In Situ Growth Studies of Artificial Layered (BA,SR,CA)CUO 2 on Quasi -Ideal SrTiO 3 Substrates by High Pressure Rheed
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GERTJAN KOSTER, GUUS J.H.M. RIJNDERS, DAVE H.A. BLANK, HORST ROGALLA Dept. of App. Phys., Low Temperature Div., University of Twente, PO box 217, 7500 AE, Enschede, The Netherlands. ABSTRACT The layered structure of oxides, like the high-T, cuprates, has been topic of research for some years now. The possibility to control thin film deposition on an atomic level has made fabrication of artificial structures and junctions accessible by depositing atomic layers or molecular blocks sequentially. Perfectly smooth substrate surfaces are hereby a prerequisite. Using Pulsed Laser Deposition (PLD), different perovskite oxide materials have been deposited on SrTiO 3 substrates. With in situ high pressure Reflection High Energy Electron Diffraction we studied growth at different temperatures and oxygen pressures. Ex situ XRD and AFM have been used to study the morphology after deposition. Here we applied a new approach in obtaining layer-by-layer growth implied by the way of depositing the material, almost regardless of the deposition conditions. By alternating intervals of high supersaturation depositing one unit cell layer with intervals of lower supersaturation, one is able to force a layer-by-layer growth mode, which is in principle only feasible with PLD. We applied this technique to fabricate the layered infinite structure (Ba,Sr,Ca)CuO 2 with artificial layered modulation, which have been characterized by XRD and AFM. INTRODUCTION New developments in thin film techniques offer the possibility for atomic engineering of oxide materials. Especially in the case of perovskite-like oxide materials one has the ability to
form new, artificial layered crystal structures. For the infinite layer structure ACuO 2 (A=Ba, Sr or Ca) several groups have fabricated artificial layered structures in search for new superconducting compounds. For superlattices containing only Sr and Ca [1,2], no superconductivity was found, however, Norton et al. have demonstrated superconducting artificial layered structures with Ba and Sr1 .x,Cax grown by PLD [3] The idea is that by periodically inserting layers where smaller cations are substituted for larger cations, extra oxygen may be incorporated thereby creating charge carriers. Later, Balestrino et al. also found superconductivity using the same deposition technique, however only in case of superlattices with Ba and Ca [4]. Both groups verified the artificial periodicity of the as-grown films with XRD [5], after calibration of the growth rates of the individual constituents by thickness measurement. In this paper we present RHEED in combination with PLD as a suitable Atomic layer-bylayer or Molecular Block-by-Block (ALL) technique to monitor the growth of the 'infinite layer' system. For this, the RHEED monitoring system, usually used at a low pressure, has been modified to operate at relatively high oxygen pressures needed for the synthesis of oxide materials by PLD [6]. In order to use RHEED as a growth rate monitor, it is necessary that the growth proceeds in a layer-by-layer (2D) mode.
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