Electronic Properties of a Functionalized Noble Metal Nanoparticles Covalent Network

Functionalized gold and silver nanoparticles have been prepared and characterized by means of spectroscopic and morphological techniques together focused on electrical measurements on cast deposited films. The Au and Ag nanoparticles have been functionalized with a on purpose prepared conjugated dithiol, 9,9-didodecyl-2,7-bis-thiofluorene (FL), giving rise to organic solvents soluble AuNPs-FL and AgNPs-FL samples, respectively. In the case of AuNPs-FL, well separated nanoparticles, with an average size of about 4 nm, assembled into bidimensionally monolayer network and with regular spatial distributions have been observed by TEM. Synchrotron radiation-XPS data support the observed network formation, showing that all bifunctional ligands end-groups are covalently bonded to metal noble atoms at the nanoparticles surfaces. In order to investigate their interesting conduction properties, electrical measurements evidenced a non-ohmic behavior in the case of the AuNPs-FL thin film, with a conduction mechanism that strongly depends on polarons and bipolarons along the carbon active chain belonging to the fluorene bridge. By increasing the stacked layers of the AuNPs-FL thin film, the conductivity behavior changed following approximately the ohmic law. On the contrary, AgNPs-FL shows higher conductivity, and upon an aging process, a diode behavior was observed that opens perspectives as flexible optoelectronics devices.