The tip diameter of a typical AFM is 5-10nm. The diameter of a typical atom is ~1-2 angstrom. How can AFM have an atomic resolution if the tip radius is greater than the atoms?
There are several different types of AFM's and/or different modes in which they can be operated. Not all of them allow atomic resolution to be achieved and atomic resolution is not obtained with every kind of specimen.
Typically, resolution on the scale of (sub-) atomic distances is more easily obtained in the vertical direction. I.e. if you scan a single nanoparticle which lies on an atomically flat surface, you will get a good idea of its height with an AFM. On the contrary, the lateral scan profile (as your question suspects) is a convolution of tip shape and particle shape and you cannot expect to observe real lateral dimensions with the AFM (in this case, btw., the same applies to an STM). Nor can you usually expect to obtain atomic resolution near the top of the nanoprticle.
One AFM mode which does sustain atomic resolution is the so-called tuning fork non-contact AFM. One of the developers (F.-J. Giessibl) is on RG and you could check his publications for more information.
As a general rule you may assume that you can obtain atomic resolution when there are no other perturbations. Atomic resolution is most "easily" obtained on atomically flat terraces of crystals. Then the tuning fork detector, which is based on a high quality factor oscillator circuitry (of which tip and tip holder are essential parts) is able to detect tiny variations between different positions at the atomic scale. This technique is indeed amazing!
The curvature of the tip of cause much larger than the atoms on the sample but the effectively only few atoms on the top of the tip scan the samples. As in the AFM the force is drastically decrease even few atoms far from the actual tip. So we got the atomic resolution in afm and stm.
There are several different types of AFM's and/or different modes in which they can be operated. Not all of them allow atomic resolution to be achieved and atomic resolution is not obtained with every kind of specimen.
Typically, resolution on the scale of (sub-) atomic distances is more easily obtained in the vertical direction. I.e. if you scan a single nanoparticle which lies on an atomically flat surface, you will get a good idea of its height with an AFM. On the contrary, the lateral scan profile (as your question suspects) is a convolution of tip shape and particle shape and you cannot expect to observe real lateral dimensions with the AFM (in this case, btw., the same applies to an STM). Nor can you usually expect to obtain atomic resolution near the top of the nanoprticle.
One AFM mode which does sustain atomic resolution is the so-called tuning fork non-contact AFM. One of the developers (F.-J. Giessibl) is on RG and you could check his publications for more information.
As a general rule you may assume that you can obtain atomic resolution when there are no other perturbations. Atomic resolution is most "easily" obtained on atomically flat terraces of crystals. Then the tuning fork detector, which is based on a high quality factor oscillator circuitry (of which tip and tip holder are essential parts) is able to detect tiny variations between different positions at the atomic scale. This technique is indeed amazing!
Just as a demonstration of the potential resolution of AFM from those crazy kids at IBM, they have achieved resolution of atomic bonding (at low temperature, high vacuum)
http://www.sciencemag.org/content/337/6100/1326.short
Typically AFM gives nanometer resolution even with the sharpest tip.
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