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Transmission Electron Microscopy

Transmission Electron Microscopy

In 1931, physicist Ernst Ruska—building on the idea that magnetic fields can direct an electron beam just as lenses can direct a beam of light in an optical microscope—developed the first prototype of the electron microscope. This development led to the development of the field of electron microscopy. In the transmission electron microscope (TEM), electrons are produced by a hot tungsten element and accelerated by a potential difference in an electron gun, which gives them up to 400 keV in...

Overview of Electron Microscopy

Overview of Electron Microscopy

The wavelengths of visible light ultimately limit the maximum theoretical resolution of images created by light microscopes. Most light microscopes can only magnify 1000X, and a few can magnify up to 1500X. Electrons, like electromagnetic radiation, can behave like waves, but with wavelengths of 0.005 nm, they produce significantly greater resolution up to 0.05 nm as compared to 500 nm for visible light. An electron microscope (EM) can create a sharp image that is magnified up to 2,000,000X.

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Updated: May 9, 2026

Asymmetric Thermoelectrochemical Cell for Harvesting Low-grade Heat under Isothermal Operation

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Published on: February 5, 2020

Microbead-separated thermionic energy converter with enhanced emission current.

Karl A Littau¹, Kunal Sahasrabuddhe, Dustin Barfield

¹Stanford University, Stanford, California, USA. klittau@stanford.edu

Physical Chemistry Chemical Physics : PCCP

|July 25, 2013

Summary

Researchers optimized vacuum thermionic energy converters by controlling the gap between electrodes. A 5 μm gap yielded 0.61% efficiency, with potential for significant future improvements in power and efficiency.

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Area of Science:

Energy Conversion
Materials Science

Background:

Thermionic energy converter (TEC) efficiency is limited by space-charge effects.
Precise control over the inter-electrode gap is crucial for optimizing TEC performance.

Purpose of the Study:

To fabricate and characterize vacuum thermionic energy converters with controlled inter-electrode gaps.
To investigate the impact of inter-electrode separation on device efficiency and power output.

Main Methods:

Utilized barium dispenser cathodes and thin-film tungsten anodes.
Employed size-specific alumina microbeads to precisely control the inter-electrode gap.
Fabricated vacuum TEC devices with varying gap sizes.

Main Results:

Device efficiency and current output were strongly dependent on the inter-electrode gap.
A maximum device efficiency of 0.61% was achieved at an inter-electrode gap of approximately 5 μm.
Demonstrated a practical method for fabricating TECs with controlled gaps.

Conclusions:

Inter-electrode gap control is critical for overcoming space-charge limitations in TECs.
The demonstrated fabrication method allows for optimization of TEC performance.
Future work focusing on reducing space charge and enhancing anode work function could lead to significant efficiency gains.