Crystallographic Orientation of Epitaxial Transition Observed for Nb (bcc) on MgO and Cu (fcc)

Single-crystalsKang Seo*, Norfolk State University (NSU), Norfolk, Virginia 23504

Mahadevan Krishnan, Enrique Valderrama, Alameda Applied Sciences Corporation (AASC), San Leandro, California 94577

Xin Zhao, Anne-Marie Valente-Feliciano, Joshua Spradlin, Larry Phillips, Charles Reece, Thomas Jefferson National Accelerator Facility (JLAB), Newport News, Virginia 23606

SummaryNiobium thin films were grown on (001) MgO single-crystal using a

coaxial energetic deposition. The quality of the substrate surface and

epitaxial Nb layers were investigated by XRD Bragg-Brentano and

pole figure measurements. Depending on growth temperature, in-plane

XRD show Kurdjumov-Sachs (KS) as well as Nishiyama-Wassermann

(NW) epitaxial relationships for (110) and (001) Nb on (001) MgO.

Calculation of the interface energy in rigid lattice models finds one KS

and two NW minima. For the NW case the optimal atomic diameter

ratio dbcc/dfcc=0.866 and 1.061, whereas for the KS case it is at

dbcc/dfcc=0.919. Transitions of this type are usually induced by a change

in the lattice parameter ratio resulting from a relaxation process in the

early stage of the growth.

X-ray Analysis

S

iK

dK

2

1

S

1

Rocking curve

X-ray diffraction is one of the most powerful and widely used

techniques for accurate characterization of the lattice parameters,

mismatch, and thickness of epitaxial materials.

Schematic of scan vector of

2theta-omega scan and rocking

curve in reciprocal space

Schematic of scan vector of pole

figure measurement in reciprocal

space

Out-of-plane XRD

Phi scan {110} for (110) Nb on (111) Cu at Ts=500°C

The center spot indicates

the grains oriented with

(110) planes parallel to

the substrate, while four

spots at 60 of tilt

correspond to diffraction

intensities from {110} in-

plane texture. The angle

between (110) and (100)

in cubic materials is 45°

that those four peaks

emanate from Nb with

(001)Nb ‖ (001)MgO.

Conclusions

Bragg-Brentano XRD revealed that epitaxial (110) Nb films on MgO

substrate were grown under 400°C of deposition temperature and (001)

Nb films at higher 600°C, while the diffraction peaks of Nb films were

changed from single orientation to a mixed state (110) and (001) plane

of 500°C. In-plane XRD (110) and (001) Nb/MgO phi scan with a

variety of different NW (Nishiyama-Wasserman) -KS (Kurdjumov-

Sachs) states that show the transition independently from substrate

temperature. In this state of the transition the NW at orientation θ= 0°

one-peak structure is superposed by the two KS peaks appearing at

about ±10° relative to the NW direction. For (110) Nb on (111) Cu

substrate, optimal ratio is very close to the KS minimum with

orientation θ = 5.3°. Clearly, the lattice parameter ratio is an important

variable in the epitaxial growth.

* e-mail: kiseo@nsu.edu

+ The financial support of this investigation by the #DE-FG02-07ER84741 to

AASC is gratefully acknowledged.

Ts (°C) Substrate RRR Tc (K) B-B XRD

DOE146-0702-4 RT/150 (001) MgO 7 9.0 (110) Nb

CED-080510-26 300/300 (001) MgO 48 9.24-9.26 (110) Nb

CED-072210-10 500/500 (001) MgO 181 9.25 (110) & (002) Nb

CED-071410-3 700/700 (001) MgO 316 9.22-9.25 (002) Nb

Sample Information

30 35 40 45 50 55 60 65

(002

) N

b

(110

) N

b

(002

) M

gO

(d)

(c)

(b)

(a)

Inte

nsi

ty (

arb. un

it;

cps)

2theta-theta (degree)

Bragg-Brentano XRD patterns of Nb films on (001) MgO obtained as a

function of substrate temperatures of (a) 150C, (b) 300C, (c) 500C, and

(d) 700C.

In-plane (texture) XRD

Phi scan {110} for (110) Nb on (100) MgO at Ts=300°C

50 100 150 200 250 300 350Phi (°)

0

400

1600

3600

Inte

nsity (

counts

)

4.3°

94.1° 185.3

°

275.9

°

39.6

°

149.4

°

220.7

°

330.1

°

58.9

°

129.8

°

239.9

°

310.5

°

35.3°

35.2 °35.7 °

19.3

°

Phi scan {110} for (100) Nb on (100) MgO at Ts=700°C

0 50 100 150 200 250 300 350Phi (°)

0

2500

10000

22500

Inte

nsity (

counts

)

0.5°

89.5°

181.1°

271.5°

44.7°

135.3°

226.3°

315.7°

44.8°

Mg

O

Nb

45°

Mg

O

Nb (1st stage)

Nb (2nd stage)

35.3°

19.3°

50 100 150 200 250 300 350Phi (°)

0

1000

2000

3000

4000

5000

6000

7000

Inte

nsity (

counts

)

5.3°

Cu

Nb

(a) (b)

(c) (d)