Page 37 - Engineered Interfaces in Fiber Reinforced Composites

20 Engineered interfaces in Jiber reinforced composites

Table 2.4 (Contd.)

Technique Atomic process and type of information
Spectroscopy
Auger electron The sample surface is bombarded with an incident high energy electron
spectroscopy (AES) beam, and the action of this beam produces electron changes in the target
atoms; the net result is the ejection of Auger electrons, which are the
characteristics of the element. Because of the small depth and small spot
size of analysis, this process is most often used for chemical analysis of
microscopic surface features.
X-ray photoelectron When a sample maintained in a high vacuum is irradiated with soft X-rays,
spectroscopy (XPS) photoionization occurs, and the kinetic energy of the ejected
photoelectrons is measured. Output data and information related to the
number of electrons that are detected as a function of energy are generated.
Interaction of the soft X-ray photon with sample surface results in ionization
from the core and valence electron energy levels of the surface elements.
Secondary ion mass The sample surface is bombarded with a beam of around 1 keV ions of
spectroscopy (SIMS) some gas such as argon and neon. The action of the beam sputters atoms
from the surface in the form of secondary ions, which are detected and
analyzed to produce a characterization of the elemental nature of the
surface. The depth of the analysis is usually less than a nanometer, making
this process the most suitable for analyzing extremely thin films.
Ion scattering spectroscopy In ISS, like in SIMS, gas ions such as helium or neon are bombarded on
(ISS) the sample surface at a fixed angle of incident. The ISS spectrum normally
consists of a single peak of backscattered inelastic ion intensity at an energy loss
that is characteristic of the mass of surface atom. From the pattern of scattered
ion yield versus the primary ion energy, information about elements present on
the sample surface can be obtained at ppm level.
Infrared (IR) and Fourier The absorption versus frequency characteristics are obtained when a beam
transform infrared (FTIR) of IR radiation is transmitted through a specimen. The absorption or
spectroscopy emission of radiation is related to changes in the energy states of the
material interacting with the radiation. In the IR region (between 800 nm
and 250 pm in wavelength), absorption causes changes in rotational or
vibrational energy states. The components or groups of atoms that absorb
in the IR at specific frequencies are determined, providing information
about the molecular structure. The FTIR technique employs a moving
mirror to produce an optical transformation of the IR signal, with the
beam intensity after the interferometer becoming sinusoidal. FTIR has been
extensively used for the study of adsorption on polymer surfaces, chemical
modification and irradiation of polymers on the fibersurfaces.
Raman spectroscopy (RS) The collision between a photon of energy and a molecule results in two
different types of light scattering: the first is Rnyleigh scattcring and the
second is Raman scattering. The Raman effect is an inelastic collision
where the photon gains energy from or loses energy to the molecule that
corresponds to the vibrational energy of the molecule. Surface-enhanced
Raman spectroscopy has been successfully used to obtain information
about adsorption of polymers onto metal surfaces, polymer-polymer
interaction and interdiffusion, surface segregation, stress transfer at the
fiber-matrix interface, and surface structure of materials.