BET (Brunauer, Emmett, and Teller) surface area analysis is the most widely used technique for determining the exposed specific surface area of a solid sample on the molecular scale. This method calculates surface area based on the monolayer capacity– the quantity of gas molecules or atoms that form a single layer on the surface.

Typically, nitrogen gas (N2) is used as the adsorbate due to its strong affinity for solid surfaces. The analysis is usually performed at cryogenic temperatures, where the gas is introduced at low pressures, and the amount adsorbed is measured to determine surface area using the BET method. For materials with low surface area, krypton gas (Kr) is commonly used as an alternative adsorbate. With a lower vapor pressure (2.5 mmHg) compared to N2 (760 mmHg) at 77.3 K, Kr allows for determining more sensitive pressure changes during adsorption, resulting in greater accuracy.

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