The determination of the critical load like the ‘abrupt
change in the frictional force’ has to be referenced.
Extensive research carried out by experiments shows
that the inflection point in the frictional curve is the
point where the diamond indenter contacts another layer
of multilayers, It is evident that both friction and
acoustic emission modes can eventually be used for
conventionally critical load determination, but the friction
mode can additionally reflect the changes at different
metallic film layers. The critical load was not
sensitive to deposition temperature and post-heating
process, but sensitive to the number of layers and the
thickness of film. The critical load of metallic films
increases approximately linear with film thickness.