Variable pressure SEM

Leo 1455VP scanning electron microscope

The Leo 1455VP SEM with Oxford Instruments INCA analysis system is a highly versatile analytical SEM capable of working in both low vacuum mode, for imaging and qualitative X-ray analysis of uncoated and delicate (including 'type') specimens, and at high vacuum for imaging and quantitative analysis. In low vacuum mode the pressure may be reduced to as little as ~200 Pa, although best image resolution will be obtained at approximately 10-60 Pa.

The Leo is fitted with a four quadrant diode backscattered electron detector for imaging average atomic number contrast. Mixed images, in both secondary electron and backscattered electron modes, may be obtained which give both topographic and average atomic number information.

Digital images can be captured at resolutions up to 3072x2304 pixels giving a file size of 6.9 MB.

With an EDX detector and INCA analysis system, non-destructive qualitative and quantitative determination can be carried out for elements with an atomic number greater than five (boron). Detection limits are of the order of 0.2 wt.%, depending on the type of specimen, the elements of interest etc. Analyses can be undertaken in spot mode or the beam rastered to acquire X-ray element maps of areas of the sample surface. For quantitative analysis the sample must be prepared as a polished block or section and the surface carbon coated.

The instrument has a large chamber capable of accommodating samples up to around 15x15x15 cm and can be set up with a long working distance for imaging at low magnifications (x20). In low vacuum mode, and at short working distances, images may be obtained at magnifications in excess of 10,000x, giving sub-micron resolution. The Leo software contains a routine for automatically acquiring image montages over large areas of the sample surface.

A Peltier cooling stage can be attached for freezing samples down to -30 ^oC, most useful for imaging specimens which may otherwise dehydrate within the SEM.

The instrument can also be modified for operation in STEM mode for ultra-high resolution, transmission mode imaging of ultra-thin specimens.

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