From Surface Materials to Surface Technologies
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The following article is an edited version of the Von Hippel Award address, given by recipient Gabor A. Somorjaiat the 1997 MRS Fall Meeting. Somorjai received the Materials Research Society's highest honor for "his extraordinary multidisciplinary contributions to the atomic-level understanding of materials surfaces and surface processes with technological importance in hetergeneous catalysis, corrosion, and tribology."
Introduction Arthur R. Von Hippel was a pioneer in his belief that applications of science must be pursued and understood on the molecular level. The foreword to his famous book, Dielectrics and Waves—published
in 1954—states, "The electrical engineer has to remember that he is an applied scientist and join his colleagues of physics and chemistry in a cooperative venture of molecular electrical engineering." The search for correlations between macroscopic surface phenomena and molecular level behavior of surfaces has guided all my research efforts over the past 32 years. During this period, my research focused mostly on studies of surface chemical properties on adsorption and heterogeneous catalysis and more recently on mechanical properties of surfaces on tribology. The electrical, magnetic, and optical properties of surfaces have also become understood on the molecular level during this period. As a result, new surface technologies were developed that would not have been possible without the rise and widespread application of molecular surface science. Let us first consider selected examples of these surface technologies that exploit the unique chemical, electrical, magnetic, optical,
MRS BULLETIN/MAY 1998
and mechanical properties of surface materials. The catalytic converter (Figure 1) in its present version oxidizes unburned hydrocarbons and CO while reducing nitrogen oxides to dinitrogen: -CH 2 - + 3/2 O2 -^ CO2 + H2O
(1) (2)
2CO + 2NO ™ N2 + 2CO2
(3)
Air separation to oxygen and nitrogen is accomplished by molecular sieves that are microporous alumina-silicates properly modified by the incorporation of lithium or calcium ions (Figure 2). These materials have higher heat of adsorption for N2 (~7 kcal/mole) than for O2 (~3 kcal/ mole) because of the large quadrupole moment of nitrogen, thereby preferentially releasing oxygen. Conversely, microporous carbon that is engineered to have a bimodal distribution of pores adsorbs the smaller size O2 (3.46 A) in its small pores over N2 (3.64 A), thereby preferentially releasing N2 (Figure 2). The Pentium microprocessor had over 5 million transistors in a less than 3 cm2 area device. The number of transistors has been increased to 8 million and then to 11 million in subsequent generations of these devices. Figure 3 shows some of the details of its intricate threedimensional structure along with the various materials that make up such a device. The working steps of the Xerox machine that utilizes the selective placement and displacement of surface space charge for copying documents are shown in Figure 4. The magnetic disk drive (Figure 5) provides
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