If you want to emboss leather, you press a stamp into the material, leaving behind a pattern in relief. Several years ago, chemist Thomas Kempa envisioned that a similar principle could be used to pattern new physical states within two-dimensional crystals. Today, his "lattice embossing" technique can be used to elicit unique properties with potential applications in quantum computing and next-generation sensors and instruments.
Image caption: Thomas Kempa
Image credit: Will Kirk / Johns Hopkins University
Kempa, an associate professor in Johns Hopkins University's Department of Chemistry, just received a five-year, $1.3 million award from the Gordon and Betty Moore Foundation to expand his new concept. The foundation describes its Experimental Physics Investigators Initiative as "advancing the frontier of fundamental research in experimental physics by supporting brilliant mid-career scientists."
Kempa called the support "transformational." While a breakthrough recently validated the lattice embossing concept, the Moore Foundation grant will allow him to lay the groundwork for a new field that explores and controls fundamental excitations within two-dimensional crystals. Precise control over these excitations (excitons, phonons, and magnons) and their long-range order lies at the heart of unlocking technology breakthroughs.
"The big vision lies in figuring out how to use our lattice embossing platform to create a next-generation quantum computer that runs on excitons," Kempa said.
Kempa is one of 22 researchers named to the Moore Foundation's 2025 cohort. Experimental Physics Investigators receive $1.3 million over five years to pursue innovative research goals and try new ideas unlikely to attract financial support from conventional funding sources, according to the foundation's website. The program is designed to offer scientists the flexibility to pivot as their research dictates.
Kempa says he set out on his "passion project" well aware of the promises and limitations of existing strategies for extracting new phenomena from 2D materials. "What if I just design a periodic potential, with the right symmetry and size, and place it in contact with a 2D crystal? What will happen then?" he asked himself.
For decades, scientists have been using a tool called scanning tunneling microscopy to manipulate matter at the atomic scale. This method involves bringing a metal tip close to a substance's surface and applying a voltage potential. The voltage can then be used to move electrons from the tip into the substance, or to shift individual atoms to other nearby positions. What if, Kempa wondered, you could arrange billions of these tips into any pattern you want, and then use them to impose new properties onto the material beneath?
Since creating such an array of tips using conventional fabrication routes is anything but realistic, Kempa turned to what he calls the chemist's toolbox and realized that a molecular lattice—specifically, a metal-organic framework, or MOF—could be used to accomplish much of what he envisioned.
Hybrid materials with programmable properties, MOFs feature large pores often used to store gases. Kempa came up with the idea of slicing through a MOF to obtain a single layer with a unit cell that repeats in two dimensions. This lattice, he explained, has molecular groups that are regularly positioned with atomic precision above and below the plane of the MOF crystal. By tuning the size, spacing, charge state, and pattern of these groups, he was able to use them just like the little tips in a scanning tunneling microscope, localizing and tuning the quantum features of the excitons in the surface he applied them to.
At first, the idea seemed almost as unrealistic as producing billions of metal tips. He had to figure out how to grow MOFs as pristine single layers, how to program the MOFs to take on the shapes and symmetries he wanted, and how to build devices that contain the MOFs while harboring perfect interfaces with the material below. The first breakthrough came when he applied—or embossed—the MOF to a two-dimensional tungsten diselenide semiconductor, transforming the semiconductor's previously undefined emissions into narrow, well-defined quantum emissions.
"We had the crazy idea that merging molecular lattices that have the right design with other 2D materials can basically open up a plethora of new possibilities in controlling quasi-particle states," Kempa said. In theory, as researchers learn to confine, direct, and manipulate the excitons' quantum features, they'll be able to make entire hardware platforms to store charge, do computation, and transmit information over long distances.
The Kempa research group's expertise spans the areas of physical, inorganic, and materials chemistry. Lab members develop new methods to prepare and study low-dimensional inorganic crystals from nanoparticles to molecular wires to sheets a few atoms thick, whose exceptional properties render them intriguing platforms for optoelectronic devices, energy conversion systems, and quantum computing architectures.
Kempa's previous honors include a DARPA Young Faculty Award, an NSF CAREER Award, a Toshiba Distinguished Young Investigator Award, a Dreyfus Foundation Fellowship in Environmental Chemistry, and two Johns Hopkins Discovery Awards. He was also named a Kavli Fellow by the National Academy of Sciences and a Mercator Fellow by the German Research Foundation. Kempa is a co-founder and co-director of the Hub for Imaging and Quantum Technologies, a Bloomberg Distinguished Professor cluster at Hopkins.
