Theodore Lee Einstein - US grants

A new Materials Research Group is established to investigate surface kinetic processes such as adsorbate diffusion, faceting, crystal growth, and etching by explicitly addressing the role of surface steps in these processes. The experimental techniques being utilized include scanning tunnelling microscopy, surface infrared absorption spectroscopy, high-resolution low-energy electron diffraction, and low energy electron microscopy. Theory being applied includes molecular dynamics and energy minimization with semi-empirical potentials, Monte Carlo simulation, dynamic modeling of step motion and reaction rate theory. Simple atomic adsorbates such as hydrogen, oxygen, and nitrogen are being studied on vicinal nickel (100) and silver (110) single crystal surfaces. The research is organized in three integrated general areas: equilibrium structure and energies of surfaces, adsorbate- and self-diffusion on surfaces, and dynamics of step motion.

9225080 Williams This project will apply a range of modern surface science techniques to investigate the effects of applied electrical currents on the surface migration of atoms on metal surfaces. The phenomenon is known as surface electromigration (EM). Interestingly, EM on surfaces is rather poorly understood, though it is considered to potentially be of substantial technological interest. In the past it has been studied, but not in depth, with modern surface structure tools. Surface mass transport will be investigated experimentally by studying the changes of step structure under an applied electrical current using low-energy electron microscopy. %%% This project will investigate how surface atoms move or do not move under the influence of an applied electric field. The changes in surface morphology will be followed with a new surface microscope that allows real-time data collection of surface structure images. This is a low-energy electron microscope. The phenomenon of surface electromigration is surprisingly poorly understood. It has been studied for many years, but not with the modern techniques of this project. The objective is to obtain definitive data about surface electromigration, which is acknowledged to be potentially of great technological significance, particularly in the microelectronics industry. ***

The Analytical & Surface Chemistry Program of the Division of Chemistry, in the Directorate of Mathematical & Physical Sciences of the National Science Foundation, will support research by Theodore L. Einstein of the University of Maryland, College Park and Ludwig Bartels of the University of California, Riverside. The goal of this work is to understand how particular organic molecules assemble into large regular honeycomb patterns with open pores having diameters of 5 nm. To explore how general this behavior is, Bartels will perform experiments on different molecules and substrate materials in conjunction with theoretical calculations by Einstein that seek to explain the short-range structure in terms of hydrogen bonds and the large pores in terms of the electronic structure of the substrate. With a command of the interaction mechanisms, Bartels and Einstein will seek to engineer the size of open pores and perhaps also the pattern of the molecular networks. Such surfaces can serve as templates for growing patterned films on surfaces for applications ranging from storage technology to heterogeneous catalysis. Educational benefits include the training of graduate students and postdoctoral associates in state-of-the-art techniques for imaging at the atomic scale and for simulating systems in which comparatively small energies and subtle effects determine the overall geometry. It is also an outstanding opportunity for synergistic and close collaboration between physics-based theory and chemistry-based experiment, offering the involved students highly interdisciplinary training.

Technical. This project aims to develop understanding and materials techniques needed to control and exploit the effects of disorder and substrate interactions on the electronic properties of graphene. Graphene-substrate interactions will be studied to enable tuning of the electronic bandstructure, including opening a bandgap. High-mobility graphene enabled by this research will contribute to advanced device development, and allow the study of phenomena associated with Dirac fermions not accessible in particle physics, including Klein tunneling, Zitterbewegung, and the Schwinger mechanism. New low-temperature quantum phases may be observable in high-quality graphene, such as the fractional quantum Hall effect. Adsorbate interactions with graphene will be used to study electronic phenomena such as superconductivity in highly doped graphene and the Kondo effect in graphene with transition-metal impurities, as well as the study of ordering and phase transitions in the adsorbate layer. This research is expected to yield high-mobility graphene directly applicable to high-speed analog electronic devices operating at higher frequencies than presently possible, enabling high performance applications in communications and sensing. Producing a bandgap in graphene through substrate interaction may also enable high-speed, low-power logic applications of graphene transistors. Additionally, understanding interactions between graphene and the environment may lead to new types of chemical and biochemical sensors based on high-mobility graphene.
Non-Technical. The project addresses fundamental research issues in a topical area of electronic/photonic materials science and condensed matter physics having technological relevance. Basic understanding gained is expected to lead to improved device performance, and to allow design of new components. The project integrates research and education providing students with hands-on laboratory experience and training while conducting forefront research. Two Ph.D. students will be trained in state-of-the-art interdisciplinary research in nanoelectronics and surface science. The investigators will work with the graduate students to design and implement nanotechnology demonstrations involving graphene and graphite, and used in outreach to K-12 students and teachers from under-represented groups.

In this project, funded by the Macromolecular, Supramolecular and Nanochemistry Program of the
Chemistry Division, Prof. Theodore L. Einstein of University of Maryland and Prof. Ludwig Bartels of
the University of California, Riverside, and their students will use a combination of scanning tunneling
microscopy and methods of statistical mechanics, especially Monte Carlo simulations and lattice-gas
modeling, to understand the formation of large regular self-organized networks of acene-related
molecules on substrates with prominent metallic surface states and the role of the resulting nanoscale
pores in providing boundaries that modify the arrangements and reactions of small adsorbates like CO
therein. With international collaborators they will test theories of modification (from large surfaces) key
reaction rates because of altered entropy of mixing in the confined pores and will study the relation of the
superstructure to the surface state on the close-packed face of the copper substrate and investigate the
corrections to a simple picture of dot-induced pore formation. They will also take advantage of research in
two dimensional (2D) materials dominated by electronic states with many similarities to metallic surface
states.

This project will provide state of the art modeling and/or laboratory experiences for graduate and
undergraduate students who will be learning the techniques of scanning probe microscopy and
complementary Monte Carlo simulations and calculations of correlation functions, as well as ab initio
electronic structure calculations to help parameterize the statistical mechanical studies. The project
consists of an exploration of the formation of regular porous superstructures by organic molecules on
substrates with slowly decaying 2D electronic states. The validation of the novel explanation of pore
stabilization by 2D quantum-dot-like states will be pursued. The impact of such states on the distribution
of small adsorbates (especially carbon monoxide) within the pore will be scrutinized. Calculations of
associated parameters will require use of the latest advances in incorporating van der Waals interactions
into density functional theory computations. Through leadership by a theorist experienced in statistical
physics, this project will foster systematic perspective, deeper understanding and faster testing of results
for phase and pattern formation and predictions promising alternative substrates and adsorbates. The
proposed work is expected to have impact on industrial methodologies and society at large by providing
access to large arrays of identical nanoscale cells in which one can do the experimental equivalent of
parallel computation. Control of such structures will allow tuning of cell sizes to select for favorable
configurations and enhance particular reactions, as well as to explore natural fluctuations. The work will
also provide opportunities for educational and outreach activities with proven broad national,
international and societal impact.