The Technology
Electron microscopy has become a pivotal tool in numerous fields of study, such as materials science and biology. Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) produce images of a sample by scanning it with a focused electron beam (e-beam) or launching the e-beam through the sample. The e-beam interacts with the sample and produces an image that contains information about the sample’s composition. The fundamental limit on the highest resolution possible in microscopy, such as SEM and TEM, is the wavelength of the particle, which for electrons is on the order of pico-meters (10-12 m). In practice, state-of-the-art electron microscopes are still about two orders of magnitude away from this fundamental limit.
The reason preventing electron microscopes from reaching their fundamental resolution limit is the interaction between electrons (space charge) causing additional broadening of beams made up of multiple electrons and sets a limit on the resolution of electron microscopy. Of course, when the density of the electron in the beam is low enough, this effect becomes negligible. However, working with one electron at a time (beams of single electrons or a low density e-beam) implies longer integration times in the detection process to obtain a reasonable signal to noise ratio, which sets a limit on the response time of electronic microscopes and how fast can be the events such microscopes are able to follow Properly shaped e-beams can compensate for both the space charge and the diffraction. In short, this is achieved by designing the quantum wavefunction of the electrons such that it balances its own self-repulsion and simultaneously also its natural broadening tendency due to diffraction. Shaping the e-beam can be done by different masks, by interacting with photonic structures or other ways.
Advantages
- Higher SNR with short integration time
- No compromising on the spatial resolution
- Longer depth of field
- Improve the coherence of the beam in the TEM so that the resolution of the imaging of a thin sample will be increased
Applications and Opportunities
- Electron accelerators
- High-flux electron microscopy with short integration time
- Electron lithography
- High intensity X-ray sources
- Contrast enhancement in electron microscopy
- Optical tweezers to manipulate micrometer-sized particles
- Micro-motors to provide angular momentum
- Improving channel capacity in optical and radio-wave information transfer
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