91. Looking for a topological insulator in the tetradymite familyZipporah Rini Benher, Sandra Gardonio, Mattia Fanetti, Polina M. Sheverdyaeva, Paolo Moras, Matjaž Valant, 2019, published scientific conference contribution abstract Abstract: Materials that are topological insulators (TI) manifest a novel state for their electrons. They possess topological surface states that are not destroyed by the presence of non-magnetic impurities on their surfaces. This unique property lies in the bulk band structure and it is typically found in narrow gap semiconductor with strong spin-orbit coupling.
Bi2Se3 and Bi2Te3 belong to the class of compounds called tetradymites and are considered as the 3D-prototypical TI materials. However, these compounds are not usually insulators but have metallic bulk conductivity as a consequence of intrinsic defect doping: vacancies and anti-site defects. For these reasons, it is difficult to electrically gate these materials for the manipulation and control of charge carriers for realizing devices. This led to the search for other topological materials, which might have better insulating behavior in their bulk.
Theoretical studies have pointed out that ternary variants of the Bi2Se3 and Bi2Te3, such as Bi2Te2Se, Bi2Te2S, Bi2Se2S Sb2Te2Se and Sb2Te2S, should be stable TIs and potentially offer a chemical way to control TI behavior, in particular by lowering native doping. Among the cited ternary compounds, Bi2Se2S should manifest a genuine topological spin-transport regime hosting an isolated Dirac cone with the Dirac point in the gap as well. However, it has been poorly studied from the TI experimental perspective.
Therefore, to uncover the full potential of the predicted topological electronic properties of the Bi-Se-S system, in this presentation we will revisit the crystallographic and electronic structure of Bi2Se3-Bi2S3 solid solutions. The combined use of bulk and surface sensitive techniques such as X-ray diffraction (XRD), low energy electron diffraction (LEED), scanning electron microscopy (SEM) with Energy Dispersive X-ray spectroscopy (EDX) and X-ray photoemission spectroscopy (XPS) was applied to analyze single crystal samples grown by us. The quality of the single crystals was suitable for rigorous measurement of the electronic properties by means of Angle Resolved Photoemission Spectroscopy. We unambiguously showed that within a certain solid solution range, the single crystals of Bi-Se-S have a rombohedral structure with the topological surface states as theoretically predicted.
Keywords: topological insulators, ternary tetradymite, electronic properties.
Published in RUNG: 19.12.2019; Views: 4054; Downloads: 0
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96. Prihodnji scenariji rabe tal na celotnem območju Parka Škocjanske jame z uporabo prostorskega modela DynaCLUEKlemen Cotič, 2019, undergraduate thesis Abstract: Spremembe rabe tal, kot posledica naših dejavnosti, imajo pomemben vpliv na različne okoljske prvine, kot npr. raven biotske raznovrstnosti in erozijo tal. V tem delu se ukvarjamo s spremembo rabe tal v prihodnosti na širšem območju Regijskega parka Škocjanske jame, z uporabo geografskih informacijskih sistemov, statistike in prostorskega modeliranja. Najprej smo z uporabo zbirke različnih lokacijskih dejavnikov (nadmorska višina, naklon reliefa, ekspozicija tal, oddaljenost od cest, naselij, pedološke profile tal itd.) statistično analizirali prostorsko razporeditev rabe tal s pomočjo logistične regresije. Njivske površine se pojavljajo predvsem na območjih psevdoglenih distričnih tal, trajni nasadi pa niso odvisni od tipa tal. Zaraščene površine in gozd se pojavljajo na celotnem območju, brez močnega vpliva posameznih spremenljivk. Na podlagi različnih dokumentov in uradnih statistik smo zatem razvili tri različne scenarije rabe tal do leta 2035. V prvem se travniške in kmetijske površine obnovijo na raven iz leta 1985, drugi se osredotoča na širitev poselitvenih in industrijskih površin, tretji pa upošteva smernice trajnostnega razvoja. Po simulaciji z modelom DynaCLUE lahko ugotovimo, da se posamezne rabe tal, neodvisno od velikosti scenarija pojavljajo na podobnih mestih. Ne glede na to dejstvo razviti scenariji pomagajo določiti območja, kjer je večja verjetnost za širjenje naselij ali pa kjer je večja verjetnost opuščanja kmetijskih površin.
Keywords: prihodnji scenariji, raba tal, Park Škocjanske jame, logistična regresija, DynaCLUE
Published in RUNG: 17.10.2019; Views: 5201; Downloads: 149
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97. 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, published scientific conference contribution abstract Keywords: Bismuth selenide, topological insulator, hydrothermal synthesis, surface properties
Published in RUNG: 30.09.2019; Views: 3526; Downloads: 0
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