Secondary electron emission from the entrance and exit surfaces of thin carbon foils under fast ion bombardment |
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Authors: | CR Shi HS Toh D Lo RP Livi MH Mendenhall DZ Zhang TA Tombrello |
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Affiliation: | Division of Physics, Mathematics and Astronomy, California Institute of Technology, Pasadena, california 91125, USA |
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Abstract: | The total secondary electron emission (SEE) yield from the entrance and exit surfaces of thin carbon foils under fast ion (16O, 19F, 35Cl) bombardment has been measured as a function of the ion energy and the ion beam current intensity. Using a retarding field, the energy distribution of secondary electrons integrated over almost all angles of emission in the backward and forward directions has also been measured. It is found that total forward emission is larger than backward emission by factors of up to 2.5, 2.7 and 3.4 for 16O+3, 19F+3 and 35Cl+5, respectively. It is suggested that the enhancement of forward SEE may be partly due to effects from the instantaneous charge state of the heavy ion beam in the solid in addition to the binary collisions of the projectile with individual electrons in the target. It is also shown that the total SEE yield from the entrance and exit surfaces of the target foils decreases with ion beam current intensity; this may be a beam-induced temperature effect. The total SEE yield in both the forward and backward directions is less sensitive to surface conditions for high velocity ions than for low velocity ions and the total yield from both surfaces of the foils is proportional to the ion stopping power in the target, where the constant of proportionality depends on the properties of material. |
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