Special Issue Preface pubs.acs.org/JPCB
Cite This: J. Phys. Chem. B 2018, 122, 401−404
Autobiography of Miquel B. Salmeron
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CHILDHOOD I was born in Santa Coloma de Farners, a town in the province of Girona in Catalonia, the ancestral place of origin of my mother’s family. As a child I attended a Catholic school in Mataró, an industrial town 30 km north of Barcelona. The school, for boys only, combined kindergarten, elementary, and high school. Impressions in a child’s brain are deep and lasting, so it is not surprising that I have kept some of my most vivid memories from that time. I see myself during class breaks in school playing and indulging in my favorite game of narrating adventure stories improvised on the spot to a chorus of other boys, who listened and interrupted to insert their own stories, so that the narrative became collective, meandering left and right toward some unknown finale, unimportant per se, except that it served to keep our brains connected as in a symphonic performance. All this happened in Catalan, our native language, which was highly repressed during Franco’s fascist regime following the Spanish civil war. On one unforgettable occasion I was caught speaking Catalan in class with other students and punished with the task of writing 1000 times, “I will not speak in Catalan”. This was a shocking awakening of consciousness revealing the cultural oppression of post-civil war Catalonia. At the time the school was divided into two sections: one for the poor, the other for the rich (in spite of the fact that the school was founded by Saint Joseph of Calasanz in 1597 with the express mission of educating the poor). This division was justified by the syllogism that, to help the poor, money was necessary, and since tuition from the students of well-to-do families could provide it, it followed that the ends justified the means. Not surprisingly, the quality of the teachers was lower in the “poor student” section. I spent several years in that section since my family could not afford the higher tuition. My father, who had received a reasonably good education in a Seminary before the civil war (as education was free for candidates to the priesthood), quickly realized that I would not progress unless I moved to the “rich” section, which happened with great economic sacrifice for my family. The following years, however, bring happy memories. I learned quickly and insatiably. I wrote poetry because our compulsory periodic essay writing had to be several pages long if written in prose, but one page was acceptable if written as a poem. I now wish I had kept those poems (of childish quality to be sure), although I still remember one after nearly 60 years. My father was the real inspiration for my eagerness to absorb knowledge of all kinds, literary and scientific. He conveyed to me a love for science and a passion for reading, which was his main entertainment. I imitated him by reading during the long summer vacation periods all of his books (except those in Latin), and particularly those on natural science, a nicely illustrated Bible, and his adventure books.
was earning as a tutor. I enrolled in the five-year “Licenciatura in Mathematics” program, but after my second year, I changed to Physics. I found the math professors to be the best, and so became deeply engrossed in Calculus, Vector Analysis, Complex Variables, Hilbert Spaces, and the like. Physics lessons, however, were less engaging, with the exception of classical mechanics, taught by an inspiring young professor who helped me understand that conservation laws are the foundation of physics. I finished my Physics “Licenciatura” in 1967. To fill several gaping holes in my physics education, I taught myself by reading Landau’s “Mechanics” and “Electricity” books, which I found difficult at first, but a joy to read as I understood them better and better in successive readings. From Landau I came to understand the deep connection between symmetry and conservation laws. One day, in my last University year, Professor Gauthier from the University of Toulouse (France) came to give a seminar, a rare event at the time. His seminar about the solid state and magnetism made me understand what science and research really meant. After his seminar I ran up to him and implored him to take me to his lab. True to his promise of help, I soon received a letter with application forms for a Fellowship at the University of Toulouse, which was awarded to me two months later. That was one of the happiest days of my life. A few weeks later, small suitcase in hand, I traveled to Toulouse to pursue the equivalent of a Master’s degree in Solid State Physics. Living in France was an exciting experience, and not only scientifically; I was caught up in the political storms of the May 1968 revolution. My physics studies were spiced with readings of Marx, Engels, Marcuse, and Mao. Thinking of this later, I could not figure out how I was able to understand those books. In addition to absorbing science and politics, during that time I also learned to ski and rock climb, cementing a passion for mountain sports of all kinds, which I have practiced and enjoyed ever since. The Toulouse experience is worth mentioning because it was there that I became an experimentalist under the supervision of Prof. Ferdinand Pradal, who left Spain after the Civil war as part of the exodus of people escaping Franco’s victory. Prof. Pradal gave me as a research topic the study of the interaction of electrons with surfaces. I was given an Ultek Ion Pump and vacuum chamber, which a previous user had managed to destroy by blowing up the glass viewport during high vacuum operation. For me that meant dismantling the pump and chamber down to the last screw in order to remove the glass shards embedded in walls, titanium elements, and anything else inside. After this, I modified an electron gun salvaged from a discarded TV tube, replacing its broken filament. I learned enough electronics to build a power supply for the gun, which meant learning how to solder resistors, capacitors, transistors, and other components. I also built the electron detector: a spherical grid mounted in front of a spherical screen where the secondary electrons emitted by the sample were collected, the grid serving as a high band-pass
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UNIVERSITY YEARS Childhood ended abruptly after leaving school. In 1962 I enrolled as an undergraduate at the University of Barcelona, thanks to a fellowship from the government as well as money I © 2018 American Chemical Society
Special Issue: Miquel B. Salmeron Festschrift Published: January 18, 2018 401
DOI: 10.1021/acs.jpcb.7b10660 J. Phys. Chem. B 2018, 122, 401−404
The Journal of Physical Chemistry B
Special Issue Preface
filter. This early building experience served me well in my later scientific career. Ultimately, I finished my degree in 1970 with a Master’s thesis entitled “Anisotropy of the secondary electron emission of Cu single crystals bombarded by electrons, and construction of a retarding field Auger analyzer to study surface composition”.
upon returning to Barcelona as Minister of Education in Catalonia, created the new CERCA system of Institutes and ICREA, where researchers are recruited based solely on professional excellence. In 2003 Mas-Colell recruited me as a Scientific Advisor to help in the creation of the “Institut Catala de Nanocience i Nanotecnologia”, one of the CERCA Institutes. To this day I am still involved in an advisory role in his great and highly successful scientific initiative. Many of my fellow postdocs and students from that time later became professors in the US and Europe.
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PHD THESIS In 1970 Prof. Pradal took me to a conference in Grenoble with the purpose of introducing me to Prof. Nicolas Cabrera, a Spanish-born American scientist who had recently moved from the University of Virginia to Madrid, under the auspices of a new Spanish Education Minister (equivalent to Department Secretary in the US). Prof. Cabrera got his PhD in Paris under Louis de Broglie, of the wave−particle duality, and later worked with Sir Neville Mott in the UK. He was famous for his theory of oxidation of metals and crystal growth around spiral dislocations. The new Spanish Education Minister wanted to establish a new type of university, called “Autonomous”, with the intention of creating a new system that would improve science research and education in Spain. One of these “Autonomous” Universities was built in Madrid (UAM) and another in Barcelona (UAB). Prof. Cabrera hired me as a research assistant to work on my PhD while at the same time teaching laboratory classes to undergraduate physics students. In Madrid, Prof. Cabrera worked on the theory of helium scattering and diffraction. Through him I understood the importance of thermodynamics, which he explained to students and collaborators with masterful clarity. It was in Cabrera’s group, under the supervision of Prof. Juan Rojo, that I worked for my PhD, filing in 1975. My thesis centered on Auger electron spectroscopy and plasmon excitations in metal surfaces. Together with Artur Baró (another student) and Juan Rojo, we initiated the Surface Science laboratory from scratch, which expanded with successive students and researchers and became one of the finest in Europe. The outstanding reputation of Prof. Cabrera brought a string of visitors from all over the world who spent time in Madrid giving outstanding seminars. I still remember one given by Prof. Ilya Prigogine who, to please the audience, alternated his presentation language from French to English, a disconcerting experience for me given my good French background but poor understanding of spoken English at the time.
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INTERLUDE AT THE AUTONOMOUS UNIVERSITY OF MADRID After two years in Berkeley I returned to Madrid in August 1977, with joint appointments as a Physics professor at the UAM and a Staff Scientist at the Consejo Superior de Investigaciones Cientificas (CSIC), the Spanish Research Council. I worked in the Physics Department, developing a He scattering instrument to study diffraction in search of the surface resonances predicted by Cabrera’s theory, according to which the particles (He, H2, etc.) could stay trapped in bound states for some time, which could affect their reactivity. Academic life, however, was not the same as when I was a student. The political and administrative environment in the UAM had changed for the worse. The autonomy granted by the former Education Minister in the early 1970s, the main reason for Prof. Cabrera’s return to Spain, eroded after the change of Minister. The practices of the old Spanish academic establishment, where positions are filled for life after passing a competition, in reality perpetuated the cronyism and complacency which pervaded many University Departments. Stripped of autonomy except in name, the departments of the UAM were slowly sliding into the traditional system of tenured chairs, with little incentive for promotion or advancement based on accomplishments. Amazingly and in spite of this adverse environment, the Physics Department of the UAM continued to be the best in Spain, a tribute to Prof. Cabrera’s choice of faculty members. For me, however, the time was ripe for change.
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BACK TO THE USA That change came in 1983, following a phone call from Prof. Somorjai in Berkeley. A new “Center for Advanced Materials” had been created at the Lawrence Berkeley National Laboratory, and he strongly encouraged me to apply. Coincidentally, a position was also open at Exxon Corporate Research Laboratories, in New Jersey, where I had just spent a fourmonth sabbatical. I thus contemplated three possibilities: Berkeley, New Jersey/New York, and the UAM in Spain. I loved New York, but I also loved Berkeley. Finally I decided for Berkeley, attracted by its unique cultural and scientific environment, and by fond memories of my postdoctoral time. I moved there in August 1984, at 38 years of age, ready to start from scratch. I chose as my research topic the study of surfaces using scanning tunneling microscopy (STM), with which I had become acquainted during a visit to Madrid earlier that same year by Binning and Rohrer, who received the Nobel Prize for their invention in 1986. STM opened up the possibility of obtaining “pictures” of individual atoms and molecules, showing their binding site and their motions. I found the allure of this new technique irresistible and immersed myself fully in it. At that time computers were not yet commonly used in our research. The
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POSTDOCTORAL STUDY IN BERKELEY One of the visitors to the UAM was Prof. Gabor Somorjai, from the University of California, Berkeley (UCB). His visit and seminar stirred my interest and made me decide to pursue postdoctoral studies in Berkeley. After obtaining a Fulbright Fellowship, I moved to the USA in August 1975, married and with 3 children. My two years in Berkeley were another lifechanging experience. The scientific environment at UC Berkeley, and the Lawrence Berkeley National Laboratory (LBNL) on the hills (known then as the Rad Lab), was very stimulating. There I met and established contacts with illustrious scientists, both local and visitors. I will mention Professors Leo Falicov from the Physics Department, and Leo Brewer from Chemistry, with whom I had extensive discussions. Among the visiting professors, I will mention Gerhard Ertl from Munich (who later moved to Berlin, and won the Nobel prize in 2007), Manuel Cardona, director of the Max-Planck Society Institute in Stuttgart, and others. It is there also that I met Prof. Andreu Mas-Colell, who, 402
DOI: 10.1021/acs.jpcb.7b10660 J. Phys. Chem. B 2018, 122, 401−404
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SURFACE SCIENCE IN THE 21ST CENTURY: AMBIENT PRESSURE STUDIES In the year 2000 I initiated yet another new project, aimed at bringing surface science from the idealized world of high vacuum environments to the ambient pressures of the real world. Most of the spectroscopic tools based on electron probes, which made surface science so successful, operate in high vacuum conditions. Thanks to an internal funding program from the LBNL aimed at supporting new, high-risk ideas, I initiated a new project to address this situation. In collaboration with C. Fadley and Z. Hussain, scientists working at the Advanced Light Source (the Berkeley Synchrotron), with postdocs Hendrik Bluhm, Eleonore Hebenstreit, and with Frank Ogletree, we designed a new electron spectrometer capable of operating under gas pressures up to several Torr, an instrument which we called “Ambient Pressure X-ray Photoelectron Spectroscopy” (APPES or APXPS). With this technique, and in rapid succession, we attacked several outstanding problems of the time. First we clarified the old controversy of the premelting of ice (does the ice surface melt before 0 °C?), a controversy dating back to the time of Lord Kelvin and Michael Faraday. We found that although a thin water film at the surface becomes disordered or liquid, the thickness of this film depends strongly on the presence of even minute amounts of adsorbed impurity molecules, which our APPES could measure in situ for the first time. Next, in collaboration with John Hemminger from U.C. Irvine, we demonstrated that, in saline water droplets present in the stratosphere, the halide component segregates preferentially to the surface which, when exposed to solar radiation, triggers reactions implicated in ozone depletion. Other studies related to water followed soon, including the growth of water films on metals and oxides in equilibrium with the vapor, working in collaboration with the groups of Prof. Gordon Brown from Stanford University, and Anders Nilsson from SLAC, now at Stockholm University. In collaboration with Prof. Somorjai, from U.C. Berkeley, we demonstrated that catalyst surfaces can change and restructure, often dramatically, in the presence of reactant gases, bringing forth a new understanding of catalyst structure during a reaction. The success of the APPES led to collaborations with Prof. Robert Schlögl from the Fritz-Haber Institute and with the company SPECS from Berlin, Germany. From this an improved system based on our original design was developed and soon became commercially available through SPECS, and from other companies soon after. It is very gratifying to see that many synchrotron facilities in the world have installed the commercial APPES instruments (with names such as NAPPS, APXPS) that are open for use by all scientists. In these years I also became deeply involved in scientific administrative tasks in the laboratory, including being part of the team that created the Nanoscience Institute known as the Molecular Foundry in 2002 and one of its facility directors, and later director of the Materials Science Division, from 2008 to 2012.
images were acquired by recording line traces of the scanning tip on a chart recorder paper as it moved over the surface. My first STM paper, published in 1987 in Phys. Rev. B, showed the structure of stepped Au(334) in air. Frank Ogletree, one of my first postdocs, wrote the code for a program (Fortran and later C +) for data acquisition that allowed us to record images in digital form and to display them with vivid colors on graphic monitors. To this day I still keep a beautiful image of a layer of carbon atoms on platinum acquired in air, a structure today called graphene. For several years Frank and I collaborated and further developed the STM technique. Our efforts led to an STM instrument made by commercial companies based on our initial designs: McAllister Technical, which built the scanning hardware, and RHK Technology, which built the electronic controller. This was one of the first commercial STM instruments in the USA. Over the following years, with STM I studied the structure of atoms and molecules on surfaces, particularly water, focusing on molecular manipulation, using the STM tip to excite specific vibrations and electronic transitions that triggered diffusion, rotation, and dissociation of the molecules.
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NANOTRIBOLOGY
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WATER
Special Issue Preface
In the mid 1990s my interests expanded to the area of tribology, the science of friction, adhesion, and lubrication, phenomena poorly understood at the atomic level. I built an atomic force microscope (AFM), because the atomically sharp tip of this instrument embodies the sharp asperities found in real macroscopic contacts. Another instrument that I built is the surface forces apparatus (SFA), following the lead of Prof. Jacob Israelachvili from UC Santa Barbara. In this instrument two curved surfaces are pressed against each other to simulate a flat contact with exquisite control of pressure and displacement distance. With a joint student with Prof. Y. Ron Shen of the U.C. Berkeley Physics Department, we used optical sum frequency generation to study the structure of molecules in the interface between two glass samples covered with lubricating molecules. This was the first time, to my knowledge, that spectroscopic methods were used while pressure was applied to lubricant molecules. More than 80 papers were produced as a result of these projects.
Water is a material that has always fascinated me. It pervades everything on earth: living things, the atmosphere, rain, oceans. In contact with water, materials dissolve and corrode; this raises the question of what the atomic scale structure of the solid− liquid interface is. I wanted to understand hydrophilicity: Why does water spread on some surfaces and bead up forming droplets in others, as on the petals of flowers and on plant leaves? I started to study water in the mid-1990s using the STM and AFM techniques. A talented student, Jun Hu from Shanghai, was the first to use electrostatic force AFM to acquire images of molecularly thin water films on mica. Later, we used STM at low temperature (to immobilize the water molecules) on metal surfaces in vacuum, and studied their binding to form tiny droplets of a few molecules. This beautiful work was carried out by many students and postdocs over several years, and resulted in the publication of more than 80 papers on the subject.
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MOVING ON TO NEW DIRECTIONS These advances in surface science, while satisfactory, are still far from complete. Many important phenomena take place in environments reaching several atmospheres of gases, much higher than what is possible in our current APXPS instruments, or under liquids. Extending the pressure range, and particularly including liquid environments, is a task I have embraced in the 403
DOI: 10.1021/acs.jpcb.7b10660 J. Phys. Chem. B 2018, 122, 401−404
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past few years, and good progress has already been made. With STM, with X-rays, and with other spectroscopies, I now study solid−gas at atmospheric pressure, and solid−liquid interfaces with the goal of bringing fundamental understanding to the phenomena taking place there. Many of these are related to catalysis, to environmental sciences like reduction of CO2, to corrosion, and to photo- and electrochemistry. The presence of intense electric fields at the electrode−electrolyte interface poses new challenges that have been the object of decades of intense studies. Together with colleagues, students, and postdocs I am developing new techniques based on the use of ultrathin membranes transparent to X-rays and to electrons to make solid−gas and solid−liquid interfaces accessible to fundamental studies with the highest level of atomic spatial and spectroscopic resolution, which will enable new discoveries to improve our understanding of materials science in realistic environments.
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EPILOGUE My long experience has taught me several lessons that I would like to share with those who have been patient enough to read this short autobiography. The first is that finding a goal in life that is both the purpose of your profession and your passion is the key to happiness and success. Feynman captured the essence of this when he spoke of “the pleasure of finding things out,” just because they are there, just because natural phenomena are beautiful, just to satisfy your curiosity. I was lucky that curiosity toward science in general was imbued in me by my father talking about planets, stars, and other things that he read about and recounted to me as topics of wonder. I was also fortunate that, in spite of the economic, political, and cultural difficulties that surrounded my early years, I had a family which, although not rich, was very supportive, even my mother in spite of her early opposition to my going to the University to pursue a career that she did not understand. Their support and belief in me made possible my escape from the cultural and intellectual mediocrity of life in Spain in the long decades of 1950s and 1960s. The second lesson and advice that I would like to convey is that experimentalists in particular need to understand the instruments they use in an intimate way. Like children building toys, students need to tinker with instruments, which often means taking them apart, breaking them, and rebuilding them. I recommend this as the best way to later develop the initiative to invent new gadgets and methods to solve scientific problems or to simply satisfy a curiosity. Finally, the third lesson is that since science is rarely a solitary endeavor, particularly in experimental research, one must be able to attract and to associate with colleagues, students, and postdocs, people with whom to share your enthusiasm, much as I did by storytelling in my childhood, but now at a higher intellectual level. I have been extremely blessed in this endeavor, and it is to my parents, family, friends, mentors, advisors, and many talented and motivated students and postdocs that I owe whatever success I can claim.
Miquel B. Salmeron
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DOI: 10.1021/acs.jpcb.7b10660 J. Phys. Chem. B 2018, 122, 401−404
