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Submitted on 1 Jan 1989
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DIRECT OBSERVATION OF ATOMIC IMAGE OF HIGH Tc SUPERCONDUCTORS BY FIELD ION
MICROSCOPY
Q. Gao, Zhen Zhang, S. Xu, S. Feng, S. Wang
To cite this version:
Q. Gao, Zhen Zhang, S. Xu, S. Feng, S. Wang. DIRECT OBSERVATION OF ATOMIC IMAGE OF
HIGH Tc SUPERCONDUCTORS BY FIELD ION MICROSCOPY. Journal de Physique Colloques,
1989, 50 (C8), pp.C8-487-C8-488. �10.1051/jphyscol:1989883�. �jpa-00229981�
COLLOQUE DE PHYSIQUE
Colloque C8, Supplement au nOll, Tome 50, novembre 1989
DIRECT OBSERVATION OF ATOMIC IMAGE OF HIGH T, SUPERCONDUCTORS BY FIELD ION MICROSCOPY
Q.J. GAO, Z.X. ZHANG*, S.Y. XU, S.Q. FENG and S.Z. WANG
Fepartment of Physics, Beijing University, Beijing 100871, P.R. China Department of Radio-Electronics, Beijing University, Beijing 100871, P. R . China
Abstract---The structure of superconducting Bi2Sr2CalCu208+f has been examined in atomic detail by field ion microscopy. According to our results we suggest that only the copper end planes are preferentially imaging in superconducting Bi Sr Ca Cu 0
2 2 1 2 8+6' The atomic image of YBa2Cu307-x
-
covered tungsten tip has also been examined.The dbcovery 6y Maeda et al, /1/ of high T superconducting Bi-Sr-Ca-CUTO system led to the subsequent study by Tarascon et al. /2/ and other scholars. They concluded that there are two superconducting phases, the low-T phase (85K) and the high-Tc phase (ILOK) in this system.
Tarascon et al. gave the crystal kbstructure of Bi Sr Ca Cu 0 with a = b = 3.818i, c=30.6h.
2 2 1 2 8
Zhu et al. /3/ suggest that a main phase with orthorhombic symmetry in Bi-Sr-Ca-Cu-0 system was found to be a=5.44d, b=5.35; and cz30.66h. Electron diffraction performed on these crys- tals showed an incommensurate superstructure, that is modulated structure, along b direction.
In this first study we focus on imaging Bi2Sr2CalCu208+r by FIM. We chose the nominal compo- sition of 1112 or 1113 ( denoted by cation stoichiometry ) superconducting Bi2Sr2CalCu208+6 which were synthesized by solid state reaction method. The sample tips were prepared from
small sharp-pointed fragments which were got by crushing the superconducting ceramic flakes.
Atomic resolution images were obtained with either argon or neon as imaging gas.
Atomic resolution images of the 2212 superconducting phase show almost parallel doublet rows of image spots separated by nonimaging layer as shown in Fig.1. Measured spacfngs and d d t h of these doublet rows were found to be about 151 and 3-6i respectively, approximately the same as the half of c-axis parameter and the distance between two close copper atoms along c-axis of Bi2Sr2CalCu208. Some brightest spots in the images are likely from adsorbed contamination because of the poor vacuum (at 5x10-' torr). These results were repeatedly observed from dif- ferent tips. The results of transmission electron microscopy study of these tips (after field evaporation and FIM imaging as shown in Fig.2) shows that the complicated modulated structure along 1:110] direction and the orientation of the needle axis perpendicular to the C-axis.
Compared with the crystal substructure given by Tarascon et al., we suggest that only the Cu
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1989883
end planes are preferentially imaging.
Recently perfect epitaxial growth of superconducting YRa Cu 0 thin films have been achieved 2 3 7-x
on (loo), (110) SrTiO and (100) Zr02 substrates using a modffied planar dc magnetron sput-
3 6 2
tering system and the critical current density of 1.4~10 A/cm at 77K has been measured on (100) SrTi03 substrate by Xiong and Wang 141. A YBa Cu 0 epitaxial thin layer covered on
2 3 7-x
tungsten tip was produced in dc magnetron sputtering system. The streaking structure has been observed on the surfaces between (011) and (031) of tungsten tip. It has the feature of structure in YBa2Cu307-x, which was revealed by Kellogg./5/ and Melmed 161. And it seems that the streaking structure comes from YBa Cu 0 covered by sputtering on tungsten tip. It is
2 3 7-x
more likely that the (021) or close to (021) plane of tungsten is the favoured plane for the epitaxial growth of YBa2Cu307-x.
The authors acknowledge H.Zhang for supplying the superconducting Bi2Sr2CalCu208+6. materials;
G.Xu, Z.X.Liu, T.Zhang and M.M.Ling for taking part in experiment.
c-axis
of Bi2Sr2CalCu208+6 at about 9%.
2 Onm I
Fig.2. A tip of Bi2Sr2CalCu208+6 after field evaporation and FIM imaging.
/I/ H.Maeda, Y.Tanaka, M.Fukutomi and T.Asano, Jpn. J.A.P.,7(1988)L209.
/2/ J.M.Tarascon, Y.Lepage et al., Phys. Rev.,Bx(1988)9382.
/3/ X.Zhu, S.Q.Feng et al., J. Modern Phys., B2(1988)563.
/4/ G.C.Xiong and S.Z.Wang, submitted to Appl. Phys. Lett., April, 1989.
151 G.L.Kellogg and S.S.Brenner, Appl. Phys. Lett., 2(1987)1851.
/6/ A.J.Melmed, R.D.Shul1, C.K.Chiang and H.A.Fowler, Science., =(1988)176
