Multiphoton lithography based 3D micro/nano printing Dr Qin Hu EPSRC Centre for Innovative Manufacturing in Additive Manufacturing University of Nottingham Multiphoton lithography  Also known as direct laser lithography, direct laser writing or two-photon polymerisation  Create arbitrary 3D nano/micro structures  Based on NIF fs laser induced multi-photon polymerization  Direct fabrication without a mask  Materials: polymers, ceramics, metals, hybrid…  Resolution: ~100 nm Femtosecond laser beam Excited state Photoresist Virtual state Substrate Lifetime: ~ 10-15sec Ground state Micro-stereolithography vs. Multiphoton lithography Micro stereolithography Multiphoton lithography Essential CAD design, 2D layer preparation function, laser scanning & elements controlling system with monitoring devices Mechanism for One-photon absorption Multi-photon absorption polymerisation (Linear absorption) (Non-linear absorption) Laser type UV laser NIR femtosecond laser Resolution ~ 1 µm ~ 100 nm Polymerisation at any desired Strategy for 3D Polymerisation at the surface location fabrication → layer-by-layer approach → Built 3D structure ‘recording’ the beam path Systems Nanoscribe Specifications Galvo mode Piezo mode Lateral feature size ≤ 200 nm ≤ 200 nm Vertical feature size ≤ 1500 nm ≤ 1000 nm Writing speed Typ. 10 mm/s Typ. 100 µm/s Range Ø 200 µm 300x300x300 µm3 Accessible writing area 100x100 mm2 100x100 mm2 Fabrication procedure J Biomed Optics 17 (2012) 081405 Feature size  Resolution: ~ 100 nm  Methods for making sub-resolution features o With additional radical quenchers o Using highly sensitive initiator o Repolymerization o Combined with stimulated emission depletion (STED) Nanotechnology 16 (2005) 846; Appl Phys Lett 89 (2006) 173133; 90 (2007) 071106; Annu Rev of Biochem 78 (2009) 993; Optics Express 21 (2013) 10831; Nano Letters 13 (2013) 5672 Materials  Compositions o Photoinitiators o Monomer o …  Requirements o Transparent in the visible and near infrared regions o Fast curing speed so that only the resin in the focal point is polymerized o Resisting to the solvent used in the later washout process o Suitable mechanical property and thermal stability to main the shape Material capability: polymer  Multiphoton induced polymerisation Material capability: metal  Multiphoton induced photoreduction of metal ions  Common metals: Ag and Au HAuCl H O → Au nanoparticles 4∙ 2 Nano Today 5 (2010) 435 Material capability: hybrid Polymerization Polymer resin Polymer Two-photon simultaneously induced + Metal Metallic salts/acids Metal reduction e.g. HAuCl 4 EDX mapping: Au IP-L + Au SU8 + Au