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SUMMARY:Nanomechanics of coatings for electronic and optical applications 
 - Steve Bull\, School of Chemical Engineering and Advanced Materials\, New
 castle University
DTSTART:20120301T160000Z
DTEND:20120301T170000Z
UID:TALK34582@talks.cam.ac.uk
CONTACT:Stephen Walley
DESCRIPTION:In most coating applications damage resistance is controlled b
 y the mechanical properties\nof the coating\, interface and substrate. For
  electronic and optical applications the design of coating-\nsubstrate sys
 tems has been predominantly controlled by their functional properties but 
 more recently\nthe mechanical response of the system has been used to enha
 nce functional properties\, as in\nthe case of strained silicon/SiGe micro
 electronic devices where tensile strain has been used to enhance\nmobility
  and increase device speed. As coatings become more complex\, with multila
 yer and\ngraded architectures now in widespread use\, it is very important
  to obtain the mechanical properties\n(such as hardness\, elastic modulus\
 , fracture toughness\, etc.) of individual coating layers for use in\ndesi
 gn calculations and have failure-related design criteria which are valid f
 or such multilayer systems.\nNanoindentation testing is often the only via
 ble approach to assess the damage mechanisms\nand properties of very thin 
 coatings (<1μm) since it can operate at the required scale and provides\n
 fingerprint of the indentation response of the coating/substrate system. F
 inite element analysis of indentation load displacement curves can be used
  to extract materials properties for design\; as coating thicknesses decre
 ases it is observed that the yield strength required to fit the curves inc
 reases and scale-dependent materials properties are essential for design. 
 Similarly the assessment of fracture response of\nvery thin coatings requi
 res modeling of the indentation stress field and how it is modified by pla
 sticity\nduring the indentation cycle. An FE approach using a cohesive zon
 e model has been used to\nassess the locus of failure and demonstrates the
  complexity of adhesive failure around indentations\nfor multilayer coatin
 gs. Finally the mechanical design of a metallization stress sensor based o
 n nanoindentation-derived materials properties\, non-linear elastic and pl
 astic behaviour and the treatment of geometrical non-linearities (stress s
 tiffening) will be discussed.
LOCATION:Mott Seminar Room\, Cavendish Laboratory\, Department of Physics
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