Bruce E Koel | Princeton University (original) (raw)

Papers by Bruce E Koel

Surface Science, 2004

Adsorption and reaction of CH3I (methyl iodide) on Pt(111) and the (2×2) and (√3×√3)R30° Sn/Pt(11... more Adsorption and reaction of CH3I (methyl iodide) on Pt(111) and the (2×2) and (√3×√3)R30° Sn/Pt(111) surface alloys was investigated primarily by using temperature programmed desorption (TPD) and high-resolution electron energy loss spectroscopy (HREELS). CH3I adsorbs molecularly on Pt(111) at 100 K, and 34% of the adsorbed CH3I monolayer decomposes during heating above 200 K in TPD. Competition occurs during heating

Review of Scientific Instruments, 2016

Materials analysis and particle probe: A compact diagnostic system for in situ analysis of plasma... more Materials analysis and particle probe: A compact diagnostic system for in situ analysis of plasma-facing components (invited) Review of Scientific Instruments 83, 10D703 (2012);

Review of Scientific Instruments, 2020

Applied Physics Letters, 2016

AIP Physics Desk Reference, 2003

Bimetallic surfaces formed by the evaporation of Fe onto a Pt(1 1 1) single crystal at 350 K in u... more Bimetallic surfaces formed by the evaporation of Fe onto a Pt(1 1 1) single crystal at 350 K in ultrahigh vacuum were examined by X-ray electron spectroscopy, low energy electron diffraction (LEED), and low energy ion scattering. Some alloying occurs upon deposition, but heating thick Fe films to 600-850 K causes diffusion of Fe into the near-surface region and forms an alloy layer at the surface which contains 0.5-ML Fe. Annealing to 750 K orders the alloy and results in formation of a diffuse 2 � 2 LEED pattern. This procedure produces Fe-containing alloy surfaces that are more thermally stable against Pt surface segregation than expected from the behavior of Pt80Fe20(1 1 1) bulk crystals, and significant amounts of Fe are stabilized in the surface layer until temperatures as high as 950 K. Alloying with Fe causes a þ0.40-eV chemical shift in the Pt(4f7=2) peak, but no chemical shift of the Fe(3d5=2) peak in the bulk of the crystal. 2002 Elsevier Science B.V. All rights reserved.

We have demonstrated a method of fabricating long-range arrays of 2D metallic microstructures on ... more We have demonstrated a method of fabricating long-range arrays of 2D metallic microstructures on glass surfaces and measured the optical resonances of those structures. Gold and silver stripes are fabricated using microcontact printing with PDMS gratings and electroless plating techniques without the use of resist masks or etching. Changing the blaze angle and periodicity of the gratings used to make the PDMS stamps varies the line widths. The optical response of these fabricated transmission gratings was evaluated by measuring the transmission spectra while varying ...

In the first funding period (18 months), we continued our work on elucidating the underlying prin... more In the first funding period (18 months), we continued our work on elucidating the underlying principles that govern chemical reactions occurring on bimetallic and alloy surfaces. Our goal is to aid in the atomic level explanation of the reactivity and selectivity of alloy and bimetallic cluster catalysts and to provide a fundamental basis for the design of new catalysts with h'nproved performance. Our approach is to use a battery of surface science methods to obtain fundamental data on the thermochemistry and kinetics of the adsorption and reaction of molecules on extensively characterized, single-crystal bimetallic surfaces. We measure changes in chemisorption bond strengths, adsorption site distributions, and hydrocarbon fragment stability and reactivity and correlate these results with the geometric and electronic structure of the metal atoms on the surface. Often, our aim is to carefully design experiments that isolate the several factors (e.g., ensemble and ligand effects) that control surface chemisra'yand catalysis on bimetallic and alloy surfaces in order to better understand the importance of each contribution. In the past 18 months, we have continued to study how alkali promoters strongly affect the reactions of hydrocarbons on Pt and Ni surfaces by altering the electronic structure and inducing significant site-blocking effects. We have shown that bismuth coadsorption provides benchmark data on ensemble sizes required for chemical reactions on Pt and Ni surfaces. Surface alloys of Sn/Pr are being used for detailed probing of ensemble sizes and also reactive site requirements.

Assembly of nanometer-scale objects by using a Scanning Probe Microscope (SPM) as a robot is a pr... more Assembly of nanometer-scale objects by using a Scanning Probe Microscope (SPM) as a robot is a promising aproach for the fabrication of nanoelectromechanical systems (NEMS). This paper describes several techniques for positioning nanoparticles, linking them to form subassemblies, and moving entire subassemblies. These are first steps towards the hierarchical construction of complex nanoassemblies. Results of experiments conducted in ambient air and in liquid environments are presented. Nanomanipulation in liquids opens new research directions involving interactions with single biomolecules, and fine control of forces between tips, particles and surface substrates.

Proceedings. 1998 IEEE International Conference on Robotics and Automation (Cat. No.98CH36146), 1998

Precise control of the structure of matter at the nanometer scale will have revolutionary implica... more Precise control of the structure of matter at the nanometer scale will have revolutionary implications for science and technology. Nanoelectromechanical systems (NEMS) will be extremely small and fast, and have applications that range from cell repair to ultrastrong materials. This paper describes the first steps towards the construction of NEMS by assembling nanometer-scale objects using a Scanning Probe Microscope as a robot. Our research takes an interdisciplinary approach that combines knowledge of macrorobotics and computer science with the chemistry and physics of phenomena at the nanoscale. We present experimental results that show how to construct arbitrary patterns of gold nanoparticles on a mica or silicon substrate, and describe the underlying technology. We also discuss the next steps in our research, which are aimed at producing connected structures in the plane, and eventually three-dimensional nanostructures.

Nanotechnology, 1998

Experimental results that provide new insights into nanomanipulation phenomena are presented. Rel... more Experimental results that provide new insights into nanomanipulation phenomena are presented. Reliable and accurate positioning of colloidal nanoparticles on a surface is achieved by pushing them with the tip of an atomic force microscope under control of software that compensates for instrument errors. Mechanical pushing operations can be monitored in real time by acquiring simultaneously the cantilever deflection and the feedback signal (cantilever non-contact vibration amplitude). Understanding of the underlying phenomena and real-time monitoring of the operations are important for the design of strategies and control software to manipulate nanoparticles automatically. Manipulation by pushing can be accomplished in a variety of environments and materials. The resulting patterns of nanoparticles have many potential applications, from high-density data storage to single-electron electronics, and prototyping and fabrication of nanoelectromechanical systems.

The Journal of Physical Chemistry, 1989

A Cu-catalyzed reaction procedure was found for the selective formation of dimethylchlorosilane [... more A Cu-catalyzed reaction procedure was found for the selective formation of dimethylchlorosilane [(CH3)2HSiCl] from the direct reaction of CH3C1 with solid Si. The new procedure is a two-step process. A Cu/Si sample is prepared by evaporating Cu onto clean polycrystalline Si under ultrahigh vacuum, and the Cu/Si surface is first activated by exposure to 10% HSiCl3/CH3Cl at 598 K. After the HSiCl3/CH3Cl mixture is evacuated from the reactor, the activated Cu/Si surface is reacted in fresh CH3C1. For low surface concentrations of Cu, the partially hydrogenated silane, (CH3)2HSiCl, is selectively produced. Trichlorosilane was also found to activate polycrystalline Si (in the absence of Cu) for production of highly chlorinated methylchlorosilanes at a much higher rate than on the Cu/Si surface but with poor selectivity to (CH3)2HSiCl. All reactions are carried out at atmospheric pressure in a reactor that is attached to an ultrahigh-vacuum chamber. This allows surface analysis by Auger electron spectroscopy, which detected SiCl* on reacted surfaces. These SiCl* sites, which appear necessary for methylchlorosilane formation, are apparently formed during activation by HSiCl3. Reactions on the Si and Cu/Si surfaces were studied in an atmospheric pressure, differential reactor, which was attached to an ultrahigh-vacuum system that contained an Auger spectrometer. Auger electron spectroscopy (AES) provides elemental surface composition and some chemical bonding information for Si because the Si(LVV) Auger transition is sensitive to the valence state of Si. All reactions were carried out at 598 K because this corresponds to the highest temperature used in previous studies on Cu3Si bulk alloys8 and it is in the upper temperature range t Department of Chemical Engineering.

Introduction Platinum-based catalysts are used in a wide variety of industrial hydrocarbon reacti... more Introduction Platinum-based catalysts are used in a wide variety of industrial hydrocarbon reactions, for example, in hydrogenation, isomerization and oxidation. Sn is frequently added to Pt catalyst formulations as a promoter that suppresses hydrocarbon decomposition and improves reaction selectivities. Unlike pure Pt, which is known to catalyze only acetylene decomposition, Sn/Pt(111) alloys have been shown to enable cyclotrimerization of acetylene to benzene [1]. The current investigation provides molecular insight into differences in acetylene adsorption and reactivity on Pt and Pt-Sn alloys by combining density functional theory (DFT) calculations with vibrational analyses to explain vibrational spectra obtained with high resolution electron energy loss spectroscopy (HREELS) and evolution of products from temperature desorption (TPD).

Reactions of 24 formed by condensation of 2 gas, with adsorbed water films as models for ice surf... more Reactions of 24 formed by condensation of 2 gas, with adsorbed water films as models for ice surfaces were studied on a Au(111) substrate at low temperatures under ultrahigh vacuum (UHV ) conditions. Two thermal reaction paths were found, primarily by using infrared reflection–absorption spectroscopy (IRAS) and temperature programmed desorption (TPD) techniques. One path evolved gas phase HONO (nitrous acid) and 3 (nitric acid) below 150 K, independent of both the crystallinity of the ice film and the exposure of NO2. In contrast, another reaction pathway depended strongly on these variables and was conveniently monitored by the formation of oxygen adatoms on the Au(111) substrate surface. The latter reactions only occurred following multilayer adsorption of 2 (present as N2O4) and only if the adsorption was on amorphous ice clusters and not crystalline ice. The extent of these reactions was proportional to the concentration of ‘free-OH’ groups on the ice film, indicating that water...

Microscopy and Microanalysis

Langmuir

Acetic acid adsorption and reactions at multiple surface coverage values on Ni(110) were studied ... more Acetic acid adsorption and reactions at multiple surface coverage values on Ni(110) were studied with temperatureprogrammed desorption (TPD) and infrared reflection absorption spectroscopy (IRAS) at 90−500 K. The experimental measurements were interpreted with density functional theory (DFT) calculations that provided information on adsorbate geometries, energies, and vibrational modes. Below the monolayer saturation coverage of 0.36 ML at 90 K, acetic acid adsorbs mostly molecularly. Above this coverage, a physisorbed layer is formed with dimers and catemers, without detectable monomers. Dimers and catemers desorb as molecular acetic acid at 157 and 172 K, respectively. Between 90 and 200 K, the O−H bond in acetic acid breaks to form bridge-bonded bidentate acetate that becomes the dominant surface species. Desorption-limited hydrogen evolution is observed at 265 K. However, even after the acetate formation, acetic acid desorbs molecularly at 200−300 K due to recombination. Minor surface species observed at 200 K, acetyls or acetates with a carbonyl group, decompose below 350 K and generate adsorbed carbon monoxide. At 350 K, the surface likely undergoes restructuring, the extent of which increases with acetic acid coverage. The initial dominant bridge-bonded bidentate acetate species formed below 200 K remain on the surface, but they now mostly adsorb on the restructured sites. The acetates and all other remaining hydrocarbon species decompose simultaneously at 425 K in a narrow temperature range with concurrent evolution of hydrogen, carbon monoxide, and carbon dioxide. Above 425 K, only carbon remains on the surface.

Journal of Nuclear Materials

Lithium (Li) coatings on plasma facing components (PFCs) have been proposed as potential solution... more Lithium (Li) coatings on plasma facing components (PFCs) have been proposed as potential solutions to first wall and divertor challenges in tokamak fusion reactors. We report on the thermal behavior of ultrathin pure Li films deposited on polycrystalline substrates of molybdenum (Mo) and a molybdenum alloy (titanium zirconium molybdenum, TZM). These Li films were studied under controlled ultrahigh vacuum (UHV) conditions and thermal stabilities were primarily compared via temperature programmed desorption (TPD) measurements. In addition, on TZM, which is of particular interest, we obtained additional spectroscopic data using Auger electron spectroscopy (AES) and low energy ion scattering (LEIS) to further characterize the film structure and composition. The monolayer of Li in these films in contact with the substrate is bound much stronger than in bulk Li films, and thermally desorbs at much higher temperatures. Interfacial Li on Mo(poly) has a higher thermal stability than that on TZM(poly), where the limiting values for the desorption activation energies, E d , are 3.56 and 2.84 eV, respectively, in the low coverage, high temperature desorption tail. LEIS indicates some clustering or interdiffusion of the Li films on the TZM substrate at 500 K. No appreciable irreversible absorption of Li occurs on Mo or TZM under the conditions of these experiments.

Nature Communications

Development of earth-abundant electrocatalysts for hydrogen evolution and oxidation reactions in ... more Development of earth-abundant electrocatalysts for hydrogen evolution and oxidation reactions in strong acids represents a great challenge for developing high efficiency, durable, and cost effective electrolyzers and fuel cells. We report herein that hafnium oxyhydroxide with incorporated nitrogen by treatment using an atmospheric nitrogen plasma demonstrates high catalytic activity and stability for both hydrogen evolution and oxidation reactions in strong acidic media using earth-abundant materials. The observed properties are especially important for unitized regenerative fuel cells using polymer electrolyte membranes. Our results indicate that nitrogen-modified hafnium oxyhydroxide could be a true alternative for platinum as an active and stable electrocatalyst, and furthermore that nitrogen plasma treatment may be useful in activating other non-conductive materials to form new active electrocatalysts.