Periodic Reporting for period 1 - SMART-X (Study of carrier transport in MAterials by time-Resolved specTroscopy with ultrashort soft X-ray light)
Berichtszeitraum: 2020-03-01 bis 2022-02-28
SMART-X targets the training of Early-Stage Researchers for their productive insertion in the academy as well as in the forthcoming job market. To achieve this goal, SMART-X faces two urgent scientific challenges, the development of a novel green energetic paradigm and a new nanoelectronics era. To pursue this needed progress, the understanding of the physical properties that enable these technological advancements is mandatory. For instance, solar cell prototypes based on perovskite (PSCs) have reached a remarkable conversion efficiency of 20%, making this material the most intriguing and reliable option for future photovoltaics. Two main hurdles have hampered the market exploitation of PSCs so far, namely the presence of moving defects affecting the dynamics of polaronic carriers and the presence of lead - a toxic constituent. Our ability to understand fundamental processes involving interactions between electrons, lattice (phonons) and photons that are at play in perovskites is an essential prerequisite for the further development of technological applications based on these materials.
Moreover, the future technology era for dissipation-less opto- and nanoelectronics rests on unexplored principles, such as topology and correlated-electron phenomena. Extensive applications are anticipated for the design of novel energy-efficient circuits and energy-conversion systems based on the use of this new technology. For instance, Weyl and Dirac semimetals are a new state of topological quantum matter, which can radicalize science and technology. These materials often called the “new 3D graphenes” exhibit linear energy dispersion (Dirac-like cones) in all three dimensions in k-space. Weyl semimetals host pairs of massless fermions with opposite chirality and topological charge acting as magnetic monopoles in the reciprocal space. Their unique topological properties can have an impact on electron transport, which remains largely unexplored.
A promising approach for the study of ultrafast dynamics in complex materials is ultrafast X-ray spectroscopy. This technique allows the study of light-matter interaction with an unprecedented temporal and spatial resolution with the further advantages of being element-selective and oxidation- and spin-state specific. Indeed, in this spectral region, the photon absorption occurs locally at the atomic cores. X-ray measurements at atom-specific absorption edges allow the investigation of both the electronic and the structural environment of the probed atom, providing a local probe of the dynamics under study. The investigation of the properties of core electrons at ultrafast time scales promises to enlighten the dynamics occurring in complex materials, such as topological matter, quantum matter, and light-harvesting complexes.
The SMART-X network will study the key processes that regulate electron and charge transfer in complex systems by the development of ultrafast soft X-ray spectroscopy beyond the state of the art.
Moreover, the future technology era for dissipation-less opto- and nanoelectronics rests on unexplored principles, such as topology and correlated-electron phenomena. Extensive applications are anticipated for the design of novel energy-efficient circuits and energy-conversion systems based on the use of this new technology. For instance, Weyl and Dirac semimetals are a new state of topological quantum matter, which can radicalize science and technology. These materials often called the “new 3D graphenes” exhibit linear energy dispersion (Dirac-like cones) in all three dimensions in k-space. Weyl semimetals host pairs of massless fermions with opposite chirality and topological charge acting as magnetic monopoles in the reciprocal space. Their unique topological properties can have an impact on electron transport, which remains largely unexplored.
A promising approach for the study of ultrafast dynamics in complex materials is ultrafast X-ray spectroscopy. This technique allows the study of light-matter interaction with an unprecedented temporal and spatial resolution with the further advantages of being element-selective and oxidation- and spin-state specific. Indeed, in this spectral region, the photon absorption occurs locally at the atomic cores. X-ray measurements at atom-specific absorption edges allow the investigation of both the electronic and the structural environment of the probed atom, providing a local probe of the dynamics under study. The investigation of the properties of core electrons at ultrafast time scales promises to enlighten the dynamics occurring in complex materials, such as topological matter, quantum matter, and light-harvesting complexes.
The SMART-X network will study the key processes that regulate electron and charge transfer in complex systems by the development of ultrafast soft X-ray spectroscopy beyond the state of the art.
Development of laser technology:
FASTLITE successfully reported the design and implementation of a mid-infrared femtosecond laser source based on optical chirped-pulsed amplification (OPCPA), based on ytterbium pump lasers. The aim of this system is to serve as a high-repetition-rate (50 kHz) table-top driver for high-harmonic generation up to the water window (300 - 500 eV), characterized by record CEP stability.
Growth of perovskite thin films
Thermal evaporation offers the unique possibility of accurately controlling the deposition of smooth and uniform multilayers of perovskite materials, avoiding the use of toxic solvents. The possibility of growing perovskite by evaporation was evaluated using as prototype material all inorganic CsPbI3. This material has received large attention if fabricated by spin-coating from solution. However, there is little research about the effect that a different fabrication process will produce. The objective is to develop a deposition process to accurately control the thickness, uniformity, and composition of the perovskite thin film. IIT successfully studied morphology and optical properties of evaporated perovskite films that will be used within the network for further investigations by ultrafast x-ray spectroscopy.
Growth of 2D materials
Successful epitaxial growth and in situ characterization of single- and few-layer HfTe2, ZrTe2, and HfxZr1-xTe2 2D materials, as well as few-layer MoTe2, has been achieved by NCSRD. The main interest in studying HfTe2, ZrTe2, and HfxZr1-xTe2 are due to the theoretical and first experimental evidence indicating that HfTe2 and ZrTe2 are type I and type II topological Dirac semimetals with Dirac points located along high-symmetry path in the Brillouin zone.
Development of the theoretical toolbox
MPG investigated the possibility to model time-resolved X-ray absorption spectroscopy with TDDFT in hexagonal boron nitride (hBN), a two-dimensional material with a wide bandgap and a polar covalent B-N bond. Spectra were calculated under different irradiation conditions and compared with experimental data provided by ICFO.
FASTLITE successfully reported the design and implementation of a mid-infrared femtosecond laser source based on optical chirped-pulsed amplification (OPCPA), based on ytterbium pump lasers. The aim of this system is to serve as a high-repetition-rate (50 kHz) table-top driver for high-harmonic generation up to the water window (300 - 500 eV), characterized by record CEP stability.
Growth of perovskite thin films
Thermal evaporation offers the unique possibility of accurately controlling the deposition of smooth and uniform multilayers of perovskite materials, avoiding the use of toxic solvents. The possibility of growing perovskite by evaporation was evaluated using as prototype material all inorganic CsPbI3. This material has received large attention if fabricated by spin-coating from solution. However, there is little research about the effect that a different fabrication process will produce. The objective is to develop a deposition process to accurately control the thickness, uniformity, and composition of the perovskite thin film. IIT successfully studied morphology and optical properties of evaporated perovskite films that will be used within the network for further investigations by ultrafast x-ray spectroscopy.
Growth of 2D materials
Successful epitaxial growth and in situ characterization of single- and few-layer HfTe2, ZrTe2, and HfxZr1-xTe2 2D materials, as well as few-layer MoTe2, has been achieved by NCSRD. The main interest in studying HfTe2, ZrTe2, and HfxZr1-xTe2 are due to the theoretical and first experimental evidence indicating that HfTe2 and ZrTe2 are type I and type II topological Dirac semimetals with Dirac points located along high-symmetry path in the Brillouin zone.
Development of the theoretical toolbox
MPG investigated the possibility to model time-resolved X-ray absorption spectroscopy with TDDFT in hexagonal boron nitride (hBN), a two-dimensional material with a wide bandgap and a polar covalent B-N bond. Spectra were calculated under different irradiation conditions and compared with experimental data provided by ICFO.
Significant advancements beyond the state-of-the-art are expected as an outcome of the SMART-X project in different disciplines and sectors:
- Advances in 2D material engineering.
The improvements in the synthesis of mono-elemental films, transition metal dichalcogenides, and ditellurides on selected optical substrates foreseen in the project will allow the fine control of thickness, surface coverage, and uniformity, defectivity, and chemical purity. This material engineering was somehow limited so far because the fabrication of devices mainly relies on exfoliated materials.
- Development of theoretical methods.
There are currently very few first-principles methods for X-ray absorption, especially in real-time-TDDFT and the development proposed here will be significant for the simulation of a very wide range of X-ray and strong field experiments beyond the work proposed in the network.
- Advances in the investigation techniques available at FELs.
Sub-ten nanometer transient grating combined with the multicolor options of the new light sources permits the realization of transient nanometric structures that could mimic e.g. nanodots, still maintaining the chemical selectivity and the ability to time resolve the transport dynamics.
- Development of tabletop, bright soft X-ray source.
High-order harmonics are generated when an intense laser pulse is focused on a gas medium: due to the strongly nonlinear interaction, very high odd harmonics of the driving pulse optical frequency can be generated, leading to the production of a train of light bursts with attosecond duration in the XUV and soft X-ray spectral region. Novel schemes based on HHG for pump-probe experiments on isolated atoms/molecules, liquid, and solid-state samples will be developed.
- Development of high-speed X-ray detection
A significant challenge in X-ray spectroscopy is the ability to measure very small changes in the absorption near the K-edges of the atomic elements under investigation with a very high signal-to-noise ratio. Schemes with high detection efficiency in the soft X-ray spectral range and a high-speed readout for “pump-on” and “pump-off” measurements are a prerequisite for the success of these experiments with low-photon-flux tabletop sources. The development of novel CMOS detectors is foreseen for this purpose.
- Advances in 2D material engineering.
The improvements in the synthesis of mono-elemental films, transition metal dichalcogenides, and ditellurides on selected optical substrates foreseen in the project will allow the fine control of thickness, surface coverage, and uniformity, defectivity, and chemical purity. This material engineering was somehow limited so far because the fabrication of devices mainly relies on exfoliated materials.
- Development of theoretical methods.
There are currently very few first-principles methods for X-ray absorption, especially in real-time-TDDFT and the development proposed here will be significant for the simulation of a very wide range of X-ray and strong field experiments beyond the work proposed in the network.
- Advances in the investigation techniques available at FELs.
Sub-ten nanometer transient grating combined with the multicolor options of the new light sources permits the realization of transient nanometric structures that could mimic e.g. nanodots, still maintaining the chemical selectivity and the ability to time resolve the transport dynamics.
- Development of tabletop, bright soft X-ray source.
High-order harmonics are generated when an intense laser pulse is focused on a gas medium: due to the strongly nonlinear interaction, very high odd harmonics of the driving pulse optical frequency can be generated, leading to the production of a train of light bursts with attosecond duration in the XUV and soft X-ray spectral region. Novel schemes based on HHG for pump-probe experiments on isolated atoms/molecules, liquid, and solid-state samples will be developed.
- Development of high-speed X-ray detection
A significant challenge in X-ray spectroscopy is the ability to measure very small changes in the absorption near the K-edges of the atomic elements under investigation with a very high signal-to-noise ratio. Schemes with high detection efficiency in the soft X-ray spectral range and a high-speed readout for “pump-on” and “pump-off” measurements are a prerequisite for the success of these experiments with low-photon-flux tabletop sources. The development of novel CMOS detectors is foreseen for this purpose.