Yamamura obtained an empirical formula of relative sputtering yields for monoatomic targets bombarded by low energy ions at oblique incidence as follows: y (θ) =Y (θ) /Y (0°) =t

f

• exp{- g (t- 1) }

t=secθ where f and g are fitting parameters depending on the measured curve of sputtering yields.

We pointed out that g=f • cosθ

0

where θ

0

is the optimum incidence angle of ions at which sputtering yield Y (θ

0

) reaches the maximum. An analytical expression for θ

0

was derived and its physical meaning was discussed in the paper.

Finally

Yamamura formula could be written with the unique parameter f. The calculated results showed the equation given was accurate within a relative error of ±12%for targets Si and Ni bombarded by ions Ar and H in the low-energy range.