Adhesion forces between tungsten spherical microparticles and tungsten substrates with different roughnesses have been measured using the Atomic Force Microscopy (AFM) colloidal probe technique. Mean roughnesses of the tungsten substrates were measured by AFM and were ranked in three categories i.e. nanoscale, sub-microscale and microscale roughnesses. Experimental Hamaker constant of 37 ± 3.5 × 10 −20 J has been obtained using a spherical tungsten particle of 10.5 µm in radius and a tungsten substrate with nanoscale root-mean-square roughness of rms = 11.5 nm. It was shown that larger roughness of the order rms = 712 nm induces a two order of magnitude decrease on the adhesion of tungsten microparticles compared to a smooth tungsten surface with nanoscale roughness. Comparison with the van der Waals-based adhesion force model of Rabinovich which integrates the roughness of surfaces showed good agreement with experimental pull-off forces even when roughness of the substrate is close to the micrometer range. In such case, measurements have shown that dependency of adhesion force with particle size (in the micrometer range) has a secondary influence compared to the roughness of surfaces.

Copper particles, generated using an atmospheric pressure plasma jet (APPJ), are characterized and their generation is studied. The particle synthesis is based on the vaporization/condensation process. In our study, we used a radiofrequency (RF) plasma jet operating in an inert gas and copper bulk metal as source material. The RF power effects on the plasma characteristics are investigated. Correlating the information obtained by optical emission spectroscopy (OES), with visual investigations and with the profilometric electrode surface analyses we identify a RF power threshold when particles starts to be formed. Moreover, the metal vaporization stabilized after a couple of minutes of discharge operation. The influences of RF power over the particles shape, mean size and size distributions are studied.

Polymer-based nanocomposites have recently received considerable attention due to their unique properties, which makes them feasible for applications in optics, sensors, energy, life sciences, etc. The present work focuses on the synthesis of nanocomposites consisting of a polytetrafluorethylene-like matrix in which metallic nano-silver are embedded, by using multiple magnetron plasmas. By successively exposing the substrate to separate RF magnetrons using as combination of target materials polytetrafluorethylene (PTFE) and silver, individual control of each deposition process is insured, allowing obtaining of structures in which silver nanoparticles are entrapped in-between two PTFE layers with given thicknesses. The topographical and morphological characteristics investigated by means of Scanning Electron Microscopy and Atomic Force Microscopy techniques evidenced the very presence of Ag nanoparticles with typical dimension 7 nm. The chemical composition at various depositing steps was evaluated through X-ray Photoelectron Spectroscopy. We show that the presence of the top PTFE layer prevents silver oxidation, while its thickness allows the tailoring of optical properties, as evidenced by spectroellipsometry. The appearance of chemical bonds between silver atoms and PTFE atoms at interfaces is observed, pointing out that despite of pure physical deposition processes, a chemical interaction between the polymeric matrix and metal is promoted by plasma.

No abstract

No abstract