gas adsorption porosimetry

**Gas Adsorption Porosimetry** is a **technique that measures pore structure by analyzing the adsorption and desorption of gas molecules (N₂, Ar, Kr)** — the adsorption isotherm provides BET surface area, pore size distribution, and pore volume. **How Does Gas Adsorption Work?** - **Isotherm**: Measure gas uptake vs. relative pressure ($P/P_0$) at constant temperature (77 K for N$_2$). - **BET**: Brunauer-Emmett-Teller model extracts specific surface area from the multilayer adsorption region. - **BJH**: Barrett-Joyner-Halenda model extracts pore size distribution from the desorption branch. - **DFT Methods**: Non-Local DFT (NLDFT) provides more accurate pore size distributions, especially for micropores. **Why It Matters** - **Micropores**: Can measure pores down to ~0.4 nm (far smaller than mercury porosimetry). - **Low-k Films**: With adapted configurations, can characterize porosity in thin low-k dielectric films. - **Standard Method**: ISO and ASTM standard method for surface area and pore characterization. **Gas Adsorption Porosimetry** is **molecular rulers for pores** — using gas molecules to probe pore sizes from sub-nanometer to hundreds of nanometers.