| 1. |
- Calvani, P., et al.
(författare)
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Infrared spectroscopy of two-dimensional electron systems
- 2019
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Ingår i: European Physical Journal: Special Topics. - : Springer Science and Business Media LLC. - 1951-6401 .- 1951-6355. ; 228:3, s. 669-673
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Tidskriftsartikel (refereegranskat)abstract
- © 2019, EDP Sciences, Springer-Verlag GmbH Germany, part of Springer Nature. We have used grazing-angle infrared spectroscopy with polarized radiation to detect the Berreman effect (BE) in the two-dimensional electron systems (2DES) which form spontaneously at two interfaces: one between an amorphous film LaAlO3 and its SrTiO3 substrate (LAO/STO), and another at the interface between the topological insulator (TI) Bi2Se3 and its sapphire substrate. In both systems we have thus extracted the 2DES parameters at different temperatures. In the quasi-2DES under amorphous LAO, the surface density ns is higher than under crystalline LAO, while the mobility is nearly the same and the thickness d is 7 nm. In ultrapure Bi2Se3 on sapphire, preliminary data provided d
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| 2. |
- Falsetti, E., et al.
(författare)
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High conductivity of ultrathin nanoribbons of SrRuO3 on SrTiO3 probed by infrared spectroscopy
- 2018
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322 .- 2045-2322. ; 8:1
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Tidskriftsartikel (refereegranskat)abstract
- SrRuO3(SRO) is a perovskite increasingly used in oxide-based electronics both for its intrinsic metallicity, which remains unaltered in thin films and for the ease of deposition on dielectric perovskites like SrTiO3, (STO) to implement SRO/STO microcapacitors and other devices. In order to test the reliability of SRO/STO also as high-current on-chip conductor, when the SRO dimensions are pushed to the nanoscale, here we have measured the electrodynamic properties of arrays of nanoribbons, fabricated by lithography starting from an ultrathin film of SRO deposited on a STO substrate. The nanoribbons are 6 or 4 nm thick, 400, 200 and 100 nm wide and 5 mm long. The measurements have been performed by infrared spectroscopy, a non-contact weakly perturbing technique which also allows one to separately determine the carrier density and their scattering rate or mobility. Far-infrared reflectivity spectra have been analyzed by Rigorous Coupled-Wave Analysis (RCWA) and by an Effective Medium Theory, obtaining consistent results. With the radiation polarized along the nanoribbons, we obtain a carrier density similar to that of a flat film used as reference, which in turn is similar to that of bulk SRO. Moreover, in the nanoribbons the carrier scattering rate is even smaller than in the unpatterned film by about a factor of 2. This shows that the transport properties of SRO deposited on STO remain at least unaltered down to nanometric dimensions, with interesting perspectives for implementing on-chip nano-interconnects in an oxide-based electronics. When excited in the perpendicular direction, the nanoribbons appear instead virtually transparent to the radiation field, as predicted by RCWA.
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| 3. |
- Nucara, A., et al.
(författare)
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Infrared study of the quasi-two-dimensional electron system at the interface between SrTiO3 and crystalline or amorphous LaAlO3
- 2018
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Ingår i: Physical Review B. - 2469-9969 .- 2469-9950. ; 97:15
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Tidskriftsartikel (refereegranskat)abstract
- We have used grazing-angle infrared spectroscopy to detect the Berreman effect (BE) in the quasi-two-dimensional electron system (q-2DES) which forms spontaneously at the interface between SrTiO 3 (STO) and a thin film of LaAlO 3 (LAO). From the BE, which allows one to study longitudinal optical excitations in ultrathin films like the q-2DES, we have extracted at different temperatures its thickness, the charge density and mobility of the carriers under crystalline LAO (sample A), and the charge density under amorphous LAO (sample B). The latter quantity turns out to be higher than in sample A, but a comparison with Hall measurements shows that under amorphous LAO the charges are partly localized at low T with a low activation energy (about 190 K in units of kB) and are thermally activated according to a model for large polarons. The thickness of the q-2DES extracted from our spectra turns out to be 4±1 nm for crystalline LAO and 7±2 nm for amorphous LAO.
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