Tin Nanospheres: A Tip Qualification Tool

Using a titanium sample for tip qualification is a standard procedure for certifying tip quality and for estimating the effective probe radius for nanomechanial measurements. This has been discussed in a previous post and while a reliable and quantitative method, it suffers the risk of damaging the probe in process of tip qualification as the titanium sample is quite hard. Another non-quantitative method is to use tin nanospheres on HOPG. Tin is quite soft and by controlling the substrate temperature nucleation can be controlled quite precisely. A sample with approximately 20 nm spheres is ideal for identifying a host of tip problems.  In truth they aren't "spheres" as they are only 8-10 nm tall and 20-ish nm in diameter

In this study several ScanAsyst Air SiN probes that "failed" were used to image this sample sample. PeakForce tapping was used with ScanAsyst, but any imaging mode would work. Because of the symmetric point-like nature of the objects, and because the radius of the Sn spheres (~ 20 nm) is close to the probe radius (~ 2 nm, but < 20 nm).

This allows one to effectively directly image the functional part of the probe. In the first two images one finds objects that look at least half-normal.

In the first image the spheres are all surrounded by something of a halo. The spheres are always in the left margin of this halo. In general, any image with self-similar features can be assumed to reflect imaging artifacts.

The second also reflects self-similar features. The objects all have a similar shape with a tail extending to the top left. What is interesting is that the density of objects is much higher as well. The objects all have multiple companions showing that the functional image surface is split into multiple parts.

While the first two images could be glossed as normal, the third and fourth images show radically damaged probes.

The last image shows a probe so broadened in radius that no objects are visible.