Special Issue Preface pubs.acs.org/JPCB
Cite This: J. Phys. Chem. B 2018, 122, 399−400
At the Cutting Edge of Surface Science: A Tribute to Miquel B. Salmeron moved to the United States to investigate surface catalysis; while working with his postdoctoral mentor, Prof. Somorjai, he discovered that hydrogen molecules dissociated with highest probability when they hit step-edge platinum atoms in a “stepping up” direction as compared to any other direction (J. Chem. Phys. 1977, 67, 5324), and that the presence of patches of subsurface oxygen gave rise to new adsorption sites of lower binding energy for adsorbates such as hydrocarbons (J. Phys. Chem. 1981, 85, 3840). From that point on, a young, new surface scientist joined the journey to “face the devil”. This short tribute, from one of his long-time friends and collaborators, a former postdoctoral researcher, and a former student, aims to highlight Miquel’s milestone scientific contributions in physical chemistry, especially in the field of surface science, where he followed the strategy of developing new instruments when needed, combining them with other traditional approaches, and encouraging interdisciplinary collaborations. Throughout, Miquel has combined vigorous energy and a lively imagination to paint pictures explaining novel and unexpected mechanisms at surfaces and interfaces, which he has done while managing a large, diverse, multinational group with his signature care and dedication. We hope the readers of J. Phys. Chem. will also enjoy this scientific introduction to Miquel’s cutting-edge approaches and his deep knowledge of surface physical chemistry as well as materials science. Since the early 1990s, Miquel Salmeron’s name has been a steady presence in the field of scanning probe microscopy (SPM), including scanning tunnelling microscopy (STM), atomic force microscopy (AFM), and a variation of AFM to image, without contact, liquid films at surfaces (J. Phys. Chem. B 1996, 100, 9). At the Lawrence Berkeley National Laboratory (LBNL), where Miquel has worked since 1984 as a staff scientist, group leader, and director of the Materials Science Division (November 2008 to August 2012), he has led his team in constructing multiple state-of-the-art SPM instruments (Catal. Lett. 1992, 14, 263; Langmuir 1994, 10, 367; NanoSurface Chemistry; Rosoff, M., Ed.; Marcel Dekker, Inc.: New York, 2001; Chapter 6, p 243). These cutting-edge microscopes enabled his team to provide significant new insights in surface physical chemistry. In 1996, Miquel’s team utilized AFM in ultrahigh vacuum (UHV) to quantitatively investigate the nanoscale friction force between the sharp AFM probe and surfaces. They discovered that the friction−load relation for a nanoscale tip is proportional to the true contact area between the tip and sample, and followed the classical Johnson Kendall Roberts (JKR) model (J. Vac. Sci. Technol., B 1996, 14, 1289; Proc. R. Soc. London, Ser. A 1971, 324, 301) for adhesive contacts. Using UHV STM, Miquel visualized the interaction of molecules with metal and semiconductive surfaces in
r. Wolfgang Pauli once said: “God made the bulk; the surface was invented by the devil.” Yet, almost everything interacts with the outside world through its surface: from the physical sense of touch to the chemical action of catalysts, surfaces matter everywhere. Despite the complexity and grand challenges of surface science, generations of scientists have embarked on the difficult journey of unraveling the atomic scale structure and processes occurring on a surface. Numerous ingenious methods, ideas, and technologies have been developed throughout the history of surface science, particularly in the last five decades. Many unanticipated phenomena and new insights have been revealed about surface structure, properties, and chemical reactivities, with breathtaking surface reconstructions, beautifully ordered self-assembled monolayers, and remarkable pressure-induced surface reactions, all enabled by the continuous advances and development of instrumentation. Today, The Journal of Physical Chemistry honors a world leader and visionary among these scientists, Dr. Miquel B. Salmeron, by introducing this special issue in celebration of his 70th birthday. Miquel’s independent scientific career began in Spain over four decades ago in the field of solid state physics. In 1975, he
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© 2018 American Chemical Society
Special Issue: Miquel B. Salmeron Festschrift Published: January 18, 2018 399
DOI: 10.1021/acs.jpcb.7b10661 J. Phys. Chem. B 2018, 122, 399−400
Special Issue Preface
The Journal of Physical Chemistry B unprecedented detail (Science 2016, 351, 6272; J. Phys. Chem. C 2016, 120, 8227). At room temperature, Cu(111) surfaces were seen to decompose into clusters upon exposure to CO molecules due to weakening of Cu−Cu interactions by binding to CO. Cluster formation activated the surface for water dissociation, which is an important step in the water−gas shift reaction. Miquel’s surface science quest did not stop with small molecular adsorbates and clean metal surfaces. He used SPM to study large molecules such as thiol self-assembled monolayers, long-chain alcohols (Langmuir 1994, 10, 367; J. Phys. Chem. B 2000, 104, 3140), and water clusters and thin films. Miquel is among the first to indicate that, at room temperature, water films grow by forming 2D clusters at lower than 25% humidity, and proceed to form large 2D islands above 25% humidity along the epitaxial directions of the underlying surfaces, such as mica (0001) (Science 1995, 268, 267). He also demonstrated strong anisotropy in friction for quasicrystals, where sliding along the periodic direction showed 8 times greater friction than sliding along the aperiodic direction (Science 2005, 309, 1354), highlighting the strong connection between friction and atomic scale structure. One of Miquel’s most impactful contributions was his development of what is now called ambient pressure photoelectron spectroscopy (APPES, or APXPS, referring to the Xray excitation source). By inserting a set of differentially pumped chambers with electrostatic lenses connected by small apertures at focal points, XPS can be performed with the surface exposed to various gases up to ambient pressures, a feat previously considered impossible (Rev. Sci. Instr. 2002, 73, 3872). With APPES, liquids in equilibrium with their vapor phase and catalysts in the presence of reactants can all be studied (Science 2005, 307, 503; Surf. Sci. Rep. 2008, 63, 169). The extension of the surface science experimental regime from traditional UHV conditions to ambient pressures has had a major impact in the field, and the technique has led to implementation in many synchrotron facilities around the world as well as research laboratories that have combined labbased X-ray sources with the ambient pressure analyzer inspired by Miquel, and sparked new commercial products. Miquel has always emphasized teamwork and interdisciplinary approaches. Over the past three decades, he has collaborated with fellow scientists worldwide, combining theoretical and computational methods in conjunction with experimental surface spectroscopy and structural methods such as low energy electron direction (LEED), infrared spectroscopy (IR), and transmission electron microscopy (TEM). One pioneering work was his X-ray absorption spectroscopy (XAS) using synchrotron X-ray sources (Nucl. Instr. Methods Phys. Res. A, 2009, 600, 151). Miquel and his colleagues at LBNL put together the first such instrument and demonstrated its feasibility under ambient pressure and temperature conditions. Since then, there have been multiple new generations created by scientists worldwide. Miquel’s recent work using X-ray transparent membranes to separate the liquid in an electrochemical cell from the vacuum of the beamline has opened the way for spectroscopic studies of the nature of the electrical double layer (Science 2014, 346, 8310). With this new method, he probed the structure of water near gold electrodes and its bias dependence. He showed that the interfacial water molecules have a different orientation from those in bulk: ∼50% of the molecules lie flat on the surface with saturated hydrogen bonds and another substantial fraction with broken hydrogen bonds. At negative bias, the population of molecules
with broken hydrogen bonds increases, producing a spectrum similar to that of bulk water. Unlike the stereotypical “geeky scientist”, Miquel is equally “interdisciplinary” outside of surface science. He bikes to work daily, where the Berkeley hills have stopped many of his younger peers. We would not wish to race him even today. He often says: “Biking those hills is easy once you know the surface potential.” Another secret we reveal to his peers: Miquel draws many of the illustrations in his publications, thanks to his artistic skills. As an adjunct professor at the University of California, Berkeley, he teaches surface and material science classes to graduate students. His students are inspired by his relentless pursuit of new and improved cutting-edge instrumentation and methods, novel ideas, and innovative experiments. Little fear of Dr. Pauli’s devil is seen in Miquel’s education and research in surface science. His group is famous as a miniature “United Nations” with researchers from Europe, Asia, Africa, North America, all with diverse cultures and languages working together as a team; this often includes challenging each other to appreciate exotic foods from other places, including a group ritual involving consuming chicken feet at dim sum, learning to aerate wine by pouring it into a glass container similar to a medieval alambique (“porro” in Catalan) and pouring it from the spout held at arm length, or sustaining oneself during long hours in the lab with a ridiculously high consumption of extremely strong coffee. May this issue bring as many beautiful SPM images and new scientific insights as Miquel would always hope to see. Pauli’s devil should watch out; scientific teams are trained, ready, and equipped!
Robert W. Carpick Gang-yu Liu John C. Hemminger, Guest Editors
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DOI: 10.1021/acs.jpcb.7b10661 J. Phys. Chem. B 2018, 122, 399−400
