Mechanochemistry at Nanoscale Metallic Contacts: How Stress and Voltage Drive Tribopolymerization

Area of Science:

• Mechanochemistry
• Surface Chemistry
• Tribology
• Nanotechnology

Background:

• Contact-induced reactions of confined molecules are poorly understood mechanochemical phenomena.
• Tribopolymerization, stress-induced polymerization, forms insulating nanolayers, causing conductance loss and limiting electrical contact reliability, especially in nanoelectromechanical systems (NEMS).

Purpose of the Study:

• Investigate stress and voltage-driven tribopolymer growth in platinum (Pt/Pt) nanocontacts using atomic force microscopy (AFM).
• Develop and validate a new contact-mechanics-corrected model for analyzing tribopolymerization kinetics.
• Quantify coupled stress- and field-driven mechanochemical reactions at nanoscale interfaces.

Main Methods:

• Utilized atomic force microscopy (AFM) to study tribopolymer growth in Pt/Pt nanocontacts.
• Developed a contact-mechanics-corrected model incorporating stress-dependent reaction kinetics and realistic contact mechanics with power-law tip geometries.
• Applied a stress-assisted thermal activation model to analyze reaction kinetics.

Main Results:

• Measured tribopolymerization kinetics follow a stress-assisted thermal activation model, confirming its mechanochemical origin.
• The new model accurately extracts a unified activation volume (ΔV = 5.6 ± 1.4 Å3) across varying contact areas and stresses.
• Applied voltage accelerates tribopolymerization similarly to stress, quantifiable via a new activation parameter and a field-induced bond-stretching model.

Conclusions:

• Provided a general approach for quantifying coupled stress- and field-driven mechanochemical reactions at nanoscale interfaces.
• Gained mechanistic insights into tribopolymerization-induced electrical degradation of nanocontacts, crucial for device reliability.
• The findings offer a pathway to mitigate electrical degradation in nanocontacts.