3d pfm pdms
TRANSCRIPT
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)