In a recent study, W-based granular metals have been prepared by EBID with the aim of investigating the electrical transport properties during the growth process and the exposure to air. The deposits consist of metallic nanoparticles embedded in an insulating matrix. The electrical conductivity of the granular metal is a function of the metal content of the deposit, which depends on the beam parameters used during the deposition. In the investigation the authors found an increase of the electrical conductivity during the growth process, which they attributed to the growth of the metal particle's diameter. After the deposition the microscope is vented to study the degradation of the electrical conductivity during exposure to air. As shown in the figure below, the conductivity decreases with time at a rate that depends on the material's composition.

In particular, the lower the metal content the faster the decrease. The degradation is thought to be due to the effect of oxidation. Moreover, the degradation rate is linked to the density of the deposit. In view of the possible utilization of EBID deposits for applications, the composition of the granular metal has to be carefully chosen to minimize the ageing effect. Therefore, granular metals from different gas precursors employed in the EBID process will be investigated. Finally, covering the deposit with a protective SiOx layer such as the one that can be obtained from the precursor tetramethylsilane (TMS) – currently under investigation – may prevent long timescale degradation of the electrical conductivity.

The researchers presented their work in Nanotechnology.