Ambient-dependent Agglomeration and Surface-Enhanced Raman Spectroscopy Response of Self-Assembled Silver Nano-particles for Plasmonic Photovoltaic Devices

The agglomeration/dewetting process of thin silver films provides a scalable method of obtaining self-assembled nanoparticles (SANPs) for plasmonics based thin-film solar photovoltaic (PV) devices. Here, we show the effect of annealing ambiance on silver SANP average size, particle/cluster finite shape, substrate area coverage/particle distribution and how these physical parameters influence optical properties and surface-enhanced Raman scattering (SERS) responses of SANPs. Statistical analysis performed indicates that generally Ag SANPs processed in the presence of a gas (Argon and Nitrogen) ambiance tend to have smaller average size particles compared to those processed under vacuum. Optical properties are observed to be highly dependent on particle size, separation distance as well as finite shape. The greatest SERS enhancement was observed for the argon processed samples. There is a correlation between simulation and experimental data that indicate argon processed AgNPs have a great potential to enhance light coupling when integrated to thin-film PV. 1 Introduction As-deposited thin metallic films are generally metastable or unstable and readily de-wet from a solid substrate when heated even well below their melting temperature 1-2. The process of agglomeration/de-wetting proceeds in two ways: nucleation and growth of holes, and spinodal dewetting 1, 3-5. This process is a relatively economical means of obtaining both simple and complex nano-structures from thin metal films 5-10 compared to traditional methods such as e-beam lithography. Whilst dewetting during film processing has been reported to have undesirable effects on micro-and nano-systems, agglomeration has become the method of choice for catalyzed growth of nanotubes/nanowires and electronic and photonic devices 3. Dewetting of thin metallic films (both liquid and solid) to obtain mono/multi-dispersed nanoparticles has been demonstrated with a range of metals including: gold (Au), silver (Ag), nickel (Ni), copper (Cu) and alumina (Al), among others 1, 3-4, 10-1. However, Ag film dewetting has been mostly investigated as candidate for plasmonic sensing 12-18 and plasmonics-enhanced solar photovoltaics (PV) devices 19-31 applications. This is because Ag is generally considered to have the most suitable optical properties for solar cell applications. Silver nanoparticles exhibit highly intense and localized surface plasmon resonances (LSPR) and low absorption in the visible and near