Separation of nanocolloids driven by dielectrophoresis: A molecular dynamics simulation

The nonequilibrium molecular dynamics (MD) method was used to model the nanocolloids and the solvent particles. By introducing a non-uniform electric field, colloids were polarized to have opposite polarities. Separation of colloids driven by dielectrophoresis (DEP) could be seen clearly under a strong electric field at low temperatures. Analyzing the ratio of DEP velocities of colloids to thermal velocities of neutral solvent particles showed that when the ratio was correspondingly big, collision between colloids and solvent particles would be intense, making the DEP velocity of colloids fluctuate frequently. By changing the electric field strength, it was found that the enhancement of electric field strength would quicken the separation of colloids. But when the electric field strength increased to a certain degree, the separation motion would be slow because of the strong friction resistance of the solvent particles to the colloids. Moreover, studying the separation reason of colloids based on the potential energy showed that after colloids were polarized, the attractive potential energy among the colloids would be weaker than before, while the increase of temperature would reduce the attractive potential energy and increase the repulsive potential energy, which accorded with the DLVO theory. Supported by the National Hi-Tech Research and Derelopment Program of China (“863” Project) (Grant No. 2006AA04Z351) and the National Natural Science Foundation of China (Grant Nos. 50675033, 30770553)     

碳纳米管受介电泳作用三维运动仿真

利用溶于介电液中的碳纳米管在外加交变电场作用下极化产生介电泳力和液体粘滞阻力的共同作用,建立了碳纳米管受力和运动模型;对碳纳米管的运动过程进行了仿真,得到了碳纳米管从特定初始点开始的三维运动轨迹和可以实现组装的碳纳米管初始点分布区域.计算了碳纳米管运动过程中所受介电泳力和速度的变化规律,距离电极间隙越近,碳纳米管受力和速度越大,最大分别能达到10^-9 N和10⁵μm/s的数量级.仿真结果为碳纳米管介电电泳组装提供指导.     

基于介电泳效应的高速抛光电极分布仿真研究与实验验证

目的解决传统平面环抛过程中存在的两种问题:(1)抛光液受抛光盘和工件旋转离心力作用而抛光液在加工区域分布不均,导致加工工件高平面度差;(2)抛光液受到的离心力作用限制了抛光盘转速,导致抛光效率低。方法提出一种基于介电泳效应的平面抛光方法(DEPP),在抛光区域增加一个非均匀电场,利用中性粒子在非均匀电场中极化后受介电泳力的作用,使其具有向电极和抛光区域中心运动的现象,降低旋转离心力对抛光液的甩出作用,实现对平面工件的高速、高精度抛光。采用有限元分析软件数值模拟极化后磨粒所受介电泳力对离心力的抑制作用,优化产生非均匀电场的不同电极宽度,得到最优非均匀电场电极分布参数,实际测量优化电极后抛光液所受介电泳力的大小和方向,最后搭建试验平台验证介电泳效应高速抛光平面工件的有效性。结果提高抛光盘转速,进行抛光磨砂玻璃对比实验,加工1 h以后,采用介电泳效应抛光能完全去除玻璃磨砂层,工件平整度好,最终RMS值为0.276λ;无介电泳效应抛光后,工件中心部分磨砂层仍有存在,工件平整度相对较差,最终RMS值为0.694λ。通过测量加工去除量,介电泳效应抛光比无介电泳效应抛光的去除率提升了18%结论通过仿真模拟和实验验证,证明了调整电极布置形式以及优化电极分布参数后,介电泳效应高速平面抛光的方法能够有效提升抛光效率和抛光后工件表面平面度。     

介电泳抛光方法及其电极形状的实验研究

目的验证介电泳抛光方法的有效性,研究电极形状对介电泳抛光方法均匀性、抛光效率和去除率的影响。方法选取直径76.2 mm的单晶硅片为实验对象,进行传统化学机械抛光(CMP)实验和使用4种电极形状的介电泳抛光实验,每隔30 min测量硅片不同直径上的表面粗糙度以及硅片的质量,然后对测量的数据进行处理和分析。结果与传统CMP方法比较,使用介电泳抛光方法抛光的硅片,不同直径上的表面粗糙度相差小,粗糙度下降速度快,使用直径60 mm圆电极形状介电泳抛光时相差最小,粗糙度下降最快。介电泳抛光方法去除率最低能提高11.0%,最高能提高19.5%,最高时所用电极形状为内径70 mm、外径90 mm的圆环。结论介电泳抛光方法抛光均匀性、效率和去除率均优于传统CMP方法。     

Tin oxide nanosensor fabrication using AC dielectrophoretic manipulation of nanobelts

Nanobelts are a new class of semiconducting metal oxide nanowires. The ribbon-like nanobelts are chemically pure and structurally uniform single crystals, with clean, sharp, smooth surfaces, and rectangular cross-sections. Positive and negative dielectrophoresis (DEP) was demonstrated for the first time on semiconducting oxide nanobelts. This effect was then used for the fabrication of a nanodevice, which consisted of SnO₂ nanobelts attached to castellated gold electrodes defined on a glass substrate, and covered by a microchannel. The SnO₂ nanobelts (width ∼ 100-300 nm, thickness ∼ 30-40 nm) were suspended in ethanol and introduced into the microchannel. An alternating (AC) voltage of ∼9.8 V peak to peak, with variable frequency, was applied between the electrodes (minimum electrode gap ∼ 20 μm), which corresponds to an average electric field strength of less than 2.5 × 10⁵ V/m. In the 10 Hz-1 kHz range, repulsion between the nanobelts and the electrodes occurred, while in the 1-10 MHz range, attraction was observed. Once the nanobelts touched the electrodes, those that were sufficiently long bridged the electrode gaps. The device was characterized and can potentially be used as a nanosensor.     

介电电泳细胞分析芯片结构设计及富集效率优化

为了研制高富集效率的介电电泳细胞分析芯片,首先从介电电泳力出发,推导了悬浮细胞所受的介电电泳力公式。通过对比常规微电极的电场强度分布,选择叉指式阵列微电极构建介电电泳芯片;通过模拟不同结构参数下微通道中的电场分布对芯片结构参数进行优化设计。针对Hep G2肝癌细胞,分别分析了细胞受介电电泳力、流体力以及重力作用下的运动情况,获得了Hep G2肝癌细胞富集的初步优化条件。为了对模拟结果进行验证,采用微加工技术制作了介电电泳细胞分析芯片。以Hep G2肝癌细胞为待测样品,当芯片所施加正弦交流电压为5 V,频率为4 MHz时,获得了88.89%的富集效率。     

碳纳米管非对称接触结构制作及电学性能研究

实验研究了多根或单根单壁碳纳米管与非对称金属电极接触结构的制作方法。先用介电泳方法(DEP)将碳纳米管定向排列在Au电极对之间,再用电子束光刻(EBL)在碳纳米管的一端加工Al电极,获得多根碳纳米管与金铝电极的非对称接触结构。先用EBL在Au电极对一端覆盖Al电极,再用DEP排列碳纳米管,实现单根碳管与金铝电极的非对称接触结构。非对称结构器件的电学测试研究表明,器件的I-V曲线不再对称,呈现出整流特性。     

基于光诱导介电泳的微粒自动化操作实验研究

采用等离子体增强化学气相沉积方法(PECVD)制备了氢化非晶硅(a-Si∶H)光电导薄膜,并利用双面胶技术封装ODEP芯片。构建了包括光投影模块和视频监控模块的ODEP自动化操作实验平台。以聚苯乙烯微粒为操作对象,进行微米尺度粒子的ODEP自动化操作实验,并深入研究了交流电压、投射光颜色和光电极形状对微粒运动速度的影响。实验结果表明,在交流电压频率和投射光颜色相同的条件下,粒子的运动速度与交流电压的幅值成线性关系,施加的交流电压幅值越大,微粒的运动速度越大。在交流电压的幅值和频率相同的条件下,投射光为白色时,粒子的运动速度最大;投射光为蓝色时,粒子的运动速度最小。当投射光为白光,电压为20V,频率为20kHz时,10μm和20μm聚苯乙烯微粒的最大运动速度分别为143μm/s和158μm/s。