Structural transitions in electron beam deposited Co-carbonyl suspended nanowires at high electrical current densities.

Gian Carlo Gazzadi,Stefano Frabboni

doi:10.3762/bjnano.6.134

Abstract

Suspended nanowires (SNWs) have been deposited from Co–carbonyl precursor (Co2(CO)8) by focused electron beam induced deposition (FEBID). The SNWs dimensions are about 30–50 nm in diameter and 600–850 nm in length. The as-deposited material has a nanogranular structure of mixed face-centered cubic (FCC) and hexagonal close-packed (HCP) Co phases, and a composition of 80 atom % Co, 15 atom % O and 5 atom % C, as revealed by transmission electron microscopy (TEM) analysis and by energy-dispersive X-ray (EDX) spectroscopy, respectively. Current (I)–voltage (V) measurements with current densities up to 107 A/cm2 determine different structural transitions in the SNWs, depending on the I–V history. A single measurement with a sudden current burst leads to a polycrystalline FCC Co structure extended over the whole wire. Repeated measurements at increasing currents produce wires with a split structure: one half is polycrystalline FCC Co and the other half is graphitized C. The breakdown current density is found at 2.1 × 107 A/cm2. The role played by resistive heating and electromigration in these transitions is discussed.

Highlights

The growing importance of nanotechnology and nanoscience in advanced applications and fundamental research requires nanofabrication techniques that are highly resolved but at the same time flexible and feasible with research laboratory equipment
The selected area electron diffraction (SAED) pattern taken on the central dark region, 35 nm wide and 55 nm long, shows single spots arranged in a rectangular lattice that correspond to the face-centered cubic (FCC) structure of Cobalt, oriented along the [112] zone axis
The fact that cobalt does not stabilizes back into the hexagonal close-packed (HCP) phase at the end of the measurement, when the suspended nanowires (SNWs) return to room temperature (RT), is a consequence of the nanosize cross-section of the wire: FCC structure at RT is often reported for both Co nanoparticles and nanowires in the diameter range of tens of nanometers [33]

Summary

Introduction

The growing importance of nanotechnology and nanoscience in advanced applications and fundamental research requires nanofabrication techniques that are highly resolved but at the same time flexible and feasible with research laboratory equipment. We deposit free-standing suspended nanowires (SNWs) using Co–carbonyl precursor (Co2(CO)8), and study their behavior under high electrical current density, following the same approach used for Pt–metallorganic SNWs [23].

Results

Conclusion