Real-time ellipsometry for probing charge-transfer processes at the nanoscale
Nanoscale charge transfer is important to both the frontier of fundamental science and to applications in molecular electronics, photonic, electronic, optical, imaging, catalysis, sensing devices, photovoltaics, and energy savings and storage. For many of those applications, plasmonic metal nanoparticles are coupled with molecules and/or semiconductors, where nanoparticles act as an electron-bridge. Metal nanoparticles experience charge transfer either by a hopping mechanism involving transient charging of the nanoparticle and/or by electron storage and delocalization among/in the nanoparticles. This electron transfer affects the electron density in the metal, and the plasmon resonance, and therefore, can be detected spectroscopically. This chapter discusses examples of exploitation of spectroscopic ellipsometry as a real time research tool that advance description and understanding of charge transfer phenomena involving (i) chemisorption of metals on semiconductor surfaces, (ii) growth of plasmonic nanoparticles on polar semiconductors, (iii) coupling plasmonic nanoparticles to graphene, and (iv) charge transfer between plasmonic nanoparticles and biomolecules, activating sensing processes.
