(Cross-sectional view of nanoporous Au film on Si wafer)

Nanoporous materials has many potential applications due to their special character: very large surface/volume ratio. For example, if people put a nanoporous gold cantilever into a certain circumstance, such as a gas, the nanoporous structure might be sensitive to the gas so that the surface energy would vary subsequently. The change of surface energy would be indicated by a certain mechanical response. Thus, it is of interest to fabricate specimens with nanoporous structure and characterize their mechanical properties.

• How can we make nanoporous material

The basic idea of making nanoporous material is de-alloying the less noble element from an alloy so that the porous structure will form on
the left more noble element during de-alloying. The alloy which contains two elements is single-phase solid solution alloy. For our case,
we start with Au/Ag alloy which atomic percentage is about 37% for Au and 63% for Ag. De-alloying method could be:

• High concentrated Nitric Acid
  

• Electro-chemical de-alloying: Put the Au/Ag alloy into diluted HClO4 solution and applying current through to take out the Ag.

Size of the ligaments of the nanoporous structure is in the order of 10 ~ 100 nm.
We can get different average ligament size by controlling the de-alloying recipe.

• How our specimen looks like and how we test it

Dimension of free-standing nanoporous Au beam:

• 7 um long, L
• 150~200 nm wide, W
• 100 nm thick, h

Nano-indenter is applied at the center of the beam.

• Applied load, f, is recorded
• Deflection, d, at the center of the beam is recorded

• How we analyze the data to get mechanical properties