Triple-Beam Focussed-Ion-Beam Microscope

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The Carl Zeiss XB1540 Cross-Beam focussed-ion-beam microscope at University College London is a unique instrument in a unique location. The instrument is located in a brand new purpose-built class 10,000 cleanroom in the basement level of the London Centre for Nanotechnology in the heart of the capital city. The instrument is equipped not only with an in situ field-emission scanning electron microscope for gallium-free imaging, but also an in situ low-voltage argon-ion-miller for gallium-free nanofabrication. We believe this to be the only such triple-beam combination in the UK.The Achilles' heel of the FIB is that the gallium beam inevitably damages the surface of any milled or imaged sample. The damage consists of both gallium implantation and amorphisation. To some extent this can be ameliorated by using low beam currents (at a cost of longer milling times) and/or low voltages (at a cost of worse imaging contrast). A much more powerful technique is to mill nanoscale features using the conventional FIB and then polish the sample using a broad-beam argon ion miller so as to remove the gallium-implanted and amorphised layer. Not only is argon inert and less mobile than gallium and therefore will do much less damage to the sample, but also the ion energy can be reduced to as low as 30 eV. This greatly reduces the depth of damage done to the sample. When fabricating functional devices and materials using FIB it is important to get some kind of feedback as to when the fabrication is complete. Using the SEM to image the structure is clearly one feedback method, but topology is not the whole story. What one really wants is functional feedback / in other words measuring the device functionality during FIB milling to give feedback to the milling process. For electronic devices this can be done straightforwardly by using electrical connections to the device. Many functional nanoelectronic devices, however, only work at low temperatures / examples include most spintronic, ferroelectric, qubit, multiferroic and superconducting devices.At UCL we have therefore installed a liquid-helium-cooled sample holder with multiple feedthroughs for electrical measurements. This has allowed us to measure in real-time the current-voltage characteristics of superconducting devices as they are being fabricated by FIB.As a result of both the unrivalled performance of the XB1540 FIB and these two unique experimental capabilities, we believe that the UK academic community in materials science, the physical sciences and the life sciences will benefit greatly from access to this instrument.