We fabricated the silver nanoparticles on a substrate using a PVD method. To estimate the diameter it evident one can use a scanning electron microscope. But the estimation of the real shape of nanoparticles is complicated. Is there any method to clarify it?
Thanks in advance
Daler R. Dadadzhanov
You have the standard particle size conundrum for irregular particles. That's why equivalent diameters tend to be used for comparative purposes. There is a shape distribution (and maybe 20+ shape parameters can be defined) as well as the size distribution. For irregular particles then more than one number is needed to describe 'size'.
In imaging often the circular equivalent is used - the circle diameter with the same number of pixel elements as your (irregular) particle. Note that this is a 2-D descriptor and shape is a 3-D issue for irregular particles - so we need knowledge of the z-axis - or some assumption thereof. How do we know that the particle is coin/disc shaped or spherical when they may look the same under the microscope?
ISO9276-6 has all shape parameters between 0 an 1 for mathematical convenience. Thus, aspect ratio is breadth/length and not the converse. Also see the attached.
Dear Daler R. Dadadzhanov , I agree Alan F Rawle completely, but if you want to have a fast idea about what your nanoparticles look like, SEM images let you see them on the fly. To study their profile SEM or TEM can help too. to see them properly you need polish a cut of your glass substrate or if available you can use a FIB to cut them. It is even possible to reconstruct 3D a single NP by means of the destructive technique of image and slice (repeatedly you cut a section of one of your NPs with a FIB, and then take an image of the section, a new slice and a new image of the section and so on. Finally you can rebuilt the NP 3D by stacking of the images of each section (slice). If you need a statistical description the process should be performed on a large number of NP´s which probably will be quite expensive.
Hope it helps!
FESEM provides quite good 3D images to study morphology, whereas TEM gives only 2D micrographs.
For further analysis regarding surface-profile, stiffness and shape of the particles you may also perform AFM; or in more specific cases PFM.
For certain materials, Raman imaging also provides some very useful information. Specially, confocal Raman imaging can build an entire 3D structure.
However, electron microscopy is always the best option for rudimentary size, shape, and morphology analysis; particle size-distribution etc.
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