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This guide covers Scanning Probe Microscopy and Optical Spectroscopy techniques, including AFM, STM, and more. Learn about their applications and principles in nanomaterial analysis. Discover how these techniques are used for imaging surfaces, measuring properties, and fabricating nanostructures. Dive into Chemical Characterization methods like Optical Spectroscopy, Absorption, and more for in-depth analysis of nanomaterials. Explore the intricate world of nano-characterization with this comprehensive resource.
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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
Characterization of Nanomaterials NANO 101 Introduction to Nanotechnology
Characterization Techniques • Structural Characterization • Scanning electron microscopy • Transmission electron microscopy • Scanning probe microscopy • Chemical Characterization • Optical spectroscopy • Electron spectroscopy
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
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
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
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
STM • STM is measuring electron density and not nuclear position http://www.aist-nt.com/content/stm
STM video • Notice: size, complexity of equipment, sample prep
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
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
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
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/
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
MFM • Image magnetic domains, Rare earth – Transition metal thin film http://www.science.uva.nl/research/cmp/qem/research_projects/patterned_magnetic_films.html
Scanning Acoustic Microscope • Good for finding cracks and voids in material • Failure Analysis http://www.soest.hawaii.edu/HIGP/Faculty/zinin/Zi-SAM.html
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
Characterization Techniques • Structural Characterization • Scanning electron microscopy • Transmission electron microscopy • Scanning probe microscopy • Chemical Characterization • Optical spectroscopy • Electron spectroscopy
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)
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
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
Summary: Techniques used to study nanostructures • Bulk/ensemble characterization techniques • Information is average for all particles • Surface/individual characterization techniques • Information about individual nanostructures