Electrical contact melting on nanoscale
(Result of the month 02/2007)

Figure 1: Four Tungsten Tips at nanowire before probing. Left and right tip: current. Top and bottom tip: voltage.

Four-point probing is an essential method to measure the electronic properties of devices. Four-point probing allows to characterise low resistance devices by eliminating the contact resistance. This is even more important for nanodevices: the contact area has to be kept small because the nanostructures and the probe must not be damaged mechanically. However, these measurements show that contact resistance still plays a role in another sense: a too large sensing current density might heat up the contact region and even destroy the contact by melting.

Figure 2: After electrical 4-point probing. Tips and parts of the wire melted.

Figure 1 shows a SEM image of four Tungsten tips contacting a ZnSe/Si bicrystalline nanowire on a Silicon substrate. This is before electrical 4-point probing. The left and right tip carry the sensing current, the top and bottom tip sense the voltage drop.

The situation after the 4-point probing is shown in figure 2: the right tip is shortened and has a droplet at its end. The left tip is also shortened and has a droplet, too. Furthermore the nanowire has melted almost to the left voltage contact. Melted material is apparently deposited at the left side of the image.

Sample by courtesy of:
Prof. Leo W.M. Lau, University of Western Ontario, Canada

Measurements performed by:
Omicron NanoTechnology GmbH

This result has been obtained with :
UHV Gemini Column
UHV NANOPROBE

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