Application of charge contrast imaging in mineral characterization

Charge contrast imaging (CCI) is a new imaging mode in the variable pressure scanning electron microscope (VP-SEM) that allows for the imaging of microstructures in various non-conductive and semi-conductive materials. The exact mechanism for CCI is still debatable; however, it is agreed that there is an optimal charge compensation whereby contrast between high-density and low-density charge traps is accentuated. This phenomenon is not observable with secondary electron and backscattered electron detectors in the conventional high-vacuum SEM. In this paper, optimum operating conditions for CCI are presented for gibbsite and nickel hydroxide. User-friendly methods for finding this optimum contrast are provided as well as the benefits and potential pit-falls of the technique. The work was performed on the Hitachi S3000N VP-SEM, which allows analysis in the high-vacuum and low-pressure (<270 Pa) region.