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