The Influence of Deposition Pressure on the Incorporation of Target and Ambient Oxygen Into Laser Ablated Material
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THE INFLUENCE OF DEPOSITION PRESSURE ON THE INCORPORATION OF TARGET AND AMBIENT OXYGEN INTO LASER ABLATED MATERIAL M. ZHU TIDROW,* S.C. TIDROW** W.D. WILBER AND R.L. PFEFFER U.S. Army Research Laboratory, Electronics and Power Sources Directorate, Attn: AMSRL-EP-EC-H Fort Monmouth, NJ 07703-5601. *Geo-Centers, P.O. Box 428, Newton Upper Falls, MA 02164 **National Research Council Associate
ABSTRACT Oxygen plays an essential role in the growth of a variety of oxides such as high-Tc superconductors, ferroelectrics, ferrites and dielectrics. The oxygen available for film growth during laser ablation can come from two sources: the target material and the ambient deposition atmosphere. The amount of oxygen incorporated from these two sources at room temperature has been investigated over a range of deposition pressures. This was accomplished using 180 as a tracer during pulsed laser deposition of amorphous films from Cu and CuO targets. It was found that the total amount of oxygen incorporated by the amorphous films increases with chamber pressure up to approximately 35 mTorr. For pulsed laser deposition from the oxide target, the major fraction of the oxygen within the deposited material comes from the target. For the oxide target, the amount of oxygen incorporated from the ambient atmosphere is strongly pressure dependent with a maximum near 35 mTorr. These results are compared to earlier work with YBa 2 Cu30 7. INTRODUCTION Laser ablation has become a popular method for the deposition of many different materials, particularly oxides [1]. One of the advantages of laser ablation, or pulsed laser deposition (PLD), when compared to other deposition methods such as sputtering and chemical vapor deposition, is that controlling the stoichiometry of a multicomponent thin film is relatively easy. However, controlling volatile elements can be difficult even for PLD. For the successful deposition of oxides, achieving the proper oxygen stoichiometry is a critical factor. Understanding the mechanisms by which oxygen is incorporated into laser ablated material is an important step in learning how to control the oxygen stoichiometry of films grown by PLD. During PLD of an oxide, the oxygen necessary for film growth can come from two sources: 1) the ambient atmosphere of the deposition chamber during deposition; and 2) the bulk oxide material used as the target. In order to differentiate between these two sources of oxygen, we have used a deposition atmosphere enriched with 50% 180. By measuring the fraction of 180 present in the deposited material, one can determine the source of the incorporated oxygen. We assume that the 180 and the 160 isotopes behave identically Mat. Res. Soc. Symp. Proc. Vol. 311. ©1993 Materials Research Society
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during the deposition process; they are the same electronically and the small mass difference between 160 and 180 is an order of magnitude less than the difference in mass between oxygen and either yttrium, barium or copper. A third source of oxygen, the atmosphere of the deposition chamber af
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