Thickness scaling of ferroelastic domains in PbTiO3 films on DyScO3

Abstract

We report on the thickness dependence of the ferroelastic domains of PbTiO 3 films grown on (110)-DyScO 3 with low thicknesses (up to 240 nm), which fall outside the validity range of the square root law proposed by Roytburd. For slow-grown films, the data reveal the linear thickness dependence predicted by Pertsev and Zembilgotov, using a complete elastic description, while a 2/3 scaling exponent is found for fast-grown films. Extremely long domains running all through the samples have been observed in the latter case, compared to the short domains observed in slow-grown films. These differences are ascribed to the in-plane anisotropy for domain wall nucleation, which is likely caused by the anisotropic elastic modulus of the substrate. V C 2013 AIP Publishing LLC.[http://dx.doi.org/10.1063/1.4823536]The response of domains and domain walls crucially affects (and often determines) the dielectric properties and switching behavior of ferroelectrics. This is particularly important in thin films where the ferroelectric (180 ) and ferroelastic (non-180 ) domain walls are formed in order to comply with the stringent electrical (large depolarizing field) and mechanical (substrate mismatch strain and clamping) boundary conditions.The size of the domains increases with increasing film thickness as a result of the balance between the depolarizing field energy (for 180 domains) 1 or elastic strain energy (for non-180 domains) 2 and the domain wall formation energy. Thus, the thinner the films, the larger the domain wall density and the greater the influence of the walls on the ferroelectric properties. Moreover, domain walls break spatial symmetry and could add functionalities to the films when present in large amounts. 3 It is therefore most relevant to have good control of the domain formation and the density of domain walls. 4 Domain formation in ferroelectrics has been largely studied. 2,3,[5][6][7][8][9][10][11][12][13][14][15] In order to adapt to the substrate and to locally minimize the mismatch strain or the depolarizing field, the domains form in a periodic manner. 6,7 It is known that there is a quadratic dependence, W / d 1=2 , of the domain width (W) with the crystal thickness (b). In ferroelastic domains (typically 90 domains), this b 1=2 dependence is an approximation in the regime of d ) W. 2 For smaller thicknesses, a linear dependence has been predicted by Pertsev and Zembilgotov (P&Z), 8 but it has not been experimentally confirmed yet.In this paper we investigate the thickness dependence of the periodicity of ferroelastic 90 domains (a/c twins) in the lower thickness regime using PbTiO 3 films grown on DyScO 3 substrates. This combination is chosen because there is a very small lattice mismatch between film and substrate at the growth temperature. This minimizes the formation of defects during growth. As the films are cooled down strain develops and can be relaxed by forming a/c domains. The absence of defects allows these domains to form in a very periodic fashion. 13,16 Interestingly, when the films...

Super switching and control of in-plane ferroelectric nanodomains in strained thin films

“…1a) 35 . X-ray diffraction (XRD) reciprocal space mapping (RSM) shows the presence of a and c domains, as well as additional intensity oscillations in the diffuse scattering because of their periodic arrangement [33][34][35] . In Pb x Sr 1 À x TiO 3 films, by substituting Pb by Sr (decreasing x), the tensile strain can be continuously increased.…”

“…GmbH) by pulsed laser deposition using a pulsed KrF excimer laser (l ¼ 248 nm), from Pb x Sr 1 À x TiO 3 targets with 4 atomic % excess lead. The substrates were treated to get a single ScO 2 termination 33,46 , allowing the growth of high-quality SrRuO 3 bottom electrodes. The growth was followed in situ by reflection highenergy electron diffraction and the films thickness was determined from the reflection high-energy electron diffraction intensity oscillations, together with X-ray reflectivity.…”

Domain Wall Architecture in Tetragonal Ferroelectric Thin Films

“…[19] Even if a-domains are wanted, the controlled formation of these domains and of their associated 90° a/c domain walls in thin films requires post growth annealing [20] or substrate termination control. [21] Hence, for devices based on domain-wall motion in tetragonal ferroelectrics, understanding and controlling the distribution and morphologies of a-and c-domains is essential. [14] First and foremost, this requires their observation.…”

Controlled stripes of ultrafine ferroelectric domains

“…We use the impositions because of ferroelasticity and ferroelectricity to control ferroelectric/ferroelastic domain patterns. The existence of an a/c domain structure was observed before in PbTiO 3 on DyScO 3 substrates 16 , and the domain width of an anisotropic a/c domain pattern was compared with existing theory 17 . However, no direct evidence for the origin of the anisotropy was given, which would allow controlling the final pattern.…”