As synthetic methods have progressed to produce semiconductor nanocrystal quantum dots (QDs) of high crystalline quality, increased attention has been paid to the surface of these particles as they possess large surface to volume ratios that can drastically influence the properties of the QDs. These surfaces are often passivated by ligands after synthesis that provide not only crystal termination, reducing unfavorable dangling bonds, but also provide colloidal stability and reduce irreversible aggregation. Frequently for applications it is necessary to exchange the growth ligands that yield superior control over the size and distribution of the particles for ligands that provide the samples with certain functionalities. Successful execution and subsequent use of these ligand exchanged samples often requires the samples to undergo multiple rounds of purification. Recently, gel permeation chromatography (GPC), a form of size exclusion chromatography, has been established as a method of purifying QDs that yields a repeatable QD surface. PbS QDs are desirable for application such as IR sensing and solar photovoltaics and while they have seen considerable research efforts there are multiple aspects of the surface chemistry that are not yet well understood. Namely, how the ligand density of a well purified sample varies with size and shape of the nanocrystal, susceptibility to oxidation, and how detrimental oxidation of the surface of these particles may be to the resulting performance and stability of the samples are areas worthy of further investigation. Here we utilize QD purification via GPC to yield stable and repeatable particles, in which to investigate the ligand population as a function of nanocrystal size and surface oxidation.

PbS quantum dot surface chemistry investigated via purification with gel permeation chromatography

2019 Spring National Meeting

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