PhD Thesis Arne Lüker final version V4 - Cranfield University

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Characterisation of Ferroelectric Thin Films
In this geometry the sample is moved through an angle θ whilst the detector is scanned
though an angle 2θ – producing a so-called θ-2θ scan. At values of 2θ for which the
lattice spacing d satisfies the Bragg condition nλ=2dsinθ a peak appears from which d
can be derived. The peak intensity gives a qualitative measure of the preferential
orientation.
In this study a Siemens D5005 diffractometer was used for all the XRD measurements.
The X-ray tube emitted CuKα radiation (λ=1.5406 Å) at 40 kV and 30 mA. In general, θ-
2θ scans were conducted between 20 and 60° in increments of 0.04° with a dwell time of
1 sec per increment. The main peaks in the XRD-spectra of both BST and PST were the
(100), (110) and (111) lattice planes. The latter one was hidden under the strong Pt (111)
peak. By knowing the position of these peaks one could characterise the crystallisation of
the perovskite thin film.
3.2.2 Scanning Electron Microscopy (SEM)
Scanning electron microscopy (SEM) was the primary imaging technique used
throughout this study. Its many benefits include minimal sample preparation
requirements, a wide magnification range and the ability to resolve features below 10 nm.
The system used during the investigation was a Sirion XL30 Schottky Field Emission
Gun (SFEG) SEM. This type of SEM utilises a sharp, tungsten-based tip at which a very
high electric field concentrates (> 10 7 V/m). Under these circumstances electrons can
tunnel through the reduced potential barrier and are then accelerated up to the required
beam voltage. Field emission SEMs have a very high brightness (current density per solid
angle) compared to conventional therionic emitters. This means that they can provide a
high electron density over a smaller spot area, obtaining high resolution (better than 1.5
nm under ideal conditions) at relatively low acceleration voltage (5 kV).
Samples inspected under the SEM were prepared in such a way as to minimise the
effect of charging on the image. Wafers and flat samples were attached to the sample
holder using double sided adhesive conductive carbon tapes. Cross sections were holded
by a metalic spring. For low resolution imaging (< 5,000) an Everhart-Thornley
secondary electron detector was used. Higher resolutions were achieved by setting the