8
OPTICAL AND VIBRATIONAL
SPECTROSCOPY
8.1. INTRODUCTION
One of the main ways to study and characterize nanoparticles is by the use of
spectroscopic techniques. We begin this chapter with some introductory comments
on the nature of spectroscopy, and then discuss various ways in which it can enhance
our understanding of nanoparticles.
There are several types of spectroscopy. Light or radiation incident on a material
with intensity Io can be transmitted (IT), absorbed (I*), or reflected (IR) by it, as
shown in Fig. 8.1, and these three intensities are related by the conservation of
intensity expression
I, = I, + I, + I R
(8.1)
Ordinarily the incoming or incident light Io is scanned by gradually varying its
frequency v = o / 2 n or wavelength 2, where Av = c, and c = 2.9979 x 10’ - 3 x
10’ m/s is the velocity of light. In a typical case an incident photon or “particle” of
light with the energy E = h 01 ( h = h / 2 n is the reduced Planck’s constant) induces a
transition of an electron from a lower energy state to a higher energy state, and as a
Introduction to Nanotechnology, by Charles P. Poole Jr. and Frank J. Owens
ISBN 0-471-07935-9. Copyright p 2003 John Wiley & Sons, Inc.
194