Figure 2: Relationships between absorption features and ligands.
From: Optical determination of crystal phase in semiconductor nanocrystals
(a) Powder XRD patterns of three CdSe NCs with standard ZB (red) and WZ (green) phases, as well as a ZB CdSe nanocrystal synthesized in the presence of sodium oleate (ZB*, grey). (b) Absorption spectra of the same three CdSe NCs, comparing the E0 and E1 peaks. The E1 peaks accurately reflect the underlying crystal structure, but the band-edge transitions of ZB* look the same as an E0-matched WZ nanocrystal rather than ZB. The inset shows the zeroth and second derivative of the absorption spectra band-edge regions, showing distinct differences between the standard ZB and WZ spectra, but the ZB* spectrum exhibits a band-edge almost identical to standard WZ. (c) Absorption spectra of as-synthesized ZB and WZ NCs with matched band-edge energies in hexane, in comparison with their spectra after ligand exchange with MPA in aqueous solution. Insets show second derivatives of the spectra to depict their distinguishable phase-dependent E1 transitions. Red and green shades indicate the energy ranges of E1,ZB and E1,WZ peaks, respectively, which are clearly separated. (d) Extracted E0 and E1 transitions for WZ and ZB NCs as-synthesized (AS) and after ligand exchange with the indicated ligands. OAc, oleic acid; OLA, oleylamine; OPA, octylphosphonic acid; OT, octanethiol; TBP, tributylphosphine; TOPO, trioctylphosphine oxide; TPP, triphenylphosphine.
