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End date: 2019 × Start date: 2014 × DDC: 660 × Version: publishedVersion × WGL Institute: PDI ×

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    Ferroelectric Control of the Spin Texture in GeTe
    (Washington, DC : ACS Publ., 2018-1-30) Rinaldi, Christian; Varotto, Sara; Asa, Marco; Sławińska, Jagoda; Fujii, Jun; Vinai, Giovanni; Cecchi, Stefano; Di Sante, Domenico; Calarco, Raffaella; Vobornik, Ivana; Panaccione, Giancarlo; Picozzi, Silvia; Bertacco, Riccardo
    The electric and nonvolatile control of the spin texture in semiconductors would represent a fundamental step toward novel electronic devices combining memory and computing functionalities. Recently, GeTe has been theoretically proposed as the father compound of a new class of materials, namely ferroelectric Rashba semiconductors. They display bulk bands with giant Rashba-like splitting due to the inversion symmetry breaking arising from the ferroelectric polarization, thus allowing for the ferroelectric control of the spin. Here, we provide the experimental demonstration of the correlation between ferroelectricity and spin texture. A surface-engineering strategy is used to set two opposite predefined uniform ferroelectric polarizations, inward and outward, as monitored by piezoresponse force microscopy. Spin and angular resolved photoemission experiments show that these GeTe(111) surfaces display opposite sense of circulation of spin in bulk Rashba bands. Furthermore, we demonstrate the crafting of nonvolatile ferroelectric patterns in GeTe films at the nanoscale by using the conductive tip of an atomic force microscope. Based on the intimate link between ferroelectric polarization and spin in GeTe, ferroelectric patterning paves the way to the investigation of devices with engineered spin configurations.
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    Selective control of molecule charge state on graphene using tip-induced electric field and nitrogen doping
    (London : Nature Publishing Group, 2019) Pham, Van Dong; Ghosh, Sukanya; Joucken, Frédéric; Pelaez-Fernandez, Mario; Repain, Vincent; Chacon, Cyril; Bellec, Amandine; Girard, Yann; Sporken, Robert; Rousset, Sylvie; Dappe, Yannick J.; Narasimhan, Shobhana; Lagoute, Jérôme
    The combination of graphene with molecules offers promising opportunities to achieve new functionalities. In these hybrid structures, interfacial charge transfer plays a key role in the electronic properties and thus has to be understood and mastered. Using scanning tunneling microscopy and ab initio density functional theory calculations, we show that combining nitrogen doping of graphene with an electric field allows for a selective control of the charge state in a molecular layer on graphene. On pristine graphene, the local gating applied by the tip induces a shift of the molecular levels of adsorbed molecules and can be used to control their charge state. Ab initio calculations show that under the application of an electric field, the hybrid molecule/graphene system behaves like an electrostatic dipole with opposite charges in the molecule and graphene sub-units that are found to be proportional to the electric field amplitude, which thereby controls the charge transfer. When local gating is combined with nitrogen doping of graphene, the charging voltage of molecules on nitrogen is greatly lowered. Consequently, applying the proper electric field allows one to obtain a molecular layer with a mixed charge state, where a selective reduction is performed on single molecules at nitrogen sites. © 2019, The Author(s).