Abstract :

Atomically precise noble metal clusters (APNMCs) belong to an emerging class of materials with unusual properties. They are considered to be an intermediate phase of matter bridging atoms and nanoparticles. Such atomically precise entities are composed of a few to hundreds of atoms of metals with a definite ligand shell, forming molecules of definite composition. One of the fundamental interests in studying clusters is to understand the evolution of physical and chemical properties of matter as it grows from its constituents, i.e. atoms or molecules. They eliminated a major issue in nanoscience – polydispersity. They also opened up possibilities for unique investigations which were not possible in the past. A large number of clusters are known today with their compositions being determined by advanced mass spectrometry. While spectroscopy, chemistry, catalysis, and applications of all of them are intensely pursued, the absence of precise structures makes a thorough understanding of their properties difficult.

This work is centered around these unique materials. The structure of APNMCs are generally studied through single-crystal x-ray diffraction. But in the past decade, there had been investigations to go beyond SCXRD, to understand the structure of these materials. APNMCs, in general, are sensitive to the electron beam. The first part will discuss a simple method that was developed to image cluster crystals using a conventional transmission electron microscope, where beam-induced damage is minimized. The second part will discuss results from atom probe tomography (APT) investigations done on single crystals of clusters. These studies were performed on a silver cluster, [Ag29(BDT)12(TPP)4]3− (where BDT and TPP are 1,3-benzene dithiol and triphenylphosphine, respectively.