Colloidal indium nitride nanocrystals spontaneously accumulate large electron densities (7.4 × 1020 cm-3), independently of size.[1] This behavior, which can be reversibly-controlled using (electro)chemical approaches, makes these materials attractive candidates for charge-storage applications at the nanoscale. Unfortunately, many fundamental quantities that inevitably control the behavior of charge in semiconductor materials, such as the band potentials or the energy of the Fermi and charge-neutrality levels, remain challenging to define and measure for these self-standing crystalline units. We show how a direct optical spectroscopic method,[1] based on the analysis of the plasmonic resonance associated with the delocalized charge stored in each nanocrystal, allows to quantify precisely the charge storage density of colloidal InN nanocrystals, which are shown to possess a high volumetric capacitance (~70 F cm-3), on the order typically associated with that of supercapacitors in energy harvesting and storage applications.[2] We then show how the size-dependence of the conduction band edge potential and the charge-neutrality level of InN nanocrystals can be extracted for the first time from these studies. Interestingly, indium nitride nanocrystals do not exhibit size-dependent variations of charge-carrier kinetic energy (i.e. quantum confinement) down to sizes that are much smaller than the bulk excitonic Bohr radius, which contrasts sharply with the behavior associated with semiconductor nanocrystalline materials. This “quantum-confinement resilience” effect, which is suggested to arise from the strongly non-parabolic dispersion of the conduction band and the intricate nature of surface states in InN nanocrystals, will be discussed in relation to other charge-storing colloidal materials.

Colloidal indium nitride nanocrystals as nanoscaled charge-storage units, and the origin of the quantum-confinement resilience effect

2019 Spring National Meeting

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