AFM and PFM Sample Preparation

The ceramic targets were not analysed using atomic force microscopy (AFM) or piezoresponse force microscopy (PFM) in this work therefore the discussion for sample preparation for AFM and PFM will be limited to thin films.

In this work the AFM analysis technique was used to image surface topography. This requires the film be placed flat on the sample stage to avoid a false topography map. To ensure the sample does not move when the

(B + D) + (A + C) A + B + C + D (A + B) + (C + D)

AFM tip touches the sample surface, the film was attached to the sample surface using double sided adhesive tape.

For PFM analysis the thin film was placed onto the sample stage and secured using conductive carbon adhesive tape. A metallic wire connecting the sample to ground is positioned and secured using a small drop of conducting silver glue. The wire supplies the voltage to the sample and the silver glue ensures conductivity around the circuit.

3.3. References

AGILENT TECHNOLOGIES. (2011). AFM – Nanotechnology Measurements

Division User Manual. Santa Clara, USA: Agilent Technologies.

BIRKHOLZ, M. (2006). Thin Film Analysis by X-Ray Scattering. Weinheim: Wiley-VCH.

BRYDSON, R. (2007). Electron Energy-loss Spectroscopy and Energy Dispersive X-Ray Analysis. KIRKLAND, A., J. L. HUTCHINSON, eds.

Nanocharacterisation. Cambridge: Royal Society of Chemistry.

CASTELLANO, R. N., L. G. FEINSTEIN. (1979). Ion-beam deposition of thin films of ferroelectric lead zirconate titanate (PZT). J. Appl. Phys. 50(6), pp.4406-4411

CHRISEY, D. B., G. K. HUBLER. (1994). Pulsed laser deposition of thin

films. Chichester New York: J. Wiley.

CRACIUN, F., P. VERARDI, M. DINESCU, G. GUIDARELLI G. (1999). Reactive pulsed laser deposition of piezoelectric and ferroelectric thin films.

Thin. Solid. Films. 344, pp.90-93

CULLITY, B. D. (2001). Elements of X-Ray Diffraction. 3rd Edition. London: Prentice-Hall International.

FEI COMPANY. (2010). An introduction to electron microscopy [online]. Oregon, USA: FEI. [Accessed 5 June 2011]. Available from: http://www.fei.com/uploadedFiles/Documents/Content/Introduction_to_EM_b ooklet_July_10.pdf

GOODHEW, P. J., J. HUMPHREYS, R. BEANLAND. (2001). Electron

Microscopy and Analysis. 3rdEdition. London: Taylor and Francis.

KELSALL, R. W., I. W. HAMLEY, M. GEOGHEGAN. (2005). Nanoscale

Science & Technology. Chichester: Wiley.

KRUPANIDHI, S. B., N. MAFFEI, M. SAYER, K. ELASSAL. (1983). rf planar magnetron sputtering and characterization of ferroelectric Pb(ZrTi)O3. J.

LORETTO, M. H. (1994). Electron Beam Analysis of Materials. 2nd Edition. London: Chapman and Hall.

OHRING, M. (2002). Materials science of thin films: deposition and structure. 2nd Edition. New York: McGraw.

SURFACE. (2006). Pulsed laser Deposition Excimer Laser Manual -

TuiLaser. Hückelhoven, Germany: Surface.

WILLIAMS, D. B., B. C. CARTER. (1996). Transmission electron microscopy:

Chapter 4

Optimisation of Pulsed Laser Deposition Conditions for

BiFeO

– PbTiO

Thin Films on PtSi Substrates

This chapter begins with a review of literature to date relating to BiFeO3 – PbTiO3 thin films. The reported effect of varying pulsed laser deposition conditions on the films structure and stoichiometry are also described.

The later part of this chapter looks at the effect of varying post anneal temperature on film structure and morphology and describes the optimum pulsed laser deposition conditions for BiFeO3 – PbTiO3 thin films on preferentially orientated Pt/TiOx/SiO2/Si substrates (refer to page 50 for a discussion on substrate types and orientation). X-ray diffraction data was used to analyse the development of crystal structure as the post-anneal temperature was increased.

4.1. Background

In the past decade, ferroelectric research has seen an increased amount of publications relating to thin films due to their potential commercial applications. There are relatively few reports on the structural, electrical or magnetic properties of bismuth ferrite lead titanate (xBiFeO3 - (1-x)PbTiO3) thin films especially for thin films around the morphotropic phase boundary (MPB) (Chen, 2010), (Khan, 2007b), (Gupta, 2009), (Khan, 2008a), (Lui, 2008), (Sakamoto, 2006), (Singh, 2008), (Chen, 2011). The little research carried out on bismuth ferrite lead titanate thin films has centred around compositions lying within or around the MPB produced using a variety of processing techniques including chemical solution deposition, sol-gel synthesis and pulsed laser deposition.

This chapter as well as following chapters reports on two compositions either side of the MPB of xBiFeO3 - (1-x)PbTiO3, x = 0.6 and 0.7, due to the enhanced electrical properties shown in their bulk counterparts.

Singh reported on manganese doped bismuth ferrite lead titanate thin films of compositions around the morphotropic phase boundary, deposited on (111) orientated Pt/TiOx/SiO2/Si substrates, by chemical solution deposition using the spin coating technique (Singh, 2008). Although the room temperature dielectric constant suggested that the films had reasonable insulation resistance, the ferroelectric measurements showed the presence of leaky hysteresis behaviour. Lui reported on the preparation of xBiFeO3- (1-x)PbTiO3 thin films where x = 1 to 0.7 using sol-gel synthesis on LaNiO3/SiO2/Si substrates (Lui, 2008). A rhombohedral to cubic phase transition for x = 0.9 was identified. Remnant polarization of 2Pr= 3.4 µCcm-2

and 4.1 µCcm-2 were reported for films where x = 0.2 and 0.3. Sakamoto reported on manganese doped, bismuth ferrite lead titanate thin films x = 0.5 to 0.9 prepared by chemical solution deposition on Pt/TiOx/SiO2/Si substrates (Sakamoto, 2006). Good surface morphology was observed and all the films showed weak ferromagnetism at room temperature. For films of composition 0.7Bi(Fe0.95Mn0.05)O3 – 0.3PbTiO3 ferroelectric polarization electric field (P-E) hysteresis loops were observed, although some leakage components were included at room temperature. The electric resistivity of the

films was improved in the low temperature region and the remnant polarisation and coercive field of the films at -190 C were approximately 50 µCcm-2and 150 kVcm-2.

A significant improvement in the electrical properties of xBiFeO3 - (1- x)PbTiO3 thin film was reported by Khan (Khan, 2007b) with the use of pulsed laser deposition (PLD) as the processing technique. Although measurements were carried out at -10°C to reduce the leakage current Khan reported good electrical properties with fully saturated hysteresis loops. The remnant polarisations 2Pr up to 100 µCcm−2 at a field amplitude of 820

kVcm−1 and switchable polarisation up to 80 µCcm−2 at 375 kVcm-1 for the 0.6BiFeO3- 0.4PbTiO3composition were reported.

Recently doping has been used in attempt to reduce the leakage current of bismuth ferrite lead titanate thin films and achieve fully saturate hysteresis loops. Chen (Chen, 2010) (Chen, 2011) reported on thin films deposited by pulsed laser deposition of 0.72Bi(Fe1-xTix)O3-0.28PbTiO3 (x = 0 and 0.02) on Pt/TiOx/SiO2/Si substrates. By B-site ionic substation of the Ti4+ for Fe3+ the ferroelectric and dielectric properties of the films were reported to be improved from that of the undoped composition. In both the doped and undoped films the preferential orientation was along the (001) tetragonal. Although P-E ferroelectric hysteresis loops were not completely saturated a large remnant polarization of 80 µCcm-2 was obtained in the doped films at room temperature.