The Development of Commercial ESCA Instrumentation: A

Waters Symposium: Electron Spectroscopy for Chemical Analysis edited by

Waters Symposium

John P. Baltrus National Energy Technology Laboratory U.S. Department of Energy Pittsburgh, PA 15236

The Development of Commercial ESCA Instrumentation: A Personal Perspective Michael A. Kelly Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305-2205; [email protected]

The last three decades have seen an explosion in our understanding of material surfaces brought about by the development of new surface-sensitive analytical tools. One of the most generally useful of these is electron spectroscopy for chemical analysis (ESCA) or X-ray photoelectron spectroscopy (XPS), which permits one to determine the elemental composition and chemical bonding of atoms in the near-surface region of almost any solid by bombarding it with low energy (1–2 keV) X-rays and measuring the kinetic energy of the emitted electrons. Early development of this technique occurred in the 1960s at Uppsala University, at University of California, Berkeley, and in other research laboratories around the world, and has grown steadily since then, producing an extensive literature on the theory and applications of ESCA. A few texts that provide good overviews of the field are included in the references (1–4). The publication of Kai Siegban’s book ESCA (5) in 1967 created great excitement among instrument manufacturers because it showed that this powerful new spectroscopy, useful across a wide variety of fields, might create a significant new market for instruments. At this time of optimism, the spectral linewidths observed from solids were limited by instrumental factors, and there was speculation that ESCA might become the “NMR of solids”—providing, through the shifts in binding energy observed between an element in different bonding states (the “chemical shifts” of ESCA lines), a fingerprint of all the elements and bonds present. While this optimism has not been fully realized, in the subsequent three decades ESCA has found widespread use in nearly all materials-related disciplines—today it is difficult to find a journal devoted to surface phenomena that does not include relevant measurements made by ESCA. This success has been the product of scientists who have created a large body of knowledge regarding the use of the technique, and instrument manufacturers, who through competition and ingenuity, have supplied a constantly improving measurement capability. This article is a personal perspective of one whose efforts to create and improve commercial spectrometers spans the last three decades. While my direct experience relates to work done primarily at Hewlett-Packard and Surface Science Instruments, I have tried to include some of the key work done at other companies, particularly in the early days. This article is not meant to be a comprehensive survey of ESCA or even of these development efforts, though, and I apologize for the many omissions I have undoubtedly made. 1726

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Early Commercial Instruments Eyeing potential markets that would complement their other products, a surprising number of manufacturers embarked on ESCA instrument development programs, and in the early 1970s, no less than six companies announced the availability of ESCA spectrometers: Varian Associates, Hewlett-Packard, DuPont, McPherson in the United States, and AEI and Vacuum Generators (VG) in the United Kingdom. The technical challenges in developing a commercial instrument were significant. In addition to the need for good vacuum, a suitable low-energy X-ray source, and a practical sample-handling system, it was imperative that an instrument possess sufficient sensitivity, so materials could be analyzed in a reasonable time. This last constraint was the Achilles’ heel of the technique: the production of X-rays—itself an inefficient process—followed by the small probability that an emitted photoelectron could escape from a solid without losing energy, be energy analyzed and detected, results in the detected signal being 1015 times lower than the excitation.

Figure 1. A diagram of Varian’s IEE spectrometer. The sample, mounted on the outside of a small cylinder, is illuminated by an annular Al(kα) X-ray source. Photoelectrons are energy analyzed in an axially symmetrical spherical sector, then imaged onto an electron multiplier. The large solid angle collected results in a count rate about 60 times that of earlier hemispherical analyzers (see Figure 2).

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Hence, a 100 W X-ray source might produce an output signal of only a few hundred electrons per second from a given ESCA line, making the technique very slow and insensitive. A number of imaginative designs have been introduced that have significantly higher throughput than Siegbahn’s earlier instruments, but sensitivity remains a key impediment to improving instruments even today. Following the early work of B. Henke (6, 7), most of the early entries incorporated a hemispherical electron energy analyzer, in use as a beta spectrometer for nuclear measurements since the 1930s, to measure electron energies. A traditional X-ray source with an aluminum or magnesium anode was used to excite the sample: these elements have narrow kα emission lines (< 1 eV FWHM) and energies high enough to excite at least one useful core level of every element (except hydrogen). All manufacturers added significant innovations to improve performance and ease of use for applications they envisioned would emerge. In the early years, it was not clear how surface sensitive ESCA was, or the rate at which spectra from clean surfaces was obscured by contamination. As a result, these early designs varied widely in the quality of vacuum available. Varian Associates, the first company to introduce an instrument, announced the availability of its IEE (induced electron emission) spectrometer in 1969. It used an innovative design in which an annular X-ray source illuminated the sample and a spherical analyzer, with a collection efficiency about 60 times that of a conventional hemispheric analyzer (8, 9) to determine the energy of photoemitted electrons. A schematic of the instrument is shown in Figure 1. Developed by John Helmer and Norbert Weichert in the group responsible for Varian’s NMR product line, the technique was seen as a potential organic analysis tool. Stig Hagstrom, a student of Siegbahn’s, consulted for the group. The instrument was computer controlled and used a retarding lens between the sample and analyzer to permit “constant resolution” spectral

acquisition in which a wide spectral region was scanned by varying the retardation rather than the pass energy of the analyzer. Special, nonmagnetic ion pumps were designed to produce a high vacuum. A gold spectrum taken using this instrument is compared with one from Siegbahn’s laboratory in 1966 and some other early instruments in Figure 2. The development of this complex instrument with such a limited staff in less than two years was a remarkable accomplishment, and was indicative of the enthusiasm that existed in many of the instrument companies in these early years. Sales, unfortunately, were slower in coming—some instruments were sold to large chemical companies, but issues relating to sample handling and increasing competition from competitors led Varian to withdraw from the market in about 1974. At that time, about 20 of these instruments had been sold. McPherson Instruments introduced a spectrometer based upon Siegbahn’s earlier design in about 1970. It featured a large, hemispherical analyzer with considerable flexibility in the size and shape of sample it could accommodate, a computer controller for spectrometer operation and for data acquisition, and the ability to add other techniques such as Auger spectroscopy and ultraviolet photoelectron spectroscopy (UPS). Digital signal processing was also developed to subtract the instrumental linewidth by Fourier techniques, a real innovation at the time. Kai Siegbahn consulted with the company early in the development program led by John Rendina. Perhaps one of the most original and practical early designs was done in the analytical labs of DuPont, based upon a unique electron energy analyzer using focusing, retarding lenses that formed high-pass and low-pass filters (10), designed by J. D. Lee and an X-ray source designed by H. Herglotz. A schematic drawing of the instrument is shown in Figure 3. A prototype of this instrument was built for DuPont’s internal analytical laboratory, run by W. M. Riggs,

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Binding Energy / eV Figure 2. A comparison of the Au(4f) spectra taken in Siegbahn’s laboratory with those from three early commercial instruments. The Varian design shows an improvement of a factor of 60; the DuPont instrument a factor of 1000, and the Hewlett-Packard spectrometer in between these. All of these instruments used a nonmonochromatized X-ray source except the HP, which shows better energy resolution and a higher signal-to-background ratio as a result.

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Figure 3. A schematic of the DuPont spectrometer design. Having a significantly higher throughput than any of the other early instruments, it is compact and has quite adequate energy resolution for most applications. Electrons collected from the sample are deflected into a drift region where a reflective low-pass filter and a transmitting high pass filter define the energy resolution of the collected spectrum. The spectrum is scanned by varying the initial retarding field.


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who advocated its development as a product and did pioneering applications studies of the spectra of polymers. Having an impressive throughput as Figure 2 shows, the design was compact, less expensive than other instruments, and over its lifetime, shown to be particularly useful for industrial problems. In the early years, though, because few appropriate applications had been defined, it did not attract much of a market. DuPont discontinued production in about 1976, but transferred the design to Shimadzu who has very successfully exploited its capabilities since then. AEI introduced an instrument in 1970 using a design concept similar to Siegbahn’s, but incorporating X-ray, ultraviolet, and electron sources so that ESCA, UPS, and Auger spectra could be obtained—the first multitechnique instrument to include ESCA. Shortly after introduction, pumping was improved so that analyses could be done at pressures of 10᎑10 Torr, and an ion-etching capability was added so that samples could be cleaned in situ. The development team included I. W. Drummond, G. A. Errock, and J. M. Watson (11). A team including D. Latham, K. Yates, and M. W. Roberts at VG in the United Kingdom developed a multitechnique ultrahigh vacuum (UHV) instrument that included ESCA in about 1971 (12). They had marketed an ultraviolet (UPS) spectrometer in 1968. The 1971 instrument included UPS, LEED, and Auger spectroscopies, a hemispherical electron energy analyzer, and an X-ray source with a retarding lens for ESCA. Pressures of 10᎑10 Torr were achieved using oil diffusion pumps, and the instrument enjoyed considerable success especially in Europe.

ESCA at Hewlett-Packard Hewlett-Packard (HP) became interested in ESCA through one of the company’s technical advisors, Luis Alvarez, who touted the technique as a broadly applicable characterization tool for solids. Siegbahn was on a sabbatical at the University of California, Berkeley laboratory, and a collaboration between Siegbahn and the company ensued that led to the introduction of an instrument in 1971 (13, 14). The extensive development effort was led by Don Hammond at HP, an expert in quartz technology who had contributed significantly to HP’s frequency and time technology. It involved several senior staff scientists: Hugo Fellner-Feldegg, who designed the X-ray monochromator, Frank Barnett who did the electron optics design, and Frank Ura who developed processes to fabricate many of the unique components, and other contributors. Since little was known about the natural widths of ESCA lines in solids, the instrument was designed to maximize, insofar as possible, both energy resolution and count rate. To this end, three confocal monochromator crystals were used to produce a bright, monochromatic source, and goldcoated glass hemispheres, ground to a precise shape, were used as the electron energy analyzer. A “dispersion compensation” scheme invented by Siegbahn was used to improve the instrument sensitivity at a given energy resolution. This scheme took advantage of the fact that the monochromator imaged different energy X-rays on different parts of the sample. By orienting the electron energy analyzer properly, it is possible to cancel this dispersion in the monochromator with an opposite dispersion in the analyzer (15), allowing all of the dif-

quartz substrate θ

aligned, single-crystal quartz wafer

Figure 4. A diagram of the Hewlett-Packard spectrometer. X-rays from an Al anode are reflected from three bent quartz monochromator crystals (one shown), and the Al(kα) line is dispersed across the sample. Photoelectrons are retarded and imaged into a wide entrance slit of a traditional hemispherical analyzer. The geometry and lens magnification are arranged so that the analyzer dispersion cancels the X-ray energy variation across the sample. Analyzed electrons strike a position-sensitive detector, so a range of energies are collected simultaneously.

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atomic planes bent

Figure 5. Fabrication of the X-ray monochromator. A thin wafer of single-crystal quartz is angle oriented to take advantage of a strong Bragg reflection. This wafer is then spherically bent and brazed to a substrate with a matched thermal expansion coefficient, so the atomic planes in the wafer are curved. This crystal is then illuminated with X-rays from a properly placed small source, so that a bright image is formed on the sample surface. In the HP spectrometer, θ is about 11 degrees and the width of the Bragg peak is about 0.2 eV.


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fracted X-rays to be used without compromising resolution. Later a multichannel detector was added to improve the throughput further (16). A schematic of this instrument is shown in Figure 4. As can be seen in Figure 2, its count rate was not as high as the DuPont instrument, but it clearly led the field in energy resolution and signal-to-background ratio. The real heart of the development of this instrument was the monochromator, which relied heavily on the group’s experience with quartz. To make a focusing Bragg reflector, a thin wafer of single-crystal quartz with its crystalline axis carefully aligned was bent and brazed to a concave quartz substrate so its atomic planes curved as shown in Figure 5. In addition to its selective reflection of only the Al(kα) X-ray line, it eliminated other X-rays—background and spurious peaks—from reaching the sample and greatly decreased the damage to sensitive samples. I became involved in the development effort after a prototype of the instrument was complete and the decision was made to offer it as a product. It was the first UHV instrument HP had made and a new manufacturing division “Scientific Instruments” was created to produce and sell it as well as a line of mass spectrometers. I was charged with making this working prototype a supportable, profitable product. Having had essentially no experience in producing more than one of anything, it was quite a shock to realize all the effort required to document, manufacture, and support this very clever design. Fortunately, I was in the company of a very capable group of engineers and scientists, whose efforts, after many late hours and false starts, made it a well-characterized, reliable instrument. A picture of it is shown in Figure 6.

Figure 6. A picture of the HP ESCA instrument. The rod in front allows three samples to be conveyed through a load-lock, into a small preparation chamber and then into the spectrometer. The dome houses the hemispherical analyzer; ion pumps that separately pump the X-ray source and analysis chamber are seen in the bottom of the photograph.

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Market Reaction This was the first monochromatized instrument on the market and the most expensive because of its complexity. It attracted considerable attention, particularly throughout the academic community, because the monochromator often provided improved spectra from samples of interest. Despite the attention, however, there was great reluctance to purchase such an expensive instrument without a specific application to justify it; in particular on the part of the industrial community. Since ESCA was a new technique, there were few people with experience using it and few well-defined applications for it. In addition, there was intense competition between the six instrument suppliers in this small market. Our small development team became at once involved in the sales efforts; since the customers were generally scientists, technical discussions abounded. This for me was a challenging and rewarding experience. Potential customers in the academic community included many of the world’s premier physicists and chemists, engaged in a wide variety of interesting research areas. Their interest was exhilarating, and their demands on the instrumentation were a great stimulus to understand the technique more thoroughly and to invent new ways to apply it. It was also an international effort: visiting customers in Russia, where a potential customer might appear with a suitcase full of cash, or in Japan where a sales call proceeded with rigorous formality, greatly increased my awareness of the world and the diversity of uses for analytical techniques. Industrial problems flooded our applications laboratory, run by L. H. Scharpen, where there was great pressure to provide data that would be significant enough to lead to the purchase of an instrument. While HP initially enjoyed the benefits that the monochromator provided, other manufacturers soon offered one as an accessory, and a number of other problems emerged. First, many users, particularly those in industry, were interested in a range of techniques to investigate surface phenomena—Auger Spectroscopy, UPS, and SIMS in particular—and wanted great flexibility in terms of the size and kind of samples that could be analyzed. The HP instrument was designed to optimize the ESCA measurement, which greatly reduced the flexibility of the design, so adding accessories— even ways to heat or cool the sample, let alone adding techniques—came at a significant engineering expense. To make matters worse, several unexpected problems emerged that cast doubts on the reliability of HP’s monochromatized design. The first of these involved the analysis of insulating samples: many such samples yielded quite acceptable spectra when analyzed on competitive instruments, but produced badly distorted ones in ours. Also, the detection system using a vidicon TV camera as a position-sensitive electron detector proved to be nonlinear, so line shapes and relative peak areas were distorted. These problems were corrected, but not without losing some momentum in the marketplace. Market Shake-out Other manufacturers faced competitive problems too: the need for a UHV environment, better energy resolution, better sample-preparation capabilities, and the availability of multiple techniques, led to some difficult choices. To remain


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competitive, significant ongoing engineering and applications efforts were needed; at the same time it was not clear whether a sufficient market existed to support even half the companies engaged in the field. As a result, all the original manufacturers except AEI and VG, who were already offering competitive multitechnique instruments, abandoned the field by the mid 1970s. From a customer’s perspective, too, economics were dominant. While prospective users saw value in the technique, they were reluctant to invest the $200K per year needed to support one instrument, the needed infrastructure, and a qualified scientist to operate it. A multitechnique instrument offered several capabilities for a small additional cost, and so was easier to justify, and had a higher probability of solving important problems. While a wide variety of important application areas had been identified by 1975—catalysis, thin-film analysis, adhesion and surface cleanliness studies—nearly all were one-ofa-kind research or product development problems. It was difficult to see any market for which a dedicated instrument could be built and sold in quantity. Companies that had developed multitechnique instruments (AEI and VG) saw a profitable future in the research market, along with new companies entering the market. One was Physical Electronics, Inc. (PHI), which, to extend its dominant position in Auger instrumentation, introduced an ESCA spectrometer using a double-pass cylindrical mirror analyzer in about 1974 (17). These three companies grew with the field, and are producing productive, sophisticated instruments today. LeyboldHereaus also introduced an instrument in the mid-1970s (18) but withdrew it in about 1990. With about 200 instruments in use around the world by 1976, the next decade saw a great upsurge in applications for ESCA. Its reputation as a dependable, quantitative surface technique was extended to fields as diverse as geology, art history, medicine, semiconductor processing, and laser technology. Corporations in chemical and electronic industries began to include surface-sensitive techniques in their R&D laboratories, and the value of ESCA as a general-purpose surface characterization tool began to be recognized. Surface Science Instruments Hewlett-Packard discontinued its ESCA product line in 1976 for economic reasons: the GC–MS market was experiencing robust growth in environmental and medical screening, so the company decided to focus the resources of its new Scientific Instruments division on that product line. The management was generous to a group of us who had been part of the ESCA effort (L. H. Scharpen, W. A. Peterson, C. E. Bryson, and me), and sold us the components of an instrument to start an analytical-service laboratory. We were unable to attract any venture capital or bank funding, so we began very conservatively with personal funds. Surface Science Laboratories, as we named it, exposed us to a wealth of applications: from thin-film coatings on architectural window glass, tooth sections from dentists, strawberries from farmers, to laser windows, catalysts, and hard-disk lubricants from high-tech industries. We became sufficiently profitable to launch a hardware development effort, aimed initially at providing accessories for HP ESCA 1730


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Figure 7. An early example of chemical-state mapping. A photocopy of the typed word “map” was scanned by the 150 micron diameter X-ray spot on the SSI instrument, and the C 1s line observed. The carbon in the paper (cellulose, with few C⫺C bonds) is chemically shifted from the toner (largely graphitic). The contrast shown represents the fraction of the signal that is graphitic.

customers. One of these accessories, a position-sensitive detector using a resistive anode encoder, was developed jointly with C. Carlson of NASA’s Space Sciences Laboratory—a quantitative, reliable detector that has found use in a variety of scientific instruments (19). As we learned more about the needs of the industrial community through our service laboratory, we began plans to make and market an instrument ourselves, tailored more for industrial users than previous ones had been. We formed a division “Surface Science Instruments” (SSI) to execute the plan, led by R. L. Chaney who had also done instrument development at HP, and funded by the profits from our analytical laboratory. Our experience suggested that there was a large, untapped market for this versatile measurement, which the instruments then available were not addressing. A primary feature we wished to add was an ability to analyze smaller areas than the 10–100 mm2 then possible (20). While still much larger than the 10᎑4 mm2 of current Auger analyzers, this smaller size would enable several new capabilities: many small samples could be introduced into the analysis chamber simultaneously and then analyzed automatically; and ESCA depth profiling (determining elemental composition as a function of depth in the sample by removing successive surface layers by ion etching) would become practical, since a relatively small crater needed to be ion etched (21). It would also be possible to scan a surface mechanically and present the concentration of a specific element or chemical state as a function of position, thereby making chemical-state mapping possible. Improving the spatial resolution without severely compromising the instrument sensitivity was a significant design problem, but by employing some tricks in the electron optics, we were able to achieve an X-ray spot diameter of 150 µm with acceptable counting rates. An early chemical map of the word “map” from a photocopy of the word typed on a piece of paper is shown in Figure 7. The image presented is of the C 1s line of graphite, the form of carbon present in the ink. Photoelectrons from the carbon in the paper have been excluded, because paper is primarily cellulose, which contains only C⫺O bonds that can be distinguished because they exhibit about a 2 eV chemical shift from the graphitic bonds.


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Figure 8. Two views of the SSI instrument. (left) The vacuum system is controlled from the small panel above the instrument; the introduction chamber is to the left. The microscope is used to position the sample for analysis. (right) A close-up of the analyzer with the microscope removed; the hemispherical analyzer is at the rear (truncated to save space); the monochromator is beneath the dark cover to the left of the analyzer. Other ports house the X-ray source, ion etch gun, and charge neutralizer.

We used the automated features of the instrument to good advantage in what became a mainstay of our analytical service business—the measurement of lubricant thickness on hard disks. Perhaps the only real “routine” application we encountered, a protocol developed by R. Linder and P. Mee enabled us to measure the lubricant thickness to about 1 Å in a minute or less by measuring only the C 1s line. In its heyday, this single measurement was performed on hundreds of samples a day and produced the majority of the laboratory’s profit. In addition, the instrument enabled the analysis of larger samples with good energy resolution, good visualization of the sample during analysis, and flexible data-analysis software that was easy to use, even for relatively unsophisticated users. A picture of it is shown in Figure 8. It found good market acceptance worldwide, and between 1981 when it was introduced and 1988 about 150 instruments were sold. The company merged with Kevex Corp. in 1984, which became the subject of a hostile takeover bid in 1988. It was ultimately acquired by VG Instruments (not the initiator of the takeover), and the product line was discontinued shortly thereafter. SSI was the only small company to market an ESCA instrument and the only one to depend on ESCA alone for its survival. A Maturing Market As applications for ESCA became more clearly defined, productivity became important, particularly in industrial environments; since only one of the multitechniques could be used at a time, an organization with a variety of analytical needs preferred independent instruments for each technique. As a result, multitechnique instruments, while still significant, became less dominant. Competitive pressures, too, stimulated new designs, offering improved spatial resolution, www.JCE.DivCHED.org

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higher sensitivity and better sample handling. Some specific examples are: •

PHI introduced a highly automated instrument, the Quantum 2000, in the mid-1990s, featuring a rastered 10-micron diameter X-ray spot for imaging a surface with photoelectrons, and a revolutionary sample-handling system using vacuum-compatible motors to provide very precise and flexible computer-controlled positioning capabilities. The instrument provides highresolution spectra from a point or from an area being scanned, providing high-quality elemental maps.

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VG developed an imaging lens, which, with some very clever electron optics, permits two modes of operation: a spectroscopic mode, in which the ESCA spectrum of a small area of a sample could be obtained as a function of the electron-escape angle so depth and composition information can be collected simultaneously, and an imaging mode in which the analyzer is tuned to a particular energy and a spatial image of photoelectrons emanating from the sample is accumulated (22). This system is incorporated in their current “Theta Probe.”

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Kratos (formerly AEI) developed a novel “snorkel lens”—a magnetic-immersion lens that substantially increased the collection efficiency of photoelectrons and improved charge neutralization of insulating samples, while maintaining energy resolution (23). This lens, together with an innovative spherical analyzer (24) provides a high spatial-resolution imaging mode for elemental maps in their latest instrument, the Axis Ultra.

(All of these instruments, available today, use monochromatic X-ray sources, produce spectra with improved energy resolu-


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Annual Sales / $M

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tion and count rates, and have more versatile sample handling capabilities than earlier spectrometers. There were also new instruments introduced aimed as special market segments.) •

Scienta, in Sweden, introduced an instrument for the “high end” research market, built upon the extensive background in ESCA at Uppsala University, featuring a bright, rotating anode X-ray source and superior energy resolution of 0.27 eV (25). It has become a major supplier of electron energy analyzers to synchrotron researchers in recent years.

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Thor Research in the United Kingdom introduced another unique instrument, the photoelectron spectromicroscope (PESM) in the early 1980s. Based upon an invention of D. W. Turner (26), it produced energy-analyzed images with micrometer spatial resolution and high collection efficiency from samples mounted in a high magnetic field. SSI acquired this technology in the mid 1980s and sold one system to a synchrotron research group (27), but was unable to continue its development.

ESCA Today As a basic research tool, ESCA has been a profound success and its use has increased dramatically over the last two decades. The field has also been extended significantly by the use of synchrotron radiation as a bright X-ray source, which has opened new areas of research in solid-state physics, molecular biology, and many other disciplines. From a commercial standpoint, though, the technique has not been an unqualified success for manufacturers. My estimate of the world ESCA market since its inception is given in Figure 9. Given its success as a characterization tool, it is an enigma that there has been little growth in instrument sales since 1985, which from the standpoint of manufacturers makes the market a marginal one and inhibits their ability to invest in new designs. 1732


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Why is this so? One can cite competitive techniques— Auger spectroscopy or SIMS, with better spatial resolution or sensitivity—as possible causes, but they have not fared much better in the marketplace. Are there insufficient monitoring or routine uses for ESCA, the key to a growing instrument market? I think a wealth of routine, important industrial measurements exist, but that there is a cost-effectiveness problem with ESCA: the measurement is too costly for most such uses. If one amortizes the capital and operating costs of an instrument, its infrastructure, and a qualified analyst, one ESCA spectrum costs about $100. Despite speed and technique improvements, this is not different than it was 20 years ago. As a result, except for very high volume applications, most potentially effective routine measurements are too expensive to implement. The Future W. M. Riggs cataloged the innovations made during the development of ESCA and Auger instrumentation in an interesting article published in Research Policy (28) in which he assesses the role of users and manufacturers in the process. Advanced users today are buying components rather than complete instruments and exploring other areas such as photoelectron diffraction (29) and measurements at higher in situ pressures (30, 31)— fundamental extensions of the technique, which Riggs’ research shows have traditionally been done by instrument users rather than manufacturers. There are also possibilities, in the future, that brighter X-ray sources or better ways of cleaning or depth-profiling materials will be found, or ways to measure chemical shifts more precisely will be discovered. Without some significant advance, though, it would appear that ESCA will remain an important research tool, but not one of growing industrial importance. I believe ESCA has a much brighter future that this suggests, though—that much of its importance and contribution has yet to be realized. It has a major relatively untapped attribute: it is perhaps the only surface-characterization technique that can be made operator independent. Software routines exist to provide automatic elemental analyses of surfaces; surface charging of insulating samples is under control in new instruments (32, 33); and extensive databases of chemical shifts exist (34). Consequently, it should be possible to build instruments that provide reliable surface analyses for nonspecialist users. If such instruments can be built at a reasonable cost, a wealth of cost-effective industrial applications should emerge. Manufacturers are already responding to this need: the new instruments mentioned above from the three major suppliers are automated, have high throughputs, and are addressing the cost effectiveness issue for higher volume applications. Simplified instruments tailored to specific markets are also becoming available, such as the Kratos Amicus (based upon the old DuPont design) and the VG Sigma Probe. In any case, ESCA will continue to contribute fundamental information about surfaces and thin films in a wide variety of fields. Instrument manufacturers have enabled this by providing high-quality spectrometers for the world research community. It has been a great privilege to participate in the early years of this development and to interact with the creative people the field has attracted.


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Acknowledgments Many people have contributed to the thoughts presented here but I would like to thank particularly for their help and recollections: John Helmer, Don Hammond, Paul Larson, Bill Riggs, Chuck Fadley, Dick Brundle, Alan Carrick, John Walstenholm, Dave Surman, Simon Page, Ramish Champaneria, and John Moulder. Literature Cited 1. Surface Analysis, the Principal Techniques; Vickerman, J. C., Ed.; John Wiley & Sons: Chichester, United Kingdom, 1997. 2. Practical Surface Analysis; Briggs, D., Seah, M. P., Eds.; John Wiley and Sons: New York, 1978. 3. Electron Spectroscopy, Theory, Techniques and Applications; Brundle, C. R.; Baker, A. D., Eds.; Academic Press: New York, 1978. 4. Surface Analysis by Auger and X-Ray Photoelectron Spectroscopy; Briggs, D., Grant, J. T., Eds.; IM Publications: Chichester, United Kingdom, 2003. 5. Siegbahn, K.; Nordling, C.; Fahlman, A.; Nordberg, R.; Hamrin, K.; Bergmark, J.; Karlsson, S.; Lindgren, I.; Lindberg, B. ESCA: Atomic, Molecular and Solid-State Structure Studied by Means of Electron Spectroscopy; Almqvist & Wiksells AB: Stockholm, Sweden, 1967. 6. Henke, B. L. In Advances in X-ray Analysis; Plenum Press: New York, 1962; Vol. 5, p 285. 7. Henke, B. L. In X-ray Optics and Microanalysis; Academic Press: New York, 1963. 8. Helmer, J. C.; Weichert, N. H Appl. Phys. Lett. 1968, 13, 266. 9. Weichert, N. H.; Helmer, J. C. IEE—A New Type of X-ray Photolelectron Spectrometer; Proceedings of the 18th Denver Conference on Application of X-ray Analysis, Aug 6–8, 1969. 10. Lee, J. D. RSI 1972, 43, 1291. 11. Drummond, I. W.; Errock, G. A.; Watson, J. M. GEC J. Sci. Tech.1974, 41, 94. 12. Brundle, C. R.; Roberts, M. W.; Latham, D.; Yates, K. J. Elect. Spectr. 1974, 3, 241. 13. Siegbahn, K.; Hammond, D.; Fellner-Feldegg, H.; Barnett, E. F. Science 1972, 176, 245.

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