An insidious nanoscale instability process is the quasi-asymptotic settling due to lubricant flow processes in drive, alignment and adjustment elements such as lead-screws and micrometer drives. It has been thought that this progresses at the nanoscale over many minutes, but conventional position-metrology instrumentation is typically less stable than recent process tolerances over the timescales involved, so quantification of these issues has been lacking.
Researchers in the field of single-molecule biophysics utilized optical tweezers [Figure 1] in a configuration that allowed quantitative comparison of the stabilities of screw-driven and piezomotor-driven stages with sub-nanometer sensitivity over many minutes . As in many semiconductor-industry applications, the test setup stacks coarse-positioning (resolution 0.1 micron) and fine-positioning motion elements (resolution 0.1 nanometer) in a sophisticated microscopy configuration. By swapping the coarse-positioning stage between screw-driven and piezomotor-driven models, the long-term, nanoscale stability provided by the piezomotors was quantitatively revealed.