47014-AC5
Thin Film Growth of Amorphous Metal-Phosphorus Alloys
The main goals of the research are to investigate fundamental aspects of the chemical vapor deposition (CVD) of thin films of amorphous metallic alloys. Our initial results were based on the use of the single source precursor cis-H2Ru(PMe3)4 for the growth of ultra thin films of amorphous ruthenium-phosphorus alloys (RuP). We have made significant progress in each of three key areas: 1. Organometallic Precursor Synthesis, 2. Construction of New CVD Reactor for Rapid Screening, 3. Film Growth and Characterization Studies.
1. Organometallic Precursor Synthesis. In order to evaluate the effects that precursor composition and structure have on film growth and properties we have investigated the synthesis, characterization and growth of several classes of potentially new organometallic precursors. For phosphorus containing metallic alloys the ideal precursor should have a source of P, a reasonable level of volatility and ligands which can form stable leaving groups during the growth/decomposition process. With these requirements in mind, for Ru, we have prepared precursors based on the bis-trifluoromethyl pyrazolate ligand (Pz) as well as the series of di-hydrides based on trialkyl phosphite ligands of general formula H2Ru(P(OR)3)4 (R= Me, Et, i-Pr) (1-3). New multinuclear Ru complexes based on Pz include Ru2(μ-Pz)2(CO)4(PMe3)2 (4), Ru2(μ-Pz)2(μ-CO)2(PMe3)4 (5), Ru3(μ-Pz)(μ-H)(CO)10 (6), and Ru2(μ-Pz)2(η6-C6H6)2 (7). We have also explored the synthesis of volatile rhodium based organometallic precursors which have the potential for the growth of amorphous RhP films. New complexes here include Rh(PMe3)3(η1-Pz) (8), cis-RhH2(PMe3)3(η1-Pz) (9) and [Rh(PMe3)4]+[Pz]- (10). Complexes 1-10 have all been characterized spectroscopically as well as by single crystal X-ray diffraction studies. We have initiated a systematic evaluation of these compounds as CVD precursors for the growth of amorphous metal-phosphorus alloys.
2. Construction of New CVD Reactor for Rapid Screening. For the most promising CVD precursors our long term goals are to study these materials in collaboration with the research group of Professor John Ekerdt (UT Chemical Engineering) with whom we have had a long term collaborative interaction. The Ekerdt group have access to many of the instruments required for advanced materials characterization studies of thin films, and can perform many measurements in situ without exposure of sensitive samples to the air. However, these studies are time consuming and we quickly realized that we needed a method of rapidly screening new compounds to identify promising new CVD candidates. We therefore designed and built a simple, yet versatile, hot wall, CVD reactor for this purpose and have begun initial screening studies on the compounds noted above. The new reactor is capable of achieving temperatures from room temperature up to ca. 700 °C in the growth chamber and can be operated under partial vacuum (several torr) up to atmospheric pressure with a variety of inert, or reactive carrier gasses (N2, Ar, H2 etc.).
3. Film Growth and Characterization Studies. We have successfully grown thin films of RuP alloys using the new screening reactor with compounds 1-3 (above). These precursors all contain trialkyl phosphite ligands (P(OR)3) which are considerably less expensive than the trialkyl phosphines such as PMe3. Since the bond linkage in these ligands is "P-O-C" an important question is whether or not the O and C atoms are cleanly removed during the growth process. Initial materials characterization studies (XPS, XRD) show that the films are amorphous and contain both Ru, P and O. However, the level of oxygen, as detected by XPS, decreases significantly on sputtering of the surface. Since these samples were exposed to the air it is reasonable to assume that part of the oxygen comes from atmospheric sources introduced after film growth. We are currently investigating film growth and characterization with these compounds under rigorously anaerobic conditions.
Support from the ACS Petroleum
Research Fund has been pivotal to the ongoing success of this project. Three
graduate students have received meaningful levels of financial support, in
addition to the undergraduate SUMR scholar. The multidisciplinary nature of the
research has meant that all the students have been involved in state-of-the-art research in several
important areas including synthesis of new organometallic precursors, CVD
reactor design and fabrication, CVD film growth and materials characterization
studies. A Summer Research Fellowship (SRF) also provided funds to support
Professor John Stankus from The University of The Incarnate Word (UIW),
