ELECTRON BACK SCATTER DIFFRACTION.

Electron back scatter diffraction patterns are used to measure the orientations of individual grains and grain boundary misorientations in polycrystals.  Within the group the technique is used widely (i) to characterize overall statistics of grain size and orientation distributions, (ii) to select specific grain boundary types for subsequent micromechanical testing, and (iii) for mapping lattice curvature and strains within individual grains and semiconductor devices.  (strain mapping with CrossCourt2 from BLG Productions)

MICROMECHANICAL TESTING.

We are developing new methods of testing mechanical properties at the micron scale, using a combination of focussed ion beam (FIB) machining to produce bend test specimens.  A nanoindenter is then used to test the specimens.  We are exploring how well elastic, plastic and fracture properties can be extracted from the measured load-displacement data. The methods are being applied to testing individual grains and grain boundaries in polycrystalline metals, and ion-irradiated surface layers.

DISLOCATION BASED ANALYSIS OF CRACK TIP PLASTICITY.

We are developing dynamic and static simulations to understand the mechanics of crack propagation in different materials and loading environments.  We have used dynamic discrete dislocation simulations to study stage I (mode II) fatigue crack propagation thresholds, and brittle fracture of microcracks.  Current work is using dislocation based boundary elements for a static analysis of multiply kinked and branched cracks that are often found in intergranular stress corrosion cracking.

FUNDAMENTALS OF FATIGUE CRACK INITIATION.

A long term interest is in understanding micro-mechanisms of strain localization and crack initiation in metals and alloys under fatigue loading.  We have conducted fundamental studies of dislocation patterning and PSB formation in Cu single crystals using electron channelling contrast imaging. Current interests have moved to engineering materials, specifically Ti alloys in which we are studying effects of microtexture on crack initiation.  This includes fruitful collaborations with Prof Fionn Dunne’s group in Engineering Science.

STRAIN MAPPING IN SEMICONDUCTOR MATERIALS & DEVICES.

Strain is an increasingly important aspect of the design and performance of wide range of semiconductor systems.  We are continuing to improve and apply our electron backscatter diffraction based strain analysis to mapping nanoscale strain distributions in GaN and SiGe systems. Work on GaN includes collaboration with Carol Trager-Cowan at University of Strathclyde.