The role of induced contrast in images obtained using the environmental scanning electron microscope

Generation of contrast in images obtained using the environmental scanning electron microscope (ESEM) is explained by interpretation of images acquire d using the gaseous secondary electron detector (GSED), ion current, and th e Everhart-Thornley detector. We present a previously unreported contrast c omponent in GSED and ion current images attributed to signal induction by c hanges in the concentration of positive ions in the ESEM chamber during ima ge acquisition. Changes in positive ion concentration are caused by changes in electron emission from the sample during image acquisition and by a dis crepancy between:the drift velocities of negative and positive charge carri ers in the imaging gas. The proposed signal generation mechanism is used to explain contrast reversal in images produced using the GSED and ion curren t signals and accounts for discrepancies in contrast observed, under some c onditions, in these types of images. Combined with existing models of signa l generation in the ESEM, the proposed model provides a basis for correct i nterpretation of ESEM images.