Review: Developments in micro/nanoscale fabrication by focused ion beams

The integration of nanohole array based plasmonic sensors into microfluidic systems has enabled the emergence of platforms with unique capabilities and a diversified palette of applications. Recent advances in fabrication techniques together with novel implementation schemes have influenced the progress of these optofluidic platforms. Here, we review the advances that nanohole array based sensors have experienced since they were first merged with microfluidics. We examine established and new fabrication methodologies that have enabled both the fabrication of nanohole arrays with improved optical attributes and a reduction in manufacturing costs. The achievements of several platforms developed to date and the significant benefits obtained from operating the nanoholes as nanochannels are also reviewed herein. Finally, we discuss future opportunities for on-chip nanohole array sensors by outlining potential applications and the use of the abilities of the nanostructures beyond the optical context.

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On-chip nanohole array based sensing: a review

This work combines focused ion beam sputtering and ultra-precision machining as a first step in fabricating metal alloy microcomponents. Micro-end mills having ∼25 μm diameters are made by sputtering cobalt M42 high-speed steel and C2 micrograin tungsten carbide tool blanks. A 20 keV focused gallium ion beam is used to define a number of cutting edges and tool end clearance. Cutting edge radii of curvature are less than or equal to 0.1 μm. Micro-end mill tools having 2, 4 and 5 cutting edges successfully machine millimeter long trenches in 6061-T4 aluminum, brass, 4340 steel and polymethyl methacrylate. Machined trench widths are approximately equal to the tool diameters, and surface roughnesses (Ra) at the bottom of micromachined features are ∼200 nm. Microtools are robust and operate for more than 6 h without fracture. Results from ultra-precision machining aluminum alloy at feed rates as high as 50 mm/minute and an axial depth of 1.0 μm are included.

/pdf/micromilling-of-metal-alloys-with-focused-ion-beam-18rl7rjf52.pdf

Micromilling of metal alloys with focused ion beam–fabricated tools

Cryo-electron tomography (cryo-ET) is emerging as a revolutionary method for resolving the structure of macromolecular complexes in situ. However, sample preparation for in situ Cryo-ET is labour-intensive and can require both cryo-lamella preparation through cryo-focused ion beam (FIB) milling and correlative light microscopy to ensure that the event of interest is present in the lamella. Here, we present an integrated cryo-FIB and light microscope setup called the Photon Ion Electron microscope (PIE-scope) that enables direct and rapid isolation of cellular regions containing protein complexes of interest. Specifically, we demonstrate the versatility of PIE-scope by preparing targeted cryo-lamellae from subcellular compartments of neurons from transgenic Caenorhabditis elegans and Drosophila melanogaster expressing fluorescent proteins. We designed PIE-scope to enable retrofitting of existing microscopes, which will increase the throughput and accuracy on projects requiring correlative microscopy to target protein complexes. This new approach will make cryo-correlative workflow safer and more accessible.

PIE-scope, integrated cryo-correlative light and FIB/SEM microscopy.

This paper presents techniques for fabricating microscopic, curvilinear features in a variety of workpiece materials. Micro-grooving and micro-threading tools having cutting widths as small as 13 {micro}m are made by focused ion beam sputtering and used for ultra-precision machining. Tool fabrication involves directing a 20 keV gallium beam at polished cylindrical punches made of cobalt M42 high-speed steel or C2 tungsten carbide to create a number of critically aligned facets. Sputtering produces rake facets of desired angle and cutting edges having radii of curvature equal to 0.4 {micro}m. Clearance for minimizing frictional drag of a tool results from a particular ion beam/target geometry that accounts for the sputter yield dependence on incidence angle. It is believed that geometrically specific cutting tools of this dimension have not been made previously. Numerically controlled, ultra-precision machining with micro-grooving tools results in a close match between tool width and feature size. Microtools are used to machine 13 {micro}m wide, 4 {micro}m deep, helical grooves in polymethyl methacrylate and 6061 Al cylindrical workplaces. Micro-grooving tools are also used to fabricate sinusoidal cross-section features in planar metal samples.

/pdf/microgrooving-and-microthreading-tools-for-fabricating-j44f434cbr.pdf

R. Syms

Papers

Focused ion beam milling