1. Silica Coated Bi2Se3 Topological Insulator Nanoparticles: An Alternative Route to Retain Their Optical Properties and Make Them BiocompatibleBlaž Belec, Nina Kostevšek, Giullia Della Pelle, Sebastijan Nemec, Slavko Kralj, Martina Bergant Marušič, Sandra Gardonio, Mattia Fanttti, Matjaž Valant, 2023, izvirni znanstveni članek Ključne besede: topological insulator, bismuth selenide, photo-thermal material, biocompatibility, nanoparticles
Objavljeno v RUNG: 22.02.2023; Ogledov: 671; Prenosov: 0
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4. Silica coated Bi[sub]2Se[sub]3 topological insulator nanoplatelets : the way of making them colloidally stable but preserving their optical propertiesBlaž Belec, Nina Kostevšek, Sebastjan Nemec, Slavko Kralj, Sandra Gardonio, Mattia Fanetti, Matjaž Valant, 2021, objavljeni povzetek znanstvenega prispevka na konferenci Ključne besede: topological insulator, optical properties, topological surface states, silica-coated
Objavljeno v RUNG: 27.09.2021; Ogledov: 1643; Prenosov: 0
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5. Chemical (in)stability of an interface between metals and Bi[sub]2Se[sub]3 topological insulatorKatja Ferfolja, Mattia Fanetti, Sandra Gardonio, Matjaž Valant, 2019, objavljeni povzetek znanstvenega prispevka na konferenci Opis: Our research is dedicated to a study of an interface between a Bi2Se3 topological insulator (TI) and various metals due to the essential need for providing a metal contact for devices. The main objective is to characterize structural and chemical properties at the interface, where the electronic properties of the TI can be affected. The structure of the interface and processes happening at it are investigated by microscopy (SEM, TEM, STM) and spectroscopy techniques (EDX, XPS).
The research started with the noble metals: Ag, Au and Pt. A good stability was observed for Au and Pt, whereas Ag reacted with Bi2Se3 already at room temperature, producing Ag2Se and AgBiSe2 phase. Interface stability was also checked at high temperature and results showed that the Au coating undergoes a coalescence process starting from 100 °C whereas the interface with Pt does not show any change at least up to 350 °C.
At present we are focused on the interface with Ti, a metal which is regularly used as an adhesive layer in electrical contacts. At low coverage (<30 nm) Ti forms an extremely flat film, smoother than Au, Ag or Pt. At higher coverage the film undergoes buckle delamination, likely induced by stress release. The observed morphology indicates that a chemical interaction leads to the growth of the initial smooth Ti epitaxial film. Se interdiffusion and formation of interfacial TixSey phase is envisaged, as suggested from preliminary TEM observations of the interface structure.
The presented results show the importance of the processes happening at the interface, especially solid-state chemical reactions, which are often neglected in the study of systems with metal/TI interfaces. Such instability has to be taken into account since the produced phases can affect transport properties of the material, increase a contact resistance or affect functionality of devices.
Ključne besede: Bi2Se3, interface, topological insulator, chemical instability
Objavljeno v RUNG: 20.08.2021; Ogledov: 1384; Prenosov: 9
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6. Electronic properties of phases in the quasi-binary Bi[sub]2Se[sub]3-Bi[sub]2S[sub]3 systemZipporah Rini Benher, Sandra Gardonio, Mattia Fanetti, Paolo Moras, Asish K. Kundu, Chiara Bigi, Matjaž Valant, 2021, izvirni znanstveni članek Opis: We explored the properties of the quasi-binary Bi2Se3–Bi2S3 system over a wide compositional range. X-ray diffraction analysis demonstrates that rhombohedral crystals can be synthesized within the solid solution interval 0–22 mol% Bi2S3, while at 33 mol% Bi2S3 only orthorhombic crystals are obtained. Core level photoemission spectroscopy reveals the presence of Bi3+, Se2− and S2− species and the absence of metallic species, thus indicating that S incorporation into Bi2Se3 proceeds prevalently through the substitution of Se with S. Spin- and angle-resolved photoemission spectroscopy shows that topological surface states develop on the surfaces of the Bi2Se3−ySy (y ≤0.66) rhombohedral crystals, in close analogy with the prototypical case of Bi2Se3, while the orthorhombic crystals with higher S content turn out to be trivial semiconductors. Our results connect unambiguously the phase diagram and electronic properties of the Bi2Se3–Bi2S3 system.
Ključne besede: topological insulator, quasi-binary Bi2Se3-Bi2S3 system, electronic properties
Objavljeno v RUNG: 29.03.2021; Ogledov: 1685; Prenosov: 0
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8. Synthesis of adsorbent-free ultrathin Bi2Se3 Topological Insulator Platelets and Its Inherent Surface PropertiesBlaž Belec, Katja Ferfolja, Tanja Goršak, Nina Kostevšek, Sandra Gardonio, Mattia Fanetti, Matjaž Valant, 2019, objavljeni povzetek znanstvenega prispevka na konferenci Ključne besede: Bismuth selenide, topological insulator, hydrothermal synthesis, surface properties
Objavljeno v RUNG: 30.09.2019; Ogledov: 2810; Prenosov: 0
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9. Au and Ag on the Bi2Se3(0001) Surface: Experimental Electronic and Physical PropertiesSandra Gardonio, Mattia Fanetti, Katja Ferfolja, Matjaž Valant, objavljeni povzetek znanstvenega prispevka na konferenci Opis: Binary bismuth chalcogenides, Bi2Se3 and Bi2Te3, have been extensively studied as reference topological
insulators (TIs). These materials are bulk insulators with topological surface states (TSS) crossing the
Fermi level. In contrast to conventional surface states of metals, the TSS are extremely robust
against local modifications at the surface, such as adsorbed adatoms, localized defects or changes in the surface termination. This aspect makes the TIs attractive for applications in spintronics, plasmonics, quantum computing and catalysis.
A theoretical model of charge transport by the TI surface states predicts that the TSS survive, provided that bonding at the metal/TI interface is weak. Ab-initio calculations have been done to understand the electronic properties of Au, Ni, Pt, Pd and graphene layers in a contact with Bi2Se3. These calculations showed that for Au and graphene the spin-momentum locking of TSS is maintained at the interface. In another theoretical study, Ag and Au thin layers on Bi2Se3 have been predicted to show a large Rashba splitting and a high spin polarization of the Ag quantum wells, providing a great potential for development of the spintronic devices. Finally, the calculations have foreseen that the presence of the robust TSS affects the adsorption properties of metals (Au bi-layer and clusters of Au, Ag, Cu, Pt, and Pd) supported on TI, in some cases resulting in the enhancement of the catalytic processes.
Despite the fundamental importance of the metal/TI interfaces and a number of theoretical studies
predicting exotic interfacial phenomena, the experimental knowledge about the metals on the TI surfaces is surprisingly limited, especially concerning combined study of morphology, growth mode, electronic and chemical properties.
In order to exploit the predicted physical properties of such systems, it is especially important to extend the study above the diluted coverage regime and to understand what is the growth morphology of the metal on the TI surface, to what extent the metal overlayer interacts with the TI substrate, how the TSS change with the presence of the metal overlayer and what is the reactivity of the system at the different stages of the overlayer growth.
Within this frame, we present a comprehensive surface sensitive study, of Au and Ag on Bi2Se3 by means of ARPES, XPS, SEM, LEED and XRD. The obtained results allow us to discuss the relation between electronic and physical properties at two of the most important model metal/TI interfaces
Ključne besede: topological insulator, electronic properties, synchrotron radiation
Objavljeno v RUNG: 27.06.2019; Ogledov: 2820; Prenosov: 0
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10. Growth, morphology and stability of Au in contact with the Bi[sub]2Se[sub]3(0 0 0 1) surfaceMattia Fanetti, Iuliia Mikulska, Katja Ferfolja, Paolo Moras, P. M. Sheverdyaeva, M. Panighel, A. Lodi-Rizzini, I. Píš, S. Nappini, Matjaž Valant, Sandra Gardonio, 2018, izvirni znanstveni članek Ključne besede: metal contact, topological insulator contact, growth mode, electronic properties, chemical properties, photoemission spectroscopy, microscopy
Objavljeno v RUNG: 05.12.2018; Ogledov: 3157; Prenosov: 0
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