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Lateral piezoelectric response across ferroelectric domain walls in thin films
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View: Figures


Image of FIG. 1.
FIG. 1.

Surface topography of 70 nm -axis PZT (a), 250 nm PZT including -axis domains (b), (001)-BFO (c), and (111)-BFO (d) thin films performed by AFM, showing rms roughnesses of 4 Å for -axis PZT, 1.3 nm for thicker PZT, and 2 nm for BFO. Horizontal scale bar is in (a) and (b), in (c), and in (d).

Image of FIG. 2.
FIG. 2.

PFM measurements of a square down-polarized ferroelectric domain written on an up-polarized 70 nm PZT film by applying while scanning over a area. The VPFM measurement shows a 180° phase contrast [(a) and (i)] with a corresponding minimum in the amplitude at the domain wall [(b) and (j)]. In the LPFM signal, two opposite features are observed in the phase at the domain walls [(c) and (k)], perpendicularly to the AFM cantilever, with a corresponding rise in the amplitude [(d) and (l)]. The orientation of the cantilever is indicated in inset in (c) and (k). Horizontal scale bar is for (a)–(d) and for (i)–(l). The fast scan direction, the same for all measurements, is along the cantilever length. For the first measurement set, line cuts corresponding to the vertical lines in [(a)–(d)] are shown in [(e)–(h)].

Image of FIG. 3.
FIG. 3.

Double-pass PFM measurement of domains written on a 250 nm PZT film by applying to the tip. The first pass [(a)–(d)] is done in strong contact with a setpoint of 0.5 V, while the interleave pass [(e)–(h)] is performed with different lift heights providing weak contact in the upper part and no contact in the lower part, as indicated in (e). (i) Typical force curve (in solid line) with the strong, weak and noncontact configuration in the first and second passes (upper and lower part of (e)–(h), see horizontal dotted or dashed lines giving the used setpoint for the different passes). The cantilever orientation is given for all measurements in (b). The fast scan direction is perpendicular to the length of the cantilever. The scale bar is . (j) Representation of the tip/cantilever and sample configurations in the three regimes described in (i).

Image of FIG. 4.
FIG. 4.

EFM measurements performed in tapping [(a) and (b)] and torsion [(c) and (d)] modes on domains written on a 70 nm PZT film. The VEFM signal measured in the same set of domains immediately after domain writing (a) and one month later (b) shows an intensity decrease in an order of magnitude (both measurements were performed with a tip lift of 30 nm and a dc bias applied to the tip and are shown with a vertical scale of 2°). The TEFM signal observed with (c) and −3 V (d) dc bias applied to the tip immediately after writing was not observable after one month (not shown). The horizontal scale bar is (a), (b), and (c) and (d). The orientation of the long axis of the rectangular domains is indicated by the arrow in each measurement.

Image of FIG. 5.
FIG. 5.

(a) Representation of the torsion of a cantilever/tip system that could occur if the underlying surface is tilted by an angle at a domain wall, in block color. The state without surface tilting is represented by the dotted line, and the line-sketch of the cantilever. Evolution of vertical deflection [(b), dashed line] and horizontal torsion [(c), solid line] angles as a function of the applied vertical (b) or horizontal (c) force with a superimposed constant vertical force of 10 nN applied at the tip apex. The inset in (b) shows the side view of the vertical deformation of the cantilever. The two insets in (c) represent front views of the deflection and torsion of the cantilever/tip system.

Image of FIG. 6.
FIG. 6.

Sketch of domain wall shear in presence of an out-of-plane field , indicated by the dashed arrow. The initial domain wall positions are indicated by the dotted lines. The horizontal arrows represent the lateral motion of the domain walls.

Image of FIG. 7.
FIG. 7.

Schematic representation of the vertical deflection (a) and lateral torsion (b) of the tip/cantilever system resulting from a change in height of the surface [full and dotted lines in (a)] or in an in-plane displacement of the surface (b) leading to vertical and lateral signals on the photodiodes, respectively.

Image of FIG. 8.
FIG. 8.

(111)-oriented BFO film: VPFM phase (a) and amplitude (d) and LPFM phase (b) and (c) and amplitude (e) and (f) after writing a rectangle with positive voltage. In insets of (b) and (c), the orientation of the cantilever during LPFM measurement is given. The horizontal scale bar is . The fast scan directions is along the length of the cantilever. (measurements (a) and (d) were made at the same time as (b) and (e)).

Image of FIG. 9.
FIG. 9.

(001)-oriented BFO film. (a) and (c), VPFM (b), (d) and LPFM phases after writing large rectangles with negative (dark color in VPFM) and positive (bright color in VPFM) voltage with slow scan axis along . Circular nanodomains were then written with voltage pulses. (c) and (d) are a zoom in the region indicated by the rectangle in (a) and (b). For points, numbers and arrows, see text. (e) gives a schematic representation of the polarization orientation of (a) and (b): light and dark gray correspond to down and up out-of-plane component of the polarization, respectively, and the arrows indicate its in-plane orientation (two adjacent arrows indicate the mix of components). (f) gives crystalline axis orientation and in-plane polarization variants orientation, and − gives the out-of-plane component. The horizontal scale bar is .

Image of FIG. 10.
FIG. 10.

Schematic representation of the unit cells and of the polarization projected in the (110) plane in regions 1 to 4 of Figs. 9(c) and 9(d) (see numbers): at the domain wall between 3 and 4 (a) or 1 and 2 (b). The effect of a field oriented along [001] is given by the curved arrows and the resulting shear displacements at the surface due to the bulk, , or to the domain wall, , are represented by straight arrows along [] or .


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Lateral piezoelectric response across ferroelectric domain walls in thin films