Energy deposition of heavy ions in freestanding 2D materials


Energy deposition of heavy ions in freestanding 2D materials

Creutzburg, S.; Schwestka, J.; Inani, H.; Tripathi, M. K.; Heller, R.; Klingner, N.; Niggas, A.; Lehnert, T.; Leiter, R.; Kozubek, R.; Facsko, S.; Kaiser, U.; Kotakoski, J.; Schleberger, M.; Aumayr, F.; Wilhelm, R. A.

2D materials are promising candidates for electronic and photonic applications in future devices. Their properties can be tailored by surface sensitive modification techniques, like ion irradiation. Usually single charged ions are used, which deposit the main part of their kinetic energy in depths well below the surface. Only a tiny fraction is converted into the sputtering of target atoms. In contrast, highly charged ions (HCIs) carry additional potential energy in the keV regime, which may even exceed their kinetic energy. The deposition of the potential energy causes intense excitation and ionization of the electronic system of the target atoms in a shallow surface region. The high density of electronic excitations may lead to local temperatures above the sublimation point and finally to the creation of nanostructures. Even for freestanding 2D materials, like carbon nanomembranes, which consist of only a few atomic layers, pore formation induced by HCIs was observed. The small thickness of 2D materials enables spectroscopic measurements of the HCIs after transmission with respect to their charge state and kinetic energy. From our data we can estimate the amount of energy deposited in the material and therefore available for pore formation. In the present study, the influence of target properties on the charge exchange and on the neutralization dynamics is investigated. Spectroscopic measurements of the charge state of transmitted ions were performed using monolayers consisting of graphene, MoS₂ and hBN, which show different band gap energies between 0 and 6 eV, conductance properties (semi-metallic, semi-conducting and insulating) and layer structures.

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Publ.-Id: 30287