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The second term is the particle-in-a-box confinement energy for an electron-hole pair in a spherical quantum dot and the third ... AFM Images of CdSe Quantum Dots ... – PowerPoint PPT presentation

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Title: i s o


1
Coaches Meeting 2011 Materials Science
Wisconsin Science Olympiad
  • i s o
  • Illinois Science Olympiad

2
New Rules - Materials Performance and Nano focus
  • Structure and Performance Relationships
  • Students will perform laboratory based
    experiments designed to evaluate the relationship
    between the atomic/molecular structure and the
    performance characteristics of common materials.
  • Structure and Characteristics of metals,
    ceramics, polymers, semi-conductors and
    composites. - Utilizing stress-strain curves to
    evaluate the Youngs modulus.

3
Nanomaterials - focus on nanoparticles and
carbon nanotubes.
  • General introductory topics regarding the
    physical and chemical properties that arise
    within the nano size regime.
  • surface area to volume ratios
  • quantum effects
  • nanomaterials visualization.
  • Understand SEM, TEM, AFM micrographs scaling
  • Cubic crystal structures.
  • Formula, density, dimensions. Miller Indices, and
    use of x-ray data to determine unit cell
    dimensions. Internet based modeling and/or
    simulations may be incorporated into event tasks
    and questions.

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Materials Characteristics
7
? Density
8
Materials Characteristics
  • Metals low electronegativity metal cationic
    atoms in a sea of delocalized electrons.
    Metallic bonds from electrostatic interaction -
    different from ionic bonds.
  • Conducts electrons on the delocalaized valence
    level sea of electrons
  • malleable/ductile, hard, tough, can be brittle.

Iron
9
Ceramics
  • covalent and ionic bonding of inorganic
    non-metals. electrons are localized in bonds -
    poor conductors, brittle and very thermally
    stable.
  • The crystal structure of bulk ceramic compounds
    is determined by the amount and type of bonds.
    The percentage of ionic bonds can be estimated by
    using electronegativity determinations.
    Resistance to shear and high-energy slip is
    extremely high.
  • Atoms are bonded more strongly than metals fewer
    ways for atoms to move or slip in relation to
    each other. Ductility of ceramic compounds is
    very low and are brittle. Fracture stresses that
    initiate a crack build up before there is any
    plastic deformation and, once started, a crack
    will grow spontaneously.

Alumina Al2O3
http//mst-online.nsu.edu/mst/ceramics/ceramics3.h
tm
10
Semi-conductors
  • Metalloid in composition (w/ exception).
    Covalently bonded. More elastic than ceramics.
  • characterized by the presence of a band gap where
    electrons can become delocalized within the
    framework.

11
Polymers
  • macromolecules containing carbon covalently
    bonded with itself and with elements of low
    atomic number
  • molecular chains have long linear structures and
    are held together through (weak) intermolecular
    (van der Waals) bonds. Low melting temp.

12
Materials Performance
  • Optical properties (Quantum Dots, LEDs)
  • Magnetic properties (ferrofluids)
  • Electronic Properties ( semiconductors)
  • Thermal and Mechanical Properities (plastics,
    metals, ceramics)

13
Mechanical Performance
  • Stress Vs. Strain relationship

http//www.yourbuilding.org/Article/NewsDetail.asp
x?p83id1570
14
Linear Deformation - Stress and Strain
Stress - force applied over a given area. Units
of lbs/in2 or Gigapascals
Strain - Deformation of material as a change in
dimension from initial. Unitless
15
Stress, Strain, and Youngs Modulus
Youngs Modulus - a measure of material
stiffness - E s/e F/A l/L
Hookes Law F k?x spring constant k F/?x
16
True elastic behavior vs. elastic region
Glass
Rubber
Vable, M. Mechanics of Materials Mechanical
properties of Materials. Sept. 2011
17
Relationship of E and materials characteristics
Polymers
m E
http//www.nrc-cnrc.gc.ca/eng/ibp/irc/cbd/building
-digest-157.html
18
E, Youngs Modulus GPa psi
Rubber 0.01-0.1 1500-15000
Teflon 0.5 75,000
Nylon 2 - 4 290,000-580,000
Aluminum 69 10,000,000
Glass 50 - 90 n/a
Copper 117 17,000,000
Steel 200 29,000,000
Diamond 1220 150 -175 million
19
Example Question
20
A different application of Youngs Modulus
The deflection d of the mid-point of a centrally
loaded simple beam of uniform rectangular cross
section is given byd (Wl3)/(4ab3Y) For a
circular beam of radius r the expression becomesd
(Wl3)/(12pr4Y) where Y is the Youngs Modulus
http//blog.cencophysics.com/2009/08/beam-deflecti
on-youngs-modulus/
21
Nanomaterials - Nanoworld
  • The size regime of the nanoworld is 1 million
    times smaller than a millimeter.

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SEM, TEM, AFM Images of CdSe Quantum Dots

200 nm
Picture C.P. Garcia, V. Pellegrini , NEST
(INFM), Pisa. Artwork Lucia Covi http//mrsec.wis
c.edu/Edetc/SlideShow/slides/quantum_dot/QDCdSe.ht
ml http//www.jpk.com/quantum-dots-manipulation.20
7.en.html?imageadf24cc03b304a4df5c2ff5b4f70f4e9
24
Surface area to volume ratio
Volume
Surface Area
25
  • Consequences of Large Surface Area to Volume ratio

Gas law P nRT
V
As volume decreases, SA increases as does
pressure
26
Electron conducting band gaps
- Conducting is flow of e- from VB through the
C.B. In metals, CB is linked to VB directly
- Semiconductors require some energy input to
overcome a gap between VB and CB
- Insulators have a band gap too large to
overcome, thus they insulate against e-
conduction.
27
Characteristics of Light
Wave-like properties Wavelength (?) or Frequency
(?) c ?? (c is the speed of light, 3.0x108
m/s) Particle-like properties A photon is a
packet of energy (E) E h? h c/ ? (h 6.6
x 10-34 J s) E 2.0x10-25/ ? (hc 2.0 x 10-25
J m)
28
Band gap, quantum effects, color
As size decreases, the electrons of the
nanoparticle become confined to a smaller space,
and the band gap increases
29
Calculate particle size based on UV-Vis
spectroscopy - Particle in a Box
CdSe Quantum dots, 1.5 - 2 nm in size
http//www.beilstein-journals.org/bjnano/single/ar
ticleFullText.htm?publicId2190-4286-1-14E1
30
Crystal Structure
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The size and shape of a unit cell is described,
in three dimensions, by the lengths of the three
edges (a, b, and c) and the angles between the
edges (a, ß, and ?). These quantities are
referred to as the lattice parameters of the unit
cell.
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Simple Cubic
Only Po has this structure
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Example Questions
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Characterizing a Crystal
48
Interference in Scattered Waves
X-ray Diffraction in Crystalline Solids
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Diffraction Patterns
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X-Ray powder diffraction patterns
54
Miller Indices - Understanding crystal
orientation
55
http//www.doitpoms.ac.uk/tlplib/miller_indices/pr
intall.php
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Additional Great Resources
www.nano.gov www.mrsec.wisc.edu/nano http//www.te
rrificscience.org/lessonpdfs/PolymerLab06.pdf http
//phet.colorado.edu/en/simulation/photoelectric h
ttp//phet.colorado.edu/en/simulation/semiconducto
r http//phet.colorado.edu/en/simulation/conductiv
ity http//phet.colorado.edu/en/simulation/wave-in
terference
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