Repozitorij Univerze v Novi Gorici

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Impact of longitudinal electron beam properties on free electron laser emission
Matija Stupar, 2013, diplomsko delo

Najdeno v: osebi
Ključne besede: diplomske naloge, laserji na proste elektrone, gruče elektronov, elektronski snopi
Objavljeno: 25.04.2014; Ogledov: 3904; Prenosov: 264
URL Polno besedilo (0,00 KB)
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Chemical and structural investigation of the cobalt phthalocyanine
Matija Stupar, 2015, magistrsko delo

Opis: In the last two decades, studies on organic molecules mimicking substances of fundamental importance in nature, like chlorophyll or hemoglobin, have attracted researchers’ attention. These molecules are building blocks for a family of materials also referred to as “organic semiconductors”. Such compounds can be implemented in numerous applications, ranging from data-storage to light harvesting. Some of their fundamental advantages include low cost, light weight, relatively easy engineering and mechanical flexibility, compatible with bending plastic substrates. In this thesis work we investigated the chemical, structural and electronic properties of cobalt phthalocyanines (CoPc). These molecules have promising applications in the field of magnetic data storage and spintronics in general, due to the ferromagnetic properties of the cobalt atom. Several techniques like photoemission core-level spectroscopy and valence band spectroscopy, together with X-ray absorption, have been used in order to determine the CoPc properties in gaseous phase, i.e. in the absence of interaction with the surrounding environment. Another set of experiments was devoted to the commissioning of the CITIUS time-resolved photoemission setup, that will be used in future studies of CoPc molecules on surfaces.
Najdeno v: osebi
Ključne besede: Cobalt phthalocyanine (CoPc), photoemission spectroscopy (PES), X-ray absorption spectroscopy (XAS), synchrotron radiation, laser, high order harmonic generation (HHG), time resolved spectroscopy
Objavljeno: 29.09.2015; Ogledov: 5649; Prenosov: 212
.pdf Polno besedilo (2,96 MB)

Advantages and disadvantages of experiments with ultrashort two-color pulses
Matija Stupar, 2020, doktorska disertacija

Opis: Advances in the development of lasers have led to a new class of radiation sources generating coherent, tunable, ultrashort light pulses in the spectral region ranging from infrared to soft X-rays. This includes high-order harmonics generation in gas (HHG), on which relies the CITIUS facility at University of Nova Gorica (Slovenia), and free-electron lasers (FELs), such as the facility FERMI at Elettra-Sincrotrone Trieste (Italy). The distinctive structure of HHG and FEL radiation paved the way to time-resolved experiments, which are performed to investigate events occurring on a short, or very short, temporal scale, from picoseconds to femtoseconds. This work focuses on the advantages and disadvantages of some experimental techniques based on using these novel light sources to investigate the microscopic and/or ultrafast dynamics of matter samples, which have been previously driven out of equilibrium. Advantages rely on the implementation of various applications based on two-color schemes and, more specifically, include the possibility of acquiring two-dimensional frequency maps, measuring electrons’ effective masses, or investigating electronic properties decoupled from the influence of the lattice. Particular focus will be put on experimental methods relying on photoelectric effect and photoelectron spectroscopy. In all experiments, we took advantage of one or more specific properties of HHG and FEL sources, such as controllable chirp, to study laser dressed states in helium, variable polarization, to study electronic properties of iron-based pnictides and ultrashort pulses (< 10 fs) to study the purely electronic dynamics in transition metal dichalcogenides. On the other hand, the study of the interface between a molecule and a topological insulator revealed some intrinsic limitations and physical drawbacks of the technique, such as spurious effects originating from the high power pulses, like multiphoton absorption and the space charge effect, or the reduction of experimental resolution when pushing for shorter and shorter pulse durations. Some disadvantages are also connected to the current state-of-the-art in the field of ultrashort laser systems, where a trade-off needs to be found between repetition rate and laser power. Finally, state-of-the-art experiments based on the ability to generate ultrashort pulses carrying orbital angular momentum in visible, near-infrared as well as extreme UV range will be presented. The use of these pulses opens the door to the investigation of new physical phenomena, such as probing magnetic vortices using extreme ultraviolet light from a free-electron laser or imprinting the spatial distribution of an ultrashort infrared pulse carrying orbital angular momentum onto a photoelectron wave packet.
Najdeno v: osebi
Ključne besede: ultrafast lasers, two-color experiments, photoemission, high-order harmonic generation, free-electron lasers, hot-electrons dynamics, surface science, pump-probe photoemission, ultraviolet photoemission, orbital angular momentum
Objavljeno: 02.12.2020; Ogledov: 679; Prenosov: 19
.pdf Polno besedilo (19,78 MB)

Orbital-dependent electron dynamics in Fe-pnictide superconductors
A. Thamizhavel, Damjan Krizmancic, Giovanni De Ninno, Jurij Urbančič, Primož Rebernik Ribič, Barbara Ressel, G. Adhikary, Kalobaran Maiti, Matija Stupar, 2018, izvirni znanstveni članek

Opis: We report on orbital-dependent quasiparticle dynamics in EuFe 2 As 2, a parent compound of Fe-based superconductors, and a way to experimentally identify this behavior using time-and angle-resolved photoelectron spectroscopy across the spin density wave transition. We observe two different relaxation timescales for photoexcited d x z/d y z and d x y electrons. While the itinerant d x z/d y z electrons relax faster through the electron-electron scattering channel, d x y electrons form a quasiequilibrium state with the lattice due to their localized character, and the state decays slowly. Our findings suggest that electron correlation in Fe pnictides is an important property, which should carefully be taken into account when describing the electronic properties of both parent and carrier-doped compounds, and therefore establish a strong connection with cuprates
Najdeno v: osebi
Ključne besede: photoelectron dynamics, Fe based superconductors
Objavljeno: 29.11.2018; Ogledov: 1515; Prenosov: 0
.pdf Polno besedilo (2,37 MB)

Interface phenomena between CdTe and ZnTe: Cu back contact
Alessio Bosio, Roberta Ciprian, Alessio Lamperti, I Rago, Barbara Ressel, Greta Rosa, Matija Stupar, E Weschke, 2018, izvirni znanstveni članek

Opis: Thin film technology has reached a maturity to achieve conversion efficiencies of the order of 22%. Among thin films, CdTe-based photovoltaic modules represent 80% of the total production. Nonetheless, some issues concerning back-contact are still open. In industrial process a chemical etching is required in order to make the CdTe film surface rich in Te. The Te-excess is fundamental in order to form a stable telluride compound with copper and to obtain an ohmic, low-resistance back-contact. Moreover, the Te-excess hinders the fast diffusion of copper in CdTe and its achievement of the junction region, preventing the destruction of the device. In this paper we study a ZnTe:Cu buffer layer deposited onto a CdTe film, characterized by a naturally Te-rich surface obtained with a particular chlorine heat treatment without any chemical etching. Copper diffusion and the CdTe/ZnTe:Cu interface were studied by x-ray
Najdeno v: osebi
Ključne besede: solar cells, CdTe, ZnTe:Cu back contact
Objavljeno: 29.11.2018; Ogledov: 1631; Prenosov: 0
.pdf Polno besedilo (2,23 MB)

Coupling of autoionizing states by a chirped laser pulse
Barbara Ressel, Jurij Urbančič, Primož Rebernik Ribič, Špela Krušič, Žiga Barba, Mateja Hrast, Klemen Bučar, Andrej Mihelič, Matjaž Žitnik, Matija Stupar, David Gauthier, Giovanni De Ninno, 2020, objavljeni povzetek znanstvenega prispevka na konferenci

Opis: We have observed the autoionization of the laser-coupled 2s2p 1Po and 2p2 1Se resonances in helium. The ions were collected while varying the frequency and delay of the extreme-ultraviolet (EUV) excitation pulse with respect to the linearly chirped visible (VIS) laser pulse. From the measured frequency-delay map the Autler- Townes splitting, the EUV-VIS cross-correlation and the linear chirp parameter were extracted.
Najdeno v: osebi
Ključne besede: High Harmonic Generation
Objavljeno: 29.06.2020; Ogledov: 825; Prenosov: 0
.pdf Polno besedilo (654,72 KB)

Dissecting Mott and charge-density wave dynamics in the photoinduced phase of 1T-TaS[sub]2
Alberto Simoncig, Matija Stupar, Barbara Ressel, Tanusree Saha, Primož Rebernik Ribič, Giovanni De Ninno, 2021, izvirni znanstveni članek

Opis: The two-dimensional transition-metal dichalcogenide 1T−TaS2 is a complex material standing out for its puzzling low temperature phase marked by signatures amenable to both Mott-insulating and charge-density wave states. Electronic Mott states, coupled to a lattice, respond to coherent optical excitations via a modulation of the lower (valence) Hubbard band. Such dynamics is driven by strong electron-phonon coupling and typically lasts for tens of picoseconds, mimicking coherent structural distortions. Instead, the response occurring at the much faster timescale, mainly dominated by electronic many-body effects, is still a matter of intense research. By performing time- and angle-resolved photoemission spectroscopy, we investigated the photoinduced phase of 1T−TaS2 and found out that its lower Hubbard band promptly reacts to coherent optical excitations by shifting its binding energy towards a slightly larger value. This process lasts for a time comparable to the optical pump pulse length, mirroring a transient change of the onsite Coulomb repulsion energy (U). Such an observation suggests that the correction to the bare value of U, ascribed to the phonon-mediated screening which slightly opposes the Hubbard repulsion, is lost within an interval of a few tens of femtoseconds and can be understood as a fingerprint of electronic states largely decoupled from the lattice. Additionally, these results enforce the hypothesis, envisaged in the current literature, that the transient photoinduced states belong to a sort of crossover phase instead of an equilibrium metallic one.
Najdeno v: osebi
Ključne besede: ultrafast phenomena, time resolved photoemission, strongly correlated systems, transition metal dichalcogenide
Objavljeno: 13.04.2021; Ogledov: 150; Prenosov: 0
.pdf Polno besedilo (1,34 MB)

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