Analysis, characterization and some properties of polyacrylamide-Ni(II) complexes

The complexation of polyarylamide (PAam) with Ni(II) metal ions at different concentrations was investigated. The metal complexes were characterized by fourier transform infrared spectroscopy (FTIR), UV-visible, differential scanning calorimeter (DSC) and atomic force microscope (AFM). FTIR spectroscopy was used to study the characteristic shifts of the absorbance bands of C=O and N-H2. UV-visible spectroscopy was used to follow the complex formation of PAam-Ni(II) and showed the appearance of a new band that was absent both in PAam and Ni(II) salt solutions. Thermal parameters, such as the glass transition temperature (Tg) and the melting point (Tm) of the polymer-metal complex have been measured by DSC. The variation of Tg and Tm with different Ni(II) concentrations was attributed to the complexation of the native polymer during the increasing of Ni(II) concentration. AFM was used to study the surface morphology of PAam films and its complexation with Ni(II) at different concentrations. The root mean square roughness increased as the Ni(II) concentration increases

Study on the morphology of polyacrylamide – silica fumed nanocomposite thin films

Silica fumed nanoparticles were dispersed in polyacrylamide thin films by direct mixing. Atomic Force Microscopy study was carried out in order to analyze the surface roughness. Height distribution of surface roughness changes from Gaussian like for polyacrylamide to skew asymmetric when increasing the silica concentration. The length of the distribution tail increases, indicating the formation of multi-scale features that increase in number and size, as the silica increase.The authors acknowledge the financial support of the German research foundation (DFG), French academy of sciences and French Ministry of Foreign Affairs, Prof. Philippe Meyer and the Meyer Foundation

Nanoscale Heterogeneity of Multilayered Si Anodes with Embedded Nanoparticle Scaffolds for Li-Ion Batteries

A new approach on the synthesis of Si anodes for Li‐ion batteries is reported, combining advantages of both nanoparticulated and continuous Si films. A multilayered configuration prototype is proposed, comprising amorphous Si arranged in nanostructured, mechanically heterogeneous films, interspersed with Ta nanoparticle scaffolds. Particular structural features such as increased surface roughness, nanogranularity, and porosity are dictated by the nanoparticle scaffolds, boosting the lithiation process due to fast Li diffusion and low electrode polarization. Consequently, a remarkable charge/discharge speed is reached with the proposed anode, in the order of minutes (1200 mAh g−1 at 10 C). Moreover, nanomechanical heterogeneity self‐limits the capacity at intermediate charge/discharge rates; as a consequence, exceptional cycleability is observed at 0.5 C, with 100% retention over 200 cycles with 700 mAh g−1. Higher capacity can be obtained when the first cycles are performed at 0.2 C, due to the formation of microislands, which facilitate the swelling of the active Si. This study indicates a method to tune the mechanical, morphological, and electrochemical properties of Si electrodes via engineering nanoparticle scaffolds, paving the way for a novel design of nanostructured Si electrodes for high‐performance energy storage devices

Site-Specific Wetting of Iron Nanocubes by Gold Atoms in Gas-Phase Synthesis

A key challenge in nanotechnology is the rational design of multicomponent materials that beat the properties of their elemental counterparts. At the same time, when considering the material composition of such hybrid nanostructures and the fabrication process to obtain them, one should favor the use of nontoxic, abundant elements in view of the limited availability of critical metals and sustainability. Cluster beam deposition offers a solvent- and, therefore, effluent-free physical synthesis method to achieve nanomaterials with tailored characteristics. However, the simultaneous control of size, shape, and elemental distribution within a single nanoparticle in a small-size regime (sub-10 nm) is still a major challenge, equally limiting physical and chemical approaches. Here, a single-step nanoparticle fabrication method based on magnetron-sputtering inert-gas condensation is reported, which relies on selective wetting of specific surface sites on precondensed iron nanocubes by gold atoms. Using a newly developed Fe-Au interatomic potential, the growth mechanism is decomposed into a multistage model implemented in a molecular dynamics simulation framework. The importance of growth kinetics is emphasized through differences between structures obtained either experimentally or computationally, and thermodynamically favorable configurations determined via global optimization techniques. These results provide a roadmap for engineering complex nanoalloys toward targeted applications.Peer reviewe

Inoculation of silicon nanoparticles with silver atoms

Peer reviewe

Tuning the onset of ferromagnetism in heterogeneous bimetallic nanoparticles by gas phase doping

In the nanoregime, chemical species can reorganize in ways not predicted by their equilibrium bulk behavior. Here, we engineer Ni-Cr nanoalloys at the magnetic end of their compositional range (i.e., 0–15 at. % Cr), and we investigate the effect of Cr incorporation on their structural stability and resultant magnetic ordering. To ensure their stoichiometric compositions, the nanoalloys are grown by cluster beam deposition, a method that allows one-step, chemical-free fabrication of bimetallic nanoparticles. While full Cr segregation toward nanoparticle surfaces is thermodynamically expected for low Cr concentrations, metastability occurs as the Cr dopant level increases in the form of residual Cr in the core region, yielding desirable magnetic properties in a compensatory manner. Using nudged elastic band calculations, residual Cr in the core is explained based on modifications in the local environment of individual Cr atoms. The resultant competition between ferromagnetic and antiferromagnetic ordering gives rise to a wide assortment of interesting phenomena, such as a cluster-glass ground state at very low temperatures and an increase in Curie temperature values. We emphasize the importance of obtaining the commonly elusive magnetic nanophase diagram for M-Cr (M=Fe, Co, and Ni) nanoalloys, and we propose an efficient single-parameter method of tuning the Curie temperature for various technological applications.Peer reviewe

Gas-Phase Synthesis of Trimetallic Nanoparticles

To this day, engineering nanoalloys beyond bimetallic compositions has scarcely been within the scope of physical deposition methods due to the complex, nonequilibrium processes they entail. Here, we report a gas-phase synthesis strategy for the growth of multimetallic nanoparticles: magnetron-sputtering inert-gas condensation from neighboring monoelemental targets provides the necessary compositional flexibility, whereas in-depth atomistic computer simulations elucidate the fast kinetics of nucleation and growth that determines the resultant structures. We fabricated consistently trimetallic Au–Pt–Pd nanoparticles, a system of major importance for heterogeneous catalysis applications. Using high-resolution transmission electron microscopy, we established their physical and chemical ordering: Au/Pt-rich core@Pd-shell atomic arrangements were identified for particles containing substantial amounts of all elements. Decomposing the growth process into basic steps by molecular dynamics simulations, we identified a fundamental difference between Au/Pt and Pd growth dynamics: Au/Pt electronic arrangements favor the formation of dimer nuclei instead of larger-size clusters, thus significantly slowing down their growth rate. Consequently, larger Pd particles formed considerably faster and incorporated small Au and Pt clusters by means of in-flight decoration and coalescence. A broad range of icosahedral, truncated-octahedral, and spheroidal face-centered cubic trimetallic nanoparticles were reproduced in simulations, in good agreement with experimental particles. Comparing them with their expected equilibrium structures obtained by Monte Carlo simulations, we identified the particles as metastable, due to out-of-equilibrium growth conditions. We aspire that our in-depth study will constitute a significant advance toward establishing gas-phase aggregation as a standard method for the fabrication of complex nanoparticles by design.Peer reviewe

Aggregation vs Surface Segregation: Antagonism over the Magnetic Behavior of NiCr Nanoparticles

Annealing is a valuable method for fine-tuning the ultrasmall magnetic properties of alloy nanoparticles (NPs) by controlling their sizes, modifying their surfaces, and affecting their magnetic interactions. Herein, we study the effect of moderate annealing (450°C) on strongly interacting NiCr nanoparticle assemblies (0 <= atom % Cr ≤ 15) immediately after deposition. Concurrent temperature-dependent electron microscopy and magnetization data demonstrate the interplay of two competing factors, namely, enhanced particle aggregation and element-specific surface segregation, on the magnetic properties, with the former boosting and the latter suppressing them. Strong interparticle interactions can lead to a magnetic response different from that of superparamagnetic particles, namely, from canonical spin-glass (0 atom % Cr) to correlated spin-glass (5-15 atom % Cr) behavior below higher spin-glass transition temperatures T-g (20-350 K). The observation of "high-field susceptibility" below cryogenic temperatures (≤20 K) is ascribed to the presence of inhomogeneity/defects caused by Cr segregation. This work emphasizes the necessity of taking into account the delicate balance of such competing factors to understand the magnetic properties of nanoparticulate samples

Hydrogen Flux through Size Selected Pd Nanoparticles into Underlying Mg Nanofilms

The application of Mg for hydrogen storage is hindered due to the slow absorption of hydrogen in Mg films. Herein, the hydrogenation process is explored theoretically using density functional theory calculations, and energy barriers are compared for hydrogen diffusion through Pd nanoparticle/Mg film interfaces and their variations, i.e., Pd(H)/Mg(O). Decomposing the mechanism into basic steps, it is shown that Pd undergoes a strain‐induced crystallographic phase transformation near the interface, and indicated that hydrogen saturation of Pd nanoparticles enhances their efficiency as nanoportals. Using energetic arguments, it is explained why hydrogen diffusion is practically prohibited through native Mg oxide and seriously suppressed through existing hydride domains. Hydrogen flux is experimentally investigated through the nanoportals in Pd‐nanoparticle decorated Mg films by pressure‐composition isotherm measurements. An r ≈ t1/3 relationship is theoretically calculated for the radial growth of hemispherical hydride domains, and this relationship is confirmed by atomic force microscopy. The diffusion constant of hydrogen in Mg films is estimated as DHfilm ≈ 8 × 10−18 m2 s−1, based on transmission electron microscopy characterization. The unique nanoportal configuration allows direct measurement of hydride domain sizes, thus forming a model system for the experimental investigation of hydrogenation in any material