Anal. Chem. 1980, 52,2213-2214 (20) Oida, M.; Aritaka, T. Nippon Ganka Gakkai Zasshi 1978, 8 0 , 1225. (21) Meffert, H.; Diezel, W.; Sonnichsen, N. Experientia 1978, 32, 1397. (22) Smith, J. 8.;Ingerman, C. M.; Silver, M. J. J. Lab. Clh. Med. 1978, 88, 167. (23) Funasako, M.; Yamaji, I.; Makayama, I.; Tsuda, T.; Hamaro, Y. Rinsho Kagaku 1975, 16, 614. (24) Murata, R. Osaka-shiritsu Diagaku Igaku Zasshi 1978, 25. 209. (25) Placer, 2.A.; Cushman, L. L.; Johnson, B. S. Anal. Bioctmm. 1968, 16, 359 and references cited therein. (26) Ke, P. J.; Woyewoda, A. D. Anal. Chim. Acta 1979, 706, 279 and references cited therein. (27) Gutteridge, J. M. C. Anal. Biochem. 1975, 69, 518 and references cited therein. (28) Gutteridge, J. M. C., HRC CC J . H&h Resolut. Chromatogr. Chromatcgr. COmmUn. 1978, 1 , 311 and references cited therein. (29) Arya, S.S.;Yadugiri; Parihar, D. B. J. FoodSci. Techno/. 1974, 1 1 , 226. (30) Bond, A. M.; Briggs, M. H.; Deprez, P. P.: Jones, R. D.; Wallace, G. G. Lancet 1960, 1087. (31) Schauenstein, E.; Esterbauer, H.; Zollner, H. I n "Aldehydes in Biological Systems. Their Natural Occurrence and Biological Activities"; Lagnado. J. R., Ed.; Gore, P. H., Translator; Pion, Academic Press: London/New York, 1977; pp 133-140 and references cited therein. (32) Marnett. L. J.; Reed, G. A. (ICRDB Special Listing) Current Cancer
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Research on Effects of Chemical Carcinogens on Nucleic Acids, Proteins and Chromosomes: Dec 1978; p 27. (33) Marnett, L. J.; Tuttle, M. A. Cancer Res. 1980, 4 0 , 276.
A. M. Bond* P. P. Deprez R. D. Jones G . G . Wallace Division of Chemical and Physical Sciences Deakin University Waurn Ponds 3127, Victoria, Australia
M. H. Briggs Division of Biological and Health Sciences Deakin University Waurn Ponds 3217, Victoria, Australia
RECEIVED for review August 15, 197!3. Resubmitted July 31, 1980. Accepted July 31, 1980.
Quantitative Surface Analysis of Copper-Nickel Alloys by Secondary Ion Mass Spectrometry Sir: Secondary ion mass spectrometry (SIMS) is estabS+ is extremely sensitive (15)to the chemical environment lishing a place for itself among surface analytical techniques of the specific element, e.g., an increase in S+ of the order of (1) largely due to its extreme sensitivity ( 2 ) (lo4 monolayer 102-103 occurs upon oxidation or oxygen coverage of a clean for some metals and some molecules), the detectability of all metal surface. Benninghoven (15) has determined absolute elements as well as isotopic and isomer sensitivity ( 3 ) ,the secondary ion yields for many clean and oxygen-covered ability to access working surfaces ( 4 ) such as catalysts and metals. electronic devices, and sensitivity to molecular and crystal We have applied eq 2 to the I C u + / l N i + SIMS ratio obtained structure in the outer two to three atomic layers of a material from a series of CuNi alloys for which the bulk composition was accurately known and the surface composition after Ar+ (5, 6). The ability to ionize and detect large involatile and thermally fragile molecules deposited on metal surfaces (7? bombardment had been determined (16) by Auger electron 8) and matrix-isolated organic species (9) has also been demspectroscopy. The alloy samples were obtained from Tohoku onstrated. Quantitative analysis by SIMS has not been as University, Sendai, Japan, and the method of Auger analysis fruitful as these other applications due to large variations in of the surface composition after Ar+ bombardment has been the secondary ion yield as a function of chemical environment, published previously (16). Details of the design of the SIMS i.e., the so-called matrix effect (10). The purpose of this system and pumping facilities have been described elsewhere correspondence is to show that SIMS can provide precise (12). The SIMS were acquired by pulse counting techniques quantitative surface analysis in cases where the absolute using a 3-keV primary Ar+ current of lo4 A/cm2. The samples secondary ion yields are known. A series of CuNi alloys of were cleaned in the UHV system by heating to -800 "C and known surface composition is used to illustrate this point. then bombarding a t room temperature with Ar+ for periods The positive (negative) secondary ion intensity IMc+(-)of -1 h. After such treatment, the SIMS yield of impurity [count/s] for isotope i of element M recorded during ion ions was down in the background level. bombardment of a sample is related to the total yield of The experimental I C u + / I N i + SIMS ratios for several CuNi secondary ions, SM,+(-) [ions/ion], defined as the number of alloy samples which had been pretreated by Ar+ bombardment secondary ions of M, emitted per incoming primary ion, acare plotted in Figure 1 as a function of bulk composition cording to ( 1 1 ) (upper abscissa) and surface composition as determined by Auger electron spectroscopy (lower abscissa) for similar bombarded samples. The Auger spectra show that the surface layers are enriched with nickel after extended Ar+ bomIn eq 1,j o is the primary ion flux [ions/s], [Mi] is the atomic bardment. The Icu+/INi+ ratio was calculated by using the fraction of element M in the target, P(M+) is the detector = 0.003; SNi+ = 0.00s) ion yields (15) for pure Cu and Ni (Sc:u+ efficiency, and T(E,R) is the transmission of the ion optical and the relationship 1 = ([Cu] [Nil) which, substituted in system which depends upon the energy of the ion and resoeq 2 , yields lution setting of the mass spectrometer. The above expression applies to atomic ions and represents a simplification of the complete secondary ion emission process for it neglects the (3) angular dependence of secondary ion emission and cluster ion formation (12-14). With constant spectrometer parameters, where [Nil is the atomic fraction of surface nickel. The plot eq 1 indicates that, to a first-order approximation, the ratio of eq 3 in Figure 1 shows excellent agreement with the exof secondary ion intensities of two elements M and N from perimental data. a given sample can be expressed as These results and their significance can be summarized as follows. (i) The agreement between the calculated and experimental data shows that the alloy surface concentrations determined by SIMS are consistent with those previously
+
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result is expected only if the local electronic environment about each element in the alloy is very similar to that encountered in the pure metal, Le., the so-called “alloying effects” (10) are minimal. Indeed, theoretical studies (17) of the electronic structure of CuNi alloys using the coherent potential approximation (18)have found that charge exchange between the two constituents of the alloy is very small, the constituent atoms remaining essentially neutral as they are in the pure metals. This suggests that SIMS is a powerful tool for investigating alloying effects and electronic structure changes between pure metals and their alloys; the deviation in the ion yield ratio S M , + / S N , + of the alloy from that of the metals is a measure of the electronic perturbation of the alloy matrix. Ln a previous SIMS investigation of solid solutions of transition elements including Cu in Ni, Blaise and Slodyian (19) observed a “reinforcement phenomenon” in the ion production from solute elements on the basis of knowledge of the bulk composition. Our results show that, at least for the CuNi case, this “reinforcement phenomenon” is most likely due to differences in the surface and bulk concentrations. We conclude that SIMS is a powerful technique for determining the surface concentrations of alloys and studying local atomic electronic changes between alloys and their metal constituents. LITERATURE C I T E D Figure 1. The Cu+/Ni+ secondary ion ratio vs. surface and bulk composition (circles) for a series of CuNi alloys. The curve represents a plot of e q 3.
established by Auger electron spectroscopy. (ii) SIMS can be employed for quantitative surface analysis if the ion yields SM,+(-) for elements in specific environments are known. (iii) The empirical calculation of Zcu+/ZNi+ from eq 2 by using the ratio of ion yields SCu+/SNif from the pure Cu and Ni metals, and its agreement with the alloy data indicates that the ion yield ratio for the CuNi alloys is unchanged from that of the pure metals. The first result shows that the SIMS and Auger spectral information result from the same surface region of the sample. The sampling depth of SIMS is only about two to three atomic layers due to the small escape depth of secondary ions. The Auger determinations (16) of the surface compositions were carried out with the Auger peaks near 100 eV for which the electron escape depths are less than 10 A. The second result illustrates the necessity for developing a method of determining and tabulating absolute secondary ion yields for elements in a variety of different chemical environments, i.e., different compounds or matrixes, before SIMS can be used as a general quantitative surface analysis tool. Although Benninghoven (15)has determined such yields for a variety of metals, much work remains to be done before a general tabulation for elements in various compounds can be compiled. The third, and probably most significant, result shows that the ratio of absolute ion sputtering yields from the pure metals Cu and Ni is transferable to the alloys of those metals. This
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(1) Day, R. J.; Unger, S. E.; Cooks, R. G. Anal. Chem. 1980, 52, 557A. (2) Hewitt, R. W.; Shepard, A. T.; Baltinger, W. E.; Winograd, N. Anal. Chem. 1978, 50, 1286. (3) Honda, F.; Fukuda, Y.; Rabalais, J. W. Chem. Phys., 1980, 47, 59. (4) Gardella, J. A., Jr.; Hercules, D. M. Anal. Chem. 1980, 52, 226. (5) Dawson, P. H.; Tam, W. C. Surf. Sci. 1979, 87, 464. (6) Hopster, H.; Brundle, C. R. J. Vac. Sci. Techno/. 1979, 76, 548. (7) Day, R. J.; Unger, S. E.; Cooks, R. 0.Anal. Chem. 1980, 52, 353. (8) Benninghoven, A.; Sichterman, S. Org. Mass Spectrom. 1978, 12, 1180. (9) Jonkmn, H. T.; Michl, J.; King, R. N.; Andrade, J. D. Anal. Chem. 1978, 50, 2078. (10) Deline, V. R.; Katz. W.; Evans, C. A., Jr. Appl. Phys. Lett. 1978, 33, 832. (11) G i m a a c k , K. I n “Inelastic Ion-Surface Collisions”; Toik, N. H., Tully, J. C., Heihnd, W., Whtte, C. W., Eds.; Academic Press: New York. 1977; p 153. (12) Honda, F.; Lancaster, G. M.; Fukuda, Y.; Rababis, J. W. J. Chem. Phys. 1978, 69, 4931. (13) Lancaster, G. M.; Honda, F.; Fukuda, Y.; Rabalais, J. W. J. Am. Chem. Soc. 1979, 107, 1951. (14) Honda, F.; Fukuda, Y.; Rabahis, J. W. J. Chem. Phys. 1979, 70, 4834. (15) Benninghoven, A. Surf. Sci. 1975, 53, 596. (16) Watanabe, K.; Hashiba. M.; Yamashina. T. Surf. Sci. 1977, 69,721. (17) Seib, D. H.; Spicer, W. E. Phys. Rev. 6: Solid State 1970, 2, 1676. (18) Soven, P. Phys. Rev. 1969, 778, 1136. (19) Blaise. G.; Soldylan, G. J. Phys. (Orsay, F r . ) 1974, 35, 237.
Yasuo F u k u d a F u m i h i r o Honda J. Wayne Rabalais* Department of Chemistry University of Houston Houston, Texas 77004
RECEIVED for review June 9, 1980. Accepted August 4,1980. This material is based upon work supported by the National Science Foundation under Grant No. CHE-7915177.
Kinetics of Back-Extraction of Nickel Dithizonate Sir: It has already been demonstrated that for many metal chelate systems the rate of extraction as well as the yield increases in inverse proportion to the hydrogen ion concentration. This can be attributed to a mechanism in which the rate-determining step is the reaction of the hydrated metal 0O03-2700/80/0352-2214$01 .OO/O
ion with the ligand anion, whose aqueous phase concentration naturally increases as the [H30f] decreases. By the same token one might expect the back-extraction rates to increase with increasing [H,O+]. If this is the case, as was indicated in preliminary experiments, it becomes interesting to explore 0 1980 American Chemical Society
