Control of Plasmonic and Interband Transitions in Colloidal Indium Nitride Nanocrystals

Abstract

We have developed a colloidal synthesis of 4-10 nm diameter indium nitride (InN) nanocrystals that exhibit both a visible absorption onset (∼1.8 eV) and a strong localized surface plasmon resonance absorption in the mid-infrared (∼3000 nm). Chemical oxidation and reduction reversibly modulate both the position and intensity of this plasmon feature as well as the band-to-band absorption onset. Chemical oxidation of InN nanocrystals with NOBF4 is found to red-shift the absorption onset to ∼1.3 eV and reduce the plasmon absorption energy (to 3550 nm) and intensity (by an order of magnitude at 2600 nm). Reduction of these oxidized species with Bu4NBH4 fully recovers the original optical properties. Calculations suggest that the carrier density in these InN nanocrystals decreases upon oxidation from 2.89 × 10(20) cm(-3) to 2.51 × 10(20) cm(-3), consistent with the removal of ∼4 electrons per nanocrystal. This study provides a unique example of the ability to tune the optical properties of colloidal nanomaterials, and in particular the LSPR absorption, with reversible redox reactions that do not affect the semiconductor chemical composition or phase.

Synthetic Strategies for Semiconductor Nanocrystals Expressing Localized Surface Plasmon Resonance

“…where ɛ m is the dielectric constant of the surrounding medium and γ is a LSPR peak‐broadening factor based on the total carrier scattering frequency . Although this estimation is a significant simplification of the Drude model that ignores geometrical considerations, it is generally sufficient and employed frequently to obtain an estimation of the carrier density within spherical particles by solving Equation (2) for ω p by using empirical ω sp and γ values, and subsequently solving Equation (1) for ρ …”

“…For the III–V family, the reaction of a solution of In 2 S 3 with NaNH 2 in an inert environment produces plasmonic InN NCs that can be solubilized with oleylamine (OAm) surfactant ligands . The particles exhibit strong mid‐IR absorbance with a LSPR peak near 3 μm.…”

“…[9] Although this estimation is as ignifi-cant simplificationo ft he Drude model that ignores geometrical considerations, it is generally sufficient and employed frequently to obtain an estimation of the carrier density within spherical particles by solving Equation (2) for w p by using empirical w sp and g values, and subsequently solving Equation (1) for 1. [12,20,22,25] First, LSPR resultsi nt he formation of an evanescent electric field in the immediate area around the surface of the NC knowna st he near-field effect.Avisualization of the near-field effect stemming from photoexcitation in an electron microscope is shown in Figure 1. [31] This resonance increases the absorptionc ross-section and resultsi nahuge enhancementi n local light absorption, which is ap roperty that has received considerable interest in recent years fore nhancement of the efficiency of solar cells and applicationsinp hotocatalytic nanotechnologies.…”

“…The majorityo fs tudies concerning plasmonic SC NCs focus on copperc halcogens, [12,14,15] however there has been ar ecent burst of reports extending the topic to silicon NCs, [16][17][18] semiconducting oxides, [19,20] ternary chalcogens, [21][22][23] as well as IV-VI systems. [24][25][26] LSPR modes in NC and QD samples can be ad irect result of the synthesis procedure, [22] develop gradually with oxidative air exposure, [12,27] or be engineered with postsynthesis treatments. [28] This Minireview will serve to offer both ac urrent overview of the field of plasmonic SC NCs, as well as brief details of several differing synthesis methods therein.…”

Growth of InN quantum dots to nanorods: a competition between nucleation and growth rates

“…Exciton Bohr radius of InN is reported to be  8 nm [21]. However, in literature nanoparticles below 30 nm is considered as QDs [22,23].…”