Hot Electron Injections Induced By Planar Surface Plasmon Resonance Effect

Finding higher efficiency schemes for electron-hole separation is very important for realizing more efficient conversion of solar energy in photovoltaic and photocatalytic devices.Besides the conventional study of electron-hole separation in semiconductor devices,plasmonic energy conversion device has been proposed as a promising tool for efficiently improving the separation of electron-hole.In this thesis,the electron transfer in these two models were studied by a new imaging method at single nanoparticles scale in real time.The fundamentals of hot-electron generation,injection and regeneration are studied,which is expected to be benefit for the development of high efficiency conversion of solar energy in photovoltaic and photocatalytic devices.In this thesis,we constructed a Schottky junction consisted of single CdS nanoparticle and a planar gold film,and investigated the optical images of the CdS nanoparticles in a real time manner by surface plasmon resonance microscopy under different conditions.More specific:0.05 mg/mL CdS suspension was modified onto a gold film covered Quartz glass coverslips,with the addition of 0.05 mol/L Na2S as the reaction buffer.When illuminating the interface with blue light(?<540 nm),with the absorption of the blue light,photo-induced electrons were trapped at Schottky junction,resulting in the injection of electron from CdS nanoparticle to gold film.The accumulated holes can oxidize the S2-in the solution,the oxidized product S deposited onto the CdS nanoparticle,resulting in the enhancement of the SPR Intensity.In a backward process,when shining a red beam(660 nm)into gold film via Kretschmann configuration,hot electrons excited by the surface plasmon polaritons(SPPs)propagating in the gold film.The high energy hot electron can inject electron into CdS nanoparticle,resulting the reduction of S back into S2-.The dissolution of S decrease SPR Intensity.The Bi-directional electron transfer crossing the metal/semiconductor interface can be readily imaged by SPR microscopy.By using the recently-developed plasmonic microscopy,the bi-directional electron transfer crossing the metal/semiconductor interface was monitored by utilizing the deposition and dissolution of S at the CdS nanoparticle surface.Compared with Local SPR,such Planar SPR is much easier to modulate.The characterization of such Schottky junction is also much simple than LSPR,facilliating the investigation of Schottky junction in a full scale.The present work advances the understanding on the mechanism of hot electron transfer,which is anticipated to help the rational design and optimization of plasmonic-semiconductor hybrid nanomaterials with great implications in broad application fields including photocatalysis,photovoltaic devices,and photoelectrochemical sensing.