New method dramatically simplifies study of 2D materials

A novel technique that produces high-quality and large-area two-dimensional (2D) materials inside a protected environment could open up new avenues for exploiting the materials’ electronic properties. An international team of material scientists, including researchers from the University of British Columbia (UBC), unveiled the technique in Advanced Science.

Dubbed Kinetic In-situ Single-layer Synthesis (KISS), the method involves bringing a bulk sample of a layered material in contact with a substrate such as gold or silver directly inside a vacuum.

“This enables in-situ exfoliation of 2D materials, yielding large, high-quality samples devoid of contaminants and impurities,” said Dr. Matteo Michiardi from UBC Blusson QMI and Physics and Astronomy, who worked on the study with colleagues from KTH Royal Institute of Technology in Sweden, the University of Groningen in the Netherlands, and Aarhus University in Denmark.

“Our results can provide a new platform to study a wide variety of new systems that have so far been elusive, such as the superconductivity in two dimensions, the quantum spin Hall effect or the burgeoning field of 2D magnetism.”

“The method is remarkably simple, requiring only the equipment commonly found in a typical surface science laboratory, making it easily accessible and straightforward for surface science labs worldwide.”

Since the discovery of graphene—a single layer of graphite that exhibits outstanding physical properties that don’t exist in its bulk form—in 2004, the field of 2D materials research has expanded rapidly.

The most commonly used methods to produce 2D materials to date were chemical vapour deposition, molecular beam epitaxy, and mechanical exfoliation, which present major drawbacks.

With chemical vapour deposition and molecular beam epitaxy (MBE), which involve evaporating the elements onto a substrate, researchers face complexities such as defining new stable growth recipes, selecting appropriate substrates, and working on samples that are not well-ordered.

Mechanical exfoliation is carried out using adhesive tape to lift flakes from the material’s bulk form and then transfer them to a vacuum. This results in exfoliated 2D flakes that are small and susceptible to contamination, with the latter being especially problematic for air-sensitive samples.

Using the KISS method, the contamination problem is eliminated as the material is produced inside a vacuum from the start.

“Gold or silver substrates work particularly well with the KISS method. Once cleaned through standard vacuum techniques, they show dangling chemical bonds that stick out of their surface. The affinity of the bulk exfoliative materials to these dangling bonds is really high, which means that the sample tends to stick more to the substrate than to the bulk of itself,” Dr. Michiardi said.

The quality of the samples produced using KISS was verified with several surface-sensitive techniques, including Angle-Resolved Photoemission Spectroscopy (ARPES).

“ARPES is an in-vacuum technique we’re very familiar with here at Blusson QMI. It allows us to produce an image of the 2D flake and map the electronic structure of the sample, which is what researchers around the world are very interested in,” Dr. Michiardi noted. “The KISS technique has already been widely adopted here at Blusson QMI, yielding important primary results."