Buried Liquid Metal Interfaces: Oxides and Surface Water-Driven Hydrogen Bubbles

Area of Science:

• Materials Science
• Surface Chemistry
• Fluid Dynamics

Background:

• Liquid metals like eutectic gallium indium (EGaIn) are crucial for electrical and thermal contacts.
• The interface between liquid metals and substrates is critical for device performance.
• Understanding oxide layer formation during liquid metal spreading is essential.

Purpose of the Study:

• To investigate the interface between eutectic gallium indium (EGaIn) and air-impermeable substrates.
• To determine the role of the native oxide layer during EGaIn spreading.
• To explore the formation of hydrogen bubbles at the liquid metal-substrate interface.

Main Methods:

• Time-of-flight secondary ion mass spectrometry (TOF-SIMS) was employed.
• Macroscopic fluid dynamic experiments were conducted.
• EGaIn was injected across silicon nitride (Si3N4) and glass substrates.

Main Results:

• An oxide layer was consistently found between EGaIn and both Si3N4 and glass substrates.
• EGaIn reacts with interface water molecules, generating hydrogen bubbles.
• Bubble formation is dependent on relative humidity, substrate surface chemistry, and gas permeability.

Conclusions:

• The native oxide of EGaIn remains between the liquid metal and impermeable substrates.
• Hydrogen bubble formation is a significant phenomenon at the EGaIn-substrate interface.
• Findings offer critical insights for liquid metal applications involving various substrates.