AFM uses a tip to scan the surface of the sample and tip goes up and down according to the nature of the surface. This concept is similar to the way in which a blind person understanding a surface by running his fingers all over the surface. Since AFM uses the method of feeling the surface using mechanical probe, it is capable of producing a 3D image of the sample by probing all the surfaces. It is also enables users to manipulate the atoms or molecules on the sample surface using the tip.
SEM uses an electron beam instead of light for imaging. It has a large depth in field which enables users to observe a more detailed image of the sample surface. AFM also has a more control in amount of magnification as an electromagnetic system is in use. In SEM, the beam of electrons is produced using an electron gun and it goes through a vertical path along the microscope which is placed in a vacuum. Electrical and magnetic fields with lenses focus the electron beam to the specimen. Once the electron beam hits on the sample surface, electrons and X-rays are emitted. These emissions are detected and analyzed in order to put the material image on the screen. Resolution of SEM is in nanometer scale and it depends on the beam energy. Since SEM is operated in a vacuum and also uses electrons in the imaging process, special procedures should be followed in sample preparation.
Hoping this helps you
I agree with Dr. Hammadi
I would like to add something else.
AFM can scan both conducting and non conducting materials without a pre-treatment.
For SEM, non conducting materials have to be covered with a thin conducting film.
Dear Oraas Adnan Hatem,
Scanning electron microscopy (SEM) :
SEM is used to investigate the surface morphology of polymeric materials.
Here, the specimens must be electrically conductive, at least at the surface, and electrically grounded to prevent the accumulation of electrostatic charges at the surface.
Polymeric specimens tend to charge when scanned by electron beam, especially in secondary electron imaging mode, which causes faults & other image artifacts. Therefore, polymetric materials are usually coated with an ultra thin coating of an electrically conducting material, such as gold, which is deposited on the sample either by low vacuum sputter-coating or by high vacuum evaportaiton.
Beacuse the inherent resolution of most SEM instruments is roughly 1nm, it is difficult to image the dispersion of nanoparticles in a polymer matrix. However, SEM is a valuable tool for investigating the fracture-surface morphology of carbon nanotubes-containing biopolymer nanocomposites. Nowadays, SEM combined with energy dispersive X-ray spectroscopy has frequently used to study the degree of dispersion of nanoparticles in polymer nanocomposites.
SEM analysis produce a two-dimensional image & gives information about the sample including external morphology (texture), chemical composition when used with the EDS feature and orientation of materials making up the sample.
Atomic force microscopy (AFM) :
AFM is a powerful technique that enables the imaging of almost any type of surface, including polymers, ceramics, composites, glass & biological samples.
AFM is used to measure and localize many different forces, including adhesion strength, magnetic forces and mechanical properties.
AFM consists of a sharp tip that is aproximately 10to 20 nm in diameter, which is attached to a cantilever. AFM tips & cantilivers are micro-fabricated from Si or Si3N4. The tip moves in response to tip-surface interactions, and this movement is measured by focusing a laser beam with a photodiode.
AFM is operated in two modes:
01. Contact mode: AFM tip is in continuous contat with the surface. It is only used for specific measurement, such as surface curve measurements.
02. Tapping mode: AFM cantilever is vibrated above the sample surface such that the tip is only in intermittent contact with the surface. It helps to reduce shear forces associated withthe tip movement. This mode is recommended mode used for AFM imaging.
Comparison between SEM and AFM :
Unlike the electron microscope which provides a 2-D porjection or a 2-D image of a sample AFM porvides a true 3-D surface profile. In addition, the samples viewed by AFM do not require any special treatements ( i.e. metal/ carbon coatings) that would irreversibly change or damage the sample. Again, SEM requires an expensive vacuum environment for proper operation, most AFM modes can work perfectly well in ambient air.
01. In principle, AFM provides higher resolution than SEM.
02. It has been demonstrated that AFM can provide true atomic resolution in ultra-high vacuum (UHV) and, more recently, in liquid environments.
03. High resolution AFM is comparable in resolution to SEM and TEM.
04. A disadvantage of the AFM technique compared to SEM is the image size.
05. SEM can image an area in the order of millimeters by millimeters with a depth of field in the order millimeters. AFM can image a maximum height in order of micrometers and maximum scanning area of approximately 150 by 150 micrometers.
Thus, the researchers uses both of them.
I hope I have answered your question.
With Best Regards,
Samir G. Pandya
Dear Oraas Adnan Hatem ,
AFM- Surface topography; where as SEM-Surface Morphology
Apart from the aforementioned points
AFM -ambient atmosphere, however, SEM- vacuum, hence topographical feature of the living system possible.
No need special surface characteristic or edge for contrast in surface topography in AFM.
High height resolution in AFM.
The sample must be flat in AFM.
AFM image is 3 D
SEM image is 2D
SEM gives morphology while AFM gives topography. We cannot use SEM to determiine surface roughness values, which can be only calculated by AFM
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