystallization of an amorphous or nanocrystalline silicon layer deposited onto a SiC:B layer. The SiC:B layer covers a commercially well available glass substrate, serving as diffusion barrier, contact layer and dopand source. For silicon absorber deposition a low pressure chemical vapour deposition was used. The successively applied e‐beam crystallization process creates poly‐silicon layers with grain sizes up to 1 × 10 mm² with low defect densities. The high electronic quality of the absorber is reflected in open circuit voltages as high as 545 mV, which are realized making use of the well‐developed a‐Si:H hetero‐emitter technology. Copyright © 2011 John Wiley & Sons, Ltd.     

电子束曝光技术及其应用综述

综述了几种目前已得到应用和正在发展中的电子束曝光技术,包括基于扫描电镜(SEM)电子束、高斯电子束、成型电子束和投影电子束曝光技术等,并分析比较了这些技术各自的特点、应用及发展前景.     

Patterning Si at the 1 nm Length Scale with Aberration‐Corrected Electron‐Beam Lithography: Tuning of Plasmonic Properties by Design

Patterning of materials at single nanometer resolution allows engineering of quantum confinement effects, as these effects are significant at these length scales, and yields direct control over electro‐optical properties. Silicon is by far the most important material in electronics, and the ability to fabricate Si‐based devices of the smallest dimensions for novel device engineering is highly desirable. The work presented here uses aberration‐corrected electron‐beam lithography combined with dry reactive ion etching to achieve both: patterning of 1 nm features and surface and volume plasmon engineering in Si. The nanofabrication technique employed here produces nanowires with a line edge roughness (LER) of 1 nm (3σ). In addition, this work demonstrates tuning of the Si volume plasmon energy by 1.2 eV from the bulk value, which is one order of magnitude higher than previous attempts of volume plasmon engineering using lithographic methods.     

A Cocatalytic Electron‐Transfer Cascade Site‐Selectively Placed on TiO2 Nanotubes Yields Enhanced Photocatalytic H2 Evolution

Separation and transfer of photogenerated charge carriers are key elements in designing photocatalysts. TiO₂ in numerous geometries has been for many years the most studied photocatalyst. To overcome kinetic limitations and achieve swift charge transfer, TiO₂ has been widely investigated with cocatalysts that are commonly randomly placed nanoparticles on a TiO₂ surface. The poor control over cocatalyst placement in powder technology approaches can drastically hamper the photocatalytic efficiencies. Here in contrast it is shown that the site‐selective placement of suitable charge‐separation and charge‐transfer cocatalysts on a defined TiO₂ nanotube morphology can provide an enhancement of the photocatalytic reactivity. A TiO₂–WO₃–Au electron‐transfer cascade photocatalyst is designed with nanoscale precision for H₂ production on TiO₂ nanotube arrays. Key aspects in the construction are the placement of the WO₃/Au element at the nanotube top by site‐selective deposition and self‐ordered thermal dewetting of Au. In the ideal configuration, WO₃ acts as a buffer layer for TiO₂ conduction band electrons, allowing for their efficient transfer to the Au nanoparticles and then to a suitable environment for H₂ generation, while TiO₂ holes due to intrinsic upward band bending in the nanotube walls and short diffusion length undergo a facilitated transfer to the electrolyte where oxidation of hole‐scavenger molecules takes place. These photocatalytic structures can achieve H₂ generation rates significantly higher than any individual cocatalyst–TiO₂ combination, including a classic noble metal–TiO₂ configuration.     

3D Micro‐ and Nanostructures via Interference Lithography

Interference lithography (IL) holds the promise of fabricating large‐area, defect‐free 3D structures on the submicrometer scale both rapidly and cheaply. A stationary spatial variation of intensity is created by the interference of two or more beams of light. The pattern that emerges out of the intensity distribution is transferred to a light sensitive medium, such as a photoresist, and after development yields a 3D bicontinuous photoresist/air structure. Importantly, by a proper choice of beam parameters one can control the geometrical elements and volume fraction of the structures. This article provides an overview of the fabrication of 3D structures via IL (e.g., the formation of interference patterns, their dependence on beam parameters and several requirements for the photoresist) and highlights some of our recent efforts in the applications of these 3D structures in photonic crystals, phononic crystals and as microframes, and for the synthesis of highly non spherical polymer particles. Our discussion concludes with perspectives on the future directions in which this technique could be pursued.     

Binary and Ternary Polymer‐Mediated “Bricks and Mortar” Self‐Assembly of Gold and Silica Nanoparticles

An amine‐functionalized polymer has been used to simultaneously assemble carboxylic acid functionalized gold and silica nanoparticles into extended aggregates. This three component assembly process is highly versatile, with aggregate morphology controlled through stoichiometry, and nanoparticle segregation within the aggregate regulated through order of component addition.     

Synthesis and Properties of a Water‐Soluble Single‐Walled Carbon Nanotube–Poly(m‐aminobenzene sulfonic acid) Graft Copolymer

Poly(m‐aminobenzene sulfonic acid) (PABS), was covalently bonded to single‐walled carbon nanotubes (SWNTs) to form a water‐soluble nanotube–polymer compound (SWNT–PABS). The conductivity of the SWNT–PABS graft copolymer was about 5.6 × 10^–3 S cm^–1, which is much higher than that of neat PABS (5.4 × 10^–7 S cm^–1). The mid‐IR spectrum confirmed the formation of an amide bond between the SWNTs and PABS. The ¹H NMR spectrum of SWNT–PABS showed the absence of free PABS, while the UV/VIS/NIR spectrum of SWNT–PABS showed the presence of the interband transitions of the semiconducting SWNTs and an absorption at 17 750 cm^–1 due to the PABS addend.     

Solution‐Processable Hole‐Generation Layer and Electron‐Transporting Layer: Towards High‐Performance,Alternating‐Current‐Driven,Field‐Induced Polymer Electroluminescent Devices

The effect of solution‐processed p‐type doping of hole‐generation layers (HGLs) and electron‐transporting layer (ETLs) are systematically investigated on the performance of solution‐processable alternating current (AC) field‐induced polymer EL (FIPEL) devices in terms of hole‐generation capability of HGLs and electron‐transporting characteristics of ETLs. A variety of p‐type doping conjugated polymers and a series of solution‐processed electron‐transporting small molecules are employed. It is found that the free hole density in p‐type doping HGLs and electron mobility of solution‐processed ETLs are directly related to the device performance, and that the hole‐transporting characteristics of ETLs also play an important role since holes need to be injected from electrode through ETLs to refill the depleted HGLs in the positive half of the AC cycle. As a result, the best FIPEL device exhibits exceptional performance: a low turn‐on voltage of 12 V, a maximum luminance of 20 500 cd m^?2, a maximum current and power efficiency of 110.7 cd A^?1 and 29.3 lm W^?1. To the best of the authors' knowledge, this is the highest report to date among FIPEL devices driven by AC voltage.     

Soft‐Contact Optical Lithography Using Transparent Elastomeric Stamps and Application to Nanopatterned Organic Light‐Emitting Devices

Conventional photolithography uses rigid photomasks of fused quartz and high‐purity silica glass plates covered with patterned microstructures of an opaque material. We introduce new, transparent, elastomeric molds (or stamps) of poly(dimethylsiloxane) (PDMS) that can be employed as photomasks to produce the same resist pattern as the pattern of the recessed (or non‐contact) regions of the stamps, in contrast to other reports in the literature^[1] of using PDMS masks to generate edge patterns. The exposure dose of the non‐contact regions with the photoresist through the PDMS is lower than that of the contact regions. Therefore, we employ a difference in the effective exposure dose between the contact and the non‐contact regions through the PDMS stamp to generate the same pattern as the PDMS photomask. The photomasking capability of the PDMS stamps, which is similar to rigid photomasks in conventional photolithography, widens the application boundaries of soft‐contact optical lithography and makes the photolithography process and equipment very simple. This soft‐contact optical lithography process can be widely used to perform photolithography on flexible substrates, avoiding metal or resist cracks, as it uses soft, conformable, intimate contact with the photoresist without any external pressure. To this end, we demonstrate soft‐contact optical lithography on a gold‐coated PDMS substrate and utilized the patterned Au/PDMS substrate with feature sizes into the nanometer regime as a top electrode in organic light‐emitting diodes that are formed by soft‐contact lamination.     

Self‐Assembled Shape‐Memory Fibers of Triblock Liquid‐Crystal Polymers

New thermoplastic liquid‐crystalline elastomers have been synthesized using the telechelic principle of microphase separation in triblock copolymers. The large central block is made of a main‐chain nematic polymer renowned for its large spontaneous elongation along the nematic director. The effective crosslinking is established by small terminal blocks formed of terphenyl moieties, which phase separate into semicrystalline micelles acting as multifunctional junction points of the network. The resulting transient network retains the director alignment and shows a significant shape‐memory effect, characteristic and exceeding that of covalently bonded nematic elastomers. Its plasticity at temperatures above the nematic–isotropic transition allows drawing thin well‐aligned fibers from the melt. The fibers have been characterized and their thermal actuator behavior—reversible contraction of heating and elongation on cooling—has been investigated.     

Structure–Property Relationship of Pyridine‐Containing Triphenyl Benzene Electron‐Transport Materials for Highly Efficient Blue Phosphorescent OLEDs

Three triphenyl benzene derivatives of 1,3,5‐tri(m‐pyrid‐2‐yl‐phenyl)benzene (Tm2PyPB), 1,3,5‐tri(m‐pyrid‐3‐yl‐phenyl)benzene (Tm3PyPB) and 1,3,5‐tri(m‐pyrid‐4‐yl‐phenyl)benzene (Tm4PyPB), containing pyridine rings at the periphery, are developed as electron‐transport and hole/exciton‐blocking materials for iridium(III) bis(4,6‐(di‐fluorophenyl)pyridinato‐N,C^2′)picolinate (FIrpic)‐based blue phosphorescent organic light‐emitting devices. Their highest occupied molecular orbital and lowest unoccupied molecular orbital (LUMO) energy levels decrease as the nitrogen atom of the pyridine ring moves from position 2 to 3 and 4; this is supported by both experimental results and density functional theory calculations, and gives improved electron‐injection and hole‐blocking properties. They exhibit a high electron mobility of 10^?4–10^?3 cm² V^?1 s^?1 and a high triplet energy level of 2.75 eV. Confinement of FIrpic triplet excitons is strongly dependent on the nitrogen atom position of the pyridine ring. The second exponential decay component in the transient photoluminescence decays of Firpic‐doped films also decreases when the position of the nitrogen atom in the pyridine ring changes. Reduced driving voltages are obtained when the nitrogen atom position changes because of improved electron injection as a result of the reduced LUMO level, but a better carrier balance is achieved for the Tm3PyPB‐based device. An external quantum efficiency (EQE) over 93% of maximum EQE was achieved for the Tm4PyPB‐based device at an illumination‐relevant luminance of 1000 cd m^?2, indicating reduced efficiency roll‐off due to better confinement of FIrpic triplet excitons by Tm4PyPB in contrast to Tm2PyPB and Tm3PyPB.     

Pyridine‐Containing Electron‐Transport Materials for Highly Efficient Blue Phosphorescent OLEDs with Ultralow Operating Voltage and Reduced Efficiency Roll‐Off

A series of pyridine‐containing electron‐transport materials are developed as an electron‐transport layer for the FIrpic‐based blue phosphorescent organic light‐emitting diodes. Their energy levels can be tuned by the introduction of pyridine rings in the framework and on the periphery of the molecules. Significantly reduced operating voltage is achieved without compromising external quantum efficiency by solely tuning the nitrogen atom orientations of those pyidine rings. Unprecedented low operating voltages of 2.61 and 3.03 V are realized at 1 and 100 cd m^?2, giving ever highest power efficiency values of 65.8 and 59.7 lm W^?1, respectively. In addition, the operating voltages at 100 cd m^?2 can be further reduced to 2.70 V by using a host material with a small singlet‐triplet exchange energy, and the threshold voltage for electroluminescence can even be 0.2–0.3 V lower than the theoretical minimum value of the photon energy divided by electron charge. Aside from the reduced operating voltage, a further reduced roll‐off in efficiency is also achieved by the combination of an appropriate host material.     

Creation of Bifunctional Materials: Improve Electron‐Transporting Ability of Light Emitters Based on AIE‐Active 2,3,4,5‐Tetraphenylsiloles

2,3,4,5‐Tetraphenylsiloles are excellent solid‐state light emitters featured aggregation‐induced emission (AIE) characteristics, but those that can efficiently function as both light‐emitting and electron‐transporting layers in one organic light‐emitting diode (OLED) are much rare. To address this issue, herein, three tailored n‐type light emitters comprised of 2,3,4,5‐tetraphenylsilole and dimesitylboryl functional groups are designed and synthesized. The new siloles are fully characterized by standard spectroscopic and crystallographic methods with satisfactory results. Their thermal stabilities, electronic structures, photophysical properties, electrochemical behaviors and applications in OLEDs are investigated. These new siloles exhibit AIE characteristics with high emission efficiencies in solid films, and possess lower LUMO energy levels than their parents, 2,3,4,5‐tetraphenylsiloles. The double‐layer OLEDs [ITO/NPB (60 nm)/silole (60 nm)/LiF (1 nm)/Al (100 nm)] fabricated by adopting the new siloles as both light emitter and electron transporter afford excellent performances, with high electroluminescence efficiencies up to 13.9 cd A^–1, 4.35% and 11.6 lm W^–1, which are increased greatly relative to those attained from the triple‐layer devices with an additional electron‐transporting layer. These results demonstrate effective access to n‐type solid‐state emissive materials with practical utility.     

An Electrical Rectifier Based on Au Nanoparticle Array Fabricated Using Direct‐Write Electron Beam Lithography

Close‐packed arrays of Au nanoparticles are produced in patterned regions by electron beam (e‐beam) lithography using a highly sensitive direct–write resist, N⁺AuCl₄^?(C₈H₁₇)₄Br. While the e–beam causes dewetting of the resist to nucleate Au nanoparticles, the following step of thermolysis aids particle growth and removal of the organic part. Thus formed arrays contain Au nanoparticles. Such arrays are patterned into ≈10 μm wide stripes between Au contact pads on SiO₂/Si substrates to realize electrical rectification. Under forward bias, the device exhibits a threshold voltage of +4.3 V and a high current rectification ratio of 3 × 10⁵, which are stable over many repetitive measurements. The threshold voltage of the rectifier can be reduced by applying an electric stress or by varying the electron dosage used for array formation. The nanoparticle rectifier element could be transferred onto flexible substrates such as PDMS, where the nanoparticle coupling is influenced by swelling of the substrate. Obviously, the nanoparticle size, shape, and the spacing in array are all important for the rectifier device performance. Based on the electrical measurements the mechanism of rectification is found to be due to switching of electrical conduction with applied bias, from short–distance tunneling to F–N type tunneling followed by transient filament formation.     

Solvent‐Assisted Low‐Temperature Crystallization of SnO2 Electron‐Transfer Layer for High‐Efficiency Planar Perovskite Solar Cells

A high‐quality polycrystalline SnO₂ electron‐transfer layer is synthesized through an in situ, low‐temperature, and unique butanol–water solvent‐assisted process. By choosing a mixture of butanol and water as a solvent, the crystallinity is enhanced and the crystallization temperature is lowered to 130 °C, making the process fully compatible with flexible plastic substrates. The best solar cells fabricated using these layers achieve an efficiency of 20.52% (average 19.02%) which is among the best in the class of planar n–i–p‐type perovskite (MAPbI₃) solar cells. The strongly reduced crystallization temperature of the materials allows their use on a flexible substrate, with a resulting device efficiency of 18%.