Energy-Dispersive Spectroscopy in A 400Kv Electron Microscope
A Si(Li) detector for X-ray energy dispersive spectroscopy (EDS) has been installed on a 400 kV EM, the JEM-4000EX, which is also interfaced with a scanning device (ASID40) and electron energy loss spectrometer (ASEA40). The EM's basic performance, i.e., resolving power, is 0.23 nm at 400 kV. X-ray microanalysis in a high-voltage EM has many advantages, but few reports have been published because of some severe instrumental problems originating from it's high energy electron beam. To overcome these problems many modifications have been made on the EM column.The modifications are divided into two aspects. One is the reduction of bremsstrahlung and the other is the protection of the Si(Li) detector from hard X-ray radiation from the upper parts of the detector, especially condenser lens (CL) aperture. To reduce bremsstrahlung many parts of the wall which electron beam might hit are covered with graphite and the materials for CL fixed apertures are changed to light elements. To protect the detector X-ray shielding parts made of heavy metals (W, Ta, Pb) and with a total thickness of more than 30 mm are set between the CL aperture and the Si(Li) detector.