Advanced nanostructure and device fabrication

纳米科学技术是近年来发展最快的研究领域之一。这种快速增长的基础是纳米级制造的能力。有两种方法：涉及化学合成和自组装的“自下而上”方法，以及通过光刻产生或复制纳米结构的“自上而下”方法。对于“自上而下”方法，通常使用电子束光刻（EBL）、聚焦离子束（FIB）蚀刻/光刻和纳米压印光刻（NIL）来产生纳米结构。在过去的17年里，崔的研究一直集中在使用NIL和EBL的纳米结构和器件制造上。在NIL中，模具（印模）的表面图案通过机械接触引起的材料位移被复制到材料中。EBL是最通用的纳米光刻方法，但产量非常低。因此，提供高分辨率和高通量的NIL被认为是用于批量生产不涉及需要在它们之间精确对准的多级纳米结构的器件的最实用的技术。这项拟议的研究涵盖了三个应用，其中纳米纤维起着核心作用：1）批量制造高纵横比AFM尖端，2）用于生物和化学传感的纳米结构等离子体器件，以及3）用于锂离子电池电极的纳米结构硅。1)原子力显微镜（AFM）在绘制非平坦表面时受到固有的限制，其中针尖不能完全跟随样品表面。这个问题的自然解决方案是使用可以更精确地跟随样品表面的薄且高纵横比的尖端。目前，高纵横比的AFM针尖是商业上可获得的，但价格非常高，因为这些针尖是一个接一个地制造的。崔的团队已经开发出一种批量制造工艺，其中整个常规AFM针尖的晶片同时加工成高纵横比针尖。该公司已经申请了美国临时专利，并将于2014年初成立一家公司，将这项技术商业化。目前的建议的目的超越了制造基本的高纵横比的提示，并将集中在使用非常规的蚀刻方法与倾斜补偿的提示的制造。2)等离子体激元是金属中自由电子的集体振荡。当这种振荡被限制在金属表面时，它被称为表面等离子体;当被限制在金属纳米结构（例如金属岛）时，它被称为局部表面等离子体。当电磁激发频率与等离子体激元的共振频率匹配时，振荡的振幅将最高。由于共振频率对金属表面的介电变化非常敏感，因此可以用作无标记的生物和化学传感器来检测DNA杂交等事件。在这里，我们将专注于基于局部表面等离子体共振的生物传感器的设计，制造和表征，以实现高灵敏度与低成本的设备制造使用NIL的目标。3)与广泛使用的碳阳极材料相比，硅提供高一个数量级的理论储能容量。然而，硅的主要问题是它在充电/放电过程中迅速降解，导致循环寿命短。为了提高其寿命，纳米结构硅已经被研究。在这里，我们的目标是制造高纵横比（深度/直径> 1000）的纳米级孔阵列在硅使用电化学蚀刻，与孔的安排（阵列周期性）所定义的预图案化使用NIL。主要优点是电化学蚀刻和NIL都是低成本和高产量的工艺，可用于批量生产。

Nanoscale science and technology has been one of the fastest growing research areas in recent years. Fundamental to this rapid growth is the capability of fabrication at the nanoscale. There are two approaches: the “bottom up” approach that involves chemical synthesis and self-assembly, and the “top down” approach in which nanostructures are generated or duplicated by lithography. For the “top down” method, electron beam lithography (EBL), focused ion beam (FIB) etching/lithography and nanoimprint lithography (NIL) are generally used to create nano-structures. Cui’s research in the past 17 years has been centered on nanostructure and device fabrication using NIL and EBL. In NIL, a surface pattern of a mold (stamp) is replicated into a material by mechanic contact-induced material displacement. EBL is the most versatile nanolithography method yet with very low throughput. Therefore NIL, which offers both high resolution and high throughput, is considered the most practical technique for volume production of devices that do not involve multi-level nanostructures requiring precise alignment among them. This proposed research covers three applications for all of which nanofabrication plays a central role: 1) batch fabrication of high aspect ratio AFM tips, 2) nano-structured plasmonic devices for bio- and chemical sensing, and 3) nano-structured silicon for Li ion battery electrode. 1) Atomic force microscope (AFM) suffers from the intrinsic limit when mapping a non-flat surface where the tip cannot fully follow the sample surface. The natural solution to this issue is to use thin and high aspect ratio tips that can follow the sample surface more precisely. At present, high aspect ratio AFM tips are commercially available, but at a very high price because these tips are fabricated one by one. Cui’s group has developed a batch fabrication process where an entire wafer of regular AFM tips are processed simultaneously into high aspect ratio tips. A US provisional patent has been filed and a company will be established in early 2014 to commercialize this technology. The objective of the current proposal goes beyond fabricating basic high aspect ratio tips, and will be focused on the fabrication of tips with tilt compensation using unconventional etching methods. 2) Plasmon is the collective oscillation of free electrons in metal. When such oscillation is confined to the metal’s surface, it is called surface plasmon; and when confined to a metal nanostructure (e.g. a metal island), it is called localized surface plasmon. The amplitude of the oscillation will be highest when the electromagnetic excitation frequency matches the resonant frequency of the plasmon. As the resonant frequency is very sensitive to dielectric changes on metal surfaces, it can be used as a label-free bio- and chemical sensor to detect events such as DNA hybridization. Here we will focus on the design, fabrication and characterization of biosensors based on localized surface plasmon resonance, with the goal of achieving high sensitivity with low-cost device fabrication using NIL. 3) Compared to the widely used carbon anode material, silicon offers one order higher theoretical energy storage capacity. However, the main issue with silicon is that it degrades rapidly during the charge/discharge process, leading to a short cycle life. To improve its lifetime, nano-structured silicon has been investigated. Here our objective is to fabricate high aspect ratio (depth/diameter > 1000) nanoscale hole arrays in silicon using electrochemical etching, with the hole arrangement (array periodicity) defined by pre-patterning using NIL. The key advantage is that both electrochemical etching and NIL are low cost and high throughput processes that are viable for volume production.