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Lecture 2
01/03/2010
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Definition of Nanotechnology
Comprised of “nanostructures” or “nanomaterials” that possess at least one dimension that measures approximately less than 100nm AND exhibit novel properties.
The art and science of building stuff that doesstuff at the nanometer scale.
R. Smalley, Rice University
Nobel Prize Winner
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The Big Picture of the Nanotechnology Story
Synthesis of Nanostructures
Explore the Properties
Characterization TestingExplore/speculate
Applications
New processing techniques• Controlled structure, size…• Reduce cost
New Characterization and Testing techniques• Better resolution….
New applications!!!!!!
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TOP-DOWN AND BOTTOM-UP FABRICATION
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TOP-DOWN FABRICATION• Start with a large piece of material• Remove sections of material to “carve” a specific
pattern or shape• Has been used for centuries
to manufacture artwork, tools and devices
Mountain Rushmore was carved out of stone using a “top-down” process
These silicon wafers are patterned and etched to form micro/nanoscalefeatures that together form transistors and other microelectronics components on a computer microchip
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BOTTOM-UP FABRICATION• Start with catalyst particles and/or
a substrate• Expose to a gas or liquid• Reaction leads to the growth of a
solid nanostructure or nanoscaleself-assembled layer
• Properties such as temperature, pressure, surface quality, composition, catalyst size, etc. influence growth characteristics
An example of how a silicon nanowire might be grown:
(1) Silicon rich gas flows across a substrate on which a gold nanoparticle lies;
(2) Reaction between the gold and silicon gas leads to the precipitation of solid silicon; nanowire growth continues until conditions change (i.e. the gas flow is turned off)
Most natural processes such as tree growth are “bottom-up”methods
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Outline• Introduction – Nanotechnology – definition, application areas…• The Element Carbon – Structure, Chemistry….• Fullerenes: Structure, Physics and Chemistry.
– Article Discussion – Kroto• Carbon Nanotubes: Structure, Synthesis and Properties.
– Article Discussion – Iijima• Carbon Nanotubes: Applications.
– Article Discussion – Wong• Graphene – a new generation of materials.
– Article Discussion – Novoselov
Testing and Characterization on Nanoscale• Part 1. Electron microscopy (SEM, TEM)• Part 2. Raman microspectroscopy….
– Article Discussion – Rao• Part 3. Atomic Force Microscopy (AFM)• Part 4. Nanoindentation• Part 5. Study of properties (optical, electrical)
Introduction to MEMs 39(Modified from Sidney Harris Science Cartoons)
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Commercialization of Nanotechnology: Why Carbon ?
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The Element Carbon –Structure, Chemistry, Phase Diagrams
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Structure of an Atom
Periodic Table of Elements
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Electronic Structure of the Carbon Atom
in the ground state
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Schematic Representation of the “s” and “p” Orbitals
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Cloud Representation of a sp3 Hybrid Orbital
47http://wine1.sb.fsu.edu/chm1045/notes/Geometry/Hybrid/Geom05.htm
sp3 Hybridization of Carbon
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Covalent Bonding of sp3 Hybrid Orbitals
http://www.cem.msu.edu/~reusch/VirtualText/intro3.htm
sp3 orbital σ bond
49Shaded regions are regions of high electron probabilities where covalent bonding occurs.
Three-dimensional Representation of sp3 Covalent Bonding (Diamond Structure)
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sp2 orbitals
p-orbitals
sp2 Hybridization of Carbon
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Covalent Bonding of sp2 Hybrid Orbitals
1 π bond1 σ bond
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Three-dimensional Schematic of the Graphite Structure
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sp Hybridization of Carbon
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Covalent Bonding of sp Hybrid Orbitals
2 π bonds1 σ bond
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Sigma (σ) bond -> Head-on overlap
Pi (π) bond -> Sideway overlap
Type of bonding
Hybrid type No. of sigma bonds
No. of pi bonds
C-C sp3 1 0
C=C sp2 1 1
C≡C sp 1 2
Summary of Three Types of Bonding
ππ
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Carbon-Couples Bond Energies and Lengths
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Ternary “Phase” Diagram of Carbon Allotropes
Graphene
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Carbon Phase Diagram
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Schematic illustrating the change in the position of the triple point as a function of particle size.
As shown the nanodiamond phase is the most stable phase at ambient conditions.
3-D Phase Diagram for Carbon
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diamond
graphite
Comparison of the cluster size dependence of the heat of formation DHf(sp3) and DHf(sp2). The fits to the sp3 (open circles) and sp2 (crosses) data are given by the dashed and solid lines, respectively 61
Schematic representation of the most stable carbon phase depending on the size of the carbon
structure
rings
fullerenes
nanodiamond
nanographitegraphite
System size, # of atoms
Cohesive energy
~30 ~1100 ~25,000
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Carbon Nanomaterials: Ternary Bonding Diagram
Nanodiamond
Nanotubes
Fullerenes
Hydrocarbons
spn
Corannulene
CumuleneAdamantane
Carbyne (sp1)Diamond (sp3)
Graphene (sp2)
Adapted from M. Inagaki, New Carbons, 2000Heimann et al., Carbon, 1997
sp3+sp2+spamorphous carbon,DLC, glassy carbon,
carbon black, etc.
sp3+sp2+spamorphous carbon,DLC, glassy carbon,
carbon black, etc.
spn, (1<n<3, n=2)
Classification based on:-hybridization type of C atoms -characteristic size of clusters
Classification based on:-hybridization type of C atoms -characteristic size of clusters
Fullerene family
sp2 + π
Csp + 2πsp3
=C=C=
Nanosizedmorphology of graphite-based
materials
Ovalene
Carbo
n whi
sker
s,
cone
s and
polyh
edra
l
crys
tals
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Graphene is a 2D building material for carbon materials of all other dimensionalities. It can be wrapped up into 0D buckyballs, rolled into 1D nanotubes or stacked into 3D graphite.
Geim et al., The rise of grapheme, Nature 2007
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Range of geometrical characteristics of selected carbon entities and their simplest assemblies observed at the nano-scale.
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Paper Reviewhttp://ece480.cankaya.edu.tr/ ----- under “ASSIGNMENTS”
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Grading
• Attendance: 10%• Homework: 20%• Class Participat.: 10%• Midterm: 20%• Ppt/Poster: 20%• Final: 20%
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Writing 1 PAGE report• Use “Word”• Your name• Put tittle: Review of …..• Write it ALONE - BY YOURSELF!
• What is new and novel?• Summary
– Aim of the study, objectives…– Techniques used: for production, characterization…– Results
• Pros and Cons (Artilar ve Eksiler)– Do the results (of the experiments) justify the hypothesis/theory– Strong and weak points
• Suggestions or other comments• References
• Hard and soft copies needed• Bring it to class
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