A new formula for secondary emission yield

Abstract

Mathematical expressions for the secondary emission yield as a function of impact voltage and direction are required by computer programs for ray tracing, which are also intended to follow secondary trajectories. It is shown that the accuracy requirements are quite severe for lower voltage impacts, up to about three times V/sub max/ (where V/sub max/ is the voltage at which the normal secondary emission ratio reaches its maximum value, delta /sub max/), but are less stringent above this range. A new formula for the low-voltage region, which agrees with experimental data better than the formula of R.G. Lye and A.J. Dekker (1957), is proposed. For the voltage region above 4 V/sub max/, the Lye and Dekker formula is retained, with a smooth transition centered between 3 and 4 V/sub max/. The directional effect is modeled by adjusting the values of delta /sub max/ and V/sub max/ before applying either formula, rather than applying either Bruining's or Muller's correction factor afterward. This results in an automatic modeling of the known absence of any appreciable directional effect below about half V/sub max/. Some experimental verification of the formula used to modify delta /sub max/ is presented.>