Scanning Electron Microscopy


The use of field emission processes as a means of generating high brightness sources of both electrons and ions is becoming of increasing practical use in electron/ion optical systems. A review is given of the source optics and emission characteristics of a zirconium oxide coated, <100> oriented, tungsten (Zr0/W(l00)), thermal field emitter electron (TFE) source and a liquid metal ion source (LMIS). The primary interest at present is the use of these high field sources in microprobe focusing columns where beam sizes of < 0.5 µm and target current densities of ~ 1 to 10 A/cm2 (in the case of a LMIS) and 102 to 104 A/cm2 (in the case of a Zr0/W(100) TFE) are required. For predicting the performance of field emission sources in microprobe columns source properties such as beam energy spread (∆E), angular intensity (I ' ) and virtual source size (dv) are of interest. For the LMIS experimental values of ∆E, I ' and dv are found to depend on particle charge to mass ratio and total source current. Similarly for the Zr0/W(100) TFE experimental values of ∆E increase with I'. A computer program, known as SCWIM, has been designed to model point-to-plane source geometries and is used to model such emitter parameters as dv and I'.

Included in

Biology Commons