Collaborative Research: Transport Imaging of Semiconductor Nanowires

技术：本项目将桥接SiC和Si纳米线的VLS（气液固）生长/加工与纳米级成像技术相结合，研究合成、加工和接触/传输行为之间的关系。传输成像结合了近场光学的扫描分辨率和扫描电子显微镜（SEM）的电荷产生束控制。目标是通过光的重组发射来监测电荷的运动，从而实现“图像传输”。该技术建立在标准阴极发光（CL）的基础上，但有很大的不同，因为它保留了发射光的空间信息，从而可以直接测量空间分辨的少数载流子扩散、应用场下的迁移寿命产品和接触电阻——否则难以在单个纳米线上测量的参数。该项目旨在利用在扫描电镜内运行的原子力显微镜(AFM)/近场扫描光学显微镜（NSOM），将这种成像达到~ 50-100纳米的尺度。通过将电子束激发与光学集合解耦，人们可以沿着导线长度在~ 100 nm到微米的距离上成像电荷的传输。将使用Nanonics MultiView 2000系统，该系统允许对光纤尖端或样品进行独立扫描。测量将在单独桥接的SiC和Si纳米线以及ZnO和GaN线上进行。VLS纳米线合成/加工研究是合作研究的重要组成部分。该技术已成功用于固体晶须和纳米线的生长；桥式生长已在硅微沟槽中得到证实。桥式结构已被发现使刚性连接到沟槽的接收侧，使它们对大规模设备制造感兴趣。它们还为传输成像的外偏置应用提供了理想的结构。具体目标包括1)演示半导体纳米线的直接传输成像，2)传输测量作为纳米线直径的函数，3)测量接触电阻和载流子注入，4)研究VLS工艺催化剂和表面钝化对光学和传输性质的作用。非技术性：项目涉及电子/光子材料科学领域的基础研究问题，具有较高的技术相关性。此外，该项目还为三名研究生和至少6-8名本科生和高中生提供教育和培训。NPS为美国军队所有分支的现役军官以及来自30多个国家的学生提供教育。这些学生反映了美国现役部队的多样性，许多人在完成服务后将他们的技术教育转化为正式劳动力的领导职位。加州大学伯克利分校的一名研究生将参与合作，加州大学伯克利分校将利用其夏季本科工程研究项目（SUPERB）的优势，让本科生和夏季学生参与进来。将特别强调征聘妇女和人数不足的学生。这两个pi在指导女性和代表性不足的群体方面都有良好的记录，并一直积极参与本科和K-12的外展活动。研究结果会透过出版刊物和讲座，以及在新计划和大学校园局的公众外展场所公布。

Technical: This project combines VLS (vapor-liquid-solid) growth/processing of bridged SiC and Si nanowires with a nanoscale imaging technique to study relationships between synthesis, processing, and contact/transport behavior. Transport imaging combines the scanning resolution of near field optics with the charge generation beam control of a scanning electron microscope (SEM). A goal is to "image transport" by monitoring the motion of charge via the recombination emission of light. The technique builds upon standard cathodoluminescence (CL), but is significantly different, since it maintains spatial information of the emitted light, which allows for direct measurement of spatially resolved minority carrier diffusion, mobility-lifetime products under applied fields, and contact resistance--parameters otherwise difficult to measure on a single nanowire. The project aims to take this imaging to the ~ 50-100 nm scale with the use of an atomic force microscope (AFM)/near field scanning optical microscope (NSOM) operating inside an SEM. By decoupling the e-beam excitation from the optical collection, one can image transport of charge over distances from ~ 100 nm to microns along wire lengths. A Nanonics MultiView 2000 system will be used, which allows for independent scanning of fiber tip or sample. Measurements will be performed on individually bridged SiC and Si nanowires, as well as ZnO and GaN wires. VLS nanowire synthesis/processing research is an integral part of the collaborative research. This technique has been successfully demonstrated for the growth of solid whiskers and nanowires; bridged growth has been demonstrated within silicon microtrenches. The bridged structures have been found to make rigid connections to the receiving side of the trench, making them of interest for large scale device fabrication. They also provide ideal structures for application of external bias for transport imaging. Specific goals include 1) demonstration of direct transport imaging in semiconductor nanowires, 2) transport measurements as a function of nanowire diameter, 3) measurement of contact resistance and carrier injection, 4) study of the role of VLS process catalyst and surface passivation on optical and transport properties. Non-technical: The project addresses basic research issues in a topical area of electronic/photonic materials science with high technological relevance. Additionally, the project provides education and training for three graduate students and a minimum of 6-8 undergraduate and high school students. NPS educates active duty officers in all branches of the US forces, as well as students from 30+ countries. The students reflect the full diversity of the US active duty force and many take their technical education into positions of leadership in the regular workforce upon completion of their service. A UC Berkeley graduate student will work in collaboration, and UCB will take advantage of its SUPERB ((Summer Undergraduate Program in Engineering Research at Berkeley) program to involve undergraduate and summer students. Special emphasis will be placed on recruitment of women and underrepresented students. Both PIs have strong records of mentoring women and underrepresented groups and have been active in undergraduate and K-12 outreach. The results will be disseminated through publication and presentation, as well as public outreach venues at both NPS and UCB.