Quantitative Surface Coverage Calculations via Solid-State NMR for Thin Film Depositions: A Case Study for Silica and a Gallium Amidinate

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• 作者：Peter J. Pallister ; Sydney C. Buttera ; Seán T. Barry
• 刊名：Journal of Physical Chemistry C
• 出版年：2014
• 出版时间：January 23, 2014
• 年：2014
• 卷：118
• 期：3
• 页码：1618-1627
• 全文大小：410K
• ISSN：1932-7455

文摘

For the interrogation of precursor nucleation for vapor deposition processes like atomic layer deposition (ALD) and chemical vapor deposition (CVD), a modified method for quantitative analysis of surface coverage was undertaken via NMR. The initial chemisorption of a new gallium(III) alkyl amidinate compound was investigated on high-surface area silica. N,N鈥?Diisopropylacetamidinatediethylgallium(III) (2) was found to have excellent volatility with no decomposition during a ramped thermogravimetric analysis experiment. Stepped-isotherm experiments showed a 1 Torr vapor pressure at 64 掳C. Compound 2 was exposed to a pretreated high-surface area silica substrate at 100, 200掳, and 300 掳C and was found to exhibit stable, persistent chemisorbed surface species at all three temperatures. Substrates were analyzed by ²⁹Si and ¹³C solid-state nuclear magnetic resonance spectroscopy (SS-NMR) and ¹H high-resolution NMR. At 100 and 200 掳C the reactivity of compound 2 to geminal and lone hydroxyl surface sites varied slightly eliminating either one or both ethyl groups to produce an alkylated (or nonalkylated) gallium acetamidinate on the silica surface and producing fractional coverages of 0.087鈥?.088. At 300 掳C there was a larger degree of reactivity producing a minor amount of the same surface species as at 100 and 200 掳C but also producing additional chemisorbed products likely arising from the decomposition of the ligand framework but ultimately giving a fractional coverage of 0.232 on hydroxyl-terminated silica.