Probing hot-electron effects in wide area plasmonic surfaces using X-ray photoelectron spectroscopy

Abstract

Plasmon enhanced hot carrier formation in metallic nanostructures increasingly attracts attention due to potential applications in photodetection, photocatalysis, and solar energy conversion. Here, hot-electron effects in nanoscale metal-insulator-metal (MIM) structures are investigated using a non-contact X-ray photoelectron spectroscopy based technique using continuous wave X-ray and laser excitations. The effects are observed through shifts of the binding energy of the top metal layer upon excitation with lasers of 445, 532, and 650 nm wavelength. The shifts are polarization dependent for plasmonic MIM grating structures fabricated by electron beam lithography. Wide area plasmonic MIM surfaces fabricated using a lithography free route by the dewetting of evaporated Ag on HfO2 exhibit polarization independent optical absorption and surface photovoltage. Using a simple model and making several assumptions about the magnitude of the photoemission current, the responsivity and external quantum efficiency of wide area plasmonic MIM surfaces are estimated as 500 nA/W and 11 × 10−6 for 445 nm illumination.

Plasmoelectric Potential Mapping of a Single Nanoparticle

“…The absolute value as well as the sign of this potential will be affected by the deviation between the excitation frequency and the SPR frequency. Promisingly, the discovery of the plasmoelectric potential defies the photon-energy limitation of the photoelectric conversion process, and has increasingly attracted researcher’s focal interest. − Via the introduction of a well-defined thermodynamic model, A. Polman and co-workers have discovered that the charge transfer in plasmoelectric potential is dictated by the principle of minimal free energy under steady state excitations . M. Moskovits et al have reported that, owing to this plasmoelectric effect, gold nanoparticles can change their charge states when the UV–visible spectrum is measured .…”

Hot Electrons in TiO2–Noble Metal Nano-Heterojunctions: Fundamental Science and Applications in Photocatalysis

“…Similarly, XPS has also been used to survey hot electron effects in wide plasmonic areas [ 156 , 157 ] while also providing insights into the evolution of the energy band structure of the Schottky junctions that are widely used in plasmonic photocatalysis ( Figure 9 ).…”