2. Auger electron spectroscopy is a surface sensitive analytical technique used mainly to determine elemental compositions of material and, in certain cases to identify the chemical states of surface atom.

3. 1.Etching the sample with X-rays or electron bombardment 2.A vacancy is created in an atomic core level 3.An electron from an upper level fill the hole 4.The energy difference liberated, and it can form of a photon (XRF) or eject an Auger electron.

4. Auger emissions are described in term of the type of orbital transition involved in the production of an electron. KLL: 1.removes a K electron 2.transition of an L electron to the K orbital 3.ejection of second L electron LMM & MNN are also common transitions. Auger electron emission and X-ray fluorescence are competitive processes: Lower atomic number auger electron emission Higher atomic number X-ray fluorescence

6. Measurement of kinetic energies of the emitted electrons is performed. Spectra typically displayed as a derivative dN(E)/dE

9. Sensitivity to atoms of low atomic number Minimal matrix effect High spatial resolution Detailed examination of solid surface Non-destructive Rapid analysis

10. Classical methods Optical microscope Resolution is limited by diffraction effects to about wavelength of light  classical methods  modern microscopic methods  spectroscopic methods

11. Modern microscopic methods (higher resolution) Scanning electron microscopy (SEM) Scanning probe microscopy (SPM) Scanning tunneling microscopy (STM) Atomic force microscopy (AFM) classical and modern microscopic methods provide information about the physical nature or morphology of surfaces but less about their chemical nature.

12. Scanning Electron Microscopy SEM

13. They take advantage of the short wavelength of electrons. As the wavelength is shorter, higher resolution is possible than with regular light microscopes Electron microscopes were developed around the same time as the development of television sets (1960s) and utilize much of the same technology

14. Electron Interactions: All Types Sample Cathodaluminescence Secondary e – Backscattered e – Incident e – Auger e – X-rays Elastically Scattered e – Inelastically Scattered e – Unscattered e – Electron Beam-Specimen interactions

15. SEM is very good for looking at surfaces SEM cannot show color With the right detectors SEM can be used to determine the elements in a sample SEM can go to high magnifications, but cannot achieve magnifications as high as those achieved with Transmission Electron Microscopy

16. Principles and Construction of the SEM

17. + - Magnet lenses Beam deflector Filament Focussed Electron beam Electrons Stub Sample

18. …..….. - + Magnet lenses Beam deflector Filament Focussed Electron beam Electrons Stub Sample Reflected electrons Electron detector

19. Fly Head Bee Eye

20. Leaf With Bacteria This is an image of an aluminum copper alloy formed using backscattered electron imaging. The light area is mostly copper and the dark area is mostly aluminum.

21. Intel’s transistors – current and near-future M. Deal Stanford, 6/30/2005 SEM showing the vertical growth of nanowires for electronic devices (Stanford) Human hair

22. Single-walled nanotubes (SWNTs) Multi-walled nanotubes (MWNTs)

23. Bi/opalPb/opal NaNO 3 /opal 2 µm500 nm 20 µm After annealing at Т > T m NaNO 3 /opal

24. 300nm Latex opal 300nm on Latex opal 240nm 240nm Substrate 5μm SEM image

25. SEM Images: Improved Depth of Focus Secondary electrons of SEM provide higher depth of focus compared to optical microscopy. Optical ImageSEM Image screw cells From Brundle From Flegler

27. 1. Relatively easy to use 2. Large depth of focus 3. Large magnification range (> 80,000X) 4. 3D images 6. High resolution 1-5 nm 5. Can produce images whose contrast is based on composition variations 7. Characteristic x-rays used to identify and image elemental distributions

28. Inability to produce color Specimen must be stable under vacuum. Specimen at least must exhibit slight electrical conductivity.

29. Scanning Tunneling Microscope

30. Introduction STM has unique capability to resolve topological and electronic structures at atomic level.  Ability to operate in a variety of different environments such as air, reactive gases, liquids, electrolytes and biological fluids.  Application: electrochemistry, biology, tribology, medicine...

31. Basic principles Phenomenon of tunneling According to quantum mechanics, a subatomic particle can pass through a spatial region in which the particle’s kinetic energy is less than its potential energy.

32. The tunnel current will change with the tip location on the surface (eq. 1). The tunneling current is held constant by a feedback mechanism that moves the tip up and down so that s remains constant. Tip movement is controlled by the voltage at z-piezo. This voltage yields a topographic profile of the surface.

33. e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- < 1nm Resolution in z is 0.01 nm and in x/y is ~0.2 nm, resulting in atomic resolution images. I t= V exp(- Cd)

34. Constant current mode

35. Structure of crystal surface Metals, Semiconductors, Superconductors and Oxides Adsorption, surface Diffusion and Surface Chemistry Thin film morphology, Nucleation, Growth, etc Surface electronic structure Organic molecules, Biological molecules Atom manipulation and Nanolithography

36. Atomic Force Microscope

38. STM-single atom interaction STM-single atom interaction AFM-several atoms on tip interact with several atoms on surface AFM-several atoms on tip interact with several atoms on surface AFM STM

39. In contact AFM electrostatic and/or surface tension forces from the adsorbed gas layer pull the scanning tip toward the surface. It can damage samples and distort image data. Therefore, contact mode imaging is heavily influenced by frictional and adhesive forces compared to non-contact or tapping mode. In contact AFM electrostatic and/or surface tension forces from the adsorbed gas layer pull the scanning tip toward the surface. It can damage samples and distort image data. Therefore, contact mode imaging is heavily influenced by frictional and adhesive forces compared to non-contact or tapping mode. Non-contact imaging generally provides low resolution and can also be hampered by the contaminant layer which can interfere with oscillation. Non-contact imaging generally provides low resolution and can also be hampered by the contaminant layer which can interfere with oscillation. TappingMode AFM was developed as a method to achieve high resolution without inducing destructive frictional forces both in air and fluid. With the TappingMode technique, the very soft and fragile samples can be imaged successfully. TappingMode AFM was developed as a method to achieve high resolution without inducing destructive frictional forces both in air and fluid. With the TappingMode technique, the very soft and fragile samples can be imaged successfully.

40. Polymer latex particle on mica ContactNoncontact Vibrating (tapping) Cantilever soft hard hard Force 1-10nN 0.1-0.01nN Friction large small small Distance 10nm Damage large small small

41. Contact Mode Advantages: High scan speeds The only mode that can obtain “atomic resolution” images Rough samples with extreme changes in topography can sometimes be scanned more easily Disadvantages: The combination of lateral forces and high normal forces can result in reduced spatial resolution and may damage soft samples (i.e. biological samples, polymers, silicon) due to scraping Advantages and Disadvantages of the 3 main Types of AFM

42. Tapping Mode AFM Advantages: Higher lateral resolution on most samples (1 to 5nm) Lower forces and less damage to soft samples imaged in air Disadvantages: Slightly lower scan speed than contact mode AFM Advantages and Disadvantages of the 3 main Types of AFM