Scanning internal photoemission microscopy for the identification of hot carrier transport mechanisms

Abstract

Linear and nonlinear internal photoemission in a thin-film metal-insulator-metal heterosystem, i.e., a Ta-TaOx-Ag junction, together with surface reflectivity are mapped with a lateral resolution of better than 5 μm. The spatial correlation of the different signals and time-resolved internal photoemission spectroscopy reveal excitation mechanisms and ballistic hot carrier injection. The internal photoemission yield variation with Ag layer thickness is quantitatively explained by above-barrier injection. The hot-spot-like behavior of the two-photon induced internal photoemission observed for short pulse excitation is attributed to local field enhancements because of Ag-film thickness reduction and plasmonic effects at structural defects.

Burstein-Moss Effect Behind Au Surface Plasmon Enhanced Intrinsic Emission of ZnO Microdisks

“…A similar SP-assisted electron transfer process has also been observed in ZnO quantum dots and ZnO microflowers decorated by Au NPs and confirmed by time-resolved photoluminescence (TRPL) in our previous work1920, which exhibits the delayed lifetime of the photoluminescence. According to the diagram, the enhancement of NBE intensity is related to several factors: (1) the overlap extents between the defect emission spectra of ZnO and absorption spectra of Au NPs, which indicates the coupling efficiency; (2) the absorbance of Au NPs, which hints the coupling strength and (3) the morphology and spatial density of the Au NPs, which influences the local field enhancement induced by hot-spots effect2122. With increasing the sputtering time of Au NPs from 0 s to 90 s, the absorbance of Au NPs is increased gradually even in the reduction of spectral overlap.…”

Few-Cycle Laser Pulse Induced Plasmon Assisted Thermionic Injection in Metal-Insulator-Metal Junctions

“…The intensity dependence (diamonds in Fig. 1c) yields a nonlinear exponent of 2.5 indicating a mixture of two-photon and three-photon processes as it is expected for the given MIM junction having an internal barrier height of 1.8 eV [5]. For a top electrode thickness of 40 nm the injection current drops below the detection limit (≈1 pA).…”

Nanoscale Quantum Optics

“…Thus lateral transfer is difficult to directly measure. However, transient charging after photoexcitation [101], induced photocurrents in heterostructures [102], exciton microscopy [103], and photoemission of excited electrons provide access to nanoscale charge transport phenomena. Ultrafast electron transport is significant in the ultrafast demagnetization observed in ferromagnets after pulsed excitation [104].…”