electrode with a fine tip needle electrode (detector), which can be easily accommodated with these scintillating BSE detectors. The needle detector and cylindrical geometry (wire) have also been extensively surveyed. Cathodoluminescence Cathodoluminescence is another mode of detection involving the photons generated by the beam-specimen interaction. This mode has been demonstrated to operate also in ESEM by the use of the light pipes after they were cleared of the scintillating coating previously used for BSE detection. However, not much is known on its use outside the experimental prototype originally tested. Clearly, ESEM is more powerful and meaningful under this detection mode than SEM, since the natural surface of any specimen can be examined in the imaging process. Cathodoluminescence is a materials property, but with various specimen treatments required and other limitations in SEM the properties are obscured or altered or impossible to detect and hence this mode of detection has not become popular in the past. The advent of ESEM with its unlimited potential may provoke more interest in this area too, in the future. X-rays The characteristic elemental X-rays produced also in the ESEM can be detected by the same detectors used in the SEM. However, there is an additional complexity arising from the X-rays produced from the electron skirt. These X-rays come from a larger area than in SEM and the spatial resolution is significantly reduced, since the “background” X-ray signals cannot be simply “suppressed” out of the probe interaction volume. However, various schemes have been proposed to solve this problem. These methods involve spot masking, or the extrapolation technique by varying the pressure and calibrating out the effects of skirt, whereby considerable improvement has been achieved. Specimen current In vacuum SEM, the specimen absorbed current mode is used as an alternative mode for imaging of conductive specimens. Specimen current results from the difference of electron beam current minus the sum of SE and BSE current. However, in the presence of gas and the ensuing ionization, it would be problematic to separate this mode of detection out of the generally operating gaseous detection device. Hence this mode, by its definition, may be considered as unsustainable in the ESEM. Shah and Becket assumed the operation of the specimen absorbed current mode if the conductivity of their specimen was assured during the examination of wet botanical samples; in fact, Shah by 1987 still considered the ionisation products in gas by SE