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Difference Between Scanning Tunneling and Atomic Force MicroscopesBY: Muniba Safdar | Category: Biotech-Research | Submitted: 2010-10-24 05:11:48
Article Summary: "Information about Scanning Tunneling Microscopy (STM) and Atomic Force Microscopy (AFM) ;their advantages & disadvantages, resolution, composition and applications..."
Scanning Tunneling Microscopy (STM) and Atomic Force Microscopy (AFM) or scanning force microscopy (SFM) are inventions of Scanning Probe microscopy a technique that forms images of surfaces using a physical probe that scans the specimen. An image of the surface is obtained by mechanically moving the probe in a raster scan of the specimen, line by line, and recording the probe-surface interaction as a function of position. STM is a powerful instrument that is used for imaging surfaces at the atomic level while AFM is one of the primary tools for imaging, measuring, and manipulating matter at the Nano-scale.
Scanning Tunneling Microscopy (STM) was invented in 1981 and was developed by Gerd Binnig and Heinrich Rohrer.
Atomic Force Microscopy (AFM) was invented in 1985 and was also developed by Gerd Binnig and Heinrich Rohrer.
STM gives two-dimensional image of the atoms.
AFM gives three-dimensional surface profile of the Nano-objects.
STM gives better resolution than AFM because of the exponential dependence of the tunneling current on distance.
The force-distance dependence in AFM is much more complex when characteristics such as tip shape and contact force are considered.
STM uses a sharpened conducting tip.
AFM uses a conductive AFM cantilever (typically silicon or silicon nitride with a tip radius of curvature on the order of nanometers) with a sharp tip (probe) at its end that is used to scan the specimen surface.
STM relies on electrical current between the tip and the surface.
AFM relies on movement due to the electromagnetic forces between atoms.
STM record the tunneling current.
AFM does not record the tunneling current but the small force between the tip and the surface.
STM uses a sharpened conducting tip (metallic tip).
AFM uses a conductive AFM cantilever.
In case of STM Interaction between probe and material surface is monitored is tunneling current.
While in AFM Interaction between probe and material surface is monitored is van der Waals force.
In STM Tip and substrate are in very close proximity but not actually in physical contact.
While in AFM Tip and substrate are actually in physical contact.
ATTACHMENT OF TIP:
Tip is not attached to a tiny leaf spring in case of Scanning tunneling microscopy.
In Atomic force microscope Tip is attached to a tiny leaf spring, the cantilever, which has a low spring constant. Bending of this cantilever is detected, often with the use of a laser beam, which is reflected from the cantilever.
Tip mounts on the scanner when we have scanning tunneling microscope.
Sample mounts on the scanner when we have atomic force microscope.
STM's Tip is kept at a short distance from the surface.
While AFM's Tip is not kept at a short distance from the surface but it gently touches the surface.
STM can visualize and even manipulate atoms.
AFM can easily image non-conducting objects i.e., DNA and proteins etc.
STM is a powerful instrument that is used for imaging surfaces at the atomic level. STM is being used for the conductance of single molecule.
The AFM is one of the primary tools for imaging, measuring, and manipulating matter at the Nano-scale.
ADVANTAGES & DISADVANTAGES:
• In STM the two parameters are integrally linked for voltage calculation.
• AFM offers the advantage that the writing voltage and tip-to-substrate spacing can be controlled independently.
• AFM gives three-dimensional image while STM only gives two-dimensional image. This is the advantage of AFM over STM.
• Resolution of STM is higher than AFM. STM gives true atomic resolution.
• An AFM cannot scan images as fast as a STM, requiring several minutes for a typical scan, while a STM is capable of scanning at near real-time, although at relatively low quality.
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