Today Homework #4 Due Scanning Probe Microscopy, Optical Spectroscopy 11 am NanoLab Tour

1. Today • Homework #4 Due • Scanning Probe Microscopy, Optical Spectroscopy • 11 am NanoLab Tour • Tomorrow • Fill out project outline • Quiz #3 in regular classroom • Next week • Energy and Nanotechnology

2. Characterization of Nanomaterials NANO 101 Introduction to Nanotechnology

3. Characterization Techniques • Structural Characterization • Scanning electron microscopy • Transmission electron microscopy • Scanning probe microscopy • Chemical Characterization • Optical spectroscopy • Electron spectroscopy

4. Scanning Probe Microscopy (SPM) • AFM & STM • Measure feedback from atomically defined tip • Many types of feedback (dependent on tip) • Magnetic Force Microscopy • Magnetic material (iron) coated tip • magnetized along tip axis • Scanning Thermal Microscopy • Scanning Capacitance Microscopy • Capacity changes between tip and sample • Scanning Acoustic Microscopy

5. Scanning Tunneling Microscopy (STM) • Developed by Binnig and Rohrer in 1982 • Tunneling • Very dependent on distance between the two metals or semiconductors By making the distance 1 nm smaller, tunneling can increase 10X

6. Scanning Tunneling Microscopy (STM) Instrument: Scanning Tip • Extremely sharp • Metal or metal alloys (Tungsten); Conductive • Mounted on stage that controls position of tip in x, y, z • Typically kept 0.2 - 0.6 nm from surface Tunneling Current: ~ 0.1 - 10 nA Resolution: 0.01 nm (in X and Y directions) 0.002 nm in Z direction Source: Univ. of Michigan

7. Scanning Tunneling Microscopy (STM) Constant Current Mode: • As tip moves across the surface, it constantly adjusts height to keep the tunneling current constant • Uses a feedback mechanism • Height is measured at each point Constant Height Mode: • As tip moves across surface, it keeps height constant • Tunneling current is measured at each point • No feedback loop

8. STM • STM is measuring electron density and not nuclear position http://www.aist-nt.com/content/stm

9. STM video • Notice: size, complexity of equipment, sample prep

10. Atomic Force Microscopy (AFM) • Can be used for most samples • Measures: • Small distances: • Van der Waals interactions • Larger distances: • Electrostatic interactions (attraction, repulsion) • Magnetic interactions • Capillary forces (condensation of water between sample and tip) Source: photonics.com Source: Nanosurf

11. Atomic Force Microscopy (AFM) • Scan tip across surface with constant force of contact • Measure deflections of cantilever http://content.answers.com/main/content/wp/en/1/1a/Atomic_force_microscope_block_diagram.png

12. AFM • Atmospheric technique • Easy sample prep Protein surface/ contact AFM Low Temp needed for atomic resolution http://cen.acs.org/articles/91/i51/Atomic-Force-Microscopy-Provides-Astonishing.html AFM at NIST in MD http://www.nist.gov/cnst/nanofab/nanofab_afm3000.cfm

13. Common Feedback Modes • Contact • Tip is dragged across sample, adjusted for constant force against tip • Tapping • Tip oscillates at a certain frequency which is sensitive to distance from sample • Used for more delicate samples http://virtual.itg.uiuc.edu/training/AFM_tutorial/

14. Scanning Probe Techniques Other tip-surface force microscopes: • Magnetic force microscope • Scanning capacitance microscope • Scanning acoustic microscope Some instruments combine STM and AFM Uses: • Imaging of surfaces • Measuring chemical/physical properties of surfaces • Fabrication/Processing of nanostructures • Nanodevices

15. MFM • Image magnetic domains, Rare earth – Transition metal thin film http://www.science.uva.nl/research/cmp/qem/research_projects/patterned_magnetic_films.html

16. Scanning Acoustic Microscope • Good for finding cracks and voids in material • Failure Analysis http://www.soest.hawaii.edu/HIGP/Faculty/zinin/Zi-SAM.html

17. Scanning Capacitance Microscope • Capacitance is used for feedback loop • Ability to store electrical charge http://www.pa.msu.edu/~ghosh/printresearchSiC.html http://www.ma-tek.com/service_detail.php?path=65

18. Characterization Techniques • Structural Characterization • Scanning electron microscopy • Transmission electron microscopy • Scanning probe microscopy • Chemical Characterization • Optical spectroscopy • Electron spectroscopy

19. Chemical Characterization • Optical Spectroscopy • Absorption • Photoluminescence (PL) • Infrared Spectroscopy (IR or FTIR) • Raman Spectroscopy • Electron Spectroscopy • Energy-Dispersive X-ray Spectroscopy (EDS) • Auger Electron Spectroscopy (AES)

20. Optical Spectroscopy:Absorbance/Transmittance • Absorbance:electron excited from ground to excited state • Emission:electron relaxed from excited state to ground state • Transmittance:“opposite” of absorbance: A = -log(T) • Information about electronic structure • Nano -> size dependent electronic structure N&N Fig. 8.10

21. Abs/Emission • Abs/PL are complimentary • Both are size dependent Diameter vs absorption and photoluminescence of various sizes of CdSe0.34Te0.66 QDs http://www.azom.com/article.aspx?ArticleID=10454

22. Summary: Techniques used to study nanostructures • Bulk/ensemble characterization techniques • Information is average for all particles • Surface/individual characterization techniques • Information about individual nanostructures