electronic structure of materials- nanotechnology-can

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

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