different instrumental concepts em ployed. B I G - B E A M I O N P R O B E S . Since the
complex instrumentation required for high spatial resolution microanalysis and ion imaging is not involved, the big-beam SIMS instrumentation is much simpler and easier to use. Sur face analyses are performed by low current density primary ion beams while the desired spectra are acquired. Depth profiling usually employs highdensity primary beams (hence more rapid sputtering) for routine analysis over depths of several thousand ang stroms. Several masses can be moni tored if rapid peak switching facilities are available. To realize efficient use of the copi ous and rapidly generated data, a SIMS instrument requires either a hardwired or computerized data sys tem. This is especially true for depth profiling. In this mode, ions are pro duced from all elements in the sample volume and that volume is consumed and lost for future analysis. Thus, the ability to successively monitor as many masses as possible during a given profile permits more efficient material consumption and ion genera tion. As can be seen by the above discus sion, the instrumentation used for
SIMS is quite varied and ranges from rather simple systems to the highly so phisticated ion microprobes and mi croscopes. The needs of a laboratory must be kept in mind when evaluating the overall technique as well as a par ticular instrument. Future Instrumentation
In addition to the continued evolu tion of the present instrumental con cepts, new instrumental concepts are being developed. General Ionex of Ipswich, Mass., will have a SCANIIRtype instrument available in mid1975. As the development of the glow discharge techniques progresses and they show reasonable promise, com mercialization of the appropriate in strumentation seems quite likely. One of the more analytically impor tant instrumentation developments is presently taking place. This is the combining of two or more analytical techniques in the same analytical sys tem to permit rapid use of the comple mentary nature of the different sur face and microanalytical techniques. Several manufacturers are or will soon be offering combined scanning elec tron microscopes and scanning Auger microprobes (Physical Electronics, Varian Associates, Vacuum Genera tors, and Etec Corp.). Auger electron
spectrometry and ESCA have been combined in a single instrument by Physical Electronics and ΑΕΙ Scientif ic Apparatus, albeit with significantly different approaches. As the capabili ties and limitations of each technique are delineated and as more analytical ly demanding materials analysis prob lems are attacked, other combined systems will almost certainly be devel oped. References
(1) C. A. Evans, Jr., Anal. Chem., 47, 818A (1975). (2) R. G. Wilson and G. R. Brewer, "Ion Beams with Applications to Ion Implan tation," Wiley, New York, N.Y., 1973. (3) P. W. Palmberg, G. K. Bohn, and J. C. Tracy, Appl. Phys. Lett., 15, 254 (1969). (4) H. Weinberg, Caltech, Pasadena, Calif., private communication, 1974. (5) H. Liebl, J. Appl. Phys., 38, 5277 (1967). (6) H. Tamura, T. Kondo, and H. Doe, "Advances in Mass Spectrometry," Vol V, ρ 441, A. Quayle, Ed., Institute of Pe troleum, London, England, 1971. (7) A. E. Banner and B. P. Stimpson, Vac uum, in press (1975). (8) R. Castaing and G. Slodzian, J. Microsc, 1, 395 (1962). (9) N. R. Daly, Rev. Sci. Instrum., 31, 264 (1960). Research supported in part by the National Science Foundation Grants DMR 72-03026 and MPS 74-05745.
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