Nanoscale Characterization of Metal Films Adhesion for Plasmonic Applications

The fabrication of ultrathin gold (Au) films on dielectric or semiconductor substrates is central to a variety of different plasmonic and microelectronic devices, such as photovoltaics, metamaterials and optical sensors. Au, with its superior optical and electrical properties, is the most common used material for plasmonic applications. However, the noble metal presents a challenge for the fabrication of ultrathin films on silicon substrates due to its chemical inert character. In order to overcome this issue, a metallic intermediate layer, like Titanium (Ti), is commonly used. This adhesion layer ensures sufficient bonding, yet it fails to preserve the noble metal thin film properties. This PhD project is dedicated to investigate the potential of organic adhesion layers and study the three-fold relationship of fabrication, microstructural analysis and its effect on thin film properties. The project introduces aminopropylsilatrane (APS) as a new adhesion promoter for Au thin films on silicon dioxide, and compares it to established organic adhesion layers, such as amino-propyltrimethoxysilane (APTMS) and mercapto-propyltrimethoxysilane (MPTMS), as well as to the metallic adhesion layer, Ti. APS is able to form a sub 10nm-thick, continuous Au film with an ultrasmooth surface and high chemical purity. Moreover, its solution-based protocol enables a faster and easier fabrication without generating harmful by-products. Electron microscopy methods and chemical surface techniques were employed to characterize the microstructure and different steps of the thin film fabrication process. Electrical measurements show a high conductivity of the Au thin films adhered by the organic linkers. In addition, thermal experiments indicate the potential of annealing the Au thin film to further increase its electrical conductivity. The results of the PhD study expand the understanding of adhesion layer effects on Au thin films and introduce APS as a new component, extending thin film fabrication possibilities to build superior plasmonic devices.