n.
Outermost layer of a material or substance.
Because the particles ( atom s or molecule s) on the surface have nearest neighbours beside and below but not above, the physical and chemical properties of a surface differ from those of the bulk material; surface chemistry is thus a branch of physical chemistry . The growth of crystal s, the actions of catalyst s and detergent s, and the phenomena of adsorption , surface tension , and capillarity are aspects of behaviour at surfaces. The appearance of the surface, whether achieved with electroplating , paint , oxidation-reduction , bleaching (see bleach ), or another means, is aesthetically important.