Surface excess
= Surface excess
The interfacial excess of a species relative to bulk reference phases extrapolated up to a chosen reference surface. An excess <number density> per area is denoted $\Gamma$; its molar counterpart is $\Gamma/N_A$. When an interface is dominated by a molecular layer, an effective area per adsorbed molecule is $\Sigma=1/\Gamma$. The reference-surface convention matters in multicomponent systems.