Imaging localized plasmon resonances in vacancy doped Cu3-xP semiconductor nanocrystals with STEM-EELS

TL;DR

This study uses STEM-EELS to directly observe and measure localized plasmon resonances in vacancy-doped Cu3-xP nanocrystals, linking vacancy concentration to plasmonic behavior in semiconductor nanocrystals.

Contribution

It demonstrates the direct measurement of Cu(I) vacancies and their associated localized plasmon resonances in Cu3-xP nanocrystals using high-resolution STEM-EELS.

Findings

Cu(I) vacancies can be directly visualized in STEM images.

Localized plasmon resonances are observed and match calculations based on vacancy concentration.

Two distinct localized resonances are identified in the nanocrystals.

Abstract

Copper binary compounds are often intrinsic p-type semiconductors due to the presence of Cu(I) vacancies, with corresponding hole carriers in the valence band. If the free carrier concentration is high enough, localized plasmon resonances can be sustained in nanocrystals, with frequencies in the infra-red (<1 eV), with respect to the typical resonances seen in the visible range in the case of metals (Ag, Au, ...). The localization of the resonances can be demonstrated with scanning transmission electron energy loss spectroscopy (STEM-EELS) by combining high spatial and high energy resolutions. Here we demonstrate that Cu(I) vacancies can be directly measured from the STEM images in Cu(3-x)P hexagonal nanocrystals. Two localized resonances can be seen from STEM-EELS, which are in agreement with the resonances calculated from the vacancy concentration obtained from the STEM.