We have research interests in chemical physics, surface and materials chemistry, polymer dynamics, nanoscience and water sustainability.
The innovative use of sophisticated gas-surface scattering instruments and atomic-resolution scanning probe microscopes combined with appropriate theory and numerical simulations have led to advances in these areas of research. The unifying theme in the Sibener Group is to expand understanding of interfacial phenomena at the molecular level that spans fundamental knowledge discovery to applications such as energy systems. Specific areas of interest include: Surface reaction dynamics; gas-surface interaction potentials; phonon structure of surfaces and thin films; gas-surface collisional energy transfer; surface metallurgy and metallic oxidation; self-organization of molecular and polymer thin films including chiral systems; surface dynamics of polymers; superconducting radio frequency (SRF) materials for advanced accelerators; national security with focus on trace gas detection and chemical defense; water purification; ice chemistry in terrestrial and astrophysical environments; hierarchical assembly of functional nanomaterials for energy applications; and electronic and vibronic structure of nanoscale electronic interfaces. Examination of collective behavior in nanoparticle assembled materials studied at the single nanoparticle limit at cryogenic temperatures with scanning tunneling and conductive AFM spectroscopy is a recent addition to the program. Increasingly, studies in the group combine expertise in molecular beam scattering with scanning tunneling/atomic force microscopy visualization of dynamically evolving interfaces.
Research Interests:
Surface Reaction Dynamics
Multiply-modulated molecular beam scattering techniques are used for the elucidation of heterogeneous reaction mechanisms and dynamics These experiments examine the potential energy surfaces that govern the dynamics of volatile reaction products as a function of adsorbate density, including how interadsorbate effects influence potential energy surfaces. Kinetically-activated reagents are employed to enhance the reaction rate and selectivity of heterogeneous reactions, such as for the Synthesis Gas reaction on rhodium. Another example is how synergistic effects involving UV light and atomic oxygen influence the reactivity of photoactive polymer surfaces, important for delineating how materials react in low-Earth-orbit environments. The group’s newest efforts focus on geometry- and stereo-selected reaction dynamics.
Interfacial Phonon Structure
Single phonon inelastic He scattering is a surface sensitive method that can be used to map out the full surface phonon structure of clean or molecule-covered interfaces. Recent work has focused on new electronic interfaces, developed at Caltech, that have improved redox properties for electronic and electrochemical applications. Combined experiments and quantum dynamics calculations have shown how molecular vibrations can hybridize with and modify the phonon band structure of methyl-Si(111) interfaces.
Gas-Surface Collisional Energy Exchange
Studies of gas-surface collisional energy exchange have helped define understanding of the hierarchy of interfacial energy-exchange processes responsible for energy accommodation, sticking, and gaseous condensation. This work is quantitatively addressing how single, few, and multiphonon events contribute to energy exchange under an extraordinarily broad range of dynamical conditions. Quantitative comparisons and beautiful agreement with large-scale molecular dynamics simulations have led to improved understanding of energy and momentum exchange at complex molecular interfaces that are of importance not only for fundamental understanding, but for the refinement of advanced aircraft and spacecraft flight surfaces.
Superconducting Materials and Surface Metallurgy
Another ongoing effort is in the area of surface metallurgy and metallic oxidation, where molecular beam and time-lapse STM studies have elucidated definitive oxidation mechanisms for atomic, energetic, and electron-assisted processes. The group is currently examining the oxidation and nitridation of Nb to improve understanding of how surface-to-bulk oxygen and nitrogen transport occurs, and how it can influence the performance of superconducting RF cavities used in particle accelerators.
Self-Organization of Polymer Thin Films and Chiral Molecular Systems
The dynamical properties and organization of molecular and polymeric thin films is another current focus of the group. Atomic force microscopy is being used to examine the pathways by which defects evolve and annihilate during the annealing of polymers. Recent work has led to the development of new methods, now widely adopted, for guiding the spatial organization of diblock copolymers in nano-confinement while achieving near structural perfection. Experiments being done at elevated temperatures above the glass transition where real-time/real-space dynamics for domain organization, grain boundary mobility, and defect elimination can be followed, revealing precise details of the mechanism and kinetics for polymer organization in thin films. In separate work on molecular systems, our current focus is on understanding and controlling the chirality of adsorbed films.
Surface Dynamics of Polymers
The Sibener Group has pioneered the use of low energy, nondestructive neutral atom inelastic scattering to probe the surface vibrational characteristics of polymer surfaces. This has proven to be a most incisive approach, revealing how polymer dynamics change due to nano-confinement as film thickness approaches the radii of gyration of the polymer chains. Helium scattering has also been used to assess how surface vibrational dynamics change when going from the amorphous to the complex crystalline phase of PET.
Ice, Water Sustainability, Environmental Interfaces, and Astrochemistry
The group has several ongoing projects that focus on the chemistry of ice, especially the trapping and release of adsorbed and embedded trace gases for purposes of environmental, astrophysical, and national defense science. Recently, work in this area has demonstrated that high-energy gas-surface collisions can embed species into ice once energetic barriers have been exceeded. These latter experiments are significant for many fields, including trace gas collection and detection, climate change, and astrophysical chemistry involving planetary systems, interstellar dust, and comets. We are one of the lead groups at UChicago that is participating in the Institute for Molecular Engineering’s new Water Research Initiative. This new effort has components that are associated with the catalytic destruction and filtering of contaminants.
Hierarchically Assembled Functional Nanomaterials and Directed Self-Assembly
A powerful route for the creation of functional nanomaterials is hierarchical self-assembly. Here one can use top-down/bottom-up methods to organize complex structures that would be prohibitively time consuming to fabricate using traditional lithography-only paradigms. The group has been using such methods for the synthesis of functional photovoltaic thin film devices, ultra-high density magnetic systems involving magnetic nanoparticles, and highly efficacious surface enhanced Raman (SERS) substrates.
Selected References
Correlating Polymer Structure, Dynamics, and Function with Atomic Force Microscopy, Julia G. Murphy, Jonathan G. Raybin, and Steven J. Sibener, J. of Polymer Science, 1, 1-17 (2021).
A New Method of Isotope Enrichment and Separation: Preferential Embedding of Heavier Isotopes of Xe into Amorphous Solid Water, K. D. Gibson and S. J. Sibener, Physical Chemistry Chemical Physics 23, 7902-7907 (2020).
Suppression of Nano-Hydride Growth on Nb(100) Due to Nitrogen Doping, R. Darren Veit, Rachael G. Farber, Nathan S. Sitaraman, Tomas A. Arias, and S. J. Sibener, J. Chem. Phys. 152, 214703/1-10 (2020).
Reaction Kinetics and Influence of Film Morphology on the Oxidation of Propene Thin Films by O(3P) Atomic Oxygen, Michelle R. Brann, Rebecca S. Thompson, and S. J. Sibener, J. Phys. Chem. C, 124, 7205-7215 (2020).
Chain-Length Dependent Reactivity of Alkanethiolate Self-Assembled Monolayers with Atomic Hydrogen, Jeffrey D. Sayler, Sarah Brown, and S. J. Sibener, J. Phys. Chem. C 123, 26932-26938 (2019).
Direct Imaging of Interfacial Fluctuations in Confined Block Copolymer with In Situ Slow-Scan-Disabled Atomic Force Microscopy, Jonathan G. Raybin, Julia G. Murphy, Moshe Dolejsi, and S. J. Sibener, ACS Nano 13, 11741-11752 (2019).
Rapid Laser-Induced Temperature Jump Decomposition of the Nerve Agent Simulant Diisopropyl Methylphosphonate under Atmospheric Conditions, Rebecca S. Thompson, Michelle R. Brann, Ellen H. Purdy, Jacob D. Graham, Alison A. McMillan, and S. J. Sibener, J. Phys. Chem. C 123, 21564-21570 (2019).
Sticking Probability of High-Energy Methane on Ices of Astrophysical Interest, Rebecca S. Thompson, Michelle R. Brann, and S. J. Sibener, J. Phys. Chem. C 123, 17855-17863 (2019).
Atomically-Resolved Oxidative Erosion and Ablation of Basal Plane HOPG Graphite Using Supersonic Beams of O2 with Scanning Tunneling Microscopy Visualization, Ross Edel, Tim Grabnic, Bryan Wiggins, and S. J. Sibener, J. Phys. Chem. C 122, 14706-14713 (2018).
Separation of Isotopes in Space and Time by Gas-Surface Atomic Diffraction, Kevin J. Nihill, Jacob D. Graham, and S. J. Sibener, Phys. Rev. Lett. 119, 176001 (2017). This article was accompanied by an American Physical Society Viewpoint Article: Viewpoint: Atom Scattering Picks Out the Heavyweights, October 23, 2017, Physics 10, 116. https://physics.aps.org/articles/v10/116.
Capture of Hyperthermal CO2 by Amorphous Water Ice via Molecular Embedding, Grant G. Langlois, Wenxin Li, K. D. Gibson, and S. J. Sibener, Invited Feature Article for the Special Issue: “Dynamics of Molecular Collisions XXV – Fifty Years of Chemical Reaction Dynamics”, J. Phys. Chem. A, 119, 12238-12244 (2015).
Festschrift Issue of The Journal of Physical Chemistry C Dedicated to Steven J. Sibener, J. Phys. Chem. C 119, (July 2, 2015).