Electrical conductance behavior of thin Ni catalyst films during intermittent direct current magnetron sputtering

Abstract

Electrical conductance of thin Ni films, deposited on insulating SiO2 substrates, was investigated for the initial stage of magnetron sputtering for the purpose of optimize control of catalyst particles sizes of carbon nanotubes. The conductance was not proportional to the deposition time in the early phase of deposition. The conductance rapidly increased, after a period of near-insulating behavior from the start of deposition, and thereafter the increase of conductance was almost proportional to the total deposition duration. The period of near-insulating behavior and the rapid increase of conductance in the early deposition phase were attributed to growth of island structures in the initial deposition and formation of a continuous film through the connection of islands. The effect of base vacuum pressure prior to sputtering deposition also was investigated by conductance measurements. It was demonstrated that measuring electrical conductance during sputtering deposition was a convenient tool to examine the structures in the deposited film.

Formation of Thermally Stable, High-Areal-Density, and Small-Diameter Catalyst Nanoparticles via Intermittent Sputtering Deposition for the High-Density Growth of Carbon Nanotubes

“…We previously reported a decrease in conductance for Ni films deposited under a higher base pressure due to the formation of oxidized nickel films by the oxygen remaining in the vacuum chamber at higher oxygen partial pressures [ 31 ]. Figure 4 shows that for a lower ON/OFF time ratio, the higher areal density of grain boundaries and the smaller size of Ni nanoparticles causes a reduction in the conductance of the Ni films.…”

“…The surface morphology, smaller particle-like or granular nanoisland structures on the substrate, was observed after the deposition of a Ni and Fe metal via direct current (DC) magnetron intermittent sputtering (apparatus [ 31 ]) on thermally oxidized silicon (th-SiO/Si). In this paper, we use “nanoparticles” to mean these particle-like or granular nanoisland structures.…”

“…To characterize these metal catalyst films, we have previously proposed an electrical characterization method (intermittent sputtering) for films with a sub-nanoscale thickness, which involves the measurement of electrical conductivity during the interval between magnetron sputtering and the analysis of island formation during sputtering deposition. We evaluated the quality of monometallic Ni [ 31 , 32 ] and Fe metal catalyst films using this method, followed by CNT growth on a Fe catalyst. Fe catalysts on an AlO buffer layer on Si substrates (Fe/AlO/Si) are commonly utilized as CNT catalysts, on which high-areal-density and small-diameter CNTs are obtained.…”

Hydrophilic DLC Surface Induced by Nanostructures Formed by RF O₂ Plasma Etching With Metal Micromasks

“…The tolerance and stability of Ni is possibly due to the high reactivity between Ni and carbon. The metals, such as Ni and Fe, are often utilized as catalyst to grow carbon nanotube to have high chemical reactivity with carbon [14], [15]. In the case of the Fe micromask, which is also reactive with carbon, the Fe also remained for a longer time on the top of the nanostructures, which resulted in an increase in the height of the nanopillars.…”