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

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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.