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Title: Mechanistic Studies of Chain Termination and Monomer Absorption in Molecular Layer Deposition

Abstract

Here, molecular layer deposition (MLD) is of growing interest as a vapor-phase method for depositing ultrathin polymeric films. The amount of material deposited per cycle of MLD is believed to be strongly dependent on the number of available surface reaction sites. However, the factors that alter the number of reactive sites during cycling have not been well understood. In this work, we provide concrete evidence that although chain termination reactions may reduce the number of reaction sites, the adsorption or absorption of monomers allows for the introduction of new reaction sites. These absorbed monomers are strongly bound to the film and allow the films to recover from growth defects introduced by chain terminations. A mathematical model for growth is developed and suggests that these absorptions eventually lead to the characteristic steady-state growth rate seen for MLD processes. Fits of the model to the experimental data for polyurea MLD indicate that ~3% of the chains experience termination events during each cycle at steady state, with any given chain having an ≈50% chance to be terminated before reaching 22 cycles; this termination is then compensated for by uptake of new monomers. Together, these results indicate that typical MLD growth involves the continuousmore » occurrence of termination reactions and the renucleation of chains within the film via the absorption of monomers.« less

Authors:
ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1]
  1. Stanford Univ., Stanford, CA (United States)
Publication Date:
Research Org.:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1476141
Grant/Contract Number:  
AC02-76SF00515; CHE-1213879; CHE-1607339
Resource Type:
Accepted Manuscript
Journal Name:
Chemistry of Materials
Additional Journal Information:
Journal Volume: 30; Journal Issue: 15; Journal ID: ISSN 0897-4756
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Bergsman, David S., Closser, Richard G., and Bent, Stacey F. Mechanistic Studies of Chain Termination and Monomer Absorption in Molecular Layer Deposition. United States: N. p., 2018. Web. doi:10.1021/acs.chemmater.8b01468.
Bergsman, David S., Closser, Richard G., & Bent, Stacey F. Mechanistic Studies of Chain Termination and Monomer Absorption in Molecular Layer Deposition. United States. doi:10.1021/acs.chemmater.8b01468.
Bergsman, David S., Closser, Richard G., and Bent, Stacey F. Fri . "Mechanistic Studies of Chain Termination and Monomer Absorption in Molecular Layer Deposition". United States. doi:10.1021/acs.chemmater.8b01468. https://www.osti.gov/servlets/purl/1476141.
@article{osti_1476141,
title = {Mechanistic Studies of Chain Termination and Monomer Absorption in Molecular Layer Deposition},
author = {Bergsman, David S. and Closser, Richard G. and Bent, Stacey F.},
abstractNote = {Here, molecular layer deposition (MLD) is of growing interest as a vapor-phase method for depositing ultrathin polymeric films. The amount of material deposited per cycle of MLD is believed to be strongly dependent on the number of available surface reaction sites. However, the factors that alter the number of reactive sites during cycling have not been well understood. In this work, we provide concrete evidence that although chain termination reactions may reduce the number of reaction sites, the adsorption or absorption of monomers allows for the introduction of new reaction sites. These absorbed monomers are strongly bound to the film and allow the films to recover from growth defects introduced by chain terminations. A mathematical model for growth is developed and suggests that these absorptions eventually lead to the characteristic steady-state growth rate seen for MLD processes. Fits of the model to the experimental data for polyurea MLD indicate that ~3% of the chains experience termination events during each cycle at steady state, with any given chain having an ≈50% chance to be terminated before reaching 22 cycles; this termination is then compensated for by uptake of new monomers. Together, these results indicate that typical MLD growth involves the continuous occurrence of termination reactions and the renucleation of chains within the film via the absorption of monomers.},
doi = {10.1021/acs.chemmater.8b01468},
journal = {Chemistry of Materials},
number = 15,
volume = 30,
place = {United States},
year = {2018},
month = {7}
}

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