Secondary photon emission studies of ion bombarded beryllium

Abstract

The secondary photon emission which arises during ion bombardment of Be metal foil by 200–3000 eV Kr +, Ar +, Ne +, O 2 + and N 2 + was studied. By measuring the secondary photon emission yield of four Be(I) and one Be(II) emission lines as a function of incident ion energy information pertinent to the excitation process was obtained. Using a model based on a velocity dependent excitation process, the random collision cascade theory of sputtering; and making allowance for non-radiative de-excitation of the excited sputtered atoms and/or ions, it was possible to account for the observed energy dependent yields. The results of this model indicate that the secondary photon emission yield, Y i ex of a given emission line, i, can be expressed as: Y i ex( υ m) ∝ J( μA/cm 2) · S(no./ion) · exp[−( A/ a) i / υ m], where J is the incident ion current density, S the sputtering yield; υ m is the velocity corresponding to the maximum energy transferred between the incident ion of energy E 1, mass M 1 and the target atom of mass M 2, i.e. υ m = (8M 1E 1/(M 1+M 2) 2) 1 2 ;(A/a) i is the non-radiative de-excitation parameter for state i. Values for the ( A/ a) i parameters were found to be ≈(1–3) × 10 7 cm/s for the Be(I) and Be(II) states; a decrease to ap;(5–7) × 10 6 cm/s upon O 2 + bombardment was observed for the Be(I) states, the value for the Be(II) state did not change.