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61.
Chemical (in)stability of interfaces between different metals and Bi[sub]2Se[sub]3 topological insulator
Sandra Gardonio, Matjaž Valant, Katja Ferfolja, Mattia Fanetti, 2018, published scientific conference contribution abstract

Abstract: In recent years a classification of materials based on their topological order gained popularity due to the discovery of materials with special topological character – topological insulators (TI). TI have different band structure than regular insulators or conductors. They are characterized by a band gap in the bulk of the material, but at the surface they possess conductive topological surface states (TSS) that cross the Fermi level. TSS are a consequence of the non-trivial bulk band structure and have properties that differ from ordinary surface states. They are robust toward contamination and deformation of the surface. Additionally, they are also spin polarized, which means that an electron spin is locked to a crystal momentum and, therefore, backscattering during transport is suppressed [1]. Due to their specific properties the TI could be used in fields of spintronics, quantum computing and catalysis [2]. The investigation of the interfaces between metals and the TI has not been given much attention even though its characterization is interesting from fundamental physics and applicative point of view. (In)stability of the contacts with metal electrodes, in a form of a chemical reaction or diffusion, has to be taken into account since it can affect the transport properties of the material or increase the contact resistance. Our research is dedicated to the study of the metal/TI interfaces, in particular to Bi2Se3 with deposited metals that are relevant for electrical contacts (Au, Ag, Pt, Cr, Ti). The thermal and chemical stability of the interfaces are of fundamental importance for understanding the contact behavior, therefore, we focused our work to the characterization of these properties. The metal/TI interfaces are investigated mainly with an electron microscopy (SEM, TEM, STM), EDX microanalysis and XRD. Our previous studies showed that the interface between Bi2Se3, and Ag deposited either chemically or from a vapor phase, results in the formation of new phases already at room temperature [3]. On the contrary, Au deposited on the Bi2Se3 surface shows very limited reactivity and is stable at RT, but diffusion and coalescence of the metal are observed starting from 100 °C [4]. In this contribution, we will present further characterization on the evolution of the Ag/Bi2Se3 and Au/Bi2Se3 interfaces, show preliminary results about recently investigated systems (Pt/Bi2Se3, Ti/Bi2Se3) and compare the thermal and chemical stability of the systems under investigation.
Found in: osebi
Keywords: thermal lens spectrometry, photothermal beam deflection spectroscopy, dye remediation, photothermal technique, photocatalytic degradation, reactive blue 19, TiO2 modification
Published: 20.08.2021; Views: 183; Downloads: 0
.pdf Fulltext (100,42 KB)

62.
Chemical (in)stability of an interface between metals and Bi[sub]2Se[sub]3 topological insulator
Sandra Gardonio, Matjaž Valant, Katja Ferfolja, Mattia Fanetti, 2019, published scientific conference contribution abstract

Abstract: 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.
Found in: osebi
Keywords: Bi2Se3, interface, topological insulator, chemical instability
Published: 20.08.2021; Views: 142; Downloads: 1
.pdf Fulltext (133,34 KB)
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