Optical and electronic properties of silver nanoparticles embedded in cerium oxide.

Jacopo Stefano Pelli Cresi,Giovanni Bertoni,Sergio D’Addato,Sergio Valeri,Maria Chiara Spadaro,Enrico Silvagni,Stefania Benedetti,Paola Luches

doi:10.1063/1.5142528

Abstract

Wide bandgap oxides can be sensitized to visible light by coupling them with plasmonic nanoparticles (NPs). We investigate the optical and electronic properties of composite materials made of Ag NPs embedded within cerium oxide layers of different thickness. The electronic properties of the materials are investigated by x-ray and ultraviolet photoemission spectroscopy, which demonstrates the occurrence of static charge transfers between the metal and the oxide and its dependence on the NP size. Ultraviolet-visible spectrophotometry measurements show that the materials have a strong absorption in the visible range induced by the excitation of localized surface plasmon resonances. The plasmonic absorption band can be modified in shape and intensity by changing the NP aspect ratio and density and the thickness of the cerium oxide film.

Highlights

In recent years, research activities on active catalysts for environmental protection have gained an increased relevance and urgency, due to the widespread concern for global warming
Cerium oxide based catalysts are active in a number of important environmental reactions, the most successful commercial applications being in car catalytic converters and in antiparticulate filters for diesel engines.[1]
The morphology of the molecular beam epitaxy (MBE)-grown Ag NPs embedded between two CeO2 layers was investigated by TEM

Summary

Introduction

Research activities on active catalysts for environmental protection have gained an increased relevance and urgency, due to the widespread concern for global warming. Static charge transfer processes,[19,20,21,22] as well as more complex interaction mechanisms,[23,24,25] have been identified on model systems made of metal NP supported on cerium oxide surfaces The influence of such processes on the functionality of the composite materials has been recognized, the resulting optical properties are comparatively less understood. Composite systems made of Ag NPs embedded within cerium oxide matrixes have recently been investigated and a long-living and efficient plasmon-mediated charge transfer has been hypothesized, based on the results of fast transient absorption spectroscopy.[26] a superior LSPR-induced catalytic activity of Ag/CeO2 systems under visible light irradiation was recently demonstrated.[11, 27]. The samples investigated in this study are Ag NPs of variable size and density embedded within or supported on CeO2 films. Pure CeO2 films of different thickness without Ag NPs were grown and measured for comparison

Å Ag NPs 1 nm CeO2

Results and discussion

Conclusions