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Opis: 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.
Najdeno v: ključnih besedah
Povzetek najdenega: ...full potential of the predicted topological electronic properties of the Bi-Se-S system, in this presentation...
Ključne besede: topological insulators, ternary tetradymite, electronic properties.
Objavljeno: 19.12.2019; Ogledov: 2877; Prenosov: 0
Polno besedilo (6,45 MB)

Opis: The interest in biopolymers has increased due to the depletion of the fossil fuel reserve and the environmental impact caused by the accumulation of non-biodegradable plastic-based packaging materials. Many biopolymers have been developed from food waste products to reduce this waste and, at the same time, to obtain new food packaging materials. Chitosan is thus an alternative to synthetic polymers, and a raw material for new materials. To assess the suitability of a material as a food packaging material, it is necessary to study their mechanical and permeability properties. Mechanical properties allow to predict the behaviour of films during transportation, handling and storage of packaged foods. Barrier properties play a key role in maintaining the food product quality. Properties values depend on the type of chitosan used. Mechanical and barrier properties of pure chitosan films are suitable for food packaging and active packaging. These properties can be modified by combining chitosan with other components such as plasticizers, other polysaccharides, proteins and lipids. These combinations adapt the properties of the final polymer to the needs of the food to extend its useful life, while maintaining quality properties of the food and the biodegradability of the polymer. Chitosan displays antimicrobial activity against a wide range of foodborne filamentous fungi, yeast, and gram-negative and gram-positive bacteria. This antimicrobial property and film-forming capacity has made chitosan the reference polymer to develop active packaging with the ability to inhibit the growth of microorganisms and improve food safety. Regarding the optical properties, pure chitosan films in the visible range show high transmittance values, being optically transparent films. This is an important parameter related to the acceptability of the films by the consumer. In addition, chitosan-based films exhibit remarkable UV absorbance, which allows to protect food from lipid oxidations induced by UV radiation.
Najdeno v: ključnih besedah
Povzetek najdenega: ...necessary to study their mechanical and permeability properties. Mechanical properties allow to predict the behaviour...
Ključne besede: Film, Mechanical properties, Barrier properties, Antimicrobial, UV protect, Active food packaging
Objavljeno: 14.12.2020; Ogledov: 1668; Prenosov: 0
Polno besedilo (701,19 KB)

Najdeno v: ključnih besedah
Povzetek najdenega: ...topological insulator, optical properties, topological surface states, silica-coated...
Ključne besede: topological insulator, optical properties, topological surface states, silica-coated
Objavljeno: 27.09.2021; Ogledov: 1190; Prenosov: 0
Polno besedilo (23,68 MB)

Najdeno v: ključnih besedah
Ključne besede: chitosan:cellulose composites, biocompatible materials, beam deflection spectrometry, porosity determination, structural characterisation, thermal properties
Objavljeno: 30.06.2022; Ogledov: 441; Prenosov: 40
Polno besedilo (84,71 KB)

Najdeno v: ključnih besedah
Povzetek najdenega: ...Bacteria, Electrical properties, Electrochemical cells, Electrodes, Sensors...
Ključne besede: Bacteria, Electrical properties, Electrochemical cells, Electrodes, Sensors
Objavljeno: 26.09.2022; Ogledov: 337; Prenosov: 12
Polno besedilo (4,87 MB)