Equilibrium structure and shape of Ag and Pt nanoparticles grown on silica surfaces: From experimental investigations to the determination of a metal-silica potential.

A combination of experimental and numerical investigations on metallic silver and platinum nanoparticles deposited on silica substrates is presented, with a focus on metal-substrate interactions. Experimentally, the nanoparticles, obtained by ultra-high vacuum atom deposition, are characterized by grazing-incidence small-angle x-ray scattering and high resolution transmission electronic microscopy to determine their structure and morphology and, in particular, their aspect ratio (height/diameter), which quantifies the metal-substrate interaction, from the as-grown to equilibrium state. Numerically, the interactions between the metal and the silica species are modeled with the Lennard-Jones (12, 6) potential, with two parameters for each metal and silica species.

Sudden collective atomic rearrangements trigger the growth of defect-free silver icosahedra.

The growth of Ag clusters on amorphous carbon substrates is studied by X-ray scattering experiments, whose final outcome is imaged by electron microscopy. The real-time analysis of the growth process at room temperature shows the formation of a large majority of icosahedral structures by a shell-by-shell growth mode which produces smooth and nearly defect-free structures. Molecular dynamics simulations supported by calculations reveal that the shell-by-shell mode is possible because of the occurrence of collective displacements which involve the concerted motion of many atoms of the growing shell.

Effect of Nanographene Coating on the Seebeck Coefficient of Mesoporous Silicon.

Nanographene-mesoporous silicon (G-PSi) composites have recently emerged as a promising class of nanomaterials with tuneable physical properties. In this study, we investigated the impact of nanographene coating on the Seebeck coefficient of mesoporous silicon (PSi) obtained by varying two parameters: porosity and thickness. To achieve this, an electrochemical etching process on p + doped Si is presented for the control of the parameters (thicknesses varying from 20 to 160 µm, and a porosity close to 50%), and for nanographene incorporation through chemical vapor deposition.

Combined atomistic simulations to explore metastability and substrate effects in Ag-Co nanoalloy systems.

The Ag/Co nanoalloy system is a model system situated energetically at the limit of stability of the core-shell chemical ordering with respect to a simple phase separation behavior. This makes the system highly susceptible to effects of the environment, such as interaction with a substrate. However, kinetic effects may also be exploited by careful atom-by-atom particle growth that allows to lock in certain out-of-equilibrium configurations, such as off-center, quasi-Janus and even Janus type particles.

Structural and optical characterization of nanoalloys mixing gold or silver with aluminium or indium: evolution under various reactive environments.

In this study, the atomic and chemical structure and the optical response of AB bimetallic nanoparticles (BNPs) combining gold or silver (A) with aluminium or indium (B) were investigated at various stoichiometries in order to examine if stable alloyed phases could exist and promote the emergence of localized surface plasmon resonance (LSPR) in the UV range. The structure and morphology of BNPs of a few nanometres, produced by laser vaporization, were analysed by transmission electron microscopy (TEM) and optical absorption measurements were performed on matrix-embedded BNPs. Information about the oxidation state of the BNPs can be inferred from a comparison between experimental optical spectra and Mie calculations in the dipolar approximation.

Plasmon-driven methanol oxidation on PtAg nanoalloys prepared by improved pulsed laser deposition.

The methanol oxidation reaction (MOR) is crucial in many energy-conversion devices. Although intensive efforts have been devoted to improving the MOR catalytic activity of Pt-based catalysts by treatment or alloying, enhancing the MOR catalyst performance utilizing solar energy has been less investigated. PtAg nanoalloys, combining the intrinsic catalytic activity of Pt toward the MOR with the visible spectrum plasmonic response of Ag, are expected to be a good MOR catalyst for solar energy, however, it remains challenging to incorporate these immiscible elements into a nanoalloy in a controlled way using conventional synthetic techniques.

The five shades of oleylamine in a morphological transition of cobalt nanospheres to nanorods.

Understanding of cobalt nanorods' (Co NRs) formation still remains challenging when it comes to enhancing their anisotropic properties applicable in magnetic or catalytic areas. Herein, we propose a mechanism for the morphological transition from spherical cobalt nanoparticles (NPs) to Co NRs over time (9 h) in a mixture of [CoCl(PPh)] and oleylamine (OAm). In the literature, we described how spherical Co NPs are synthesized via a disproportionation process.

From metastability to equilibrium during the sequential growth of Co-Ag supported clusters: a real-time investigation.

Atomic motions and morphological evolution of growing Co-Ag nanoparticles are followed in situ and in real time, by wide and small angle X-ray scattering obtained simultaneously in grazing incidence geometry (GISAXS and GIWAXS), in single or multi-wavelength anomalous modes. The structural analysis of the experimental data is performed with the aid of equilibrium Monte Carlo simulations and of molecular-dynamics simulations of nanoparticle growth. Growth is performed by depositing Co atoms above preformed Ag nanoparticles.

Reversed size-dependent stabilization of ordered nanophases.

The size increase of a nanoscale material is commonly associated with the increased stability of its ordered phases. Here we give a counterexample to this trend by considering the formation of the defect-free L1 ordered phase in AgPt nanoparticles, and showing that it is better stabilized in small nanoparticles (up to 2.5 nm) than in larger ones, in which the ordered phase breaks in multiple domains or is interrupted by faults.

Thin Films with Perpendicular Tetragonally Packed Rectangular Rods Obtained from Blends of Linear ABC Block Terpolymers.

A binary blend of poly(isoprene--styrene--(2-vinylpyridine)) (ISP) triblock terpolymers, having the same chain length but different compositions, was used to achieve an ordered lattice with 4-fold symmetry of rectangular-shaped rods of poly(isoprene) (I) and poly(2-vinylpyridine) (P). In given conditions, the I and P domains were oriented perpendicularly to the substrate, providing an appealing type of templates for nanopatterning. Thin films were prepared by spin coating, exposed to solvent vapor (providing morphological reorganization), and then characterized by atomic force microscopy, transmission electron microscopy, and grazing-incidence small-angle X-ray scattering.

Solvothermal Vapor Annealing of Lamellar Poly(styrene)-block-poly(d,l-lactide) Block Copolymer Thin Films for Directed Self-Assembly Application.

Solvothermal vapor annealing (STVA) was employed to induce microphase separation in a lamellar forming block copolymer (BCP) thin film containing a readily degradable block. Directed self-assembly of poly(styrene)-block-poly(d,l-lactide) (PS-b-PLA) BCP films using topographically patterned silicon nitride was demonstrated with alignment over macroscopic areas. Interestingly, we observed lamellar patterns aligned parallel as well as perpendicular (perpendicular microdomains to substrate in both cases) to the topography of the graphoepitaxial guiding patterns.

Platinum and platinum based nanoalloys synthesized by wet chemistry.

Platinum nanocrystals and their derivatives with palladium and cobalt are of fundamental interest due to their wide field of application in chemistry and physics. Their properties are strongly dependent on their shape and composition. However the chemical route is far from allowing control of both shape and composition.

Color-switchable, emission-enhanced fluorescence realized by engineering C-dot@C-dot nanoparticles.

This paper reports the preparation and properties of color-switchable fluorescent carbon nanodots (C-dots). C-dots that emit dark turquoise and green-yellow fluorescence under 365 nm UV illumination were obtained from the hydrothermal decomposition of citric acid. Dark green fluorescent C-dots were obtained by conjugating prepared C-dots to form C-dot@C-dot nanoparticles.

Local tuning of CoPt nanoparticle size and density with a focused ion beam nanowriter.

Ultra-small CoPt nanoparticles (NPs) with a mean diameter of 1.3 nm (around 100 atoms) were deposited on a thin 5 nm self-supported amorphous carbon membrane. The effects of focused irradiation with a newly developed Ga(+) ion source were studied by transmission electron microscopy.

Controlling structure and morphology of CoPt nanoparticles through dynamical or static coalescence effects.

The structure and morphology of 1 to 3 nm size CoPt nanoparticles have been investigated in situ and in real time under different conditions: growth at 500 degrees C or at room temperature (RT) followed by annealing at 500 degrees C. The small-angle x-ray scattering measurements show size and temperature dependent growth mode with particle motions on the surface, while wide-angle scattering results, supported by Monte Carlo simulations, allow structure identification. If icosahedra are systematically detected at the first growth stages at RT, annealing at 500 degrees C yields the decahedral structure from the quasistatic coalescence of icosahedral morphology.