IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 26, NO. 3, APRIL 2016

7500104

Characterization by X-Ray Diffraction of Non-c-Axis
Epitaxial Bi2Sr2CaCu2O8+δ Thin Films
K. Endo, S. Arisawa, T. Kaneko, I. Tsuyumoto, Y. Tateno, and P. Badica
Abstract—Thin films of Bi2 Sr2 CaCu2 O8 (Bi-2212) with thenon-c-axis (117) orientation were grown by MOCVD on (110)LaAlO3 single crystal substrate. XRD θ − 2θ scans show thatfilms contain also (119) and (011)Bi-2212 impurity grains. We
propose and report characterization of the non-c-axis films byXRD ϕ − ψ scans. By this approach, the assumed theoreticalfilm–substrate relationship of the (117) Bi-2212 grains is demonstrated experimentally. The result also confirms twinning in thespan rooflike (117) Bi-2212 grains. The impurity (119) and (011)
Bi-2212 grains are also rooflike and in-plane aligned according tofilm–substrate relation and AFM images so that the film can beconsidered in-plane epitaxial.
Index Terms—MOCVD, thin film, XRD ϕ − ψ scans,(117)Bi2 Sr2 CaCu2 O8 .

I. I NTRODUCTION

HIGH Temperature Superconductors (HTS) are intrinsic
composite structures composed of superconducting andnon-superconducting layers. Anisotropy of the properties ishigh. The coherence length in the ab-plane is about 5–300 times
greater than that along the c-axis. For some intrinsic Josephson
tunneling devices, the non c-axis HTS thin films may offer theadvantage of exploitation of a longer coherence length thanfor typical c-axis films. Furthermore, in HTS the coherence
length along the c-axis (ξc ∼ 0.01−0.2 nm) is quite small
when compared to classic superconductors such as Nb (ξ ∼40 nm). This situation makes at present challenging fabricationof multilayered Josephson tunneling devices based on HTSc-axis oriented thin films. Namely, the non superconducting
layers should have the thickness small, i.e. comparable to thecoherence length along the c-axis of the HTS. On the otherhand, integration of non c-axis thin films combining HTS
with other materials can lead to design of new and complex
heterostructures for fabrication of devices with improved orManuscript received September 8, 2015; accepted January 27, 2016. Dateof publication February 11, 2016; date of current version March 8, 2016. Thiswork was supported by JSPS KAKENHI Grants 15K05997 and 15K06449(Japan). The work of P. Badica was supported by MEN-UEFISCDI, under thePN II program, under Grants 138/2012 and 3/2012 (Romania).
K. Endo, T. Kaneko, and I. Tsuyumoto are with the Kanazawa Institute ofTechnology, Hakusan 924-0838, Japan (e-mail: kendo@neptune.kanazawa-it.
ac.jp; bif-rost@eagle-net.ne.jp; tsuyu@neptune.kanazawa-it.ac.jp).
S. Arisawa is with the National Institute for Materials Science, Tsukuba
305-0047, Japan (e-mail: arisawa.shunichi@nims.go.jp).
Y. Tateno is with the Kanazawa Institute of Technology, Hakusan 924-0838,
Japan, and also with the Furuuchi Chemical Corporation, Akoh 678-0172,
Japan (e-mail: furuuchi-tateno@topaz.ocn.ne.jp).
P. Badica is with the National Institute of Materials Physics, 077125
Magurele, Romania (e-mail: badica2003@yahoo.com).
Color versions of one or more of the figures in this paper are available online
at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/TASC.2016.2529005

new functionality taking advantage of the synergetic effects atinterfaces. Therefore, growth of top quality non c-axis thin films
and heterostructures [1]–[5] can be rewarding.
It was demonstrated that Bi-based (Bi-Sr-Ca-Cu-O) superconductors exhibit the intrinsic Josephson junction (IJJ) effect[6], [7]. The IJJ effect was also observed in YBa2 Cu3 O7 [8],[9]. The Bi-based superconductor is more suitable for device
applications because of its higher anisotropy parameter. UsingBi-based superconducting single crystals, various methods ofIJJ fabrication have been developed and different IJJ device
prototypes have been reported [9]–[12]. For Bi-based thin films,
usually c-axis oriented growth is easily obtained. For such acase, the IJJ effect was demonstrated by fabricating a mesa
structure [13]. Despite this success, for some device applications a higher number of junctions defined by the stacked
alternative superconducting and insulating layers of the crystal
structure are required. This translates into a higher thicknessof the c-axis film and this has some limitation considering thedecrease of the film quality for thick films. To overcome theaddressed limitation of the c-axis films, it would be of practicalinterest to grown non c-axis films and to design IJJ devices
using such films.
In our previous works [5 and therein refs] we have growndifferent non c-axis HTS thin films or heterostructures. Superconducting layer was of YBa2 Cu3 O7 or Bi2 Sr2 Ca2 Cu3 O10 .
In this work we report growth of a non c-axis epitaxial (117)
Bi2 Sr2 CaCu2 O8 (Bi-2212) thin films on appropriate (110)LaAlO3 (LAO) single crystal substrate. We show characterization of these films by XRD ϕ − ψ scans. This proposed
approach applied on (117) Bi-2212 films has the potential to
be used for structural characterization of other non c-axis films.
The result of the XRD ϕ − ψ scans experimentally demonstrates the assumed film-substrate relationship according to thelattice coincidence theory. It also supports the idea of twin
formation in the specific roof-like grains from the non c-axisfilms. It is worthy to mention that we have recently reported
high critical current densities in (001)Bi-2212 thin films grownby MOCVD in which we observed defects such as dislocations
parallel to the ab-plane and anti-phase boundaries consideredeffective for strong flux pinning [14]. Assessment of other typesof defects in Bi-2212 films such as twins can be of interestfor the flux pinning control and better understanding of vortex
dynamics details.
II. E XPERIMENTAL
Samples were prepared by metal organic chemical vapor
deposition (MOCVD). Source materials (Toshima Manufacturing Co. Ltd.) were Bi(o-tolyl)3 and M(DPM)2 with M = Sr,1051-8223 © 2016 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission.
See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.

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IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 26, NO. 3, APRIL 2016

Fig. 1. Film–substrate lattice matching relationship for the growth of the nonc-axis (117)Bi-2212 thin film. Same in-plane relation is for (119)Bi-2212
impurity grains. The lattice misfits between the film and the substrate along the[001] and [110] directions of the substrate are 0.98% and 8.95%, respectively.

Fig. 3. Film–substrate lattice matching relationship between the (011)Bi-2212
and (110) LAO planes.

Fig. 2. XRD θ − 2θ scan of the (117)Bi-2212 film.

Ca and Cu. DPM is the abbreviation for dipivaloylmethanateligand. Vapors were supplied to reaction tube in Ar-carrier
gas stream with the following flow rates: 100, 300, 300, and
70 ml/min for Bi, Sr, Ca and Cu, respectively. The substrateplaced on a susceptor was inductively heated at 500–800 ◦ C.
The thin film presented in this work was grown at 600 ◦ C for adeposition time of 45 h on a (110)LAO single crystal substrate
produced by Furuuchi Chemical Co. The miscut angle of the
as-received (110)LAO single crystal substrates, as measured
by atomic force microscopy (AFM), was below 0.3◦ . Oxygen
was introduced in the reaction tube with a partial pressure of
2.6 kPa and a flow rate of 640 ml/min. The total pressure in thechamber was 6.7 kPa. More details on equipment are presented
in [15], [16]. The average film thickness was ∼50 nm. The
thickness was determined considering mass established frommeasurements of Inductively Coupled Plasma (ICP-AES, SPS
7700, Hitachi High-Tech Science Co.) Spectroscopy and thetheoretical density of the Bi-2212 phase (6.6 g/cm3 ).
X-ray diffraction (XRD) measurements were performed onUltima (Rigaku Co.) and X’Pert MRD (Panalytical Co.) diffractometers (CuKα radiation).
The morphology of the non c-axis films was observedby AFM using a SPA 400 (Hitachi High-Tech Science Co.)equipment.
III. R ESULTS AND D ISCUSSIONSThe substrate was selected to match the most probable theoretical in-plane relationship (Fig. 1) between the lattices of thesubstrate and the film.
Growth of the film with (117) orientation can be observed
from the XRD θ − 2θ pattern presented in Fig. 2. However,other diffraction lines are present and they are ascribed to (011)and (119) orientations of Bi-2212. In the case of (011) Bi-2212,

Fig. 4. XRD ϕ − ψ scans of the (117)Bi-2212 film. (a) Schematic of themeasurement. (b) ϕ − ψ experimental results for the (0010) plane (2θ =29.048◦ ) of the non-c-axis Bi-2212 film.

this plane matches the (110) LAO plane as shown in Fig. 3,
while for the (119) Bi-2212 it is as in Fig. 1.
The XRD ϕ − ψ scans were performed for 2θ = 29.048◦
corresponding to (0010) plane of Bi-2212. For a fixed ψ within(−85◦ , 85◦ ), ϕ—scan was measured. A schematic drawing ofthe measurement is shown in Fig. 4(a). The ψ—step was of 5◦ .
Experimental results are presented in Fig. 4(b). The two observed peaks have (ϕ, ψ) values of (87.5◦, −50◦ ) and (90.75◦,45◦ ). A ψ value of 45◦ or 50◦ is comparable to the theoreticalvalues of 41.03◦ for (117) and 48.23◦ for (119) orientations ofBi-2212. The differences may arise from the contribution of thesubstrate miscut angle. By RHEED, Kuroda et al. [1] obtained
an angle of about 48◦ in a (11n)Bi-2212 thin film. It was notpossible for our resolution of the measurement to separate theENDO et al.: CHARACTERIZATION BY XRD OF NON-c-AXIS EPITAXIAL Bi2 Sr2 CaCu2 O8+δ THIN FILMSFig. 5. Schematic image showing formation of inclined facets of the spanrooflike grains containing twins.

7500104(117)/(119) accommodate the (011) Bi-2212 grains. The grainsof (011) should have a roof-like morphology that is formed asalready explained for the (117) or (119) Bi-2212 grains, andthe top line of the roof theoretically develops perpendicular
to that for the (117) or (119) Bi-2212 grains. In AFM it was
not possible to identify grains with such orientation and in
the ϕ − ψ space (Fig. 4(b)) of the (0010) Bi-2212 plane, thecorresponding peaks of (011) Bi-2212 should be located closeto ψ = ±90◦ where measurements were not performed yet. We
shall also note that for the films deposited at a higher growthtemperature (i.e. above 600 ◦ C) the peak of (011) Bi-2212 inthe XRD θ − 2θ patterns cannot be observed and, hence, theformation of this impurity phase is suppressed.
IV. C ONCLUSION
Non c-axis films of (117) Bi-2212 were obtained by
MOCVD. Substrate was the (110) LAO single crystal. The film
was characterized by structural and microstructural measurements and it shows in-plane epitaxy. The in-plane epitaxy forthe (117) and impurity (119) Bi-2212 was demonstrated experimentally by ϕ − ψ XRD scans. This confirms the assumed
theoretical film-substrate lattice matching relation for the (117)/(119) Bi-2212 grains and formation of the twins in the nonc-axis grains developing with a span roof-like morphology.
XRD θ − 2θ measurements indicate the presence of the (011)
Bi-2212 impurity. This phase based on the film-substrate relation and AFM images is in-plane aligned preserving the overall
in-plane epitaxy of the film.
XRD ϕ − ψ scans of non c-axis film proposed in this work
are useful for characterization of other inclined films.
R EFERENCES

Fig. 6. AFM image and cross-section view of the span rooflike grains.

two orientations. We conclude that there is a relatively good
agreement between the theoretical and experimental values
within the experimental errors.
The measurement indicates that c-axis is inclined with theindicated ψ angles in respect to the normal to the substrate surface (Fig. 5). The non c-axis film grows in the c-axis direction
by a layer-by-layer mechanism through addition of ab-planes
similar to the growth of the c-axis thin film, but the c-axis isinclined versus the substrate surface. When the two opposite
inclined growing fronts merge (Fig. 5), a span roof-like grain
forms and it contains a twin boundary. Therefore, XRD ϕ − ψscan results prove the formation of twins in the non c-axis film.
The span roof-like morphology of the grains is revealed byAFM (Fig. 6) and it is in good agreement with the results ofXRD measurement. AFM also suggests that films are in-planeepitaxial. The experimental value of ϕ at ψ ∼= 45◦ close to 90◦(Fig. 4(b)) and the ϕ experimental data for the substrate surface(not shown) indicate that the film is epitaxial for the (117) or(119) Bi-2212 grains given their similar in-plane film-substratelattice matching relation (Fig. 1). From the film-substrate lattice
matching relation for the (011) Bi-2212 grain (Fig. 3), thein-plane epitaxy of the film is preserved; the grains of[1] K. Kuroda et al., “(11n)-oriented BiSrCaCuO thin film formed on
SrTiO3 (110) substrate by RF magnetron sputtering,” Jpn. J. Appl. Phys.,vol. 29, no. 10, pp. L1816–L1818, Oct. 1990.
[2] H. Ozawa et al., “Development of intrinsic surfaces, and their electronicstructures and stability of non-c-axis YBCO epitaxial films,” IEEE Trans.
Appl. Supercond., vol. 7, no. 2, pp. 2161–2164, Jun. 1997.
[3] P. Haibach, U. Frey, H. Adrian, F. Lankes, and K. F. Renk, “Transversal thermovoltages of (119) Bi2 Sr2 CaCu2 O8+δ thin films on vicinal(110) SrTiO3 substrates,” Physica C, vol. 282–287, no. 2, pp. 655–656,Aug. 1997.
[4] H. Wakana, A. Yokosawa, and O. Michikami, “Non-c-axis-oriented
EuBa2 Cu3 O7−δ thin films grown on Al2 O3 (1–102) substrates with
CeO2 buffer layers,” Jpn. J. Appl. Phys., vol. 38, no. 10, pp. 5857–5862,Oct. 1999.
[5] K. Endo, P. Badica, S. Arisawa, H. Kezuka, and T. Endo, “Growth aspects of thin-film composite heterostructures of oxide multicomponent
perovskites for electronics,” Jpn. J Appl. Phys., vol. 51, Nov. 1–6, 2012,
Art. ID 11PG091.
[6] R. Kleiner, F. Steinmeyer, G. Kunkel, and P. Müller, “Intrinsic Josephsoneffects in Bi2 Sr2 CaCu2 O8 single crystals,” Phys. Rev. Lett., vol. 68,
no. 15, pp. 2394–2397, Apr. 1992.
[7] G. Oya, N. Aoyama, A. Irie, S. Kishida, and H. Tokutaka, “Observation ofJosephson junction like behavior in single-crystal (Bi,Pb)2 Sr2 CaCu2 Oy ,”Jpn. J. Appl. Phys., vol. 31, no. 7A, pp. L829–L831, Jul. 1992.
[8] M. Rapp, A. Murk, R. Semerad, and W. Prusseit, “c-Axis conductivity and intrinsic Josephson effects in YBa2 Cu3 O7−δ ,” Phys. Rev. Lett.
vol. 77, pp. 928–931, Jul. 1996.
[9] S. J. Kim, Y. I. Latyshev, and T. Yamashita, “3D intrinsic Josephson
junctions using c-axis thin films and single crystals,” Supercond. Sci.
Technol., vol. 12, no. 11, pp. 729–731, Nov. 1999.
[10] P. Badica, K. Togano, S. Awaji, K. Watanabe, and H. Kumakura, “Reviewon Bi-Sr-Ca-Cu-O whiskers,” Supercond. Sci. Technol., vol. 19, no. 10,
R81–R99, Aug. 2006.

7500104

IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, VOL. 26, NO. 3, APRIL 2016[11] H. B. Wang, K. Maeda, J. Chen, P. H. Wu, and T. Yamashita, “Threedimensional arrays of BiSrCaCuO-2212 intrinsic Josephson junctions andzero-crossing Shapiro steps at 760 GHz,” Appl. Phys. Lett., vol. 80, no. 9,
pp. 1604–1606, Mar. 2002.
[12] L. Ozyuzer et al., “Emission of coherent THz radiation from superconductors,” Science, vol. 318, pp. 1291–1293, Nov. 2007.
[13] K. Endo, P. Badica, H. Sato, and H. Akoh, “New growth approach ofhigh-quality oxide thin films for future device applications: Independent control of supersaturation and migration,” Supercond. Sci. Technol.,vol. 19, no. 5, pp. S221–S225, Feb. 2006.

[14] H. Yamasaki and K. Endo, “Nanostructural defects for effective flux
pinning in high-quality Bi2 Sr2 CaCu2 O8+x epitaxial thin films withhigh critical current density,” Supercond. Sci. Technol., vol. 27, no. 2,pp. 025014–025024, Jan. 2014.
[15] K. Endo, H. Yamasaki, S. Misawa, S. Yoshida, and K. Kajimura, “Highquality superconducting thin films of Bi2 Sr2 Ca2 Cu3 Ox grown in situ bymetalorganic CVD,” Nature, vol. 355, no. 6358, pp. 327–28, Jan. 1992.
[16] K. Endo, H. Ishikawa, P. Badica, and K. Kajimura, “MOCVD growth andAFM observation of non c-axis oriented Bi2223 surperconducting thinfilms,” Physica C, vol. 372, pp. 1071–1074, Aug. 2002.