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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
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Characterization of Nanomaterials
NANO 101Introduction to Nanotechnology
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Characterization Techniques
• Structural Characterization• Scanning electron microscopy• Transmission electron microscopy• Scanning probe microscopy
• Chemical Characterization• Optical spectroscopy• Electron spectroscopy
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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
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Scanning Tunneling Microscopy (STM)
• Developed by Binnig and Rohrer in 1982• Tunneling• Very dependent on distance between the
two metals or semiconductorsBy making the distance 1 nm smaller, tunneling can increase 10X
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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 nAResolution:
0.01 nm (in X and Y directions)0.002 nm in Z direction Source: Univ. of Michigan
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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
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STM
• STM is measuring electron density and not nuclear position
8http://www.aist-nt.com/content/stm
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STM video
• Notice: size, complexity of equipment, sample prep
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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: NanosurfSource: photonics.com
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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
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AFM • Atmospheric technique• Easy sample prep
12AFM at NIST in MDhttp://www.nist.gov/cnst/nanofab/nanofab_afm3000.cfm
Protein surface/ contact AFM
Low Temp needed for atomic resolutionhttp://cen.acs.org/articles/91/i51/Atomic-Force-Microscopy-Provides-Astonishing.html
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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
13http://virtual.itg.uiuc.edu/training/AFM_tutorial/
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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
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MFM
• Image magnetic domains, Rare earth – Transition metal thin film
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http://www.science.uva.nl/research/cmp/qem/research_projects/patterned_magnetic_films.html
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Scanning Acoustic Microscope
• Good for finding cracks and voids in material• Failure Analysis
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http://www.soest.hawaii.edu/HIGP/Faculty/zinin/Zi-SAM.html
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Scanning Capacitance Microscope
• Capacitance is used for feedback loop• Ability to store electrical charge 17
http://www.pa.msu.edu/~ghosh/printresearchSiC.htmlhttp://www.ma-tek.com/service_detail.php?path=65
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Characterization Techniques
• Structural Characterization– Scanning electron microscopy– Transmission electron microscopy– Scanning probe microscopy
• Chemical Characterization– Optical spectroscopy– Electron spectroscopy
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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)
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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
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Abs/Emission
• Abs/PL are complimentary
• Both are size dependent
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Diameter vs absorption and photoluminescence of various sizes of CdSe0.34Te0.66 QDshttp://www.azom.com/article.aspx?ArticleID=10454
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Summary: Techniques used to study
nanostructures• Bulk/ensemble characterization techniques
– Information is average for all particles
• Surface/individual characterization techniques– Information about individual nanostructures