Livonia, MI 48154 (USA). [**I This research was supported by the US Department of Energy, Office of Industrial Technologies (OIT), through a contract with ...
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CVD of Ce02-Doped Y203-Stabilized Zirconia onto Dense and Porous Substrates** By Mohammad H. Siadati, Timothy L. Ward,* Jeffrey Martus, Paolina Atanasova, Changfeng Xia, and Robert W. Schwartz Fabrication of dense films of mixed-conducting oxides on porous surfaces is of interest for membrane, sensor, fuel cell, and battery applications. In this work, atmospheric-pressure metal-organic chemical vapor deposition was used to fabricate CeOzdoped Yz03-stabilized Z r 0 2 films on dense silicon and porous alumina substrates. Aerosol-assisted delivery of a toluene solution of the precursors Zr(tfac)4,Y(hfac)3,and Ce(tmhd), was used to deposit films with thicknesses around 1 pm. The effects of carrier gas O2content (0-5 mob%), H 2 0 vapor (0-3.4 mol-%), deposition temperature (3O0-60O0C),and the type of substrate on film morphology, composition, and purity were investigated. The porous substrate had a marked effect on the film morphology, producing a columnar film structure with column diameters that roughly approximated the particle diameter of the substrate (-0.5 pm). Lower temperatures (300 "C) provided a more uniform film with better connectivity between columnar structures than deposition at 400 and 600 "C, and higher precursor concentrations produced very non-uniform films with exaggerated growth features. Keywords: MOCVD, Zirconia, P-Diketonate, Film, Porous substrates
1. Introduction Yttria-stabilized zirconia (YSZ) is a well-known multicomponent oxide with diverse properties and a variety of potential applications. Its oxygen ionic conductivity along with its excellent chemical and thermal stability at elevated temperatures have made it a viable material for applications such as membranes, gas sensor$ and fuel cells"] However, the steady-state oxygen permeability of YSZ in the absence of electrodes and an external circuit is limited by the value of its electronic conductivity, which is very To improve its electronic conductivity, ceria14] and terbia,[5*61 whose cations are multivalent, have been incorporated as dopants into the YSZ. Oxygen permeabilities 23 orders of magnitude higher than YSZ have been reported with terbia dopant addition,l6I and about 50 times higher
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Prof. T. L. Ward, M. H. Siadati, €!Atanasova, C. Xia Center for Microengineered Materials Department of Chemical and Nuclear Engineering University of New Mexico Albuquerque, NM 87131 (USA) Dr. R. W. Schwartz Sandia National Laboratories Advanced Materials Laboratory 1001 University Blvd. SE Albuquerque, NM 87106 (USA) J. Martus 14108 Ingram Livonia, MI 48154 (USA) This research was supported by the US Department of Energy, Office of Industrial Technologies (OIT), through a contract with Sandia National Laboratories (DE-AC04-94AL85000). Sandia National Laboratories is a multi-program laboratory operated by Sandia Corporation, a Lockheed Martin company, for the US Department of Energy.
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with ceria additions.[41Another strategy to provide an improved oxygen diffusion rate through this material is to minimize the diffusion resistance by reducing the thickness of the doped Y S Z layer. For this reason, we are interested in fabricating thin, dense films of this material on porous supports in order to maximize oxygen transport (flux) rate and provide mechanical integrity. Vapor-phase techniques for fabricating films of YSZ include metal-organic chemical vapor deposition (MOCVD)[7-231 and electrochemical vapor deposition (EVD)[14-191 on porous supports. EVD involves reaction of metal halides with H20 or 0 2 at very high temperatures inside the pores of a support, with continued deposition after pore blockage via ionic diffusion of oxygen through the deposit. There has also been prior research on MOCVD of the individual oxides, ZrOz, CeOz, and Y203, from P-diketonate p r e c ~ r s o r s . [ ~MOCVD ~~'] can generally be conducted at much lower temperature than halide-based EVD, which can be a significant advantage. The prior MOCVD of these materials has been on dense substrates, and there has been no prior examination of morphology and microstructure evolution on porous substrates. There are contradictory reports in the literature on the necessity of oxidizing agents to provide fully oxidized and carbon-free ZrOz deposits from P-diketonate In this paper, we report investigations on the deposition of ceria-doped YSZ (CYZ) on both dense and porous supports at atmospheric pressure by aerosol-assisted chemical vapor deposition (AACVD) using metal-organic P-diketonate precursors. AACVD has been used previously for MOCVD of Zr02,[12,133 and was used in this work for several reasons. AACVD is capable of delivering a constant ratio of different precursors by virtue of atomization of a
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homogeneous solution of the precursor compounds, which overcomes the complexities associated with controlling two or more different precursor partial pressures during delivery. In addition, the short evaporation time of the precursors when dispersed as micrometer or submicrometer particles minimizes the time that the precursor is exposed to elevated temperatures prior to entering the CVD reactor. This is particularly valuable with precursors that have limited stability at their normal sublimation temperatures, which is common with MOCVD precursors. A variety of film properties are important for the intended applications of thin-film mixed-conducting zirconia materials. These include the crystalline phase content, elemental composition, impurities (such as C), morphology, and microstructure. Phase content, elemental composition, and impurities all impact the ionic and electronic conductivity, and thus directly affect application performance. The microstructure and morphology largely dctermine whether the film will be leak-tight to the passage of gases, as well as affecting mechanical and electrical properties of the film. In the research reported below, we have used both dense and porous substrates to investigate and contrast the growth behavior and morphology of CYZ films deposited from P-diketonate precursors at atmospheric pressure. The effects of 02,H20 vapor, and deposition temperature on the morphology, composition and impurities of the films were also investigated.
2. Results and Discussion 2.1. Deposition on Silicon Substrates All experiments on silicon substrates (native oxide surface) were conducted using atmospheric-pressure aerosolassisted CVD (AACVD), as described in the Experimental section. A precursor solution concentration (total metal) and deposition time of 0.01 M and 2 h, respectively, were used. Figures 1 and 2 show the effect of 0 2 and H20 vapor in the N2 carrier gas on the C contamination in the films, as determined by Auger electron spectroscopy (AES). In Fig-
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Fig. 1. Effect of HzO vapor concentration in carrier gas on C content of asdeposited films at 400°C with different levels of Oz in the carrier gas.
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Fig. 2. Effect of deposition temperature on C content of as-deposited films produced in the absence of 0 2 with different levels 01H20 vapor.
ure 1,it is evident that very high C contamination in as-deposited films occurs in the absence of 02,even when H 2 0 vapor is present (deposition temperature of 400 "C).In the presence of 5 mol-% 02,the C contamination was reduced from approximately 50 at.-% to less than 10 at.-%, with no significant dependence on the presence of HzO vapor. Similar results were obtained in deposition experiments performed with porous alumina substrates in the presence of 5 YO02.These observations do not agree with the results of Balog et al.,[=] who reported good purity Z r 0 2 using the same precursor (Zr tetrakis(trifluoroacetylacetonate), Zr(tfac)4) with or without 02.However, Hwang and Kim reported some metallic nature in films deposited from Zr(tfac)4 with O2 levels below 5 v01.-YO, though they did not explicitly provide C content.[2fi1The importance of 0 2 to reduce C contamination has also been reported for ZrOz deposition from other kdiketonate precursor^.[^,^] These prior reports have not used an organic solvent in precursor delivery as we have; however, we have conducted deposition experiments utilizing solvent (toluene) only and have not observed carbon deposition. We therefore believe that the precursor is the source of C in the films. Deposition temperature also impacts C contamination significantly in the absence of 02,as indicated in Figure 2. In the absence of 02,the C content was significantly lower for films deposited at 300 "C than at 400 "C, and H2O vapor had a substantial impact on the C level at 300 "C, compared with a minimal effect at 400 "C. This indicates that H20 vapor may promote cleaner decomposition of the precursor at lower temperature, where the purely pyrolytic decomposition rate is not so dominant. We have not, however, studied the decomposition mechanism or kinetics sufficiently at this time to verify this. Kim et al.i71reportcd a similar observation on the effect of H 2 0 vapor on ZrOp deposition using Zr acetylacetonate. They found that H2O vapor in conjunction with O2 led to reduced C contamination, but that it was not effective as the primary oxidizing agent. They speculated H20 may be more effective than 0 2 in removing certain C-containing species, especially at lower 0948-1907/97/0611-0312$17.50+.50/0
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Deposition temperatures, which would also be consistent with our observations. Water vapor has also been reported to be superior to O2 for depositing C-free films of A1203from A1 acetylacetonale and ZnO from Zn and to be effective for oxidizing residual fluoride contaminants from Group I1 acetyla~etonates.[~'~ However, the mechanism by which H20 vapor affects MOCVD is still not clear for our results or the prior studies. Our results indicate that the presence of a small amount of O2 in the gas atmosphere is the most important element in reducing C levels to below 10 at.-%; however, this is still a rather high level of C contamination. Though carbon can be removed by calcination in O2 or air, additional work is needed to identify conditions to eliminate C incorporation during deposition. Higher levels of O2 in the deposition chamber were not used due to the fire hazard associated with toluene vapor from the atomized precursor solution (see Experimental). No fluorine contamination was revealed by AES in any of the samples (detection limit 0.30.5 at.-%). The elemental composition of the films was also impacted by the presence of O2 and H20 in the gas phase. Figures 3 and 4 show the elemental composition as Y/Zr 0.3
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and Ce/Zr ratios for films deposited under varying O2 and H20 levels. The Y/Zr ratio (Fig. 3) was not significantly affected by the presence of H20, but was lowered slightly in the presence of 5 % 02.The Y/Zr ratio was below the nominal (precursor solution) ratio of 0.28 in both the presence and absence of 02.In contrast, the Ce/Zr ratio (Fig. 4) in the films was much lower than the solution value when either 0 2 (5 YO)or H 2 0 vapor (1.8-4.1 YO)was present. Only in the absence of 0 2 and H20 was the Ce/Zr ratio nearly equal to the solution value. This may indicate that the Ce(tmhd), precursor reacts or oligomerizes readily in the gas phase in the presence of an oxidant under the conditions employed here. This would be consistent with other reports on the reactivity of the Ce(trr~hd)~ precursor, which indicate that it should be the most reactive of the precursors used here.[23*241 Composition results obtained using porous substrates were in reasonably good agreement with those from dense substrates. Scanning electron microscopy (SEM) analysis of the films deposited on dense substrates in the presence of O2 typically revealed a columnar growth pattern (Fig. 5a), which led to a nodular, but relatively uniform, surface (Fig. 5b). The nodular features of the deposit surface, which are apparently the tops of growth columns. were approximately 0.1 pm in diameter, which is roughly the column diameter evident in the film cross-section. The contact between the grains at the surface appeared good in the plan view SEM (Fig. Sc). The film in Figure 5 was obtained with 5 % O2 and 1.8 % H 2 0 vapor.
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The examination of microstructure and morphology was then extended to atmospheric pressure AACVD of Ce-YZ r - 0 onto porous a-A1203substrates. These disc supports were fabricated in our laboratory, as described in the Experimental section. The experiments conducted with porous supports were all done using 5 YO 0 2 and 2.5 % H20 vapor in the carrier gas, and the effects of temperature and precursor concentration were investigated. Limited elemental composition data were obtained for the films on porous supports. However, the data for a film deposited at 400 "C using 0.01 M precursor solution are included in Figures 1 , 3 , and 4 for comparison with the dense substrate results. The C contamination, lack of F contamination, and elemental ratios of the films on porous substrates were consistent with the films deposited on silicon substrates. X-ray diffraction (XRD) of as-deposited films on porous substrates revealed the peaks of the (r-A1203substrate and broad features of very fine-grained stabilized Zr02 (Fig. 6). Peak width analysis of Figure 6 using the Scherrer equation indicated a crystalline grain size of approximately 4 nm. Such a small grain size is not surprising for low temperature deposition. There was no evidence of secondary oxide phases in any of the experiments.
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Fig. 5. Three SEM views of a CYZ film deposited on Si substrates at 400°C in an atmosphere of 5 % O2 and 1.8% H20: a) cross-sectional view, b) plan view, and c) 45" angle view of top surface revealing topology of surface.
which was indicated to be much smaller by XRD. From the cross-sectional views in Figure 7, the growth of all the films has a columnar nature. At 300 "C a columnar nature cannot be definitely established because the film thickness is comparable to the grain diameter, giving the grains similar dimensions in all directions. The improved connectivity between columnar grain boundaries at 300 "C is also evident in the cross-sectional SEM. Although these Pilms appear similar in thickness based on SEM observations, mass measurements of the deposits (error about +1 %) indicated a decrease in the average deposition rate at 600 "C (Fig. 8). This could be an indication of gas-phase reaction, leading to precursor decomposition before reaching the substrate. For example, gas-phase reactions may become significant in the thermal boundary layer that approaches the substrate surface at the higher temperature. However, natural convection in downward impinging flow reactors is very sensitive to substrate temperature, and can cause substantial effects on diffusional (and thermal) boundary layers, which could lead to a decrease in transport of the precursors to the substrate. Our data do not allow us to distinguish between these two related explanations. The column diameter on the porous-supported deposits was typically similar to the particle diameter of the underlying support, though it was somewhat larger in the 300 "C deposit, as noted previously. In contrast, the depos-
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Fig. 6. X-ray diffraction of film deposited at 400°C onto porous a-AlzO3 substrate.
Figure 7 shows SEM plan and cross-sectional views of films deposited onto porous supports at temperatures of 300, 400, and 600 "C using a precursor concentration (total metal) of 0.01 M. There was a very evident change in the morphology of the deposit surface with changing deposition temperature, especially between 300 and 400 "C.The size of grains at the surface at 300°C was larger and the grains were much better connected than at higher temperature. Here, "grains" refers to the main morphological growth features, rather than the true crystalline grain size,
Fig. 7. Cross-sectional and plan views (SEM) of CYZ films deposited onto porous a-A1203substrates at temperatures of a) 300 "C, b) 400 "C,and c) 600 "C under conditions of 5 % O2 and 2.5 % H20 in the carrier gas.
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Fig. 8. Effect of temperature on deposition rate for AACVD on porous aAi203supports.
its obtained on the dense substrates possessed columns of diameter about 0.1 pm (Fig. 5). The difference in the deposit column size between the dense and porous substrates is probably related to the discontinuous nucleation surface that exists with the porous substrates, as discussed further below. Deposition on the porous substrates resulted in much rougher films that also appeared porous. Proper interpretation of these morphological observations requires an understanding of deposit nucleation and growth on a porous support, which is currently very poor. Gas-phase precursor concentration may also be a very important variable in defining deposition rate and deposit characteristics. At 400 "C and a total precursor concentration of 0.05 M (five times higher than the experiments described previously), a deposit morphology was obtained which appeared somewhat columnar in nature (Fig. 9), but
Fig. 9. Cross-sectional (a) and plan (b) view SEM of films produced using precursor total metal concentration of 0.05 M.
with much more non-uniformity in the morphology and column height. The film was also considerably thicker for the same deposition time than at a total precursor concentration of 0.01 M. The mass deposition rate at 0.05 M and 400°C was approximately twice that at 0.01 M. Figure 10 contrasts at higher magnification the columnar morphology of films deposited using 0.01 M and 0.05 M solution concentration. Under the same flow and temperature conditions, either reaction- or transport-limited deposition would be expected to give a deposition rate directly proportional to precursor concentration. The weaker dependence observed here might be explained by either gas-phase reaction or incomplete precursor particle evaporation at the higher concentration, which would cause the gas-phase precursor concentration to be less than expected. Though we Chern. Vap Deposition 1997,3, No. 6
Fig. 10. Cross-sectional SEM comparing films deposited at a) 300°C and b) 400 "C using 0.01 M precursor concentration. and at c) 400 "C using 0.05 M precursor concentration. For all films the deposition time was 2 h and carrier gas contained 5 % 0 2 and 2.5 % HzO.
have not conducted experiments to discriminate between these two scenarios, the decrease in deposition rate at 600°C revealed in Figure 8 is supportive of the gas-phase reaction explanation. Comparing the films in Figure 10 deposited at 400°C (b and e), it appears that the columnar structures typically nucleate and grow from a single substrate particle. For films deposited using thc lower precursor concentration, the column diameters are approximately constant across the film thickness. At 400°C with 0.05 M precursor concentration, the morphological structures also apparently started with a diameter of the substrate particle, but many expanded substantially in diameter as they grew upward. This type of growth behavior and morphology was not seen at lower precursor concentration, even at higher temperatures. The classical arguments about the competitive effects of nucleation rate, surface reaction rate, and transport rate on CVD morphology in chemical vapor deposition[311provide some insight to these observations. The discussion below presumes continuum regime diff~sion[~'J at the scale of the surface features, which is appropriate at atmospheric pressure and the feature sizes reported here. Assuming that initial deposit nucleation occurs uniformly, deposit growth proceeding from the topmost (most accessible) surfaces of substrate particles probably proceeds in a manner similar to growth proceeding from a smooth dense substrate. However, between the topmost surfaces of the substrate surface particles are spaces where the growth initiation surface is recessed, requiring diffusion of the precursors into the pores or openings. Depending on the relative rates of surface reaction versus diffusion, two distinct deposit morphology types could be expected from: (i) reaction rate much faster than diffusion rate (diffusion-limited at the local scale), and (ii) reaction rate very slow compared to dif-
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fusion rate (reaction-limited at the local scale). In case (i), rapid reaction prevents the precursor from diffusing into pores or openings, leading to localized concentration gradients and producing a deposit which grows only from the separated topmost surfaces of support particles. In this case, localized concentration variations and reaction rates would be expected to produce non-uniform growth features, which might appear similar to the tooth-like growths seen in Figure 1Oc. Non-uniform or slow nucleation relative to growth could also produce similar morphologies. In case (ii), the absence of transport limitations would allow the growth rates from recessed surfaces to be similar to the topmost surfaces. Deposition would proceed on substrate surfaces in a more conformal manner, leading toward pore filling and, eventually, a more level and uniform deposit. This situation is promoted by lower deposition temperatures (slower surface reaction) and lower reactor pressure (enhanced transport). It is likely that the superior structure of the deposit at 300 "C (Fig. 10a) is at least partially due to this effect. It would be instructive to look at even lower temperatures; however, the precursor decomposition requirements generally set the minimum acceptable deposition temperature. Though we have not reported low-pressure results here because we were interested in the features of atmospheric-pressure CVD, we have previously observed low-pressure deposition to provide smoother MOCVD film m o r p h o l ~ g y . [ ~ * ~ ~ ]
3. Conclusions Aerosol-assisted chemical vapor deposition was demonstrated as a suitable technique to produce thin films of controlled-composition multicomponent oxides. Micrometerthick films of Ce02-doped Y203-stabilized Z r 0 2 were deposited onto porous alumina substrates, as well as onto dense silicon substrates. The results indicate that crystalline multicomponent films can be obtained. and that solution composition can be manipulated to change film composition. However, under the deposition conditions investigated, C incorporation into deposits remained at -8 at.-%, though this may be removed with thermal processing. Perhaps the largest obstacle for membrane applications of supported films of these and similar materials is the elimination of film defects that allow gas leakage. This requires a better understanding of the relationships between film morphology and microstructure, and the deposition conditions and substrate characteristics. The work reported here has demonstrated differences in the film morphology for films deposited onto porous substrates compared to those deposited onto smooth dense substrates, which certainly has implications for the fabrication of leak-tight membranes. Deposition temperature, precursor concentration, and gas composition were also shown to have important effects on film morphology and deposition rates. Lower deposition temperature and precursor concentration
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facilitated more uniform films with better contact between morphological grains of the film; whereas higher temperatures and concentrations led to non-uniform growths, which, in the most extreme cases, had very poor intergranular contact. These morphological observations are consistent in a qualitative sense with expectations based on the relative rates of diffusion, reaction, and nucleation. However, more work is needed to definitively determine how these processes govern morphology, microstructure, and, ultimately, the successful fabrication of useful supported thin films such as membranes.
4. Experimental The film fabrication reported here was carried out utilizing aerosolassisted CVD (AACVD) of a toluene solution of P-diketonate precursors Figure 11 shows a schematic of the experimental apparatus. The precursor solution was first atomized in an aerosol generator (TSI Model 3076), and was then passed through a wam-walled (150°C) stainless steel tube, which functioned as an evaporation zone for the solvent and precursor aerosol. The temperature of the evaporation zone was controlled by thermocouple feedback to an Omega CN9000A controller, which powered the heating tape. The carrier gas was NZ with variable O2 content. For some experiments, €120 vapor carried by Nzwas introduced between the end of the precursor evaporation zone and the entry to the CVD reactor. A controlled delivery rate of H 2 0 vapor was obtained by using a small peristaltic pump to deliver water droplets to a glass tube. which had the wall temperature controlled at -150"C, and through which a Nzcarrier gas flowed (Fig. 11). This arrangement also preheated the H20 vapor stream prior to mixing with the precursor vapor stream. The entire gas mixture then flowed to the coldwall reactor where it impinged in a downward flow configuration onto the substratc. which was heated from below by a spot heater lamp (Research Inc. Model 4085). The water vapor was varied from 0 to 4.1 mol-% of the total gas feed. All experiments were carried out at atmospheric pressure (8.3 x 10' Pa) in the reactor. The precursors were Zr(tfac)4 (tfac = trifluoroacetylacetonate), Y(hfac)3 (hfac = hexafluoroacetylacetonate),and Ce(tmhd), (tmhd = tetramethylheptanedionate), used as-received from Strem. We have reported previously on the use of the tmhd compounds of these metals to deposit stabilized zirconia, which required a deposition temperature of 550°C or higher [9]. The combination of precursors reported here enabled deposition to be conducted at lower lemperatures (2.50-30OoC), and provided a better match of decomposition temperatures between the precursors. This is generally desirable whcn trying to deposit multicomponent materials of controlled composition. The precursors were completely dissolved in high purity toluene to provide solutions with a total metal concentration of either 0.01 or 0.05 M. The metal ratio in solution for all of the experiments reported here was Ceo.~sYo.20Zro.7z, which corresponds to a reported single-phase mixed-conducting oxide composition [4]. Toluene was used in preference to tetrahydrofuran, which is also an acceptable and proven AACVD solvent for pdiketonate compounds [13], because it has lower volatility and leads to less solvent concentration due to evaporation in the atomizer. Flammability and explosion hazards must be considered using atomizcd organic solvents at high temperature in the presence of 0 2 . For the work reported here at atmospheric pressure, O2 levels were kept at 5 mol-% or lower to avoid explosion hazards. We and others have reported safe operation at higher relative oxygen levels using reduced operating pressures [9,13]. Two types of substrates were used for film deposition: silicon (native oxide surface) and porous a-A1203fabricated in our laboratory. The porous alumina substrates were prepared from polycrystalline a-alumina powder (Sumitomo AKP-20, particle diameter = 0.4-0.6 p n ) , which was spray dried with polyvinyl alcohol added as a binder. Disks (OSinch (1.27 cm) diameter) were compacted in a Carver press under 5Ml0 psi (3.5 MPa), and were sintered in air at 1150"C for 4 h. The sintering process served to initiate necking between particles and add strength to the substrate. The pore diameter of the porous supports was approximately 0.5 pm based on scanning electron microscopy (SEM). The samples were characterized by SEM (Hitachi S-SOO), X-ray diffractometry (XRD) (Siemens D-5000), and Auger electron spectroscopy (AES). AES data were collected using a cylindrical mirror analyzer (PHI
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10-155), with an electron beam energy of 3 keV, at a base pressure of torr. The Arm ion gun with ion beam current intensity of 10 mA!cm2 at 1 keV beam energy and 4 x lo-’ torr pressure was applied for etching the surface impurities of the films. Estimation of the elemental composition by AES was based on experimental sensitivity factors. The Auger peaks of C (KLL) at 271 eV, 0 (KLL) at 512-518 eV, Zr (MNN) at 141 eV, Y (MNN) at 121 eV, and Ce (MNN) at 674eV were used for the estimation of the composition and stoichiometry of the samples These AES peak positions correspond to the values measured for the pure oxides; ZrOz, Y203. and CeOz (Aldrich Chemical). The shape and the peak positions for the oxides are different from the handbook values, which refer to metals.1331Therefore, it was expected that the handbook sensitivity factors would also not be adequate for the mixed oxide materials. A standard powder was synthesized, and analysis by X-ray fluorescence and atomic absorption spectroscopy showed a composition of C ~ . o s Y o . 0 6 ~ Z r ~ . zWhen ~ O o . the ~ ~ ~handbook . sensitivity factors were applied to thc A E S spectra of this standard powder, the estimated composition of Ceo.zlYo.lzZro.cnOo.60 was significantlydifferent from the known composition, and indicated the critical need of experimental sensitivity factors The experimental sensitivity factors were obtained from Auger spectra of the pure oxides and the standard mixed oxide powder, and were applied for the estimation of the thin film compositions. A comparison of the experimental and handbook sensitivity factors is provided in Table 1. Received: April 8, 1997 Final version: August 5,1997 Table 1. Comparison of handbook and experimental Auger sensitivity factors. Sensitivity factor for Handbook Experimental[a,b]
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[a] Data taken after 3 min of Ar@sputtering to remove surface impurities. [b] Based on standard powder with composition of Ceo.osYo.NzZro.w400 hR4.
[I] W. L. Worrell, in Solid Electrolytes (Ed S. Geller), Springer, New York 1977. 121 S. F. Palguev, V. K. Gilderman, A. D. Neujmin, J. Electrochem. SOC. 1975,122,745. [3] J. H. Park, R. N. Blumenthal. J. Electrochem. SOC.1989,136,2867. [4] B. Cales, J. F. Baumard, J. Electrochem. SOC.1984,131,2407.
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I Fig. 11. Apparatus for conducting stagnation flow AACVD.
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