反冲原子对低速离子轰击Si表面时电子发射产额的影响

在兰州重离子加速器国家实验室电子回旋共振离子源高电荷态原子物理实验平台上,用低能(0.75keV/u≤EP/MP≤10.5keV/u,即3.8×105m/s≤vP≤1.42×106m/s)He2+,O2+和Ne2+离子束正入射到自清洁Si表面时二次电子发射产额的实验结果.结果表明电子发射产额γ近似正比于入射离子动能EP/MP.在相同动能下,γ(O)γ(Ne)γ(He),对于原子序数ZP比较大的O2+和Ne2+离子,ZP大者反而γ小,这与较高入射能量时的结果截然不同.通过计算不同入射能量下入射离子的阻止能损S,发现反冲原子对激发二次电子的作用随入射离子能量的降低显著增大,这正是导致在较低能量范围内二次电子发射产额与较高入射能量时存在差异的主要原因.

Slow highly charged ions induced electron emission from clean Si surfaces

The electron emission yields from the interaction of slow highly charged ions (SHCI)He²⁺,O²⁺and Ne²⁺ with clean Si surface are measured separately. It is found that electron emission yield γ increases proportionally to projectile kinetic energy E_P/M_P ranging from 0.75 keV/u to 10.5 keV/u (i.e. 3.8×10⁵ m/s≤v_P≤ 1.42×10⁶ m/s), and it is higher for heavy ions (O²⁺and Ne²⁺) than for light ion (He²⁺). For O²⁺and Ne²⁺, γ increases with Z_P decreasing in our energy range, and it shows quite different from the result for higher projectile kinetic energy. After calculating the stopping power by using TRIM 2006, it is found that the fraction of secondary electrons induced by recoil atoms increases significantly at lower projectile energy, thereby leads to the differences in γ for heavy ions O²⁺and Ne²⁺between lower and higher projectile kinetic energy.