Si(Li) detector

An EDS (energy dispersive X-ray spectrometry) detector, which uses a lithium (Li)-doped silicon (Si) single-crystal semiconductor as a detector element.
An electron beam incident onto a specimen generates characteristic X-rays, and the X-rays enter the detector element. They generate electron-hole pairs in the detector element with their numbers proportional to the X-ray energy. An anode (collector electrode) is placed at the backside of the element. By applying a voltage between the X-ray incident plane and the collector electrode, the generated electrons are collected to the collector electrode. Then, the X-ray energy is determined by measuring the amount of the charge collected.
The Si(Li) detector can detect the X-rays with energies ranging from 0.1 to 40 keV. This means that the detector can analyze the characteristic X-rays ranging from boron (B: atomic number 5) to uranium (U: atomic number 92). The energy resolution of the detector is approximately 130 to 140 eV (for FWHM of Mn Kα 5.9 keV). To prevent the diffusion of Li doped at applying a voltage and also to reduce thermal noise and a dark current, the detector element is cooled with liquid nitrogen.
Currently, the silicon-drift detector (SDD) has widely been used, which has a higher count rate (X-ray detection per unit time) than the Si(Li) detector and can be used by Peltier cooling instead of liquid-nitrogen cooling.