Nanosecond Laser Assisted Fabrication of Large Area Metallic Nanostructures and Their Potential Applications
Techniques for processing nanoscale metallic and semiconductor structures with spatial order and tunable physical characteristics, such as size and shape, are important for realizing broad applications in areas such as magnetism, optics, electronics, biosensing, and drug delivery. Laser annealing is widely applied in modern semiconductor manufacturing processes for crystallizing amorphous structures into polycrystalline structures using thermal energy from laser illumination. This project aims to develop nanosecond laser assisted photothermal annealing technologies for high throughput nanofabrication of metal nanostructures on both planar and nonplanar surfaces using pulse laser induced rapid heating and nanomorphology evolution processes. This technology allows direct printing/transfer of functional devices on rigid substrates such as glass, silicon, as well as on flexible, low melting temperature substrates such as plastic and polymer. By controlling optical patterns through means of using phase-shifting photomask or pre-patterning the metal film to take advantage of the structured substrate, as well as selecting desired laser illumination duration, light wavelength, pulse number and dosage energy, thermal energy can be selectively deposited at target locations to melt materials within that area followed by nanomorphology evolution driven by surface tension. Such a low cost, high throughput and high spatial resolution nanofabrication technology could provide numerous applications in various areas including photonic devices, nanoelectronics, bio/chemical sensors, and devices for improved energy capturing and conversion in large area.
We further developed a novel gold nanoparticle embedded PDMS micropillar array to measure cell force in a large scale. The gold nanoparticles serve as point source like scattering hot spots in dark field images, where PDMS pillars and cells are almost invisible. By fitting the gold nanoparticle image with Gaussian point spread function, 30 nm pillar localization precision could be achieved even using a low N.A. 20x objective lens. This precision is comparable to prior reported fluorescent pillars imaged by a high magnification optical system with 60x or 100x objective lenses. Our plasmonic pillar sensor allows for monitoring collective cell behavior in a much larger area without sacrificing the force resolution. The plasmonic pillar also has the potential for directly delivering molecules into live cells through transient holes on the cell membrane opened by rapidly expanding cavitation bubbles, which are photothermally generated by gold nanoparticles sitting on pillar tip under laser triggering pulses.