The sputtering process and sputtered ion emission

In this review an attempt is made to delineate those physical characteristics of the sputtering event which are of importance for the discussion of sputtered ion emission. Emphasis is placed on the grossly disordered nature of the sputtering site as the sputtered atoms depart. The electronic nature of a disordered site is discussed and attention is drawn to the inapplicability of bulk density of states concepts to this region. In particular, it is argued that the concept of a band gap in the surface state density is inappropriate. Sputtered ion emission models are reviewed with respect to their consistency with the physics of the sputtering event and with the general features of sputtered ion emission. It is argued that a self-consistent model can be developed in the framework of which sputtered ion emission from oxidized surfaces, from clean alloy surfaces, and from the pure elements can be understood.