Electrical Sintering of Silver Nanoparticle Ink Studied by In-Situ TEM Probing

Metallic nanoparticle inks are used for printed electronics, but to reach acceptable conductivity the structures need to be sintered, usually using a furnace. Recently, sintering by direct resistive heating has been demonstrated. For a microscopic understanding of this Joule heating sintering method, we studied the entire process in real time inside a transmission electron microscope equipped with a movable electrical probe. We found an onset of Joule heating induced sintering and coalescence of nanoparticles at power levels of 0.1–10 mW/m3. In addition, a carbonization of the organic shells that stabilize the nanoparticles were found, with a conductivity of 4 105 Sm−1

Size-Dependent Materials Properties Toward a Universal Equation

Due to the lack of experimental values concerning some material properties at the nanoscale, it is interesting to evaluate this theoretically. Through a “top–down” approach, a universal equation is developed here which is particularly helpful when experiments are difficult to lead on a specific material property. It only requires the knowledge of the surface area to volume ratio of the nanomaterial, its size as well as the statistic (Fermi–Dirac or Bose–Einstein) followed by the particles involved in the considered material property. Comparison between different existing theoretical models and the proposed equation is done

Discrete plasticity in sub-10-nm-sized gold crystals

Although deformation processes in submicron-sized metallic crystals are well documented, the direct observation of deformation mechanisms in crystals with dimensions below the sub-10-nm range is currently lacking. Here, through in situ high-resolution transmission electron microscopy (HRTEM) observations, we show that (1) in sharp contrast to what happens in bulk materials, in which plasticity is mediated by dislocation emission from Frank-Read sources and multiplication, partial dislocations emitted from free surfaces dominate the deformation of gold (Au) nanocrystals; (2) the crystallographic orientation (Schmid factor) is not the only factor in determining the deformation mechanism of nanometre-sized Au; and (3) the Au nanocrystal exhibits a phase transformation from a face-centered cubic to a body-centered tetragonal structure after failure. These findings provide direct experimental evidence for the vast amount of theoretical modelling on the deformation mechanisms of nanomaterials that have appeared in recent years

Tetrahedral (T) closed-shell cluster of 29 silver atoms & 12 lipoate ligands, [Ag29(R-a-LA)12](3-): antibacterial and antifungal activity

Accepted author manuscriptHere we report on the identification and applications of an aqueous 29-atom silver cluster stabilized with 12 lipoate ligands, i.e. Ag29(R-α–LA)12 or (29,12), wherein R-α–LA = R-α-lipoic acid, a natural dithiolate. Its uniformity is checked by HPLC-ESI-MS and analytical ultracentrifugation, which confirms its small dimension (∼3 nm hydrodynamic diameter). For the first time, this cluster has been detected intact via electrospray ionization mass spectrometry, allowing one to confirm its composition, its [3-] charge-state, and the 8-electron shell configuration of its metallic silver core. Its electronic structure and bonding, including T-symmetry and profound chirality in the outer shell, have been analyzed by DFT quantum-chemical calculations, starting from the known structure of a nonaqueous homologue. The cluster is effective against Methicillin-Resistant Staphylococcus aureus bacteria (MRSA) at a minimum inhibitory concentration (MIC) of 0.6 mg-Ag/mL. A preformed Candida albicans fungal biofilm, impermeable to other antifungal agents, was also inhibited by aqueous solutions of this cluster, in a dose–response manner, with a half-maximal inhibitory concentration (IC50) of 0.94 mg-Ag/mL. Scanning electron micrographs showed the post-treatment ultrastructural changes on both MRSA and C. albicans that are characteristic of those displayed after treatment by larger silver nanoparticles.Ye

Direct observation of the mechanical properties of single-walled carbon nanotubes and their junctions at the atomic level

Starting from an amorphous C film, single-walled carbon nanotubes were obtained in situ in a high-resolution electron microscope by the combined effect of irradiation and axial strain. Ductile nanotubes developed either a junction or a linear chain of C atoms before failure. These facts have been put in direct evidence for the first time. Tight-binding calculations indicate that the bonding in the linear chain is of a cumulene type.This work was supported by the CONYCYT, Argentina, by special funds from Texas Materials Institute and the Center for Nano and Molecular Technology (UT-Austin), CONACYT, México, the University of the Basque Country, DGES, and by the EU research training network NANOPHASE (HPRN-CT-2000-00167).Peer reviewe