Fig. 2: ITO-In2O3 core–shell colloidal nanocrystals.
From: Control of electronic band profiles through depletion layer engineering in core–shell nanocrystals
a TEM images of the nanocrystals at different stages of the synthesis. Starting from an aliquot of the core (C0), layers of In2O3 progressively form a thicker shell around the ITO nuclei (S1–S5). Scale bar is 50 nm for each panel. b Comparison between the Sn-dopant concentrations obtained from inductively coupled plasma mass spectrometry (ICP-OES) and X-ray Photoelectron Spectroscopy (XPS) as a function of shell thickness (\({{{{t}}}}_{{{{s}}}}\)). The higher Sn/Tot values of the volume sensitive ICP-OES measurements with respect to the surface sensitive XPS measurements indicate that Sn atoms remain segregated in the core of the NCs. Dashed lines are to guide the eye. c Normalized absorbance of typical ITO-In2O3 core–shell samples with increasing shell size, in as-synthesized (dotted lines) and photodoped (solid lines) cases, with a \({{{{t}}}}_{{{{s}}}}\) of 0.15 nm (blue), 1.85 nm (orange), and 2.3 nm (red). Growing an undoped shell continuously redshifts the energy of the localized surface plasmon resonance (LSPR) peak in the NIR. After 20 min of UV exposure, the intensity of the LSPR peak increases significantly, reaching values up to almost double its initial absorbance. d Top panel: Absorbance of sample S5 (\({{{{t}}}}_{{{{s}}}}\) = 4.25 nm), as-synthesized (dotted line) and photodoped (solid line). The fitting of the experimental data using the multi-layer optical model is depicted by the orange lines. Bottom panel: Numerical simulations of the absorbance of the same ITO-In2O3 NC with \({{{{t}}}}_{{{{s}}}}\) = 4.25 nm (dotted green lines) and the simulation with extra electrons (i.e., photodoping, solid green line).
