Transmission Electron Microscope Basics and history

Microscopy: VLM vs. TEM Eyes can resolve 0.1-0.2 mm Microscopy shows details below this (0.1 mm) In TEM technique viewing screen displays electron intensity as light intensity Resolution as Rayleigh Criterion (smallest distance that can be resolved): 𝛿= 0.61λ 𝜇𝑠𝑖𝑛𝛽 → 1.22λ 𝛽 (for TEM) VLM:  ≈ 300 nm → corresponds to 1000 atom diameters TEM:  < 0.1 nm (IVEM + Cs correction) TEM produces high resolution images and diffraction patterns Characterization of (nanoscale) materials Microscopy: VLM vs. TEM

History L. Broglie (1925): theory about electrons wave-like characters Davisson and Germer + Thomson and Reid (1927): classis electron- diffraction experiments Knoll and Ruska (1932): electron lenses into practical reality and use to produce electron images (Noble prize) First TEM (1936): Metropolitan-Veckers EM1 Commercial production (1939): Siemens and Halske Bollman and Hirsch: technique for thin metal foil to electron transparency and theory of electron-diffraction contrast ’Bible of TEM’ Nowadays: HRTEM, HVTEM, IVEM, STEM, AEM… History

SIGNALS FROM Electron radiation Electrons cause ionizing radiation which produce wide range of signals Best signals accomplished by using small electron beam (<5 nm, at best <0.1 nm) Analytical electron microscopy: XEDS and EELS Depth of field: a measure of how much of examined object remains in focus at the same time Depth of focus: distance which over the image can move relative to the object and still remain focus Narrowing beam increases depth of field and depth of focus but decreases intensity SIGNALS FROM Electron radiation

TEM Limitations Expensive: 5-10 $ / eV Sampling: with high resolution only small part of sample can be look at the same time (103 mm3) Interpreting transmission images: 3D samples as 2D images Electron beam damage and safety: ionizing radiation can damage samples and radiation can harm tissue Specimen preparation: ’thin’ electron transparent samples <100nm TEM Limitations

Electron properties Both particle and wave characteristics In TEM: accelerating electron through potential drop momentum is imparted λ= ℎ 𝑝 = ℎ (2 𝑚 0 𝑒𝑉) 1/2 (<100keV, non-relativistic electron wavelength) λ= ℎ [2 𝑚 0 𝑒𝑉(1+ 𝑒𝑉 2 𝑚 0 𝑐 2 ] 1/2 (for relativistic wavelengths) Increase in accelerating voltage decreases the wavelength of electrons V (accelerating voltage of microscopy) vs. eV (energy of electrons) Electron properties