Information on SIMS Channel Plate Gain

The following description is taken from Hunter J.J.Jr., Quantitative Considerations in Imaging Secondary Ion Mass Spectrometry, February 1991, Dissertation submitted to the factulty of the University of North Carolina, Chapel Hill, NC:

(...)
The line scan data for the effect of DMCP gain on lateral image resolution are given in Figure (...). The effect of increasing the DMCP gain on the apparent Al bar width, calculated from line scan data, for the 3.0 micrometer Al bar is shown in Figure (not displayed)

To illustrate the limit of decreasing the DMCP gain, Figure 4.25 shows the effect of DMCP gain on observed ion image intensity. Figure 4.25 shows that the lower DMCP gains give lower observed intensity than the higher DMCP gains. Increasing the DMCP gain from 2.0 to 3.0 results in a > 300 increase in signal intensity. (...)

Figure 4.25. Relative %Intensity as a function of DMCP gain

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Since there appears to be two distinct regions in the data given in Figure 5.1 (i.e. high EM count rate > 10^4 and low EM count rate < 10^4), these data were fit in these two regions using Cricketgraph (28) on a Macintosh SE computer (29). Curve fitting of the data in Figure 5.1 obtained in the low count region over which only a single ion event/(readout pixel) shows nearly a linear response. For the high count rate region (i.e. the region in which multiple ion events/(pixel readout) are observed), a non-linear fit of the type:
Y = mulitplier * X^exponent
was required for a good fit (correlation coefficient of 0.998). The results of the curve fit are given in Table 5.1.
Figure 5.1. DMCP response curve for increasing EM count rates

                             Multiplier    Exponent
Boron
 High count rate (>10^4)     8.58x10^4     .622
 Low count rate (>10^4)      1.34x10^5     .971

SiO
 High count rate (>10^4)     1.10x10^5     .619
 Low count rate (>10^4)      2.10x10^5     .982