What is Atomic Force Microscopy (AFM)?
Atomic Force Microscopy (AFM) is a type of high-resolution scanning probe microscopy with a resolution on the order of fractions of a nanometer. AFM works by measuring the
forces between a sharp probe (or tip) and the surface of a sample. As the tip scans over the sample's surface, it deflects according to the forces it encounters, which are then measured and used to construct an image.
How does AFM work?
AFM uses a
cantilever with a sharp tip that interacts with the sample surface. The cantilever bends in response to the forces between the tip and the sample. A
laser beam reflects off the back of the cantilever into a photodetector, which records the deflection. This information is processed to create a topographic map of the sample surface.
What is Scanning Tunneling Microscopy (STM)?
Scanning Tunneling Microscopy (STM) is another powerful technique used in nanotechnology to image surfaces at the atomic level. Unlike AFM, STM relies on the quantum mechanical phenomenon of
tunneling. When a sharp conducting tip is brought very close to a conducting or semiconducting surface, a tunneling current occurs between the tip and the sample, which is used to create an image.
How does STM work?
In STM, a sharp metallic tip is positioned extremely close to the sample surface. When a
bias voltage is applied between the sample and the tip, electrons tunnel through the vacuum between them, creating a tunneling current. This current is sensitive to the distance between the tip and the surface, allowing the STM to map the surface at the atomic scale by maintaining a constant current while scanning.
What are the Key Differences between AFM and STM?
While both AFM and STM are used for imaging surfaces at the nanoscale, they operate on different principles. AFM measures mechanical forces between the tip and sample, making it suitable for both conducting and non-conducting samples. STM, on the other hand, relies on tunneling current and is mainly used for conducting or semiconducting materials. The choice between AFM and STM depends on the specific requirements of the research, such as the type of material and the desired information.
Conclusion
Both AFM and STM are essential tools in the field of nanotechnology, providing unparalleled insights into the structure and properties of materials at the nanoscale. Their ability to image and manipulate individual atoms and molecules makes them indispensable for advancing our understanding and development of nanomaterials and nanodevices.
