Focused Electron Beam Deposition of Nanowires from Cobalt Tricarbonyl Nitrosyl (Co(CO)(3)NO) Precursor

Nanowires deposited by focused electron beam-induced deposition (FEBID) of cobalt tricarbonyl nitrosyl (Co(CO)(3)NO) precursor have been thoroughly characterized from an electrical, magnetic, and structural point of view. Deposit composition and deposition yield have been studied as a function of beam energy and current. Atomic concentrations are weakly dependent on beam parameters and have average values of 49 at % for Co, 27 at % for O, 14 at % for N, and 10 at % for C. Deposition yield decreases as the beam energy increases, and strong enhancement (67x) is observed for deposition at 130 degrees C substrate temperature. FEBID nanowires are highly resistive (rho = 6.3 m Omega cm at RT), and resistivity increases as T decreases with a power law behavior typical of metal-insulator (M-I) nanogranular systems. Nonmagnetic behavior is revealed by magnetoresistance (MR) measurements. After 400 degrees C vacuum annealing, conductivity of the nanowire is greatly improved (rho = 62 mu Omega cm at RT), and a metallic-like resistivity is fully recovered. MR angular plots display a (cos theta)(2) dependence typical of anisotropic MR (AMR) in ferromagnets, with AMR values of 0.85%. Co concentration in the deposit is not significantly increased though. TEM structural analysis reveals that before annealing the deposit has a CoO fcc structural phase with nanograins size around 1 nm. After annealing, a new Co hcp phase shows up beside CoO fcc, and coarsening (10 - 15 nm) and interconnection of the Co nanograins are observed, providing the conditions for ferromagnetism and metallic electrical transport.