Tailoring the electronic properties of transition-metal dichalcogenides via hydrogen-assisted phase, strain, and band gap engineering

Proponente Marco Felici - Professore Associato
Sottosettore ERC del proponente del progetto
Componenti gruppo di ricerca
Componente Categoria
Leonetta Baldassarre Componenti il gruppo di ricerca
Francesco Mauri Componenti il gruppo di ricerca

In their two-dimensional (2D), monolayer form, transition metal dichalcogenides (TMDs) undergo an indirect-to-direct band-gap transition, which greatly enhances their radiative efficiency and is of high interest for optoelectronics. Furthermore, 2D-TMDs present clear evidence of polymorphism: in their most stable phase, the 2H structure, they are indeed direct-gap semiconductors, but their (semi)metallic 1T' phase can be easily stabilized by chemical treatments, mechanical deformations, or laser/electron-beam exposure. The possibility to locally induce an insulator-to-metal transition in 2D-TMDs has obvious technological implications, with tantalizing prospects for the realization of ultrathin devices. In this project, we propose to selectively trigger the 2H-1T' transition by exposing the sample surface to a controlled flux of hydrogen ions. Indeed, H chemisorption plays a key role in the chemical treatments that stabilize the 1T' phase. Moreover, H exposure leads to the formation of atomically thin micro- and nanobubbles on the surface of bulk TMDs. The formation of these bubbles, whose size and position can be controlled via electron-beam lithography, results in (1) a local exfoliation of the uppermost TMD layer, i.e., in a huge boost of the radiative efficiency and (2) in a significant lattice expansion, allowing for the introduction of large, site-controlled mechanical stresses in the sample. First of all, such stresses will be exploited to further manipulate the (strain-dependent) 2H-1T' transition. Also, the effects of the giant, strain-induced pseudo-magnetic fields associated with nanobubble formation should allow for the realization of valleytronic elements such as valley filters and beam splitters. This is particularly important in the context of 2H-1T' hybrid devices, where topological metallic states are expected to form at the edges of 1T' domains and would thus represent preferential channels for topologically protected valley transport.


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