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Quantification of ink diffusion in microcontact printing with self-assembled monolayers
G Gannon1, J A Larsson, J C Greer
1Tyndall National Institute, Lee Maltings, Prospect Row, Cork, Ireland.
Langmuir : the ACS Journal of Surfaces and Colloids
|December 4, 2008
Summary
Ink spreading in microcontact printing is limited by temperature and concentration. Molecular dynamics simulations reveal diffusion rates increase significantly at higher temperatures and lower ink concentrations, impacting pattern fidelity.
Area of Science:
- Materials Science
- Nanotechnology
- Computational Chemistry
Background:
- Microcontact printing (micro-CP) faces limitations due to ink spreading.
- Alkanethiol self-assembled monolayers (SAMs) on gold are commonly used in micro-CP.
- Pattern broadening is a critical issue affecting micro-CP resolution.
Purpose of the Study:
- To quantify the temperature and concentration dependence of hexadecanethiol (HDT) ink spreading on HDT SAMs.
- To understand the fundamental limitations of micro-CP related to ink diffusion.
- To compare simulation data with experimental observations of pattern broadening.
Main Methods:
- Molecular dynamics (MD) computer simulations were employed.
- 18 distinct printing conditions were modeled using periodic simulation cells.
- Simulations covered a range of temperatures (270 K to 371 K) and ink concentrations (7 to 42 molecules per cell).
Main Results:
- Computed alkanethiol ink diffusion rates on SAMs approach bulk liquid rates.
- Diffusion rates increased up to 20-30 times at low concentration and high temperature.
- Autophobicity of alkanethiol surfaces was insufficient to prevent spreading.
Conclusions:
- Overinking and diffusion on SAMs contribute to pattern broadening in micro-CP.
- Spreading occurs on both fully and partially formed SAMs.
- Calculated spreading rates define fundamental limits for micro-CP stamp contact time and pattern width.
