Platinum Silicide AFM Probes

All standard AFM probes materials are either insulating (silicon nitride) or quickly forming an insulating surface oxide layer (silicon) and therefore they are not intrinsically conductive. In order to obtain an electrically conductive AFM probe, AFM tip and AFM cantilever have to be coated with a conductive material. However, one of the strengths of Atomic Force Microscopy is the capability of resolving even tiniest features down to Nanometer sizes. If now an AFM tip is coated with a conductive material, the radius of the AFM tip of the coated AFM probe compared to the AFM probe base will increase. Choosing the thickness of this conductive layer is a trade-off between resolution (thin layers required), as well as conductivity and durability (thick layers preferred).

One concept to overcome this trade-off problem between AFM resolution and layer thickness is the transformation of the AFM tip material into a conductive state. In a so-called silicidation process a metal layer is deposited onto a silicon AFM tip. During a subsequent heat process the metal diffuses into the silicon and forms a metal-silicide. Due to the cone-shape of the AFM tip there is an excess of metal at the AFM tip apex. The metal excess together with diffusion forms a massive silicide apex with a height much larger than the initial metal thickness. Also, this conductive silicide apex is harder than the initial metal. When starting with the same Platinum coating thickness as for a normally coated AFM tip, the resulting AFM tip radius of the Platinum Silicide AFM tip will be smaller than that of the standard Pt-coated AFM probe due to the fact that the initial silicon AFM tip material has been transformed.

In 2012 NANOSENSORSTM,  the AFM probes technology leader, introduced the first commercially available platinum silicide AFM probes. The major innovation of this conductive AFM probes manufacturing concept is, that by thermally treating the metal-coating on the silicon of the AFM tip, not only just a coating is being applied, but the AFM tip apex is transformed from a “coating only” to a “solid conductive” state. Due to the silicidation process, this is not only happening on the surface of the AFM tip, but also reaches deeper into the base material of the AFM probe. The result is, that even when the AFM tip gets slightly worn, it will still remain conductive. A regular metal coated AFM probe would cease being conductive as soon as the conductive metal layer on the surface of the AFM probe wears off. Additionally, the resulting conductive apex of the Platinum Silicide AFM probe is harder and has a smaller radius compared to a standard metal coated AFM probe.
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