Workshop on the Chemistry of Information Technology

Welcome!

AcknowledgementsThe American Chemical Society Petroleum Research

Fund Type H Grant Program

The National Science FoundationScience 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) h = E (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 Electron-Proton Interaction

More Appropriate Picture

+-

+

-t1t0 t2

CHARGEDISTRIBUTION

INDUCEDPOLARIZATION

F = qE (1)

Ind

uce

d P

ola

riza

tio

n

Electric Field

Polarization = µ = (2)

Polarizability: A Microscopic View

Applying an Electric Field to the Hydrogen Atom

Magnitude of the Effect Will Depend on

Orbital Type

NS

O

N

N

N

O

N

N

O N+

O-

O

N

Charge Transfer Type -Electron Molecules

NC

CC

C

C

C

CO

H

H

H

H

H

H

HH

H

H

H

NC

CC

C

C

C

CO

H

H

H

H

H

H

HH

H

H

H

Resonance Structures

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 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 -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.