An Advanced SEM-FIB Dual Beam Microscope for Three-Dimensional Mesoscale Fabrication, Imaging and Analysis

The growth and fabrication of modern structures and devices has now developed in order to exploit the full three-dimensional behaviour of the materials used. Whether its in structural materials, such as ultra-fine ceramic-metal composites, or in functional materials, where transistor structures composed of a 3D 'latticework' of key components, there is a pressing need to understand the structure, composition and physico-chemical properties of modern materials in three dimensions. Over the past 5 years we have developed transmission electron tomographic techniques to investigate, with nanometre resolution, the internal architecture of many materials systems, including heterogeneous catalysts, nanotubes and quantum dots. However, it is important to link the structure-properties relationships over many length scales, from nanometres (10-9m) to microns (10-6m) through to millimetres (10-3m). Although, x-ray tomography and related techniques are used with great effect at length scales ~ few microns, this proposal addresses the development of techniques to give the ability to analyse, in three dimensions, the structure and composition of a range of materials at a meso-scale, from 10's microns to 10 nm, bridging the gap between transmission electron tomography and x-ray tomography.Such 3D analysis can now be undertaken using a combined scanning electron microscope (SEM) / focussed ion beam (FIB) microscope. This instrument, known as a 'Dual Beam microscope', uses the milling action of a gallium ion beam to reveal internal surfaces and an electron beam to record successive image slices (to give 3D morphology). Either secondary electrons (for maximum surface detail) or back-scattered electrons (which has atomic number contrast) can be used to form images.The instrument will have a field emission gun (FEG) electron source for optimum brightness and image resolution, and advanced analytical tools including an electron backscattered diffraction (EBSD) detector for 3D crystallographic studies, and an energy-dispersive X-ray (EDX) detector system to map the composition of the specimen in 3D. It will have an internal micromanipulator for handling micron-sized specimens and an in-situ straining stage will be incorporated to measure the mechanical response of micron-sized components. As well as yielding new areas of research combining electron and ion sources, the individual components of the Dual Beam will have a performance better than any of the single-beam SEMs and FIB currently available to us. In particular, the EBSD system will be ~100x faster than our present system and milling times with the FIB reduced by up to a factor of 5.In addition to the 3D imaging and analysis, we propose to use a dual beam workstation to fabricate novel electronic device structures and develop novel sample geometries for a wide range of state-of-the-art transmission electron microscopic techniques. In particular, for TEM specimens the dual beam requested in this proposal allows low energy ion thinning of membranes to remove implantation damage. Subsequent micromanipulation of the plucked free-standing membrane onto a specially prepared grid will then allow full 360 degree tilt and rotation when in the TEM, vital for advanced electron tomographic analysis.