Dear Mir

I don't think that except from surface morphology and surface pattern, you can find out size of the nanoparticles only from SEM and AFM, for that and especially for metal nanoparticles you need to first analyse the XRD spectra followed by TEM, HRTEM, SAED and DLS.

I hope this will help you out.

HI..

U can find the size of the nano particles up to some extent with the help of the scale provided in the SEM image. But its is always good to measure size with the help DLS(Dynamic Light scattering) which gives u the average number of particles and size distribution.

Mainly SEM and AFM is used to determine the surface morphology.

I think AFM is a bit slow to scan enough (for good statistics) particles.

Application of a SEM depends on size of your particles and resolution of your SEM. If particles are well visible, you definitely can use SEM. Place a drop of particle suspension (in water or alcohol) on plastic substrate. You need plastic to achieve big difference in Z (mean atomic number) of substrate and metal. Coat specimen with thin layer of carbon and observe at higher voltages (15-25 kV). Signal in backscattered electrons will give better difference in contrast between particles and substrate for easy thresholding with image analysis software.

AFM as well as SEM may work, it depends how the particles are fixed to the substrate. We successfully made such experiments for small metal clusters on semiconductors (size between ca. 20-30 nm minimum and about 200-300 nm), as well as for thin films witj polycrystalline structure, where the individual crystallites (="particles") need to be resolved. Cheers, Dirk

Dear All, thank you very much for your support. I really appreciate it. I also would like to know, is there any ways to know about the size of the nano particles from its optical spectra. I mean if I know the optical transmittance, absorbance, can I find the size of the particles ? Thanks for your support.

I don't think so. There had been some people in other discussions here on RG who claimed that one can derive nanoparticle size from UV spectra, but I had not become convinced. Either use DLS or Laser Doppler spectroscopy (which uses mesurement of the Brownian motion for particle size calculation)

Usually nanoparticles have a good adhesion with a glass made microscope slide due to both capilary forces and electrostatic forces. You just have to put a drop of a solution containing the nanoparticles and let it dry to have them well stuck onto the surface. Regarding AFM you will have to take some precautions and usually intermittent contact modes are prefered as they minimize the force applied onto the nanopaticle as well as the friciton one. If your NP are made of soft material (bio material or polymer) ou will have to minimize the normal contact force in order to avoid any elastic deformation of the measures NPs. The later will have to be well dispersed on the surface so that the probe may reach the substrate between two particles. By doing so you will be able to measure the height of the NP (if it is a sphere or a cylinder it will be equal to its diameter). Small in plane dimensions are hard to measure because of the finite shape of the probe which convoluate with the real shape of the NPs. Special probes (sharpened ...) may help to reduce this problem. The resolution of the AFM is less than 1 Angstrom in Z. This works fine with 3 to 5 nm particles although they tend, from time to time, to stick to the probe apex certainly because of the water meniscus forming between the surface and the probe tip when contact is made.

You can use ImageJ software to determine the average size of nanoparticles in SEM, TEM image.

Link to download ImageJ: https://imagej.nih.gov/ij/download.html

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