Collaborative Research: Plasma-Surface Interactions in Hydrogen Plasma-Induced Transitions from Carbon Nanotubes to Diamond Nanostructures

摘要国家科学基金项目申请号：CTS-0613629 / 0613501项目负责人：Aydil， E.S. / Maroudas, d .合作单位：明尼苏达大学/马萨诸塞大学阿默斯分校第四族材料的纳米结构薄膜，如碳纳米管（CNTs）、硅、锗和金刚石，在太阳能电池、生物或化学传感器、过滤器、散热器、大功率半导体器件和分子电子学中具有广泛的现有和潜在的应用。所有这些薄膜都是由SiH4、CH4和GeH4等气体等离子沉积而成；等离子体是一种由电子、离子和活性自由基组成的电离气体，是通过对低压气体施加射频电场而产生的。纳米结构的Si， Ge和C薄膜只有在相应的原料气在H2中大量稀释，等离子体中存在大量的氢原子时才能产生。对控制这些薄膜成核和生长的等离子体表面相互作用的基本理解对于调整它们的性质是必不可少的。因此，本研究的目标是研究等离子体-表面相互作用，特别是氢在等离子体沉积碳纳米管和H2等离子体诱导碳纳米管向金刚石转变中的作用。我们想知道通过等离子体沉积产生的碳纳米管、碳纳米纤维和氢化非晶碳是否可以在低温下通过暴露于等离子体解离H2形成的H原子而转化为金刚石。为了达到这个目标，我们提出了一项研究计划，将等离子体和表面表征实验与原子尺度模拟相结合。计算结果将与实验数据进行比较，从模拟中获得的见解将用于指导新的实验研究。等离子体表面相互作用以及这些相互作用对薄膜性能的影响是等离子体加工中最不为人所知的方面。有一个至关重要的需要，以补充经验过程的发展和特征与关键的基本过程的系统分析。为此，拟议的研究旨在将等离子体和表面诊断测量和结构表征与化学反应和结晶机制的计算原子尺度研究联系起来，以解决技术上重要和科学上有趣的现象，即碳纳米管的生长和结构转变为碳纳米管和其他碳形式的金刚石。拟议的项目跨越了物理、化学、化学工程、材料科学以及应用和数值数学之间的传统界限。因此，它提供了理想的方法来训练学生解决技术上重要的问题，使用综合的，最先进的实验和计算方法。这些项目让本科生参与研究，特别是鼓励那些在理工科领域代表性不足的学生，并广泛传播物理、化学、电子材料和等离子体工程领域的研究成果。我们期望我们的研究策略、方法和结果将适用于研究其他IV族材料及其合金的生长和加工，如Ge、Si/Ge和SiC，并有可能推动低温等离子沉积IV族薄膜的技术进步，这在我们的日常生活中有各种应用。该项目由美国国家科学基金会/美国能源部基础等离子体科学与工程伙伴关系资助。

ABSTRACTNational Science FoundationProposal Number: CTS-0613629 / 0613501Principal Investigator: Aydil, E.S. / Maroudas, D.Affiliation: University of Minnesota / University of Massachusetts-AmherstProposal Title: Collaborative Research: Plasma-Surface Interactions in Hydrogen Plasma-Induced Transitions from Carbon Nanotubes to Diamond Nanostructures Nanostructured thin films of group IV materials, such as carbon nanotubes (CNTs), silicon, germanium, and diamond have a broad range of existing and potential applications in solar cells, biological or chemical sensors, filters, heat sinks, high-power semiconductor devices, and molecular electronics. All of these films are grown by plasma deposition from gases such as SiH4, CH4 and GeH4; a plasma is an ionized gas consisting of electrons, ions, and reactive radicals and is created by application of radio-frequency electric fields to low-pressure gases. Nanostructured Si, Ge, and C films are produced only when the corresponding feed gases are heavily diluted in H2 with copious amounts of atomic H present in the plasma. Fundamental understanding of the plasma-surface interactions that govern the nucleation and growth of these films is essential for tailoring their properties. Accordingly, the goal of the proposed research is to investigate the role of plasma-surface interactions, and specifically the role of H, in the plasma deposition of CNTs and in the H2 plasma-induced CNT-to-diamond transition. We ask whether CNTs, carbon nanofibers, and hydrogenated amorphous carbon produced by plasma deposition can be transformed into diamond at low temperatures by exposure to H atoms formed by plasma dissociation of H2. Toward this goal, we propose a research plan that integrates plasma and surface characterization experiments with atomic-scale simulations. The computational results will be compared with the experimental data and the insights gained from the simulations will be used to guide new experimental studies. Plasma-surface interactions and the effects of these interactions on the film properties are among the least understood aspects of plasma processing. There is a crucial need to complement empirical process development and characterization with systematic analysis of the key fundamental processes. To this end, the proposed research aims to link plasma and surface diagnostic measurements and structural characterization with computational atomic-scale studies of chemical reactions and crystallization mechanisms to address technologically important and scientifically interesting phenomena, namely, growth of CNTs and structural transitions to diamond of CNTs and other carbon forms. The proposed project cuts across traditional boundaries between physics, chemistry, chemical engineering, materials science, as well as applied and numerical mathematics. Thus, it provides ideal means for training students to address technologically important problems using an integrated, state-of-the-art experimental and computational approach. The PIs involve undergraduate students in research, particularly encouraging students who are underrepresented in science and engineering, and disseminate broadly the research results in the physics, chemistry, electronic materials, and plasma engineering communities. We expect that our research strategy, methodology, and results will be applicable to studying the growth and processing of other group IV materials and their alloys, such as Ge, Si/Ge, and SiC,and potentially enable technological advancements in low-temperature plasma deposition of group IV films, which have a variety of applications in our daily lives.This project was funded through the NSF/DOE Partnership in Basic Plasma Science and Engineering.