Introduction to Materials - Sample Preparation Topic for Transmission Electron Microscopy - page 5

irreversibly. The challenge in developing new materials is to master all of the param-
eters of this system in order to reproduce the properties or functions needed for a
specific application. In biology, the goal is to know all of the parameters of the living
matter.
Diverse materials result from the natural evolution of a rock, mineral, organic
material, or biological material or from the synthetic process for man-made mate-
rials. In addition, the mechanisms of growth or formation are different depending
on whether materials are found in the solid state or liquid state or in intermediary
solid-liquid states. Depending on the conditions of temperature, pressure, chemi-
cal gradient, kinetics of diffusion (atomic, ionic, or molecular diffusion), and the
dynamics of the system, microstructures can be very diverse in materials science
and biology.
A material's microstructure contains its structural organization on different
scales. It also contains data on the chemical and structural phase distribution, the
nature and concentration of defects formed, and the type of chemical bonds present
in the material. All of these structures give a particular material its properties
and functions. To understand their relationships, certain scales of observation are
pertinent.
A given material type will be used for a particular function.
The interesting properties of a material are those that correspond to the physical
and structural characteristics of the material or blend of materials.
Metals are used for their electrical conduction and their individual mechanical
properties. Semiconductors are mainly used for applications in electronics due to
their electronic structure. Ceramics, because of their very high fusion points, low
density, the nature of covalent and/or ionic chemical bonds, and mechanical prop-
erties, will have a widely varying range of applications, from the manufacture of
aerospace materials to electronic components. Ceramics are also often combined
with other materials. Polymers are used in a large number of different fields from
industrial materials to biomaterials.
In physics, interest will lie in “systems in equilibrium” when analyzing atomic
structures. Indeed, in order to be sure of the material structure, it must be stable; in
other words, it must have reached its state of equilibrium. Minerals are an obvious
example. One may also need to study the dynamics of the system, which can be
done artificially before observation or in situ in the microscope (see Chapter 4).
Nevertheless, among the newer materials, multilayered nanostructured materials are
far from being in thermodynamic equilibrium in their applied state.
Multilayer materials are composed of layers of different types of materials and
have a 2D geometry that gives them very special properties tied to the proximity
of the interfaces between the layers. Physical properties such as superconductiv-
ity, giant magnetoresistance, and ferromagnetism all correspond to the interaction
mechanisms at the atomic scale. These mechanisms are associated with charge
transfer mechanisms, magnetic induction, and electron spin exchange, and there-
fore deal with electronic structure. These materials have particular properties, often
corresponding to different oxides that have variable oxygen concentrations or atoms
that may have multiple charges. The combination of different types of materials
having different structures and chemistry, as well as the proximity of interfaces,