The Experts below are selected from a list of 267 Experts worldwide ranked by ideXlab platform
Gabor A Somorjai - One of the best experts on this subject based on the ideXlab platform.
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Surface Science of single site heterogeneous olefin polymerization catalysts
Proceedings of the National Academy of Sciences of the United States of America, 2006Co-Authors: Seong H Kim, Gabor A SomorjaiAbstract:This article reviews the Surface Science of the heterogeneous olefin polymerization catalysts. The specific focus is on how to prepare and characterize stereochemically specific heterogeneous model catalysts for the Ziegler–Natta polymerization. Under clean, ultra-high vacuum conditions, low-energy electron irradiation during the chemical vapor deposition of model Ziegler–Natta catalysts can be used to create a “single-site” catalyst film with a Surface structure that produces only isotactic polypropylene. The polymerization activities of the ultra-high vacuum-prepared model heterogeneous catalysts compare well with those of conventional Ziegler–Natta catalysts. X-ray photoelectron spectroscopic analyses identify the oxidation states of the Ti ions at the active sites. Temperature-programmed desorption distinguishes the binding strength of a probe molecule to the active sites that produce polypropylenes having different tacticities. These findings demonstrate that a Surface Science approach to the preparation and characterization of model heterogeneous catalysts can improve the catalyst design and provide fundamental understanding of the single-site olefin polymerization process.
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The Development of Molecular Surface Science and the Surface Science of Catalysis: The Berkeley Contribution†
The Journal of Physical Chemistry B, 2000Co-Authors: Gabor A SomorjaiAbstract:Since the early 1960s, Surface Science has uncovered the atomic and electronic structures of Surfaces and the nature of chemical bonding of adsorbed monolayers of atoms and molecules. Surface instrumentation was developed to carry out these studies as well as to monitor Surface reactions, stoichiometric and catalytic. Metal, oxide, molecular crystal, and polymer Surfaces have been investigated on the molecular scale. Studies in vacuum and at low pressures that used electrons, ions, and atoms as Surface probes have been extended in recent years to high pressures and studies of solid−liquid interfaces by using photon scattering techniques and Surface probe microscopes. My laboratory in Berkeley has participated in the development of molecular Surface Science and heterogeneous catalysis during the past 35 years. The following is a personal review of our contributions to the field.
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The Development of Molecular Surface Science and the Surface Science of Catalysis: The Berkeley Contribution†
The Journal of Physical Chemistry B, 2000Co-Authors: Gabor A SomorjaiAbstract:Since the early 1960s, Surface Science has uncovered the atomic and electronic structures of Surfaces and the nature of chemical bonding of adsorbed monolayers of atoms and molecules. Surface instr...
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modern Surface Science and Surface technologies an introduction
Chemical Reviews, 1996Co-Authors: Gabor A SomorjaiAbstract:The development of both new catalysts, sensors, and ever smaller semiconductor-based devices, required understanding and characterization of Surfaces on the molecular level; in turn leading to the birth of new Surface Science-based technologies. Because of the need for atomic level scrutiny of Surface properties, a large number of techniques have been invented and developed since the 1950s. These techniques employ photons, electrons, and ions to determine Surface structure, Surface composition, oxidation states of Surface atoms, and bonding of adsorbates; done with ever increasing spatial resolution, time resolution, and energy resolution. In this paper the author shall first focus on several of the new Surface Science concepts that were developed as a result of studies during the past 30 years. Then, he shall review their impact on the development of several Surface technologies: catalysis (including environmental catalysis), microelectronics, disk drive storage, and sensors. 50 refs.
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The Surface Science of heterogeneous catalysis
Surface Science, 1994Co-Authors: Gabor A SomorjaiAbstract:The development of a high pressure cell that can be incorporated into ultrahigh vacuum chambers permitted Surface Science studies of active catalysts. Model catalysts, usually single-crystal Surfaces of ~1 cm2 Surface area, can be used to study important catalytic reactions ranging from hydrocarbon conversion over platinum to ammonia synthesis over iron. The new concepts, or phenomena, uncovered by the Surface Science investigations of heterogeneous catalysis of these model systems include: (1) high reaction rates and strong bonding at defects and on rough Surfaces; (2) adsorbate-induced restructuring of metal Surfaces that control the reaction rates; (3) the presence of a strongly chemisorbed overlayer which covers much of the active metal Surface; (4) the bonding and reaction rate modifying influence of coadsorbates; and (5) the unique activity of certain oxide-metal interfaces.
Hans-joachim Freund - One of the best experts on this subject based on the ideXlab platform.
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Towards Realistic Surface Science Models of Heterogeneous Catalysts: Influence of Support Hydroxylation and Catalyst Preparation Method
Catalysis Letters, 2013Co-Authors: Martin Sterrer, Hans-joachim FreundAbstract:Surface Science studies allow processes important for heterogeneous catalysis to be investigated in greatest detail. Starting from the simplest model of a catalytic Surface, a metal single-crystal Surface under ultrahigh vacuum conditions, enormous progress has been made in the last decades towards extending the Surface Science of catalysis to technically more relevant dimensions. In this perspective, we highlight recent work, including our own, dealing with the influence of water on metal-support interactions in Surface Science studies of oxide-supported metal nanoparticle model catalysts. In particular, the effect of hydroxyl groups on nucleation and sintering of metal nanoparticles, and Surface Science investigations into catalyst preparation using wet-chemical procedures are addressed. Graphical Abstract
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innovative measurement techniques in Surface Science
ChemPhysChem, 2011Co-Authors: Hans-joachim Freund, Niklas Nilius, Thomas Risse, Swetlana Schauermann, Thomas A SchmidtAbstract:We describe four new experimental techniques advanced during the last decade in the authors' laboratory. The techniques include photon scanning tunneling microscopy; aberration-corrected low-energy electron microscopy in combination with photoelectron emission microscopy, microcalorimetry, and electron-spin resonance spectroscopy. It is demonstrated how those techniques may be applied to solve fundamental problems in Surface Science with growing demands to tackle complex nanoscopic systems, and, in particular in catalysis Science, which, without the availability of those techniques, would be difficult if not impossible to address.
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Models in heterogeneous catalysis: Surface Science quo vadis?
physica status solidi (a), 2001Co-Authors: Hans-joachim Freund, Thomas Risse, Norbert Ernst, Heiko Hamann, Günther RupprechterAbstract:Model catalyst systems have been prepared by growth of small metal aggregates on thin well ordered oxide films of alumina and silica. These systems lend themselves to structural and morphological characterization via scanning probe microscopies and transmission electron microscopy and bridge to a certain extent the materials gap between metal single crystal studies and the investigation of real catalyst samples. Recently, the classical Surface Science techniques applied under ultrahigh vacuum conditions have been augmented by non-linear optical techniques, such as sum frequency generation, which can also be applied under ambient gas pressures. Thus, the pressure gap between studies in Surface Science under realistic conditions can he bridged.
P.a. Thiel - One of the best experts on this subject based on the ideXlab platform.
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Discussion on the Surface Science of quasicrystals
Philosophical Magazine, 2008Co-Authors: P.a. ThielAbstract:This paper contains a short review of four aspects of the Surface Science of quasicrystals, together with a list of challenges for the scientific community in the near future. The first issue concerns the ability of Surface Science to shed light on bulk atomic structure. The second is the use of Surfaces as quasiperiodic templates, particularly for films of periodic metals. Here, enforcing quasiperiodicity in the film may lead to unusual magnetic, tribological or adsorption properties. The third aspect concerns the effects of Surface phasons and phonons on dynamical interactions with adsorbates, such as sticking coefficient, as well as on diffusion between the Surface and near-Surface region. The final area is tribology, where studies of quasicrystals have suggested that both adhesion and phononic friction may be important.
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Discussion on the Surface Science of quasicrystals
Philosophical Magazine, 2008Co-Authors: P.a. ThielAbstract:International audienceThis paper contains a short review of four aspects the Surface Science of quasicrystals, together with a challenging list of open questions to be addressed by the scientific community in the near future. The first issue concerns the ability of Surface Science to shed light on bulk atomic structure. The second is the use of Surfaces as quasiperiodic templates, particularly for films of periodic metals. Here, enforcing quasiperiodicity in the film may lead to unusual magnetic, tribological, or adsorption properties. The third concerns the effects of Surface phasons and phonons on dynamical interactions with adsorbates, such as sticking coefficient, as well as on diffusion between the Surface and near-Surface region. The final area is tribology, where studies of quasicrystals have suggested that both adhesion and phononic friction may be important
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Quasicrystals : A short review from a Surface Science perspective
Langmuir, 1998Co-Authors: Cynthia J. Jenks, P.a. ThielAbstract:Quasicrystals are materials of both intellectual and practical importance. Although some level of understanding can now be applied to their bulk electronic and atomic structure, the same cannot be said of their Surface properties. In this article, we point out some of the key issues in the Surface Science of quasicrystals at present.
Michael A Henderson - One of the best experts on this subject based on the ideXlab platform.
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a Surface Science perspective on tio2 photocatalysis
Surface Science Reports, 2011Co-Authors: Michael A HendersonAbstract:The field of Surface Science provides a unique approach to understanding bulk, Surface and interfacial phenomena occurring during TiO2 photocatalysis. This review highlights, from a Surface Science perspective, recent literature that provides molecular-level insights into photon-initiated events occurring at TiO2 Surfaces. Seven key scientific issues are identified in the organization of this review. These are: (1) photon absorption, (2) charge transport and trapping, (3) electron transfer dynamics, (4) the adsorbed state, (5) mechanisms, (6) poisons and promoters, and (7) phase and form. This review ends with a brief examination of several chemical processes (such as water splitting) in which TiO2 photocatalysis has made significant contributions in the literature.
J Krim - One of the best experts on this subject based on the ideXlab platform.
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Surface Science mems and nems progress and opportunities for Surface Science research performed on or by microdevices
Progress in Surface Science, 2013Co-Authors: Diana Berman, J KrimAbstract:Abstract Micro- and Nano-Electro-Mechanical Systems (MEMS and NEMS) represent existing (MEMS) and emerging (NEMS) technologies based on microfabrication of micron to nanometer scale miniature mechanical components (gears, latches, mirrors, etc.) that are integrated with electrical elements to allow for electro-mechanical actuation and/or capacitive displacement detection. One common aspect of MEMS and NEMS devices is that they have mechanical functionality that may include moveable parts whose motion is controlled by external electrical connections. Current fabrication methods, along with high Surface to volume ratios, make MEMS and NEMS devices highly susceptible to Surface forces and adsorbed Surface species, to the point where the devices are now being increasingly utilized as sensitive probes in fundamental Surface Science studies. This sensitivity can potentially be used to great advantage if the devices can be made to operate reproducibly in well controlled environments. This review highlights a number of such recent studies, beginning with an overview of the fabrication processes employed for silicon, metal, diamond, graphene and carbon nanotube – based device technologies. A discussion of how traditional Surface Science studies on passive two-dimensional substrates compare to and contrast with studies performed on, or by, MEMS and/or NEMS devices, is also included. The overall goal is to highlight areas of current opportunity for Surface scientists in the flourishing arena of micro- and nano-device fabrication and technology.
