Revealing the Building Blocks of New Material
Describing the human genome, finding the Higgs boson – some major scientific advances have already happened this century. Materials science wants to add to the list with an initiative known as “materials by design,” or the ability to create materials with specific properties to order through the ability to control molecular assemblies on the atomic level. The stakes are high: artificial photosynthesis, room-temperature superconductors, and batteries that make the large scale storage of renewable energies feasible are all potential products.
There’s one big stumbling block to materials by design that just never seems to get any smaller: How do you design a material when you don’t understand the building blocks? For example, the first high-temperature superconductor was discovered in 1986 yet scientists still don’t entirely know how they work. Some exotic materials have theoretical underpinnings – indeed, topological insulators were predicted before they were discovered – but the ability to fabricate them successfully remains out of reach.
Spying on Emergent Properties
Nuclear magnetic resonance (NMR) spectroscopy is already used to examine the structure and molecular dynamics of several classes of materials, from polymers to liquid crystals to building materials. Such advances in NMR techniques as multinuclear and multidimensional scanning are ensuring that it will remain a valuable tool for investigating the next generation of materials.
Already, researchers have examined 63Cu and 17O NMR chemical shift data to study cuprates, one class of high-temperature superconductor. A combination of multinuclear and magic angle spinning NRM spectroscopy has been used to investigate the structure and adsorption behavior of metal-organic framework compounds. And an advanced NMR spectroscopy technique called depth-resolved βNMR is being used to study transition metal oxide thin-film heterostructures.
Some other examples of the use of NMR spectroscopy in materials science research include:
- Characterizing the surface features of silicon nanoparticles
- Analyzing the structure of lignin polymers
- Characterizing graphite oxide, from which graphene can be prepared
- Validating the structure of ultrastrong and stiff layered polymer nanocomposites
Electron paramagnetic resonance (EPR) spectroscopy is an analogous technique that is also being used in materials science research. For example, researchers trying to discover why solar panels made from layers of amorphous silicon seem to lose current efficiency much more quickly than solar panels made from crystalline silicon have used EPR spectroscopy to gain a clearer understanding of the amorphous silicon layers’ internal structure.
Advanced Techniques for Advanced Materials
The ever-growing number of solid-state techniques, as well as continuing improvements in resolution of the spectra of solid materials, ensures that NMR will remain a vital tool in materials science research. From polarizing spins to tagging samples with specific isotopes to pulsed field gradients, methods exist for extracting information from large molecules and complicated structures.
On the theoretical side, ab initio calculations of NMR and EPR data based on different quantum chemistry frameworks like density functional theory and Hartree-Fock theory have made great progress. NMR spectroscopy is fully integrated into materials science research and will continue to improve with our understanding of matter itself.