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The Birth and Evolution of Surface Science: Child of the Union of Science and Technology

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The Birth and Evolution of Surface Science: Child of the Union of Science and Technology The birth and evolution of surface science: Child of the union of science and technology C. B. Duke* Xerox Wilson Center for Research and Technology, 800 Phillips Road, 114-38D, Webster, NY 14580 This contribution is part of the special series of Inaugural Articles by members of the National Academy of Sciences elected on May 1, 2001. Contributed by C. B. Duke, January 14, 2003 This article is an account of the birth and evolution of surface science Surface science is the child of the union of science and as an interdisciplinary research area. Surface science emanated from technology. Essentially all of the concepts and theoretical tools the confluence of concepts and tools in physics and chemistry with used in the field emanate from condensed-matter physics and technological innovations that made it possible to determine the physical chemistry. Examples include electron scattering and structure and properties of surfaces and interfaces and the dynamics emission for surface characterization, electron tunneling for of chemical reactions at surfaces. The combination in the 1960s and surface imaging, and the use of density functional theory for the 1970s of ultra-high-vacuum (i.e., P < 10؊7 Pascal or 10؊9 Torr) prediction of surface structures and reaction dynamics. The technology with the recognition that electrons in the energy range productive application of these to surface science has been from 50 to 500 eV exhibited inelastic collision mean free paths of the enabled by four waves of rapidly improving experimentation. order of a few angstroms fostered an explosion of activity. The results The first wave came in the 1960s when the combination of Ͻ Ϫ7 were a reformulation of the theory of electron solid scattering, the reliable metal ultra high vacuum (UHV, i.e., P 10 Pascal or Ϫ9 nearly universal use of electron spectroscopies for surface character- 10 Torr) systems and the use of electron spectroscopy for ization, the rise of surface science as an independent interdisciplinary surface characterization gave birth to the field. The second wave research area, and the emergence of the American Vacuum Society began in the 1980s when the rise of semiconductor microelec- (AVS) as a major international scientific society. The rise of microelec- tronics generated electronics of sufficient reliability that multi- tronics in the 1970s and 1980s resulted in huge increases in compu- ple sophisticated experimental probes of surfaces could be used tational power. These increases enabled more complex experiments simultaneously in multiport UHV systems on a routine basis. and the utilization of density functional theory for the quantitative Beginning in the early 1970s it became customary to have a prediction of surface structure and dynamics. Development of scan- variety of sample preparation and analysis experiments in the ning-probe microscopies in the 1990s led to atomic-resolution images same vacuum chamber. Unfortunately, all of the equipment needed for this diversity of measurements rarely was functional of macroscopic surfaces and interfaces as well as videos of atoms at the same time. By the mid-1980s much of this problem had moving about on surfaces during growth and diffusion. Scanning disappeared, and the goal of having many sample preparation probes have since brought solid–liquid interfaces into the realm of and characterization techniques operating simultaneously in the atomic-level surface science, expanding its scope to more complex same vacuum system became a practical reality. This same systems, including fragile biological materials and processes. microelectronics revolution, based on the inexorable doubling of cost͞performance figures of merit of computing power roughly n 1965, although vacuum systems were available for stabilizing every 2 years, transformed theoretical surface science from the Isurfaces for hours, neither the composition nor the structure of use of illustrative simple models into a quantitative predictor of a solid surface could be determined experimentally as may be surface structures and properties. The third wave, initiated by ascertained by inspection of the preeminent surface science text of the invention of the scanning tunneling microscope in 1982 and the day, Semiconductor Surfaces (ref. 1; for an expanded reference its coming to maturity in the 1990s, led to the age of imaging in list, see Supporting References, which is published as supporting surface science. Atomic-resolution images of highly complex information on the PNAS web site, www.pnas.org). By the mid- macroscopic surfaces and videos of the dynamics of their evo- 1980s both the atomic composition and structure could be deter- lution generated by scanning probe microscopies have become mined quantitatively for both clean and adsorbate-covered single routine, thereby revolutionizing our understanding of deposi- crystal surfaces of elements and simple compounds (2). Today, the tion, growth, etching, and chemical reactions at surfaces. The morphology of such surfaces and the dynamics of chemical reac- fourth wave, the application of surface science techniques to tions on them (including growth) are readily observed and pre- examine more complex systems, including liquid–solid interfaces dicted (3). Moreover, the atomic-level characterization of surfaces and fragile biological samples, is only now beginning, although has moved from the realm of ‘‘vacuum’’–solid surfaces to liquid– its consequences may well dwarf those of its predecessors. Each solid interfaces (3). This article is an account of how this remarkable of these four waves is discussed in turn, indicating the interplay transformation, a scientific revolution in the sense of Thomas Kuhn between the attendant scientific advances and their technolog- (4, 5), came to be. It is the story of the birth of surface science as ical enablers to provide insight into the origins of surface science an interdisciplinary area of research and its continuing evolution as an interdisciplinary field of research. caused by the interplay between concepts in condensed-matter The Birth of Surface Science physics and evolving technologies like semiconductor microelec- The first chapter of this story occurred between 1964 and 1973 tronics, vacuum processing, and the construction of ever more because of the confluence of three factors: UHV technology, the flexible and robust scanning probe microscopes. In addition, many availability of single crystal samples, and discoveries in the of the process technologies that are used to fabricate modern physics of electron–solid interactions. For many years the tech- microelectronic and electrooptic devices emanated from semicon- ductor surface science during the decades of the 1970s through 1990s. Thus, this article also is the story of surface science as a Abbreviations: AVS, American Vacuum Society; UHV, ultra high vacuum; LEED, low-energy wellspring of the semiconductor processing innovations that have electron diffraction; STM, scanning tunneling microscope; AFM, atomic force microscopy. created the device hardware of the digital age. *E-mail: [email protected]. 3858–3864 ͉ PNAS ͉ April 1, 2003 ͉ vol. 100 ͉ no. 7 www.pnas.org͞cgi͞doi͞10.1073͞pnas.0730358100 Downloaded by guest on September 30, 2021 Fig. 1. Schematic illustration of an incident electron or position beam of wave vector k ϭ kЌ ϩ k‡, scattered elastically from a single crystal into a state characterized by the wave vector kЈϭkЈ|| ϩ kЈЌ; kЈ‡ ϭ k|| ϩ g(hk); g(hk) ϭ 2␲ ϩ ϭ ϫ ͞ ⅐ ϫ (hb1 kb2), b1 a2 a3 [a1 a2 a3], etc. The magnitude of k is related to the Fig. 2. Attenuation lengths of electrons in solids as a function of their ϭប2 2͞ ប energy E of the incident electrons via E k 2m, in which is Planck’s energy. An early compilation (17) of a variety of experimental data are given constant and m is the mass of the electron. The construction of the reciprocal by the dots. An interpolation formula is shown by the solid line. At the time lattice associated with the single crystal surface also is shown. The vec- that these data were compiled, the attenuation lengths were regarded as tors g(hk) designate the reciprocal-lattice vectors associated with the identical to the inelastic collision mean free paths, although later it was lowest-symmetry Bravais net parallel to the surface. [After Duke (20), with realized (18) that these quantities could differ by roughly 50%. [Adapted from permission.] Seah and Dench (17) with permission.] ENGINEERING nology of producing and measuring low pressures (‘‘vacuum’’) scattering of such electrons via the creation of collective exci- under controlled conditions had been advancing steadily, driven tations of valence electrons was a vital element in their inter- by industries such as vacuum-tube electronics and television (6). actions with solids (12–16). Moreover, as indicated in Fig. 2 (17, By the mid-1960s, it had progressed to the point that apparatus 18) in this low-energy range the inelastic-collision mean free for generating UHV was readily available and could be com- paths for electrons are only a few angstroms, leading to the vastly bined in commercial instrumentation with electron, ion, and important conclusion that electrons being elastically scattered by photon sources, versatile sample manipulators, and detectors for or emitted from the solid must have come from the top few the measurement of scattered electron, photon, and ion beams atomic layers. This combination of readily available technology (7). A UHV environment is essential for surface science exper- for electron scattering and emission experiments in UHV, single imentation because UHV pressures are required for a surface to crystal samples, and the insight that these experiments probe the remain stable for the time required (i.e., hours) to characterize surface rather than the bulk of a solid set off an explosion of its composition and structure. The development of commercial activity beginning in the late 1960s that defined surface science metal UHV vacuum technology was important because before research as we know it today. that time a good glass shop was required to do UHV experi- This explosion had, moreover, institutional and personal as ments.
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