Institut des Matériaux, de Microélectronique et des Nanosciences de Provence

Using atomic resolved scanning tunneling microscopy, we present here the experimental evidence of a silicene sheet (graphenelike structure) epitaxially grown on a close-packed silver surface [Ag(111)]. This has been achieved via direct condensation of a silicon atomic flux onto the single-crystal substrate in ultrahigh vacuum conditions. A highly ordered silicon structure, arranged within a honeycomb lattice, is synthesized and present two silicon sublattices occupying positions at different heights (0.02 nm) indicating possible sp2-sp3 hybridizations.

On-surface synthesis is appearing as an extremely promising research field aimed at creating new organic materials. A large number of chemical reactions have been successfully demonstrated to take place directly on surfaces through unusual reaction mechanisms. In some cases the reaction conditions can be properly tuned to steer the formation of the reaction products. It is thus possible to control the initiation step of the reaction and its degree of advancement (the kinetics, the reaction yield); the nature of the reaction products (selectivity control, particularly in the case of competing processes); as well as the structure, position, and orientation of the covalent compounds, or the quality of the as-formed networks in terms of order and extension. The aim of our review is thus to provide an extensive description of all tools and strategies reported to date and to put them into perspective. We specifically define the different approaches available and group them into a few general categories. In the last part, we demonstrate the effective maturation of the on-surface synthesis field by reporting systems that are getting closer to application-relevant levels thanks to the use of advanced control strategies.

sp2 hybridized carbons constitute a broad class of solid phases composed primarily of elemental carbon and can be either synthetic or naturally occurring. Some examples are graphite, chars, soot, graphene, carbon nanotubes, pyrolytic carbon, and diamond-like carbon. They vary from highly ordered to completely disordered solids and detailed knowledge of their internal structure and composition is of utmost importance for the scientific and engineering communities working with these materials. Multiwavelength Raman spectroscopy has proven to be a very powerful and non-destructive tool for the characterization of carbons containing both aromatic domains and defects and has been widely used since the 1980s. Depending on the material studied, some specific spectroscopic parameters (e.g., band position, full width at half maximum, relative intensity ratio between two bands) are used to characterize defects. This paper is addressed first to (but not limited to) the newcomer in the field, who needs to be guided due to the vast literature on the subject, in order to understand the physics at play when dealing with Raman spectroscopy of graphene-based solids. We also give historical aspects on the development of the Raman spectroscopy technique and on its application to sp2 hybridized carbons, which are generally not presented in the literature. We review the way Raman spectroscopy is used for sp2 based carbon samples containing defects. As graphene is the building block for all these materials, we try to bridge these two worlds by also reviewing the use of Raman spectroscopy in the characterization of graphene and nanographenes (e.g., nanotubes, nanoribbons, nanocones, bombarded graphene). Counterintuitively, because of the Dirac cones in the electronic structure of graphene, Raman spectra are driven by electronic properties: Phonons and electrons being coupled by the double resonance mechanism. This justifies the use of multiwavelength Raman spectroscopy to better characterize these materials. We conclude with the possible influence of both phonon confinement and curvature of aromatic planes on the shape of Raman spectra, and discuss samples to be studied in the future with some complementary technique (e.g., high resolution transmission electron microscopy) in order to disentangle the influence of structure and defects.

H2O, CO2, SO2, O2, H2, H2S, HCl, chlorinated hydrocarbons, NO, and other trace gases were evolved during pyrolysis of two mudstone samples acquired by the Curiosity rover at Yellowknife Bay within Gale crater, Mars. H2O/OH-bearing phases included 2:1 phyllosilicate(s), bassanite, akaganeite, and amorphous materials. Thermal decomposition of carbonates and combustion of organic materials are candidate sources for the CO2. Concurrent evolution of O2 and chlorinated hydrocarbons suggests the presence of oxychlorine phase(s). Sulfides are likely sources for sulfur-bearing species. Higher abundances of chlorinated hydrocarbons in the mudstone compared with Rocknest windblown materials previously analyzed by Curiosity suggest that indigenous martian or meteoritic organic carbon sources may be preserved in the mudstone; however, the carbon source for the chlorinated hydrocarbons is not definitively of martian origin.

Supramolecular chemistry on a surface has produced a large variety of atomically controlled systems, but practical applications are seriously restricted by the use of weakly cohesive non-covalent bonds and by the confinement to a metal surface. Here we report on the formation of a well-ordered organometallic sheet consisting of two-dimensional polymeric phthalocyanine. Remarkably, the growth demonstrated on a metal surface can be extended onto a thin insulating film. We thus expect the intrinsic properties to be preserved, and the system should be easily transferable to real devices.

We explore the use of continuous scanning during data acquisition for Bragg coherent diffraction imaging, i.e., where the sample is in continuous motion. The fidelity of continuous scanning Bragg coherent diffraction imaging is demonstrated on a single Pt nanoparticle in a flow reactor at [Formula: see text] in an Ar-based gas flowed at 50 ml/min. We show a reduction of 30% in total scan time compared to conventional step-by-step scanning. The reconstructed Bragg electron density, phase, displacement and strain fields are in excellent agreement with the results obtained from conventional step-by-step scanning. Continuous scanning will allow to minimise sample instability under the beam and will become increasingly important at diffraction-limited storage ring light sources.

) spinel structure. Using FTIR spectra, the elastic and thermodynamic properties were estimated. It was observed that the particle size had a pronounced effect on elastic and thermodynamic properties. Magnetic measurements were performed up to 700 K. The prepared ferrite samples present the highest Curie temperature, which decreases with increasing particle size and which is consistent with finite-size scaling. The thickness of the surface shell of about 1 nm was estimated from size-dependent magnetization measurements using the core-shell model. Besides, spin resonance, magnetostriction, temperature coefficient of resistance (TCR), and electrical resistivity properties have been scientifically studied and appear to be different according to their size. The optical properties of synthesized NZFAO nanoparticles were investigated, and the differences caused by the particle sizes are discussed on the basis of the phonon confinement effect. This effect was also inspected by the Raman analysis. Tuning of the physical properties suggests that the Ni-Zn-Al ferrite samples may be promising for multifunctional diverse applications.

We present a study of the structural, electronic, vibrational, and elastic properties of the orthorhombic NiSi structure by means of the density-functional theory and the density-functional perturbative theory, with the Perdew-Burke-Ernzerhof generalized gradient approximation of the exchange-correlation functional, within its spin-polarized version. The optimized lattice parameters, the formation energy, and vibrational properties are found in agreement with experimental data. We show that NiSi is not ferromagnetic, with a low density of states at the Fermi level. Elastic constants have been calculated by means of three different approaches for comparison. In the first two, the calculated energy $E$ is fitted as a function of the deformation, atomic positions are either relaxed or not relaxed during the simulations. Atomic relaxations are shown to modify significantly elastic constants. In the third approach we have related acoustic velocities to elastic constants. NiSi is shown to be highly anisotropic. In particular the linear bulk modulus along $b$ axis is much larger than along other axes. Polycrystalline elastic properties and Debye temperature have been also evaluated for a complete description of elastic properties.

A general review is presented concerning jointly the crystallographic structures and the solid−solid and solid−liquid transition temperatures and enthalpies in the pure normal alkanes, as well as the structural and thermodynamic behavior of their synthetic binary, ternary, and multinary model mixtures and of real petroleum waxes. A major part of the structural and thermodynamic data of the literature, relative to the pure n-alkanes, are listed from methane up to the alkane with carbon atom number equal to 390. Variation relationships of the crystallographic long c-parameter that corresponds to the periodicity of the molecule layer packing along their axis, melting temperatures, and transition enthalpies are given as a function of the carbon atom number. The study of the literature on the n-alkane mixtures highlights the existence of isostructural binary, ternary, and multinary intermediate solid solutions which can be likened to a single pseudocomponent. This intermediate solid solution is equivalent to a hypothetical pure n-alkane whose carbon atom number is equal to the average carbon atom number of the mixtures. As a result, the solubility of these multinary solid solutions or real multiparaffinic waxes in linear, cyclic, or aromatic light solvents is identical to that of the pure n-alkanes: pseudobinary eutectic crystallization of the model or real wax as a single pseudocomponent on one hand and the light solvent on the other hand.

Photovoltaic generation has stepped up within the last decade from outsider status to one of the important contributors of the ongoing energy transition, with about 1.7% of world electricity provided by solar cells. Progress in materials and production processes has played an important part in this development. Yet, there are many challenges before photovoltaics could provide clean, abundant, and cheap energy. Here, we review this research direction, with a focus on the results obtained within a Japan-French cooperation program, NextPV, working on promising solar cell technologies. The cooperation was focused on efficient photovoltaic devices, such as multijunction, ultrathin, intermediate band, and hot-carrier solar cells, and on printable solar cell materials such as colloidal quantum dots.

We report on the magnetic properties of thoroughly characterized Zn(1-x)Co(x)O epitaxial thin films, with low Co concentration, x = 0.003-0.005. Magnetic and EPR measurements, combined with crystal field theory, reveal that isolated Co2+ ions in ZnO possess a strong single ion anisotropy which leads to an "easy plane" ferromagnetic state when the ferromagnetic Co-Co interaction is considered. We suggest that the peculiarities of the magnetization process of this state can be viewed as a signature of intrinsic ferromagnetism in ZnO:Co materials.

The human body is an intricate biochemical-mechanical system, with an exceedingly precise hierarchical organization in which all components work together in harmony across a wide range of dimensions. Many fundamental biological processes take place at surfaces and interfaces (e.g., cell-matrix interactions), and these occur on the nanoscale. For this reason, current health-related research is actively following a biomimetic approach in learning how to create new biocompatible materials with nanostructured features. The ultimate aim is to reproduce and enhance the natural nanoscale elements present in the human body and to thereby develop new materials with improved biological activities. Progress in this area requires a multidisciplinary effort at the interface of biology, physics, and chemistry. In this Review, the major techniques that have been adopted to yield novel nanostructured versions of familiar biomaterials, focusing particularly on metals, are presented and the way in which nanometric surface cues can beneficially guide biological processes, exerting influence on cellular behavior, is illustrated.

In this paper, we show the coexistence of the bipolar and unipolar resistive-switching modes in NiO cells realized using an optimized oxidation process of a Ni blanket layer used as the bottom electrode. The two switching modes can be activated independent of the cell switching history provided the appropriate programming conditions are applied. The bipolar and unipolar switching modes are discussed as driven by electrochemical- and thermal-based mechanisms, respectively. The switching versatility between these two modes is demonstrated both for large oxidized Ni films and for Ni films oxidized at the bottom of small dimension contact holes. The perspective of selecting the desired switching mode in a scaled device made in a small diameter single hole is highly attractive because the specific advantages of the two modes broaden the application scope of the cell and enable larger flexibility in terms of memory architecture.

Abstract As an important metal three-dimensional printing technology, electron beam melting (EBM) is gaining increasing attention due to its huge potential applications in aerospace and biomedical fields. EBM processing of Ti-6Al-4V as well as its microstructure and mechanical properties were extensively investigated. However, it is still lack of quantitative studies regarding its microstructural evolution, indicative of EBM thermal process. Here, we report α′ martensitic transformation and α/β interface evolution in varied printing thicknesses of EBM-printed Ti-6Al-4V block samples by means of atom probe tomography. Quantitative chemical composition analysis suggests a general phase transformation sequence. By increasing in-fill hatched thickness, elemental partitioning ratios arise and β volume fraction is increased. Furthermore, we observe kinetic vanadium segregation and aluminum depletion at interface front and the resultant α/β interface widening phenomenon. It may give rise to an increased α/β lattice mismatch and weakened α/β interfaces, which could account for the degraded strength as printing thickness increases.

Channel hot-carrier degradation presents a renewed interest in the last NMOS nodes where the device reliability of bulk silicon (core) 40 nm and Input/Output (IO) device is difficult to achieve at high temperature as a function of supply voltage VDD and back bias V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">BS</sub> . A three mode interface trap generation is proposed based on the energy acquisition involved in distinct interactions in all the V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">GS</sub> , V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DS</sub> (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">BS</sub> ) conditions as a single I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DS</sub> lifetime dependence is observed with V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">GD</sub> > 0. This gives a new age(t) function useful for accurate DC to AC transfers. Positive temperature activation is explained by the rise of ionization rate with electron-electron scattering (medium I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DS</sub> ) and multi vibrational excitation (higher I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DS</sub> ) which increase the H desorption by thermal emission. The use of forward VBS has shown no gain under CHC for both device types. The main limitation occurs under reverse V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">BS</sub> = -V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DD</sub> in IO where the smaller temperature activation partially compensates the larger damage. In that case a security margin can be established giving a limit of V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">BS</sub> = -V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DD</sub> /2 for design reliability.

A strong polarity effect on the temperature dependence of the leakage current in TiN/HfO2/SiO2/Si capacitors is reported. A model is proposed to explain these experimental results that combines tunneling through the stack and Frenkel–Poole hopping in the HfO2 layer, depending on the value of the gate voltage. It is shown that the polarity effect most probably results from the anisotropy of the band diagram of the HfO2/SiO2 stack, as well as from the location of the shallow traps with respect to the conduction band of the HfO2 layer. Comparison of the model with the experimental results allows an estimate of the trap depth to be between 0.5 and 0.8 eV.

The screening properties of dielectric nanocrystals are analyzed. General arguments confirmed by detailed numerical calculations are presented. It is shown how macroscopic components of the electric field can still be defined for sizes larger than a few Fermi wavelengths and can still be obtained from the bulk dielectric function. The decrease of the average dielectric response with decreasing size is found to be due to the breaking of polarizable bonds at the surface and is not due to the opening of the band gap induced by the confinement.

Depending on the size of the smallest feature, the interaction of light with structured materials can be very different. This fundamental problem is treated by different theories. If first order theories are sufficient to describe the scattering from low roughness surfaces, second order or even higher order theories must be used for high roughness surfaces. Random surface structures can then be designed to distribute the light in different propagation directions. For complex structures such as black silicon, which reflects very little light, the theory needs further development. When the material is periodically structured, we speak about photonic crystals or metamaterials. Different theoretical approaches have been developed and experimental techniques are rapidly progressing. However, some work still remains to understand the full potential of this field. When the material is structured in dimension much smaller than the wavelength, the notion of complex refractive index must be revisited. Plasmon resonance can be excited by a progressing wave on metallic nanoparticles inducing a shaping of the absorption band and of the dispersion of the extinction coefficient. This addresses the problem of the permittivity of such metallic nanoparticles. The coupling between several metallic nanoparticles induces a field enhancement in the surrounding media, which can increase phenomena like scattering, absorption, luminescence, or Raman scattering. For semiconductor nanoparticles, electron confinement also induces a modulated absorption spectra. The refractive index is then modified. The bandgap of the material is changed because of the discretization of the electron energy, which can be controlled by the nanometers size particles. Such quantum dots behave like atoms and become luminescent. The lifetime of the electron in the excited states are much larger than in continuous energy bands. Electrons in coupled quantum dots behave as they do in molecules. Many applications should be forthcoming in the near future in this field of research.

Abstract Phases with spontaneous time-reversal ( $${{{{{{{\mathcal{T}}}}}}}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>T</mml:mi> </mml:math> ) symmetry breaking are sought after for their anomalous physical properties, low-dissipation electronic and spin responses, and information-technology applications. Recently predicted altermagnetic phase features an unconventional and attractive combination of a strong $${{{{{{{\mathcal{T}}}}}}}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>T</mml:mi> </mml:math> -symmetry breaking in the electronic structure and a zero or only weak-relativistic magnetization. In this work, we experimentally observe the anomalous Hall effect, a prominent representative of the $${{{{{{{\mathcal{T}}}}}}}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>T</mml:mi> </mml:math> -symmetry breaking responses, in the absence of an external magnetic field in epitaxial thin-film Mn 5 Si 3 with a vanishingly small net magnetic moment. By symmetry analysis and first-principles calculations we demonstrate that the unconventional d-wave altermagnetic phase is consistent with the experimental structural and magnetic characterization of the Mn 5 Si 3 epilayers, and that the theoretical anomalous Hall conductivity generated by the phase is sizable, in agreement with experiment. An analogy with unconventional d-wave superconductivity suggests that our identification of a candidate of unconventional d-wave altermagnetism points towards a new chapter of research and applications of magnetic phases.

Polarization switching in ferroelectrics has been thought to occur only through the nucleation and growth of new domains. Here we use in situ synchrotron x-ray scattering to monitor switching controlled by applied chemical potential. In sufficiently thin PbTiO₃ films, nucleation is suppressed and switching occurs by a continuous mechanism, i.e., by uniform decrease and inversion of the polarization without domain formation. The observed lattice parameter shows that the electric field in the film during switching reaches the theoretical intrinsic coercive field.