摘要： The terms “surface quality” and “subsurface mechanical damage” (SSD) are often loosely used. Here we define surface quality as a measure of the level of perfection a workpiece surface exhibits after finishing and cleaning. A perfect surface is defined as a surface free of mechanical, structural, and chemical modification relative to bulk. Note surface quality does not include surface roughness, which is treated separately in Chapter 4. In practice, there is no such thing as a perfect surface, because a variety of microscopic and molecular surface modifications may occur on or just below the surface of the workpiece. As illustrated in Figure 3.1, surface modifications include the following: ? Subsurface mechanical interactions (SSD), which may lead to fracturing, plastic flow, or densification at the surface. ? Foreign particles or residue that may be deposited on the surface as particles land or precipitate during drying. ? Chemical and structural interactions that may result from changes in surface molecular moieties or by altering the near-subsurface (Beilby) layer. These factors affecting surface quality may vary significantly in scale length, from tens of μm to Angstrom level.