This package will take techniques previously used to measure strain at the nanoscale in silicon and apply them to piezo electric materials. Whilst some of the other work packages look at device characteristics or characterising strain on a larger scale, this work package is exclusively about measuring strain at the nanoscale. To do this it will use destructive methods such as Transmission Electron Microscopy (TEM), novel holographic TEM and Scanning Electron Microscopy (SEM) to measure the electric field created by strain in piezo electric materials and compare them to predictive modelling. In order to understand why devices are working, or why they are not, you need to be able to measure the strain, as this is what is going to determine the piezoelectric affect. In order to compare different samples and different devices, we need to do this in an accurately replicable and reliable manner. TEM is a microscopy technique in which a beam of electrons is transmitted through an ultra-thin sample, interacting with the specimen as it passes through whilst SEM produces images of a sample by scanning it with a focused beam of electrons to measure the electric field at the surface of a material. These techniques were used to characterize for strain in silicon resistors in 2003-2004. Piezo electric materials, however, are more complex than silicon and therefore may be more difficult to measure. The novel holographic TEM method was invented by Nanostrain partner, Dr. Martin Hÿtch, to measure strain in 2007. This technique is ideally suited for these materials as it provides a map of the strain, showing how it varies across the sample rather than just measuring it in one place. This technique is highly accurate and also means that we can use samples that are thicker than some other techniques used for this purpose. Each of these methods, however, presents its own challenges. With TEM, specimens need to be made extremely thin- up to 500nm thick -as electrons would otherwise be absorbed into the sample. In cutting out the sample slices, it is possible to introduce damage that will change the strain. SEM also has particular specimen preparation issues. As part of this package, researchers will be looking to define a procedure to prepare the samples so that we can carry out the measurements in an exact and replicable way. TEM is also a destructive technique, meaning that samples must be destroyed in order to be measured. By completing experiments in situ, researchers will be able to observe this response under the microscope. CNRS is leading this package and will be working predominantly on the holographic measurement and the complimentary TEM measurements. BAM will lead the work on specimen preparation and NPL will compare measurements with what we might expect with modelling. NPL and PTB will also work on in situ SEM. For more information on Work Package 3, please contact Martin Hytch at: martin.hytch@cemes.fr
