The scanning electron microscope (SEM) was primary developed for imaging applications. With the introduction of the Si(Li) energy dispersive spectrometer (EDS), simultaneous imaging and x-ray microanalysis became possible. However, long working distance and high current were needed because the position and small solid angle of the EDS detector. SEM was initially and is still optimized for imaging applications, where the high spatial resolution is generally obtained at short working distance. With the introduction of an annular silicon drift detector (SDD) system, scanning electron microscopy is facing a revolution. This detector is inserted below the objective lens which gives a higher solid angle (up to 1.2 sr). In consequence, a lower working distance and probe current can be used. An improved spatial resolution becomes possible during x-ray microanalysis.
For quantification microanalysis where the absorption of the x-ray is important, the value of the takeoff angle is important. Lower value increases the absorption in the sample. Also current correction models, suppose a fix value of takeoff angle. However, preliminary results indicate that this large takeoff angle range does not affect the correction model when the absorption effect is small or moderate. The accuracy of the quantification with an annular SDD was evaluated with the standardless1 and f-ratio method23. The effect of this detector geometry and position on the correction model is currently studied.
The annular SDD with is larger solid angle will clearly revolution the quantification microanalysis by moving from point analysis to quantitative micrograph with simultaneous electron imaging. Also, since the count rate can be as high as 1,500 kcps with our system, which lower significantly the detection limit of elements as well the minimum feature sizes of different phases that can be distinguished.