Scanning probe microscopy imaging of metallic nanocontacts

We show scanning probe microscopy measurements of metallic nanocontacts between controlled electromigration cycles. The nanowires used for the thinning process are fabricated by shadow evaporation. The highest resolution obtained using scanning force microscopy is about 3 nm. During the first few electromigration cycles the overall slit structure of the nanocontact is formed. The slit first passes along grain boundaries and then at a later stage vertically splits grains in the course of consuming them. We find that first the whole wire is heated, and later during the thinning process as the slit forms the current runs over several smaller contacts and less power is needed.

Figure 1

(a) STM image of an electron-beam-evaporated Au wire of 7 nm thickness ($U_T=10$ V, $I_T=0.5$ nA, and $\Delta z=37$ nm). (b) AM-SFM image of a sputtered Pd wire after EM thinning ($\Delta z=233$ nm)

Figure 2

AM-SFM images of Au nanowire of 30 nm nominal thickness before (a) and after (b) EM. The resolution limit is around 3 nm. The initial resistance of the wire was 40 $\Omega$ and the EM started at around 1.2 V.

Figure 3

Color-coded results of a careful analysis overlayed with an SFM image of the original nanowire (Fig. 2). Positions where the slit passes along grain boundaries: green; positions where the slit has removed grains completely: blue. Hatched blue regions are partly removed grains. Grains through which the slit has passed: red.

Figure 4

(a) Overall EM process, with two lines of constant dissipated power as a guide to the eye. (b) Conductance of the nanocontact below ten conductance quanta observed during EM thinning.