Simulation Of Secondary Electron Emission Induced By Swift Ions

Ion induced secondary electron emission is an important result of interactions between ion and the surface of a solid, which could be utilized for the design of particle detectors. It draws extensive attention in theoretical and experimental studies. Complex projectile induced electron emission is one of the aims of studies in recent years. For complex projectiles, such as He+ (as He2+ and bound electron projecting) and H2+ ion, the main complication is the change of its charge state when it penetrate through the solid. The action of H2+ is far more complex than simple H+ ion in the solid. The stopping power of H2+ is significantly different from that of the separated H atomic ion. Accordingly, secondary electron emission yield induced by H2+ also differs from that induced by monatomic ion H+.In this thesis, the secondary electron emission induced by the complex projectile was studied by Monte-Carlo simulation method, concerning the change of the projectile charge state. The calculated results are compared with experimental measurements.Our main results can be summarized as the following:1. Backward secondary electron emission for He+ incident on Al, Cu and C was simulated. The bound electron of He+ plays an important role in the process of electron emission. The electron yields induced by He+, He2+ and e- have different contributions to the total backward electron emission yield. The velocity effect of electron emission near the maximum of electronic stopping power mainly depends on the bound electron. For the target of higher atomic numbers, such as Cu, the velocity effect is not obvious. But for the target of lower atomic numbers, such as C and Be, this effect will obviously be observed. The contribution fractions of electrons emitted by close collision to the total backward emission yield are 0.5, 0.55 and 0.42 for C, Cu and Al, respectively. The effect of high energy (E>100 eV)δelectron on the backward electron yield is also considered in detail, and only theseδelectrons with energy of a few hundreds eV play an important role in backward electron emission.Electron emission from carbon induced by swift H2+ ion was investigated. The projectile H2+ splits into H+ ion and e- at a certain depth in the solid. H2+, proton pairs H++H+ and e- make different contributions to the total backward electron yield. The molecular effect [R(Yb)] in the backward electron emission is from 0.85 to 1.09 in the energy range from 400 keV to 3000 keV. The ratios of forward electron yield to2. backward yield increase with energy and decrease with target thickness. The molecular effect [R(Yf)] in the forward electron emission decreases with target thickness at a certain energy. When the projectile energy is greater than 3700 keV, ratio R(Yf) in the forward electron emission will be greater than one [R(Yf)>1] for the target thickness of 1000 ?.3. The incidence angle dependence of secondary electron emission induced by swift H2+ ion was also studied. The relationship of the electron emission yield and statistics with the projectile angle is investigated. The results show that backward electron emission yield deviates from inverse cosine law, due to the role of the valence electrons of H2+. The ratio of forward electron emission yiled to backward yield at inclining incidence is different from that at normal incidence. The electron emission statistical distribution is independent of the incident angle. The values of b, the deviation parameter from Poission distribution, increase with projectile energy.