表面能是创造物质表面时，破坏分子间化学键所需消耗的能量。在固体物理理论中，表面原子比物质内部的原子具有更多的能量，因此，根据能量最低原理，原子会自发的趋于物质内部而不是表面。表面能的另一种定义是，材料表面相对于材料内部所多出的能量。把一个固体材料分解成小块需要破坏它内部的化学键，所以需要消耗能量。如果这个分解的过程是可逆的，那幺把材料分解成小块所需要的能量就和小块材料表面所增加的能量相等。但事实上，只有在真空中刚刚形成的表面才符合上述能量守恒。因为新形成的表面是非常不稳定的，它们通过表面原子重组和相互间的反应，或者对周围其他分子或原子的吸附，从而使表面能量降低。

Surface energy, or interface energy, quantifies the disruption of intermolecular bonds that occur when a surface is created. In the physics of solids, surfaces must be intrinsically less energetically favorable than the bulk of a material (the molecules on the surface have more energy compared with the molecules in the bulk of the material), otherwise there would be a driving force for surfaces to be created, removing the bulk of the material (see sublimation). The surface energy may therefore be defined as the excess energy at the surface of a material compared to the bulk, or it is the work required to build an area of a particular surface. Another way to view the surface energy is to relate it to the work required to cut a bulk sample, creating two surfaces.