The protecting ligand shell of nanoparticles plays a crucial role in determining their chemical and biological properties, yet its structure is not well established. By analyzing scanning tunneling microscopy (STM) images, it was discovered that a binary mixture of thiolated ligands phase separates forming stripe or Janus structures.1, 2 However, the images obtained so far could only reveal domains. In addition, theory and simulation studies have predicted the existence of many complex morphologies in multicomponent ligand shells.3, 4 Thus, it is of strong theoretical and experimental interests to achieve STM images at the highest possible resolution from which molecular arrangements of the ligand shell can be determined explicitly. Herein, we report our acquisition and analysis of high-resolution STM images of mixed monolayer coated Au nanoparticles. We show that the ligand shell of Au nanoparticles coated with 11-Mercapto-1-undecanol (C11ol) and 4-Mercapto-1-butanol (C4ol) are composed of stripe patterns whose distinct head groups are spaced ~ 0.5 nm and ~ 1.0 nm along the stripes and in the perpendicular direction, respectively. The characteristic length of the stripes shown here agrees with the values previously reported.1 In another sample, Au nanoparticles coated with mercaptopropionic acid (MPA) and octanethiol (OT) accommodate stripes of different wavelengths, i.e. three headgroups and two headgroups wide, and molecular �defects�. We also present high-resolution STM images of the Janus structure where constitutional ligands and their interfacial boundary are resolved. We believe this approach opens the possibility to explore other complex ligand structures to understand deeper structure-property relationships of nanoparticles.1. Jackson, A. M.; Myerson, J. W.; Stellacci, F., Nat Mater 2004, 3, 330-336.2. Stellacci, F.; Et al., 2013, (Submitted).3. Pons-Siepermann, I. C.; Glotzer, S. C., ACS Nano 2012, 6, 3919-3924.4. Pons-Siepermann, I. C.; Glotzer, S. C., Soft Matter 2012, 8, 6226-6231.

High-resolution scanning tunneling microscopy characterization of mixed monolayer coated gold nanoparticles

246th National Meeting (2013)

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