Research directions / Objectives
The research activities of the team are focused in the directions of Observational as well as Theoretical Astrophysics.
- Observational Astrophysics
The observational efforts of the group are based on data obtained with Skinakas Observatory, Space observatories (e.g. Chandra, XMM-Newton, Hubble Space Telescope, Spitzer Space Telescope, Herschel Space Telescope), and other major ground-based telescopes. The members of the team lead research programs in the following areas:
- X-ray emission from black holes (characterization of variability and spectra as indicators of black-hole mass and physical processes in accreting material).
- Multi-wavelength emission from accreting X-ray pulsars (connection between gas reservoir and accretion, interaction of pulsar magnetosphere and the accretion flow).
- X-ray emission from Anomalous X-ray pulsars (interpretation of their X-ray spectra in the context of accretion from a fall-back disk).
- Accreting binary populations in nearby galaxies (connection of accreting binaries and star-formation activity; the nature of Ultra-luminous X-ray sources; parameters influencing accreting binary formation and evolution).
- Mid-infrared properties of Luminous and Ultraluminous Infrared Galaxies (LIRGs/ULIRGs) (the nature of activity in the most luminous galaxies in the Universe).
- Star formation and stellar populations in Hickson Compact Groups.
- Multi-wavelength studies of interacting galaxies (the evolution of star-formation and nuclear activity along the merger sequence).
- Extragalactic large-scale jets (study of the polarization and the magnetic field structure in large scale jets emanating from accreting supermassive black holes).
- Interstellar magnetic fields (measurment of the interstellar magnetic field in our Galaxy by measuring the polarization of background sources).
- Detection of exoplanets (intensive monitoring with Skinakas of exoplanet candidates for the identification of exoplanets and measurements of their parameters).
- Theoretical Astrophysics
The theoretical efforts of the group are focused in the following areas:
- X-ray emission from accreting black-holes (modeling the physical processes in the accretion flow, and the resulting energy and Fourier spectra).
- Anomalous X-ray pulsars (modeling of the accretion flow onto X-ray pulsars; interpretation of observational results in the context of the fall-back disk model).
- Jets from accretion flows (emission mechanisms in astrophysical jets; spectrum, variability, and polarization of resulting emission).
- Dark matter (constraints on the nature of dark matter particles by modeling their high-energy signatures).
- Physical processes in star-formation.
- Modeling the Spectral Energy Distribution of Galaxies (deriving the physical connection between the interstellar medium and star formation in galaxies).
- Astrostatistics (Application of statistical methods in astrophysical problems).
The group is fundamentally interested in complex systems and applications. After making several contributions in the area of nonlinear metamaterials we focused on superconducting metamaterials were we brought about new properties such as left handedness, existence of breathers and chimeras and various other nonlinear modes. Currently our work is targeting the merging of complex systems with machine learning (ML) and attempts to produce meaningful and useful applications.
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Research directions / Objectives
The objectives are three fold, the following:
The study of low-dimension materials including C-based and Si-based materials as well as 2D-transition metal dichalcogenides (e.g. MoS2); their exploitation in nanoelectronics (especially in the form of nanoribbons, nanotubes and nanowires) and in the production and storage of green energy.
The study of magnetism of small metallic grains and their exploitation for producing advanced magnetic storage materials and new generation of sensors.
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Objectives:
The lab studies quantum materials, an umbrella of systems engaging atomic-scale building blocks, bearing strongly interacting elementary units (cf. charge carriers and electric/ magnetic moments) that give rise to collective phenomena, with remarkable physics (cf. quantum size-effects, spin liquids, superconductors, magnetoelectrics etc).
From size-controlled hybrid nanorystals to molecule-based materials, atomic structure insights enable the exploitation of selected crystalline solids for opportunities in innovative theranostics (e.g. image-guided therapeutics) or novel ways to supersede limitations in energy technologies (e.g. power transmission & use).
With the purpose to understand how the material's atoms are arranged and how their elementary units function, team members are encouraged to exploit our facilities in order to
- prepare/create solid-state compounds, for example, pertinent to mixed-valent transition metal oxides (chalcogenides or halides)
- measure basic physical properties, such as magnetic susceptibility, dielectric permittivity and electrical/thermal transport or optical activity
- correlate the macroscopic physical properties with the nanoscale rearrangements observed by synhcrotron X-ray and neutron scattering methods
- develop experimental tools involving external stimuli (e.g. pressure, magnetic field, laser light etc).
More elaborate experiments are done in collaboration with other research groups around the world. Strong links with theoretical teams assist our experimental efforts to choose the optimum set of materials and to justify our experimental findings.
Research Topics
Motivation:
Frustration arises when a system cannot minimize all the pair-wise interactions simultaneously because of local geometric constraints. Competing or frustrated interactions extend beyond the condensed matter physics and into biological materials, as for example, nature has the ability to "resolve" frustrated interactions in order to carry out some targeted biological activity.
Activity:
Frustration may give-rise to novel and complex phenomena that motivate us to (i) develop new class of materials, (ii) study cooperative phenomena in magnetism (e.g. magnetoelectric coupling) that provide fertile ground for testing theories of interacting systems that possess different spatial dimensions and sign of interactions that may impose local anisotropy of the basic interacting unit, the spin. Such fundamental studies can uncover mechanisms that benefit potential applications in low-power consumption devices and/or energy havesting technologies.
Literature:
Motivation:
Nanostructures with controlled size and shape, where magnetic and optical properties coexist, are most promising for innovative technologies (e.g. ranging from information storage to biomedical theranostics). Such a demand may be well-addressed when enhanced or collective magnetic/ photonic properties are established in nanoscale systems made of multiple subunits arranged in a controlled topological fashion through heteroepitaxial connections or self-assembled in secondary (e.g. cluster-like) structures.
Activity:
A major focus of our team entails the combination of chemistry and physics for the development of inorganic nanomaterials with potential in diverse applications. For this purpose, elaborate colloidal chemistry strategies are employed to control the nucleation and growth of nanocrystals (cf. zinc-blend, rock-salt, spinel, perovskite structural types) at moderate temperatures, while their multifunctional character is studied by bulk and local probe techniques. Moreover, directed-assembly of inorganic nanocrystals is chosen to provide a facile avenue to impart a collective nature in application-specific physical properties, offering the possibility for magnetically-driven image-guided diagnosis and therapy.
Literature:
Motivation:
Limitations of energy materials, and in particular for power transmission and storage, necessitates to decipher their workings at different length and time scales. In such an endeavor, cutting-edge tools are developed and implemented in real-word environments. Unique insights drawn in this way at the molecular or atomic level of matter, help understanding complex phenomena that are fundamentally important for discovering smart energy solutions. Amongst others, materials that could potentially transport electricity with zero resistance (cf. superconductivity) are the holy grail for improving dramatically the energy efficiency in electronics and power applications.
Activity:
It is our aim to identify structural rearrangements that accompany the different flow of electrons (i.e. from the charge reservoir to the conducting layer and vice-versa) in superconductors and the motion of charges in structurally related solid-state battery materials. Our activities devise alternative chemical pathways for single-phase model systems and based on them, attempt to parameterize the conditions leading to phases operating at elevated (critical) temperatures and/or offering the possibility to store higher energy density. The Lab strives to understand the physical or chemical interactions occurring on the atomic scale of intercalated layered transition metal chalcogenides / oxides. The outcomes contribute to clarifying the broader role of electronically-driven locally broken symmetries in triggering a phenomenon and creating useful physical properties.
Literature:
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We are exploring the interface between chemistry and physics of novel correlated electron systems and other bulk or nanoscale quantum materials that tackle energy-efficient technologies.
Activity:
In order to study different aspects of the structure, dynamics and functionality of new materials, the team engages:
- preparative solid-state chemistry & nanochemistry lab portfolios;
- various synthetic techniques including sol-gel and redox precipitation processes, in addition to conventional solid-state and colloidal chemistry high-temperature methods are been implemented. Nanocrystal functionalisation and bulk sample growth optimisations, with tools working at elevated temperatures (up to 1850 K), are available. There is great expertise in handling air-and moisture- sensitive compounds under anaerobic conditions, involving Schlenk lines and dry-box techniques.
- experimental stations for automated physical property measurements;
- materials bearing electronic phenomena and phase transitions, are tackled by a multimodal approach requiring strategic collaborations and appropriate development of in-house magnetic, dielectric, transport experimental and spectroscopic probes that are integrated in sophisticated sample environments, where applied electromagnetic stimuli can be flexibly utilized (e.g. low temperatures, high magnetic fields and elevated pressures).
- unique experimental tools (sought through peer-reviewed proposals) at European (ISIS-UK; PSI-Switzerland; ESRF-FR) and US (SNS-ORNL, NSLS-BNL) user-facilities of neutron, synchrotron X-ray and muon science.
Infrastructure Equipment
DC Magnetometer & AC Susceptometer, based on a MagLab-EXA 2000 multi-measurement system (Oxford Instruments) offers high resolving power in deciphering static and dynamic phenomena in low-moment, correlated electron systems of either bulk or nanoscale forms.
Applications:
Invaluable insights on the physical property materials response by measuring the moment versus applied magnetic field (e.g. hysteresis loops) or moment versus temperature, for deciphering static and dynamic phenomena associated with magnetic and superconducting materials. Its sensitivity is very high, therefore a small amount of sample is enough to ensure reliable signals. Automated measurements allow precise determination of the charasteristics of the superconducting state (e.g. crticial temperature, Meissner effect etc), as well as those of the Curie, Néel, and spin-glass states, including parameters such as the blocking or freezing temperatures of ferromagnetic, antiferromagnetic, superparamagnetic systems.
Specifications:
(a) High magnetic field (H= 0-7 Tesla), (b) Low-temperature liquid Helium cryostat (T= 1.8-350 K), (c) DC moment extraction (~10-4 emu), (d) AC susceptibility (~10-6 emu), f= 0.01-10 kHz, (e) samples of a few milligrams, can be accomodated in diverse morphologies, ranging from films and (nano)crystals to bulk forms – typical container, gelatin capsule ~15 mm long, with O.D. ~5 mm. The software measurement sequencer (open source) provides a set of high level actions to enable you to write and control measurements in a way that suit your own specific requirements.
The facility provides a modular experimental station to study the electrical characteristics of energy materials (e.g. electrode materials for Li/Na-ion rechargeble batteries), and beyond that the evolution of electric and magnetic dipole orders, as well as their degree of coupling, which is an identifying feature of a novel magneto-electric systems (e.g. sensors, high-capacity four-state logic memories etc.).
Applications:
This experimental station provides computer-controlled physical property measurements entailing a home-built modular sample environment offering to probe temperature (down to 2 K) and frequency (up to 2 MHz) dependent phenomena under externally applied electromagnetic stimuli (e.g. magentic fields up to 7 Tesla). It is equipped with custom-designed probes for mounting samples in various forms (e.g. polycrystalline pellet, single crystal, films), while the flexible integration of various types of digital measurement instruments allows automated data collection of physical quantities, including, Capacitance and Dielectric Loss, Voltage, Electric DC Current and Impedance etc.
Specifications:
Indicative capabilities include:
- low level sensitive measurements of current down to 10 aA (10 x10-18 A), electric polarization to charge levels down to 1 fC, very high resistance up to 210 PΩ (1018 Ω) and even I-V characteristics by a two-electrode configuration
- low noise voltage (down to 50 nV) measurements, characterization of low resistance/resistivity specimen by a standard four-wire setup (10 μΩ - 10 MΩ) and even Hall effects by Van der Pauw wiring
- impedance spectroscopy for precise measurement of capacitance and loss over a choice of frequencies, ranging from 50 Hz - 20 kHz, with a precision (AH 2700) bridge, and extended up to 2 MHz (with an option for DC-bias ±40 V), with an LCR meter (Agilent E4980A).
- continuous flow cryostat (T= 1.8-320 K)
- superconducting magnet (H= 0-7 Tesla)
The nanochemistry facility entails exploitation of elaborate colloidal chemistry approaches (ambient and high-temperature) to harness nanoscale size and shape-guiding mechanisms that afford various kinds of functional nanocrystals (single-phase, core@shell, anisotropic, hybrid particles) with tunable response (semiconducting, metallic, magnetic etc). Multidimensional nanostructures, such as cluster-like nanoarchitectures or periodic nanoparticle superlattices could also be realized by exploiting our know-how on directed assembly methods in liquid media.
Applications:
The aim is to provide a user-oriented platform for cost-efficient, easily scaled-up fabrication of novel inorganic nanoparticles, as well as their complete understanding that facilitates their use in diverse and interdisciplinary applications, from data storage and electronics to catalysis and biomedical imaging/therapy.
Basic Tools:
Projects benefit from controlled requirements for nanocrystal growth under anaerobic conditions met by the offered tools (e.g. Schlenk techniques, including digital temperature control growth conditions, Ar-circulating glove-boxes) that are combined with an armory of in-house characterization methods (structural, optical, electrical, dielectric, magnetic etc.).
- Chemical hoods equipped with vacuum-inert gas lines (Schlenk type), Glove-boxes, Centrifuges, Digital temperature controlled heating mantles, Magnetic stirrer hot plates, Incubators, Analytical balances
- Conventional and CCD-assisted stereoscopes, KBr hydraulic press, Glass-blowing propane torch
- Single and two-zone programmable furnaces (up to 1600°C) for vacuum or gas-flow reactions, High-vacuum line with portable programmable furnace for CVT (cf. sublimation & degassing), Thermogravimetric analysis
In everyday life generating and measuring temperature is straightforward, but in the quantum world, which reflects the behaviour of atoms, controlling the temperature is extremely more challenging. At very cold temperatures (cf. -269°C or near zero on the Kelvin temperature scale), as atoms are frozen, we can 'see' unique phenomena that would otherwise be masked by the thermal motion of atoms. As, complex materials are more likely to uncover their quantum properties at cold sample environments, low temperature refrigeration is an essential requirement.
Applications:
A tailored-made, small-scale facility that supplies liquid helium (He) for the needs of our variable-temperature physical property measurement equipment. Reaching temperatures of a few degrees Kelvin that is super cold with respect to ambient, employs artificial means, resting on a pumped helium system, built around a digitally controlled pulsed tube cryorefrigerator. With this technology, warm helium gas comes in contact with the Cold Head, where its thermal energy is absorbed into the 4 K (-269°C) heat exchanger. The process reduces the He-gas temperature, increasing its density, dropping it lower inside a condensing chamber; until it contacts the 4 K surface, where it condenses.The facility recycles the valuable helium gas that boils off from the liquid He dewars of the SQUID magentometer and the magento-electric workstation cryostat operating in our Lab.
Specifications:
The CRYOMECH PT410 re-liquefier is designed to recondense the boil off from liquid helium dewar/cryostats. As the boil off rates may vary depending on the type of temperature-dependent experiments being carried out, we have developed a peripheral medium-pressure vessel assembly, where the excess He gas is stored for future use. This gas is prone to contamination from impurities, like O2 and N2 species, which can reduce the efficiency of the re-liquefier. To this extent a custom-made, digitally-controlled He-gas purification system has been engineered to remove the impurities from the He-gas stream by means of chemical adsorption techniques. All in all, the facility is designed to return the liquid helium to the original dewar/cryostat, establishing a closed He loop, with an average liquefication rate of about 10 lt/day.
Simultaneous Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC) based on a computer-controlled SDT Q600 TA-instruments apparatus.
Applications:
SDT Q600, is an analysis system capable of performing DSC and TGA at the same time, and as such it removes experimental and sampling variables in data analysis. The information provided differentiates endothermic and exothermic events, which have no associated weight change (e.g. melting and crystallization or even long-range magnetic order) from those which involve a weight change (e.g. degradation).
Specifications:
The SDT measures the heat flow and weight changes associated with transitions and reactions in materials, from ambient temperature and up to 1500°C. The system entails a physical property sensor (cf. thermocouple, balance), a controlled atmosphere (e.g. noble gas, O2/air) furnace and a temperature programmer, all interfaced to a computer, allowing for a bi-modal operation, namely:
TGA characterizes any material that exhibits weight loss or phase changes as a result of decomposition, dehydration, and oxidation. Two modes are commonly used for investigating thermal stability behavior in controlled atmospheres: (a) dynamic, in which the temperature is increased at a linear rate, and (b) isothermal, in which the temperature is kept constant.
DSC is acomplissed by employing a single heat source and two symmetrically located and identical sample platforms at the end of two parallel beams. Thermocouples, welded at the center of the sample platforms, measure the differential heat flow to the sample and reference as both are heated at a uniform rate by the furnace. Sample temperature is also monitored directly by the thermocouple in the sample platform. With proper calibration, the heat flow associated with endothermic and exothermic transitions in materials can be measured to a high degree of accuracy and precision (+ 2%). Without calibration, the heat flow results obtained are qualitative (DTA).
Sample-containing cup sizes
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alumina ceramic 40 µL, 90 µL (recommended for DSC-TGA studies)
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platinum 40 µL, 110 µL (recommended for TGA-DTA studies)
A preparative solid state chemistry laboratory is set up, where various synthetic techniques including sol-gel and redox precipitation processes, in addition to conventional solid-state high-temperature methods, are been implemented.
The materials straddle to a portfolio of transition metal oxides, mixed-metal chalcogenides, and all the way to hybrid perovksites.
In addition, intermetallic compounds can be grown with an arc-melting furnace (>2000 oC) equipped with a water-cooled copper hearth. The system is easily purged (vacuum & Ar-gas) allowing specimens of metal ingots to be rapidly formed with good purity.
Basic Tools:
- Glove-boxes for Air- and Moisture- Sensitive Compounds
- High Vacuum (P<10-4 mbar) or Helium-Flow Glass Line for Medium-Temperature (<1100 oC) for Solid-State Syntheses.
- High-Temperature Programmable Electric Furnaces (<1600 oC) for Solid-State Reactions.
- Chemical Vapor Transport Reactions (<1000 oC)
- Intercalation Reactions ("Soft Syntheses" at 40-80 oC).
- Solvo-/ Hydro- thermal Reactions (Teflon-lined Autoclaves: 23 mL, 250 oC, 1800 psi).
- Thermal Evaporator (Thick Film Growth: ~100 μm ).
Where necessary samples are flame sealed in evacuated glass or silica ampules and annealed at the required temperatures.
Distinctions
U.S. Grant Award (Fulbright Greece)
Fulbright Award (FORTH Research Highlights)
3rd Applied Research & Innovation Competition («Η ΕΛΛΑΔΑ ΚΑΙΝΟΤΟΜΕΙ»)
Chaire TOTAL de la Fondation Balard (Pôle Chimie Balard)
Outreach
Disorder in Magnetic Nanocrystals May Improve Cancer Treatment (BNL Feature Story)
Alexandros Lappas 2016-2017 Fulbright Visting Scholar (Greek Alumni Speak - Highlights Achivements)
Frustration in Two-dimensions (ESRF Scientific Highlights)
On-line lectures/ interviews
Tweaking Nanoscale Magnetism (E-MRS 2021 Spring Meeting, Symp-S - Invited Talk; credit IESL-FORTH)
Nanomaterials for Energy & Health Applications (ERT TV 'O3' - Interview; Greek language)
In the Battle Against Cancer (TV CRETA 'De Facto' - Interview; Greek language)
Broader Readership
Nanoscale Particle Organization & Photonics (credit IESL-FORTH)
Nanocrystals: Good Things in Small Packages (credit IESL-FORTH)
Lab website (early times)
Functional Nanocrystals and Quantum Magnetism Lab (External Website)
The Functional Polymer Nanostructures group aims at developing functional nanostructured materials, which possess specifically designed properties and tuning capabilities. The group focuses on understanding the relationship between microstructure-dynamics-properties of polymeric and hybrid materials, and on optimizing properties and designing novel advanced and functional materials.
The main activities include the investigation of: the morphology and dynamics of multi-constituent polymers (including polymer mixtures, block copolymers, homopolymer / copolymer mixtures, star and hyperbranched polymers) in bulk and in restricted geometries; the study of polymer surfaces, interfaces and thin films and the development of polymer coatings; the investigation of functional and responsive polymer materials and material surfaces; the study of polymer nanocomposites; the development of nanoparticulate catalysts for the chemical industry as well as the development of polymeric materials for applications in the field of energy. The investigation involves the design of the functional materials, the characterization of the structure, chain conformations and the dynamics in the melt, in solution and close to surfaces or under severe confinement as well as the study of the thermal, surface, mechanical, rheological, optical, optoelectronic and magnetic properties and their response to selected external stimuli. Such systems target specific applications ranging from every day commodity products, to greenhouse films in agriculture, to coatings-paints and adhesives for the automotive and aerospace industries as well as polymer electrolytes for batteries.
Research Topics
The Functional Polymer Nanostructures group aims at developing functional nanostructured materials, which possess specifically designed properties and tuning capabilities. The group focuses on understanding the relationship between microstructure-dynamics-properties of polymeric and hybrid materials, and on optimizing properties and designing novel advanced and functional materials.
The main activities include the investigation of: the morphology and dynamics of multi-constituent polymers (including polymer mixtures, block copolymers, homopolymer / copolymer mixtures, star and hyperbranched polymers) in bulk and in restricted geometries; the study of polymer surfaces, interfaces and thin films and the development of polymer coatings; the investigation of functional and responsive polymer materials and material surfaces; the study of polymer nanocomposites; the development of nanoparticulate catalysts for the chemical industry as well as the development of polymeric materials for applications in the field of energy. The investigation involves the design of the functional materials, the characterization of the structure, chain conformations and the dynamics in the melt, in solution and close to surfaces or under severe confinement as well as the study of the thermal, surface, mechanical, rheological, optical, optoelectronic and magnetic properties and their response to selected external stimuli. Such systems target specific applications ranging from every day commodity products, to greenhouse films in agriculture, to coatings-paints and adhesives for the automotive and aerospace industries as well as polymer electrolytes for batteries.
The Materials Synthesis Laboratory (MSL) has extensive experience on the synthesis, characterization and applications of polymeric and organic/inorganic hybrid materials, polymer colloids, “smart” stimuli-responsive materials, water-soluble/amphiphilic polymers, biologically active (co)polymers, supramolecular assemblies, micellar nanostructures, polyelectrolytes/polyampholytes, microgels/hydrogels and the modification of flat and curved surfaces. The group has extensive experience on “living” and controlled polymerization techniques such as, Group-Transfer Polymerization, Atom Transfer Radical Polymerization (ATRP) and Reversible Addition Fragmentation Chain-Transfer (RAFT), to prepare polymers of controlled macromolecular characteristics (i.e. molecular weight, and molecular weight distribution, composition and architecture). MSL is an internationally-renowned group in the field of multi-responsive and biocompatible/biodegradable polymers for biomedical applications such as targeted and controlled drug delivery, gene therapy and tissue engineering.
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Our mission, research focus and main scientific directions
We aim to understand the underlying mechanisms underpinning the behavior of soft materials by linking fundamentals (molecular interactions and conformations) to microscopic structure and dynamics (in two and three dimensions) and final material properties (mechanical, optical, interfacial). Our long-term goal is the molecular design of soft materials with tailored performance.
The rigorous study of the properties of soft materials involves devising protocols, using state-of-the art experimentation and developing specialized setups, as well as synergy of synthesis, specialized characterization, theory, simulations, and physical experiment (including access to specialized infrastructure). Examples of in-house instrumentation include evanescent wave dynamic light scattering, in-situ combination of rheometry with light scattering or microscopy, high-frequency rheometry and nonlinear rheometric tools.
The group’s strength lies on the experimental study of dynamics and rheology of well-characterized materials and determination of the physical origin of their response. Our ambition is to maintain and further enhance the Institute’s position as international pillar in soft matter research.
In this direction, we address outstanding problems in polymer and colloid physics, challenge theories, and open new directions. Current thematic directions (with main goals in parenthesis) are listed below:
- Associating polymers and networks (tailor mechanical reinforcement toward strong and deformable networks)
- Repulsive and attractive colloids (role of attractions in the flow of colloidal glasses)
- Colloidal gels (new routes to novel states, optimize processing conditions to tune properties)
- Anisotropic colloidal particles (rich state behavior and flow phenomena)
- Polymer topology (viscoelasticity, resistance to stretching due to interlocking, supersoft elastomers)
- Biomacromolecules and hydrogels (biological problems, protein solutions, mixed hydrogels)
- High pressure effects (phase behavior, dynamics, supramolecular polymers, industrial applications)
- Soft composites (tailor rheology and mechanics, bridge polymeric and colloidal behavior)
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The activity focuses on advanced materials and devices for energy, environment and electronic applications.
Research Topics
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An emerging activity focusing on exploration of quantum computing and hardware development that enables quantum technologies to be experimentally developed. Developed devices are based on polariton condensates, low dimensionality electronic quantum systems, spin waves and III-Nitride based qubits aiming at high temperature quantum information systems.
Research Topics
Quantum nanoelectronics technology comes into stage mainly to give an answer to the speed and energy consumption dilemma of semiconductor nanoelectronics. MRG is working towards an in-depth investigation of the most profound manifestation of the effects of quantum coherence on macroscale and the related quantum phenomena that hold the maximal potential to become emergent new generation electronics. The main objectives tackled are the following:
- Quantum transport in quasi 1D superconductors
- Relaxation of non-equilibrium quasi particle excitations in superconductors
- Size dependence of critical temperature of superconductors
This is a new activity for the group that was officially launched in early 2018 based on the excellence of the group in both the growth of state of the art compound semiconductor hetero (nano)structures as well as in the realization of novel nanodevices.
A future quantum technological era based on the manipulation of spin, quantum superposition, and coherence is foreseen to radically transform technology, science and society. MRG investigates integrated qubits towards room temperature computing. The focus is on the development of novel concepts based on III-nitrides quantum dots exploiting specific material properties such as large bandgap and relatively long high temperature decoherence time. In addition single electron transistor (SET) structures based on 2DEG and 2DHG heterostructures are investigated by fabricating demanding top-down plasma etching and by electrostatic isolation through top metal gates, employing aggressive e-beam lithography with device scaling projected down to 10nm. Finally MRG will study the roadmap for the integration of the GaN QD technology into the FDSOI process.
The future miniaturisation of electronic circuits following Moore’s law will require the introduction of increasingly disruptive technologies to limit power consumption and optimise performance per circuit area. Spin wave computing aspires to complement and eventually replace CMOS in future microelectronics. Spin wave computing has the potential for significant power and area reduction per computing throughput while reducing cost by alleviating lithography requirements.
MRG is partner in an EU FET type funded project (“CHIRON”) that started in April 2018. As a first step towards the vision of a full spin wave computer, CHIRON envisions hybrid spin wave–CMOS circuits that can be readily integrated alongside CMOS. CHIRON will fabricate basic logic gates, such as inverters and majority gates, demonstrate their operation, and assess their performance. As transducers between the CMOS and spin wave domains in hybrid circuits, CHIRON will develop magnetoelectric and multiferroic nanoresonators, based on nanoscale bulk acoustic resonators, which bear promise for high energy efficiency and large output signal. MRG develops FBAR type nanoresonators targeting membrane thickness below 50nm and operating frequency higher than 10GHz while investigating their performance with numerous magnetostrictive materials. In addition different RF device designs and materials approaches like highly strained or doped III-nitride layers will be investigated.
Quantum simulators promise to provide unprecedented insights into physical phenomena not accessible with classical computers and have the potential to enable radically new technologies. Analog dynamical quantum simulators constitute a most promising class of architectures to fulfil the ultimate promise to devise quantum machines outperforming classical computers. Here, we devise versatile and practical platforms for dynamical simulators – making use of polariton condensate lattices and assess their computational capabilities, to probe important questions in fundamental and applied physics, ranging from technology‐relevant problems, concerning transport processes or glassy dynamics, via long‐standing challenges in the physics of non‐equilibrium phenomena. Optical lattices have attracted much attention, since they can replicate phase transition between a BEC and a Mott‐insulating state in a Bose‐Hubbard model. By experimentally modifying physical parameters, such as the periodic potential amplitude, temperature, and density, it is possible to control relative strength between on‐site interaction and hopping amplitude at will exploring the phase diagram of such systems. Such experiments have been of particular interest in the quantum information community since the experiment realizes a nearly ideal quantum simulator.
The macroscopic nature of exciton‐polariton condensates provides ease of optical access and probing of individual lattice sites normally not achievable in cold‐atom systems. Furthermore, the non‐equilibrium nature of exciton‐polariton systems is particularly attractive, because it provides the ability to prepare and study out of equilibrium many‐body phases in a natural driven dissipative setting and the ability to probe these phases in situ using optical approaches. Our recent experiments show that individual trapped polariton condensates can exhibit spontaneous magnetization, and that the spins of pairs of trapped polariton condensate can be controllably aligned. This constitutes a key step towards using trapped polariton condensates for the realization of interacting bosons in a driven‐dissipative spinor Bose‐Hubbard model. Hence, a lattice of polariton condensates is expected to model a non‐equilibrium interacting spin system with unusual properties. It is against this background that the field of polaritonics has emerged and these exotic objects are not simply an academic curiosity – rather as we discuss below we will use them as the basis for quantum simulators.
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Infrastructure Equipment
M4C setup (home made with COTS):
- AC Hall setup (magnetic field and current modulation modes, μ
- min < 0.05 cm2/Vsec)
- AC Seebeck setup (thermal modulation mode)
- AC Nernst setup (magnetic and thermal modulation modes)
Frontier, innovative research performed by the “PHOTONICS FOR HERITAGE SCIENCE (HS)” group for over twenty years has positioned IESL-FORTH among the leading centers worldwide for scientific research and technological development of cutting-edge laser and optical tools that offer new and efficient approaches to the diagnostics and conservation of works of art and antiquities. Emphasis is placed on: a) laser ablation methodologies for cleaning and restoration, b) laser spectroscopy for compositional analysis, c) multi spectral imaging and d) holographic metrology techniques for structural diagnosis.
The vision and the mission of this activity has been to develop state-of-the-art laser-based methods in order to a) enhance our understanding about cultural heritage (CH) materials and processes and b) provide versatile and effective tools for the analysis, diagnosis, preservation and restoration of archaeological/historical objects, works of art, and monuments.
The principal axes and the main developmental objectives of the individual activities are highlighted in the following:
Research Topics
Research at the Laser Cleaning (LC) group is developing novel laser ablation methodologies in order to meet a number of diverse conservation and cleaning challenges.
Highlights of this activity are:
- The initiation of a Bilateral collaboration between IESL-FORTH and the Conservation department of the PALACE MUSEUM in Beijing, CHINA with the aim to organize a common Laser Technology Joint Laboratory on Cultural Heritage with the name “NIKI” currently under the "One belt, One road initiative".
- The development of a prototype laser system and methodology for the removal of pollution encrustation from the Parthenon Sculptures, which ensures safe and controlled cleaning without discoloration side-effects. This methodology is being applied since 2002 in a number of sculptures at the Athenian Acropolis Monuments (i.e. the West Frieze, metopes and pedimental sculptures of the Parthenon, the >Frieze of the Athena Nike Temple, and the roof of the Caryatids’ porch in the Erechtheion).
Since 2011 it has been also included in the regular conservation practice of the Acropolis Museum and along these lines an advanced laser laboratory has been set up on the visitors’ floor where the Caryatids are exhibited. Removal of pollution accumulations from their surface takes place in this laboratory while visitors can follow live the cleaning process is carried out. Further synergies between the Acropolis Museum and IESL-FORTH have been planned in the context of an “open common laboratory” in which modern laser-based diagnostic and imaging techniques will be used for expanding the knowledge and deciding the best conservation practices for the exhibits.
Current research and activities aimed at:
- elucidation of laser induced side-effects in Cultural Heritage applications e.g. yellowing of stonework and pigments’ discoloration,
- optimisation of laser-assisted removal of polymeric over-layers from paintings,
- monitoring and control of the cleaning intervention through optical and laser-based techniques (spectral, optoacoustic, non-linear imaging, laser spectroscopies, holographic interferometry, etc.),
- realization of laser cleaning projects on important CH objects and monuments in the lab or in-situ.
Additionally, the implementation of laser technology to other challenges in Heritage Conservation is investigated.
Recently research efforts have been focused on the restoration of cracks and other pathologies found on the surface of glazed ceramics using laser irradiation; cracked glazed surfaces have been restored on the principle of laser-induced local and controlled melting of the existing glaze material (Restoration of vitreous surfaces using laser technology).
The main direction of the optical imaging activity is to develop new methods for the non-contact, non-invasive, in-situ examination and continuous inspection of CH objects. Applications include:
- mapping of varnish and paint layers,
- stratigraphic analysis and visualization of under-drawings,
- assessment of past conservation treatments,
- real time monitoring of cleaning interventions etc.,
on the basis of reflectance imaging and spectroscopy. The goal of this research is to investigate, quantify and expand the potential applications of spectral imaging on CH objects, while continuous technical developments both in hardware and software target to improve analytical capabilities.
Recently, a novel technique, Photoacoustic Imaging, predominantly developed in the context of biomedical research, has been applied on CH objects. The photoacoustic signal can overcome limitations of light and offer substantially improved detection sensitivity at high spatial resolution. The technique has been proved to be capable of uncovering “hidden” features in multi-layered CH objects such as paintings and determining the thickness of thin layers thus providing micrometric precision stratigraphic information. Finally, the potential of applying the photoacoustic signal for the in situ and real-time monitoring of laser cleaning interventions is currently investigated.
Laser Spectroscopic Analysis is necessary and sometimes vital for the examination of CH objects, since it provides information not only for their constituents but also for deterioration materials, pollutants and other substances that have developed throughout time on the objects and may lead to their aesthetic and structural decline.
Timely and accurate detection of these deterioration materials can lead to proper conservation and restoration treatments, which can safeguard and actually save the CH objects. Moreover, a series of questions can be answered such as the authenticity of artworks, style of the painter, etc, aiding the art historians to extract important information about the artist and his/her era. Furthermore, spectroscopic techniques can be applied to monitor various processes related to the protection of CH objects, such as the controlled removal of unwanted layers/encrustations, etc. using either laser radiation or any other conventional tools and methods.
PhoHS laboratory of IESL-FORTH has many years of expertise in a series of laser spectroscopic techniques, such as LIBS, LIF, Raman, SERS as well as spectroscopic techniques that use other light sources like LED-IF and Diffuse Reflectance. Along with the laboratory setups, compact/portable laser-based analytical instruments have been developed for in situ and field-deployable applications combining different spectroscopies in hybrid arrangements.
Laser Interferometry for Structural Diagnostics. The main direction of this activity is to investigate deformation, deterioration and fracture mechanisms in order to evaluate the structural condition of materials and systems.
The remote optical sensing of almost invisible defects and alterations, which allows their location, measurement and exact positioning within the structure of the object, as well as their monitoring through
- environmental and climate changes,
- conservation treatments,
- natural or provoked ageing,
- transportation or handling
are among the objectives of this research group.
This is achieved by the effective transfer of interferometric techniques and know-how to CH applications (artworks and monuments) and the continuous inspiration, design, development and implementation of new experimental processes, methodologies and instruments in order to exploit the full potential of laser metrology.
Since 2012 PhoHS at IESL-FORTH organises a series of training activities inviting conservators, conservation scientists, and other Heritage disciplines for an exciting journey to Crete to become acquainted with the latest developments on non-invasive optical technologies and explore their field applications in Cultural Heritage research and conservation.
The aim of OPTO-CH summer courses is to introduce participants to the applications of advanced laser-based technologies in Heritage Science. Lectures from experts on modern laser diagnostic and analytical techniques and laser cleaning methodologies are combined with practical demonstrations and laboratory hands-on sessions. Field experiments on-site at a selected monument in Crete are organised in order to demonstrate the applicability of the techniques in practice.
Further info at https://opto-ch.iesl.forth.gr/
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PhoHS Infrastructure and Portable Instrumentation
Access provider: Photonics for Heritage Science, IESL, FORTH
The researchers of IESL-FORTH, respond to the need for on-site material analysis with the development of portable or transportable instrumentation that has been optimized for in situ applications. A long list of related activities includes integrated analytical approaches applied in several field campaigns at museums and archaeological sites in Greece, Europe and the Middle East. The developed portable instrumentation includes:
- Laser Induced Breakdown Spectroscopy system
- Diffuse reflectance Spectroscopy
- micro-Raman Spectroscopy system,
Services
- Analysis and chemical characterization of materials in archaeological objects, artworks or historic monuments such as metals, stones, glass, paints and pigments, organic materials, etc.
- In-depth analysis of multilayered surfaces
- Investigation of degradation materials on different substrates
Related info
http://www.iesl.forth.gr/research/laser.aspx
Infrastructure Equipment
IESL-FORTH holds a number of laser systems with different wavelength, pulse duration and energy output characteristics available for laser cleaning investigations such as:
- Transportable Q-switched Nd:YAG lasers (Quantel Q-smart 850, LITRON TRLi, Spectron SL-805 modified, Quanta Palladio, BMI 5022 DNS 10) emitting both nano- and pico-second (EKSPLA SL 312) laser pulses at various wavelengths (such as 1064, 532, 355, 266 & 213 nm)
- Various excimer lasers emitting nano, pico and femto-second pulses in the UV
- A patented transportable ns Nd:YAG system with dual-wavelength beam output, developed for the laser cleaning project of the Athens Acropolis Monuments especially dedicated to remove pollution crust from stonework without any discoloration or damage
- A transportable LQS Nd:YAG system (ElEn, EOS1000) emitting IR pulses at longer pulse-widths
- An Er:YAG laser system (LITRON NANO L 200-20-Er) emitting at 2094 nm
- A continuous CO2 laser system (Coherent Diamond C20) for the patented application related to the laser conservation of glazed objects.
Various workstations adaptable for different laser cleaning applications with the ability to integrate different optical and opto-mechanical components for the most appropriate beam delivery and control are available such as:
- Handheld units (using a articulated mirrored arm)
- Automated beam scanning units for micrometer control and guidance of the laser beam to the sample (i.e. the painting surface).
The latter, a computer-driven mechanized component, can be adjusted on the basis of fluence values, spot size and pulse repetition rate enabling thus the homogeneous scanning of predefined areas.
Furthermore, a number of multi-modal diagnostic instruments for in-situ assessment of the cleaning result and monitoring of the laser ablation procedure are also available. These can be selected according to the specifications of each individual cleaning case and may be one or more of the following:
- Spectral Imaging to visualise the cleaning state
- Laser-Induced Fluorescence (LIF) to evaluate the thinning of varnish
- Vis-NIR Diffuse Reflectance spectroscopy to chemically characterise the irradiated surfaces
PhoHS group has developed an innovative, transportable ns Nd:YAG system with dual-wavelength (2λ) beam output.
The 2λ prototype, is capable of operating at two wavelengths simultaneously (infrared at 1064nm and ultraviolet at 355nm) and is able to remove thick pollution accumulations in a controlled and safe way for both the object and the operator. The combination of the two wavelengths ensures that no discoloration or damaging phenomena occur on the original substrate while revealing its unique ancient surface. The system is being used on the Athenian Acropolis Sculptures since 2000 till nowadays.
The two-wavelength laser cleaning methodology was suggested and developed in 2001 aiming to address a number of conservation challenges and side-effects; yellowing discoloration of stone surfaces being the most characteristic. The methodology allows the regulation of different laser material ablation regimes and thus can be adapted to different cleaning issues with emphasis to cases in which conventional laser cleaning methodologies (i.e. using IR wavelengths) are not effective or successful. As a general rule for the combination of the 1064nm and 355nm their relative ratio is determined on the basis of the composition and morphology of the material to be removed. In order to remove relatively thick and inhomogeneous crusts the contribution of the IR beam (which is highly absorbed by the bulk of the crust) must be dominant, while for thinner soiling layers UV favoured ablation is recommended. Further research and fine-tuning, of the 2λ methodology on different cleaning challenges provided encouraging results as for example the combination of 1064nm and 532 nm, which has been found particularly promising for the removal of biological encrustation from stonework.
Ιn 2012 the International Institute for Conservation of Historic and Artistic Works (IIC) appreciated the collaborative efforts of the Acropolis Museum and IESL-FORTH to remove controllably dark pollution crusts and reveal the authentic marble sculptures on the basis of this prototype laser system which was operating openly (but safely) at the Museum. The 2012 Keck award was jointly given to the two organisations highlighting the “Laser rejuvenation of Caryatids opens to the public at the Acropolis Museum: A link between ancient and modern Greece”.
PAλλAS is a result of the CALLOS project and was developed at the Institute of Electronic Structure and Laser of FORTH by the Photonics for Heritage Science Researchers, in collaboration with the conservators of EACA. It was created to address the analytical challenges often faced in Athenian monuments."
Introducing PAλλAS, a cutting-edge Nd: YAG system that offers a triple-wavelength output at 1064nm, 523nm, and 355nm, all in a portable design.
The three-wavelength operation can efficiently remove thick pollution accumulations and biological crust in a controlled and safe way for both the object and the operator. By combining pairs of wavelengths every time, we ensure that an efficient result occurs without any discoloration phenomena on the original substrate while revealing its unique ancient surface.
The PAλλAS laser cleaning system is one of the primary innovative tools used in the Open- to the- public conservation laboratory located in the heart of Athens at the premises of the Ephorate of Antiquities of Athens (EAA).
IRIS-II, a portable MultiSpectral Imaging instrument, enables the compositional and structural study of multi-layered Cultural Heritage surfaces. It is fully portable enabling thus the examination of objects in situ (museums, conservation laboratories, archaeological areas etc.). This imaging system, provides detailed information related to the physical and chemical properties of materials, based on reflection and fluorescence spectroscopy.
The main elements of the multi-spectral imaging system include a camera, an imaging monochromator equipped with a filter wheel of 28 band-pass filters, the objective lens, electronics and a computer that controls all the components. The camera used on the system is a monochrome digital CMOS camera. The spatial resolution is 5MPixels, while the dynamic range applied is 8 bit. This sensor is sensitive from 350 nm up to 1200 nm.
The whole system is designed to be portable and can be carried in a small case.
Finally, custom-made software, entirely developed in LabView is employed. This software enables the control of the system and the data acquisition. Additional processing software for images normalization, calibration and analysis is also developed and used.
The DHSPI (Digital Holographic Speckle Pattern Interferometry) systems have been developed and continuously optimized at IESL-FORTH with the aim to investigate and monitor deformation, deterioration, and fracture mechanisms and thus to evaluate the structural condition of materials and systems as a result of ageing, mechanical alteration and materials’ failure.
DHSPI captures microscopic alterations of sub-surface topography on the basis of high-resolution interferometric imaging. Hidden defects are revealed as visible interference fringe patterns forming locally inhomogeneous intensity distribution patterns. The deformation data are extracted through the differential displacement of the surface under investigation and the deformation value is measured by multiples of half wavelength.
DHSPI-II, the most recent model, is a compact fully portable system with a built-in data acquisition and processing unit and dedicated user-friendly software, for the system control and data post-processing which enables real-time qualitative and quantitative structural diagnosis. DHSPI-II also allows control (via cable) from a remote pc (eg laptop) which provides extra flexibility for in-situ measurements.
TECHNICAL INFO: •Laser power: 300mW •Coherence length: >30m •CCD resolution: 5MP •Spatial resolution: 144 lines/mm •Displacement resolution: ≥ 266nm •Sensor lens: C-Mount type exchangeable •Beam Divergence: >40cm@1m (Gaussian Profile)
The optimized for CH diagnostic applications photoacoustic (PA) imaging system can reveal well-hidden features in paintings or layered documents and provide structural information of optically opaque layers in artworks. Furthermore, a novel non-contact PA monitoring apparatus can record the intrinsically generated acoustic waves during laser cleaning interventions on stonework or paintings, allowing for precise control of the process.
The non-invasive PA imaging apparatus employs a Q-switched Nd:YAG laser (SL404, Spectron Laser Systems, maximum pulse energy 30 mJ, pulse duration: 10 ns, pulse repetition rate: 10 Hz) emitting near infrared radiation at 1064 nm for the efficient excitation of PA signals. Each sample is firmly fixed on a custom-made holder and irradiated using an adjustable energy fluence to generate PA waves from optically absorbing regions, which are detected in ambient air by a spherically focused non-contact transducer (NCT1-D7-P10, The Ultran Group, nominal central frequency: 1 MHz; focal distance: 10 mm; numerical aperture: 0.31). The signals are subsequently enhanced by a low-noise RF amplifier (62 dB amplification) prior their digitization and recording by an oscilloscope (DSO7034A, Agilent Technologies, bandwidth: 350 MHz). To form an image, the sample is raster scanned along its surface using a set of high precision XY motorized stages, to attain a point-by-point data acquisition in synchronization with the trigger signal of the laser source. The recorded waveforms are processed for high frequency noise elimination before the estimation of the peak-to-peak PA amplitude value, providing the contrast of the final reconstruction.
The PA monitoring apparatus either a contact or an air-coupled ultrasonic transducer for the detection of acoustic waves in the 1-5 MHz regime. Following the incidence of each cleaning pulse, the generated PA signal is digitized and recorded through a high-speed oscilloscope which is synchronized with the laser trigger. Waveforms are processed in real time using custom-developed algorithms to provide multiparametric information on the progress of laser cleaning interventions including the material’s extraction levels, the accurate determination of effective cleaning, as well as, the evaluation of potential side-effects on the substrates.
The LIBS microscope has the capacity to provide fast elemental mapping of flat surfaces, typically cross-sections of geological samples, marine shells, bones, teeth etc. The 2D-elemental maps of the scanned surface can be used to identify the distribution of mineral phases in rocks, to measure the variability of elemental proxies related to paleoenvironment in shell studies or to assess the diffusion of environmental pollutants into hard tissues.
In the present micro-LIBS workstation a Q-switched Nd:YAG laser is used (λ = 1064 nm, pulse duration: 10 ns, pulse energy 5-20 mJ). The laser beam is focused on the sample through a laser objective lens down to a spot of 40 - 60 μm in diameter. The light emitted by the plasma is transferred via an optical fiber to the spectrometer which captures LIBS spectra for each one of the laser pulses that scans the surface. According to specific analysis requirements the spectral data is processed on-line or following completion of scanning. Samples are mounted on a motorized X–Y–Z micrometric stage and translated with respect to the laser beam that remains in a fixed position. The typical translation step is of the order of 100 μm. A CCD camera enables the user to have a clear view of the sample surface and to define the area that is to be mapped (any shape is acceptable). The measurement speed is about 0.9 s per point and each map could have 500 - 6000 points (i.e. an elemental map of 4000 points is obtained in about 1 hr). A dual spectrometer unit (AvaSpec-2048-2-USB2) records the LIBS signal (spectral range: 200 - 640 nm, resolution ~ 0.2 - 0.3 nm). For higher sensitivity, the signal can be recorded by a Czerny-Turner spectrometer (Jobin Yvon, TRIAX 320) with an ICCD camera (DH734–18F, Andor Technology) (spectral range ~ 45 nm).
TriENA is a hybrid system that combines three spectroscopic analytical techniques (LIBS, LED-IF, and DR) in one portable device. It is a deliverable of the CALLOS project and has been developed at the Institute of Electronic Structure and Laser of FORTH by the Photonics for Heritage Science Researchers, in collaboration with the conservators of EACA. The system is designed to meet the analytical challenges commonly encountered on Athenian monuments.
This hybrid mobile system combines three spectroscopic techniques: Laser-Induced Breakdown Spectroscopy (LIBS), Diffuse Reflectance Spectroscopy (DR), and LED-Induced Fluorescence (LED-IF), leading to an integrated characterization of the material under examination ‘in-situ’ with no sample removal or preparation restrictions. Moreover, the rapid data acquisition and the user-friendly software increase the system's applicability in archaeometry and art conservation.
LIBS offers a qualitative and semi-quantitative multi-elemental analysis, with its main advantage being the ability to perform stratigraphic analysis on a multi-layered object. The process involves focusing a compact Nd:YAG laser (1064 nm, pulse duration = 10 ns) on the object's surface using a lens, generating a micro-plasma. The emission from the micro-plasma is transmitted through a bifurcated optical fiber into a dual spectrometer unit (Avaspec-2048-2-USB2, Avantes) with a spectral range of 200 - 660 nm and a resolution of 0.2 - 0.3 nm. The analytical information is acquired within seconds.
Differential Reflectance (DR) and LED-Induced Fluorescence (LED-IF) provide information about the molecular composition of a material. DR is based on light absorption from the material, while LED-IF relies on fluorescence induced by a LED source. Both techniques are non-destructive, which makes them highly suitable for analyzing objects in cultural heritage and archaeology. A halogen tungsten lamp is used for the DR measurements, while for the LED-IF measurements, a LED source (375, 438, or 632 nm) excites the material. For DR measurements, a halogen tungsten lamp is used, while LED-IF measurements involve exciting the material with a LED source (375, 438, or 632 nm). To capture a wider range of spectra, the signals from DR and LED-IF are recorded using a low-resolution spectrometer (Avaspec-2048L-USB2, Avantes) with a spectral range of 200 - 1100 nm and a resolution of approximately 2.5 nm.
A miniature CCD camera provides a close-up view of the object's surface during analysis, allowing for precise aiming of the laser beam using a cross-hair indicator overlaid on the image. In addition, light sources, along with the required optics and a visualization camera, are integrated into a lightweight and compact optical probe head.
LIF provides information on the chemical identity of materials (in solid or liquid state) on the basis of their fluorescence properties.
LIF has been proven valuable for several fundamental and applied studies such as the following:
• Elucidation of the fundamental mechanisms underlying laser ablation of molecular solids
• Assessment and monitoring of laser cleaning of aged varnish layers on paintings has been investigated.
The LIF set-up developed for these purposes is coupled to a laser-ablation workstation using the same beam configuration. The laser-induced fluorescence is collected (at an angle of almost 45° with respect to the normal to the sample) focused, by a telescopic lens system, into a fused silica optical fiber and transmitted into a 0.25 m Czerny-Turner spectrograph (PTI Model 01-001AD), which is coupled with an ICCD camera (Andor Technology) for the detection of the fluorescence intensity. An XYZ micrometer stage ensures accurate alignment of the telescope-fiber system relative to the irradiated area. Fluorescence emission spectra are recorded in the selected spectral regions and are post-processed to give LIF spectra of the studied surfaces.
Raman spectroscopy gives details about the molecular structure of samples on the basis of the characteristic vibrational modes of the molecule. It can be used to identify a variety of materials (minerals, pigments, organics etc.) and the fact that it is completely non-destructive makes it extremely attractive for the analysis of invaluable objects, such as artworks and archaeological objects.
Our mobile Raman microspectrometer (Exemplar Plus, ΒWTEK) uses a cw (continuous wave) diode laser working at 785 nm as excitation source. An optical probe head focusses the laser beam onto the sample surface by means of a set of objective lenses offering different levels of magnification. A white LED and a digital colour camera are included on the optical head, which allow visualization of the object’s surface and selection of the area (spot) to be analyzed. The spectrometer provides high spectral resolution (< 8 cm−1) and sensitivity, covering a spectral range between 100 – 3300 cm−1. The employed detector (Peltier-cooled) features high sensitivity with low dark counts.
Relative Humidity (RH) ageing chamber
IESL-FORTH has developed this RH ageing chamber on the basis of a series of experiments focused on the DHSPI monitoring of environmentally induced changes on objects. It is a custom-made airtight construction with a main compartment for placing the samples under examination and two compartments under the main floor which receive trays with saturated salts solutions to change the RH inside the chamber. The airflow between the main compartment and the tray's compartments is controlled via slits which may gradually be opened or closed. An RH/T logger acquires, displays and monitors the Relative Humidity (RH) and Temperature (T) of the chamber.
Light ageing chamber
IESL-FORTH has developed this light ageing chamber on the basis of a series of experiments focused on laser thinning of aged and polymerised varnishes. It is a custom-made construction in which all mock-ups/objects are arranged so to receive direct illumination from a series of mercury discharge lamps. The intensity of light exposure onto the mock-up’s surface inside the chamber is measured using a TECPEL DLM-536 Light Meter with Data Logger (which monitors the RH and Temperature of the chamber) and the light intensity value reaching the surface is modified by adjusting its relative distance from the lamp. Various protocols have been developed according to each individual experiment.
Research directions / Objectives
A wide range of laser spectroscopic methods are employed for studying key properties of novel materials at the atomic, molecular or nano-scale and for determining the composition of complex materials.
In this context, employing ultrafast time-resolved methodologies we investigate the dynamics of fundamental processes in the condensed phase which govern the macroscopic properties of matter. Materials of interest range from molecular architectures mimicking photosynthesis to 3-D photonic nanocrystals and from laser-induced plasmas to strongly correlated systems. Furthermore, by way of advanced laser pulse tailoring schemes we investigate how non-conventional excitation of matter can lead to novel functions and properties of materials.
We also work on the development of optical sensing systems based on tailor-made nanostructures fabricated by use of laser-based techniques coupled to chemical growth methods.
In parallel, we explore versatile spectrochemical methods and develop relevant instrumentation for analysis of materials responding to a broad range of challenges extending from cultural heritage diagnostics to monitoring industrial processes.
Ultrafast and nonlinear light-matter interactions:
- Study of ultrafast light-matter interactions in bulk and nanostructured materials with strong electronic correlations and nonlinear properties.
- Control of ultrafast processes during laser-mater interactions with temporal pulse shaping.
- Study of nonlinear optical properties of 3-D photonic materials.
Analytical spectroscopy and instrumentation:
- Nanosecond and Femtosecond LIBS for the analysis of solids and liquids. Study of plasma dynamics.
- LIBS linked to SSI-MS (sonic spray ionization mass spectrometry) for the analysis of biomolecules.
- Development of compact/portable laser-based analytical instrumentation (mobile LIBS, stand-off LIBS, mobile micro-Raman).
- Applications of laser spectroscopic tools in relation to industrial process monitoring.
Opto-sensing:
- Laser fabricated micro/nano-structured materials as room-temperature optical sensors.
- Molecular and nanoparticle photophysics and photochemistry – Optical thermometry.
Research Topics
In this experimental research activity ultrafast time-resolved optical spectroscopy is employed to study the ultrafast processes that occur in condensed phase materials with novel optoelectronic properties following intense optical excitation by ultrashort laser pulses and characterize their ultrfast dynaimics. By utilizing the general pump-probe methodology the ultrafast electronic, lattice and magnetic interactions taking place in solids in the picosecond and the femtosecond temporal regime are investigated. Novel bulk and nanostructured photonic materials such as semiconductors, metals and dielectrics in confined 2D and 3D architextures have high priority in our research. The applications are related to the sectors of energy, health, environment.
At sufficiently high light intensities the irradiated material undergoes structural transitions described by ablation, spallation, processing, melting, evaporation, and others. The understanding of the evolution of the material from the moment of excitation until the final resolidification is very challenging due to the high number and the complexity of the photo-physical processes that occur: electron excitation, electron-lattice cooling, phase transitions, material re-solidification, etc. For many applications it is important to control the final morphology of the irradiated surface and its macroscopical properties. This is investigated by the use of spatio-temporally shaped ultrashort laser pulses. The goal is to observe, understand and control the microscopic and primary physical processes that occur following ultrashort laser excitation in order to to control the macroscopic properties of the finally processed material such as optical, morphological, chemical properties etc.
Optical sensing is based on the modifications of the optical properties (photoluminescence, transmittance,
reflectance etc) of metal oxides (ZnO, TiO2, NiTiO3 etc) upon exposure to an external stimulus.
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Infrastructure Equipment
Ultrafast Laser Amplifier repetition rate 1 kHz, center wavelength 800 nm, maximum pulse energy 0.8 mJ, minimum pulse duration 25 fs
Test document
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The pump-probe workstation consists of a 15 cm computer-controlled delay line, with a minimum step of 0.1 μm, and a 303 mm spectrograph with a CCD imaging camera, and a lock-in amplifier. The pump beam can be selected to be either the fundamental output of a Ti:Sapphire laser amplifier at 785 nm, or te frequency doubled second harmonic, or the output of a home-built noncollinear Optical Parametric Amplifier (NOPA) at 420 nm - 750 nm.
This workstation has a dual purpose:
(i) Laser-induced Forward Transfer of thin film spots on a variety of substrates.
(ii) Surface irradiation and micro-/nanoprocessing on a variety of solid surfaces.
The input to this workstation is a Ti:Sapphire laser amplifier at 785 nm, 25 fs, <0.8 mJ per pulse and its secondary sources.
