Competition between bulk and interface plasmonic modes in valence electron energy-loss spectroscopy of ultrathinSiO2gate stacks

Abstract

Low-energy excitations ͑Շ50 eV͒ induced by fast electrons in materials can exhibit a collective and delocalized nature. Here, we study such excitations in Si/ SiO 2 / Si stacks by spatially resolved electron energy-loss spectroscopy with a sub-2 Å electron beam. Experimental spectra acquired in the SiO 2 layer are found to display delocalized contributions originating from interface plasmons, interband transitions, and Čerenkov radiation. A comparison with simulations based on a local semiclassical dielectric model, which includes relativistic effects, highlights the changes in interface plasmon coupling as the thickness of the central SiO 2 layer is reduced. We demonstrate both experimentally and theoretically that when the electron probe is located at the center of a 2 nm SiO 2 layer, the optical response expected from a bulk SiO 2 layer is suppressed and delocalized contributions dominate. As the layer thickness is reduced, the spectra become more like that of bulk Si even if the incident electrons travel only in the SiO 2 layer. This poses a major challenge for directly extracting local optical properties of ultrathin layers by electron energy-loss spectroscopy.

Investigation of the Composition of the Si/SiO2Interface in Oxide Precipitates and Oxide Layers on Silicon by STEM/EELS

“…The existence of a SiO intermediate layer at the interface between a 140 nm thick SiO 2 layer and a (111) silicon substrate was also demonstrated by Moreau et al 30 Couillard studied similar gate stacks with 2 nm and 10 nm thick oxide layers by detailed EELS investigation. 31 They observed the shift of the plasmon peaks with 0.4 nm step size. In the center of the 10 nm oxide layer, they found the typical features of SiO 2 EEL spectra but in the 2 nm oxide layer the peak shift was much lower.…”

Spatially resolved measurements of plasmonic eigenstates in complex-shaped, asymmetric nanoparticles: gold nanostars

“…In the past decades, an important number of spatially resolved EELS studies in the low-loss region (where optical transitions are measured) have been performed; for a review, see, e.g., [18,19]. Most of these experimental and theoretical studies focused on the measurement of Interface Plasmons (IPs) and, to a smaller extent, to other boundary-related excitations for different geometries such as spheres [20], cylinders [21][22][23][24][25][26][27] and single or multi-layers [28][29][30][31]. However, they essentially considered both an energy range above 4 eV, i.e., the UV spectrum, and highly symmetric configurations.…”

Current Stage of the Investigation of the Composition of Oxygen Precipitates in Czochralski Silicon Wafers

“…The material change from Si to SiO 2 leads to a plasmon energy shift to about 23 eV. 37,38 The spectra taken on the plate-like precipitates (location 2) show the characteristic form of amorphous SiO 2 layers with the plasmon loss energy at 23 eV.…”