**3. Sputtering yield**

Sputter yield Y is the average number of sputtered atoms ejected by incident ions from a solid's surface per incident ion. It is represented by

$$\text{Sptuttering Yield} \left(\text{Y}\right) = \frac{\text{No.of sputtered atoms ejected from the solid's surface} \, dy \,\text{incident ions}}{\text{number of incident ions}} \quad \text{(1)}$$

In 1923, A. Hull discovered that the yield of sputtering was proportional to the mass of impact ions, and increased with the mass of the impact ions.

Sputtering yield increases when energy of the ion exceeds a particular threshold, regardless of substrate temperature. For smooth target faces, sputtering yield rises with increasing oblique angle bombardment up to a point, then falls as the angle of bombardment rises, resulting in increased bombarding particle reflection. The impact of changing the morphology of surface on sputtering yield have been examined by researchers. Because a large portion of the energy from high bombarding energies is deposited below the region right near the surface, energy does not directly enhance the sputtering yield.

In 1973, Attention was paid to the change in sputtering yield due to the amount of target impact on the pure metal surface. This phenomenon could be caused by bombarding species being incorporated into the region near the surface, recoil interstitials straining the near the surface region, and/or ion bombardment generating a highly defective film near the region of the surface [2].
