Transcript Tutorial_Dalton_Intro

Workshop on the Chemistry of
Information Technology
Welcome!
Acknowledgements
The American Chemical Society Petroleum Research
Fund Type H Grant Program
The National Science Foundation
Science and Technology Center Program
The many faculty and staff who contributed so
generously of their time
Information Technology: An Introduction
•One of the three largest and the fastest growing component
of world economy.
•In addition to computing and communication (all forms),
sensing is becoming an important component of information
technology (e.g., the smart electric grid, embedded network
sensing, homeland security, transportation, defense, medicine,
etc.).
•Nanotechnology and information technology (and their
integration) are being actively promoted in numerous Federal
agencies (NSF, DoE, DoD, NIST, NASA, NIH, etc.). Federal
initiatives could help make IT the career of the future.
•Excellent for illustrating basic scientific concepts.
Information Technology: A Chemical Science!
•Information Technology (IT) depends on the movement and
manipulation of electrons and photons.
•These are the critical particles of the chemical world in
which we live. Chemistry can be considered the science of
understanding electron distributions and how those
distributions evolve under different influences.
•It should be clear from this workshop that concepts of
optical polarization, electrical conductivity, and chemical
reactivity are inter-related—They all involve electron
movement under the influence of some electrical potential.
Electrons and Photons and Their Interaction
•In Freshman Chemistry, we largely focused on the interaction
of electrons and photons involving absorption and emission.
Here our focus will be broader. We will be interested in index of
refraction (real part of optical susceptibility) as well as
absorption/emission (imaginary part) phenomena.
•Also, we can’t neglect protons (or neutrons—mass will be
important). All electrical potentials must be considered to
understand observed phenomena and to design new materials
and experiments to demonstrate and exploit new phenomena.
•It is our hope in this workshop to provide you with a
knowledge base to understand the materials and devices of
information technology and hopefully to design new ones.
Electrons and Electrical Potentials
•Electrons and protons are, of course, charged particles and will
experience electrostatic interactions. Light (from visible to
radiofrequency) is electromagnetic radiation and the electric field
component of light will interact with charged particles.
•For absorption of light to occur (causing excitation of electrons
from one allowed energy level to a higher level) two conditions
must be satisfied: (1) hn = DE (the light quanta must match the
energy difference between the levels) and (2) the transition matrix
must be finite (this is essentially a symmetry requirement).
•Light interacting with matter will always produce a polarization
effect (i.e., perturb ground state electron distribution).
The Simplest Potential: Single ElectronProton Interaction
More Appropriate Picture
Polarizability: A Microscopic View
F = qE
(1)
+
t0
t1
+
t2
Induced Polarization
CHARGE
DISTRIBUTION
INDUCED
POLARIZATION
Polarization = µ =  
Electric Field
(2)
Applying an Electric Field to the
Hydrogen Atom
Magnitude of the Effect Will Depend on
Orbital Type
Charge Transfer Type p-Electron
Molecules
N
S
O
N
N
N
O
N
O
N+
O-
N
O
N
Resonance Structures
H
H
H
H
H
C
H
N
C
C
C
C
C
O
H
C
H
H
H
H
H
H
H
H
H
C
H
N
C
C
C
C
H
C
H
H
H
H
C
O
An Example
Another Example
Voltage-Control of Index of Refraction
•The application of an electric field will change the charge
distribution of a material. The charge distribution defines the
velocity of light in a material through the interaction of that
charge distribution with the electric field component of light.
•The index of refraction is just the ratio of the speed of light in
a vacuum to the speed of light in a material. Thus, it is possible
to vary the index of refraction of a material by applying an
electric field (dc to optical frequencies).
•In the following slide, we provide a practical application of this
phenomena: Electrical-to-optical signal transduction (as in
loading a computer signal onto the Internet). Note in this
application, the voltage must be capable of producing a phase
shift of p in the propagated light.
An Application: Electrical to Optical Signal
Transduction
Polarization, Charge Separation, and
Charge Transport
•In the previous examples, polarization could be seen to
depend on the competition of intramolecular electrostatic
interaction with the applied electric field in determining
electron distributions. Of course, intermolecular electrostatic
interactions must also be considered.
•If intermolecular orbital interactions are strong, then charge
separation and transport can occur. Indeed, if orbitals (such
as p-orbitals) are equally and closely space a conduction band
can exist facilitating electron transport (electrical conductivity)
throughout the material. This is common with metals.
Organic materials then to be more heterogeneous so that
electrical conductivity is defined by variable range hopping
(thus, involves an activation barrier).
Treatment at Different Levels of
Sophistication
•In this workshop, you will experience the fundamental
phenomena of polarization, charge separation, and charge
transport treated at many different levels of sophistication.
•You have just experienced the most basic treatment which
has hopefully provided you with some physical intuition and
has alerted you to the importance of considering all relevant
potential functions to understand specific phenomena. The
following lectures will provide you with the quantitative tools
for understanding the phenomena relevant to information
technology, particulary, to IT involving organic materials.
•Professor Bernard Kippelen will start by providing a
mathematic basis to critical phenomena in photonics.