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7/30/2019 Electronic Structure of Materials- Nanotechnology-can
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Electronic Structure of MaterialsElectronic Structure of Materials
Teerakiat Kerdcharoen
Capability Building Center for
Nanoscience & Nanotechnology
Faculty of Science
Mahidol University
http://nanotech.sc.mahidol.ac.th
Objectives of this Lecture
New tools that help scientists understand materials at the
bottom
To understand how electronic structure determine atomic
structure (nanoscopic structure) and finally macroscopicproperties of materials
How materials function from the nanoscale point of view
Basic of nanotechnology
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State of Matter/Materials
Solid
Liquid Gas
Plasma
Many materials have unclear boundary
between each state, and may have somephases in between.
Examples:
Polymers have transition between plastic
and glass phases
State of Matter/Materials
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Understanding Scale
Structure of Materials
Macroscopic structure
- shape, roughness, hardness, flexibility, strength etc.
(process engineering and manufacturing)
Mesoscopic structure
- morphology, grain or particle size, phase
(materials engineering)
Nanoscopic (~Microscopic) structure
- molecular geometry, electronic structure
(nanotechnology)
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Structure Characterization
Macroscopic structure
- Mechanical properties (hardness, strength etc)
Mesoscopic structure- SEM, TEM, Optical microscope, XRD
Nanoscopic structure
- STM, AFM, SNOM, X-Ray Crystallography
Mesoscopic Structure
Morphology of the surface
(grain, domain, phase)
Pictures from R. W. Siegel Rensselaer Polytechnic Institute (left and middle)
Picture from NASA Ames Lab (right)
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Nanoscopic Structure
Atomic resolution
Pictures from NASA Ames Lab
Nanoscopic Structure
Atomic resolution
Pictures from NASA Ames Lab (left), Nature magazine (right)
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How small is nanometer ?
1 nm= 1/1,000,000,000 meter
1.74 meter
millimeter
micrometer
nanometer
Electronic structure
Chemical force
Geometry of molecule,nanostructure
Electronic properties
Thermodynamic
properties
Mechanical properties
Electronic Structure
Materials Properties
Why Study Electronic Structure
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Atomic Orbital
Home of electron = orbital
Probability defines shape & size of orbital
Pictures from http://www.chemguide.co.uk/
1s
2s
2p
Chemical Bonding
A bond is the force that connect 2 atoms together
H-F (hydrogen fluoride)
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Molecular Orbital
Example: The case of Hydrogen Fluoride (H-F)
Molecular orbitals are homes ofelectrons in a molecule.
Molecular OrbitalExample: The case of Hydrogen Fluoride (H-F)
Electrons condense into some regionmaking chemical bond
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Molecular OrbitalExample: The case of Hydrogen Fluoride (H-F)
Some homes span only over a limited
space or only on one atom. The
electrons in such orbitals are localized.
Theory of Electronic Structure
Electron is represented by wave function
Electron density is the probability to find
electron at a location
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Theory of Electronic Structure
To find the wave function and other properties,
one must solve the Schroedinger equation
1-D
3-D
Electrons in Metal
The model:
Electron gas (particle in a box)
Each atom donates one electron and the free electrons
can go wherever they want
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Energy is discrete (Quantum State)
Fermi Level
When we fill up the
states by electrons
the most top level is
called Fermi level.
Filled states
Empty states
Fermi level
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Band Theory
Band Theory
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Band Theory
Electronic Structure Calculation
Electrons are described by wave function.
To know the properties of these electrons,
we probe the wave function withappropriate operator.
Hamiltonian Operator
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QM: Born-Oppenheimer Approximation
Electron is 1800 times lighter than protron/neutron
Wavefunction can be expanded by a set of functions.
Slater determinant preserves antisymmetry principle andintroduces orthonormality of the wavefunction.
Total wavefunction is a product of one-electron wavefunctions
(molecular orbitals).
Hartree Approximation
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Molecular Orbital is a linear combination of Atomic Orbitals.
Molecular Orbital
Atomic Orbital
Atomic Orbital is based on radial function and spherical harmonic.
Nowadays, atomic orbital is usually based on Gaussian Type Orbitals.
Construction of MO
Quality of atomic orbitals can be controlled by mathematical functions
STO-3G
3-21G
6-31G*6-31G**
Construction of AO
Examples: H-F
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How accurate is the calculation
Chem. Phys. Lett. 321 (2000) pp. 78-82
DFT Calculation
STM Experiment
Frontier States
LUMO
(Lowest Unoccupied)
HOMO
(Highest Occupied)
The frontier states involve in electronics and
optoelectronics.
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Luminescence
When electron steps down from higher energy level to
Lower energy level, it release photon.
1) Transition due to defect
2) Interband transition
3) Intraband transition
Chemical structure from electronic structure
Molecule as we know, is a soup of electrons and nuclei.Bonding is only interpretation or explanation of this soup.
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Molecular Mechanics (MM)
- depend strongly on concepts of bonding
- neglect the electronic degrees of freedom
- follows the Newtonian laws
Molecular Mechanics consider a
molecule as system of rigid ballsconnected via springs
MM: Energy Terms
Energy of a system is a sum of all interactions
within and between the springs
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MM: Valence Terms
Valence term is the relative energy of a
spring.
MM: Valence Term
Valence terms are interactions within the springs.
A spring wants to relax to its original shape.
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MM: Valence Terms
Picture from: Peter J. Steinbach, Introduction to Macromolecular Simulation.
MM: Cross Terms
Cross term is due to coupling between 2
springs. It is a correction to independent
spring model.
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MM: Cross Terms
Cross terms are interactions between 2 or more springs.
Cross terms are corrections to the independent spring model.
MM: Non-Bond Terms
Non-Bonded term is interaction betweentwo balls.
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MM: Non-Bond Terms
Non-bond terms are interactions between the balls.
Non-bond terms are long-range interactions.
Repulsion
Attraction
RepulsionRepulsionRepulsion
Attraction
0.8 1.0 1.2 1.4 1.6 1.8 2.0
-3
0
3
V(r)
r, nm
MM: Non-Bond Terms
Non-bond terms are interactions between the balls.
Non-bond terms are long-range interactions.
Attraction
Repulsion
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MM: Sum of Energy
E = Stretching(C-H1)+Stretching(C-H2)+...
+ Bend(H1-C-H2) + Bend (H1-C-H3) +
+ Bend(H1-C-C) + + Bend (C-C=O) + .
+ Torsion (H1-C-C=O) + ... +
+ Torsion (O1=C-O2-H4)
+ vdW(H1-H4) +
+ Elec (H1-H4) +
We can design nanoscale devices
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We can model the machinery
We can simulate nanoscale phenomena
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Introductionto
Nanotechnology
Capability to manipulate, control,
assemble,produce andmanufacture
things at atomic precision
What is Nanotechnology ?
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Nobel Prize in Physics, 1965
The principles of physics, as far as I can see, do
not speak against the possibility of maneuveringthings atom by atom. It is not an attempt to
violate any laws; it is something, in principle,
that can be done; but in practice, it has not been
done because we are too big
The problems of chemistry and biology
can be greatly helped if our ability to
see what we are doing, and to do things
on an atomic level, is ultimately
developed---a development which Ithink cannot be avoided.
There is plenty of room at the bottom
-- Special Lecture in 1959 --
Richard Feynman
1800-1900: 1stIndustrial Revolution
Automation Age
1900-1950: Quantum Revolution
Atomic Age
1950-2000: IT Revolution
Electronic Age
2000-2050: Biotech Revolution
Genomic Age
2050-2100: 2ndIndustrial Revolution
Nano Age
Nanotechnology is the Future ?
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The Law of S-Curve
Nanotechnology in Nature
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Moores Law
CPU is doubled in performance every 18 months
The feature size for device in a semiconductor chip is decreasing
by a factor of 2 every one and a half year
The number of transistors the industry would be able to place on
a computer chip would double every 1.5 years
Gordon Moore
Co-Founder of Intel Corp.
Cost of constructing a new Fabs will double every
3 years
Moores Curve
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Nanocomputer
Mechanical Nanocomputer
Electronic Nanocomputer
Chemical / Biochemical Nanocomputer
Quantum Computer
The first mechanical computer was designed by Charles Babbage
(Cambridge University) in 1837 called Difference Engine No. 1
K. Eric Drexler proposed a design of mechanical nanocomputer
based on rods and gears made of molecules in 1988.
Pictures from Acc. Chem. Res. 34 (2001) 445.
Mechanical Nanocomputer
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Electronic Nanocomputer
Continue a miniaturization of current electronic computer
Elementary components are based on soft materials, i.e. organic
molecules, semiconducting polymers or carbon nanotubes, instead ofinorganic solid-state materials
Use only 1 or few electrons instead of billion electrons
Use self assembly or other patterning techniques instead of
photolithography
Chemical Nanocomputer
Computing is based on chemical reactions (bond breaking and
forming)
Inputs are encoded in the molecular structure of the reactants and
outputs can be extracted from the structure of the products
Adleman proposed DNA computing in 1994 for solving
Hamiltons path problem
Picture from http://www.englib.cornell.edu/scitech/w96/DNA.html
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Quantum Computer
Based on proposals by Bennett, Deutsch and Feynman in 1980s
Use quantum bit (qubit) from the physical properties of materials,
i.e. spin state, polarization.
Parallelism in Nature
Hybrid System
Integration between Silicon and Carbon systems
Life and Non-Life Integration
Mechanical, Electronic, Chemical and Quantum Integration
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Aviram & Ratners Molecular Diode
1974 : Aviran & Ratner proposed a model of molecular rectifier
Discovery of Conductive Polymers
1977 : Shirakawa and MacDiarmid (Nobel Prize 2000) accidentally
found that doped conjugated polymers can conduct electricity
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Discovery of OLED
1987 : Kodaks scientist developed organic light emitting diode
(OLED)
Picture from Kodak and from
Richard Friends group
Single Molecules Conduction
1996 : Tour and Weiss demonstrated electrical conduction in
molecular wire
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Discovery of Molecular Diode
1997 : Metzger discovered first D-pi-A molecular rectifier
Organic IC
1998 : de Leeuw succeed to fabricate organic IC made of 326 all-
polymer transistors
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Single-Molecule Switch
1999 : Tour and Reed demonstrate negative differential resistance
behavior in molecule
Picture from Mark Reed
Invention of Dip-Pen Nanolithography
2000 : Mirkin invented Dip-Pen Nanolithography
Picture from Mirkins Group
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Scanning Probe Microscope
Scanning Probe Microscope