Traditional solid-state compounds are infinite crystalline arrays of densely packed atoms whose interatomic interactions can result in the emergence of cooperative physical properties such as ferromagnetism, and superconductivity. These materials are the foundation of new technologies, including nanoelectronics, sustainable energy generation and storage but the synthesis of solids with predictable structures and physical properties is an immense scientific challenge, and many emerging technologies are limited by the availability of suitable materials. Our research group is designing and synthesizing structured clusters of atoms as a new class of fundamental building units called superatoms that may be used to extend the Periodic Table of the elements. We are assembling these superatoms into novel solid-state compounds and exploring their properties. This approach allows us to encode desirable physical properties in the building blocks and manipulate their coupling to create crystals with multiple, tunable functionalities and emergent cooperative properties.
Design, Synthesis and Structure
We are designing and synthesizing well-defined inorganic molecular clusters as superatoms, manipulating their structure and atomic composition to control their isolated properties. Multicomponent superatom solid-state compounds are created by combining molecular clusters with complementary attributes. For instance, the clusters Ni9Te6(PEt3)8 and C60 crystallize into the face-centered cubic structure shown below. This approach allows us to modulate how the superatoms assemble into crystals and control how they interact in the solid-state. We are using single crystal and powder x-ray diffraction to determine the structure of the individual clusters and the superatom-assembled solids
We are exploring the electrical transport properties of our materials as a function of temperature, carrier density, electric field and magnetic field to uncover exotic electrical and magnetoelectric behaviors. Many of the solids are air and moisture sensitive, requiring unusual methods for attaching electrodes and making measurements. We are developing new techniques to grow crystals on premade devices that can be cooled and measured without breaking vacuum. Using this approach, we have measured van der Pauw transport for a number of superatom solid-state compounds compounds, including the solid [Cr6Te8(PEt3)6][C60]2 shown below.
Molecular clusters exhibit a wide range of exciting magnetic properties. In our research group we are studying the magnetic properties of the individual superatoms, and the emergence of magnetically ordered phases. These magnetic phase transition can be triggered by a number of stimuli, including temperature, pressure or light. We have a number of interesting findings on the magnetism of these materials. For instance, we have demonstrated that superatomic solids assembled from molecular nickel telluride clusters and fullerenes are paramagnetic at high temperature, but they order into ferromagnets at low temperature. Moreover we have shown that when we modify the constituent superatoms, the collective magnetic properties change in predictable ways. In these materials, the magnetic moments on the superatomic molecular clusters can interact to produce long-range magnetic ordering.
We collaborate with a number of research groups to explore the unique properties of our materials.
Single Cluster Electronics
We are designing and fabricating atomically-defined single nanosystem electrical circuits by wiring inorganic molecular clusters with varied molecular connectors. These wired clusters can couple electronically to nanoscale electrodes and be tuned to control the charge transport characteristics. In collaboration with the Venkataraman Group, we measure the electrical conduction of these single cluster junctions and establish design rules for controlling the electronic coupling to molecular clusters, while laying the groundwork for technological advances at the molecular and nanoscopic scale.