A Tutorial on Electron Microscopy Jian-Min (Jim) Zuo Mat. Sci. Eng. and Seitz-Materials Research Lab., UIUC
Outline of This Tutorial I. Science and opportunities of electron microscopy II. The basic TEM, electron imaging and diffraction III. Image contrast and imaging modes of TEM IV.Electron probe formation and spectroscopy
I. The Science and Opportunities
Outline of This Tutorial I. Science and opportunities of electron microscopy II. The basic TEM, electron imaging and diffraction III. Image contrast and imaging modes of TEM IV.Electron probe formation and spectroscopy
The Basic Idea of Transmission Electron Microscopy from web source
JEOL 120 CX From Marc De Graef Developed and sold in early 80s
Electron energy Conventional TEM, 80-200 kv Medium high voltage TEM, 200-500 kv High voltage TEM, 500 kv- 3MV The Basic TEM Bright and dark field imaging Magnification at ~200x to 1 M x Electron diffraction High resolution electron microscopy Analytical TEM Microanalysis Electron energy loss spectroscopy
Electron Wavelength The idea that particles can form images like an optical wave comes from Louis de Broglie, who postulated that each particle has a characteristic wavelength given by = h / l h, the Planck constant and p the momentum of particle 2 2 E o = e = mv / 2 = p / 2m p
Electron Lens 2 d r F = m = ev B 2 dt Deflection + Rotation B is symmetrical around z-axis Electron rotate first, then focus
Image Formation using a Lens U V Magnification =Image_Size/Object_Size= V/U
Resolution Limit of Microscopes The maximum resolving power of a far-field optical microscope is defined by the Rayleigh criterion, which we also refer to as the diffraction limit: l d min = 0.61 n sin q l is the wavelength of light and nsin q is the numerical aperture In a high-resolving microscope, with oil-immersion objective lens and a large apertures,, which gives a maximum resolution of Clay, R., Court, T., The History of the Microscope. Holland Press, 1975. Hartley, W.G., The Light Microscope: Its Use and Development. Senecio Publishing Co., 1993. http://www.physik.fu-berlin.de/~bauer/habil_online/node15.html
The Real Lens Aberrations Spherical aberration C s : d = MC s q 3 M magnification Cs, 0.5 mm, 1mm, 2mm Chromatic aberration C c : d = MC c qde/e DE, change in electron energy, energy loss d
The Resolution of the Electron Lens (the microscope) -The maximum half angle b is defined by microscope apertures (aperture is the hole in a diaphragm). The microscope is a aperture by itself -Theoretical resolution -Practical resolution r r r b 2 2 th Cs r th = l 0.61 b l b = 3 r b = 0.61 C sb opt l = 0.77 C s 1/ 4 r = min 0.91 s 2 3 C l 1/ 4 2
Outline of This Tutorial I. Science and opportunities of electron microscopy II. The basic TEM, electron imaging and diffraction III.Image contrast and imaging modes of TEM IV.Electron probe formation and spectroscopy
Diffraction Contrast Bright Field Off-Axis Dark Field Dark Field
Phase Contrast and High-Resolution Electron Imaging Object Lens Back Focal Plane (diffraction) Image Plane Schematic diagram of high-resolution electron image formation, where the diffraction pattern is formed at the back focal plane of the objective lens and diffracted beams recombine to form image.
HREM of Si [110]
Outline of This Tutorial I. Science and opportunities of electron microscopy II. The basic TEM, electron imaging and diffraction III. Image contrast and imaging modes of TEM IV.Electron probe formation and spectroscopy
Electron Probe Formation M << 1 b r l b 3 b = 0.61 C sb 2 2 b opt l = 0.77 C s 1/ 4 r = min 0.91 s 3 C l 1/ 4
Optical Axis B N Cs < 0 N C s > 0 e-beam
The Major Facilities FEI Titan 80 kv CMM-MRL, JEOL2200FS NCEM-LBL, TEAM Microscopes
Digital Synthesis: The 2x2 LaMnO3/SrTiO3 Superlattice La Mn Sr Ti Superlattice Grown by J. Eckstein, Physics, UIUC