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1754. The Palomar Transient Factory core-collapse supernova host-galaxy sample : Host- galaxy distribution functions and environment dependence of core-collapse supernovaeSteve Schulze, Ofer Yaron, Jesper Sollerman, Giorgos Leloudas, Amit Gal, Angus H. Wright, Ragnhild Lunnan, Avishay Gal-Yam, Eran O. Ofek, Tanja Petrushevska, 2021, izvirni znanstveni članek Ključne besede: supernovae, galaxies, core-collapse supernovae, astronomy
Objavljeno v RUNG: 23.08.2021; Ogledov: 1792; Prenosov: 118
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1756. Codes generated by ordered algebraic structuresHashem Bordbar, 2021, objavljeni povzetek znanstvenega prispevka na konferenci Opis: Error-control codes are used to detect and correct errors that occur when data are trans-mitted across some noisy channel or stored on some medium. The study of error-control codes is called coding theory and emerged in 1948 by Claud Shannon's paper which demonstrated that by proper encoding of the data, errors induced by a noisy channel can be reduced to any desired level without sacrificing the rate of information transmission. Some algebraic structures, includes the study and discovery of various coding schemes, are used to increase the number of errors that can be corrected during data transmission. One of the classes of logical algebra is ordered algebras which were introduced by Imai and Iseki in 1966. In this note, I study the codes generating by the ordered algebraic structures such as BCK-algebras and BL-algebras. For this goal, symmetric rela-tions on these ordered structures facilitate us to design the correspondence codeword. Moreover, I show that the structure of ordered algebra and the code generated by it will be the same.
Ključne besede: coding theory, BCK-algebra, BL-algebra
Objavljeno v RUNG: 20.08.2021; Ogledov: 1937; Prenosov: 148
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1758. 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: 1885; Prenosov: 12
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1759. Chemical (in)stability of interfaces between different metals and Bi[sub]2Se[sub]3 topological insulatorKatja Ferfolja, Mattia Fanetti, Sandra Gardonio, Matjaž Valant, 2018, objavljeni povzetek znanstvenega prispevka na konferenci Opis: 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.
Ključne besede: thermal lens spectrometry, photothermal beam deflection spectroscopy, dye remediation, photothermal technique, photocatalytic degradation, reactive blue 19, TiO2 modification
Objavljeno v RUNG: 20.08.2021; Ogledov: 2273; Prenosov: 0
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1760. Room-temperature solid-state reaction at the Ag/Bi[sub]2Se[sub]3 interfaceKatja Ferfolja, Mattia Fanetti, Iuliia Mikulska, Sandra Gardonio, Matjaž Valant, 2017, objavljeni povzetek znanstvenega prispevka na konferenci Opis: Topological insulators (TI) are materials that, while having a forbidden bandgap in bulk, are conductors at their surface due to presence of surface-localized electronic states crossing the band gap. [1] TIs are possible because of a time reversal symmetry and spin-orbit coupling, which invert bulk band states in their energy positions and make the bulk band structure non trivial. Consequently, the topological surface states (TSS) emerge on the surface of these materials. Unlike ordinary surface states, TSS cannot be destroyed by contamination or defects on the surface. Additionally, TSS are also spin polarized, which means that when applying current to TI, the current will have a well defined direction of the electron spins.
The topological insulators - a relatively new class of materials - are being widely studied not only from fundamental aspects, but also from their applicative perspectives. It has been predicted that TIs could be used in fields of spintronics, electronics and catalysis. [2,3] Interestingly, only a few studies about metal/TI interfaces have been reported. This is surprising since integration of TI in the applications will often necessitate an interface with the metal, therefore, detailed knowledge on chemistry and electrical conditions at the interface will be required.
In this contribution results on research on the chemistry of the Ag/Bi2Se interface will be presented, in particularonthesolid-statereactionbetweennanoparticles.IthasbeenobservedthatwhenBi2Se3 andAgare put in contact a chemical reaction occurs at the interface, producing AgBiSe2 and Ag2Se. Interestingly, the reaction already occurs at room temperature, which is not usual for solid-state reactions. In literature this reaction has not been properly described. The authors rather described it as intercalation of the silver atoms, which we have disproved and showed that recrystallization of the new phases occurs. [3,4,5] The results will alsobediscussedincomparisonwithothertwoAg/Bi2Se3 systemsunderourinvestigation:i)Agdepositedby achemicalrouteonBi2Se3 nanoflakesandii)AgdepositedfromavapourphaseinvacuumonaBi2Se3.single crystal
Ključne besede: topological insulators, topological surface states, solid-state reaction, TI/metal interface
Objavljeno v RUNG: 20.08.2021; Ogledov: 2061; Prenosov: 0
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