Electron Microscopy and Probe Microscopy
Electron Microscopy Overview
Electron microscopy utilizes electrons instead of light to obtain high-resolution images of samples.
Very small wavelength of electrons allows for high resolution.
Electron microscopes do not use traditional glass lenses.
Instead, they use magnets (specifically electromagnets) to direct the electron beams.
Key Limitations:
Cannot examine live samples due to the vacuum environment necessary for operation, which is incompatible with living organisms.
Types of Electron Microscopy
There are two main types of electron microscopy:
Scanning Electron Microscopy (SEM)
Provides three-dimensional images of the surface of samples.
Think of "scanning" as focusing on the surface.
Transmission Electron Microscopy (TEM)
Offers images of the internal structure of samples.
Remember "transmission" as it transmits information into the inner workings of a cell.
Additional Category:
Probe Microscopy: Another category of microscopy that will be discussed in detail.
Probe Microscopy
Probe microscopy utilizes a probe that operates similarly to a record player’s needle, but with significantly greater precision.
Probes are typically made from tungsten.
The diameter of the probe tip is only one atom wide, allowing for extremely detailed imaging.
Two main types of probe microscopy are:
Scanning Tunneling Microscope (STM)
Invented in 1980 by scientists who were awarded the Nobel Prize in 1986.
Capable of examining live samples as the probe does not touch the sample.
Mechanism: The tip of the probe does not physically contact the sample; rather, there is an exchange of electrons. The current generated from this interaction is measured by a computer, which converts it to create an image.
Key Takeaways:
STM is a probe microscope.
No contact with the sample, only electron exchange.
Current measurement enables image creation.
"Scanning" refers to examining the surface; "tunneling" refers to the electronic current.
Atomic Force Microscope (AFM)
Developed by IBM scientists in 1982.
Unlike STM, the probe physically contacts the sample during examination.
Mechanism: The probe is attached to a cantilevered arm. As the probe moves across the uneven surface of the sample, it rises and falls with variations in height. A laser shines on the end of the cantilever, with the angles of reflection providing data to create an image.
Both STM and AFM rely significantly on computer technology for image processing and creation.
Note: You cannot distinguish between STM and AFM images based solely on appearance; examples will not be provided in exams.
Key Target Areas:
AFM shows physical contact with the sample, unlike STM.
Examples of Imaging with Probe Microscopy
The images produced via STM and AFM could depict atomic-level details:
E.g., Pure Gold Surface: shows gold atoms arranged in specific formations.
E.g., Nanosellulose: an artificially created substance viewed at the molecular level.
Additional images discussed in class may illustrate different atomic arrangements, but specific elements were not clearly defined.
Final Notes on Microscopy
Slides following the lecture will provide additional clarity on various types of light microscopes alongside the discussed electron microscopes.
One additional type, two-photon microscopy, was mentioned but is not required for the exam review.
Focus on the electron microscopy types and the distinctions made between STM and AFM as key concepts to grasp during study sessions.
Reiterate differences based on functionality, sample compatibility, and imaging technique between the various microscopies.