Physical Behavior of Layered Superatomic Crystals
Abstract
The objective of this project is to design a family of layered superatomic crystals (SA Cs) with tunable mechanical, thermal, and electrical properties through integrated synthesis, characterization, and modeling. SACs are a new class of multi-functional semiconductors built from atomically precise molecular building blocks (i.e., superatoms)-1 nm in size. SACs have naturally narrow bandgaps (sub eV) and far higher electrical conductivity than unary molecular crystals (their electrical conductivity is I 0"7-I 0"8 higher than pure C60 crystals). The proposed research into controlling SAC properties will lead to Army relevant-technologies for multi-domain battle including thermoelectrics and pyroelectrics for tactical unit energy independence, IR detectors for thermal mapping, structural composites with dynamically tunable mechanical properties, and solid state thermal switches for active thermal management. Our team s prior collaborative studies focused on binary SACs consisting ofC60s and similarly-sized superatoms that crystallized into superatomic analogues of atomic binary ionic compounds. We found that orientational disorder of the C60s ( e.g., free rotations) uniquely controls the thermal transport properties of these SA Cs. In this proposed project, we will establish the physical behaviors of a family of layered SA Cs assembled from two-dimensional (2D) sheets of metal chalcogenide superatoms and C60s. We have three design strategies to predictably tune the mechanical, thermal, and electrical properties of the base layered SAC, [Co6Te8(PnPr3)6l[C60]3: (I) intercalation, (2) layering, and (3) polymerization. The base SAC (Co6Te8(PnPr3)6l[C60]3 is composed of two alternating layers: a trigonal layer of Co6Te8(PnPr3)6 and a layer of close packed C60s. The three strategies to modify this SAC will work as follows: (I) intercalating small redox-active molecules will modulate the charge carrier density in the SA Cs; polar intercalants that can be orien,ted with an external electric field will lead to active control of orientational disorder and physical properties, (2) modifying the superstructure periodicity of the layered SAC will provide anisotropic control of transport, and (3) reversibly polymerizing the C60 layers will conve11 the SAC between dynamic and static structures, impacting physical properties. We will explore these synthetic strategies in three fully integrated tasks that combine Roy s expertise in SAC synthesis, Malen s expertise in mechanical and transport measurements, and McGaughey s expertise in atomistic simulations and calculations. Our complementary expertise and proven collaboration will enable advanced superatomic crystals to be designed, synthesized and studied in a feedback loop that fosters holistic understanding and engenders the discovery of new properties. The tasks are: Task I: Synthesis of SA Cs: Roy will design and synthesize the SA Cs. Our synthesis plan includes a predetermined set of modifications to single crystal SA Cs based on our three design strategies. Feedback from theoretical predictions (Task 3) validated by experimental measurements (Task 2) will guide the synthetic directions to exploit the vast SAC design space. Task 2: Measurement of SA Cs properties: Malen will measure the mechanical properties of single crystal SA Cs using nanoindentation, the thennal properties of SACs using frequency domain thermoreflectance with and without external stimuli (E-tields, high pressure), and the electrical properties of SACs using microfabricated electrodes (with Roy). Task 3: Prediction of SAC properties: McGaughey will use all-atom models and develop reduced order models in molecular dynamics simulations and lattice dynamics calculations to study the mechanical properties and thermal transport in SACs, and density functional theory calculations for the electronic band structure and transport.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Oct 16, 2018
- Source ID
- W911NF1710397
Entities
People
- Jonathan A Malen
Organizations
- Army Contracting Command
- Massachusetts Institute of Technology
- United States Army