Layla Martin-Samos

Layla Martin-Samos
Italian National Research Council | CNR · Institute of Materials IOM

PhD

About

86
Publications
24,141
Reads
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23,708
Citations
Introduction
My research interests goes from software development, refactoring and optimization to connection between theory and experiments, including multi-scaling (from atomic-scale modelling to Monte-Carlo) and methodological developments. I am actively involved in a longstanding collaboration devoted to understand and model defects and irradiation effects in semiconductors and insulators.
Additional affiliations
March 2012 - present
University of Nova Gorica
Position
  • Professor (Assistant)
December 2008 - March 2012
Italian National Research Council
Position
  • Development Scientist
November 2004 - November 2008
Università degli Studi di Modena e Reggio Emilia
Position
  • PostDoc Position

Publications

Publications (86)
Article
Finding the ground-state configuration of point defects in semiconductors is in general a high-dimensional optimization problem. However, their adiabatic potential energy surfaces (APES) can be described with few effective coordinates by exploiting symmetry arguments within the Jahn-Teller (JT) theoretical framework. In this paper, we propose a gen...
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Finding transition states and diffusion pathways is essential to understand the evolution of materials and chemical reactions. Such characterization is hampered by the heavy computation costs associated with exploring energy landscapes at ab-initio accuracy. Here, we revisit the activation-relaxation technique (ARTn) to considerably reduce its cost...
Article
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In the context of ionic transport in solids, the variation of a migration barrier height under electric fields is traditionally assumed to be equal to the classical electric work of a point charge that carries the transport charge. However, how reliable is this phenomenological model and how does it fare with respect to Modern Theory of Polarizatio...
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Among the common vacancy-related point defects in silicon, the E center is one of the most prominent due to its degrading effect in silicon-based technology. Even though it has been the subject of extensive experimental and theoretical studies, a comprehensive theoretical model capable of reproducing the experimental evidence for all three dopants...
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We present experimental measurements and ab initio simulations of the crystalline and amorphous phases of P2O5. The calculated Raman, infrared, and vibrational density of states (VDOS) spectra are in excellent agreement with experimental measurements and contain the signatures of all the peculiar local structures of the amorphous phase, namely, bri...
Conference Paper
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In this paper we study the effect on the electric fields on the formation of bulk Frenkal Pairs and on the migration of oxygen interstitials, IO, and oxygen vacancies, VO, within the framework of Density Functional Theory and Modern Theory of Polarization. At typical OXRRAM field conditions, we show that a significant effect of the electric field i...
Conference Paper
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We demonstrate the presence of small Jahn-Teller distortions for interstitial titanium in silicon at different charge states by performing ground state DFT calculations. We prove the existence of three charged transition levels within the band gap by using a non-empirical parameter-free approach, based on the GW approximation, in agreement with DLT...
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In this paper, first-principles calculations provide structural characterization of three low-index Mg surfaces—Mg(0001), Mg(101¯0), and Mg(112¯0)—and their respective surface core-level shifts (SCLSs). Inspired by the close similarities between Be and Mg surfaces, we also explore the reconstruction of Mg(112¯0). Through the calculation of surface...
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Synthetic vitreous silica is currently the preferred material for the production of optical fibres because of the several excellent properties of this glass, e.g. high transmission in the visible and IR domains, high mechanical strength, chemical durability, and ease of doping with various materials. For instance, fiber lasers and amplifiers exploi...
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Silica-based optical fibers, fiber-based devices and optical fiber sensors are today integrated in a variety of harsh environments associated with radiation constraints. Under irradiation, the macroscopic properties of the optical fibers are modified through three main basic mechanisms: the radiation induced attenuation, the radiation induced emiss...
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We report an experimental study demonstrating the feasibility to produce both pure and Ge-doped silica nanoparticles (size ranging from tens up to hundreds of nanometers) using nanosecond pulsed KrF laser ablation of bulk glass. In particular, pure silica nanoparticles were produced using a laser pulse energy of 400 mJ on pure silica, whereas Ge-do...
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We present an investigation of the optical properties of diamagnetic P centers in P-doped silica by means of first-principles calculations, including many-body perturbation theory (GW and Bethe-Salpeter Equation) techniques. The calculated absorption spectra indicate that the 6.9 eV band is originated from the presence of a large number of [(O-)3P(...
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Polyethylene (PE), one of the simplest and most used aliphatic polymers, is generally provided with a number of additives, in particular antioxidants, because of its tendency to get oxidized. Carbonyl defects, a product of the oxidation of PE, are occurring in various forms, in particular saturated ones, known as ketones, where a C=O double bond su...
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first principles study of the defects generated by displacement cascades in silicon is performed. This work is particularly focused on two defect configurations; the di-vacancy and the triinterstitial, both identified in previous Molecular Dynamics (MD) and kinetic Activation Relaxation Technique (k-ART) simulations [1, 2]. By combining structural,...
Article
An experimental investigation of Ni ions (energy 3.6 MeV/nucleon) and γ-rays irradiation effects on three different types of silica-based glasses: N-BK7 and two pure-silica (Herasil and Suprasil) samples has been conducted. Confocal micro-Raman (CMR) and –Luminescence experiments (CML) allowed investigating the glass structural and emission modific...
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Photoconductivity spectra measured in non-crystalline corannulene thin layers are compared to optical absorption in solution phase and thin films. The unexpected enhanced photoconductivity is correlated with GW–BSE theoretical predictions of corannulene gas-phase excitonic spectra. Theoretical analysis reveals a consistent contribution involving tr...
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We investigated the combined effects of temperature and X-rays exposures on the nature of point defects generated in Ge-doped multimode optical fibers. Electron paramagnetic resonance (EPR) results on samples X-ray irradiated at 5 kGy(SiO2), employing different temperatures and dose rates, are reported and discussed. The data highlight the generati...
Article
In this work we present an extensive investigation of nanoscale physical phenomena related to oxygen-deficient centers (ODC) in silica and Ge-doped silica by means of first-principles calculations, including nudged-elastic band (NEB), electron paramagnetic resonance (EPR) parameters calculations, and many-body perturbation theory (GW and Bethe-Salp...
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We present an experimental investigation on the combined effects of temperature and irradiation on Ge-doped optical fibers. Our samples were X-ray (10 keV) irradiated up to 5 kGy with a dose rate of 50 Gy(SiO2)/s changing the irradiation temperature in the range 233-573 K. After irradiation we performed electron paramagnetic resonance (EPR) and con...
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In the present paper, we report an experimental investigation of Ge-doped Optical Fibers (OFs) which were investigated by Cathodoluminescence (CL) measurements. We followed the evolution, under 10 keV electron exposure, of the emissions present in three different samples: the first one was the as-drawn fiber (pristine), the second one was irradiate...
Article
This work aims at addressing the issue of the optical signature of peroxy bridges by using first-principles methods that combine Density Functional Theory (DFT), GW (where G and W stand for one particle Green function and screened Coulomb potential, respectively) and the solution of a Bethe-Salpeter Equation (BSE) on a bulk amorphous SiO model. We...
Article
We evaluate the potential of the cathodoluminescence (CL) spectroscopy to characterize the nature and the spatial distribution of point defects in the main classes of optical fibers (OFs): Telecom-grade, radiation-hardened, and radiation sensitive. Canonical samples, that are differently doped in their cores (Ge, N, P, Ce) or their claddings (F), h...
Article
We report an experimental investigation on the radiation induced attenuation (RIA) in the ultraviolet-visible domain for Ge-doped optical fibers, during X-rays (10 keV) exposure at different temperatures. The objective is to characterize the impact of the irradiation temperature on the RIA levels and kinetics. Our data highlight that for dose excee...
Presentation
Full-text available
Presentation done at the CMMSE2016 conference and then published as: Proceedings of the CMMSE2016, 2, 570 (2016).
Conference Paper
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Due to its ubiquitous presence, high diffusivity, and reaction capabilities, hydrogen represents an important source of absorbing centers in optical fibers. Despite its well known darkening effect, the structural details and generation mechanisms of some H-related defect as e.g. the E β are not yet well understood. In this paper we apply first-prin...
Article
Silica nanoparticles were produced from germanosilicate glasses by KrF laser irradiation. The samples were investigated by cathodoluminescence and scanning electron microscopy, providing the presence of nanoparticles with size from tens up to hundreds of nanometers. The emission of the Germanium lone pair center is preserved in the nanoparticles an...
Article
We performed electron paramagnetic resonance (EPR) measurements on γ and X ray irradiated Ge doped and Ge/F co-doped optical fibers. We considered three different drawing conditions (speed and tension), and for each type of drawing, we studied Ge and Ge/F doped samples having Ge doping level above 4% by weight. The EPR data recorded for the γ ray i...
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We present a first-principles investigation of Ge paramagnetic centers in Ge-doped vitreous silica (v-SiO2) based on calculations of the electron paramagnetic resonance (EPR) parameters. We infer, by analyzing g-values differences with respect to our Ge-E′ configurations, that the EPR signal of the Ge(2) center may arise from Ge forward-oriented (G...
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A unique paradigm for intermolecular charge transport mediated by diffuse atomic-like orbital (SAMOs), typically present in conjugated hollow shaped molecules, is investigated for C20H10 molecular fragments by means of G0W0 theory. Inclusion of many body screening and polarization effects is seen to be important for accurate prediction of electroni...
Article
We applied theoretical and experimental spectroscopy tools to ad hoc silica-based "canonical" samples to characterize the influence of several dopants and of some drawing process parameters on their radiation sensitivities. We present in this paper, the recent advances and results occurring from our coupled approach. On the experimental side, we st...
Article
A first-principles investigation of E′ centers in vitreous silica (v−SiO2) based on calculations of the electron paramagnetic resonance (EPR) parameters is presented. The EPR parameters are obtained by exploiting the gauge including projector augmented wave method as implemented in the quantum-espresso package. First, we analyze the EPR parameters...
Presentation
Full-text available
Presentation done at the EuroDim2014 conference (Canterbury, United Kingdom). 13–19 July 2014. The content "First-principles calculations of EPR parameters of E ′ centers in v -SiO2" is the bulk of the paper published in Phys. Rev. B 90, 014108 (2014)
Article
Considerable effort in the past decade has been extended toward achieving computationally affordable theoretical methods for accurate prediction of the structure and properties of materials. Theoretical predictions of solids began decades ago, but only recently have solid-state quantum techniques become sufficiently reliable to be routinely chosen...
Article
Abstract—We applied theoretical and experimental spectroscopy tools to ad hoc silica-based “canonical” samples to characterize the influence of several dopants and of some drawing process parameters on their radiation sensitivities. We present in this paper, the recent advances and results occurring from our coupled approach. On the experimental si...
Article
In this work we have studied the effects of high neutron fluences (1E21 and 1E22 n/m2) and high γ-ray doses (23.8 MGy) on the structural properties of three different types of silica glasses: two high purity silica with different OH content, KU1 (800 ppm) and KS-4V (<0.2 ppm); and a commercial silica Infrasil 301 (<8 ppm). The experimental results...
Article
The electronic and optical properties of neutral oxygen vacancies, also called oxygen deficient centers (ODC(I)s), have been investigated in pure and germanium doped silica (both amorphous and α-quartz) through first-principles calculations. By means of density functional theory and many-body perturbation theory (GW approximation and the solution o...
Article
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The nonresonant tunneling regime for charge transfer across nanojunctions is critically dependent on the so-called β parameter, governing the exponential decay of the current as the length of the junction increases. For periodic materials, this parameter can be theoretically evaluated by computing the complex band structure (CBS)—or evanescent stat...
Article
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The non-resonant tunneling regime for charge transfer across nanojunctions is critically dependent on the so-called \beta{} parameter, governing the exponential decay of the current as the length of the junction increases. For periodic materials, this parameter can be theoretically evaluated by computing the complex band structure (CBS) -- or evane...
Article
The present investigation reports for the first time a detailed theoretical analysis of the optical absorption spectra of corannulene-based materials using state-of-the-art first-principles many-body GW-BSE theory. The study specifically addresses the nature of optical excitations for predictions regarding suitability for device fabrication. The we...
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IntroductionThe Band Gap ProblemWhich Gap?Deep Defect StatesConclusions References
Article
Using ab initio calculations on 108 atoms pure- and Ge-doped (2.8mol%) silica-based supercells, we performed a statistical study on the electronic structure and energetic contribution of neutral oxygen vacancies, also named Oxygen Deficient Centers (ODCs). All the 72 oxygen sites in the amorphous silica (a-SiO2) cell were considered as possible can...
Conference Paper
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RESUME: Le traitement de l'autodiffusion de l'oxygène dans l'oxyde de silicium est utilisé pour révéler les faiblesses de la modélisation des défauts dans les isolants par la Théorie de la Fonctionnelle de la Densité dans le cadre des fonctionnelles disponibles. Nous montrons que la mauvaise description de la bande interdite et des niveaux localisé...
Article
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We compare, through first-principles pseudopotential calculations, the structural, electronic, and optical properties of different size silicon nanoclusters embedded in a SiO2 crystalline or amorphous matrix with that of freestanding, hydrogenated, and hydroxided silicon nanoclusters of corresponding size and shape. We find that the largest effect...
Article
We present a first-principles systematic study of the electronic structure of SiO2 including the crystalline polymorphs α quartz and β cristobalite, and different types of disorder leading to the amorphous phase. We start from calculations within density functional theory and proceed to more sophisticated quasiparticle calculations according to the...
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The long-standing problem of the oxygen self-diffusion mechanism in silicon dioxide, a prototypical oxide, both in the crystalline and in the amorphous phase, is studied from first principles. We demonstrate that the widely used local-density approximation to density functional theory (DFT) predicts a kinetic behavior of oxygen in strong disagreeme...
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We present a cross-section scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS) and ab initio density-functional theory simulations study of the cleaved nonpolar (11̅ 00) surface (m-plane) of n-type HVPE GaN free-standing quasisubstrates. Atomically resolved empty and filled states STM topographies show that no reconstruction...
Article
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QUANTUM ESPRESSO is an integrated suite of computer codes for electronic-structure calculations and materials modeling, based on density-functional theory, plane waves, and pseudopotentials (norm-conserving, ultrasoft, and projector-augmented wave). The acronym ESPRESSO stands for opEn Source Package for Research in Electronic Structure, Simulation...
Article
Within a first-principles framework we show the dependence of the optical properties of silicon nanocrystallites embedded in a silica matrix on the crystalline vs. amorphous order of the system. Moreover we calculate how many-body effects modify the electronic and optical properties of the embedded silicon nanodots. A discussion about the different...