Electron Microprobe Analysis of Nickel-Iron-Cobalt Thin Film Wire Memory Elements A. A. Chodos Dioision of Geological Sciences, California Institute of Technology, Pasadena, Calif. 91109 FLATTHIN FILMS of nickel-iron have commonly been analyzed by X-ray fluorescence techniques dating back to about 1958 ( I , 2 ) . Since 1961 the author has used this method to analyze binary and trinary flat thin films on glass substrates nondestructively. The electron microprobe has also been used for the analysis of such films in this laboratory and elsewhere (3). However, because of sample geometry and the need to analyze for cobalt content, the analysis of cylindrical thin films on wire substrates presents an entirely different problem and is the subject of this paper. The wire diameter is commonly 5 mils and the thin film thickness a maximum of a micron. X-ray fluorescence has been used to analyze cylindrical thin films by a solution technique ( I ) as have wet chemical methods (4). The X-ray fluorescence technique utilized small samples but is used only for nickel and iron, For the wet chemical technique approximately 3 feet of wire is required in order to provide sufficient sample to permit cobalt analysis a t the level of concentration of a few per cent. In addition, the cobalt content of the copper plated beryllium-copper wire substrate gives a very high blank with consequent errors in the determination. Inhomogeneities in the cobalt content of the substrate also create problems. The technique reported here permits the simultaneous analysis for nickel, iron, and cobalt in micron and submicron sized cylindrical films. EXPERIMENTAL
Apparatus. An Applied Research Laboratories Model EMX microprobe was used at 15 kV with a specimen current of 0.04 PA. Nickel L alpha radiation was used with a KAP analyzing crystal and iron and cobalt K alpha radiations with LiF analyzing crystals. Nickel background was measured at the nickel peak location in pure cobalt; iron and cobalt backgrounds were measured in pure nickel. Standards were the pure metals. (1) T. Loomis, Bell Telephone Laboratories, Murray Hill, N. J., personal communication, 1967. (2) R. R. Verderber, Norelco Reporter, X , No. 1, 30 (1963). (3) B. W. Schumacher and S. S. Mitra, Proc. 1962 Electronics Components Conf., Washington D. C., May 1962. (4) R. M. Shoho, Autonetics Division, North American Rockwell, Anaheim, Calif., personal communication, 1967.
Table I. a factors
Element Radiation
Fe K
Co K Ni L
Fe
co
Ni
1 0,954 2.195
0.931 1 2.285
0.810 0,940 1
Procedure. Because the film is very thin, the sample is first copper plated and then mounted in epoxy at a shallow angle t o the surface and lapped. The angle lapping presents a greater cross-section of film to the microprobe beam than would be possible if samples were mounted vertically and increases the iron intensity between 20 and 70z. The copper plate prevents the electron beam from coming in contact with the epoxy while the film is being analyzed. Binary alloys of nickel-iron, iron-cobalt, and nickelcobalt were prepared using an induction furnace. These were compared to the pure elements to determine the a factors ( 5 ) which are listed in Table I . Each film was analyzed in the two locations where the angle lapping increased the film cross-section. The beam was kept centered on the film by use of an audio monitor on the iron channel and at last ten 10-second counts were taken at each location. Each reading was corrected for background and calculated as an individual analysis using a reiterative calculation of the type detailed by Lachance and Traill (6) and Bence and Albee (7). After convergence, normalization gives the composition of the film. RESULTS .4ND DISCUSSION
The trinary alloy film does not entirely fill the electron beam. This necessitates simultaneous analysis for all three elements. The spectrometer arrangement of our microprobe is such that only two of these elements can be determined using their K lines. It was therefore necessary to use the weaker L 01 line for Ni. Unfortunately, the mass absorption coefficients for (5) T. 0. Ziebold and R. E. Ogilvie, ANAL.CHEM., 36, 322 (1964). (6) G. R. Lachance and R. J. Traill, Can. Spectry., 11, No. 2-3 (1966). (7) A. E. Bence and A. L. Albee, J . Geol., July 1968, in press.
Table 11. Microprobe Analysis of Chemically Analyzed Alloys and Thin Film Iron Cobalt Nickel Nominal Chem Probe Std dev Probe Chem Sample Nominala Chemb Probec Std dev Nominal 1 2 3 4d a
19.50 18.99 18.07
18.53 18.80 17.56 18.27
19.44 18.48 17.97 18.40 18.01
d
2.50 5.06 9.64
2.53 5.58 9.74 3.50
2.11 5.36 9.87 3.86 3.71
0.07 0.07 0.22 0.07 0.13
78.00 75.95 72.29
78.94 75.61 72.70 78.24
78.45 76.16 72.15 77.74 78.28
Std dev 0.27 0.34 0.21 0.79 0.41
Synthesized by P. Human.
* Analyses by R. Shoho. c
0.35 0.32 0.30 0.73 0.35
Ten points on each sample. Fourth significant figures on all microprobe analyses in this paper are for statistical purposes only. Analysis of two different areas on thin film. ~~
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ANALYTICAL CHEMISTRY
nickel L a radiation in iron or cobalt are not well known (8) and extrapolation from known values gave analyses which were in error by approximately 20%. Therefore the empirical method of Ziebold and Ogilvie (5) was used. As copper K radiation will cause fluorescence of iron K radiation, it is necessary to evaluate any possible effect on the iron determination by the copper in the beryllium-copper substrate and the copper plate. This evaluation was made by copper plating a bulk sample of nickel-iron and taking readings across the interface. At 50% of the iron intensity of the bulk sample, the result was identical to that obtained on the bulk sample. Even at 30% intensity, the iron value was high by only 6% of the amount present, giving 20.2% Fe instead of 19.1% Fe.
(8) K. F. J. Heinrich, “X-ray Absorption Uncertainty,” in “The Electron Microprobe,” T. D. McKinley, Ed., John Wiley and Sons, New York, 1966, p 296.
The a factors were tested by analyzing three bulk samples of trinary alloy and one sample of thin film, all of which had been chemically analyzed. These comparisons are shown in Table 11. The precision of measurement and accuracy compared to chemical analysis is excellent. The method provides a rapid technique for the determination of the composition of trinary films and could be extended to the analysis of any micron or submicron sized sample. ACKNOWLEDGMENT The author is grateful to F. B. Humphrey and T. Suzuki of Caltech for the preparation of the standards, to R. M. Shoho and P. Husman of the Autonetics Division of North American Rockwell for the reference samples and chemical analyses, and to A. E. Bence of Caltech for discussions of the correction procedures.
RECEIVED for review March 11, 1968. Accepted April 10, 1968.
Spectrophotometric Determination of Pyrazolines and Some Acrylic Amides and Esters A. R. Mattocks Toxicology Research Unit,Medical Research Council Laboratories, Woodmansterne Road, Carshalton, Surrey, England
A SENSITIVE COLOR reaction for acrylamide was required in connection with studies on the neurotoxicity of this compound. This was achieved as a result of the discovery that pyrazolines, which are readily formed from the reaction of diazomethane with many acrylic and related compounds, including acrylamide, give intensely colored derivatives with certain aldehydes. The reaction of diazoalkanes with a-unsaturated carbonyl compounds to form pyrazolines is well known, and has recently been reviewed ( I ) . The reaction times vary widely, depending on the stereochemistry of the unsaturated compound ( 2 ) . Thus, ethyl acrylate (I) reacts rapidly with diazomethane in ether to give 3-ethoxycarbonyl-1-pyrazoline(11) (3, 4). CHr=CH,COOEt
cHzN2:
~ ‘ “ “ “ - (-coo‘t H
I
I[
m
The latter readily tautomerizes, for example in the presence of alcohols, to the more stable 2-pyrazoline (111) (3). Extension of this reaction to acrylic amides has not previously been reported. Acrylamide (IV) reacted very rapidly with diazomethane in methanol-ether, t o give a stable crystalline product, mp 97’ C, formulated as (V) by analogy with
(1) C. H. Jarboe in “Chemistry of Heterocyclic Compounds,” A. Weissberger, Ed., Vol. 22, Interscience, New York, 1967, p 209. (2) A. Ledwith and Yang Shih-Linn, J. Chem. SOC.(B), 83 (1967). (3) D. S.Matteson, J. Org. Chem., 27,4294 (1962). (4) A. Ledwith and D. Parry, J. Chem. SOC.(C), 1408 (1966).
0
CHpCH.CONH2 cH2N2
H
IP
P
I
p PI
(111). Infrared spectra and microanalysis supported this structure. Acidic Ehrlich reagent (4-dimethylaminobenzaldehyde) and 4-dimethylaminocinnamaldehydeare known (5) to react with some amines to give colored Schiff‘s bases. It was found that the pyrazolines (II), (111), and (V) gave strongly yellow colored derivatives with Ehrlich reagent, and with 4-dimethylaminocinnamaldehyde even stronger and more stable purple colors were formed. The derivatives are presumably Schiff‘s bases of the form (VI). The pyrazolines (11) and (111) gave identical 450 mp), with Ehrlich reagent. colored derivatives (A,, This is not surprising in view of the ease with which (11) isomerizes to (111). The colors from the above reagents are formed very rapidly at room temperature. They are stable for many hours in solution, and the intensities decrease linearly with dilution if absolute ethanol is used. The acid used in the coupling reaction is apparently not critical: HCl, HC104 and BFI are equally effective. The above color reactions have been made the basis of a spectrophotometric method for the determination of these pyrazolines, and of acrylamide and related acrylic compounds. The procedure will be described for acrylamide, but it is ( 5 ) F. Feigl, “Spot Tests in Organic Analysis,” 7th ed., Elsevier, New York, 1966, p 243. VOL. 40, NO. 8, JULY 1968
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