Building with Molecules
As told by Jacob Sagiv
When human endeavors and luck happen to join forces, something of value may be achieved.
I was born in February 1945 in Iasi, Romania – the only child of my parents six years after their wedding. In between, they were lucky to survive the holocaust in Romania allied with Nazi Germany, my father being a survivor of the Iasi “death trains” of June 1941. Two years later, we moved to Roman, a town in central Moldova region of Romania, where I spent my childhood until our emigration to Israel in 1961. This was a difficult time for my family. As a child, however, I was lucky to enjoy the pleasures of life in a small east European town of the 50s, with friends playing on the streets free of polluting cars and in the beautiful city park, or swimming in the still clear waters of the Moldova river. Also in Roman, I was fortunate to discover the taste of science.
Besides less pleasant aspects of life under a communist regime, there were also good things there, and science education in school was one of them. My parents were accountants, far from any preoccupation with science, but getting educated was a top priority in our family. Two older cousins, a math teacher and an electrical engineer, became my role models, and I was lucky to have good teachers. I fell in love with chemistry and physics right from the first science lessons at 5th grade. By the age of 10-11, I started setting up a lab in the entry hall of our small apartment, where my first successful experiment was the dry distillation of wood in a still that I built from shoe polish jars with metal lids, into which I inserted copper pipes and sealed them with tar. Later on, during high school, I prepared gunpowder at home in my lab and used it to fuel Chinese arrows. These were little rockets made by attaching a metal tube filled with gunpowder to a regular arrow. When a new batch of gunpowder exploded as I tried to homogenize the mixture and set fire to the carpet under my feet, my father decided to put an end to this activity. I was told he understands that a scientist may even sacrifice his life for the sake of science, but “not for something that has already been discovered”... This was intended not to discourage me from further playing chemistry, but not with such dangerous materials.
In 1961, by the end of my third year in high school, we finally received our permit for emigration to Israel. It was the time of a great wave of emigration of the Jewish population of Romania, and to obtain the emigration permit, we had to relinquish our Romanian citizenship. It will take a whopping 58 years to regain it – today I am a citizen of both Israel and Romania.
Teenager in a new land
Starting a new life in a new country at sixteen is, most probably, not something psychologists would recommend, even more so given the conditions offered to new immigrants in Israel at that time. After a journey of more than twenty days, by train to Venice and aboard a ship across the Mediterranean, we finally arrived to Haifa port on a hot morning of June. From the port, we were immediately transferred to the bare sands of Pardess Hanna. Nestled in dunes not far from the beach, 40 Km south of Haifa, Pardess Hanna was at that time a small township looking more like a very large village. The housing for newly arrived immigrants were asbestos huts – notoriously known today as a health hazard. Without air conditioning, the huts offered on the day of our arrival a “pleasant” indoor temperature well above 30°C! The water coming out from the tap was so hot, that, in the absence of a refrigerator, we had to make hot tea for drinking…
It was again a difficult time for all of us. I went to a kibbutz where I learned the Hebrew language while also working part time in the fields as a tractor driver. To make some money for their living, my parents had to take several random jobs until having the opportunity to learn the Hebrew language at a decent level that would allow them to work in their profession. We worked hard, but were determined to succeed and managed to overcome these integration hardships.
After nine months at the kibbutz, my Hebrew was sufficient to be admitted into the young regional high school of Pardess Hanna, established just a few years earlier. Here I was lucky again, as I had the chance to be one of only eleven pupils in a class offering high-level lessons in chemistry, physics and mathematics. We had good teachers, and my interest in chemistry led to a particularly close relationship with Rina Ravid, our wonderful chemistry teacher. As organic chemistry in Romania was taught only in the last year of the high school, and the foreign languages there in school were Russian, French and Latin, I spent the summer of 1962 learning English and the basics of organic chemistry from a nice booklet that Rina gave me. The following summer I went to work in a factory, to earn money with which I purchased a bicycle that gave me the freedom to travel throughout the scattered neighborhoods of Pardess Hanna during my last year in high school there.
In the summer of 1964, I passed successfully the “bagrut” exams (matriculation) and a month later I was already a sweating rookie in the IDF (Israel Defense Forces). About the same time, my parents left Pardess Hanna, moving to Rehovot where my father found a better job. It was the first step toward the Weizmann Institute.
I went to the military knowing that we cannot survive without it, not as a nation and not as individuals. It was the lesson learned from a long history that culminated with those who, just a quarter of a century earlier, were less lucky than my father who managed to survive the death train in Iasi. Even these very days in Israel, we can exist only as long as we have an army that ensures our existence.
I served in the artillery, and, by the time I completed my PhD studies, have already participated in two wars and numerous other mini-war operations that many no longer remember.
Chemistry at the Hebrew University of Jerusalem
In the fall of 1966, my regular military service was over and so I could start my next “career” in the reserve IDF forces as well as my undergraduate chemistry studies at the Hebrew University of Jerusalem. I enjoyed most of the courses and in particular the long days in the labs. Earlier that year, while still a soldier, I attempted admission at electrical engineering at the Technion in Haifa. I was thinking about a practical profession, I liked physics and the choice of electrical engineering fitted my role model – my cousin, the electrical engineer. Playing chemistry as a scientist seemed to me more like an unrealistic fantasy. But I was not destined to become an electrical engineer. After two years in the military, my performance at the admission exam was below the entry threshold set by the faculty of electrical engineering. I was finally free to pursue what I was destined for – the career of a research chemist. As it turned out, failures are not always failures, and this failure was indeed a blessed one! In 2010, I was awarded the Kolthoff prize of the Technion – the institution where my failure 44 years earlier paved the way to this prize!
In June 1967, I spent three weeks in the army, taking part as a reservist in the Six-Day war. About the same time, my parents finally managed to purchase an apartment in Rehovot, in a new apartment house on a street next to the campus of the Weizmann institute. A year later, this will bring me to the institute.
Student at the Weizmann Institute
The summer of 1968 was a quiet one, and so I spent it at home with my parents, looking for a summer job that will give me some income for my last undergraduate year in Jerusalem. Chatting with a neighbor, gardener at the Weizmann Institute, I came to know about the summer students program at the institute. My 54-years-long connection with the Weizmann Institute was about to start a few days later.
I was admitted to the group of Prof. Yehuda Mazur in the department of organic chemistry. Since I expressed interest in physical chemistry, while no such department existed at that time at Weizmann, professor Mazur suggested that I join a new “physical chemistry” project carried out in collaboration with Dr. Amnon Yogev. It was concerned with the development of a quantitative linear dichroism methodology in the UV-visible, that is, spectroscopy with polarized light of organic molecules oriented in stretched polymer films like polyethylene and polyvinyl alcohol (PVA). I was given the task of resuming work started a few months earlier by a student who in the meantime left in tears after a series of unsuccessful preliminary experiments… To my surprise (and delight), I was given much freedom in this research work. A paper summarizing results that I obtained during that summer was submitted to the Journal of American Chemical Society in January 1969: “Studies in Linear Dichroism. II. Measurement of the Transition Moment Vector of α,β-Unsaturated Ketones, and of Some Geometrical Properties of Steroids”, A. Yogev, J. Riboid, J. Marero, Y. Mazur, J. Am. Chem. Soc. 1969, 91, 4559. This is my first and only paper bearing my original name – Jacob (Iancu in Romanian) Meraru. Its distorted spelling (Marero) was one of the reasons for changing it. At that time, many in Israel used to replace their birth names with Hebrew-sounding versions. One issue with foreign names in Israel is that the Hebrew spelling usually omits vowels, which the reader adds depending on context. In the case of surnames like mine, the same word could read Meraru, Marero, or any other combination of m-r-r plus added vowels. I changed it to Sagiv, which sounds nice in Hebrew – an epithet used in the Bible to praise God as powerful, sublime.
Enchanted by the friendly research atmosphere and my good summer experience at Weizmann, I decided to come back for my graduate studies. A year later, linear dichroism will become the topic of my master and then doctoral work under the guidance of professors Amnon Yogev and Yehuda Mazur. Amnon and Yehuda were ideal supervisors for me. They granted me freedom of action and so I learned how to conduct independent research and solve problems that popped up along the way.
Besides the research work at Weizmann, by the end of the summer, I also managed to get married. A year later, in October 1969, we were back in Rehovot and I enrolled as a master student at the Weizmann institute. I had succeeded in my research work and so became the first master student in the faculty of chemistry admitted to the direct PhD track that was just initiated at Weizmann. This meant that instead of writing a master thesis I submitted a PhD research proposal based on the results of research carried out up to that point. This further meant that I would complete earlier my duties for the PhD degree, which was expected to happen by the end of 1973. However, expectations and reality only seldom go together.
On October 6, 1973, Egypt and Syria launched a simultaneous surprise attack on the Israeli positions along the Suez Canal and on the Golan Heights, and the day after I was already in full combat gear on the way to the Syrian front, carrying in my backpack the draft of a paper that I hoped to complete there. The official ceasefire in the Yom Kippur was declared on October 25, 1973. This, however, did not put an end to the artillery fire exchange on the Golan Heights, which went on until April 1974, when I was finally released from the army. The last sentence in the paper draft in my backpack was still where I left it on October 6, 1973… and everything concerning my research work had to be postponed accordingly.
I started looking for a postdoctoral position abroad, but my supervisor, Amnon Yogev, decided to take a sabbatical outside the institute and, being the senior student in his group, I was asked to further postpone my eventual departure in order to take care of the group in his absence. In recompense for this, Amnon told me, he agreed with the president of the institute that I would benefit of a 3-years research position at Weizmann upon my return from the postdoctoral training. With this tempting offer in mind, I postponed my departure until November 1975.
LB monolayers in my head
Leon Margulies, a colleague and friend with whom I was collaborating (both of us working on linear dichroism under the guidance of Amnon Yogev), was considering a postdoctoral position at the Max-Planck-Institut für biophysikalische Chemie in Göttingen. Chatting with him one day, a figure in a journal volume on his desk suddenly caught my attention. It showed something I had never seen before. It looked like an ordered array of sticks connected to small circles, arranged in a manner suggesting superposed regular rows of such units. “What is that?”- I asked. Leon explained this was a schematic representation of Langmuir-Blodgett (LB) monolayers studied in Hans Kuhn’s laboratory at the Max Planck institute in Göttingen. I vividly remember the strong feeling of a revelation during that chat with Leon. I looked immediately for more material about Kuhn’s group work, and, as I read through those papers, I knew that all I wanted to do was playing with such layers of ordered molecules and nothing else.
A nice response from Hans Kuhn to my letter inquiring about a postdoctoral position with him, and a Minerva postdoctoral fellowship that I was lucky to obtain and gave me the freedom to carry out independent postdoctoral research set the stage for my research in the years to come.
My daughter Michal was born in August 1975, and by November, the three of us arrived in Göttingen, where we will spend the next almost three years.
Göttingen – the excitement of discoveries
From Langmuir-Blodgett to Adsorbed Monolayers
Hans Kuhn’s Abteilung Molekularer Systemaufbau (Department of Molecular Systems Assembly) offered unique capabilities for creative research with LB monolayers. Using mixed monolayers of fatty acids and fluorescent dyes placed one on top of the other in various planned arrangements paved the way to exciting studies of energy and electron transfer across nanoscale dimensions that could not be realized otherwise. The LB method was ideally suited for this purpose. It provides precise control of the sequence and distance between individual monolayers along the out-of-plane Z axis. It does not allow, however, further manipulation of the molecular organization within the layer plane (XY). Thus, the molecular orientation in the XY plane was always random.
By the time I joined Kuhn’s department, they were examining the feasibility of a procedure that would allow also control of the in-plane orientation of elongated dye chromophores. The basic idea was that depositing a mixed monolayer containing such dye molecules on an anisotropic hydrophilic surface would induce a preferential alignment of the dye chromophores via epitaxial interactions with the surface. Some unsuccessful such experiments had already been performed using cleaved gypsum crystals as a solid substrate with an anisotropic hydrophilic surface. Knowing that my doctoral work was concerned with molecules oriented in stretched polymer films, Hans Kuhn suggested that I join this line of research. I agreed. The issue appeared to me interesting as well as challenging.
Gypsum was obviously a bad choice. Its anisotropy does not necessarily correlate with a particular orientation of dye chromophores that are geometrically unrelated to its surface motif. But more than that, gypsum is slightly soluble in water, which means that the anisotropy of its outermost surface layer is most probably lost as soon as it comes in contact with the water in a Langmuir trough. A simple well-defined anisotropic material capable of inducing a preferential uniaxial orientation of elongated molecules interacting with it was obviously a stretched polymer of the kind I had been using in my PhD work at Weizmann. Therefore, I started testing this approach. It was further necessary to stabilize the uniaxial alignment of the polymer chains on the polymer surface exposed to water in the Langmuir trough, but this seemed a manageable problem, to which I was indeed able to find satisfactory solutions. While the experiments with the gypsum crystals went on without me, I started experimenting with the stretched polymers as monolayer substrates. But all my attempts to induce uniaxial orientation of dye chromophores in LB monolayers were equally unsuccessful.
This was once again a blessed failure. It led me to realize that reorientation of molecules in LB monolayers transferred under high surface pressure from the water-air interface may not be possible, simply because molecules immobilized in such solid-like films cannot move. The obvious conclusion from these experiments was that to be able to induce in-plane molecular orientation, the monolayer-forming molecules should be free to interact with the solid surface already in the course of the monolayer build up process. With other words, not Langmuir-Blodgett, but direct monolayer formation on the solid surface by adsorption of molecules from solution. I started testing this idea and immediately obtained exciting results. I was thrilled to discover that those “stubborn” dye chromophores finally behaved according to my expectations! But how could it be that no one did it before?! I went to the library to search the Chemical Abstracts (it was long before Google and the Internet..), and with some effort finally discovered the relevant work of W. Zisman’s group at the Naval Research Laboratory, starting with their seminal article “Oleophobic Monolayers. I. Films Adsorbed from Solution in Non-Polar Liquids”, J. Colloid Sci. 1946, 1, 513. This assured me that it should indeed be possible to obtain monolayers by adsorption that resemble those prepared by the LB method. Though I rediscovered something that had already been discovered before, what I did offered an extra bonus – I found how to control the in-plane molecular organization in adsorbed monolayers. The mixed monolayers with oriented dye molecules formed by coadsorption of the dye and the main monolayer forming surfactant were more complex structures that paved the way to new research avenues, beyond what could be done with either one-component oleophobic monolayers or with LB monolayers.
Silane monolayers – OTS
Looking for some dimethyldichlorosilane, which I used to make hydrophobic glass slides for the deposition of LB monolayers according to a standard procedure employed at that time, I came across an unopened bottle like those of dimethyldichlorosilane, on the label of which appeared the name of a compound I had not been aware of until that moment – Octadecyltrichlorosilane (OTS). It was a molecule like stearic acid, in which the carboxylic acid is replaced by a silane head group. Would such a molecule make good adsorbed monolayers as well? OTS was to become the “hero” of self assembling silane monolayers.
The irreversible covalent bonding of organosilanes to a large variety of polar surfaces paved the way to many applications that are not feasible with any other monolayer system. I prepared mixed OTS-dyes monolayers and skeletonized monolayers with molecular holes left by the dissolution of the physisorbed dye molecules, and used them to demonstrate memory effects in monolayers on glass and on polyvinyl alcohol, as well as create well-defined pinhole defects in the study of electron tunneling through monolayer barriers on aluminum. All this was new and esoteric in that Mecca of LB monolayers around me. I used to update Hans Kuhn about my results, but the entire activity around me remained focused exclusively on LB monolayers. Yet, a fruitful collaboration had developed with a colleague postdoc and friend, Epaminondas (Notis) E. Polymeropoulos, who was working on electron transfer through LB films. Our joint work on the “electrical conduction through adsorbed monolayers” (J. Chem. Phys. 1978, 69, 1836) – the first one on electron tunneling through such monolayers – offered independent evidence that confirmed their ordered structure, further demonstrating the superior performance of OTS monolayers as electron barriers.
The results obtained with the adsorbed monolayers, in particular with the silane monolayers, pointed to a series of unique features of such surface entities, which rendered them attractive for basic research as well as for various technological applications that would not be possible with LB films. Yet, the adsorption was limited to the formation of a single well-defined monolayer, whereas the LB technique offered a versatile tool for the assembly of planned multilayer films of the kind used in the exciting experiments going on in Kuhn’s department. It was clear to me that bringing adsorbed monolayers to the forefront of research would demand advancing a new methodology that allows building adsorbed multilayer structures akin to those built by the LB technique. I had already a good idea (as subsequently confirmed) how to do this, but it was a challenging task for which I needed a research environment providing chemical and analytical tools that were not available at the Max Planck institute in Göttingen. Therefore, without giving too much thinking to Kuhn’s kind offer of a position at Max Planck, I decided to return to the Weizmann Institute, where a 3-years research position was supposedly waiting for me.
Back in Rehovot – hardships and victories
From monolayer to multilayer by adsorption – adventures of a young researcher
In September 1978, we were back in Israel. At Weizmann, I was to discover that promises made three years earlier were no longer remembered. All I could obtain was a bench in the laboratory of my former PhD supervisor Amnon Yogev. I had great research plans, but no money and no laboratory where I could possibly bring them to fruition.
It will take more than a year to have a one-room laboratory with a hood and some basic equipment for organic synthesis, where I launched the adventure of layer-by-layer assembly of multilayer films with two PhD students (Rivka Maoz and Julio Gun) and two master students (Lucy Netzer and Radu Iscovici). It will take another year until a first inexpensive FTIR spectrometer will be purchased for general use, including by my students. By 1981, quantitative FTIR spectroscopy has already become a main analytical tool in our monolayer work.
What we set out to do posed risky challenges that a young researcher at the start of his career is expected to avoid. The project presumed successful implementation of the following sequence of interdependent steps: synthesis of novel organosilanes (specially designed for this task) that should yield well-ordered monolayers by adsorption; post-assembly functionalization of the outer surfaces of these adsorbed monolayers by chemical processes that should preserve their ordered structure; assembly of ordered bilayers by the adsorption of a second ordered monolayer onto the functionalized outer surface of the first monolayer, repetition of the surface functionalization and adsorption operations for the formation of a trilayer, and so on. It further demanded the advancement of a methodology of surface analysis that may provide unequivocal quantitative evidence for the monolayer/multilayer surface functionalization and the monolayer/multilayer formation. Each of these steps would be a journey in terra incognita, and the failure of just one of the steps would result in the failure of the entire project; like the climber whose single wrong step would prevent him from reaching the summit of the mountain.
Why did I embark on this adventure? In retrospect, I find that my entire life as researcher has been a succession of such research adventures. I have always done what appeared to me necessary scientifically, thinking less about what has to be done to promote a career as required by the accepted indicators of academic success. I could not act differently; this was my destiny, as well as the source of the recurring difficulties I faced along the way, until these very days.
In August 1982, we submitted a communication briefly reporting the first results of our work on the layer-by-layer assembly, and in September presented them at the first international conference on LB films in Durham, Gt. Britain. The communication appeared in the February 1, 1983 issue of Journal of the American Chemical Society, and two full papers followed later during 1983 in the proceedings of the Durham conference in Thin Solid Films. A note in the April 7, 1983 issue of the magazine New Scientist refers to our work published in J. Am. Chem. Soc. under the title “Monolayer films that assemble themselves” - “Self-assembling monolayer films”. A new field of research was born – the field of self-assembling monolayers! In the Chemistry in Britain issue of November 1983, a similar note refers to our layer-by-layer self-assembly principle under the title Monolayers; Molecular self-organization.
Although not yet perfect, the feasibility of the layer-by-layer self-assembly concept has been established. In November 1983, our first comprehensive article in the series “On the Formation and Structure of Self-Assembling Monolayers” was submitted for publication (published in the August 1984 issue of Journal of Colloid and Interface Science). This is the first scientific paper making use of the new term “self-assembling monolayer”, and its first author, Rivka Maoz, will be the first student to complete a PhD degree (1985) in the new field of self-assembling monolayers. A second comprehensive article in this series followed in the September 1984 issue of J. Colloid Interface Sci. In these articles, we combined several methods of surface analysis, establishing quantitative correlations between LB and self-assembling monolayers on the basis of quantitative FTIR spectroscopy data. With these publications, a reliable foundation for the advancement of the concept of nanofabrication via planned surface self-assembly had already been laid down.
Victory and its repercussions
We managed to emerge victorious from our research adventure in the land of self-assembling monolayers, but, as it turned out, it was a victory with self-destructive consequences. By the end of 1984, the Weizmann institute decided on my promotion to associate professor without tenure. This meant that I had to leave the institute within a year, thus putting an end to the research on monolayer self-assembly at Weizmann. Most likely, this could signify the premature death of the entire newly born field of self-assembling monolayers, but it could also be that our victory would someday be celebrated somewhere else… I started checking offers from research institutions in Israel and abroad.
Recovery. A new life
On the edge of an abyss, also at this crossroads in my life, destiny was to change the anticipated course of action. Appeals by a number of influential scientists abroad, who were aware of the significance of our achievement, led to a reconsideration of my situation. I was offered the chance to run again for tenure, however, subject to a series of restrictions that had significantly affected the progress of our research. In 1989, I was finally granted the tenure.
I did not quit. Events affecting my personal life contributed to make me give up the option of relocation. In 1986, after both our marriages had ended, Rivka Maoz and I were at the beginning of our now 36 happy years of life and research partnership. This demanded that our young children – Rivka’s sons, Ehud (4) and Omri (2), my daughter Michal (11) and son Avi (4) – stay close to both their separated parents. In addition, Ehud (autistic) and Avi (with intellectual disability caused by accidental brain damage at childbirth) were (and still are) children with special needs, demanding special living conditions and medical care.
Rivka and I will become an inseparable team. The vision of nanofabrication via surface self-assembly will continue to guide our joint research, each of us contributing synergistically to its success. As before, we’ll focus efforts on doing what this vision tells us to do, giving little thought to what should be done in order to ensure the means needed for doing what we want to do. Notwithstanding funding difficulties created by this style of research, it will lead in the coming years to a series of exciting discoveries and inventions that offer unique nanofabrication capabilities based on surface self-assembly.
Self-assembly beyond the monolayer
The discovery of self-assembled silane multilayers with interlayer hydrogen bonding (1990) led to the invention of hierarchical self-assembly of non-centrosymmetric polar superlattices via spontaneous one-step intercalation into such layer-by-layer self-assembled multilayers (1990-1995). Non-centrosymmetric superlattices with intercalated fluorescent molecules were shown to exhibit the effect of second harmonic generation (in collaboration with Garry Berkovic).
Investigating the process of intercalation in silane multilayers with interlayer hydrogen bonding led to the surprising discovery of self-replicating multilayers (1996 -1998). These are multilayer structures obtained by the planned deposition, via chemically triggered intercalation, of more than a single ordered monolayer in a single self-assembly step.
The discovery of non-thermal chemical modifications induced by microwaves in a purpose-designed bilayer structure bears relevance to the understanding of possible mechanisms by which microwave radiation might affect nonthermally bilayer cell membranes in living organisms (1998).
Collaborative projects with the participation of PhD student Ke Wen, Helmuth Möhwald (Universität Mainz), Benjamin Ocko (Brookhaven National Laboratory, Upton, NY) and Alain Gibaud (Université du Maine, Le Mans) enable us to apply Synchrotron X-ray radiation to the characterization of self-assembled monolayer and multilayer structures. Likewise, X-ray photoelectron spectroscopy (XPS) has been applied at Weizmann in collaboration with Hagai Cohen.
Constructive nanolithography (CNL); Constructive microlithography (CML)
The discovery of the possible local electrochemical functionalization of a highly ordered organosilane monolayer with a conductive atomic force microscope (AFM) tip (1998-1999, in collaboration with Sidney Cohen) offered a versatile novel tool for the non-destructive nanopatterning of such monolayers. Combining the non-destructive monolayer nanopatterning with various post-patterning processes of surface self-assembly, the nanofabrication methodology referred to as constructive nanolithography paved the way to nanofabrication with monolayer templates on nanometer length scales (2000, with Sidney Cohen and PhD student Eli Frydman).
In collaboration with postdoc Stefanie Hoeppener, Lifeng Chi and Harald Fuchs (Westfälische Wilhelms-Universität, Münster), CNL was applied to the bottom-up assembly of metal parts of a nano-circuit (2002). The feasibility of planned self-assembly of metal nanoparticles on monolayer templates fabricated by CNL was further demonstrated (2002-2004, with postdoc Shantang Liu and Günter Schmid – Essen Universität).
Constructive microlithography – the extension of CNL to micrometer-millimeter length scales, by the use of a conductive stamp instead of an AFM tip, is demonmstrated in 2003 by Stephanie Hoeppener.
Contact electrochemical replication (CER); Contact electrochemical patterning and transfer (CEP-CET); Wetting driven self-assembly (WDSA)
Based on the principle of non-destructive electrochemical patterning of monolayers with an electrical stamp (CML), the invention of contact electrochemical replication (CER) of an entire monolayer pattern using the monolayer pattern itself as stamp paves the way to rapid, one-step replication of multiple monolayer patterns (2003-2008, with postdoc Stefanie Hoeppener, PhD student Assaf Zeira, and postdoc Devasish Chowdhury).
CEP-CET is a two-step process discovered while studying the CER process that allows effective non-destructive electrochemical printing and transfer of entire metal/monolayer patterns spanning length scales from centimeter to nanometer (2010-2012, with PhD students Assaf Zeira and Jonathan Berson).
WDSA – a surface self-assembly process driven by the selective adherence of a liquid to wettable surface regions patterned on a monolayer surface that is not wetted by the liquid – takes advantage of monolayer patterning by CNL, CML, or CER to create nanopatterns of various selected materials, including metals, on patterned monolayers serving as templates (2005-2007, with postdoc Devasish Chowdhury).
A new journey in terra incognita – adventures of an old researcher
By 2012 we had managed to put together a rather unique tool box of nanofabrication based on self-assembled OTS monolayers. Particularly remarkable in constructive lithography and the other nanofabrication methods derived from it is that all these processes rely on the direct non-destructive surface functionalization of an inert monolayer, assembled from the simplest and least expensive commercial organosilane – OTS. This not only eliminates the need for costly syntheses of functional monolayer forming compounds, but the patterning of OTS yields the highest density of active surface groups in a self-assembled monolayer. As it turned out, this feature will play a critical role in our research in the years to come.
It was also by 2012 that we had finally managed to have a laboratory well equipped for our research needs. We were in the possession of some unique nanofabrication tools and had great plans as to what to do with those tools. Finally, we were in the position to fulfil our promise of the power of monolayer self-assembly. It could not be better; but it was too good to be true – I forgot the clock!
In 2012, I was 67. At 67, one is expected to enjoy achievements of the past, not strive for new ones. Accordingly, by 2015, what was left from our laboratory and the research funds that we would be allowed to use would supposedly have granted us not more than the freedom to dream about our research plans…
Now, ten years later, the lesson learned from our own experience tells us once again that man-made rules cannot stop determined human beings from fulfilling their dreams. Vis-à-vis the new restrictions imposed, Rivka Maoz has gradually assumed the actual implementation of most laboratory tasks, which would decisively push forward our research. It will become an exploratory journey that keeps generating exciting new surprises.
Single-layer nanoionics (2010-2015, with the participation of postdocs Jonathan Berson, Doron Burshtain and Assaf Zeira)
Using the constructive lithography capabilities, we demonstrate the unprecedented realization of atomically-thin ion conducting surface channels with planned layouts that span lateral dimensions from nanometer to centimeter. The key to the realization of such channels is the possible non-destructive generation of dense arrays of ionic surface groups within the otherwise insulating outer surface of an OTS monolayer.
Inerfacial electron beam lithography (IEBL) – monolayer nanopatterning on lateral length scales from nanometer to centimeter
IEBL is a new surface patterning methodology, analogous to the patterning with a conductive AFM tip or stamp in constructive lithography, that exploits our discovery of a new type of interfacial solid-phase chemical transformations induced by exposure to electron beams, or X-ray radiation, or ultraviolet light. IEBL is applicable to the non-destructive patterning of self-assembled monolayers on length scales from nanometer to centimeter.
IEBL pushes the limits of chemical monolayer patterning beyond what may be realized by other patterning methods. As the structural integrity of the patterned monolayer is preserved in IEBL (no material is subtracted or added in this process), it allows, like in the constructive lithography patterning, realization of seamless chemical patterns on OTS, namely, patterns free of structural discontinuities/defects at boundaries between functionalized and unmodified surface regions. This capability is critical in the patterning of leakage-free electrically conducting paths embedded within an electrically insulating monolayer background. Currently, IEBL is the only patterning methodology that allows fabrication of continuous conducting nanowires for direct electrical connection of the nano- to the macro-world.
The development of IEBL has continued since 2012, with the participation, in its different stages, of Jonathan Berson, Doron Burshtain, Ora Bitton, Hagai Cohen, Peter Nelson, Ariel Zinger, Bedanta Gogoi, Santanu Talukder, Shuangyang Zou, Arup Sarkar. Current work focuses on the investigation of various advanced modes of implementation of the IEBL concept.
IEBL-patterned OTS monolayers exhibit puzzling electrical conduction (2017- )
Nanowire-like surface entities fabricated by several different modes of interfacial electron beam lithography applied to OTS monolayers on silicon were found to exhibit a series of intriguing electrical conduction effects, with resistivities reaching some unprecedently low values. A large body of so far accumulated experimental evidence points to a novel conduction mechanism that has yet to be elucidated, apparently involving coupled electronic-ionic transport mediated and modulated by interfacial electrical interactions with charges located outside the conducting nanowire and separated from those carrying the measured current. These results point to possible effects of high-temperature superconductivity via a mechanism akin to the electron-hole pairing proposed in 1974 in the exciton theory of superconductivity. Here, the monolayer is the center of the action – the “hero”, not just a useful aid facilitating implementation of a function somewhere else.
Current ongoing work in collaboration with the group of Eli Zeldov in the department of condensed matter physics at the Weizmann institute aims at elucidating the nature of these unusual electrical conduction effects.
As I share the story of my 47 years of monolayer self-assembly, I marvel at a déjà vu paradox: something worth a prize in 2022 is worth almost the end of a research career in 1985!
I was determined not to give up. I have worked hard to realize the unique possibilities that monolayer self-assembly may offer. Our adventures in terra incognita of self-assembling monolayers go on, and what is yet to be discovered could be more exciting than ever.
Today, a self-assembled monolayer brings us on the verge of revealing the key to the holy grail of condensed matter physics – room temperature superconductivity. As we are looking forward with a great deal of excitement, our current resources have already been exhausted, which makes us wonder once again how we could accomplish this goal…