Preparation of Substrates for IBAD-MgO Coated Conductors
- PDF / 307,042 Bytes
- 5 Pages / 612 x 792 pts (letter) Page_size
- 64 Downloads / 188 Views
1001-M04-02
Preparation of Substrates for IBAD-MgO Coated Conductors Vladimir Matias1, Jens H‰nisch1, E. John Rowley1, Chris Sheehan1, Paul G. Clem2, Noriyuki Kumasaka3, and Ichiro Kodaka4 1 MPA-STC, Los Alamos National Laboratory, Mail Stop T004, PO Box 1663, Los Alamos, NM, 87545 2 Sandia National Laboratories, Albuquerque, NM, 87185 3 Nihon Micro Coating Co., Tokyo, Japan 4 Mipox International Corp., 25821 Industrial Blvd., Hayward, CA, 94545 ABSTRACT We examine the influence of various substrate preparation procedures for ion-beam assist deposition (IBAD) texturing of MgO. IBAD-MgO nano-texturing is very sensitive to the nucleation surface, and surface roughness has an important influence on the texture of the MgO layer. We studied Hastelloy C-276 metal alloy as the substrate. The untreated substrate is leveled by either electropolishing, mechanical polishing or solution deposition. All three methods are applied to continuously moving tapes in long lengths. The RMS surface roughness decreases from 20-50 nm for the untreated substrate to 0.5 nm, 0.3 nm and 1 nm respectively. The in-plane and out-of plane crystalline alignment of the MgO layer improves as the roughness is decreased below 2 nm. INTRODUCTION Ion-beam assisted deposition, or IBAD, where an ion beam is impingent during vapor deposition of a film, has been used successfully for fabrication of textured templates for second generation high temperature superconducting wire, known as coated conductors. For a review of IBAD templates see Refs. [1, 2]. Of particular interest are the ìfastî IBAD materials where the texture develops in the first few nanometers of film deposit, i.e. at nucleation of the film. MgO was the first such material to be discovered by the Stanford University group in 1995 [3]. The work on application of IBAD-MgO to coated conductors has continued subsequently at Los Alamos National Laboratory [2] and SuperPower [4]. Preparation of substrates for IBAD-MgO has been a topic of some research in the past [5, 6]. In general, the observation was that to get near-optimum texturing in the IBAD layer, one needed fairly smooth substrates with a RMS surface roughness of 2 nm or less, on a few micrometer surface scale. Here we present a more detailed comparison of substrate preparation and show that the average surface roughness is indeed a good measure of the surface quality needed for IBAD texturing, as measured by the mosaic spreads in, and out of, the film plane. This is true when the surface roughness is less than about 2 nm. In contrast to this, it appears that above 2 nm RMS roughness other qualifications of the IBAD layers and surface condition may be needed.
EXPERIMENT A schematic of our IBAD deposition system is shown in Figure 1. Reel-to-reel tape transport is used for a continuous feed of substrate [7]. We use an electron-beam evaporator and a 22-cm long Kaufmann ion source for the IBAD process. The source material is MgO and a neutralized Ar+ ion beam has an ion energy of 1000 eV oriented at 45∞ with respect to the substrate. The fi
Data Loading...
