Alexandros Lappas | Foundation for Research and Technology - Hellas (original) (raw)

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Papers by Alexandros Lappas

Nucleation and Atmospheric Aerosols, 2010

Physical Review B, Jun 29, 2010

Thin Solid Films, 2018

Abstract Despite the fact there is a plethora of magnetic delafossite compounds in the bulk polyc... more Abstract Despite the fact there is a plethora of magnetic delafossite compounds in the bulk polycrystalline phase, so far, only a few of them have been fabricated as thin films. The challenges in the fabrication of delafossite thin films are imposed by the phase purity and stability of the composition related with the preparation conditions. Here we report the growth of a new delafossite related derivative thin film, a sodium iron oxide of the β-NaFeO2 phase, grown on a ZnO seed layer by pulsed laser deposition, using as target a single phase polycrystalline powder of β-NaFeO2. The purity of the thin films has been verified with X-ray diffraction, Scanning electron and Atomic Force Microscopy as well as Fourier Transform Infrared Spectroscopy. The crucial parameter for the growth of the thin films has been the partial oxygen pressure, as the β-NaFeO2 is obtained at 2 Pa. Applying higher or lower pressures resulted in the formation the hematite and maghemite iron oxides as secondary phases, as indicated by X-ray diffraction patterns. SEM and AFM studies confirm a good two dimensional growth for the pure phase β-NaFeO2, whereas FT-IR measurements revealed characteristic β-ΝaFeO2 bands.

Journal of the American Chemical Society, Aug 12, 2011

Nanomaterials

Metal halide perovskite nanocrystals, an emerging class of materials for advanced photonic and op... more Metal halide perovskite nanocrystals, an emerging class of materials for advanced photonic and optoelectronic applications, are mainly fabricated with colloidal chemistry routes. On the quest for new properties according to application needs, new perovskite systems of various morphologies and levels of doping and alloying have been developed, often also involving post-synthesis reactions. Recently, laser irradiation in liquids has been utilized as a fast method to synthesize or transform materials and interesting laser-induced transformations on nanocrystals were induced. These studies in general have been limited to small nanocrystals (~15 nm). In the case of halide perovskites, fragmentation or anion exchange have been observed in such laser-based processes, but no crystal structure transformations were actually observed or deliberately studied. Nanocrystals are more sensitive to light exposure compared to the corresponding bulk crystals. Additional factors, such as size, morpholo...

Nanoscale, 2022

Synchrotron X-ray scattering reveals that atomic-scale defect control manipulated by chemical sub... more Synchrotron X-ray scattering reveals that atomic-scale defect control manipulated by chemical substitution optimizes nanomagnetism and enables hyperthermia heating in core-shell iron-oxide nanocrystals.

Nanoscale, 2017

Ultra-thin and highly uniform CsPbBr3 nanowires over micron-size lengths and widths down to the q... more Ultra-thin and highly uniform CsPbBr3 nanowires over micron-size lengths and widths down to the quantum confinement regime have been fabricated via a facile, low-temperature precipitation-based method. This synthesis approach is the first of its kind that is carried out on the work-bench. The nanowires’ photoluminescence is shown to improve over time.

Current State of the Art and Perspectives, 2014

Nanotechnology Reviews, 2015

Magnetic particles of optimized nanoscale dimensions can be utilized as building blocks to genera... more Magnetic particles of optimized nanoscale dimensions can be utilized as building blocks to generate colloidal nanocrystal assemblies with controlled size, well-defined morphology, and tailored properties. Recent advances in the state-of-the-art surfactant-assisted approaches for the directed aggregation of inorganic nanocrystals into cluster-like entities are discussed, and the synthesis parameters that determine their geometrical arrangement are highlighted. This review pays attention to the enhanced physical properties of iron oxide nanoclusters, while it also points to their emerging collective magnetic response. The current progress in experiment and theory for evaluating the strength and the role of intra- and inter-cluster interactions is analyzed in view of the spatial arrangement of the component nanocrystals. Numerous approaches have been proposed for the critical role of dipole-dipole and exchange interactions in establishing the nature of the nanoclusters’ cooperative mag...

$Research paper thumbnail of Influence of magnetic interaction between impurity and impurity-liberated spins on the magnetism in the doped Haldane chain compounds PbNi${}_{2-x${A}${}_{x}$V${}_{2}$O${}_{8}$ (A = Mg, Co)$

Cancer cure schemes are based on accurate diagnosis and treatment protocols that could have minim... more Cancer cure schemes are based on accurate diagnosis and treatment protocols that could have minimal side-effects for a patient. For this purpose the scientific community seeks cost-efficient advanced materials that serve the combined role of diagnosis and therapy. However, it is imperative that a so-called theranostic material is characterised in depth for its physical, chemical and biocompatibility properties. In order to address this challenge, we have developed size-controlled (50-100 nm), water-dispersible clusters of maghemite nanoparticles (NPs), named Colloidal Nanoclusters (CNCs). Characterization techniques (including, HRTEM, X-ray scattering, Mössbauer spectroscopy, SQUID magnetometry), combined with theoretical Monte Carlo simulations have probed the microscopic mechanisms that govern the growth and magnetic behaviour of these CNCs. We have found that such controlled nanoparticle assemblies, display collective magnetic behaviour as an outcome of the intra-cluster dipolar ...

Introduction The relationship between structural instabilities and superconductivity in the high-... more Introduction The relationship between structural instabilities and superconductivity in the high- T c cuprates continues to be intriguing. In general, for any family of superconducting cuprates, T c goes through a maximum with increasing hole doping and then monotonically decreases to zero. In La 2-x Ba x CuO 4 , however, besides the expected maximum in T c near x = 0.15, a deep, narrow minimum (below 4 K) exists at x = 1/8. This remarkable suppression of superconductivity is only weakly evident in the analogous Sr-doped series and has been associated with the occurrence of a low-temperature (at T d2 ) first-order structural phase transition from orthorhombic (LTO, Bmab) to tetragonal (LTT, P4 2 /ncm) symmetry [1]. Electronic [2], spin--orbit coupling [3] and microstructural [4] models have been proposed to account for the significant changes in the superconducting properties of the Ba-doped phases that accompany the LTO#LTT phase transition. Very importantly however, early ZF- SR

Scientific reports, 2015

Inhomogeneity in the ground state is an intriguing, emergent phenomenon in magnetism. Recently, i... more Inhomogeneity in the ground state is an intriguing, emergent phenomenon in magnetism. Recently, it has been observed in the magnetostructural channel of the geometrically frustrated α-NaMnO2, for the first time in the absence of active charge degrees of freedom. Here we report an in-depth numerical and local-probe experimental study of the isostructural sister compound CuMnO2 that emphasizes and provides an explanation for the crucial differences between the two systems. The experimentally verified, much more homogeneous, ground state of the stoichiometric CuMnO2 is attributed to the reduced magnetoelastic competition between the counteracting magnetic-exchange and elastic-energy contributions. The comparison of the two systems additionally highlights the role of disorder and allows the understanding of the puzzling phenomenon of phase separation in uniform antiferromagnets.

Chemistry of Materials, 2014

Colloidal Nanoparticles For Biomedical Applications Ix, 2014

ABSTRACT Templating semiconductor nanoparticles’ growth on the surface of biological self-assembl... more ABSTRACT Templating semiconductor nanoparticles’ growth on the surface of biological self-assembled molecules is a promising avenue over the limitations that top-down techniques may impose on device fabrication. We report on two-dimensional ordered structures of preformed TOPO (trioctylphosphine oxide) capped CdSe@ZnS core-shell quantum dots (Qdots) on self-assembled peptide fibrils. An amphiphilic peptide was employed both as ligand-exchange element (via its cysteine residues) and as a structural scaffold for the ordering of Qdots at the water-chloroform interface. We discuss the topological arrangement of the Qdots as imposed by the peptide fibril film and the impact of the assembly on the materials’ photoluminescent properties, which display signatures of long-range electronic energy transfer.

AIP Conference Proceedings, 2010