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Methods for Structural and Chemical Characterization of Nanomaterials 107

■ No interaction occurs and the light is transmitted through the mate-
S
rial with its initial characteristics ( k 0 , v 0 ).
■ The wave vector is affected, but there is no change in frequency. The inci-
dent beam is dispersed over a range of “angles” via elastic scattering/
diffraction processes. Modification of the wave vector is related to the
spatial aspects of the matter (crystal structure, size, shape). These are
the classical diffractions (X-ray diffraction [XRD], electron and neutron
diffraction) and scattering techniques (small angle x-ray scattering
[SAXS], light scattering, neutron scattering).
■ The frequency of light is affected by internal excitation processes
(electronic, nuclear, etc., transitions) that lead to absorption of the inci-
. Examples of techniques that measure
dent beam at the frequency v 0
changes in the frequency of light are the absorption spectroscopy tech-
niques such as X-ray absorption spectroscopy (XAS), Raman, Fourier
transform infrared spectroscopy (FTIR), and nuclear magnetic reso-
nance (NMR) imaging. The absorption of the incident beam, depend-
ing on the nature and structure of the sample matter, can also be
used in microscopy by analyzing the absorption contrast as is done in
electronic, light, and X-ray microscopy.
■ The excited matter can relax through several processes causing the
emission of fluorescent photons (X-ray and light) or electrons (auger
and secondary electrons) having different frequencies. Examples of char-
acterization techniques utilizing these measurement principles are X-ray
fluorescence spectroscopy (XRF), luminescence spectroscopy, energy loss
spectroscopy (ELS), and X-ray photoelectron spectroscopy (XPS).
In contrast with methods that rely on the interaction of materials with
electromagnetic radiation, two techniques that were developed in the
1980s, atomic force microscopy (AFM) and scanning tunneling
microscopy (STM), take an entirely different approach in which a probe
“feels” its way along a surface at a resolution that may approach the
atomic scale. AFM and STM are advanced microscopy techniques devel-
oped to measure surface topography with angstrom level resolution. In
both cases the operating principle consists of scanning a probe in close
proximity to the surface. The location between the probe and the surface
is determined by the change in cantilever deflection and tunnel current
in AFM and STM, respectively.

Structural Characterization
In the following parts we will detail different techniques enabling the
characterization of the structure from the atomic scale to the size and
shape of the nanoparticles.