Francesco Mauri

Bio: Francesco Mauri is an academic researcher from Sapienza University of Rome. The author has contributed to research in topics: Graphene & Phonon. The author has an hindex of 85, co-authored 352 publications receiving 69332 citations. Previous affiliations of Francesco Mauri include University of Texas at Arlington & University of California, Berkeley.

New Insight in Scandium-Mediated Growth Techniques: Sc-Related Defects in 4H-SiC and 6H-SiC

Abstract: Scandium can be used to influence the stoichiometry of SiC during growth of the hexagonal polytypes. Using PL-EPR and total energy calculations in the framework of density functional theory, scandium is predicted to be built in predominantly at the Si-sublattice in form of ScSi acceptors with acceptor levels at 0.55 eV (6H-SiC) and 0.48 eV (4H-SiC). In addition, new PL-EPR spectra are found with a large anisotropy in the g-tensor suggesting defect pairs as an origin.

Bending rigidity and sound propagation in graphene

Abstract: Despite the interest raised by graphene and 2D materials, their mechanical and acoustic properties are still highly debated. Harmonic theory predicts a quadratic dispersion for the flexural acoustic mode. Such a quadratic dispersion leads to diverging atomic fluctuations and a constant linewidth of in-plane acoustic phonon modes at small momentum, which implies that graphene cannot propagate sound waves. Many works based on membrane theory questioned the robustness of the quadratic dispersion, arguing that the anharmonic phonon-phonon interaction linearizes it, which implies a divergent bending rigidity (stiffness) in the long wavelength limit. However, these works are based on effective low-energy models that explicitly break the rotational invariance. Here we show that rotational symmetry protects the quadratic flexural dispersion against phonon-phonon interaction, and that the bending stiffness of graphene is unaffected by temperature and quantum fluctuations. Nevertheless, our non-perturbative anharmonic calculations predict that sound propagation coexists with such a quadratic dispersion. Since our conclusions are universal properties of membranes, they apply not just to graphene, but to all 2D materials.

An investigation of weak CH center dot center dot center dot O hydrogen bonds in maltose anomers by a combination of calculation and experimental solid-state NMR spectroscopy

Abstract: Two-dimensional H-1-C-13 MAS-J-HMQC solid-state NMR spectra of the two anomeric forms of maltose at natural abundance are presented. The experimental H-1 chemical shifts of the CH and CH2 protons are assigned using first-principles chemical shift calculations that employ a plane-wave pseudo-potential approach. Further calculations show that the calculated change in the 1H chemical shift when comparing the full crystal and an isolated molecule is a quantitative measure of intermolecular C-(HO)-O-... weak hydrogen bonding. Notably, a clear correlation between a large chemical shift change (up to 2 ppm) and both a short (HO)-O-... distance (< 2.7 angstrom) and a CHO bond angle greater than 1301 is observed, thus showing that directionality is important in C-(HO)-O-... hydrogen bonding.

Crystallographic distortion around chromium and iron in rubies and sapphires

Abstract: The crystallographic distortion around chromium and iron has been investigated by use of both theoretical and experimental methods. Through the analysis of the isotropic and dichroic Extended X-ray Absorption Fine Structures at the Cr K-edge, the Cr–O distances have been measured in the distorted chromium coordination shell. Through ab initio molecular dynamics, the distortion of the chromium site has been independently calculated.

The Edges of Hydrogen Terminated Graphene Ribbons Energetics, Bandstructure and Magnetization

Abstract: In this thesis we have examined the edges of hydrogen-terminated single-sheet graphene ribbons by means of ab initio density functional theory calculations. Edges in different crystal symmetry directions, with different planar reconstructions and different edge-hydrogen densities were considered. The studies concentrated on the analysis of the formation energy, the bandstructure and the magnetism of the ribbons. Following our primary goal, the identification of the energetically most favorable edge configuration under different chemical conditions, the formation energy was translated to a broad sector in thermodynamical phase space via the chemical potential of molecular hydrogen. These considerations reveal that at room temperature and under ambient hydrogen pressure the monohydrogenated armchair ribbon represents the most stable configuration. In the area of negative formation energy where spontaneous breaking is possible, the dihydrogenated armchair ribbon becomes most favorable. None of the armchair ribbons analyzed in this study showed magnetism whereas zigzag ribbons can be magnetic or not depending on the edge configuration. The region where magnetism occurs, however could be reduced to low pressure, high temperature conditions. The zero-point formation energies calculated here confirm our expectations based on the analysis of the Clar structures of the ribbons.

The rise of graphene

Abstract: Graphene is a rapidly rising star on the horizon of materials science and condensed-matter physics. This strictly two-dimensional material exhibits exceptionally high crystal and electronic quality, and, despite its short history, has already revealed a cornucopia of new physics and potential applications, which are briefly discussed here. Whereas one can be certain of the realness of applications only when commercial products appear, graphene no longer requires any further proof of its importance in terms of fundamental physics. Owing to its unusual electronic spectrum, graphene has led to the emergence of a new paradigm of 'relativistic' condensed-matter physics, where quantum relativistic phenomena, some of which are unobservable in high-energy physics, can now be mimicked and tested in table-top experiments. More generally, graphene represents a conceptually new class of materials that are only one atom thick, and, on this basis, offers new inroads into low-dimensional physics that has never ceased to surprise and continues to provide a fertile ground for applications.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

The electronic properties of graphene

Abstract: This article reviews the basic theoretical aspects of graphene, a one-atom-thick allotrope of carbon, with unusual two-dimensional Dirac-like electronic excitations. The Dirac electrons can be controlled by application of external electric and magnetic fields, or by altering sample geometry and/or topology. The Dirac electrons behave in unusual ways in tunneling, confinement, and the integer quantum Hall effect. The electronic properties of graphene stacks are discussed and vary with stacking order and number of layers. Edge (surface) states in graphene depend on the edge termination (zigzag or armchair) and affect the physical properties of nanoribbons. Different types of disorder modify the Dirac equation leading to unusual spectroscopic and transport properties. The effects of electron-electron and electron-phonon interactions in single layer and multilayer graphene are also presented.