Surface Effect on Young's Modulus of Sub-Two-Nanometer Gold [111] Nanocontacts

Area of Science:

• Materials Science
• Surface Science
• Nanotechnology

Background:

• The surface bond nature of face-centered cubic (FCC) metals is debated, with theoretical predictions of hardening or softening due to measurement challenges.
• Precise experimental data on the size-dependent mechanical properties of nanocontacts is crucial for resolving this controversy.

Purpose of the Study:

• To precisely measure the size dependence of Young's modulus in gold [111] nanocontacts with clean surfaces.
• To investigate the contribution of surface effects to the mechanical properties of nanocontacts.

Main Methods:

• Utilized an in situ transmission electron microscopy (TEM)-frequency modulation force sensing method.
• Experiments were conducted under ultrahigh vacuum at room temperature.
• Measured Young's modulus as a function of nanocontact width for gold [111] surfaces.

Main Results:

• Young's modulus decreased from approximately 80 GPa to 30 GPa as nanocontact width reduced below 2 nm.
• This size-dependent decrease is attributed to surface softening.
• The Young's modulus of the outermost atomic layer was estimated to be around 22 GPa, significantly lower than the bulk.

Conclusions:

• The study provides precise experimental evidence for surface softening in gold nanocontacts.
• The findings resolve the theoretical controversy regarding surface bond nature in FCC metals.
• The results highlight the critical role of surface atomic layers in determining the mechanical properties of nanomaterials.