Science - USA (2021-12-17)

(PFM) measurements ( 21 )ofthecrystalline
LaWN 3 film synthesized on the heated sub-
strate (Fig. 1 and figs. S1 and S2). We used a
<25-nm-radius tip to probe the electromechan-
ical response of uncapped crystalline thin films

that were insulating according to conductive

atomic force microscopy (c-AFM) measure-

ments (fig. S6). Our PFM results show qual-

itatively unambiguous piezoelectric response

(Fig. 4, A to F), with 65% of more than 4000

pixels in a map (Fig. 4D) having coefficient of

determination (R^2 ) > 0.8 fit of piezoelectric

amplitude versus drive voltage (Fig. 4E). Our

statistical analysis of these measurement re-

sults (Fig. 4F) in terms of mean and median

1490 17 DECEMBER 2021¥VOL 374 ISSUE 6574 science.orgSCIENCE

500 500

400 400

300 300

200 200

100 100

00

Piezoelectric Amplitude (pm)

0 2 4 6 8 10 12

Drive Voltage (V)

65% of pixels have R

2

> 0.8

R^2 =0.800

R

2

=0.998

400

200

0

Sample Dimension (nm)

400

400

200

200

0

0

Sample Dimension (nm)

-1.2

-0.8

-0.4

0.0

0.4

0.8

1.2

Surface Height (nm)

400

200

0

Sample Dimension (nm)

400

400

200

200

0

0

Sample Dimension (nm)

1.00

0.98

0.96

0.94

0.92

0.90

0.88

0.86

0.84

0.82

0.80

R

2

40

20

0

d33,f

(pm/V)

1

1

0.95

0.95

0.9

0.9

0.85

0.85

0.8

0.8

R

2

1

2

3

4

5

6

10

2

Pixels

Mean

Q2

Q1

Q3

Q2

Mean

400

200

0

Sample Dimension (nm)

400

400

200

200

0

0

Sample Dimension (nm)

60

55

50

45

40

35

30

25

20

15

10

33,fd

(pm/V)

AC E

F

400

200

0

Sample Dimension (nm)

400

400

200

200

0

0

Sample Dimension (nm)

180

160

140

120

100

80

60

40

20

0

Response Phase (degree)

B D

Fig. 4. Piezoelectric properties of LaWN 3 thin films.(A) Atomically smooth
surface of a single LaWN 3 grain. (B) Phase, (C) linearity, and (D) slope of
each of more than 4000 pixels withR^2 > 0.8 for piezoelectric amplitude versus
drive voltage fits. (E) The best and worst fits included in this analysis resulting in

(F) a three-dimensional histogram of thesed33,fandR^2 values, indicating a mean

(green) and median (magenta) value of the piezoelectric response. Analysis of

LiNbO 3 , PZT, and (Al0.92Sc0.08)N reference samples and details of the PFM

measurements are provided in the supplementary materials (figs. S7 to S10).

5.5 5.5

5.0 5.0

4.5 4.5

4.0 4.0

33

22

11

00

qy

(2

/

)

4

4

3

3

2

2

1

1

0

0

-1

-1

-2

-2

-3

-3

-4

-4

qx (2/)

qx (2/)

10

3

2 4 6810

4

2 4 6810

5

Counts

yq

(2

/

)

Counts (a.u)

100

100

90

90

80

80

70

70

60

60

50

50

40

40

30

30

20

20

Cuk diffraction angle (deg.)

W (111)

(112)(011)

(011)

(022)(233) (013) (112)

(224) (022)(123) (134)

(004) (444)(123) (114)(125) (345)

Obs.

Calc.

Diff.

wR = 4.39

20

16

12

8

4

0

nm

-1

(010)

(010)

(200)

(020)

(020)

(200)(100) (100)

800

700

600

500

400

300

200

100

0

nm

Si(100)

LaWN 3

Pt

20

15

10

5

0

nm

-1

(110)

(110)

(121)

(211)

(121)

(211)

(110)

(220)

(220)

50

45

40

35

30

25

20

15

10

5

0

(110)

A B C E

D F

a = 5.64 Å

= 60.33 Å

Fig. 3. Crystal structure of LaWN 3 thin films.(A) Two-dimensional XRD
pattern, indicating randomly oriented polycrystalline microstructure. (B) Rietveld
refinement of XRD data for LaWN 3 thin films with a predicted rhombohedral
unit cell of R3c symmetry (space group 161) and body-centered cubic (bcc)
tungsten (W) minority phase (<5% by volume). (C) STEM–HAADF (high angle

annular dark field) image of an as-deposited crystalline film highlighting a single

grain (white) and (D) SAED from this grain showing a pseudo-cubic perovskite

[001]–type pattern. (E) High-resolution image of a single grain showing the

pseudo-cubic (011) lattice spacing and (F) the associated fast Fourier transform

indexed with a pseudo-cubic [113] type pattern.

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