Nearly all nanoindentation load-depth curves found in the literature correspond to measurement under load control. Our development of a high-performance adaptive feedforward/feedback control algorithm now makes it possible to acquire curves under depth control as well. We have utilized this algorithm to contrast load- and depth-controlled responses of a wide variety of monolithic and thin-film materials. In general, we find that depth-controlled curves exhibit higher sensitivity to transient deformation events and reveal more about underlying deformation mechanisms. Depth control is effective for passive monitoring of state-to-state transitions occurring on the time scale of transient events whereas load control involves pumping in additional energy to meet the prescribed load-time function. This extra pumped-in energy associated with load control sometimes initiates an unintended avalanche of relaxation processes that obscures the true nature of the event onset, leading to at least two published but erroneous aspects of data interpretation. Also, certain experiments unattainable under load control can be easily achieved under depth control.
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