CAREER: Harnessing Microfabrication for Chemical Control During High Pressure Synthesis of Non-Equilibrium Carbides

PART 1: NON-TECHNICAL SUMMARY

Technology often relies on the use of materials with specific properties. Since these properties arise from microscopic interactions between atoms, we depend on chemists to discover and optimize the recipes for making them. For example, the stainless steels used in surgical tools and medical implants rely on the presence of very specific amounts of chromium, which prevents oxygen from converting the iron and nickel into rust.

Although many materials can be created using high temperatures, some of them—such as diamond—also require very high pressures to form. High pressure chemistry is much less explored than traditional chemistry, but it has already led to the discovery of many exciting new materials with properties such as lossless electrical conductivity, exceptional hardness, and exotic forms of magnetism.

One major obstacle in the field is that the exceedingly small scales required to perform high-pressure reactions make it difficult for chemists to fine tune their recipes for preparing materials as easily as they can for reactions under normal pressure. This in turn makes it much more difficult to investigate and tune the new high-pressure materials being discovered.

Through this award, funded by the Solid State and Materials Chemistry program and the Ceramics program in the Division of Materials Research at NSF, Prof. Walsh's research team develops a completely new approach to high-pressure synthesis that uses cutting-edge microfabrication methods to precisely tune elemental ratios to a much higher precision than is possible with current methods.

This project supports the expert training of graduate students as they develop these next-generation methods, greatly strengthening our nation’s future scientific workforce. The award also enables the development of new educational kits that provide high school and undergraduate students with hands-on access to high-pressure science, promoting their exposure to forefront scientific disciplines.

PART 2: TECHNICAL SUMMARY

High-pressure synthesis is a rapidly growing field that is enabling the experimental exploration of uncharted phase space in search of novel materials. However, a longstanding issue in the field has been a poor control over elemental composition under the strict constraints required to access extreme pressures. This has precluded experiments that rely on an exact control of stoichiometry, such as site doping studies or high-yield syntheses, which in turn has limited the degree to which the bulk properties and stabilities of unrecoverable phases can be studied.

With this CAREER project, Prof. Walsh implements and expands novel methods developed in his laboratory to experimentally examine longstanding predictions surrounding the superconducting properties of high valence electron count mid-row carbides that until now have remained untestable. Alongside these studies, his team also examines the effect that chemical site doping has on the stability fields of unquenchable high-pressure phases.

The exquisite control of chemical composition required for these studies is enabled by a completely new approach to sample preparation that uses sputtering and microlithography to prepare micropellet precursors with precise chemical composition and spatial homogeneity. These precursors are readily integrated with the diamond anvil cell method, allowing for the collection of X-ray diffraction and spectroscopic data under extreme pressures.

The discovery of new methods for optimizing the properties and recoverability of high-pressure phases would break new ground toward their integration with existing technology infrastructure, greatly enhancing their potential for societal impact.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.