Thermo-Mechanical Effects on Electrical Transport in Carbon Nanotubes

碳纳米管(单层/多层碳原子轧制成无缝管)具有优异的电、机械、热和化学性能。有趣的是，它们优势背后的相同原因也使它们对电气、机械、热和化学领域非常敏感。实际应用，如电子、传感器和执行器、复合材料和生物医学，可能涉及在制造过程中经过机械应变和化学处理的纳米管--而不是原始的纳米管。这种超小型化设备的非常高的功率密度将导致更高的工作温度(即使在现有的计算机芯片中也可以观察到)，这将极大地改变高度受限的纳米管电子的输运性质。关于电学性质在机械或热场下的敏感性的研究(例如用机械位移调整电学性质或反之亦然)大多是理论上的。关于温度(300K)和机械力-位移对纳米管电学性质的同时影响的实验研究在文献中很少见，这一观察结果促使了本研究的提出。可能的活动及其智力优势：本研究的具体目的是：(I)开发一种以共同制造的独立式单碳纳米管样品为基础的微型机电表征仪器。尺寸为1 mm x 1 mm的设备可兼容任何类型的显微镜(光学/扫描电子显微镜/透射电子显微镜/扫描隧道显微镜)。它将使用光学显微镜分别以20皮牛顿和5纳米的分辨率测量力和位移。机械传感器(电隔离和金属化的硅微梁)也将作为电连接器来测量电流-电压信号。(Ii)在透射电子显微镜内原位研究高温对单个碳纳米管的力学性能(杨氏模数、断裂应力和应变)的影响。(3)研究碳纳米管在很宽的温度(300-500K)和机械应变(高达30%)范围内的电学性质，文献中还没有这方面的数据。该仪器将允许在单个碳纳米管上进行原位原子分辨实验，以同时获得定性信息(有关纳米管变形、缺陷产生和失效的直接视觉信息)和定量信息。关于热、机械和化学环境因素的分离和耦合效应的丰富数据将帮助研究人员深入了解这些领域的耦合。拟议活动的广泛影响：实验数据和对热、电和机械领域耦合的基本理解将为未来纳米电子、传感器和新材料的应用提供更好的设计指南。拟议的新实验工具将弥合纳米结构理论研究和实验研究之间存在的巨大差距。低成本工具的技术转让(每台25美元)将促进需要高分辨率力和位移传感的多学科研究(如机械生物学)。我们将培训一名毕业生和一名代表不足的本科生(通过宾夕法尼亚州立大学的少数族裔工程项目雇用)进行这一尖端研究。研究结果将被用作一门新的技术选修课的案例研究，该课程是PI开发的，旨在将纳米级传感器和执行器、材料科学、电子学和电子显微镜带到课堂上。我们还将培训高中教师在微米和纳米技术的基本方面，并向他们的学生提供电子显微镜(基于网络的扫描电子显微镜的远程操作)的虚拟体验，以便在这项研究项目的每一年接触到我们未来的劳动力。

Carbon nanotubes (mono/multi-layers of carbon atoms rolled into seamless tubes) are known to have superior electrical, mechanical, thermal and chemical properties. Interestingly, the same reasons behind their superiority also make them very sensitive to electrical, mechanical, thermal and chemical fields. Practical applications, as in electronics, sensors and actuators, composites and bio-medical, are likely to involve nanotubes that are mechanically strained and chemically treated during fabrication - and not the pristine ones. The very high power density of such ultraminiaturized devices will cause higher operating temperatures (observed even in the existing computer chips), which will drastically alter the transport properties of the highly confined nanotube electrons. Studies involving the sensitivity of electrical properties under mechanical or thermal fields (such as tuning electrical properties with mechanical displacement or vice versa) have been mostly theoretical. Experimental studies focusing on the simultaneous effects of temperature (300 K) and mechanical force-displacement on the electrical properties of the nanotubes are rare in the literature, an observation that motivates this research proposal.Proposed Activities and their Intellectual Merits: The specific aims of this research are, (i) Development of a micro-electro-mechanical characterization instrument with co-fabricated freestanding single carbon nanotube specimens. The 1mm x 1mm size device will be compatible with any type of microscopy (Optical/SEM/TEM/STM). It will measure force and displacement with 20 pico-Newton and 5 nm resolutions respectively, using an optical microscope. The mechanical sensors (electrically isolated and metallized silicon microbeams) will also work as electrical connectors to measure current-voltage signals. (ii) Study the effects of elevated temperature on the mechanical properties (Young's modulus, fracture stress and strain) of individual carbon nanotubes, in-situ inside the transmission electron microscope. (iii)Study the electrical properties of carbon nanotubes for a wide range of temperature (300-500K) and mechanical strain (up to 30%), for which data is not yet available in the literature. The instrument will allow in-situ atomic resolution experiments on individual carbon nanotubes for simultaneous qualitative (direct visual information on deformation, defect generation and failure of the nanotubes) and quantitative information. The wealth of data on the separate and coupled effects of thermal, mechanical and chemical environmental factors will help researchers gaining insight to the coupling of these fields.Broader Impacts of the Proposed Activities: The experimental data and the fundamental understanding in the coupling of thermal, electrical and mechanical fields will provide better design guidelines for future nanoscale electronics, sensors and novel materials applications. The proposed novel experimental tool will bridge the existing wide gap between theoretical andexperimental studies on nanostructures. Technology transfer of the low cost tool ($25/unit) will promote multi-disciplinary research (such as mechano-biology), wherever high-resolution force and displacement sensing are required. We will train one graduate and one under-represented category undergraduate student (employed through Minority in Engineering program at Penn State) in this cutting-edge research. The research results will be used as a case study in a new technical elective course, which the PI developed to bring nanoscale sensors and actuators, materials science, electronics and electron microscopy in the classroom. We will also train high school teachers in the fundamental aspects of micro and nanotechnology and give their students 'virtual' experience on electron microscopy (web-based remote operation of a scanning electron microscope) to reach out to our future workforce in the each years of this research project.