800 nm x 800 nm

Focus on the CHANGE of polarization during switching:

(1) Decompose a polarization vector into components (Px, Py, Pz), measured by three

dimensional (3D) Piezoresponse Force Microscopy (PFM)

(2) Distinguish 6 types of switching by different combinations of “switched” and “un-

switched” states of Px, Py, Pz (given by LPFM1, LPFM2, VPFM)

(3) Each scanned pixel is assigned a color according to its switching type

Polarization Difference Maps (PDMs) --- A technique to intuitively visualize ferroelastic and ferroelectric switching

11 (0o): None switch 12 (180o): All switch 13 (90o): Only VPFM switches 14 (90o): Both LPFM switches 15 (90o): One LPFM and VPFM switch 16 (90o): Only one LPFM switches

Three dimensional (3D) Piezoresponse Force Microscopy (PFM)

Vertical bend of the cantileverVPFM

Lateral twist of the cantileverLPFM

Single crystal PZT filmLPFM 1

LPFM 2

VPFM Po

Obtain a PDM

|Pbefore - Pafter | = Pdifference

LPFM1

LPFM2

VPFM

Assign color

1 μm x 1 μm

11 (0o): None switch (All dark)12 (180o): All switch 13 (90o): Only VPFM switches 14 (90o): Both LPFM switches 15 (90o): One LPFM and VPFM switch 16 (90o): Only one LPFM switches

Experiments: PDM to study ferroelectric/ferroelastic switching

Without PDM, 6 PFM phase images are needed to identify the switching type for only 1 grainWith PDM, the switching types for all grains can be shown simultaneously in 1 PDM

all 6 switching types appeared (IIIV)

1

2

45

6

31 μm x 1 μm

1

3

5 2

4

6

11 (0o): (0)(0)(0)12 (180o): (1)(1)(1)13 (90o): (0)(0)(1)14 (90o): (1)(1)(0)15 (90o): (1)(0)(1) or (0)(1)(1)16 (90o): (1)(0)(0) or (0)(1)(0)(0) for “un-switched”, (1) for “switched”

(PDM of IIIV)

surprisingly large amount of 90o switching, and small amount of 180o switching (IIIV)

PDM of II IVDark(0°),Green(90°), bright(180°)

1 μm x 1 μm

In our polycrystalline thin film:Less than 5% of grains switched 180o More than 50% of grains switched 90o

In epitaxial thin films (of the same thickness and composition):100% 180o switching

Nagarajan, V., et al., Dynamics of ferroelastic domains in ferroelectric thin films. Nat Mater, 2003. 2(1): p. 43-47.In addition: 90o switched grains are connected, potentially triggered by neighboring grains

180o switching consisting of 2 successive 90o switching!

I

II

III

PDM of I II PDM of II III PDM of I III

First direct observation

Previously predicted by statistical XRD

Domain relaxation by lateral only 90o switching (III)

Driven by neighboring grains, systematic study of the neighboring grain effects is ongoing

1 μm x 1 μm

1

3

5 2

4

6

11, 4, 6(PDM of III)

Vertical switching include both 180o and 90o switching (IIIV)

1

3

5 2

4

6

A reversal of vertical applied E field leads to vertical (both 180o and 90o) switching

1 μm x 1 μm 12, 3, 5(PDM of IIIII)