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 1

2. Characterization of Nanomaterials NANO 101 Introduction to Nanotechnology 2

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

4. 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. 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. 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. 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 8 http://www.aist-nt.com/content/stm

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

10. 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: Nanosurf Source: photonics.com

11. 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 12 AFM at NIST in MD http://www.nist.gov/cnst/nanofab/nanofab_afm3000.cfm Protein surface/ contact AFM Low Temp needed for atomic resolution http://cen.acs.org/articles/91/i51/Atomic-Force-Microscopy- Provides-Astonishing.html

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 13 http://virtual.itg.uiuc.edu/training/AFM_tutorial/

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

15. MFM Image magnetic domains, Rare earth – Transition metal thin film 15 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 16 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 17 http://www.pa.msu.edu/~ghosh/printresearchSiC.html http://www.ma-tek.com/service_detail.php?path=65

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

19. 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. 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) N&N Fig. 8.10 -Information about electronic structure -Nano -> size dependent electronic structure

21. Abs/Emission Abs/PL are complimentary Both are size dependent 21 Diameter vs absorption and photoluminescence of various sizes of CdSe 0.34 Te 0.66 QDs http://www.azom.com/article.aspx?ArticleID=10454

22. 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