Focused Ion Beam Milling of Perylene Microcrystals into Photonic Modules: Effect of Substrate and the Ion Beam Current

The focused ion beam (FIB) milling of perylene microcrystalsusing optimized beam parameters to attain photonic modules is demonstrated.The choice of various substrates (conductive: indium tin oxide coatedpolyethylene terephthalate: ITO-PET; and nonconductive: borosilicate-glasscoverslip) and the use of a protective layer revealed the effectivenessin milling and in retaining optical traits of the photonic modules.This technique paves the way for the industrial-scale production oforganic photonic modules and devices. The rapid development of organic photonic devices ispossible withan industrially viable focused ion beam (FIB) milling technique. Inthis aspect, understanding and unveiling the optimized FIB millingparameters to attain nano-/microscale shape and size precision ofmolecular crystals are essential to achieve all-organic photonic modules.Herein, we demonstrate the FIB milling on perylene single crystalsself-assembled on conductive (indium tin oxide coated polyethyleneterephthalate: ITO-PET) and nonconductive (borosilicate glass coverslip)substrates. The beam parameters of 1 nA and 30 kV accelerating voltageare desirable for effectively milling organic crystal photonic moduleslike bent or curved waveguides and disc and ring resonators. The microcrystalson the glass substrate required a thin conductive gold layer for electronmicroscopy imaging to carry out FIB milling. Removal of this goldlayer by post milling chemical processing helps to retain crystalfluorescence on a glass substrate. On the contrary, the milling ofmicrocrystals on ITO-PET does not require any additional conductivelayers but shows poor fluorescence as they are directly exposed tothe milling ion beam. These results demonstrate the importance ofoptimal milling parameters, choice of substrate (conductive or nonconductive),and a protective gold layer for effectively milling organic crystalinto useful photonic modules. Thus, this nascent and promising technologycan be transferred toward fabricating industrially relevant organic-crystal-basedmicroelectronic and nanophotonic devices.

Automated summary

The effectiveness of focused ion beam (FIB) milling of perylene microcrystals for photonic modules is demonstrated using optimized beam parameters and choice of substrates. This technique enables industrial-scale production of organic photonic modules and devices.