Polymer photonic band-gaps fabricated by nanoimprint lithography

We report on the fabrication and characterization of photonic band-gaps structures by nanoimprint lithography in a dye-doped polymer. Photonic band calculations show that photonic crystal slabs composed of a triangular array of polymer pillars could exhibit photonic band-gaps for the magnetic-like modes. The resulting structures show that the nanoimprint lithography process is well-suited to fabricate in a single-step process, these challenging photonic structures opening perspectives to realize integrated photonic band-gap circuits.     

One-kilobit cross-bar molecular memory circuits at 30-nm half-pitch fabricated by nanoimprint lithography

We have developed a process to fabricate a cross-bar structure using UV-curable nanoimprint lithography with a UV-curable double-layer spin-on resist, metal lift off and Langmuir–Blodgett film deposition. This process allowed us to produce 1-kbit cross-bar memory circuits at 30-nm half-pitch on both top and bottom electrodes. Read, write, erase and cross talking were also investigated. PACS 85.40.Hp; 81.07.-b; 81.16.Nd; 85.65.+h     

Micromagnetic studies of cobalt microbars fabricated by nanoimprint lithography and electrodeposition

Micromagnetic and macromagnetic switching properties of cobalt bars with six different aspect ratios produced by electrodeposition of cobalt into patterns defined by nanoimprint lithography were studied. It was found that microbars in the demagnetized state formed configurations with closed magnetic flux. Magnetization along the long axis of the microbars resulted in a single-domain state of magnetization for microbars of all aspect ratios. In the remanent state, magnetization in microbars with smaller aspect ratios resumed the vortex configuration. Individual remanent curves, as well as the net remanent curve, were extracted from magnetic force microscopy images for microbars with all aspect ratios, and their agreement with the macroscopic magnetization measurements is discussed.     

纳米压印技术制备表面光子晶体LED的研究

利用表面光子晶体能大幅提高发光二极管(LED)的外量子效率, 但如何制备大面积的纳米光子晶体是该研究方向的主要难点之一. 本文基于纳米压印技术在氮化镓基发光二极管(GaN-LED)表面制作孔状二维光子晶体. 通过以金属和聚合物双层掩膜干法刻蚀法, 得到了很好的光子晶体图形转移效果. 最终在LED的p-GaN层表面获得了大面积光子晶体, 周期为450 nm, 纳米孔直径为240 nm. 器件测试结果显示, 有表面光子晶体的LED比没有光子晶体的LED, 光致发光强度峰值提高到了7.2倍.     

Fabrication of molecular-electronic circuits by nanoimprint lithography at low temperatures and pressures

We have utilized a modified version of thermal nanoimprint lithography to fabricate a rewritable, nonvolatile, molecular memory device with a density of 6.4 Gbit/cm². It has the advantages of a relatively low operating temperature of (70 °C) and pressure of (<500 psi or 4.5 MPa), both of which are critical to preserving the integrity of the molecular layer. The architecture of the circuit was based on an 8×8 crossbar structure, with an active molecular layer sandwiched between the top and bottom electrodes. A liftoff process was utilized to produce the top and bottom electrodes made of Pt/Ti bilayers. The active molecular layer was deposited by the Languir–Blodgett technique. We utilized a new class of nanoimprint resist formulated by dissolving a polymer in its monomer. The formulation we used, was poly(benzyl methacrylate), dissolved in benzyl methacrylate with t-butyl peroxy 2-ethylhexanoate added as a self-initiator (8:90:2 by weight). The new resist allowed us to achieve Pt/Ti lines of 40 nm in width and 130 nm in pitch. PACS 86.65.+h; 81.16.Nd; 81.16.Rf     

Optical Magnus effect in metamaterials fabricated from ferromagnetic microwires

In homogeneous negative phase velocity media, the Doppler and Cherenkov-Vavilov effects and the refraction and pressure of light are anomalous: they are inverse with respect to the corresponding effects in conventional media. Using the geometrical optics approximation, it is shown that the optical Magnus effect in inhomogeneous negative phase velocity media is also anomalous. The effect is demonstrated by considering a metamaterial consisting of parallel amorphous ferromagnetic microwires in a magnetic field. The metamaterial proves to be a left-handed one in the realistic region of the electromagnetic spectrum. The optical properties of such a left-handed medium can be controlled by the external magnetic field.     

Plasmonic color pixels fabricated by nanoimprint process

Optical Review - Plasmonic nanostructures or metasurfaces have recently been actively researched for structural color generation. Controlling the plasmonic resonant wavelengths of surface plasmon...     

准晶结构的激光全息人工制作

报道了用激光全息刻写技术结合感光聚合材料体系制作介观尺度二维准周期结构(准晶). 并在前期工作的基础上，研究了不同曝光量对二维空气柱孔径的影响，不同偏振对准晶结构花样的影响. 实验结果显示，可以制作的二维准晶的空气柱孔径可达100nm，而且结构均匀，无缺陷面积大. 用此实验系统可以制作多种花样二维甚至是三维准晶结构. 目前，除激光全息刻写技术外，用其他传统精密机械加工技术来人工制作介观准晶体尚存在很大挑战性. 关键词： 准晶结构 光子晶体 激光全息技术     

Nano-image profiles transferred by near field phase-shifting lithography precisely simulated by finite element method and fabricated

The operating frequency of the SAW filters is limited by the gap width but not the line width. The narrow gap width is required for the high operating frequency SAW filters. Therefore, in this study, high precision nano-image profiles transferred by near field phase-shifting mask (NFPSM) lithography at various exposure-energy-intensities (EEIs) are simulated by the finite element method (FEM). The transferred energy-intensity distribution (TEID) in the photoresist during the NFPSM process (at the wavelength of 248 nm) can be accurately simulated by the FEM. The TEID at the interface between the mask and the photoresist is also simulated. The fabricated pattern widths clearly match the simulation results. The study of the simulated image profiles shows that they are dependent on the EEI. The greater the EEI is, the narrower the width and the shorter the height of the image profile. The nano-linewidth of 60 nm is simulated and fabricated. The fabricated nano-imaging profile precisely fits the simulation results. Therefore, any expected nano-image profile can easily be fabricated by way of the simulation.     

Negative refraction in semiconductor metamaterials based on quantum cascade laser design for the mid-IR and THz spectral range

We have considered the realization of metamaterials based on semiconductor quantum nanostructures, in particular, with the structural arrangement as in quantum cascade laser (QCL) designed to achieve optical gain in the mid-infrared and terahertz part of the spectrum. The entire structure is placed in a strong external magnetic field, which facilitates the attainment of sufficient population inversion, necessary to manipulate the permittivity, and enable a left-handed regime.     

Flexible subwavelength gratings fabricated by reversal soft UV nanoimprint

We present a replication process, named reversal soft ultraviolet (UV) nanoimprint, to fabricate a high- aspect-ratio flexible subwavelength grating (SWG) on a polyurethane acrylate (PUA). This nanopatterning technique consists of casting, reversal UV imprint, and dry release. The UV curing process of PUA to avoid pattern collapse is investigated. Revalpha film acts as the supporting and sacrificial layer during the whole process due to its special surface energy property. The free-standing PUA structures with a period of 200 nm and a depth of 350 nm can be automatically released from the Revalpha film by heating. The PUA resist is well suited to replicate fine patterns of the mold with high aspect ratio and large area precisely and uniformly for low surface energy and low viscosity. The measured transmittance is compared with the calculation results based on rigorous coupled-wave analysis in the wavelength region ranging from 500 to 800 nm. The experimental results agree well with the theoretical calculations.     

Confinement-induced nanocrystal alignment of conjugated polymer by the soft-stamped nanoimprint lithography

Soft-stamped nanoimprint lithography(NIL) is considered as one of the most effective processes of nanoscale patterning because of its low cost and high throughput. In this work, this method is used to emboss the poly(9, 9-dioctylfluorene)film. By reducing the linewidth of the nanogratings on the stamp, the orientations of nanocrystals are confined along the grating vector in the nanoimprint process, where the confinement linewidth is comparable to the geometrical size of the nanocrystal. When the linewidth is about 400 nm, the poly(9, 9-dioctylfluorene)(PFO) nanocrystals could be orderly arranged in the nanogratings, so that both pattern transfer and well-aligned nanocrystal arrangement could be achieved in a single step by the soft-stamped NIL. The relevant mechanism of the nanocrystalline alignment in these nanogratings is fully discussed. The modulation of nanocrystal alignment is of benefit to the charge mobilities and other performances of PFO-based devices for the future applications.     

Dual-band left-handed metamaterials fabricated by using tree-shaped fractal

<正>A method of fabricating dual-band left-handed metematerials(LHMs) is investigated numerically and experimentally by single-sided tree-like fractals.The resulting structure features multiband magnetic resonances and two electric resonances.By appropriately adjusting the dimensions,two left-handed(LH) bands with simultaneous negative permittivity and permeability are engineered and are validated by full-wave eigenmode analysis and measurement as well in the microwave frequency range.To study the multi-resonant mechanism in depth,the LHM is analysed from three different perspectives of field distribution analysis,circuit model analysis,and geometrical parameters evaluation.The derived formulae are consistent with all simulated results and resulting electromagnetic phenomena,indicating the effectiveness of the established theory.The method provides an alternative to the design of multi-band LHM and has the advantage of not requiring two individual resonant particles and electrically continuous wires,which in turn facilitates planar design and considerably simplifies the fabrication.     

软模板纳米压印技术及其对共轭高分子的取向控制研究

纳米压印模板通常需要经过电子束光刻、电子束沉积、光刻胶剥离、反应离子刻蚀等一系列复杂工艺获得,这使得纳米压印模板的制作难度大,成本高. 寻找一种灵活简单的纳米压印模板制备方法以提升纳米压印模板的制作效率,是广泛应用纳米压印技术的研究重点和难点. 本文以写好光栅结构的电子束光刻胶层为母模板,获得聚二甲基硅氧烷软模板,并以此为模板对共轭高分子聚(9,9-二辛基)芴薄膜进行纳米压印,实现光栅结构转移,成功制备出纳米光栅结构的共轭高分子薄膜. 偏振吸收谱和透射电镜结果表明,纳米压印实现图案转移的同时,还可以将共轭高分子的主链控制在光栅条纹方向,这对有机发光器件性能的提升具有重要的意义. 研究结果还表明,应用该方法同样可以对聚(9,9-二辛基芴共苯并噻二唑)薄膜进行光栅图案化,同时实现其取向控制. 关键词： 纳米压印 软模板共轭高分子 分子链取向     

Computer-generated hologram fabricated by electron-beam lithography for noise reduction

A Lohmann-type computer-generated hologram (CGH) is fabricated using an electron-beam lithographic system. A high-resolution groove width of 0.2 μm is attained in relief gratings by changing the e-beam exposures. A diffraction efficiency close to ∼30.4% is obtained by using resist-on-silicon recording materials and cell-structural apertures in a CGH. The reconstructed images exhibit fewer phase noises owing to the incorporation of a non-overflow cell structure into a CGH. The CGH is designed for reconstruction-noise reduction by using an iterative error-reduction algorithm. The designed CGH exhibits fewer reconstruction noises such that the performance function in the convergence is smaller by a factor of 1/3 than that in the first iteration. Experiments demonstrating the performance of CGHs obtained by electron-beam lithography are presented.     

Fabrication of ITO diffraction grating structure for infrared plasmonics by thermal nanoimprint lithography

Optical Review - Indium tin oxide (ITO) diffraction grating was fabricated on a polyimide (PI) film by using a combination of thermal nanoimprint lithography (NIL) process and radio frequency (RF)...     

Microlens arrays of high-refractive-index glass fabricated by femtosecond laser lithography

Microlens arrays of high-refractive-index glass GeO₂-SiO₂ were fabricated by femtosecond laser lithography assisted micromachining. GeO₂-SiO₂ thin glass films, which were deposited by plasma-enhanced chemical vapor deposition, have a refractive index of 1.4902 and exhibit high transparency at wavelengths longer than 320 nm. Using a femtosecond laser, three-dimensional patterns were written inside resists on GeO₂-SiO₂ films, and then the patterns were transferred to the underlying films by CHF₃ and O₂ plasma treatments. This combined process enabled us to obtain uniform microlens structures with a diameter of 38 μm. The heights of the transferred lenses were approximately one-quarter the height of the resist patterns, due to differences in the plasma etching rates between GeO₂-SiO₂ and the resist. The lens surfaces were smooth. When 632.8-nm-wavelength He-Ne laser light was normally coupled to the lenses, focal spots with a diameter of 3.0 μm were uniformly observed. The combined process was effective in fabricating three-dimensional surfaces of inorganic optical materials.     

Optimization of thickness and uniformity of photonic structures fabricated by interference lithography

We study the influence of the absorption of materials used for holographic fabrication of photonic structures on their uniformity along the film thickness. We demonstrate theoretically and experimentally a strong dependence of structure thickness and uniformity on the exposure dose of the interference pattern. A novel technique is proposed to overcome the absorption effect and to fabricate thick two- and three-dimensional structures, which are uniform throughout the film thickness. It consists of exposing once again the sample by an additional and independent counterpropagating uniform beam, which allows to compensate the diminution of the light intensity of interference pattern. These results are very useful for the fabrication of high quality polymer-based photonic crystals.