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The deconvoluted spectra are similar to spectra shown for pure components. Plots of intensity ratios (ana1yte:internal standard) showed the same nonlinear behavior observed for one- and twocomponent samples. Regression data for the linear regions of the three-component samples are included in Table 111. Some comparisons can be made among the three data sets in Table 111. First, because the amount of PABA in the two-component samples was twice that in the three-component samples (500 ng vs. 250 ng), the slopes for 1-NA and 4-BI are expected to differ by ratios of 1:2. Slopes for 4-BI (0.0043 vs. 0.0084) are very close to the expected ratio; however, values for 1-NA (0.0022 vs. 0.0055) differ a bit more than expected and we are unable to explain this difference. T h e relative uncertainties in slopes are significantly less for the twocomponent mixtures than they are for either the singlecomponent or three-component samples. The ratios of standard errors to the averages of the ordinate values are about twice &S small for the two- and three-component samples as they are for the one-component samples (-2.5% vs. 3.5 to 6 % ) suggesting that the internal-standard method does improve the scatter in the calibration plots by a significant amount. It is clear from these data that the internal-standard method offers significant advantages for the phosphorescence studies, and the method is made possible by the multiwavelength SIT detector and the simultaneous multicomponent kinetic methods developed in this laboratory. In this work, we used only one wavelength for each component. Earlier work with absorbance data has shown that multiwavelength data obtained with imaging detectors can
be used to resolve multicomponent mixtures (15). It has also been shown that multiwavelength absorbance and kinetic data can be combined effectively to resolve mixtures (10). It may be that the combination of these techniques to the phosphorescent data would improve the within-run and between-run imprecision of mixtures toward the limiting value of the within-run imprecision for single components. We are presently investigating this possibility.
LITERATURE CITED (1) C. M. O'Donnell and J. D. Winefordner, Clin. Chem. (Winston-Salem, N . C . ) , 21, 285 (1975). (2) R. M. Wilson and T. L. Miller, Anal. Chem., 47, 256 (1975). (3) Y. Talmi. D. C. Baker, J. R. Jadamec, and W. A. Saner, Anal. Chem., 5 0 , 937A (1978). (4) E. M. Schulman and C. Walling, J. Phys. Chem.. 77, 902 (1973). (5) R. A. Paynter, S. L. Wellons, and J. D. Winefordner. Anal. Chem., 46, 736 (1974). (6) S. L. Wellons, R. A. Paynter. and J. D. Winefordner, Specfrochirn. Acta. Part A. 30, 2133 (1974). ( 7 ) E. M. Schulman and R. T. Parker, J. Phys. Chem., 81. 1932 (1977). (8) M. J. Milano. H. L. Pardue. T. E. Cook. R. E. Santini. D. W. Maraerum. . and J. M. T.'Raycheba, Anal. Chem.,' 46, 374 (1974). (9) H. L. Felkel, Jr.. and H. L. Pardue. Anal. Chern.. 49, 1112 (1977). IO) G. M. Ridder and D. W. Margerum, Anal. Chem., 49, 2098 (1977). 11) B. G. Willis. W. H. Woodruff, J. R. Frysinger, D. W. Margerum. and H. L. Pardue, Anal. Chem., 42, 1350 (1970). 12) G. E. Mieling and H. L. Pardue, Anal. Chem., 50, 1611 (1978). 13) H. L. Felkel. Jr.. and H. L. Pardue. Ciin. Chem. ( Winston-Saiem. N.C.h I
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Received for review January 11, 1979. Accepted March 2, 1979. This work was supported by Grant No. CHE 75-1550 AD1 from the National Science Foundation.
Chemical Analysis and Structural Characterization of Transition Metal Disulfide Intercalates Steven L. Suib, Larry R. Faulkner, and Galen D. Stucky" School of Chemical Sciences and Materials Research Laboratory, University of Illinois, Urbana, Illinois 6 180 1
Richard J. Blattner Materials Research Laboratory, University of Illinois, Urbana, Illinois 6 180 1
Controlled potential electrolysis has been used to synthesize intercalates of single crystal transition metal disuifldes. Electrochemical experiments using cyclic voltammetry were undertaken to study the process of intercalation. Cyclic voltammetric studies of aqueous solutions of CuS04 and RhCI, have revealed two quasi-reversible couples for single crystal 2H-MoS2 working electrodes and irreversible behavior with 2H-TaS2 single crystal electrodes. Auger electron spectroscopy (AES), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and X-ray powder dlffractometry have been used to determine the analytical and structural composition of these intercalates. Our results indlcate that thlck and laterally nonuniform eiectropiatlng occurs with ~H-MOS,, whereas intercalation predominates with 2H-TaS2.
Over the past several years, chemists, physicists and materials scientists have studied intercalation of layered compounds. Recently, intercalates of transition metal di0003-2700/79/035 1-1060$01.OO/O
chalcogenides have been of interest for a number of theoretical and practical reasons, including superconductivity and battery studies ( 1 , 2 ) . Whittingham ( 3 ) has shown that metal dichalcogenide intercalates of group 4B and 5B can be produced electrochemically by controlled potential electrolysis of aqueous salt solutions using metal chalcogenide cathodes. Other workers (4-6) have reported similar findings. Little work has been reported concerning the chemistry of these compounds and virtually no spectroscopy has been applied to compounds of this type. Little concentrated effort has been made to clearly identify both the chemical composition and structural characteristics of the metal dichalcogenide intercalation compounds. In the present paper, Auger electron spectroscopy has been employed to analyze the surface composition of the intercalates, to check for changes of in-depth composition, and to obtain information about impurities introduced during the intercalation process. At the same time, scanning electron microscopy coupled with energy dispersive X-ray analysis experiments has been carried out to monitor the bulk analytical composition and structure of these materials. Our (C 1979 American Chemical Society
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Flgure 1. Cyclic voltammogram of CuS04 solution with MoS, working electrode. Scan rate: 66 mV/s. Supporting electrolyte: 0.1 M KCI
objective was to prepare transition metal intercalated metal disulfide compounds and to find methods that would clearly identify the compounds as being intercalated. Specifically, we originally tried to isolate transition metal intercalates with group 5B and group 6B dichalcogenides. Our synthetic experiments included the cyclic voltammetry and bulk electrolysis of C u S 0 4 and RhC1, aqueous solutions with both pressed powder and single crystal 2H-MoS2 and 2H-TaS2 working electrodes. Subsequent chemical analysis using Auger electron spectroscopy, scanning electron microscopy, and energy dispersive X-ray analyses was undertaken. EXPERIMENTAL Apparatus. Cyclic voltammograms and controlled potential electrolyses were carried out with a Princeton Applied Research Model 173 Potentiostat with a custom-built ramp generator. All SEM work was performed on a JEOL JSM-US scanning electron microscope at a primary beam energy of 25 keV or 35 keV and a nominal resolution of 5200 A. The JEOL JSM-US also provides elemental analysis via an energy dispersive X-ray system. All SEM photos are of the (001) face of the metal disulfide or intercalate. Auger electron spectrometric analyses were performed with a Physical Electronics Model 545 scanning Auger microprobe. The samples were mounted on the standard carousel at 30' grazing incidence to the primary electron beam. The sample chamber Torr prior to all analyses. Primary residual vacuum was
