The advent of attosecond pulses, produced through high-order harmonic generation (HHG) in the beginning of the millennium, has opened up for time domain spectroscopic approaches with unprecedented, attosecond, time resolution. However, typical attosecond sources are often impaired by the low repetition rate of the driving lasers, potentially resulting in measurements with insufficient...
Charge transfer processes are ubiquitous in nature. They are responsible for energy transport and signal transduction in biomolecular systems. Charge carrier dynamics play also key roles in light harvesting systems used for solar cell technologies and hydrogen fuel cells. Probing the transient local charge densities with high spatio-temporal resolution is a prerequisite for a better...
The conversion of energy, between photons, charge carriers, and the lattice is of fundamental importance to advance materials and devices, yet such insight remains incomplete due to experimental challenges in disentangling the various effects on overlapping time scales. Here, we show that attosecond core-level X-ray spectroscopy can identify these mechanisms with attosecond precision and...
The aim of this talk is to present the activity of CNR-IFN and the Physics Department of Politecnico di Milano on ultrafast spectroscopy within the SMART-X network.
Ultrafast X-ray spectroscopy allows the study of light-matter interaction with unprecedented temporal and spatial resolution with the further advantages of being element-selective and oxidation- and spin-state specific. The...
We will present an overview over our theory projects that involve the modelling of molecular dynamics and the simulation of ultra-fast X-ray spectra.
In the first part we will give an overview over potential spectroscopic methods, which can be used to identify conical intersections and non-adiabatic dynamics in the excited state dynamics of molecules. We will present a theoretical study on...
Van der Waals metallic ferromagnets (e.g. CrxTey, Fe3GeTe2) with a Curie temperature near 300 K are a new addition to the family of 2D materials. They possess perpendicular magnetic anisotropy down to a few monolayer regime and are reported to host skyrmions. Their combination with spin orbit torque materials (e.g. topological insulators (TI)) may lead to efficient charge to spin conversion...
Soft x-ray absorption and resonant inelastic x-ray scattering are briefly introduced [1]. In 2p3d resonant inelastic x-ray scattering (RIXS) one scans through the 2p XAS edge and measures the low energy excitations, including phonons, magnons, dd-excitations and charge transfer [2].Recently we measured time-resolved XAS and RIXS using the PAL-XFEL source in Pohang [3,4]. The oxygen K edge and...
Semiconducting metal-halide perovskites present various types of chemical interactions which give them a characteristic fluctuating structure sensitive to the operating conditions of the device, to which they adjust. This makes the control of structure-properties relationship, especially at interfaces where the device realizes its function, the crucial step in order to control devices...
Computer simulations are a key complement to experiments in the laboratory, providing much greater details of a molecular process than can be observed experimentally. For instance, ab initio molecular dynamics simulations are often key to the understanding of the mechanism, rate and yield of chemical reactions. One current challenge is the in-depth analysis of the large amount of data produced...
Along with the rapid development of the laser technology allowing for time-resolved studies, a remarkable progress in the synchrotron technology provides nowadays a wealth of information on the relaxation mechanisms of core-exited systems through high energy-resolution electron and X-ray spectroscopy and essentially complements the time-resolved studies [1]. We use X-ray emission spectroscopy...
FERMI is a world unique free electron laser, that thanks to the seeding scheme can deliver coherent pulses up to the carbon K edge, with an exquisite polarization, photon energy and timing control. These properties, corroborated by multi-colors emission schemes permit to perform non-linear optics time-resolved experiments, with the long dreamed achievement of the chemical sensitivity. In...
Transient X-ray near-edge absorption spectroscopy (XANES) and high harmonic generation (HHG) are powerful techniques to study structural and dynamical properties of materials. From the first-principles modelling perspective they present several challenges such as accessing core electrons, capturing correlations and excitons and describing the coupling to phonons. Overcoming these challenges...
Photoelectrochemical (PEC) water splitting is an auspicious approach to convert solar energy directly into fuel. Hitherto, TiO$_2$, WO$_3$, and α-Fe$_2$O$_3$ have been the most studied metal oxides as photoelectrodes. However, their large bandgap and extremely short charge carrier diffusion lengths are hurdles to attain higher solar-to-hydrogen conversion efficiencies. Recently, copper...
The process of High-Harmonic Generation (HHG) emits a sequence of short bursts of radiation, which are coherently driven by the generation laser, where emission events occur during each laser half cycle. Each of these short bursts is in the attosecond regime and their interference leads to the observation of odd harmonics. These attosecond pulse trains (APTs), unlike isolated pulses, are...
Electronic correlations in inner-shell ionized molecules can be probed via Auger spectroscopy. After a high-energy photon ionizes the atomic core shell close to ionization threshold, a slow photoelectron leaves the atom, not without interacting with the ionic field. Decay may take place via emission of an Auger electron, with which the photoelectron may interact. This Coulombic interaction...
Two-dimensional (2D) Hexagonal Boron Nitride (h-BN) is an insulator that has a polar covalent B-N bond. Both monolayer and bilayer (h-BN) emerge as an optoelectronic material, which can be used as photodetectors and for photocatalysis. Here in, we performed calculation for Transient absorption spectroscopy (TAS) for monolayer (h-BN) using a low intensity laser pulse, modelling the dynamics...
The theoretical characterization of the time-resolved X-ray spectra in solution requires simulation of the correlated electronic and nuclear motion with the help of advanced electronic structure methods. The goal behind this work is to use different quantum mechanical techniques to provide a realistic depiction of the coupled electronic and nuclear dynamics. For an instance, ab initio...
The main aim of this project concerns the epitaxial growth of 2D layered transition-metal dichalcogenides (TMCs) and their structural and electronic characterization by means of in-situ scanning tunneling microscopy (STM), reflection high-energy electron diffraction (RHEED), X-ray photoelectron spectroscopy (XPS) and angle-resolved photoemission spectroscopy (ARPES). Among other 2D TMCs, three...
Hydrogen production through solar water splitting is a clean solution to the actual energy demand. It can be carried out in a photoelectrochemical cell where a photoelectrode absorbs sunlight producing electron-hole pairs, then the charge carriers are collected separately to oxidize oxygen and reduce hydrogen from water. Several materials have been proposed and tested as photoelectrodes, being...
With rapid technological developments in the last twenty years, semiconductors’ functionality in various applications has led the scientific community to intensive study of perovskites. In particular, the focus is on halide perovskites, since they display an attractive set of properties for radiation detection devices, solar cells and photovoltaic systems.
As such, my PhD project will focus...
With the extremely intense short-wavelength pulses of free-electron lasers (FELs) and high harmonic sources (HHG), novel experiments with highest spatial and temporal resolution become possible. One key example is coherent diffraction imaging of individual nanoparticles. Here, the elastically scattered photons form an interference pattern, which encodes structural information in a 'snapshot'....
Detectors suitable for high repetition rate imaging and spectroscopy as well as for single photon detection are a key prerequisite for high sensitivity, transient EUV & soft X-ray absorption experiments. For this purpose existing CCD-based technologies first were compared to a new approach based on novel XUV/X-ray sensitive (scientific) CMOS sensors which recently have become commercially...
In the framework of a joint laboratory between INPHYNI and FASTLITE, we disclose the use of thick nematic liquid crystals to the temporal shaping of ultrashort pulses. We first propose to exploit the large and electrically controllable birefringence of nematic liquid crystals for precise control of the group and phase delays of femtosecond pulses, which is realized by appropriately addressing...
Group discussion and gentle introduction to how OSA Chapters operates and the benefits involved in taking part as an individual.
This will be an informal conversation, encouraging participants to ask questions in this first meeting with OSA.
