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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