In-Situ Differential Spectroscopy

In a spectrometer of the type having an electron beam generator for generating an electron beam that is directed at a sample, an electron beam positioner for directing the electron beam onto a position of the sample and thereby producing a secondary emitted stream from the sample, a secondary emitted stream positioner for positioning the secondary emitted stream onto a detector array, and the detector array for receiving the secondary emitted stream and detecting both amounts and received positions of the secondary emitted stream, where the secondary emitted stream includes at least one of electrons and x-rays, the improvement comprising a modulator for modulating the position of electron beam that is directed onto the sample, and thereby sweeping the electron beam between a first position and a second position on the sample, and an extractor in signal communication with both the modulator and the detector array, for extracting a differential signal representing a difference between signals received from the first position and signals received from the second position.