I am doing MoS2 electrical characterisation on 200 nm grains, 10 um grains and 100 um. I see an increase in mobility from 200 nm to 10 um but it saturates from 10 um it does not increase for 100 um what is the reason?
I would like to suggest to read the paper entitled "Controlling Grain Size and Continuous Layer Growth in Two-Dimensional MoS2 Films for Nanoelectronic Device Application".
Mean free path is related to vacuum level and it effects the grain structure. You should look for Thornton model. Here is a picture of thorton model in the link.
http://www.laboratory-journal.com/sites/git-labor.de/files/images/special/2304__original.jpg
In 200 nm sample grain boundary contribution to resistivity will be more compared to 10 um sample.
(10 um-100 um)The mean free path of carriers in these materials may be less than 1um, so grain boundary contribution to resistivity is relatively small compared to other contributions( i.e. above certain value of grain size, the resistivity remains almost same). mobility and resistivity are directly related. Hence your observation.
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