Electron Microscopy: Seeing Atoms

Introduction

• Tiny metal piece, 3mm across, zoomed to atomic level.
• Directly seeing atoms was considered impossible until 30 years ago.
• University of Sydney houses advanced rooms and equipment for such experiments.

Why Seeing Atoms is Difficult

• Atoms can't be seen with visible light due to larger wavelength (380-750 nm) compared to atoms (0.1 nm).
• Electrons are used instead to see atoms due to their smaller wavelength (2-3 picometers) at high velocities.

Discovery and Development

• 1924: Louis de Broglie’s hypothesis of matter having wave-like properties.
• 1926: Hans Busch proposed electromagnetic lenses to focus electrons.
• 1931: Ernst Ruska & Max Knoll built the first electron microscope (TEM).

Transmission Electron Microscope (TEM)

• Initial TEMs had low magnification and were comparable to optical microscopes.
• 1936: Otto Scherzer identified spherical aberration as a limiting factor.
• Spherical aberration occurs due to non-linear scaling of magnetic fields.

Overcoming Spherical Aberration

• Adding a diverging lens can cancel out aberration, but impossible with magnetic lenses due to their inherent properties.

Advances in Electron Microscopy

• 1955: Field ion microscope provided first acceptable atomic images.
• Albert Crewe improved TEM with directed electron sources.
• Used concepts from cathode ray tubes to improve imaging.

Breakthrough in Aberration Correction

• Knut Urban, Max Haider, and Harold Rose developed a method using asymmetric electromagnetic lenses.
• 1997: Successfully corrected spherical aberration, significantly improving TEM resolution.
• New lenses used hexapole, octopole, and decapole magnets.

Modern Achievements

• TEM resolution improved to 0.13 nm.
• 2020: Knut Urban, Max Haider, Harold Rose, and Ondrej Krivanek awarded Kavli Prize in Nanoscience.
• Aberration correction is crucial for material science and engineering research.

Conclusion

• Correcting aberrations allows detailed examination of atomic structures, crucial for scientific research.
• Every modern research facility needs advanced microscopes for atomic-level investigation.