Related Experiment Video
Updated: Aug 8, 2026
08:58
Atomic Force Microscopy Cantilever-Based Nanoindentation: Mechanical Property Measurements at the Nanoscale in Air and Fluid
Published on: December 2, 2022
Simultaneous nanoindentation and electron tunneling through alkanethiol self-assembled monolayers
Vincent B Engelkes1, C Daniel Frisbie
1Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, 55455, USA.
The Journal of Physical Chemistry. B
|May 19, 2006
Summary
This study reveals that molecular monolayers on gold surfaces deform plastically under load, with their mechanical properties depending on molecular chain length. This provides insights into the behavior of molecular junctions under mechanical stress.
Area of Science:
- Materials Science
- Nanotechnology
- Surface Science
Background:
- Molecular junctions are crucial for molecular electronics.
- Understanding the mechanical properties of self-assembled monolayers (SAMs) is essential for device stability.
- Conducting-probe atomic force microscopy (CP-AFM) is a key technique for characterizing nanoscale electrical and mechanical properties.
Purpose of the Study:
- To investigate the mechanical deformation and electrical transport properties of alkanethiol molecular monolayers under varying junction loads.
- To determine the monolayer modulus and contact transmission of molecular junctions.
- To explore the influence of molecular chain length on the mechanical behavior of these monolayers.
Main Methods:
- Fabrication of electrical tunnel junctions using alkanethiol SAMs on Au-coated Si substrates.
- Utilizing conducting-probe atomic force microscopy (CP-AFM) in a nanoindentation-like configuration.
- Measuring junction conductance as a function of applied load, rather than probe depth.
- Analyzing data using contact mechanics (Derjaguin-Müller-Toporov) and tunneling equations.
Main Results:
- Alkanethiol monolayers exhibit significant plastic deformation, with indentations of approximately 7 Angstroms at loads of 50 nN.
- Extracted monolayer modulus of approximately 50 GPa and contact transmission of approximately 2 x 10(-6).
- Monolayer modulus decreased with increasing carbon chain length for shorter chains, but this trend reversed for chains of 12 carbons or more.
Conclusions:
- Molecular monolayers undergo substantial plastic deformation, influencing junction stability and performance.
- The mechanical properties of molecular junctions are tunable by controlling the molecular chain length.
- This research provides a quantitative understanding of the interplay between mechanical load, molecular structure, and electrical transport in molecular junctions.
