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1.
STUDY OF ELECTRONIC STATES OF THIN METAL FILMS ON HEAVY METAL SURFACES
Luka Novinec, 2018, magistrsko delo

Opis: V magistrskem delu smo se osredoto£ili na pripravo in karakterizacijo heterogenih ve£plastnih tankih filmov sestavljenih iz kovin ter teºkih kovin. Za izdelavo vzorcev smo izbrali dve feromagnetni kovini, Fe in Gd, ter eno divalentno kovino iz redkih zemelj, Yb. Tanke filme smo nana²ali na kristalno povr²ino volframa W(110) ter molibdena Mo(110). V primeru Fe na povr²ini W(110) in Mo(110) ter Yb na pov²ini Mo(110) smo uspe²no dolo£ili pogoje, potrebne za nana²anje atomsko enakomernih filmov. S pomo £jo kotno odvisne fotoemisije smo preu£evali kvantna stanja v Fe in Yb filmih na Mo in W kristalih. Celotno eksperimentalno delo je potekalo na ºarkovnih linijah VUV-Photoemission in²tituta (ISM-CNR) ter BaDElPh pri sinhrotronu Elettra v Trstu.
Najdeno v: ključnih besedah
Ključne besede: electronic states, thin metal films, heavy metal surfaces
Objavljeno: 04.12.2019; Ogledov: 1682; Prenosov: 56
.pdf Polno besedilo (25,10 MB)

2.
Chemical Instability of an Interface between Silver and Bi2Se3 Topological Insulator at Room Temperature
Katja Ferfolja, Matjaž Valant, Iuliia Mikulska, Sandra Gardonio, Mattia Fanetti, 2018, izvirni znanstveni članek

Opis: Understanding an interaction at an interface between a topological insulator and a metal is of critical importance when designing electronic and spintronic devices or when such systems are used in catalysis. In this paper, we report on a chemical instability of the interface between Bi2Se3 and Ag studied by X-ray powder diffraction and electron microscopy. We present strong experimental evidence of a redox solid-state reaction occurring at the interface with kinetics that is significant already at room temperature. The reaction yields Ag2Se, AgBiSe2, and Bi. The unexpected room-temperature chemical instability of the interface should be considered for all future theoretical and applicative studies involving the interface between Bi2Se3 and Ag.
Najdeno v: ključnih besedah
Povzetek najdenega: ...topological insulators, Ag, thin metal films, interfaces, redox reaction...
Ključne besede: topological insulators, Ag, thin metal films, interfaces, redox reaction
Objavljeno: 17.06.2020; Ogledov: 1027; Prenosov: 0
.pdf Polno besedilo (3,93 MB)

3.
Structural, morphological and chemical properties of metal/topological insulator interfaces
Katja Ferfolja, 2021, doktorska disertacija

Opis: Topological insulators (TIs) represent a new state of matter that possess a different band structure than regular insulators or conductors. They are characterized with a band gap in the bulk and conductive topological states on the surface, which are spin polarized and robust toward contamination or deformation of the surface. Since the intriguing properties of the TIs are localized at the surface, it is important to obtain knowledge of the possible phenomena happening at the interface between TIs and other materials. This is especially true in the case of metals, due to the fact that such interfaces will be present in the majority of foreseen TI applications. The presented study combines microscopy and spectroscopy techniques for characterization of morphology, stability and chemical interaction at the interface between TI and metals deposited by means of physical vapor deposition. Our research is based on the interface of Bi2Se3 topological insulator with Ag, Ti and Pt – metals that can be encountered in devices or applications predicted to utilize the special properties of topological insulators. STM and SEM imaging of Ag/Bi2Se3 interface showed that Ag atoms arrange on the surface in the form of islands, whereas significantly bigger agglomerates are found at the surface steps. The interface was found to be unstable in time and resulted in the absorption of the metal into the crystal at room temperature. Evidences of a chemical reaction at the Ag/Bi2Se3 interface are presented, showing that new phases (Ag2Se, AgBiSe2 and metallic Bi) are formed. Deposition of Ti on Bi2Se3 resulted in different morphologies depending on the film thickness. At a very low coverage (<1 Å) islands are formed. However, the islands growth is hindered before the completion of a full layer due to the occurrence of a chemical reaction. No surface features could be detected by SEM for Ti coverage up to 20 nm. In contrary, when Ti thickness reached 40 nm, compressive stress triggered buckling of the deposited film. XPS analysis revealed that a redox solid-state reaction occurs at the Ti/Bi2Se3 interface at room temperature forming titanium selenides and metallic Bi. The reaction has significant kinetics even at cryogenic temperature of 130 K. Pt forms a homogenous film over the whole substrate surface, which is stable in time at room temperature. Although the interface of Pt with Bi2Se3 was found to be i less reactive compared to Ag and Ti, an interfacial phase formed upon annealing to ∼90 °C was detected by TEM cross section experiment. A model for prediction of interfacial reactions between a metal and Bi2Se3 based on the standard reduction potential of the metals and Gibbs free energy for a model reaction is presented. Based on these two values the reaction can be expected to result in the formation of binary and/or ternary selenides and Bi. Presented work shows on the importance of metal/topological insulator interfaces characterization taking into account the possibility of a chemical reaction with all of its consequences. Results should be considered for future theoretical and applicative studies involving such interfaces as well as for the possible engineering of 2D TI heterostructures.
Najdeno v: ključnih besedah
Povzetek najdenega: ...topological insulators, topological surface states, Bi2Se3, thin films, Ag, Ti, Pt, morphology, interfaces, solid-state...
Ključne besede: topological insulators, topological surface states, Bi2Se3, thin films, Ag, Ti, Pt, morphology, interfaces, solid-state reaction, metal selenides, reactivity, stability, electron microscopy, dissertations
Objavljeno: 09.06.2021; Ogledov: 401; Prenosov: 26
URL Polno besedilo (0,00 KB)
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