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Free of tool wear, residual stress, and surface damage, electrochemistry plays a significant role in precision machining. We report here a semiconductor polishing technique based on electrochemically induced chemical etching, in which the concentration distribution of electrogenerated etchant between the tool electrode and the semiconductor workpiece can be precisely controlled by the pulse frequency of the potential applied to the tool electrode. A theoretical model is established, and the finite element analysis shows that the concentration difference of the electrogenerated etchant at the peak and valley of the rough surface of the semiconductor workpiece is dependent on the frequency of the potential pulse. Consequently, the diffusion distance and concentration distribution of electrogenerated etchant at the tool electrode/electrolyte interface can be controlled effectively by tuning the frequency of pulse potential. Under a mechanical motion mode, the roughness of a raw GaAs workpiece can be reduced efficiently from 700 nm to 5.1 nm. This technique is ideal for the electrochemical polishing of semiconductor wafers.

Thehightemperaturemechanicalpropertyofseparatorsisveryimportantforsafetyoflithium-ionbatteries.However,themechanical integrity of polymeric separators in lithium-ion batteries at elevated temperatures is still not well characterized. In this paper, the temperaturedependentmicro-scalemorphologychangeofPP(polypropylene)-PE(polyethylene)-PPsandwichedseparators(Celgard 2325) was studied by in-situ high temperature surface imaging using an atomic force microscope (AFM) coupled with power spectral density (PSD) analysis and digital image correlation (DIC) technique. Both PSD and DIC analysis results show that the PP phase significantly closes its pores by means of dilation of the nanofibrils surrounding the pores in the transverse direction and shrinkage in the machine direction, when cycled at 90 ◦ C, even below the separator’s shutdown temperature (∼120 ◦ C) and its own melting temperature (165 ◦ C). This is presumably due to surface melting effect in nanostructures and should be size dependent‐the surface melting temperature may decrease with the diameter of nanofibrils. Therefore, some pore closing might happen even at operating temperatures, it will lead to capacity fade that is undesired for battery performance. © 2014 The Electrochemical Society. [DOI: 10.1149/2.0351409jes] All rights reserved.