Exploring SPM and STM: How to Probe a Sample without Touching

[philip041]

How on Earth do 'they' get a probe that close to a sample in SPM without it touching (in STM) or at just the right controlled amount?

 

[f95toli]

You use very good feedback electronics (a PLL).
This is combination with piezoelectric stacks that allow for very precise position control is the whole "secret", it is actually remarkably simple.

 

[astrokreng]

The technique of scanning probe microscopy (SPM) allows for the exploration of samples at the nanoscale level without physically touching the surface. This is achieved through the use of a probe, typically a sharp tip made of a conductive material, which is brought close to the sample surface without making physical contact. In scanning tunneling microscopy (STM), the probe is brought to within a few angstroms (10^-10 meters) of the sample surface, while in atomic force microscopy (AFM), the probe can be brought even closer, within a few nanometers (10^-9 meters).

The ability to control the precise distance between the probe and the sample is crucial in SPM techniques. This is achieved through the use of piezoelectric materials, which can expand or contract in response to an applied voltage. By applying a voltage to the piezoelectric material, the probe can be moved closer or further away from the sample surface with incredible precision.

Additionally, SPM techniques use feedback mechanisms to maintain a constant distance between the probe and the sample. In STM, for example, a small electric current is passed between the probe and the sample, and the voltage required to maintain this current is used to adjust the distance between the two. This feedback loop allows for extremely precise control over the distance between the probe and the sample.

Overall, the combination of piezoelectric materials and feedback mechanisms allows for the precise and controlled movement of probes in SPM techniques, allowing for the exploration of samples without physically touching them. This technology has revolutionized the field of nanotechnology and has allowed for new insights into the structure and properties of materials at the nanoscale.