Characterization of zinc sulfide nanoclusters via atomic force and scanning tunneling microscopy

II–VI nanocrystals or nanoclusters recently have been the subject of intensive study because of their potential use in high-speed electronics applications. We have prepared and characterized a series of ZnS nanoclusters which vary in size and type of capping groups. Capping of the nanoclusters with alkanethiols possessing charged end groups enabled their electrostatic immobilization to oppositely charged surfaces (e.g., chemically modified gold and mica). Electrostatic immobilization provided reproducible scanned probe imaging of the clusters on these surfaces. Size distributions were obtained by scanning tunneling microscopy (STM) and atomic force microscopy (AFM); mean particle diameters correlated well with values obtained by x-ray diffraction. Compressibility studies were performed and showed that the nanoclusters were relatively incompressible under typical imaging forces. This article describes the reliable and reproducible AFM and STM imaging of semiconductor nanoclusters.