Direct Quantification of Cu Vacancies and Spatial Localization of Surface Plasmon Resonances in Copper Phosphide Nanocrystals

Abstract

Copper chalcogenides and pnictogenides often behave as heavily doped p-type semiconductors due to the presence of a high density of Cu vacancies, with corresponding hole carriers in the valence band. If the free carrier concentration is high enough, localized surface plasmon resonances can be sustained in nanocrystals of these materials, with frequencies that are typically observed in the infra-red region of the spectrum (<1 eV), differently from the typical resonances featured in the visible range by metallic nanoparticles. Here, we demonstrate that Cu vacancies in hexagonal Cu 3-x P nanoplatelets can be directly quantified by scanning transmission electron microscopy (STEM) analysis. We also report for the first time the spatial localization of the plasmon resonances in individual Cu 3-x P nanocrystals by means of STEM energy loss spectroscopy (EELS), an achievement that to date had been demonstrated only on nanoparticles of noble metals. Two plasmon modes can be seen from STEM-EELS, which are in agreement with the resonances calculated from the vacancy concentration obtained from the STEM analysis. zation of the resonances. In our Cu 3-x P nanoplatelets, two

Bandgap determination from individual orthorhombic thin cesium lead bromide nanosheets by electron energy-loss spectroscopy

“…For instance, cation Pb vacancies are expected to determine intrinsic pdoping. 37 A DFT-calculated density of states shows that this picture holds for cation neutral vacancies (V Pb0 , V Cs0 ), while the opposite behavior (i.e. n-doping) is observed in the case of anion neutral vacancies (V Br0 ), in agreement with the low (high) electronegativity of Pb and Cs (Br) atoms.…”

Colloidal Synthesis of Tunable Copper Phosphide Nanocrystals

“…32,33 It was recently demonstrated that copper vacancies in copper phosphide (Cu 3−x P) nanocrystals also generate excess delocalized holes and near-IR LSPR absorption. 34,35 In contrast to the copper chalcogenides, which often undergo phase transformations with dynamic redox tuning, 36 Cu 3−x P exists as the sole copper-rich phase. This phase-stability and potential for distinct surface chemistry make Cu 3−x P a unique system for colloidal semiconductor nanoplasmonics.…”

“…Colloidal semiconductor nanocrystals capable of supporting excess delocalized charge carriers are an important class of emerging electronic materials − because of the potential for hosting tunable carrier densities. Carrier concentrations can often be modulated via defect incorporation and activation during synthesis ,− or via post-synthetic redox or photoredox manipulations. ,,− These techniques allow for access to tunable photophysical properties in semiconductor nanocrystals, including localized surface plasmon resonances (LSPRs) in the mid- or near-IR. ,− ,− Nanocrystals in which the LSPR absorption is derived from delocalized holes , are relatively uncommon, with copper chalcogenides (CuE or Cu 2– x E; E = S, Se, and Te) being the most widely studied. ,,,,,− In these materials, delocalized holes arise to compensate for copper vacancies, resulting in degenerately doped semiconductors with LSPR absorption in the near-IR that has been exploited for surface-enhanced Raman scattering, plasmon-enhanced chemical conversion, and ultrafast optical switching. , It was recently demonstrated that copper vacancies in copper phosphide (Cu 3– x P) nanocrystals also generate excess delocalized holes and near-IR LSPR absorption. , In contrast to the copper chalcogenides, which often undergo phase transformations with dynamic redox tuning, Cu 3– x P exists as the sole copper-rich phase. This phase-stability and potential for distinct surface chemistry make Cu 3– x P a unique system for colloidal semiconductor nanoplasmonics.…”

Photonics with Gallium Nitride Nanowires

“…In an attempt to study dopant distribution in semiconductors, the segregation of tin in the surface of indium tin oxide has shown an influence on dopant activation in the matrix [10]. The role of rich Cu vacancies and hence valance band holes on SPR in CuP nanocrystals studied on the basis of scanning transmission electron microscopy measurements has been reported [11]. NMR spectroscopy of copper solenoid with different Cu compositions exhibited plasmonic characteristics in a low doped regime that depends on the charge density of the carriers [12].…”