Analysis of ductile mode and brittle transition of AFM nanomachining of silicon

The goal of this research is to investigate/monitor the machining characteristics and mode transitions during AFM nanoscratching of a brittle material such as Si (100) using acoustic emission (AE). By utilizing a specially designed AFM/nano stage setup, nano experiments were performed for various AFM tip engaging depths. With the aid of AFM and FE-SEM images, not only the typical features of each mode, such as pile-ups, chip formations, and crack propagations, but major mode changes including elastic/plastic and ductile brittle/transitions are observed and analyzed. To estimate mode transition depths, such as the yielding depth, the cutting initiating depth and the crack starting depth, theoretical models are employed and compared with the experimental results. Regarding in-process AE monitoring, various AE parameters such as AE RMS, AE count rate and AE frequency contents are generated from the monitoring signals and utilized to detect the mode states and transitions. Our results, which shows reasonably close theoretical estimations and appropriate sensitivity in AE monitoring, indicate that the proposed scheme can be used to characterize machining states and to differentiate various mode transitions from plastic deformation to the brittle crack generations during nano-scale machining.

► Distinctive AFM nanomachining modes were observed and characterized.
► AE monitoring was employed to detect each of machining mode and transition.
► The applicability of the cutting theories to nanoscale machining were exemplified.