Philomela Komninou

Aristotle University of Thessaloniki | AUTH · School of Physics

We present the results of a twofold experimental and computational study of (0001) GaN/AlN multilayers forming pseudomorphic superlattices. High-Resolution Transmission Electron Microscopy (HRTEM) shows that heterostructures with four c-lattice parameters thick GaN Quantum Wells (QW) are misfit-dislocation free. Accurate structural data are extract...

We present the results of a twofold experimental and computational study of (0001) GaN/AlN multilayers forming pseudomorphic superlattices. High-Resolution Transmission Electron Microscopy (HRTEM) shows that heterostructures with GaN Quantum Wells (QW) four c-lattice parameters thick are misfit-dislocation free. Accurate structural data are extract...

The use of strained substrates may overcome indium incorporation limits without inducing plastic relaxation in InGaN quantum wells, and this is particularly important for short-period InGaN/GaN superlattices. By incorporating elastic strain into these heterostructures, their optoelectronic behavior is modified. Our study employed density functional...

Ηemocompatible nanoparticles with reactive oxygen species (ROS) scavenging properties for titanium implant surface coatings may eliminate implant failure related to inflammation and bacterial invasion. Cerium (Ce) is a rare earth element, that belongs to the lanthanide group. It exists in two oxidation states, Ce+3 and Ce+4, which contribute to ant...

Recent advances in atomically thin two dimensional (2D) anisotropic group IVA‐VI metal monochalcogenides (MMCs) and their fascinating intrinsic properties and potential applications are hampered due to an ongoing challenge of monolayer isolation. Among the most promising MMCs, tin (II) sulfide (SnS) is an earth‐abundant layered material with tunabl...

Protein amyloidosis represents the main pathological hallmark of many incurable neurodegenerative disorders and protein misfolding diseases. Nanomaterials-based approaches give rise to diagnosis and/or prediction of these proteinopathies, with regards to the multifactorial nature of their pathogenesis. Herein, crystalline truncated hexagonal shaped...

In this work, we explore the resistive switching behavior of a thin layer of SiO2 with embedded two-dimensional (2D) molybdenum disulfide, MoS2, in a conductive bridge random access memory (CBRAM) configuration. The proposed device exhibits enhanced conductance quantization behavior, reduced variability due to the suppression of the stochastic fila...

CuO nanowires with diameters between 100 and 200 nm, lengths up to ∼10 μm and a uniform distribution have been grown at 600 °C under 100 mL min⁻¹ O2 on 15 mm × 30 mm Cu foils. The CuO nanowires have a monoclinic crystal structure, grow by a vapor–solid mechanism and can be reduced to Cu under H2 at 300 °C but they are shortened, contain residual Cu...

This cover focuses on an important mechanism proposed in article number 2100190 by George P. Dimitrakopulos and co‐workers: the emanation of threading dislocations (TDs) from junctions of basal stacking fault (BSF) steps in III‐nitride semiconductors. The HRTEM image in the center is a projection along [21̅1̅0] showing such an emanating TD in an In...

Daily rates of infections and deaths collected in several countries during the first SARS-CoV2 (COVID-19) pandemic are approximated by Gaussian functions of the time elapsed since the dates of first occurrence in each country. This representation reveals designating consistently the time evolution of the country-specific daily rates and of the corr...

InGaN/GaN quantum wells (QWs) with sub-nanometer thickness can be employed in short-period superlattices for bandgap engineering of efficient optoelectronic devices, as well as for exploiting topological insulator behavior in III-nitride semiconductors. However, it had been argued that the highest indium content in such ultra-thin QWs is kineticall...

We consider the configurations of basal stacking fault (BSF) manifolds often observed in III-nitride alloy epilayers, particularly InGaN. Using high resolution transmission electron microscopy (HRTEM), we show that the folds and steps of intrinsic BSFs can acquire a Shockley-like partial dislocation character depending on the relative senses of the...

Resistive memories are promising candidates for replacing current nonvolatile memories and realize storage class memories. Moreover, they have memristive properties, with many discrete resistance levels and implement artificial synapses. The last years researcher have demonstrated RRAM chips used as accelerators in computing, following the new in-m...

The impact of film thickness to the electron–phonon coupling and the critical temperature of the superconducting transition, as well as to the structural, phonon and electronic properties of Al films in the ultrathin regime, was studied by means of ab initio calculations. The presence of the inevitable quantum fluctuations in the regime of 5 to 9 a...

The microstructure of 20 nm thick polycrystalline Co25Pd75 alloy films exhibiting perpendicular magnetic anisotropy (PMA), studied by atomic scale analytical transmission electron microscopy (TEM) techniques, is presented. Thin CoPd alloy films are considered promising candidates for pinning MgO-based perpendicular magnetic tunnel junctions (pMTJs)...

III-nitride compound semiconductors are breakthrough materials regarding device applications. However, their heterostructures suffer from very high threading dislocation (TD) densities that impair several aspects of their performance. The physical mechanisms leading to TD nucleation in these materials are still not fully elucidated. An overlooked b...

The effective stabilization of tannery sludge wastes is explored using X-Ray Absorption Fine Structure (XAFS) spectroscopies. Solidification of the Cr-rich waste was realized via vitrification of the incinerated sludge with silica and flux agents. It is demonstrated that the effective reduction of Cr(VI) and the structural role of Cr are strongly m...

In this work, the daily reported new infection cases and deaths globally due to COVID-19 are approximated by Gaussian functions of the time elapsed since the beginning of the pandemic. This approximation is shown to consistently designate the time evolution of daily rates of new cases and the total duration of the epidemic in any given region or co...

IntroductionThe nature of the surface is critical in determining the biological activity of silica powders. A novel correlation between toxicity and surface properties of bioactive glass ceramics (BGCs) synthesized via the sol–gel method was attempted in this study.Methods The behavior of BGCs after their attachment to the surface of red blood cell...

Τhe impact of decorated dislocations on the effective thermal conductivity of GaN is investigated by means of equilibrium molecular dynamics simulations via the Green-Kubo approach. The formation of In embedded nanowires in the core of dislocations in wurtzite GaN is found to affect the thermal properties of the material, as it leads to a significa...

The impact of decorated dislocations on the effective thermal conductivity of GaN is investigated by means of equilibrium molecular dynamics simulations via the Green-Kubo approach. The formation of "nanowires" by a few atoms of In in the core of dislocations in wurtzite GaN is found to affect the thermal properties of the material, as it leads to...

The effects of ultrathin AlN prelayers, with nominal thicknesses between 0 and 1.5 nm, on the spontaneous growth of GaN nanowires (NWs) on Si (1 1 1) substrates were investigated. The morphological and structural characteristics of GaN NWs were analyzed by electron microscopy and X-ray diffraction techniques. The results quantify how the AlN prelay...

The aim of this work is to elucidate how different growth mode and composition of barriers can influence the QW properties and their PL and to find optimal QW capping process, to suppress the In desorption from QWs and to maintain the QW PL efficiency. It concentrates on the technology procedure for growth of upper quantum well (QW) interfaces in I...

Ternary copper-bismuth-sulphide (CBS) semiconducting nanocrystals (NCs), with optimal band gap values of ∼1.5 eV and optical absorption coefficient α > 104 cm−1, have been investigated in recent years as an absorber material for thin film solar cells. We report on a facile hot injection method to synthesize phase-pure CBS NCs of Cu3BiS3 in the form...

Computational analysis via molecular dynamics and density functional theory simulations elucidated the structural and electronic properties of a-type basal edge dislocations lying in the ⟨1–100⟩ direction in wurtzite GaN. As a particular and predominant type of misfit dislocations, experimentally identified in coherently grown semipolar heterostruc...

In the present work, the stabilization/solidification of a Cr-rich ash obtained from the anoxic incineration of tannery hazardous wastes was studied. Chromium in the starting waste was exclusively in amorphous form and in trivalent state. The waste was embedded in fly ash-based cementitious material matrices. Calcium and sodium hydroxides, as well...

Indentation techniques were utilised to induce deformation on polar (0001) c-plane and non-polar m-plane GaN single crystal. Cracking was more sensitively dependent on the orientation of the indenter tip, compared to hardness. The indentation-induced plastic deformation and fracture sequences were studied by cathodoluminescence imaging and optical...

EDS2018, in line with the tradition setup by previous conferences in these series, aims at providing a global vision of research activities in this scientific area. It focuses on the needs stemming from technological bottlenecks related to structural defects that affect the functionality of innovative devices. In particular, attention will be given...

Extensive high resolution transmission and scanning transmission electron microscopy observations were performed in In(Ga)N/GaN multi-quantum well short period superlattices comprising two-dimensional quantum wells (QWs) of nominal thicknesses 1, 2, and 4 monolayers (MLs) in order to obtain a correlation between their average composition, geometry,...

The effect of different spacer materials (MgO, W, and Pt) on the magnetic coupling in FePt/spacer/FePt trilayers has been carefully investigated. MgO results in magnetically coupled FePt layers with perpendicular magnetic anisotropy (PMA); W gives rise to a magnetically coupled system consisting of layers with PMA and in-plane magnetic anisotropy w...

The effect of strain on the elastic constants of GaN and InN, elaborating the stain state of pseudomorphically grown heterostructures comprising these materials, is investigated. Towards this direction, density functional theory (DFT) calculations using local density approximation (LDA) are performed for studying the electronic and elastic properti...

InGaN quantum wells (QWs) grown along the polar c‐axis are currently the principal structural elements of III‐nitride optoelectronic device active regions. Further advancement of their operational wavelength range with high internal quantum efficiency in the green part of the spectrum may be facilitated through the use of short period In(Ga)N/GaN s...

The microstructure of different glass ceramic materials, obtained by thermal processing of vitrified products synthesized from tannery waste, was investigated using electron microscopy (TEM) techniques. Preliminary structural characterization was conducted by X‐Ray Diffraction (XRD) while morphologies and compositions of the materials at the mesosc...

Ultra‐thin films of selenide compound epilayers were deposited epitaxially by molecular beam epitaxy (MBE) on AlN(0001) / Si(111) templates and were studied structurally using high resolution transmission electron microscopy (HRTEM), image simulations, and geometrical phase analysis (GPA). The films comprised Bi 2 Se 3 , MoSe 2 , and HfSe 2 epilaye...

The vitrification process was applied for the stabilization and solidification of a rich in chromium ash that was the by-product of incineration of tannery sludge. Six different batch compositions were produced, based on silica as the glass former and sodium and calcium oxides as flux agents. As-vitrified products (monoliths) were either composed o...

We analyze a method to selectively grow straight, vertical gallium nitride nanowires by plasma-assisted molecular beam epitaxy (MBE) at sites specified by a silicon oxide mask, which is thermally grown on silicon (111) substrates and patterned by electron-beam lithography and reactive-ion etching. The investigated method requires only one single...

An efficient evolutionary structure prediction algorithm in combination with ab initio calculations is implemented in order to reveal energetically favorable superstructures of the III-Nitride ternary alloys. Several 2 x 2 x 2 32-atom supercells are used to explore the full range of concentrations, from x = 0 to 1. The formation enthalpies, bandgap...

The effects of an amorphous interfacial silicon nitride (SiXNY) layer on the morphology, structure and optoelectronic properties of GaN nanowires (NWs), grown on Si (111) substrates by plasma assisted molecular beam epitaxy, have been investigated. The unintentional Si nitridation, during the first stages of direct GaN NW growth on the bare Si surf...

Interatomic potential based molecular dynamics and ab initio calculations are employed to investigate the structural, thermal, and electronic properties of polar GaN/AlN core/shell nanowires. Nanowire models for the molecular dynamics simulations contain hundreds of thousands of atoms with different shell-to-nanowire ratios. The energetic and struc...

Reflectance anisotropy spectroscopy is a useful technique used for in situ observation of the metalorganic vapour phase epitaxy growth, because it does not require vacuum in the reaction chamber. With this method we are able to observe the quantum dot growth, the incorporation of indium or antimony atoms in the layer or the monolayer growth of GaAs...

GaAs/AlGaAs core-shell nanowires (NWs) were grown on Si(111) by Ga-assisted molecular beam epitaxy via the vapor-liquid-solid mechanism. High-resolution and scanning transmission electron microscopy observations showed that NWs were predominantly zinc-blende single crystals of hexagonal shape, grown along the [111] direction. GaAs core NWs emerged...

We investigate the structural properties of a series of high alloy content InGaN epilayers grown by plasma-assisted molecular beam epitaxy, employing the deposition temperature as variable under invariant element fluxes. Using transmission electron microscopy methods, distinct strain relaxation modes were observed, depending on the indium content a...

We carry out ab initio electronic structure calculations of (SixSn1 − x)3N4 using density functional theory with projector augmented-wave potentials under the generalized gradient approximation. We find that the energetically favorable structure of Sn3N4 is the face-centered cubic spinel structure, followed by the hexagonal structure which has ener...

Nanocomposite thin films incorporating silver nanoparticles are emerging as photosensitive templates for optical encoding applications. However, a deep understanding of the fundamental physicochemical mechanisms occurring during laser-matter interactions is still lacking. In this work, the photosensitivity of AlN:Ag plasmonic nanocomposites is thor...

In the present study, the effects of various types of strain and indium concentration on the total energy and optoelectronic properties of GaN nanowires (NWs) with embedded In(x)Ga(1−x)N nanodisks (NDs) are examined. In particular, the bi-axial, hydrostatic, and uniaxial strain states of the embedded In(x)Ga(1−x)N NDs are investigated for multiple...

Abstractauthoren Abstractauthoren GaN quantum dots grown in ()’orientated AlN are studied. The -nucleated quantum dots exhibit rectangular- or trapezoid-based truncated pyramidal morphology. Another quantum dot type orientated on is reported. Based on high-resolution transmission microscopy and crystal symmetry, the geometry of -orientated quantum...

The spontaneous growth of GaN nanopillars (NPs) by direct plasma-assisted molecular beam epitaxy on nitridated r-plane sapphire substrates has been studied. The emanation of metal-polarity NPs from inside an a-plane nonpolar GaN film was found to depend on both the substrate nitridation and the growth conditions. The density of NPs increased with i...

Atomically thin inherently 2D semiconductors offer thickness scaling of nanoelectronic devices and excellent response to light for low power versatile applications. Using small exfoliated flakes, advanced devices and integrated circuits have already been realized showing their great potential to impact nanoelectronics. Here, high quality single cry...

Preparation and properties of InAs/GaAs quantum dots (QDs) prepared by the MOVPE technology covered by GaAsSb strain reducing layer (SRL) with extremely long emission wavelength at 1.8 µm will be presented. Increase of the emission wavelength was achieved by the introduction of GaAsSb SRL with Sb content of about 30% in the solid phase. The high Sb...

AlN/GaN heterostructures have been studied using density-functional pseudopotential calculations yielding the formation energies of metal vacancies under the influence of local interfacial strains, the associated charge distribution and the energies of vacancy-induced electronic states. Interfaces are built normal to the polar <0 0 0 1> direction o...

The growth processes of plasma assisted molecular beam epitaxy (PAMBE) that result to heteroepitaxial growth of high crystal quality single polarity {0001} InN thin films on Si (111) substrates, with either N-face or In-face polarity, have been determined. N-face InN (000-1) films can be grown using high temperature AlN nucleation layer on Si (111)...

Bi2Se3 topological insulators (TI) are grown on AlN (0001)/Si(111) substrates by molecular beam epitaxy. In a one-step growth at optimum temperature of 300(0)C, Bi2Se3 bonds strongly with AlN without forming interfacial reaction layers. This produces high epitaxial quality Bi2Se3 single crystals with a perfect registry with the substrate and abrupt...

Heteroepitaxial non-polar III-Nitride layers may exhibit extensive anisotropy in the surface morphology and the epilayer microstructure along distinct in-plane directions. The structural anisotropy, evidenced by the “M”-shape dependence of the (112¯0) x-ray rocking curve widths on the beam azimuth angle, was studied by combining transmission electr...

We propose a process of deposition of plasmonic nanocomposites comprising magnetron sputtering of AlN:Ag multilayers combined with intermediate steps of flash annealing. When the AlN matrix structure was amorphous, thermal annealing induced the break-up of silver layers and the formation of homogeneously distributed spherical nanoparticles. On the...