Scalable fabrication of functional nanostructures on stretchable substrates by capillary-assisted particle assembly and adhesion lithography

The fabrication of metallic nanostructures on stretchable substrates enables specific applications that exploit the combination of the nano-scale phenomena and the mechanical tunability of the physical dimensions of the nanostructures. Due to the large difference in the thermal expansion coefficient between metals and polymer-based soft materials, patterning metallic nanostructures directly on a stretchable substrate is a known challenging task. In this thesis, scalable fabrications of metallic nanostructures on stretchable substrates by top-down and bottom-up methods are studied. Metallic nanostructures are first fabricated on Si substrates and subsequently transferred to stretchable substrates.In the first part of this thesis, fabrication of nanogap electrodes (NGEs) on a polydimethylsiloxane (PDMS) substrate using adhesion lithography is reported. With wafer-level processes, the nanogap is created on an Al sacrificial layer by separating two Au electrodes with an Al2O3 nanolayer. By etching the Al sacrificial layer, the NGEs are transferred to the PDMS substrate. Tunneling currents across the nanogap on PDMS are measured under various mechanical deformation statuses of the PDMS substrate. The electrical measurement results show that the nanogap distance is mechanically tunable in the quantum tunneling regime. The NGEs on PDMS might be eventually integrated with micro piezo-electric actuators to become miniaturized tunable NGEs, which could pave the way towards the application of an on-chip single-molecule detector. Apart from developing the fabrication process of the NGEs on PDMS, a yield study of the essential step of the adhesion lithography, e.g., the tape peeling process, is also conducted to understand the design principles of the NGEs. The yield of the wafer-level tape peeling process is larger than 80%.In the second part of this thesis, chip-level (~ 2 x 2 cm2) fabrication of ordered gold nanoparticles (AuNPs) on a PDMS substrate using capillary-assisted particle assembly (CAPA) technique is reported. AuNPs are first assembled on reusable Si templates with pre-defined topographical traps, and then transferred to the PDMS substrate by etching the Al sacrificial layer. The reusable assembly trap has the shape of the funnel which is designed for high assembly yield (> 90%) and precise particle placement (offset ~ 10 nm). The assembly yield, the particle position offset, the yield of the transfer process, and the reusability of the assembly template are systematically studied. Two functional AuNP structures are demonstrated using the reported fabrication process. The first structure is the plasmonic surface lattice resonance (SLR) arrays of 150 and 200 nm AuNP. The optical spectra of the AuNP arrays on PDMS are measured showing pitch-related SLR peaks that agree with the finite element method (FEM) simulation results. The second structure is the dimer of 200 nm AuNPs which has a nanogap between two AuNPs. By assembling two AuNPs in the same funnel-shaped trap, a nanogap is formed between two AuNPs. Combining Au electrodes fabricated using electron beam lithography and the lift-off process, NGEs are fabricated and successfully transferred to a PDMS substrate.