文档介绍：Chapter 7 Microanalysis
Introduction
Microanalysis implies that an analysis can be performed on a very small amount of materials, or more usually a very small part of a larger specimen.
Microanalysis in electron microscopy is an important tool for characterizing all types of solid material.
Type of electron monly used for microanalysis
SEM with X-ray spectrometer (EDS & WDS)
The electron probe microanalyser (EPMA)
is essentially a purpose-built analytical microscope of the SEM type
Transmission electron microscopes (TEM and STEM) equipped with EDS and EELS
is a analytical type TEM
X-ray spectrometer
Energy Dispersive X-ray Spectrometer (EDS)
Used for TEM and SEM
monly used
Energy resolution is not very high, but fast
Wavelength Dispersive X-ray Spectrometer (WDS)
Used only for SEM and EPMA
Energy resolution is high, but slow
X-ray spectrometer
EDS
Detector
EDS usually use Lithium drift silicon detector (Si(Li) detector) to detect X-ray.
The detector normally consists of a small piece of semiconducting silicon which is held in such a position that as many as possible of the X-rays emitted from the specimen fall upon it.
Since X-ray cannot be deflected, the detector must be in the line of sight of the specimen.
How does EDS work
Each ing X-ray excites a number of electrons into the conduction band of the silicon leaving an identical number of positively charged holes in the outer electron shells. (generating electron-hole pairs.)
The energy required for each of these excitations is only ; consequently the number of electron-hole pairs generated is proportional to the energy of the X-ray photon being detected.
An Al Ka X-ray, with an energy of , will give rise to 392 electron-hole pairs.
An Cu Ka X-ray, with an energy of , will generate 2110 electron-hole pairs.
If a voltage is applied across the semiconductor a current will flow as each X-ray is absorbed in the detector and the magnitude of the current will be exactly proportion