Reminders for this week
• Homework #4 Due Wednesday (5/20)
• Lithography Lab Due Thursday (5/21)
• Quiz #3 on Thursday (5/21) – In Classroom
– Covers Lithography, Special Nanostructures, Characterization of
Nanostructures
– Format similar to Quiz #2
Characterization of Nanomaterials
NANO 101
Introduction to Nanotechnology
2
Observations and Measurement:
Studying physical properties related to nanometer size
Needs:
– Extreme sensitivity
– Extreme accuracy
– Atomic-level resolution
http://www.viewsfromscience.com/
documents/webpages/nanocrystals.html
3
Characterization Techniques
• Structural Characterization
• Scanning electron microscopy
• Transmission electron microscopy
• Scanning probe microscopy
• Chemical Characterization
• Optical spectroscopy
• Electron spectroscopy
4
Characterization Techniques
• Individual Measurements
– Electron Microscopy
– Scanning Probe Microscopy
– Electron Spectroscopy
• Ensemble Measurements
– Optical Spectroscopy
– Crystallography
5
Structural Characterization
• Techniques already used for crystal structures
• X-Ray Diffraction
• Many techniques already used for studying the surfaces of bulk
material
• Scanning Probe Microscopy (AFM & STM)
• Electron Microscopes
• Provide topographical images
6
Crystallography
• Arrangement of atoms
• Crystals have atoms in ordered lattices
• Amorphous: no ordering of atoms
Source: Wikipedia
Source: Encyclopedia of Alternative
Energy and Sustainable Living.
7
Bragg’s Law/Scherrer Equation
• Constructrive
interference of
X-rays leads to
peaks
• Less planes for
diffraction ->
broadened
peaks
8
XRD
9
Crystallography Controls Properties
Chem. Soc. Rev., 2013, 42, 2321-2337
• BiVO4 (Monoclinic is photocatalytic, Tetragonal
is not)
10
Electron Microscopes
• Used to count individual atoms
What can electron microscopes tell us?
• Morphology
– Size and shape
• Topography
– Surface features (roughness, texture, hardness)
• Crystallography
– Organization of atoms in a lattice
Microscopes: History
• Light microscopes
– 500 X to 1500 X magnification
– Resolution of 0.2 µm
– Limits reached by early 1930s
• Electron Microscopes
Source: Wikipedia
– Use focused beam of electrons instead of light
• Transmission Electron Microscope (TEM)
• Scanning Electron Microscope (SEM)
12
Electron Microscopy
Steps to form an image
1. Stream of electrons formed by an electron source
and accelerated toward the specimen
2. Electrons confined and focused into thin beam
3. Electron beam focused onto sample
4. Electron beam affected as interacts with sample
5. Interactions / effects are detected
6. Image is formed from the detected signals
Electron Microscopes
• Electron Beam
– Accelerated and focused
using deflection coils
– Energy:
200 - 1,000,000 eV
• Sample
– TEM: conductive, very
Source: Virtual Classroom Biology
 Detection
thin!
◦ TEM: transmitted e– SEM: conductive
◦ SEM: emitted e14
EM Resolution
• Resolution dependent on:
• wavelength of electrons ()
• NA of lens system
0.612
d
NA
NA = n sin θ
• Wavelength dependent on:
• Electron mass (m)
• Electron charge (q)
h

2mqV
• Potential difference to accelerate electrons (V)

15
Transmission EM
• Magnification:
~50X to 1,000,000X
1. E-beam strikes sample and is
transmitted through film
2. Scattering occurs
3. Unscattered electrons pass
through sample and are detected
16
Source: Wikipedia
TEM
17
http://www.ammrf.org.au/myscope/tem/introduction/
TEM Samples
Nature Protocols 7, 1716–
1727 (2012)
http://advanced-microscopy.utah.edu/education/electron-micro/
• Must be ultra thin
• More difficult for biological samples
18
TEM Information
http://www.intechopen.com/books/nanowire
s-fundamental-research/silicide-nanowiresfrom-coordination-compound-precursors
http://commons.wikimedia.org/wiki/File:Mitochondria,_mamm
alian_lung_-_TEM_(2).jpg
19
Scanning EM
• Magnification:
~10X to 300,000X
1. E-beam strikes sample and electron
penetrate surface
2. Interactions occur between electrons
and sample
3. Electrons and photons emitted from
sample
4. Emitted e- or photons detected
http://virtual.itg.uiuc.edu/training/EM_tutorial
Source: Wikipedia
20
SEM: Electron Beam Interactions
• Valence electrons
• Inelastic scattering
• Can be emitted from sample
“secondary electron”
valence e+ +++
++
core enucleus
Atomic nuclei
• Elastic scattering
• Bounce back - “backscattered electrons”
Core electrons
• Core electron ejected from sample; atom excited
• To return to ground state,
x-ray photon or Auger electron emitted
21
Secondary versus Backscattered
• Top – Secondary
electron image
– Shallow escape
depth -> better
resolution
• Bottom –
Backscattered
electron image
– More sensitive to
elements of
different masses
22
SEM Samples
• Must have conductive surface
– Electrons must go around surface not stay on surface
http://www4.nau.edu/microanalysis/MicroprobeSEM/Imaging.html
23
STEM
• Still requires thin sample
• E-beam is scanned as in SEM and secondary or backscattered
electrons can be detected
http://www.sci.sdsu.edu/TFrey/Bio750/ElecMi8.gif
http://www.thenanoage.com/carbon.htm
24
Electron Spectroscopy
Energy
Auger e-
X-ray
Ground state
e- emitted;
excited state
Relaxes to ground state
1. e- or photon strikes atom; ejects core e2. e- from outer shell fills inner shell hole
3. Energy is released as X-ray or Auger electron
EDS: Energy Dispersive X-ray Spectroscopy
AES: Auger Electron Spectroscopy
EELS: Electron Energy Loss Spectroscopy
25
Electron Spectroscopy
Emitted energy is characteristic of a specific type of atom
Each atom has its own unique electronic structure and
energy levels
• AES is a surface analytical technique
<1.5 nm deep
•
•
•
•
AES can detect almost all elements
EDS only detects elements Z > 11
EDS can perform quantitative chemical analysis
EELS is sensitive to lighter elements (Carbon –
Transition Metals)
• EELs is sensitive to chemical environment
26
EDS
• Chemical Composition
Mapping
Pb paint chip, SEM,
http://www.clemson.edu/restoration/wlcc/equipment_services/equi
pment/scanning_electron_microscopy.html
Metal-Polymer Core Shell
http://www.intechopen.com/books/nanocomposites-new-trendsand-developments/ecologically-friendly-polymer-metal-and27
polymer-metal-oxide-nanocomposites-for-complex-water-treatme
AES
• AES -> Surface
chemical mapping,
depth profile
Battery Electrode Surface
http://www.azom.com/article.aspx?ArticleID=8911
J. Mater. Chem., 2010, 20, 4392-4398
28
EELS
http://stem.ornl.gov/highlight_direct_determination.shtml
29
SEM and TEM Comparison
• SEM makes clearer images than TEM
• SEM has easier sample preparation than TEM
• TEM has greater magnification than SEM
• SEM has large depth of field
• SEM is often paired with detectors for elemental
analysis (chemical characterization)