Ligand Shell Structure in Lead Sulfide–Oleic Acid Colloidal Quantum Dots Revealed by Small-Angle Scattering

• Published in: The journal of physical chemistry letters Vol. 10; no. 16; pp. 4713 - 4719
• Main Authors: Weir, Michael P, Toolan, Daniel T. W, Kilbride, Rachel C, Penfold, Nicholas J. W, Washington, Adam L, King, Stephen M, Xiao, James, Zhang, Zhilong, Gray, Victor, Dowland, Simon, Winkel, Jurjen, Greenham, Neil C, Friend, Richard H, Rao, Akshay, Ryan, Anthony J, Jones, Richard A. L
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 15.08.2019
• Subjects: Chemistry with specialization in Materials Chemistry; Chemistry with specialization in Physical Chemistry; Fysikalisk kemi; Kemi med inriktning mot fysikalisk kemi; Kemi med inriktning mot materialkemi; Letter; Physical Chemistry
• ISSN: 1948-7185; 1948-7185
• DOI: 10.1021/acs.jpclett.9b01008

Nanocrystal quantum dots are generally coated with an organic ligand layer. These layers are a necessary consequence of their chemical synthesis, and in addition they play a key role in controlling the optical and electronic properties of the system. Here we describe a method for quantitative measurement of the ligand layer in 3 nm diameter lead sulfide–oleic acid quantum dots. Complementary small-angle X-ray and neutron scattering (SAXS and SANS) studies give a complete and quantitative picture of the nanoparticle structure. We find greater-than-monolayer coverage of oleic acid and a significant proportion of ligand remaining in solution, and we demonstrate reversible thermal cycling of the oleic acid coverage. We outline the effectiveness of simple purification procedures with applications in preparing dots for efficient ligand exchange. Our method is transferrable to a wide range of colloidal nanocrystals and ligand chemistries, providing the quantitative means to enable the rational design of ligand-exchange procedures.