Iskanje po repozitoriju

A+ | A- | | SLO | ENG

Opis: An absorption cell is constructed for x-ray absorption spectroscopy of reactive, unstable or hazardous gases at room temperature. In conjunction with in-situ micro-synthesis technique relying on handling the gas in syringes it enabled a first measurement of x-ray absorption spectra in the region of K and L edges for the series of hydrides of 5p elements (SnH4, SbH3, TeH2, HI). The signal-to-noise ratio above 103 was achieved, whereby fine detail is discerned in the spectra, in particular the small sharp features above each absorption edge, testifying of coexcitations of outer electrons in the core photoeffect.
Najdeno v: ključnih besedah
Ključne besede: X-ray absorption spectroscopy Micro-synthesis absorption cell Gaseous hydrides Multielectron photoexcitations
Objavljeno: 10.02.2020; Ogledov: 2485; Prenosov: 0
Polno besedilo (756,39 KB)

Najdeno v: ključnih besedah
Povzetek najdenega: ...oxygen, electron paramagnetic resonance spectroscopy, phosphates, amorphous materials, defects...
Ključne besede: oxygen, electron paramagnetic resonance spectroscopy, phosphates, amorphous materials, defects
Objavljeno: 04.05.2021; Ogledov: 1688; Prenosov: 0
Polno besedilo (2,23 MB)

Najdeno v: ključnih besedah
Povzetek najdenega: ...electrochemical impedance spectroscopy, mixed conduction...
Ključne besede: electrochemical impedance spectroscopy, mixed conduction
Objavljeno: 07.06.2021; Ogledov: 1139; Prenosov: 30
Polno besedilo (0,00 KB)
Gradivo ima več datotek! Več...

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.
Najdeno v: ključnih besedah
Povzetek najdenega: ...thermal lens spectrometry, photothermal beam deflection spectroscopy, dye remediation, photothermal technique, photocatalytic degradation, reactive...
Ključne besede: thermal lens spectrometry, photothermal beam deflection spectroscopy, dye remediation, photothermal technique, photocatalytic degradation, reactive blue 19, TiO2 modification
Objavljeno: 20.08.2021; Ogledov: 1343; Prenosov: 0
Polno besedilo (100,42 KB)

Opis: Quantum materials display exotic behaviours related to the interplay between temperature-driven phase transitions. Here, we study the electron dynamics in one such material, CaFe$_2$As$_2$, a parent Fe-based superconductor, employing time and angle-resolved photoemission spectroscopy. CaFe$_2$As$_2$ exhibits concomitant transition to spin density wave state and tetragonal to orthorhombic structure below 170 K. The Fermi surface of this material consists of three hole pockets ($\alpha$, $\beta$ and $\gamma$) around $\Gamma$-point and two electron pockets around $X$-point. The hole pockets have $d_{xy}$, $d_{yz}$ and $d_{zx}$ orbital symmetries. The $\beta$ band constituted by $d_{xz}$/$d_{yz}$ orbitals exhibit a gap across the magnetic phase transition. We discover that polarized pump pulses can induce excitations of electrons of a selected symmetry. More specifically, while $s$-polarized light (polarization vector perpendicular to the $xz$-plane) excites electrons corresponding to all the three hole bands, $p$-polarized light excites electrons essentially from ($\alpha$,$\beta$) bands which are responsible for magnetic order. Interestingly, within the magnetically ordered phase, the excitation due to the $p$-polarized pump pulses occur at a time scale of 50 fs, which is significantly faster than the excitation induced by $s$-polarized light ($\sim$ 200 fs). These results suggest that the relaxation of different ordered phases occurs at different time scales and this method can be used to achieve selective excitations to disentangle complexity in the study of quantum materials.
Najdeno v: ključnih besedah
Povzetek najdenega: ...Fe-based superconductor, employing time and angle-resolved photoemission spectroscopy. CaFe$_2$As$_2$ exhibits concomitant transition to spin density...
Ključne besede: Electronic structure, Pnictides and chalcogenides, Time-resolved spectroscopy
Objavljeno: 13.10.2021; Ogledov: 1055; Prenosov: 4
Polno besedilo (9,56 MB)