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Nanostructuring Optical Waveguides by Focused Ion Beam Milling. Near-Field Characterization

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 Added by Carole Heritier
 Publication date 2008
  fields Physics
and research's language is English
 Authors F. Lacour




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Nanostructures have become an attractive subject due to many applications, particularly the photonic bandgap effect observed in photonic crystals. Nevertheless, the fabrication of such structures remains a challenge because of accurate requirement concerning regularity, shape, hole depth etc. of the structure. E-beam lithography permits a good control of dimensional parameters but needs a 1-step fabrication process. In our work, we have to combine traditional strip-load waveguides (SiO2/SiON/SiO2 on Si) and nanostructures whose dimension are totally different. This imposes a 2-step process where waveguides and nanostructures are successively fabricated. We have at our disposal different ways to characterize these nanostructures. A direct aspect control during and after FIB treatment can be achieved by FIB and SEM imaging. Scanning near-field optical microscopy (SNOM) is currently the most effective way to test guiding confinement in such surface structures by detecting the evanescent field.



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117 - F. Lacour 2008
We report on two novel ways for patterning Lithium Niobate (LN) at submicronic scale by means of focused ion beam (FIB) bombardment. The first method consists of direct FIB milling on LiNbO3 and the second one is a combination of FIB milling on a deposited metallic layer and subsequent RIE (Reactive Ion Etching) etching. FIB images show in both cases homogeneous structures with well reproduced periodicity. These methods open the way to the fabrication of photonic crystals on LiNbO3 substrates.
A focused ion beam is used to mill side holes in air-silica structured fibres. By way of example, side holes are introduced in two types of air-structured fibres (1) a photonic crystal four-ring fibre and (2) a 6-hole single ring step index structured fibre.
Recent advances in focused ion beam technology have enabled high-resolution, direct-write nanofabrication using light ions. Studies with light ions to date have, however, focused on milling of materials where sub-surface ion beam damage does not inhibit device performance. Here we report on direct-write milling of single crystal diamond using a focused beam of oxygen ions. Material quality is assessed by Raman and luminescence analysis, and reveals that the damage layer generated by oxygen ions can be removed by nonintrusive post-processing methods such as localised electron beam induced chemical etching.
A study of damages caused by gallium focused ion beam (FIB) into III-V compounds is presented. Potential damages caused by local heating, ion implantation, and selective sputtering are presented. Preliminary analysis shows that local heating is negligible. Gallium implantation is shown to occur over areas tens of nanometers thick. Gallium accumulation as well as selective sputtering during III-V compounds milling is expected. Particularly, for GaAs, this effect leads to gallium segregation and formation of metallic clusters. Microdisk resonators were fabricated using FIB milling with different emission currents to analyze these effects on a device. It is shown that for higher emission current, thus higher implantation doses, the cavity quality factor rapidly decreases due to optical scattering losses induced by implanted gallium atoms.
Focused-ion-beam milling is used to fabricate nanostencil masks suitable for the fabrication of magnetic nanostructures relevant for spin transfer torque studies. Nanostencil masks are used to define the device dimensions prior to the growth of the thin film stack. They consist of a wet etch resistant top layer and an insulator on top of a pre-patterned bottom electrode. The insulator supports a hard mask and gives rise to an undercut by its selective etching. The approach is demonstrated by fabricating current perpendicular to the plane Co/Cu/Co nanopillar junctions, which exhibit current-induced magnetization dynamics.
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