假塑性流体纳米压印中影响填充度的因素

作为新一代的半导体加工工艺, 直接金属纳米压印以其步骤简单、成本低等显著优点得到迅速的发展. 然而目前纳米压印中所采用的转移介质在流动状态下为牛顿流体, 牛顿流体的黏度是一个常量, 而假塑性流体具有黏度随着剪切速率的增大而逐渐减小的趋势, 更适用于纳米压印. 综合假塑性流体的剪切稀化特性以及直接金属图形转移的优点, 将不同大小的金属纳米粒子分散在基液中制成假塑性金属纳米流体并将其作为转移介质用于纳米压印中. 基于假塑性流体的Carreau流变模型利用COMSOL软件仿真分析金属纳米粒子假塑性流体参数集对图形压印转移的影响, 完成假塑性流体与牛顿流体分别作为转移介质实现图形转移的对比分析. 同时还得到了压印过程中影响填充度的各个因素, 如流体黏度、施加压强、掩模板移动速度等. 研究工作为金属纳米粒子假塑性流体制备以及纳米压印流程的设计提供了理论基础. 关键词： 纳米压印 假塑性流体 填充度     

基于电泳法和磁控溅射技术制备金纳米阵列

采用纳米球刻蚀技术中的电泳法设计了3组对照实验,通过控制电压、悬浮液的体积分数和基板正负极性,得到电泳法制备纳米球掩膜板的最佳条件,制备出排布均匀的纳米球单层密堆积结构的掩膜板.采用磁控溅射技术在掩膜板上沉积金薄膜,去除纳米球掩模板,通过扫描电子显微镜观察到周期排列的三角形棱台状金纳米颗粒阵列.测量其吸收光谱,可观察到表面等离子体共振吸收峰.     

二维气/液界面不稳定性数值模拟

 以多介质的体积分数方法和三阶PPM（Piecewise Parabolic Method）方法为基础,给出了适用于多介质流体动力学数值模拟的计算方法和程序MFPPM。利用MFPPM程序对在高压气体冲击作用下的气体/液体交界面的Richtmyer-Meshkov（RM）不稳定性及其引起的流体混合现象进行了数值模拟研究。主要研究在不同的初始扰动情况下流体混合区的发展,并细致研究了流体混合区的宽度、气泡和尖钉高度随时间的增长情况及不同初始扰动对它们的影响;同时还研究了网格尺度不同时混合区、气泡以及尖钉的构型和高度的增长情况。通过对计算结果的分析得出,流体混合区、气泡以及尖钉的发展与初始扰动有密切的关系,特别是在后期影响更为显著;混合区宽度的变化过程和尖钉相似,而气泡高度的变化基本上呈线性增长趋势,且受初始扰动的影响比较小,但是其构型却有明显差别;网格的影响也主要体现在对混合区、气泡和尖钉的构型上。     

冲击波诱导水中纳米气泡塌陷的分子动力学分析

人体中含有的纳米气泡受冲击波诱导塌陷后产生的强冲击高速纳米射流会对人体组织产生创伤.本文运用分子动力学方法,分析了冲击波引起的水中纳米气泡的塌陷行为,纳米气泡分为三种:真空、含二氧化碳和氧气纳米气泡.同时探讨了不同气体分子数、纳米气泡的直径和冲击波的冲量等因素对水中纳米气泡塌陷行为的影响.研究发现在真空纳米气泡中加入气体分子后并没有影响冲击波的传播,但在纳米气泡完全塌陷前,与真空和含1368个二氧化碳分子(或含1409个氧气分子)的纳米气泡相比,含718个二氧化碳分子(或含733个氧气分子)的纳米气泡塌陷形成的纳米射流的最大速度较大.在气泡完全塌陷后气体分子致使纳米射流的速度衰减,最终含气体分子的纳米射流的最大速度小于真空的.此外,还发现在大冲量时,纳米气泡的塌陷时间短,同一时刻冲击波经过时的密度、压力更大,气泡塌陷后纳米射流的最大速度较大,冲击力比小冲量增强很多.较大直径的纳米气泡塌陷时间长,同一时刻冲击波经过时的密度、压力较小,冲击波传播较慢,但纳米射流的最大速度较大,纳米射流冲击力更强.纳米射流的最大速度越大,含气纳米气泡的气体分子在冲击方向分散的距离更远,凹陷深度更深.     

单空位缺陷对石墨纳米带电子结构和输运性质的影响

基于第一性原理电子结构和输运性质计算,研究了单空位缺陷对单层石墨纳米带(包括zigzag型和armchair型带)电子性质的影响.研究发现,单空位缺陷使石墨纳米带在费米面上出现一平直的缺陷态能带;单空位缺陷的引入使zigzag型半导体性的石墨纳米带变为金属性,这在能带工程中有重要的应用价值;奇数宽度的armchair型石墨纳米带表现出金属特性,有着很好的导电性能,同时,偶数宽度的armchair型石墨带虽有金属性的能带结构,但却有类似半导体的伏安特性;单空位缺陷使得奇数宽度的armchair石墨纳米带导电 关键词： 石墨纳米带 单空位缺陷 电子结构 输运性质     

含少量气泡流体饱和孔隙介质中的弹性波

考虑孔隙流体中含有少量气泡,且气泡在声波作用下线性振动,研究声波在这种孔隙介质中的传播特性.本文先由流体质量守恒方程和孔隙度微分与流体压力微分的关系推导出了含有气泡形式的渗流连续性方程;在处理渗流连续性方程中的气体体积分数时间导数时,应用Commander气泡线性振动理论导出气体体积分数时间导数与流体压强时间导数的关系,进而得到了修正的Biot形式的渗流连续性方程;最后结合Biot动力学方程求得了含气泡形式的位移场方程,便可得到两类纵波及一类横波的声学特性.通过对快、慢纵波的频散、衰减及两类波引起的流体位移与固体位移关系的考察,发现少量气泡的存在对快纵波和慢纵波的传播特性影响较大.     

基于磁性纳米复合棒的“咖啡环”效应

研究了含有不溶性纳米复合棒的液滴在蒸发过程中出现的"咖啡环"效应,证实了"咖啡环"现象的形成和抑制与液滴体积、液滴浓度、基底温度、表面活性剂添加量及外加磁场等因素有关,并根据实验数据拟合"咖啡环"宽度与实验参量间的关系.证实了减小液滴体积、增大液滴浓度或升高基底温度,导致"咖啡环"变宽,而添加表面活性剂或施加外磁场则能够抑制"咖啡环"效应的出现.建立了磁性纳米复合棒在液滴蒸发过程中的受力模型,探讨了液滴重力、毛细流引起的牵引力、马兰戈尼流引起的牵引力及外加磁场提供的牵引力对"咖啡环"的形成及其宽度的调控影响规律.     

砂土的突破压力与渗透率实验

符号表A截面积，m2p压力，PaV体积流量，m3／sd颗粒平均粒径，mpc毛细压力，pa孔隙率dth突破直径，mPth突破压力，Pa黏度，kg/(m.s）k渗透率，m2，半径，表面张力，N／mL长度，m1前言三参数模型曾经再现了某种意义的毛细滞后现象[1]，但对于存在边界影响的典型重力脱湿和毛细吸湿过程始终未能模拟[2]。重要的原因是边界上的两相流体如何处于平衡并不十分清楚。窄筛分沙水中自然沉积的表层实验表明，气体进入湿饱和多孔介质存在一个压力阈值Pth。低于突破阈值时，气体与湿介质处于随遇平衡，只有达到这个值时，气体才能突破表层阻挠进人…     

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     

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.     

Sub-50 nm UV-curing nanoimprint based on fluoropolymer,CYTOP, mold

In addition to the advantages of conventional fluoropolymers (i.e., chemical resistance, optical transparency, especially low surface energy), CYTOP, a commercially available cyclic fluoropolymer, can be dissolved in a special fluorinated solvent, thus it can be coated on the substrate by a spin-coating or solution casting method. In this paper, we introduced CYTOP as a rapid prototyping mold material for UV-curing nanoimprint lithography. The CYTOP mold is fabricated by a thermal nanoimprint technique on a quartz substrate or a direct solution casting on a master mold. Nanostructures with different geometries and down to sub-50 nm feature size are faithfully duplicated by CYTOP molds through a UV-curing imprint process. The CYTOP mold preserves its lower surface energy property after 20 repeated imprint cycles and there is no peeling off problem or contamination and damage on CYTOP mold observed. However, it is found that the high aspect ratio nanostructures on the CYTOP mold are tilted or deformed after separation with the master mold.     

A sandwiched flexible polymer mold for control of particle-induced defects in nanoimprint lithography

Particle related defects are one of the key concerns for nanoimprint lithography, since the particle can amplify the defect to become much larger than the particle itself. We developed a flexible tri-layer mold for control of particle-induced defects. The mold was composed of a PDMS cushion layer sandwiched between a rigid imprint pattern layer and a plastic polyethylene terephthalate (PET) backplane. The PET foil was used as the backplane of the mold to protect the sticky PDMS surface. The PDMS as a cushion layer could locally deform to conform the shape of substrate due to its high elasticity. The multifunctional epoxysiloxane was used for the formation of an imprint layer because of its insensitivity toward oxygen during curing, high transparency, excellent mechanical strength and high resistance to oxygen plasma after cross-linking. Nanostructures with different geometries and sizes were faithfully duplicated by this mold through a UV-curing imprint process. The particle-induced defectivity was dramatically improved by the deformation of the PDMS cushion layer with a slight external pressure. 500 nm pitch grating structures were successfully imprinted on a microposts array surface, both the top and the intervening bottom portions between the microposts.     

In-situ bridging of SnO2 nanowires between the electrodes and their NO2 gas sensing characteristics

A simple and efficient way of making highly sensitive SnO₂ nanowire-based gas sensors without an individual lithography process was studied. The SnO₂ nanowires network was floated upon the Si substrate by separating the Au catalyst layer from the substrate. As the electric current is transported along the networks of the nanowires, not along the surface layer on the substrate, the gas sensitivities could be maximized in this networked and floated structures. The sensitivity was 5-30 when the NO₂ concentration was 1-10 ppm. The response time was ca. 20-60 s.     

毛细微模塑法制作聚合物微球的有序结构

用毛细微模塑法在玻璃基片上组装了聚苯乙烯微球紧密的有序阵列 .扫描电镜观察了组装后的微球排列 .结果表明 ,在毛细通道的出口端 ,聚苯乙烯的微球堆积得紧密有序 .毛细通道的尺寸 ,环境温度和聚合物微球乳液的浓度是毛细微模塑法的主要影响因素 .     

Application of Mn nano-flower sculptured thin films produced on interdigitated pattern as cathode and anode electrodes in field ionization gas sensor

The photolitography method was used for producing interdigitated configurations for cathode and anode electrodes of a field ionization gas sensor in which Mn helical nano-flowers with 3-fold symmetry were deposited using oblique angle deposition together with rotation of the substrate about its surface normal, with each rotation divided into six sections. These sections were alternately rotated at high and low speeds. Three different distances were chosen in the design between anode and cathode electrodes, namely 40, 100 and 200 μm. Physical structure and morphology of electrodes were studied by field emission scanning electron microscope and atomic force microscope analyses.The breakdown voltage of the system was studied for nitrogen, oxygen, argon, air and carbon mono-oxide gases. Investigations with these gases at different distances between anode and cathode and different gas pressures confirmed Paschen's Law. Results showed that at low pressures, decreasing the gap between electrodes increases the breakdown voltage. With fewer gas molecules between the electrodes the number of interactions between particles is reduced and higher energies are required for ionization of gas molecules. At high pressures, the breakdown voltage is decreased because of an increased number of molecular interactions. The sensor demonstrated good selectivity between the different gases and selectivity was enhanced with increasing gas pressure. A direct relationship was found at low pressures (e.g., 0.1 mbar) between the breakdown voltage and the gas ionization energy while at high pressures (e.g., 1000 mbar) this relationship was reversed.     

Slip velocity during the flow of a liquid over a solid surface

An equation is derived for the slip velocity when a nonequilibrated drop is spreading over a solid surface. This velocity is obtained as the product of the force induced by the gradient of the chemical potential along the surface with Einstein’s expression for the mobility of the molecules. A similar approach was applied to the flow in a capillary. In that case, the surface diffusion coefficient evaluated by comparing the obtained theoretical expression with experiment is orders of magnitude larger than expected. For this reason, one concludes that the observed slip is apparent and is caused by the formation of a gap of gas separating the flowing liquid from the solid surface.     

纳米通道内气体剪切流动的分子动力学模拟

采用分子动力学模拟方法研究了表面力场对纳米通道内气体剪切流动的影响规律.结果显示通道内的气体流动分为两个区域:受壁面力场影响的近壁区域和不受壁面力场影响的主流区域.近壁区域内,气体流动特性和气体动力学理论预测差别很大,密度和速度急剧增大并出现峰值,正应力变化剧烈且各向异性,剪切应力在距壁面一个分子直径处出现突变.主流区域的气体流动特性与气体动力学理论预测相符合,该区域内的密度、正应力与剪切应力均为恒定值,速度分布亦符合应力-应变的线性响应关系.不同通道高度及密度下,近壁区域的归一化密度、速度及应力分布一致,表明近壁区域的气体流动特性仅由壁面力场所决定.随着壁面对气体分子势能作用的增强,气体分子在近壁区域的密度和速度随之增大,直至形成吸附层,导致速度滑移消失.通过剪切应力与切向动量适应系数(TMAC)的关系,得到不同壁面势能作用下的TMAC值,结果表明壁面对气体分子的势能作用越强,气体分子越容易在壁面发生漫反射.     

Fabrication of high-quality colloidal crystals by a capillary-enhanced method

High-quality colloidal crystals have been prepared through a novel capillary-enhanced process, which includes both the characteristics of a sedimentation method and a capillary method. The multiple capillary forces driving the formation of colloidal crystals are composed of a primary capillary force and a secondary capillary force controlled by the ambient humidity. When the particles on the surface of the substrate transform into a gel-like layer in a high-humidity condition during the final step of the evaporative process, the secondary capillary force will be effective and fine tune the relative position between the neighboring particles in the microarray to decrease the amount of defects efficiently. Moreover, the close-packed structure can also be fabricated in a large area. Perfect colloidal crystals can easily be prepared in a short processing time by simple operation steps with the assistance of enhanced secondary capillary forces. PACS 42.70.Qs; 68.03.Cd; 68.65.Ac     

Casting mold patterning for lateral capillary force migration on PDMS microchannel

The casting molds including various shapes within axial and lateral resolution (110 μm and 5 μm) could be precisely fabricated and were suitable for the fabrication of PDMS microchannel possessing the larger inner volume for the purpose of the rapid capillary force migration. The tight bonding between PDMS mold and SiO₂/Si surface not only was governed by the flexibility and the degree of tilted angle (TA) of PDMS microchannel which shows the minimum value at the 0.2 weight ratio (W_r) of curing agent but also efficiently generates the capillary migration.     

Nanotribological properties of silicon surfaces nanopatterned by laser interference lithography

The problems caused by the adhesive force and friction force become more critical when the size of M/NEMS devices shrinks to micro/nano-scale. The nanotexture-patterned surface is an effective approach to reduce friction force on micro/nano-scale. Laser interference lithography is an attractive method to fabricate micro/nanotextures, which is maskless and allows large area periodical structures to be patterned by a couple of seconds’ exposure in a simple equipment system. We fabricate various nanogrooves with different pitch and space width on silicon wafers by laser interference lithography and chemical etching. We investigate the nanotribological properties of the patterned surfaces by AFM/FFM. We show that friction on the nano/micro-scale is related to the coverage rate of the nanogrooves, which decreases with increase in the space width and decrease in the pitch.