Control of Size Uniformity of Cu Nanoparticle Array Produced by Plasma-Induced Dewetting.

The effects of plasma parameters such as plasma density, electron temperature, and sheath voltage on the uniformity of Cu nanoparticle arrays were investigated. These parameters were controlled by varying the pressure, RF power, and substrate bias voltage. A floating harmonic method was used to monitor the plasma parameters. Uniform nanoparticle arrays were produced when hole generation was increased by using a high ion.bombardment energy. As oppose to a low energy flux condition, where small and large nanoparticles coexisted due to a small number of holes, a larger number of holes was generated and distributed more uniformly during a high energy flux condition.

Mechanism of solid-state plasma-induced dewetting for formation of copper and gold nanoparticles.

Cu and Au nanoparticles were fabricated by plasma treatment on Cu and Au films at 653 K. The nanoparticles were formed by dewetting the metallic films using plasma. Scanning electron microscopy and transmission electron microscopy investigations showed that the plasma-induced dewetting of the Cu and Au films proceeded through heterogeneous hole nucleation and growth along the grain boundaries to lower the surface energy. The amount of energy transferred to surface atoms by one Ar ion was calculated to be 16.1 eV, which was sufficient for displacing Cu and Au atoms. Compared to thermally activated dewetting, more uniform particles could be obtained by plasma-induced dewetting because a much larger number of holes with smaller sizes was generated. The plasma dewetting process is less sensitive to the oxidation of metallic films compared to the annealing process. As a result, Cu nanoparticles could be fabricated at 653 K, whereas the thermally activated dewetting was not possible.

Deposition of TiN films on Co-Cr for improving mechanical properties and biocompatibility using reactive DC sputtering.

This study reports the deposition of TiN films on Co-Cr substrates to improve the substrates' mechanical properties and biological properties. In particular, the argon to nitrogen (Ar:N(2)) gas flow ratio was adjusted to control the microstructure of the TiN films. A Ti interlayer was also used to enhance the adhesion strength between the Co-Cr substrate and TiN films. A series of TiN films, which are denoted as TiN-(Ar/N(2))1:1, Ti/TiN-(Ar/N(2))1:1, and Ti/TiN-(Ar:N(2))1:3, were deposited by reactive DC sputtering. All the deposited TiN films showed a dense, columnar structure with a preferential orientation of the (200) plane. These TiN films increased the mechanical properties of Co-Cr, such as the critical load during scratch testing, hardness, elastic modulus and plastic resistance. In addition, the biological properties of the Co-Cr substrates, i.e. initial attachment, proliferation, and cellular differentiation of the MC3T3-E1 cells, were improved considerably by deposition of the TiN films. These results suggest that TiN films would effectively enhance both the mechanical properties and biocompatibility of biomedical Co-Cr alloys.

Synthesis of copper nanoparticles by solid-state plasma-induced dewetting.

Copper nanoparticles were prepared by the plasma treatment of Cu thin films without extra heating. The Cu nanoparticles were formed through a solid-state dewetting process at temperatures of less than 450 K. The particle sizes, from 10 to 80 nm, were controlled by changing the thickness of the Cu film; the particle size increased linearly with the film thickness. The Cu nanoparticles produced by plasma treatment showed an excellent size uniformity compared to those prepared by heat treatment. In the early stage of the dewetting of the Cu film, uniformly distributed holes nucleated, and the holes grew and coalesced until the Cu nanoparticles were formed. The low operating temperatures used contributed to the production of uniform Cu nanoparticles.

Effect of the TiN content in the Pd-TiN seed layer on the microstructure and magnetic properties of Co∕Pd multilayered media.

[Co(0.2 nm)∕Pd(0.8 nm)](20) multilayered films on 15 nm Pd-TiN seed layers were fabricated by dc magnetron sputtering without heating the substrate. The effects of TiN content on microstructure and magnetic properties of the [Co∕Pd] multilayered media were studied. By increasing the TiN content in the Pd-TiN seed layer to an optimum level, coercivity of the [Co∕Pd] multilayered media increased to 6.7 kOe. However, further increase of TiN content beyond 22 vol % reduced coercivity (Hc), implying that there exists a critical TiN concentration to enhance the magnetic property of the [Co∕Pd] multilayered media. Transmission electron microscopic observations revealed that well-isolated [Co∕Pd] multilayered grains with apparent grain boundaries were achieved by controlling the TiN content in the Pd-TiN seed layer. The average grain diameter was 8 nm with a dispersion of 11.2%, grown on the Pd-TiN seed layer with TiN content of 22 vol %.