OMCVD of thin films from metal diketonates and triphenylbismuth
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I. INTRODUCTION
Metal oxides have a number of electrical and optical properties that make them potentially attractive components for new micro- and opto-electronic devices. Several methods, including organometallic chemical vapor deposition (OMCVD), have been investigated for processing thin films of these materials and all have met with some degree of success and failure.1 One of the challenges facing the use of OMCVD for the growth of any material is the availability of suitable precursors. Various investigators have described the growth of thin films of Y-Ba-Cu-O and Bi-Sr-CaCu-O by OMCVD,2"4 and we now wish to report results evaluating various metal diketonates and triphenylbismuth as potential precursors for films of complex oxides. Of particular interest are the barium compounds since few, if any, were previously thought to have suitable volatility and thermochemical properties for chemical vapor deposition. II. EXPERIMENTAL DETAILS A. Organometallic precursors
The organometallic precursors used in this work are all known compounds and are listed in Table I. The general molecular structures of these compounds are shown in Fig. 1. At the outset, only copper acetylacetonate and triphenylbismuth were known to be commercially available. Copper acetylacetonate, Cu(acac)2, was recrystallized from chloroform and sublimed at 120 °C and 1(T5 Torr. Triphenylbismuth, Bi(Ph)3, was distilled at 105 °C and 10"5 Torr. Yttrium tetramethyiheptanedionate, Y(tmhd)3, was synthesized from YC13 and the sodium salt of the diketone according to published procedures.5 The material was purified by recrystallization from hexane and
sublimed at 125-135 °C and 2 x 10"6 Torr. A melting point of 174-178 °C was measured (literature value 169172.5 °C).5 A chemical ionization mass spectrum, using C4Hio, was obtained from a sample introduced through a heated, direct-insert probe using a Finnigan MAT TSQ70 instrument. Principal mass fragments that were identified and their assignments were as follows: 639 (100%, YC 33 H 58 O 6+ , YL 3 H + , L = CnH 1 9 O 2 ), 185 (YC 5 H 4 O 2+ ), 1093 (Y 2 L 5+ ), 1037 (Y 2 C 5 iH 87 O 10+ , YL 4 H 2 + ), 677 (YC 34 H 52 O 8+ ). A nuclear magnetic resonance spectrum of the material in CC14 contained two singlets, one at 8 = 1.17 ppm and the other at 5.73 ppm, compared to published values of 8 = 1.12 ppm ((CH3)3C-) and 5.74 ppm (-CH). 5 Barium tetramethyiheptanedionate, Ba(tmhd)2, was synthesized in vacuo by the room temperature reaction of barium metal (0.1734 g, 1.263 mmol) with an excess of the parent diketone (0.9422 g, 5.124 mmol) during a 72-h period. The Pyrex reactor was cooled periodically to -196 °C to allow for removal of noncondensable gas (presumably H 2 ). Upon completion of the reaction, the excess diketone was vacuumdistilled from the flask, leaving a white solid (0.6424 g, 1.275 mmol for Ba(tmhd)2, 101.0% yield). A nuclear magnetic resonance spectrum of this material in CC14 contained two singlets, one at 8 = 1.05 ppm and the other at 5.67 ppm, compared to published values of 5 = 1.01 ppm ((
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