Atomic Layer Deposition

The goal of this project is the development of discontinuous thin film growth methods, where exactly one monolayer of a desired compound is formed per deposition cycle. The overall film thickness can then be controlled by the number of applied deposition steps with a resolution defined by the thickness of one monolayer. One way to accomplish this goal is based on self-limiting surface reactions of suitable precursor compounds A and B, which form the desired product S in a binary reaction cycle consisting of two sequential half-reactions.

Both half-reactions must be complete and self-limiting at the monolayer level, in which case the resulting total film thickness dtot can be "digitally" controlled by the number of applied deposition cycles N(A/B):

d(tot) = d(mono) · N(A/B)

The reagents A and B in the half-reactions are not necessarily chemical compounds, but can also represent a physical process such as heating, irradiation, electrochemical conversion etc.

SAMs generally fulfill the requirements of complete and self-limiting monolayer formation and are therefore promising candidates for atomic layer deposition. An example is the growth of silicon oxide films by adsorption and subsequent oxidation of long-chain alkylsiloxane monolayers.

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Both half-reactions must be complete and self-limiting at the monolayer level, in which case the resulting total film thickness dtot can be "digitally" controlled by the number of applied deposition cycles N(A/B):

d(tot) = d(mono) · N(A/B)

The reagents A and B in the half-reactions are not necessarily chemical compounds, but can also represent a physical process such as heating, irradiation, electrochemical conversion etc.

SAMs generally fulfill the requirements of complete and self-limiting monolayer formation and are therefore promising candidates for atomic layer deposition. An example is the growth of silicon oxide films by adsorption and subsequent oxidation of long-chain alkylsiloxane monolayers.

image.alternative

Each deposition cycle leaves a monolayer of silicon oxide with a thickness of about 3 Å on the surface. The overall thickness increases with the number of deposition cycles in a strictly linear and homogeneous fashion, whereby the film composition and the surface roughness remain unchanged.

image.alternative

Each deposition cycle leaves a monolayer of silicon oxide with a thickness of about 3 Å on the surface. The overall thickness increases with the number of deposition cycles in a strictly linear and homogeneous fashion, whereby the film composition and the surface roughness remain unchanged.

image.alternative

Such growth processes can be performed on a variety of different substrate materials and are probably applicable to several other technologically important materials including Al2O3, TiO2 or indium tin oxide (ITO), which are currently under investigation in our group.