Comparing XRD data for 225C and 300C growth of Si-Heusler.

Some composition assumption for sample grown at 225C.

S230 grown at 300CSi Comp = 22.9 at.%

S239 grown at 225CSi Comp = 27.8 at.%

1009080706050Co Percent Metal

1.0

0.8

0.6

0.4

0.2

0.0

x10

-2

4.10

4.05

4.00

3.95

3.90

0.12

0.10

0.08

0.06

0.04

0.02

0.00

1.003

1.002

1.001

1.000

0.999

0.998

0.997

In-P

lan

e P

ositio

n

4.0

3.5

3.0

2.5

2.0

1.5

1.0

In-P

lan

e F

WH

M 1

0-2

1.0

0.8

0.6

0.4

0.2

x10

-3

2.06

2.04

2.02

2.00

1.98

1.96

1.94

5

4

3

2

1

0

x10

-4

1.03

1.02

1.01

1.00

0.99

0.98

0.97

Integrated Intensity

Peak Position [rlu]

Peak FWHM [rlu]

L(014)h=(022)c K(014)h=(022)c L(102)h=(002)c L(011)h=(111)c

Int=0.0069

1009080706050Co Percent Metal

2.5

2.0

1.5

1.0

0.5

0.0

x10

-2

4.10

4.05

4.00

3.95

3.90

0.12

0.10

0.08

0.06

0.04

0.02

0.00

1.003

1.002

1.001

1.000

0.999

0.998

0.997

In-P

lan

e P

ositio

n

4.0

3.5

3.0

2.5

2.0

1.5

1.0

In-P

lan

e F

WH

M 1

0-2

3.0

2.5

2.0

1.5

1.0

0.5

0.0

x10

-3

2.06

2.04

2.02

2.00

1.98

1.96

1.94

1.5

1.0

0.5

0.0

x10

-4

1.03

1.02

1.01

1.00

0.99

0.98

0.97

Integrated Intensity

Peak Position [rlu]

Peak FWHM [rlu]

L(014)h=(022)c K(014)h=(022)c L(102)h=(002)c L(011)h=(111)c

Things I noticed:• (022) intensity higher for 225C growth at Heusler Comp• Large area of higher intensity and in-plane lattice matching (65-

90)%Co– FWHM shows similar trend

• No Significant difference in in-plane peak width for the two growth temperatures

• (111) very wide at 225C growth• On the 300C sample, the strain is different for each reflection (the

position traces do not collapse on top of each other) wereas they agree in the 225C sample

• Comparing Zero Strain w/Si concentration suggests zero strain if Si was 25at%

• Zero Strain doesn’t necessarily correspond with highest intensity of narrowest peak

Comparing Chemical Order

3

4

5

67

0.01

2

3

4

5

67

0.1

2

3

4

Inte

nsi

ty R

atio

1009080706050Co Percent Metal

S1/F (300C) S2/F S1/F (225C) S2/F

The idea here is to measure the chemical ordering qualitatively. I’ve divided the integrated intensity of each superlattice peak by the fundamental to remove variations in structural disorder.

F=(022)c=(014)hS1=(002)c=(102)hS2=(111)c=(011)h

•No significant changes in intensity within the “good” region (65-85)% Co•No difference in S1/F for the two temperatures•Significant difference in intensities for S2/F: the (111) peak is MUCH stronger relative to the fundamental peak for 300C growth

Comparing phi-scan FWHM• Voigt could not fit well, so I found

FWHM via max value and located max/2 in the data after background subraction

• S239 had 2 components probably due to 2 distinct populations of grain sizes. I fit the wider as a polynomial background

• Clearly, the sample grown at 225C has a narrower width at the Heusler composition

FWHM vs Comp at Two Growth Temps

Example of two components in s239 Heusler Stoichiometry Data Compare

2

3

4

567

1

2

3

4

Ph

i-Sca

n F

WH

M [D

eg

]

1009080706050Co Percent Metal

s239 (225C) s230 (300C)

8

6

4

2

No

rmed

In

ten

sity

x 1

0-3

26.025.024.023.022.021.0Phi [Deg]

Data Fit Bkg

Voigt Fit: |X|² = 2.8973Intensity: 0.001946 ± 3.8349e-05Amplitude: 0.0059389 ± 6.5139e-05Position: 23.803 ± 0.00096075FWHM: 0.2086 ± 0.0034152Shape: 10000 ± 0

0.3

0.2

0.1

0.0

No

rmed

In

ten

sity

26.025.024.023.022.021.0Phi [Deg]

s239 (225C) s230 (300C)

L-scans of (014) on s231 (Si~19at%)Grown at 150C and 1/3 as Thick as Others

• A couple bad spots at ~90% Co• Zero strain @ ~84% Co• Position/Strain changes monotonically/linearly• Width strange

4.08

4.06

4.04

4.02

4.00

3.98

3.96

3.94

Pos

ition

[rlu

]

1009080706050Co Percent Metal

60

55

50

45

40

35

FW

HM

[rlu 10-3]

6810

-4

2

4

6810

-3

2

4

68

Integrated Intensity

Some General Conclusions• Si-concentration is a bigger factor to determine strain than Co/Mn

ratio• Higher Co concentration is better ordered than Heusler

stoichiometry regardless of growth temp according to intensities• Large region of composition gives good ordering according to peak

widths• These samples are still too different to make a definitive statement

on growth temperature– Different Si concentrations– Different layer ordering when grown– Different thicknesses (at least the 150C sample)

• Improving the study:– Study Si-dependant samples– Grow all three samples in a immediately after each other rather than

venting or composition recalibration to ensure const Si btwn samples

S241: Ternary Sample Grown at 225C

43

21

0X

Po

s [m

m]

6420 Y Pos [mm]

20

15

10

5

0

L In

ten

sity 10

-3

43

21

0X

Po

s [m

m]

6420 Y Pos [mm]

10

8

6

4

2

0

K Inte

nsity 1

0-3

43

21

0X

Po

s [m

m]

6420 Y Pos [mm]

4

4

3.97 3.96

4.02

4.00

3.98

3.96

3.94

L P

osition

43

21

0X

Po

s [m

m]

6420 Y Pos [mm]

1.000

0.998

0.996

K P

ositio

n

43

21

0X

Po

s [m

m]

6420 Y Pos [mm]

807060504030

L F

WH

M 10

-3

43

21

0X

Po

s [m

m]

6420 Y Pos [mm]

35

30

25

20

15

K F

WH

M 10

-3

43

21

0X

Po

s [m

m]

6420 Y Pos [mm]

0.5

0.4

0.3

0.2

0.1

0.0

L S

hap

e

43

21

0X

Po

s [m

m]

6420 Y Pos [mm]

0.5

0.4

0.3

0.2

0.1

0.0

K S

ha

pe

• L and K scans of the (014) reflection

• Phi scans are difficult to fit – just calc FWHM from data

• Data taken at corner of ternary sample nearest Co Apex

• Along Diagonal boundary, Co~80% of metal concentration

• Along base, Si~10%

In-Plane Out-of-Plane4

32

10

X P

os

[mm

]

6420 Y Pos [mm]

1.0

0.8

0.6

0.4

0.2F

WH

M [D

eg

]

Phi-scan FWHM

Ternary General Conclusions

• Brightest peaks correspond with narrowest width which occurs at the edge of the region corresponding to Co 80% (out of metal concentration). This is the spot of best crystal structure

• Best crystal structure DOES NOT correspond to zero strain, OR Heusler Stoichiometry

• Don’t know Si concentration yet

XRF Analysis of s238,39,41

Used to tweak first slide’s results and to correlate structural data

XRF analysis on binary samples: s238(150C), s239(225C)

• Compared XRF thicknesses w/ AA monitor – Quartz crystal expected thickness during growth– Both samples came to significantly

lower thicknesses– Since reduction ~ same for each

element, composition was not effected significantly

– This is NOT effected by Duke profilometer readings, since both are calibrated to the same calibration sample and same measured sample thickness

• Fluctuation seems fairly large for Si and Co between the two samples. Mn held steady.

900

800

700

600

500

400

300

200

Thi

ckn

ess

[Å]

-6 -4 -2 0 2 4 6Sample Position [mm]

Film ThicknessSi-Heusler Number Density

s239 s238Expected: 700Å, 687Å

800

600

400

200

0

Thi

ckn

ess

[Å

]

-6 -4 -2 0 2 4 6Sample Position [mm]

s239 Component ThicknessesAssuming Si-Heusler Number Density

Co Mn Si TotalCmpr to Calc: (81%, 88%, 85%, 84%)

800

600

400

200

0

Thi

ckn

ess

[Å

]

-6 -4 -2 0 2 4 6Sample Position [mm]

s238 Component ThicknessesAssuming Si-Heusler Number Density

Co Mn Si TotalCmpr to Calc: (85%, 88%, 81%, 79%)

Mn pos way off again!

Binary Compositions

• Despite fluctuations, the offset of the Mn in s238 seems to have compensated and produced similar Si-concentrations

• Although Si is higher as expected, Co/Mn=2 pos changed and gives near zero strain (see slide 1)

• NOTE: we have no structural data (RHEED or XRD) on s238.

100

80

60

40

20

0

Com

po

sitio

n [a

t.%

]

-6 -4 -2 0 2 4Sample Position [mm]

0.1

2

4

6

81

2

4

6

810

Meta

l Ra

tio

s239 Si Heusler CoPercent MnPercent SiPercent MetalRatio

Co/Mn=2@ x=-0.4

Si=27.8 at.%

100

80

60

40

20

0

Com

po

sitio

n [a

t.%

]

-6 -4 -2 0 2 4 6Sample Position [mm]

0.1

2

4

681

2

4

6810

Meta

l Ra

tio

s238 Si Heusler CoPercent MnPercent SiPercent MetalRatio

Co/Mn=2@ x=0.1

Si=27.9 at.%

XRF analysis on Ternary• Composition values obtained and

used to correlate structural results between samples.

• Quantitative thickness comparisons detailed in table at bottom right.

• Total thickness comparison for s241 is better, giving 95% the expected value.

• Co is nominally the same low value seen in other samples

• Mn thickness matches expected here, giving large fluctuation from binary samples

• Si thickness measurement was very low even though Liang had tried to increase the Si amount

64

20

-2-4

Y P

os [m

m]

-6 -4 -2 0 2 4 6X Pos [mm]

Si

Mn

Co

15

20

25

30

35

40

45

50

3035

40

45

50

55

6065

70

15

20

25

30

35

40

45

50

55

Film CompositionAtomic Percent

64

20

-2-4

Y P

os [m

m]

6420-2-4-6X Pos [mm]

400 390

380

380

370 370

370

360

360

360 350

350

350

370

360

350

390

380

370

360

350

To

tal T

hickness [Å

]

Total Thick Calc: 390Å; (95%)Co Max: 262Å; Calc: 307Å (85%)

Min: 100Å; Calc: 115Å (87%)MnMax: 223Å; Calc: 225Å (97%)

Min: 39Å; Calc: 39Å (100%)Si Max: 206Å; Calc: 261Å (79%)

Min: 40Å; Calc: 44Å (91%)

Curiosity: Co Zero Line Misalignment

• Co Zero line seen here and in previous Si-Heusler Ternary is not at 60 degrees.

• The Equal percentage lines (prev. slide) are not parallel with this line and are actually closer to 60 degrees

• While equal percentage lines could be off due to experimental/analytical errors, the boundary can not

8

6

4

2

0

Y P

os [m

m]

86420X Pos [mm]

Sample Boundaries Equalateral Triangle

Si

Mn

Co

Co Zero Line

Possible causes of discrepancy of thicknesses from expected

• Liang says this AA lamps were at the end of their lifetime (each of them) and could cause a systematic error in deposition– Could they cause reduction AND fluctuation?

• Another possibility is the Quartz crystal may have been positioned improperly– would explain a systematic reduction in deposition, but good Mn

agreement on s241 counts against this possibility

• XRF fitting is still very much a black box– I tried fitting the data with different conditions but could find no

conditions that would improve the values– Stefan says as long as fitting procedure same for Standard and Sample,

fitting should be robust

Correlating Results (s230, s239, s241)

• Used XRF data to correlate Binary to Ternary sample

– Right: Blue trace=s239 & Green trace=s230

– Green dot is Si-Heusler

• Expected:– Pleateau of width and zero

in-plane strain in large compositional region, including Heusler

– Brightest spot & narrowest width (best ordering) not at Heusler Stoichiometry

– Best ordering at high Co

• Not Expected:– Heusler sees ~1/4% strain?– 25% Si does not intersect

w/best ordering?4

32

10

Y P

os

[mm

]

6420 X Pos [mm]

80

70

60

50

40

30

L F

WH

M [rlu

] 10

-3

43

21

0Y

Po

s [m

m]

6420 X Pos [mm]

35

30

25

20

15

K F

WH

M [rlu

] 10

-3

43

21

0Y

Po

s [m

m]

6420 X Pos [mm]

1

0.9995

0.9

99

0.999

0.9

98

5

1.001

1.000

0.999

0.998

0.997

0.996

0.995

K-P

ositio

n [rlu

]4

32

10

Y P

os

[mm

]6420 X Pos [mm]

4.02 4.01

4

3.99 3.98

3.97 3.96

3.95

3.94

4.02

4.00

3.98

3.96

3.94

L-P

ositio

n [rlu

]4

32

10

Y P

os

[mm

]

6420 X Pos [mm]

10

8

6

4

2

0

Inte

gra

ted

Inte

nsity 1

0-3

43

21

0Y

Po

s [m

m]

6420 X Pos [mm]

2 1.5

1

0.5

0.3

0.2

2.0

1.5

1.0

0.5

Ph

i FW

HM

[De

g]

• Interpolated s241missing data assuming planar geometry

S239 (Binary) -> s241 (Ternary)• Ternary data sampled at

Binary compositions to compare XRD results

• Intensity traces remarkably similar (factor of ~½ comes from thickness difference)

• L-Positions identical• In-Plane positions have

strange discrepancies below 70% Co, otherwise agree

• In general, width in ternary larger than in binary

– Wider Out-of-Plane due to thickness difference but not much

– Why is Ternary In-Plane wider?

• Phi-direction continues the trend with larger width

• Both grown at 225C• Binary 590A; Ternary 370A• Layers: Binary = CoMnCoSi…

Ternary = CoMnSi…

2

3

456

1

2

3

45

Ph

i FW

HM

[D

eg

]

1009080706050Co Pecent Metal

Phi FWHM s239 s241

0.12

0.10

0.08

0.06

0.04

0.02

Ou

t-o

f-P

lan

e [

rlu

]

1009080706050Co Pecent Metal

40

35

30

25

20

15

10

In-P

lan

e [rlu

] 10

-3

L-FWHM s239 s241K-FWHM s239 s241

4.04

4.02

4.00

3.98

3.96

Ou

t-o

f-P

lan

e [

rlu

]

1009080706050Co Pecent Metal

1.002

1.001

1.000

0.999

0.998

In-P

lan

e [rlu

]

L-Position s239 s241K-Position s239 s241

4

10-4

2

4

10-3

2

4

10-2

2

Inte

gra

ted

In

ten

sity

1009080706050Co Pecent Metal

Intensity s239 s241

S230 (Binary) -> s241 (Ternary)• Intensity traces again similar

This time the Binary is weaker• Intensity peak at ~68% in both

data sets (shows up more if linear scale)

• L-Positions again identical• In-Plane positions agree well

with slight offset from 1 in the ternary (probably diffractometer calibration)

• In general, width in ternary larger than in binary

– Wider Out-of-Plane due to thickness difference but not much

– Why is In-Plane wider?

• Phi-direction continues the trend with larger width. Slightly more discrepancy

2

3

456

1

2

3

45

Phi

FW

HM

[D

eg

]

1009080706050Co Percent Metal

Phi FWHM s230 s241

0.12

0.10

0.08

0.06

0.04

0.02

Ou

t-of

-Pla

ne

[rlu

]

1009080706050Co Percent Metal

40

35

30

25

20

15

10

In-P

lane

[rlu] 10

-3

L-FWHM s230 s241K-FWHM s230 s241

4.04

4.02

4.00

3.98

3.96

Ou

t-of

-Pla

ne

[rlu

]

1009080706050Co Percent Metal

1.002

1.001

1.000

0.999

0.998

In-P

lane

[rlu]

L-Poistion s230 s241K-Position s230 s241

4

10-4

2

4

10-3

2

4

10-2

2

Inte

gra

ted

inte

nsi

ty

1009080706050Co Percent Metal

Intensity s230 s241

• Binary grown at 300C; Ternary 225C• Binary 540A; Ternary 370A• Layers: Binary = CoMnCoSi…

Ternary = CoMnSi…

New General Conclusions

• I would say this shows good reproduction of data and gives us an idea of our error

• There could be a systematic error in composition causing the strain measurements to be off from the Heusler (1% is too far off to be from miscalibration of diffractometer) or there could be some Mn loss into the Ge substrate causing the Heusler comp to shift