There are several different types of scanning probe microscopes, the most prominent of which are atomic force microscopy (AFM) and scanning tunneling microscopy (STM). There are also many other types, which are listed at the end of this article.
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Both AFM and STM record an image of the subject by moving the probe tip of the microscope along the sample, within several nanometers of the surface but without making physical contact.
Throughout the process, the microscope senses the distance of the probe tip from the surface of the sample. It is this information that is used to create the image of the sample. However, AFM and STM differ in the method used to sense the distance from the surface.
Atomic force microscopy (AFM)
The atomic force microscope works by measuring the electrostatic force between the tip and the specimen. There are several different subtypes of this microscope, including:
- Contact AFM
- Non-contact AFM
- Dynamic contact AFM
- Tapping AFM
This type of microscope has a very high resolution to the order of fractions of a nanometer. The image is constructed based on touching the surfaces of the specimen with the probe of the microscope.
An AFM can measure the strength of the force, create an image of the surface, and manipulate the atoms on the surface of the specimen, depending on the situation.
A thin laser beam that focuses onto the cantilever and reflects onto a detector, which acts as a sensor. The cantilever bending is measured to determine the distance of the sample from the probe.
FM can be used for conductive or non-conductive samples, giving it a wider range of use. It can be used in contact mode, also known as DC mode, or tapping mode, also known as AC mode.
Scanning tunneling microscopy (STM)
A scanning tunneling microscopy (STM) measures the electrical current between the tip and the specimen.
Scanning microscopes move the probe tip back and forth over the surface of the sample to create an image that can be visualized.
STM is based on a simpler principle than AFM, but it can only be used with conducting samples. The metal probe tip and the sample are both connected to a voltage supply so that a tunnel current occurs when the tip is close to the sample.
Throughout the scan, the tip moves up and down to maintain the same current and, therefore, distance from the sample. The movement of the tip is translated into the image from the scanning tunneling microscope.
Other types of scanning probe microscopes
There are various other types of scanning probe microscopes including:
- Ballistic electron emission microscopy (BEEM)
- Chemical force microscopy (CFM)
- Conductive atomic force microscopy (C-AFM)
- Electrochemical scanning tunneling microscopy (ECSTM)
- Electrostatic force microscopy (EFM)
- Fluidic force microscopy (FluidFM)
- Force modulation microscopy (FMM)
- Force modulation microscopy (FOSPM)
- Kelvin probe force microscopy (KPFM)
- Magnetic force microscopy (MFM)
- Magnetic resonance force microscope (MRFM)
- Near-field scanning optical microscopy (NSOM)
- Photon scanning tunneling microscopy (PSTM)
- Photothermal microscopy (PTMS)
- Piezoresponse force microscopy (PFM)
- Scanning capacitance microscopy (SCM)
- Scanning electrochemical microscopy (SECM)
- Scanning gate microscopy (SGM)
- Scanning Hall probe microscopy (SHGM)
- Scanning ion-conductance microscopy (SICM)
- Scanning SQUID microscopy
- Scanning spreading resistance microscopy (SSRM)
- Scanning thermal microscopy (SThM)
- Scanning tunneling potentiometry (STP)
- Scanning voltage microscopy (SVM)
- Scanning single-electron transistor microscopy (SSET)
- Spin-polarized scanning tunneling microscopy (SPSM)
- Synchrotron x-ray scanning tunneling microscopy (SXSTM)
Reviewed by Susha Cheriyedath, MSc
Credit: Department of Industry, Innovation and Science/Youtube