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Jorn
Larsen-Basse Effect of Surface on Mechanical Properties of Solids at Various Length Scales The surface of a solid can
affect its mechanical properties in a number of different ways, depending
on material, conditions and length scale. The role of surface notches
and pits as initiation sites for brittle fracture is well known. The
so-called Rebinder effect, which involves surface weakening due to ambient
moisture, has been known for some time for brittle materials as "static
fatigue" and was previously debated as a possible factor in the
deformation of more ductile materials. Current technology in the microelectronics
area brings us into contact with a number of surface effects, which
previously had negligible influence on properties, such as electrostatic
charging and moisture-enhanced stiction. In the same arena, the silicon
wafer polishing technology depends critically on poorly understood combinations
of chemical, mechanical, and thermal effects at very small scale. Finally,
as nanotechnology develops its potential it will be necessary to consider
the role of new surface features and also the fact that the relative
role of surface atoms will escalate, as they become a large fraction
of total atoms present in a cross section. At the same time it also
becomes possible to "engineer" mechanical behavior by suitably
functionalizing the surface layers to interact with the environment
in a designed fashion. Some of the potentials that these new areas open
up will be outlined and some research challenges and opportunities will
be discussed.
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