Almost all engineering applications of metals involve their use
in polycrystalline form. Recently the emphasis in the study of mechanical properties
has moved away from the processes which occur inside the individual grains to those
which are governed by the boundaries between the grains. Diverse phenomena such as
high temperature creep, superplasticity, recrystallization, yielding and embrittlement
all depend strongly on effects at grain boundaries. Grain boundaries are also important
for diffusion phenomena as they provide pathways for diffusions into or within a material
that are orders of magnitude faster than through crystalline regions. Interactions of
grain boundaries and defects are also a topic of current research. Recent studies
emphasize the role of grain boundaries for premelting of a crystal. Despite the important
role of grain boundaries in material properties our knowledge at the microscopic level is
limited. The direct observation of grain boundary structure is limited by the lack of
spacial resolution as well as the time resolution of experimental techniques such as high
resolution transmission electron microscopy.
Thus colloidal crystals can serve as a model system to study grain boundary properties and monitor
dynamic processes that occur in the grain boundary region as they are much larger and show a much
slower dynamics which makes them accesible to experimental techniques like confocal microscopy.
Template based crystal growth
In our experiments we use a template that contains the particular grain
boundary of interest to grow the desired crystal structure. A crystal of Silica
colloids with radius of 1.5 µm is allowed to grow on this template in an index matched solution
at a very slow sedimentation speed. The process is is sketched in figure 1.The structure and the general
properties of these grain boundaries can be studied by confocal based video microscopy or
laser diffraction microscopy.
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Figure 1: Template based crystal growth.
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