Laser fabrication of plasmonic metal nanoparticles for optoelectronic devices

摘要

Metal nanoparticles (MNP) are widely researched for the fabrication of novel low cost and more energy efficient optoelectronic devices. MNPs, which exhibit surface plasmon resonance (SPR), can be incorporated into thin film photovoltaic structures and as well as into substrates for enhancing the Raman spectroscopy performance. Recent demonstration of devices with plasmonic structures has limited utility due to the need for techniques of ordered MNPs for large area fabrication that are not currently available. This work examines the suitability of laser annealing for the fabrication of metal nanoparticles in large area optoelectronic devices, as well as the potential for tuning their optical properties precisely within the structure. Gold (Au), silver (Ag) and AuAg alloy particles were fabricated with laser annealing and fully characterized. Morphology characterization of the metal nanopartlcle films (MNFs) with scanning electron microscopy (SEM) and atomic force microscopy (AFM) revealed the control over the size by adjusting initial film thickness· and laser fluence. Optical characterization with UV-VIS spectrometry demonstrated that SPR of MNFs can be tuned by adjusting the alloy composition, the dielectric constant of surrounding medium, and the size distribution. This experimental result was confirmed by simulations. Direct incorporation of large well distributed Au nanoparticles into solar cells demonstrated enhanced performance. Dense MNFs with small particles decreased the photovoltaic efficiency. By contrast, in the case of Raman, small alloy particles with SPR wavelength close to the pump wavelength demonstrated the best enhancement. High resolution metal nanoparticle tracks written by the laser demonstrated gas sensing with good sensory capability. However, their high resistivity imposes difficulties in measurements. We conclude that with suitable optimisations the laser annealing technique studied here could be utilised for the fabrication of metal nanoparticles in large area optoelectronics devices. We demonstrate a number of such applications including solar cells and gas sensors and study the effects of metal nanoparticles within these devices in this thesis.