The images of metal nanoparticles can be taken by atomic force microscope (AFM) in Tapping® (intermittent-contact) mode. The AFM imaging can be used to measure the size distribution of particles. Monolayers of metal nanoparticles can be prepared on a mica substrate by dropping small amount of 0.01% nanoparticles solution on freshly cleaved mica surfaces. We recently published results for size distribution of small nanoparticles of zinc and copper (attached).
The images of metal nanoparticles can be taken by atomic force microscope (AFM) in Tapping® (intermittent-contact) mode. The AFM imaging can be used to measure the size distribution of particles. Monolayers of metal nanoparticles can be prepared on a mica substrate by dropping small amount of 0.01% nanoparticles solution on freshly cleaved mica surfaces. We recently published results for size distribution of small nanoparticles of zinc and copper (attached).
A typical protocol for particles size measuring by AFM:
1. Check the calibration of AFM scanners by scanning of standard calibration grid.
2. Prepare the sample: put a drop of suspension (conventional concentration is about 0.1 mg/ml, but it depends on the specimen) on a fresh cleavage of mica or HOPG, incubate few minutes and blow it away by a jet of air or nitrogen.
For some kinds of particles (oxides and some organic structures) there is a problem: the particles can aggregate or produce a continuous layer on the surface. It is not good for size measuring, for prevention of this effect it is possible to use sonic spraying technique of particles deposition.
3. Install a fresh AFM probe and scan the sample in tapping mode.
4. If all were Ok, you will have some scans with single peaks - particles.
5. Manually or with a "grain analysis" tool calculate a height (Z) of every peak and analyze these data with statistics (average, distribution, etc.)
It is necessary to remember: AFM measures height of the relief (Z) with high precision (about angstrom or better), but the lateral sizes are not so accurate - obviously, diameter of the tip (it is not known exactly and it is changing by scanning) influences to these parameters.
In addition, it is important to take an adequate scan area: AFM scan is a two-dimensional array of Z-coordinates (usually 512x512). If the lateral distance between these points is about particle's size or more, obviously, there will be incorrect values of particles height on the scan.
Good luck!
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