For measuring and amplifying current during a C-AFM scan, I'm aware that a linear current amplifier is generally used but in SSRM which is mostly used to get doping profiles in semiconductors, a logarithmic current amplifier is used. I do not understand the process of conversion by using it. Can anyone explain this?
Logarithmic current scale allows to measure nicely the current within few orders (up to 8) of magnitude, which can be very useful in case of non-homogenous samples. When the tip reaches the weakly conducting area, one can still measure the current without the risk of loosing data due to insufficient A/D conversion. Once you have the result, you need to calculate it, as in general log I/U converters are used. So you may have, for instance, such ratio: 4V for 10mA, 3V for 1mA, 1V for 0.1mA and so one, unless your software can make it automatically.
Thank you Andrzej. So what you are saying is that if I had a program/software that can convert the non linear values of current w.r.t voltage, a linear amp connected to the software would do (within its current compliance range)?
Yes, basically the outcome is the same, except the conversion dynamics, as log converter provides much wider range of the measurement, which is desired in diagnostic of semiconductor materials and many others.
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