Research Profile - Department of Materials Science and Metallurgy ...

Kevin Knowles
Senior Lecturer
MA University of Cambridge
DPhil University of Oxford
+44 (0) 1223 334312
kmk10@cus.cam.ac.uk
www.msm.cam.ac.uk/kmk10/
Inorganic Microstructures
We focus on the relationship between microstructure and the
mechanical and electronic properties of engineering ceramics.
In addition to mathematical modelling, transmission electron
microscope techniques are routinely used, as well as scanning
electron microscopy, X-ray diffraction, mechanical testing and
electrical characterization.
Anodic bonding
Anodic bonding is one of the most important silicon-packaging
techniques currently used in industry. Work has been undertaken
to understand the complex nature of this process. This has
required an understanding of a wide range of materials science,
ranging from the science of asperity contacts in the presence of
electrostatic fields to the subtleties of electrochemical reactions
and the formation of cation depletion layers at anodic interfaces
in the presence of d.c. electric fields.
Zinc-oxide-based varistor materials
Varistor materials based on the ZnO–V 2
O 5
–MnO system which
can be sintered at 900°C offer the prospect of replacing current
multi-component systems that require higher processing
temperatures. These varistor systems are also of interest in their
own right for basic scientific studies on varistor action because of
their relative chemical simplicity.
van der Waals forces at interfaces in ceramic
materials
Although van der Waals forces are weak at micrometre-scale
particle separations, they become significant at the nanometre
level and are significant contributors to the cohesion and
interfacial energies of engineering ceramics in which nanometrethick
films reside at grain boundaries after high-temperature
processing. The extension of van der Waals theory to interactions
between anisotropic media at the nanoscale is being explored in
the context of novel nanomaterials such as graphene and carbon
nanotubes, as well as highly optically anisotropic ceramics such
as particles of rutile and calcite, and anisotropic biomaterials.
ATJ van Helvoort, KM Knowles, R Holmestad & JA Fernie, “Anodic
oxidation during electrostatic bonding” Philos. Mag. 84, 505–519 (2004).
H Pfeiffer & KM Knowles, “Effects of vanadium and manganese
concentrations on the composition, structure and electrical properties of
ZnO-rich MnO 2
−V 2
O 5
−ZnO varistors” J. Eur. Ceram. Soc. 24, 1199–1203
(2004).
KM Knowles, “Dispersion forces at planar interfaces in anisotropic
ceramics” J. Ceram. Proc. Res. 6, 10–16 (2005).
KM Knowles & ATJ van Helvoort, “Anodic bonding” Int. Mater. Rev. 51,
273–311 (2006).
Transmission-electron micrograph of dendritic nanocrystalline
γ-alumina structures at an anodically bonded Pyrex-Al interface
24 Research Profile