CAREER: Molecular Perspectives of Gas-Surface Reactions during Growth of Thin Film Nanostructures

Colorado School Of Mines, Golden CO

Investigators

Abstract

0846923 Agarwal This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). Intellectual Merit: This CAREER proposal integrates research and educational activities in the thematic area of gas-surface dynamics critical to nanoscale control of thin-film growth. The goals of the research program are aligned with the Colorado School of Mines? (CSM) focus on Earth resources, energy, and advanced materials. In particular, the study will concentrate on atomic and molecular layer deposition (ALD/MLD). These deposition techniques operate in alternating cycles of self-limiting, gas-solid surface reactions. Recently, ALD has been used in numerous applications due to its ability to deliver conformal films on large-area substrates with nanometer-scale control over the film?s composition and thickness. To date ALD process development has been largely empirical, and with the exception of a few metal oxides, there have been very few comprehensive studies. While ALD is largely limited to inorganic materials, MLD is an emerging technique to deposit organic films. There is a need to develop a molecular understanding of the heterogeneous chemistry that occurs in ALD/MLD processes, so that they may be developed to their fullest potential. The inherent compatibility of the two processes can be utilized for the formation of advanced inorganic-organic hybrid films. In this research and education project, ALD/MLD processes will be examined taking a fundamental science approach. A combination of state-of-the-art surface and gas-phase diagnostics has been assembled that include in situ surface infrared spectroscopy, x-ray photoelectron spectroscopy, quartz crystal microbalance, spectroscopic ellipsometry, and quadrupole mass spectrometry. The powerful capabilities of this approach are demonstrated through the PI?s recent studies on the ALD of TiO2 using O3. This project will illuminate the molecular pathways critical to ALD/MLD synthesis of metal oxides, functional polymers, and advanced metal films. Work on metal oxides will focus on the application of O3 and O radicals, which have received little attention despite becoming the oxidizers of choice for industrial processes. MLD studies will investigate two novel strategies to overcome key limitations facing organic thin film synthesis: (a) process chemistries that produce no reaction byproducts, and (b) ?smart assembly?, in which the initial reagent produces a masked functionality that is selectively activated using a second reagent. Investigation of metals will focus on the key issue of nucleation, with ruthenium serving as the model compound. The PI will further integrate the insights from these three topical areas to design molecular scaffolds for high density nucleation of ultrathin metal films on pre-functionalized surfaces. Transformative Aspects: This study can be potentially transformative as it will reveal the molecular transformations occurring during ALD/MLD processes, which will ultimately lead to novel strategies for film growth. Furthermore, this program will address one of the least understood processes in ALD, which is the initial nucleation of metals on different surfaces. Broader Impact: An inherent feature of the project is the emphasis on education and its integration with research. Specifically, three interrelated educational goals will be pursued: (a) development and assessment of a new interdisciplinary elective course in thin-film processing; (b) close mentorship and career counseling through research; and (c) participation in outreach programs designed to increase minority student recruitment and retention at the undergraduate level. The project also involves a graduate student exchange program with the Eindhoven University of Technology in The Netherlands, which will facilitate a intellectual and cultural experience for students at both institutions. The project addresses fundamental research issues in a topical area of materials science having high technological relevance in a variety of fields such as microelectronics, optoelectronics, and photovoltaics. The study is unique in the sense that it brings together a variety of state-of-the-art surface and gas-phase diagnostics to investigate gas-surface dynamics during deposition of thin films and nanolaminates through ALD and MLD. The general methodology and diagnostic tools will assist the PI is setting up a broader program for studying interfacial phenomena in other thin-film deposition processes, such as plasma-enhanced CVD. The multidisciplinary nature of the research encompasses physics, chemistry, engineering, and materials science. Besides development of new courses, several aspects of this work will be used to enhance existing courses in photovoltaics, plasma science, and microfabrication at CSM.