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EPITAXIAL ON

GROWTH SINGLE

OF Bi Sr CuO THIN FILMS CRYSTAL SURFACES.

Takuya Matsumoto, Tomoji Kawai, and Shichio Kawai, The Institute of Scientific and Industrial Research, Univ.,8-1 Mihogaoka, Ibaraki, Osaka 567 Japan.

Osaka

ABSTRACT Epitaxial growth of Bi 2Sr2CuO6 thin films on a SrTiO a misoriented SrTiO3 and a Bi 2 ýr 2iaCu2 8 single crystal have Leen performed using computer-control ed laser molecular beam epitaxy. On the SrTiO3 substrate, the 2201 films consist of two types of domains whose b-axes are perpendicular to each other. In contrast, the 2201 film on the 2212 single crystal has a complete single type of domains. Layer-by-layer growth with a half unit cell thickness of 2201 films Is observed. 1.INTRODUCTION The growth mechanism of metal oxide thin films is interesting from the view point of crystal growth chemistry. The question is what kind of minimum growth unit they have for these material and what kind of growth process occurs dominantly during the growth. The BI Sr 2 Cu0 6 (2201)

superconductor is

the most simple crystal in the series of Bi-

system. The growth mechanism of this crystal has, however, not yet been investigated adequately. To apply the Bi-system for electronic device, it is necessary to understand the influence of substrate on the epitaxial growth. In this works, we have performed the epitaxial growth of 2201 thin films on SrTiO misoriented SrTiO3 and Bi 2 Sr 2 CaCu 2 O8 (2212) single crystas using computer-controlled laser molecular beam epitaxy. The 2201 film grown on 2212 single crystal is especially interesting because the growth is expected to be pseudo-homoepitaxy. The surface structure of 2201 films is observed by in-situ reflection high energy electron diffraction (RHEED).

N02 Gas

Fig.l. The apparatus for . computer controlled laser MBE. .

CCD C~oa HEED

Mat. Res. Soc. Symp. Proc. Vol. 237. 01992 Materials Research Society

536

2.

EXPERIMENTAL

Fig.l shows the apparatus of our computer controlled laser MBE. This system consists of an ultra-high vacuum (UHV) chamber that has a base pressure of 10-10 mbar. The beam of an ArF excimer laser (193nm) is focused on a single target. The target is held on a rotating disk controlled by a pulsed motor, so that the laser beam always hits a fresh surface. The deposition rate measured by a quartz thickness monitor is found to be in proportion to the number of the laser pulses. The target is reaction method with prepared by a conventional solid-state 0 Ablated species from the target compositions of Bi 2 3Sr2Cu are accumulated on a 2121s'ingle crystal substrate placed at a distance of 5 cm in the opposite side of the substrate which is heated at 640 C. The N02 gas as an oxidizing agent is effused from a nozzle. Its orifice is 4.3 mm in diameter at a distance of 5 cm from the substrate. The operating pressure of the N02 5 mbar during the film formation. The gas is typically 1x10is operated at an incident energy of 20 RHEED gun (Physitech) keV. The RHEED patterns are taken by a CCD camera (Hamamatsu C3077) and recorded into a V