Latha Venkataraman - US grants

In this project funded by the Experimental Physical Chemistry Program of the Chemistry Division, Professor Latha Venkataraman of Columbia University will seek to reveal and understand properties of single molecules attached to metal electrodes while educating students about the interplay of physics, chemistry and engineering at the nanoscale. The size of components in the integrated circuit industry is fast approaching the nanometer scale, requiring a detailed understanding of the fundamental properties at the single molecule level. Specifically, this work proposes to develop and build a high-resolution single-axis conducting atomic force microscope to simultaneously measure the rate at which electrons are transferred across a single molecule junction, as well as the forces required to break the junction apart. Electronic properties, such as junction resistance and current-voltage characteristics, are related to intrinsic junction properties including molecular length, conformation and the alignment of the molecular orbitals with the metal Fermi level. Measurements of forces reveal bond strengths, binding energies and junction stability, properties which cannot be probed directly by electrical measurements. The research proposed here will explore both of these related but different aspects of single-molecule circuits.

An integral part of the proposed activity is to introduce nanoscience to high school, undergraduate and graduate students, aiming to recruit them to pursue careers in science. In addition, a new Nanotechnology course for senior undergraduate and graduate students will be developed which will integrate a wide range of topics, from the synthesis of nanoscale materials to their charge transport properties and incorporation into electronic devices.

This project is jointly funded by the Electronic and Photonic Materials Program (EPM) in the Division of Materials Research (DMR) and the Chemical Structure, Dynamics and Mechanisms Program (CSDM) in the Division of Chemistry (CHE).

Technical Description: Organic materials as alternates to standard silicon-based semiconductors are fast becoming viable in areas of flexible electronics, sensors and photovoltaics. However, the physical mechanism by which charge transfer occurs in relation to the chemical structure in these systems is not well understood. In this project, important architectural elements of polymers that exhibit the best performance in organic electronics and photovoltaics are dissected to their molecular analogues to study their electronic and photo-induced transport characteristics at the single-molecule level. A series of oligomeric thiophenes are analyzed as analogues of polythiophene and its derivatives to understand the transport characteristics as a function of chemical structure. The scanning tunneling microscope-based break-junction technique is used to measure single-molecule charge transport characteristics and to probe photoconductivity in single-molecule junctions. Finally, analysis to correlate results from single-molecule transport measurements to bulk organic semiconducting device characteristics is used, enabling a multi-scale approach to understanding structure and function of efficient organic semiconductors. Through a combination of synthesis and measurements at the single-molecule level, this project provides molecular design rules for the development of novel materials used for organic electronics and photovoltaics.

Non-technical Description: There is a need to understand the governing factors enabling the development of organic semiconductor materials with advanced transport properties to complement their inorganic counterparts. This project bridges the gap between the single-molecule electronic structure components of polymeric semiconductors that exhibit high mobilities and photovoltaic characteristics. Using the fundamental understanding gained from single-molecule experiments enables the design of a new class of materials, which are tested in single molecule junctions as well as device architectures. In addition to developing new compounds that impact organic electronics, an integral part of the project introduces interdisciplinary science to high school, undergraduate and graduate students, aiming to instill a desire to pursue careers in science. The nature of the project requires a close collaboration between the graduate students in the Venkataraman and Campos groups, from Applied Physics and Chemistry. A focus of the PIs is also to recruit undergraduate women and/or minority students to participate in the research and prepare them as competitive applicants for graduate school in the sciences. Finally, basic concepts in organic electronics are adapted for demonstrations at schools in Manhattan.

Colin Nuckolls, James Leighton and Latha Venkataraman, all of Columbia University, are funded by the Macromolecular, Supramolecular and Nanochemistry program in the Division of Chemistry for research to develop methods to design, create, and study single molecule chains and ribbons of silicon atoms. Pure silicon is, of course, widely used in the electronics and information technology industry and is highly valued for its properties as a semiconductor. Its semiconductor nature is the result of molecular and electronic properties that arise at the atomic level. Changes in silicon's electrical properties have been noted as the size of silicon-based devices, such as computer chips and information storage media, become smaller. The investigators are using precise molecular construction techniques to create highly electrically conductive forms of silicon with specific shapes and properties that have never before been studied. In particular, they are looking at tiny ribbons and wires of silicon that hold promise for the development of future electronic devices. This collaborative project is making an explicit connection between the properties of bulk silicon, the bedrock of information technology, and molecular forms of silicon, and is, thus, having a broad impact on the semiconductor industry. This project is having a further broad impact through a coordinated effort that spans K-8 outreach, curriculum development, and research training for undergraduate, graduate, and post-doctoral scientists.

The investigators are creating and studying atomically precise nanowires and nanoribbons of silicon that have been functionalized so they can be studied in unimolecular electrical devices. The design and synthesis of rigid, strained, and functional nanowires and nanoribbons of silicon is being used to test the impact of strain on single molecule conductance. Nanoscopic probes developed in this project are allowing the assembly and integration of these new nanomaterials into electrical devices. The combination of expertise among team members working in concert is allowing advanced molecules to be designed, synthesized, and studied in a feedback loop. This approach to research fosters a holistic understanding of these unique one-dimensional chains of silicon atoms and enhances the probability that new properties and devices will be discovered.

This project is jointly funded by the Electronic and Photonic Materials Program (EPM) in the Division of Materials Research (DMR) and by the Chemical Structure, Dynamics and Mechanisms Programs A and B (CSDM-A and CSDM-B) in the Division of Chemistry (CHE).

Nontechnical Description: The drive to miniaturize electronics has not only motivated the search for new organic and inorganic (macro)molecular materials, but has also spurred the development of tools required for studying circuits with single molecules as active elements. Most past research on creating molecular-scale electronic devices has focused on the impact of molecular structure on the device properties. This project goes beyond such studies by developing methods to exploit the environment around molecular devices in order to control and modulate electronic characteristics. The project contributes to the realization of functional molecular devices as well as expansion of an arsenal of experimental methods to study and control charge transport at the single-molecule level. An integral part of the activities include the introduction of interdisciplinary science bridging physics, chemistry and engineering to middle-school, high-school, and undergraduate students, in order to instill a desire to pursue careers in science. Both PIs' laboratories are bridged thus K-12 school students can experience, first-hand, life in interdisciplinary research environment at Columbia University.

Technical Description: There is a strong need to understand and use the environment around molecular junctions to control charge transfer characteristics and enable creating functional molecular-scale analogs of circuit elements. Most past research efforts on transport at the molecular level have focused on correlating conductance to molecular structure, while the impact of the immediate environment around the junction has largely been ignored. This project aims to use the molecular environment as an external stimulus to control and alter the electronic characteristics of single-molecule devices, exploiting electrostatic, electrochemical and supramolecular interactions. The goals of this project are two-fold: (1) to understand the effects of the environment on the conduction properties of molecular junctions; and (2) to design and measure materials that respond to the environment in a controlled manner. This interdisciplinary research project goes beyond studying the fundamental components in molecular junctions - contacts, molecules, and electrodes - to establish an understanding of the interface between the junctions and the environment. It uses the scanning tunneling microscope based break-junction technique to study solvent/encapsulant effects, redox responsive systems, and supramolecular interactions in a large number of single-molecule devices.

Professors Xavier Roy and Latha Venkataraman of Columbia University are supported by the Macromolecular, Supramolecular, and Nanochemistry (MSN) Program of the Division of Chemistry to generate self-assembled monolayers of carbene molecules on metallic surfaces, and to investigate the structure electronic properties and stability of the resulting self-assembled monolayers. Coating metallic surfaces with molecules having tunable properties imparts the surface with special functionalities suitable for a variety of practical applications, including sensing, nanoelectronics, nanofabrication and electrochemistry. The usefulness of traditional self-assembled monolayers made with thiol chemical groups on gold surfaces is limited due to the poor chemical, electrochemical and thermal stability of the metal surface coating. This research on carbene monolayers has the potential to significantly improve the stability, tunability and metal compatibility of molecular monolayers on surfaces, thus positively impacting their potential practical applications. The project integrates research with educational and outreach activities. Graduate and undergraduate students from diverse backgrounds are involved in the research; research topics are integrated in Chemistry and Applied Physics curricula; and middle-school minority students from Central Harlem in New York are exposed to nanoscience concepts. In addition, the students involved in the research are provided with an international research opportunity through collaboration with international groups in Italy and the Czech Republic.

In this research project the research team study the formation, stability, structure and electronic properties of self-assembled carbene monolayers on metallic surfaces through an interdisciplinary effort that includes chemical synthesis, x-ray spectroscopy, electrochemical characterization, electron transport measurements and theory. Carbenes are promising candidates for creating thermally and chemically ultra-stable self-assembled monolayers. Being exceptionally strong sigma-donors with unusual electronic structures, carbenes bind much more strongly to metal surfaces than traditional thiols, thus opening the door to novel applications as tunable platforms for (bio)sensing, lab-on-a-chip, electrochemistry, electrocatalysis and nanoelectromechanical systems. Carbenes could also potentially passivate nanoelectrodes and modify metal work functions while serving as novel ligands. Despite these promises and the vast scientific literature on metal-carbene complexes, the assembly and conformation of carbenes on surfaces is poorly understood, and the electronic structure and properties of the resulting monolayers are largely unknown. To address this knowledge gap, this research project focuses on three research objectives: (1) Designing and synthesizing carbene monolayers with varying electronic and steric characteristics, (2) Probing the structure and electronic coupling of carbene monolayers to metal surfaces using x-ray spectroscopy and scanning tunneling microscopy, and (3) Developing room temperature and solution-based methods to prepare carbene monolayers on metal surfaces, and characterizing the structure and electronic coupling using electrochemical and scanning probe techniques.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

Non-technical Abstract: Professors Latha Venkataraman and Luis Campos of Columbia University are aiming to create new molecular systems that can be wired into circuits to efficiently conduct electricity. Significant efforts have been made to develop molecules that can transport electrical charges at the nanometer scale, as these are important for electronic application, as well for photovoltaics and artificial photosynthesis. However, most molecules that function as conducting wires studied to date show a very rapid decrease in conductivity as their lengths are increased, limiting their applications. In this work, new families of molecular systems are designed and synthesized. The overarching goal is to create and determine the electronic properties of molecules, aiming to find systems where, for example, an increase in conductivity is observed as the molecular length is increased. This interdisciplinary work combines synthesis and measurements while also integrating research with a broad range of educational and outreach activities. The investigators train and mentor post-doctoral researchers, augment their undergraduate teaching to include results from their research, and expose K-12 school children to concepts from nanoscience and nanotechnology while also introducing them to a laboratory environment.

Technical Abstract: In this project, Professors Latha Venkataraman and Luis Campos of Columbia University use concepts of physical organic chemistry to make single-molecule junctions with wires that model 1D topological insulators, to probe their unconventional transport properties. Families of molecular systems are designed and synthesized. These include (1) wires that have radicals near the ends; (2) molecular backbones with redox active units that enable the creation and control of radical states; and (3) molecular wires with resonance structures that ensure small bond-length alternation. Scanning probe techniques are applied to measure their single-molecule conductance and to characterize transport properties as a function of molecular length. The ultimate goal of this proposed work is the development and proof of concept demonstration of systems with high conductivities and transport properties that go beyond those observed in standard conjugated molecules. The educational and outreach efforts of this proposal have three broad objectives. The PIs provide an undergraduate research experience in a multidisciplinary environment, influencing the graduate admissions through service programs, integrate their research into the Applied Physics and Chemistry undergraduate curriculum and finally, make a focused effort to bring in K-12 school children in a laboratory environment to introduce them to basic concepts in chemistry and nanoscience.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

The NSF Center for Chemistry with Electric Fields (ChEF) is supported by the Centers for Chemical Innovation (CCI) Program of the Division of Chemistry. This Phase I Center is led by Latha Venkataraman of Columbia University. Other team members are also from Columbia and include Timothy Berkelbach, Colin Nuckolls, Tomislav Rovis, and Xavier Roy. The challenge of this center is to use directional electric fields to understand, control and manipulate chemical transition states to alter the outcomes of chemical reactions. New techniques are developed to expand the range of reactions that can be controlled and manipulated by electric fields. The strategy of bringing together team members with expertise in synthesis, measurement, and computation augers well for the Center's goal of controlling and inducing new chemical pathways, accelerating catalysis, and generating a new paradigm for organic synthesis. The bold goal of this team is to electric field control such that structures, pathways, and intermediates that are not possible or practical with traditional chemical catalysis become so. Broader impacts are addressed in part through strong collaborations with Merck and Columbia Technology Ventures. Students have opportunities for self-governance and professional development. Students are co-mentored and undergraduates are included in the team. The team partners with the Harlem Children?s Zone School in New York to broaden the participation of chemistry to K-12 underrepresented groups. Development of a Chemistry Magic Show and Subway Science and Engineering address the expectations for informal science communication. The NYC location of the Phase I team provides ready access to a population that is underrepresented in STEM.

The aim of this Phase I Center is to understand, control and manipulate chemical reactions utilizing electric fields. These electric fields can originate from an external bias produced using nanoscale electrode gaps or from strategically placed charges within a catalyst. Altering transition states by an external bias is the ultimate demonstration of controlling matter away from equilibrium and toward desired reactivity. This research charts a path to controlling the environment and electric field around reaction centers to accelerate desired reactivity and selectivity, developing reaction pathways and outcomes that are otherwise inaccessible by altering reaction kinetics and thermodynamics. The CCI team combines expertise in synthesis, measurement and computation and works in two interdisciplinary research thrusts, focused on two families of reactions: (1) Isomerization and Pericyclic Reactions, and (2) Coupling Reactions. This work aims to provide a mechanistic and quantitative understanding of how electric fields can control reactions while developing routes to alter selectivity and rates in a range of reactions including the Claisen rearrangement, the Diels Alder cycloaddition, and bond activation of carbon-halogen, metal-heteroatom and carbon-carbon bonds. Chemistry is at the center of the nanoscience revolution and this proposal exploits that position bringing together like-minded scientists from a diverse set of backgrounds to design experiments to identify promising target structures, synthesize these new targets, and study their properties and reactivity in electric fields. Broader Impacts are addressed in numerous ways. In addition to developing a new form of chemistry, the overarching broader impact is to increase the participation of underrepresented groups in STEM fields and to help educate the public about the virtues, beauty, and utility of chemistry. The work aims to transform undergraduate and graduate chemical education in chemistry at the interface of synthesis, materials and electric fields.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

Nontechnical Description: The Columbia Materials Science and Engineering Center (MRSEC) - Center for Precision-Assembled Quantum Materials P(AQM) partners with faculty at Minority Serving Institutions and explores new materials systems that will enable future quantum technologies, and educates a diverse new generation of scientists and engineers who reach across disciplines to advance the frontiers of knowledge and technology. The PAQM research program comprises two interdisciplinary research groups (IRGs), both of which study materials assembled from lower-dimensional building blocks: the first group creates layered structures by stacking atomically thin sheets, and the second group uses chemically synthesized molecular clusters to create bulk materials. In both systems, the emergent properties can be controlled both by choosing different building blocks and controlling how they are assembled. PAQM seeks to harness this design freedom to create a next generation of quantum materials which provide new ways to manipulate the flow of charge, spin, and energy, and host quantum states such as superconductivity. These new properties will in turn enable future quantum technologies in computing, sensing, and communications like digital memory, switchable absorbers, and new photodetectors. PAQM trains researchers at the high school, community college, undergraduate, and graduate levels in an environment that brings together researchers from multiple science and engineering disciplines. The center engages students and teachers at the elementary and middle school levels to build interest in science. The educational and research activities of the Columbia MRSEC are designed to increase diversity at all levels, particularly in fields related to Materials Science and Engineering.

Technical Description: The Columbia MRSEC - PAQM consists of two IRGs focused on materials created by precise assembly of low-dimensional building blocks. IRG1 combines two-dimensional materials into van der Waals heterostructures (vdWH) hosting emergent quantum phenomena. Three classes of quantum phenomena ? tunable superfluids, non-equilibrium states, and topological quantum states ? motivate this work. IRG1 focuses on foundational materials issues by synthesizing high-purity crystals, creating ultraclean heterostructures, and performing detailed characterization to fully understand structure/property relationships in vdWH. These advances will propel the field and enable harnessing of quantum phenomena underpinning future quantum information, sensing and computing technologies. IRG2 designs and synthesizes atomically precise, functional materials from chemically synthesized molecular clusters (superatoms). Using a closed-loop approach that combines synthesis, theory, and characterization, the IRG2 team develops methods to control the coupling between superatoms. Tuning the superatoms? electronic, magnetic, vibrational, and symmetry characteristics allows the team to design reconfigurable phase change materials; control directional transport of energy, charge and spin; and achieve emergent quantum phenomena, properties that underpin future technologies including electronics, digital memory, switchable absorbers, and new photodetectors. Investments in new research tools and shared facilities supports this work. These research goals are propelled by collaborations, with major partners including Brookhaven National Laboratory, the Flatiron Institute, and the Max Planck Society. Industrial partnerships and an entrepreneurial seed program support translational efforts toward applications. PAQM education and outreach activities support STEM and materials education at all levels and train the next generation of interdisciplinary materials researchers in the cutting-edge area of quantum materials. Reflecting the diversity of the Columbia MRSEC faculty and its urban location, research and education are integrated with a diversity strategic plan aimed at increasing participation of underrepresented groups in materials science and related fields.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.