A5090166730- Phase-change materials and chalcogenides
- Chalcogenide Semiconductor Thin Films
- Nonlinear Optical Materials Studies
- Transition Metal Oxide Nanomaterials
- Quantum and electron transport phenomena
- Advanced Thermoelectric Materials and Devices
- Advanced Memory and Neural Computing
- Quantum Dots Synthesis And Properties
- Molecular Junctions and Nanostructures
- Glass properties and applications
- Graphene research and applications
- Solid-state spectroscopy and crystallography
- Liquid Crystal Research Advancements
- Magnetic properties of thin films
- Material Dynamics and Properties
- Surface and Thin Film Phenomena
- Physics of Superconductivity and Magnetism
- Advanced Semiconductor Detectors and Materials
- Material Science and Thermodynamics
- Perovskite Materials and Applications
- Topological Materials and Phenomena
- 2D Materials and Applications
- Advanced Chemical Physics Studies
- Intermetallics and Advanced Alloy Properties
- Crystal Structures and Properties
Sapienza University of Rome
2021-2025
RWTH Aachen University
2013-2022
Jülich Aachen Research Alliance
2012-2022
FH Aachen
2015-2020
United States Department of Energy
2019
Paul Drude Institute for Solid State Electronics
2016
Osaka University
2014
ETH Zurich
2009-2011
Scuola Internazionale Superiore di Studi Avanzati
2005-2009
Istituto Nazionale di Fisica Nucleare, Sezione di Trieste
2009
QUANTUM ESPRESSO is an integrated suite of computer codes for electronic-structure calculations and materials modeling, based on density-functional theory, plane waves, pseudopotentials (norm-conserving, ultrasoft, projector-augmented wave). The acronym stands opEn Source Package Research in Electronic Structure, Simulation, Optimization. It freely available to researchers around the world under terms GNU General Public License. builds upon newly-restructured that have been developed tested...
Fast phase change with no preconditions Random access memory (RAM) devices that rely on changes are primarily limited by the speed of crystallization. Rao et al. combined theory a simple set selection criteria to isolate scandium-doped antimony telluride (SST) subnanosecond crystallization (see Perspective Akola and Jones). They synthesized SST constructed RAM device 700-picosecond writing speed. This is an order magnitude faster than previous phase-change competitive consumer dynamic...
Artificial intelligence and other data-intensive applications have escalated the demand for data storage processing. New computing devices, such as phase-change random access memory (PCRAM)-based neuro-inspired are promising options breaking von Neumann barrier by unifying with in cells. However, current PCRAM devices considerable noise drift electrical resistance that erodes precision consistency of these devices. We designed a heterostructure (PCH) consists alternately stacked confinement...
The structure of self-assembled monolayers (SAMs) long-chain alkyl sulfides on gold(111) has been resolved by density functional theory-based molecular dynamics simulations and grazing incidence x-ray diffraction for hexanethiol methylthiol. analysis trajectories the relative energies possible SAM structures suggest a competition between ordering, driven lateral van der Waals interaction chains, disordering interfacial Au atoms, sulfur-gold interaction. We found that sulfur atoms molecules...
Aging is a ubiquitous phenomenon in glasses. In the case of phase-change materials, it leads to drift electrical resistance, which hinders development ultrahigh density storage devices. Here we elucidate aging process amorphous GeTe, prototypical material, by advanced numerical simulations, photothermal deflection spectroscopy and impedance experiments. We show that accompanied progressive change local chemical order towards crystalline one. Yet, glass evolves covalent network with...
Structural switch for fast switching Phase-change materials are important computer memory. They can quickly from glassy to crystalline using a thermal pulse and then lock in that structure long time at lower temperature. Zalden et al. probed the underlying atomic of two phase-change during this ultrafast x-rays simulations (see Perspective by Rao ). A liquid-liquid phase transition both allowed high temperatures. The lower-temperature glass locks structure, allowing long-term memory storage....
Phase change materials (PCMs) serve as useful components in electronics and photonics. Here we demonstrate that various kinds of material properties a PCM are significantly influenced by the realized mass density. Using ab initio simulations, investigate supercooled-liquid antimony subsequent transition to glassy phase. We observe phase from an undistorted high-temperature increasingly Peierls-like distorted low-temperature This also manifests both electronic density states optical...
We have investigated the controversy surrounding $(\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3})R30\ifmmode^\circ\else\textdegree\fi{}$ structure of self-assembled monolayers methylthiolate on Au(111) by first principles molecular dynamics simulations, energy and angle resolved photoelectron diffraction, grazing incidence x-ray diffraction. Our simulations find a dynamic equilibrium between bridge site adsorption novel where 2 ${\mathrm{CH}}_{3}\mathrm{S}$ radicals are bound to an Au...
We computed the Raman spectrum of amorphous GeTe by ab initio simulations and empirical bond polarizability models. The calculated is in very good agreement with experimental data contains signatures all peculiar local structures phase revealed recent simulations, namely, tetrahedral Ge defective octahedral sites for a fraction (mostly 4-coordinated) Te 3-coordinated) atoms. In particular, above $190\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}1}$ dominated structures, while most prominent...
Abstract Despite its simple chemical constitution and unparalleled technological importance, the phase‐change material germanium telluride (GeTe) still poses fundamental questions. In particular, bonding mechanisms in amorphous GeTe have remained elusive to date, owing lack of suitable bond‐analysis tools. Herein, we introduce a indicator for structures, dubbed “bond‐weighted distribution function” (BWDF), apply this method GeTe. The results underline peculiar role homopolar GeGe bonds,...
Using low-temperature scanning tunneling spectroscopy, we map the local density of states graphene quantum dots supported on Ir(111). Because a band gap in projected Ir structure around $K$ point, electronic properties QDs are dominantly graphenelike. Indeed, compare results favorably with tight binding calculations honeycomb lattice based parameters derived from functional theory. We find that interaction substrate near edge island gradually opens Dirac cone, which implies soft-wall...
We computed the Raman spectrum of cubic and amorphous Ge${}_{2}$Sb${}_{2}$Te${}_{5}$ (GST) by ab initio phonons an empirical bond polarizability model. Models phase were generated quenching from melt means molecular dynamics simulations. The calculated spectra are in good agreement with experimental data which confirms reliability models emerged All features both crystalline GST can be assigned to vibrations defective octahedra. calculations reveal that Sb-Te is much higher than Ge-Te bonds...
Abstract Phase Change Materials (PCMs) are unique compounds employed in non-volatile random access memory thanks to the rapid and reversible transformation between amorphous crystalline state that display large differences electrical optical properties. In addition amorphous-to-crystalline transition, experimental results on polycrystalline GeSbTe alloys (GST) films evidenced a Metal-Insulator Transition (MIT) attributed disorder phase. Here we report fundamental advance fabrication of GST...
Disorder-induced electron localization and metal-insulator transitions (MITs) have been a very active research field starting from the seminal paper by Anderson half century ago. However, pure insulators are difficult to identify due ubiquitous electron-correlation effects. Recently, an MIT has observed in electrical transport measurements on crystalline state of phase-change GeSbTe compounds, which appears be exclusively disorder driven. Subsequent density functional theory simulations...
Abstract Understanding the nature of chemical bonding in solids is crucial to comprehend physical and properties a given compound. To explore changes lead chalcogenides (PbX, where X = Te, Se, S, O), combination property‐, bond‐breaking‐, quantum‐mechanical descriptors are applied. The outcome explorations reveals an electron‐transfer‐driven transition from metavalent PbX (X S) iono‐covalent β‐PbO. Metavalent characterized by adjacent atoms being held together sharing about single electron...
Abstract The Ge 2 Sb Te 5 alloy has served as the core material in phase-change memories with high switching speed and persistent storage capability at room temperature. However widely used, this composition is not suitable for embedded memories—for example, automotive applications, which require very working temperatures above 300 °C. Ge–Sb–Te alloys higher content, most prominently 1 (‘212’), have been studied alternatives, but their atomic structures structure–property relationships...
Ge-Sb-Te ("GST") alloys are leading phase-change materials for digital memories and neuro-inspired computing. Upon fast crystallization, these form rocksalt-like phases with large structural vacancy disorder, to an insulating phase at low temperature. Here, a comprehensive description of electronic properties GeSb2 Te4 based on realistic, quantum-mechanically ("ab initio") computer simulations system sizes more than 1000 atoms is provided. It shown how analysis the crystallization mechanism...
Ge 2 Sb Te 5 (GST) is an important phase‐change material used in optical and electronic memory devices. In this work, crystal growth of GST at 600 K investigated by ab initio molecular dynamics. Simulations two different crystallization processes are performed. the first set simulations, crystalline nuclei generated using metadynamics method studied. second set, models containing a planar amorphous–crystalline interface considered investigated. The extracted velocities range 1 m s −1 both...
Phase-change materials are technologically important due to their manifold applications in data storage. Here we report on ab initio molecular dynamics simulations of crystallization the phase change material Ag4In3Sb67Te26 (AIST). We show that, at high temperature, observed crystal growth mechanisms and speed good agreement with experimental data. provide an in-depth understanding atomic level. At temperatures below 550 K, computed velocities much higher than those obtained from...
We carry out an ab initio study of the structural, electronic, and magnetic properties zigzag graphene nanoribbons on Cu(111), Ag(111), Au(111). Both, H-free H-terminated are considered revealing that invariably possess edge states when deposited these surfaces. In spite this, they do not exhibit a significant magnetization at edge, with exception Au(111), whose zero-temperature comparable to those free-standing nanoribbons. These results explained by different hybridization between $2p$...
Enhanced crystal nucleation in a Sc–Sb–Te phase-change material has enabled subnanosecond switching memory devices, making cache-type nonvolatile feasible. However, the microscopic mechanisms remain to be further explored. In this work, we present systematic ab initio study of relevant parent compounds, namely, Sc2Te3 and Sb2Te3. Despite similar bond lengths angles amorphous phases two displays much more ordered network without homopolar bonds. As result, local structural order is dominated...