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

Area of Science:

• Materials Science
• Surface Science
• Fluid Dynamics

Background:

• Liquid metals like eutectic gallium indium (EGaIn) are crucial for electrical and thermal contacts.
• Understanding the interface between liquid metals and substrates is vital for reliable applications.
• The behavior of the native oxide layer during liquid metal spreading is not fully understood.

Purpose of the Study:

• To investigate the interface between eutectic gallium indium (EGaIn) and air-impermeable substrates.
• To determine the state of the native oxide layer (present or absent) at the interface.
• To explore the formation of byproducts, such as hydrogen bubbles, at the liquid metal-substrate interface.

Main Methods:

• Time-of-flight secondary ion mass spectrometry (TOF-SIMS) was used to analyze the interface composition.
• Macroscopic fluid dynamic experiments were conducted to observe liquid metal spreading.
• Controlled variations in relative humidity, substrate chemistry, and gas permeability were employed.

Main Results:

• The native oxide layer of EGaIn was found to exist between the liquid metal and both Si3N4 and glass substrates.
• EGaIn reacts with interfacial water molecules, generating hydrogen bubbles.
• Bubble formation and size are dependent on relative humidity, substrate surface chemistry, and gas permeability.

Conclusions:

• The interface between EGaIn and common air-impermeable substrates is characterized by the presence of the native oxide layer.
• Hydrogen bubble generation is a significant phenomenon at this interface, affecting contact properties.
• These findings are critical for optimizing liquid metal applications in electronics and other fields.