ABSTRACT
The heart of the novel instrument combines a stable (~0.5%/hr) cold field emission gun (FEG) with superior electron optics including a symmetrical condenser-objective immersion final lens with the lowest possible natural aberrations (i.e. without correction). At the centre of the 3mm lens gap Cs = 0.8mm and the predicted secondary electron image resolution at lkV is 1.6nm. A sub-0.5nm probe is also available at 30kV. In an extended third order zone mode the sample is positioned within 0.5mm of the upper pole face and the Cs is calculated to be <0.2mm at electron beam energies limited to <5kV. This mode with a predicted resolution of ~1.2nm at lkV has now been implemented successfully, allowing images to be recorded at lkV and 150,000x (Fig. 1). In fact values down to Cs ~ 0.1mm (Fig.2) are accessible at beam energies at and below lkV. The image resolution (Fig. 1) is close to the immediate goal of lnm at lkV. However, in practice depth of field considerations (vs diffraction) may eventually limit the SEM, including this one, to about these levels o f useful performance. The design of the lens, stage, specimen holders, vacuum system, specimen chamber and EDS detector have all been fully integrated (Fig.3). This is the critical “baseball” at the heart of the new technology. Changes to the inside of the lens to improve imaging allow the outside diameter to be reduced for better
IOS access (0.3sr). The strong immersion lens also acts as a perfect electron trap. Sample sizes urrently supported are 8(x) x 4.5(y) x l(z)mm and 3mm diameter up to 1mm thick. The 1mm hick TEM style custom specimen holders have touch protection and current measuring apabilities. Up to 20° of specimen tilt is available with 8mm specimen holders and a full 90° ilt is to be provided for 2.3mm wide samples.
