PROGRAM | Chemistry and Biochemistry

By: Jia-Ming Lin Chair: Andrew Teplyakov

ABSTRACT

As massive attempts are focused on crafting thinner films, the surfaces involved are being treated as a reactant in deposition processes instead of simply a platform where the surface reactions take place. Our group focuses on silicon surface modification and the surface reactions between selected metalorganic precursors and the appropriately functionalized surfaces.

We first observed the differences in the morphology of the copper thin films deposited with Cu(hfac)VTMS on the silicon surface modified with different functionalities including -H, -NH2, and -NH- groups. The experimental surface analytical techniques including infrared spectroscopy, Auger electron spectroscopy, X-ray photoelectron spectroscopy, and microscopic investigation were supplemented by density functional theory (DFT) studies. We concluded that two major steps are involved in such a reaction: weak adsorption of a metalorganic moiety and hydrogen abstraction by its ligands.

With the help of DFT calculations, we simulated the reactions between metalorganic precursors with various ligands (including alkyl, alkoxide, alkylamide, diketonate, amidinate, and cyclopentadienyl ligands) and silicon surfaces; the pros and cons of these ligands were discussed, and in turn, several suggestions were made for future designs of novel ligands and precursor molecules.

A parallel DFT study focused on the influence from the surface functionalities including -H, -NH2, -NH-, -OH, -OCH3, and -OCF3 groups on the chemisorption process. The predictions indicated that the geometry of the precursor molecule and the basicity of the surface functionalities affect the weak attraction and the kinetic barrier of the reaction.

In order to decouple the electronic and steric effects of the surface functionalities, the reactions between tetrakis(dimethylamido)titanium and the surfaces modified with four different primary amines were studied with an approach combining spectroscopic and theoretical methods. According to the DFT predictions, the steric effect from the substituents of the primary amines overpowers electronic effect unless the size of the substituents was decreased. In addition, the computational studies of a systematic choice of substituents revealed that the reaction barrier of the hydrogen abstraction process is directly related to the acidity (positive charge) of the proton on the amine functionalities–the more acidic the proton, the lower the barrier would be.

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