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RA1: Nanotechnology / Advanced Materials

Research in the area of Nanotechnology / Advanced Materials covers a broad range of activities in materials synthesis and advanced characterization in two main pillars, i.e. hard and soft condensed matter, representing multidisciplinary research at the interface between physics, chemistry, biology, and engineering. The various activities are shown in the chart and outlined in detail below:

A. Materials synthesis/fabrication/functionalization


B. Advanced Characterization Techniques


C. Modelling and Simulation


A. Materials synthesis fabrication

Zeolites and other microporous materials

  • Zeolite membrane synthesis, characterization and testing: The objective of this activity, in terms of application, is to synthesize supported polycrystalline zeolite membranes that can be used for the separation of gas or liquid mixtures. Significant effort has been placed on developing methods for elucidating the effect of adsorption on the zeolite unit cell size which in turn could affect the membrane perm-selective properties and mechanical stability.
  • Carbon membranes for gas separation: Carbon membranes are promising for separation of gas mixtures, because they possess ultra-micropores with size comparable to the kinetic diameter of light gases. Carbon membranes were prepared by pyrolysis of furfuryl alcohol-furaldehyde resin layers deposited on porous tubular ceramic supports. It was found that induction of separation selectivity requires the deposition of multiple layers by successive deposition-pyrolysis cycles. The membrane performance is influenced by surface diffusion effects, which are detrimental in the case of separation of H2-CO2 mixtures. Characterization of carbon membranes showed the presence of very small pores in the range of 0.3-0.4 nm in a matrix of amorphous carbon. Pyrolysis in the presence of iron leads to partial graphitization of carbon, which nevertheless does not improve the separation properties of the resulting membranes.
  • Development of zeolite-based composites for sensing applications: This activity aims at the development of composite materials consisting of a magnetoelastic material strongly bound to microporous inorganic films with selective adsorption properties. Even though a magnetoelastic alloy can be used for detecting changes in the pressure or in the velocity of a fluid, it cannot be used as is, for selective sensing of one compound in a mixture. Zeolites have the ability to recognize molecules based on their size or polarity, a property that can be used in sensing applications. This transformation can be achieved by synthesizing zeolite - magnetoelastic alloy composite materials.

Materials in aerogel form

  • Ultra-transparent silica aerogels: Aerogels are unusual low-density materials having unique properties, such as high porosity, large surface area and ultra-low thermal conductivity. The synthesis of silica aerogels with ultra-high optical Figure2transmittance and minimal shrinkage has been achieved by employment of tetraalkylammonium fluoride gelation catalysts and CO2 or solvent (high temperature) supercritical drying. The optimal catalysts (tetrabutyl and tetraoctyl ammonium fluoride) lead to the preparation of monolithic aerogels in the form of plates (10 cm x 10 cm x 1 cm) with density of 0.10-0.12 g cm-3, transparency in the visible range up to 96% and extinction coefficient as low as 3.5 m-1. The specific surface area is quite high in the range 600-800 m2 g-1. Both hydrophilic and hydrophobic aerogels have been prepared with the above method.
  • Carbon aerogels: Iron-containing carbon aerogels were prepared by carbonization of resorcinol-furaldehyde aerogels containing FeCl3. The goal of this activity was to develop cathode electrode materials for high-temperature PEM fuel cells in replacement of currently employed scarce and costly platinum. Resorcinol-furaldehyde resins containing iron chloride were prepared by three different drying methods: (i) conventional drying, (ii) CO2 supercritical drying and (iii) high-temperature supercritical drying. The drying method influences considerably the porous structure of the final material. Resins and carbon prepared via CO2 supercritical drying had the highest specific surface area (400-700 m2 g-1) and pore volume (up to 1.35 cm3 g-1) located at pores in the mesopore range (5-30 nm). The highest electrochemical activity was observed for Fe-C materials with the most open porous structure (large pore size combined with large pore volume) prepared via CO2 supercritical drying.

Metal Oxide catalysts
Transition metal oxides, such as MnOx and CuO, are active oxidation catalysts. Cerium oxide, CeO2, is widely applied in catalysis because of its oxygen storage properties and redox capability. It would be of interest to combine MnOx or CuO with CeO2 towards the development of improved catalysts. Mixed oxides of varying composition were prepared with a combustion method and tested in the oxidation of representative VOCs. Catalysts were characterized in terms of their structural and surface properties with a variety of techniques. Crystalline manganese oxide phases are absent in ceria-rich materials and Mn ions are homogeneously distributed between the bulk and the surface suggesting incorporation of Mn ions in ceria structure. The mixed oxides get reduced by H2 at lower temperatures than the corresponding single oxides and Mn ions promote reduction of ceria. The surface area of mixed oxide catalysts is larger than the one of single oxides prepared with the same method. The specific activity of mixed oxides, on the other hand, is smaller than the one of single oxides indicating that in mixed oxides the structural features are improved but not the intrinsic catalytic activity.

Advanced Amorphous Materials
Non-crystalline solids offer a number of advantages over their crystalline counterparts owing to their structural flexibility and their rich responsiveness to external stimuli. Temperature, pressure and irradiation are used as external stimuli to interrogate glass structure and manipulate glass properties. Representative research activities related to the science and technology of advanced amorphous materials include:

  • Photoinduced micro-/macroscopic phenomena in amorphous semiconductors
    Amorphous semiconductors (chalcogenides) are emerging functional materials with prospect for unique applications in photonic and optoelectronic devices. They experience a variety of changes in their physical-chemical properties when illuminated with near-bandgap light. Photostructural changes in chalcogenides can be thus exploited in practical applications such as memory storage, photonics, as well as in active and passive applications of optical fibers. Recent research activities have been focused on the following directions:
    • (i) Investigations of the microscopic nature of the photoplastic effects.
    • (ii) Elucidation of the atomic mechanism in phase-change materials (optical data storage).
    • (iii) Optically induced diffusion of metals (photodoping) in non-crystalline chalcogenides.
    • (iv) Highly non-linear chalcogenide glasses with applications in Raman amplifiers.
    • (v) Light-sensitive nanostructured amorphous thin films with enhanced optical switching.
    • (vi) Development of highly nonlinear soft-glass hybrid Photonic Crystal Fibers.
  • Development of highly nonlinear soft-glass hybrid Photonic Crystal Fibers
    Photonic crystal fibers (PCFs), consisting of micrometer scaled capillaries extending down the entire length of the fibers, have become a major topic of research over the last years. Oxide based glasses, such as fused silica, is the main background material of researched PCFs. However, silicate glasses exhibit limited non-linearity and lack the ability to guide light in the mid-IR. To circumvent this shortcoming it appears necessary to consider alternative glasses for mid-IR as well as non-linear applications. We have recently introduced a novel approach for deposition of amorphous chalcogenide glass films inside the cylindrical channels of PCFs. In particular, we have demonstrated the formation of nanocolloidal solution-based chalcogenide films in PCFs. The hybrid PCF/chalcogenide fibers reveal novel optical behavior showing strong photonic bandgaps over a range covering visible and near-Figure3infrared wavelengths. The main advantage of the proposed technique is the simplicity of the deposition of amorphous chalcogenide layers inside the holes of PCF and constitutes an efficient route to the development of fiber-based devices combined with sophisticated glasses for supercontinuum generation as well as other non-linear applications.
  • Novel oxide glasses and glass ceramics prepared by a containerless laser melting techniques at very high temperature (>2500 K)
    A common method to form a glass is to cool (quench) its melt sufficiently fast in order to prevent nucleation. However, in several cases melts fail to form glasses and crystallize either due to the insufficient quenching rate or due to container-melt-induced nucleation especially if the melting temperature of the material is too high. To extend the glass forming ability of a multicomponent glass and to overcome container-contamination issues, the use of containerless processing has been proposed. A small chunk of the material is levitated on the air and heated by an infrared laser. A home-made containerless laser melting technique has been established at ICE/HT and is currently employed to synthesize novel oxide glasses with high technological (optics) and geological significance. The advantages of a containerless technique include: (i) avoidance of extrinsic nucleation effects, especially in the high temperature melt, (ii) the achievement of extremely high heating/cooling rates, and (iii) the minimization of the black-body radiation for in situ spectroscopic investigations of melts at high temperature.

Laser-assisted nanofabrication of low-dimensional materials and structures
The increasing necessity to fabricate nanoparticles and sophisticated devices/structures with tailor-made properties as well as the ever increasing requirement of miniaturizing components has boosted the applications of laser sources in nano-fabrication. The employment of lasers has several important advantages: Synthesis/fabrication time is relatively short; they operate at low temperature; the process is fast and environmentally friendly in that no hazardous substances are used and no post-fabrication treatment is needed to remove chemical byproducts, thus resulting in high purity nanostructure. Representative research activities of laser-assisted nanofabrication of low-dimensional materials and structures at FORTH/ICE-HT are briefly outlined below.

  • Epitaxial Graphene growth using infrared lasers: Currently, efforts are focused on the development of a method for the fast, single-step epitaxial growth of large-area homogeneous graphene film on the surface of SiC(0001) using an infrared CO2 Figure4laser (10.6 μm) as the heating source. The method is cost-effective, in that it does not necessitate high vacuum, it operates at low temperature and proceeds in a time scale of seconds, thus providing a green solution to EG fabrication and a means to engineering graphene patterns on SiC by focused laser beams.
  • 3D Graphene and Graphene/nc-Si nanocomposites for energy storage applications: Folding of graphene induces interesting modifications in several of its properties, i.e., chemical, optical electrical, magnetic, H2 storage capacity, etc. Recent progress at ICE-HT encompasses the fabrication of 3D graphene, i.e. graphene spheres, using near-infrared pulsed laser sources. Our approach offers a fast, one-step, method towards fabricating spherical graphene nanostructures, with very high surface area, at ambient atmosphere. A manifold of graphene structures either in pure form or decorated by nc-Si can be fabricated by controlling the experimental conditions.
  • Laser-Assisted Growth of 1D semiconducting nanostructures: We have recently advanced a novel laser-assisted method for the controlled fabrication of 1D chalcogen and chalcogen-based materials nanostructures and manipulate them by photo-oxidation. This solid-state laser-processing of semiconducting materials apart from offering new opportunities for the fast and spatially controlled fabrication of anisotropic nanostructures, provides a means of simultaneous growing and integrating these nanostructures into an optoelectronic or photonic device.

Semiconducting nanowires (NWs) for energy conversion and photonic applications
Figure5Nanowires are 1D strucrtures confined only in two dimensions, thus allowing charge carriers (electrons, holes) and photons to propagate freely along the third dimension. The high-aspect-ratio of these 1D nanostructures allows for their integration in electronic or optoelectronic devices, thus providing a platform for bridging the nanoscopic and macroscopic world. The key objectives of the current research activities at ICE-HT are:

  • the systematic development of novel neat as well as hybrid nanomaterials (based on semiconducting ZnO-nanostructures) with optimized optical and electrical properties, and
  • the fabrication and processing of novel functional nanomaterials-based devices. With respect to the technological vision main themes pursued comprise: (a) nanostructures for nanophotonics (random-lasers, nano-lasers, and photonic crystal lasers), and (b) nanostructures for energy conversion (dye-sensitized solar cells), and (c) photo-electrochemical H2 production. We are currently employing the following synthetic routes for the growth of ZnO nanostructures: growth in ionic liquids; growth by hydrothermal methods; growth through thermal decomposition of precursor compounds; growth by a high-temperature catalyst-assisted, vapor-liquid-solid method, growth inside micro- and nanostructures of photonic crystals.

Macromolecular Engineering
In the field of Macromolecular Engineering, indicative research activities are the development of novel strategies for synthesizing specialty polymers with tailored properties, the processing of polymer materials, such as multifunctional micelles, for advanced drug delivery systems, the development of complex fluids with tailored rheological properties, the development of nanostructured polymer composites, the modification of graphene and carbon nanotubes etc. Novel polymeric and hybrid materials are designed and developed for advanced applications in energy, health and environmental sectors. Materials for the new energy technologies are include polymers for PEM Fuel Cells and Li-Ion Batteries. Additionally, hybrid semiconducting polymer carbon allotrope nanostructures like fullerenes and nanotubes have been designed and synthesized with applications in the field of organic solar cells. In this case the semiconducting properties of the polymeric species are combined with those of the carbon allotropes.
Biocidal copolymers are researched to develop proper copolymeric structures that provide antimicrobial or antifouling properties on polymeric surfaces or underwater sea paints and nets. Especially, in the case of the antifouling materials the main focus is on the introduction of organic antifouling species covalently bounded onto the surface of the specific nets in order to avoid release of the active substance and thus pollution of the environment.
Functional Organic NanoParticles are developed for use as barrier or sensor materials in packaging applications especially in cases where biodegradable polymers are used. Metal NanoParticles and Metallocomplexes are being developed as semiconductors for electronic applications but also as biocidal materials in those cases where the metal ion or nanoparticles can induce biocidal activities.
Concerning computer simulations, methodologies and algorithms are developed for the multi-scale simulation of macromolecular materials and the reliable prediction of their conformational, rheological and mechanical properties. Typical systems addressed include branched polymers, polymer rings, semiconducting polymers, polymeric membranes with carbon nanotubes, polymer nanocomposites, and liquid crystal polymers. Emphasis is on the prediction of the viscosity as a function of polymer chemistry and polymer architecture (e.g., linear polymers versus ring polymers), on the enhancement of the mechanical properties of polymers filled with nanoparticles (such as graphene), on the adhesive properties of acrylic polymers and their copolymers with acrylic acid, and on the development of constitutive equations (guided by principles of non-equilibrium thermodynamics) for the unified description of microstructure, phase behavior and rheology of polymer nanocomposites.

Composite Materials
The Composite Materials group is involved in research related to the mechanical behaviour, processing, structure and morphology of fibres and composites. It also provides consultation & services to the national and European composites industry. Current research directions in the field of composites include: (a) processing and characterization of graphene and CNT nano-composites (b) interfacial studies and micromechanics of reinforcement in nano- and micro- composites (c) fabrication and characterisation of smart composites (covering microactuators, microsensors & smart systems) (d) fracture mechanics of composites and (e) composites in construction. The Institute has been a core member of the European Network of Excellence of Nanostructured Polymers and Nanocomposites (Nanofun-Poly) that involved 13 partners from 12 European countries. Moreover, the Institute is a founding member of the European Centre of Nanostructured Polymers (ECNP) which is a non-profit organization that is concerned with the provision of services to the European Industry and other stakeholders in the area of nanostructured polymers and composites.

Ionic Liquids
Ionic liquids (ILs) represent a class of materials with interesting properties, such as low vapor pressure, chemical stability, high conductivity, and low flammability. ILs are often considered as "green" alternatives to organic volatile solvents, and as a result ILs have a wide range of possible applications in catalysis and biocatalysis, in electrochemistry, in materials synthesis, in chemical analysis, etc. It is of great importance to understand how their macroscopic properties (i.e. melting point, viscosity, conductivity etc.) depend on their structural properties. The understanding of these fundamental issues will be very helpful in order to design the appropriate IL for a given application. The key objectives of the current research work at ICE-HT are: (i) to establish relationships between local structure and thermodynamic and/or viscoelastic properties of ILs, (ii) to study the effect of functional groups of the organic ions on the molecular structure and interactions of protic and aprotic ionic liquids, (iii) to characterize ionic liquid - zeolite composites for PEM fuel cell applications, (iii) to develop IL-based membranes for gas separations and (iv) to apply vibrational / electronic absorption spectroscopy in the study of classical molten salt systems, glasses and vapors.

Molecular Nanomagnets
Classical or atom-based magnets, for example, metals, metal alloys, and metal oxides, are composed solely of a high density of d- or f-orbital metal spin sites and are prepared by high-temperature metallurgical methods. Current trends in the research field of molecular magnetism mainly involve activities in three classes of molecular materials, namely, multifunctional magnetic materials, nanostructured magnetic materials, and molecular nanomagnets. At present, our activities related to this domain include: (1) Synthesis and characterization/study of 3d/4f - molecular clusters. Search for high-spin molecules, single-molecule magnets and nanoscale magnetic refrigerants. (2) Synthesis and characterization of mononuclear and dinuclear lanthanide(III) complexes. Search for homogeneous catalysts for oxidation catalysis, e.g. transformation of styrene to benzaldehyde, using "green" oxidants, e.g. hydrogen peroxide.


B. Advanced Characterization Techniques

Surface Science - Surfaces and Interfaces
Main research in this domain include processes such as thin film nucleation and growth, reactions at metal semiconductor interfaces, heterogeneous catalysis, polymer and bio-matter interaction with surfaces and surface functionalization.

  • Surface Science studies of Heterogeneous Catalysts: Realistic surface-science-compatible catalytic systems can be prepared by the use of conducting or semiconducting substrates covered with a few nm thick oxide layer which acts as the catalyst support. In the last few years our studies have focused on a rather complicated and not well understood catalytic system, the SiO2/MgCl2 supported Ziegler-Natta catalysts for olefin polymerization. The surface chemistry of these systems is followed at every stage of their preparation/ activation/ reaction, using surface sensitive techniques (XPS, UPS, SIMS, EELS) allowing a correlation of the adsorptive and catalytic activity with the size, surface structure and electronic properties of the catalyst particles.
  • Interfacial studies for organic and graphene electronics: Phenomena like charge transfer, interfacial reactions, and charge barrier formation, all localized at the interfaces formed between those layers control the macroscopic properties and performance of a microelectronic device. Work in this area is focused on the growth of thin homogenous layers of conjugated oligomers on metal or semiconducting substrates under UHV conditions, and the study of the interfaces formed by surface sensitive spectroscopies. These studies have in the last four years evolved by using graphene to replace materials that are conventionally used as electrodes in microelectronic devices. Our studies at present focus on the interfacial properties between small organic molecules used in OPVs such as NPB, a well known hole transporter, and graphene substrates. We have already shown that the hole-injection barrier of the NPB / graphene interface is improved by 40% as compared to the conventionally used NPB/ITO.

Surface Enhanced Raman Scattering
Despite the advantages of Raman spectroscopy the technique cannot be used for trace Figure6analysis since the effect is considerably weak. The weak Raman signal can be significantly enhanced when the analyte is placed on or near either to nano-rough substrates or to nano-structured colloidal clusters of noble metals (Surface Enhanced Raman Scattering, SERS). SERS is capable of identifying analytes extremely low concentrations; even single molecule detection has been reported. Quantitative evaluation by means of SERS was proved difficult, due largely to lack of nano-sized noble metal structures with analytically suitable stability and reproducibility. To overcome this problem, we have proposed a new SERS excitation/collection configuration utilizing noble metal nanocolloidal solutions with an oscillating cell in combination with 90o scattering collection geometry. The methodology involves fast collections of spectra and enables the extraction of reproducible quantitative results as well as the evaluation of the associated detection limits.
Examples of SERS/SERRS relevant applications:

  • Monitoring of the level of the antitumor drugs at extremely low concentrations (fg/mL)
  • Detection and quantification of active agents' release from host materials especially at the very early stages of the release process
  • Probing of the Multi-Walled Carbon Nanotubes presence in water suspensions; CNT embedded membrane bioreactors
  • Detection of DNA bases in DNA damage applications
  • Revealing the presence of drugs in corporal fluids
  • Exploring the nanostructured additives' migration/release from biopolymer packaging materials into food simulants

Nonlinear Optics and Laser Produced Plasmas
The increasing demand for faster processing, storage and distribution of information can only be achieved by miniaturization of the basic electronic devices down to the atomic/molecular level. Opto-electronic/photonic technologies, where light is used as information carrier instead of electrons, is expected to offer the answer. Towards this goal, the development of new photonic materials, possessing optical linear and nonlinear response suitable for such tasks are of high interest. Current research efforts are oriented towards:

  • the understanding of the physical origins of the NLO response
  • the systematic study of the relationship between molecular structure and NLO response
  • tailoring of NLO properties in order to match specific needs (e.g. 2- or 3-photon absorption, nonlinear refraction, χ(3), n2, 2nd hyperpolarizability, etc.)
Examples of NLO materials of interest:
  • Graphene and derivatives: structure/functionalization and NLO response.
  • Metal (Ni, Au, Pt, etc.) dithiolenes.
  • Molecular nano-machines & molecular shuttles: rotaxanes.
  • Azo-benzene molecular systems, cis-trans isomerization and NLO response.
  • Chiral molecular systems and NLO response.
  • Self-organization and NLO response.

Plasmas resulted from the interaction of laser radiation with matter can provide, under some conditions, rapid, remote and in-situ qualitative and quantitative elemental analysis of a sample. In principle, all states of matter can be analyzed without any preparation: solids, gases and liquids, conductive and/or dielectric. Current resent research work in this field is oriented into three different directions: combustion diagnostics, high temperature metallurgical processes' diagnostics, and environmental issues.

C. Modelling and Simulation

In the Modelling and Simulation research team strong emphasis is placed on the development of theoretical models and computer-aided simulators for the understanding and description of the structure and properties of nanostructured materials. This interdisciplinary effort has proved extremely fruitful already, as it has contributed to the attraction of several external collaborations and significant funding from EC, GSRT, and industry. The simulation activities cover several length scales from the atomistic to the macroscopic one, and address problems related to computer-aided reconstruction of porous materials, prediction of sorption and transport properties, and estimation of structural effects on the separation efficiency in mixture separations. Recent simulation work has revealed details about the hydrodynamic interactions of carbon nanotubes with porous membranes aiming to design and prepare CNT-impregnated membranes for water treatment. The prediction of mixed matrix membrane properties for gas separation applications and transport phenomena in diffusion layers of fuel cells for design purposes are among current subjects of intensive simulation work at the Institute in the frame of European projects. Similar efforts address simulation and modeling issues related with the use of polymers filled with carbon nanotubes for the design, development and pilot-scale implementation of a new generation of polymeric membranes for the treatment and re-use of industrial waste water. The Institute has been a core member of the European Network of Excellence NanoMemPro, which involved 13 partners from 13 European countries and aimed to "Expand membrane macroscale applications by exploring nanoscale material properties". The Institute coordinated all membrane modelling-related activities in the Network in addition to its participation in all membrane-related research and integration activities. Moreover, the Institute is a founding member of the European Membrane House, which is the Durable Integrated Structure of NanoMemPro.


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