In the near future, the conventional, three-dimensional materials we deal with on a daily basis are going to make way for new, two-dimensional materials with exceptional properties: more resistant than steel, lighter than aluminium and as flexible as plastic. After years of flourishing research on graphene, the interest of the scientific community is gradually moving towards the study of alternative two-dimensional materials, capable of replacing conventional semiconductors and particularly apt for the realization of compact, energy-efficient and flexible devices.

A recent study conducted by researchers at the Sapienza Department of Physics, in collaboration with the Sapienza Research Centre for Nanotechnology Applied to Engineering (CNIS), the Institute for Photonics and Nanotechnologies at the National Research Council (CNR) and the Australian National University, has proposed a novel method to create highly mechanically-deformed two-dimensional crystals. The ability to induce controlled mechanical deformations in these materials can be exploited to achieve an on-demand tuning of their electronic, optical, and transport properties. The results have been published on Advanced Materials.

Bi-dimensional (or 2D) semiconducting crystals are attracting enormous interest due to their possible use in the fabrication of tuneable nanostructures and novel electronic and optoelectronic devices. Thiese new materials are characterised by a layered structure (like graphite) that enables to isolate, via exfoliation, single layers of extremely reduced thickness (inferior to one billionth of a meter). Due to their quantum effects, which are closely related to their substantially bidimensional nature, these crystals feature the ability to emit light in a surprisingly efficient manner. This property, together with the excellent mechanical resistance and flexibility, makes these 2D materials particularly suitable for the realization of compact and highly efficient lasers and solar cells.

The novel mechanism tested by the researchers is based on the low-energy proton irradiation of these materials in their three-dimensional form (prior to exfoliation). The protons move through the superficial layer and, upon contact with the cristalline matrix, are transformed into hydrogen molecules through a fundamental chemical reaction referred to as hydrogen evolution reaction. This fundamental chemical reaction takes place a millionth of a millimetre under the surface of the irradiated crystal, leading to the formation of hydrogen bubbles at hundreds of atmospheres of pressure. The hydrogen bubbles cause a single crystal surface to rise and the surface of these irradiated samples is spotted by atomic-sized hydrogen-filled “cupolas” (nanodomes) that emit infrared light visible up to 200 degrees Celsius. This process can be engineered to produce cupolas of various sizes, in various places.

This study is characterized by a high degree of interdisciplinarity, as it involves condensed matter physics, materials science, electrochemistry, nanotechnologies, optics and mechanical engineering. The reported discoveries could have many, potentially interesting ramifications, with possible applications in the fields of photonics, nanomechanics, optomechanical actuation, sensors and green energies.

References:

Controlled Micro/Nanodome Formation in Proton‐Irradiated Bulk Transition‐Metal Dichalcogenides - D. Tedeschi, E. Blundo, M. Felici, G. Pettinari, B. Liu, T. Yildrim, E. Petroni, C. Zhang, Y. Zhu, S. Sennato, Y. Lu, A. Polimeni  - Advanced Materials (2019) DOI https://doi.org/10.1002/adma.201903795

Further Information

Antonio Polimeni 
Department of Physics
antonio.polimeni@uniroma1.it