Lecture 6: Microscopy II

1. Lecture 6: Microscopy II PHYS 430/603 material Laszlo Takacs UMBC Department of Physics

2. Useful sites: http://www.microscopyu.com/articles/optics/components.html http://em-outreach.ucsd.edu/web-course/toccontents.html Light microscopyThe principle and a commercial scope

3. Optical microscope (OM) and transmission electron microscope (TEM)

4. TEM modes:Composite image, bright field image, dark field image, selected area diffraction First image Transmitted and diffracted beams Diffraction pattern Bright field Bright field, transmitted electrons only Dark field Selected area diffraction pattern

5. Comparing imaging and diffraction in a TEM.

6. Electron diffraction from amonocrystal polycrystal glass

7. How do scanning microscopies work? • Measurement generates a value for every location: • Reflectivity of light (scanner) • Ejected electrons (SEM) • Current between tip and surface (STM) • Force between tip and surface (AFM) • Any quantity of interest Interpret numbers as intensities for display or printer. Digital image processing. Image = table of numbers

8. The principle of STM What exactly is measured? Tunneling current ~ probability of an electron tunneling out from the surface ~ electron density. Largest where the atoms are, thus we “see” the atoms - kind of.

9. 48 Fe atoms forming a “quantum collar” on a Cu (1 1 1) surface. The inner rings are not from atoms at the location.

10. STM of Si (1 1 1) 7x7 reconstructed surface

11. Surface structure • Relaxation: change of distance between the first few lattice planes. Typically, ~10% change in the first, ~1% in the second distance. • Reconstruction: change of the arrangement/ symmetry of the arrangement of atoms. • Reactive, usually picks up other atoms, e.g. O.

12. Notice that smaller circles represent atoms farther from the top layer.

13. Low Energy Electron Diffraction Cu (1 0 0) ZnO (1 0 -1 0)

14. Typical surface features after cleaving close to a lattice plane or building up a crystal from the gas phase

15. FeSi2 on a Si (111) surface Notice: • Reconstruction of Si • Relationship between the orientations of substrate and coating • Steps and kinks in the FeSi2 layers

16. Contact-mode AFM: It is a miniature profilometer, directly measures height. Best for larger-scale (at least a few nm) features.

17. The principle of field ion microscopy

18. Images taken by field ion microscope Ir (1 1 0) Pt (0 1 2)

19. E. W. Müller, Platinum Metal Rev. 9 (1965) 84-89 Vacancies Dislocations on platinum tips