in analytical chemistry, the study of that part of a solid that is in contact with a gas or a vacuum. When two phases of matter are in contact, they form an interface. The term surface is usually reserved for the interface between a solid and a gas or between a solid and a vacuum; the surface is considered to be that part of the solid that interacts with its environment. Other interfaces-those between two solids, two liquids, a solid and a liquid, or a liquid and a gas-are studied separately
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