Wigbert Siekhaus - Academia.edu (original) (raw)

Papers by Wigbert Siekhaus

Research paper thumbnail of Atomic arrangement of sulfur adatoms on Mo(001) at atmospheric pressure: A scanning tunneling microscopy study

Physical Review Letters, 1988

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Research paper thumbnail of Predicting threshold and location of laser damage on optical surfaces

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Research paper thumbnail of Reactions of modulated molecular beams with pyrolytic graphite. III. Hydrogen

The Journal of Chemical Physics, 1975

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Research paper thumbnail of Experimental study to validate a model of hillock’s formation in aluminum thin films

Journal of Applied Physics, 1996

The growth of holes and hillocks in thin films has been reported extensively and for a multitude ... more The growth of holes and hillocks in thin films has been reported extensively and for a multitude of film–substrate systems. A recently developed model [F. Y. Genin, J. Appl. Phys. 77, 5130 (1995)] which analyzes the formation of a ridge at a traveling grain boundary due to stress and capillarity driving forces provides a quantitative description of the growth of the hillocks. In order to test the model, the surface morphology of aluminum thin films deposited on oxidized silicon substrates and annealed at 450 °C in argon is investigated; the profiles of thermal hillocks are measured by atomic force microscopy. The comparison shows excellent agreement between modeled and experimental profiles.

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Research paper thumbnail of Computational Modeling of Uranium and Plutonium Hydriding- the role of Surface Oxide Layers, Oxycarbides, Carbides & Impurities

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Research paper thumbnail of Couches surfaciques a faible energie d'extraction produites par ablation au laser a photons a faible longueur d'onde

L'invention se rapporte a des photons a faible longueur d'onde utilises pour produire l&#... more L'invention se rapporte a des photons a faible longueur d'onde utilises pour produire l'ablation de matiere a partir d'une cible a faible energie d'extraction disposee sur un substrat adapte. Les photons a faible longueur d'onde ont une longueur d'onde inferieure ou egale a la longueur d'onde du visible. La composition elementaire du depot est regie par la composition de la cible et de l'environnement gazeux dans lequel se deroule le processus d'ablation. Ledit processus se deroule dans une chambre de depot sur laquelle est monte un laser a faible longueur d'onde et qui inclut un porte-substrat qu'il est possible de faire tourner, d'incliner, de chauffer et de refroidir. La matiere cible est placee sur un support qui fait tourner la cible pendant l'ablation au laser. En outre, la chambre de depot comporte une pompe a vide, un dispositif externe d'alimentation en gaz dote d'un atomiseur et d'un generateur de radicaux...

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Research paper thumbnail of Reactions of Modulated Molecular Beams with Fyrolytic Graphite I. Experimental Apparatus and Data Interpretation

An apparatus for the study of gas·-solid reactions which produce a gaseous reaction product is de... more An apparatus for the study of gas·-solid reactions which produce a gaseous reaction product is described. The reactant gas contacts the solid as a molecular beam travelli:ng in vacuum. Gaseous reaction products are monitored by a mass spectrometer as they are emitted from the surface. ~~he technique relies heavily upon the modulation of the molecular beam, which impr~ves sensitivity by shifting the information from the very noisy zero frequency (de) band to a narrow band ac mode which has considerably less noise. In addition, modulation of the reactant beam induces modulation at the same frequency in the reaction products and the phase difference between these two signals contains important kinetic information. The method of comparing theoretical models of the surface processes with the phase and amplitude information provided by the experiment is described.

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Research paper thumbnail of Advances in the Development of White-Light Interferometry for In-Situ Uranium Hydride Kinetic Data Collection

Microscopy and Microanalysis

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Research paper thumbnail of White-light interferometry for early-stage metal oxide growth characterization

Measurement Science and Technology

Oxidation of metals can provide a functional oxide film or an oxide layer that can lead to materi... more Oxidation of metals can provide a functional oxide film or an oxide layer that can lead to material degradation causing performance limiting concerns. Because of the technological and economic impacts of oxidation, understanding early-stage oxidation growth and its mechanisms is of high importance. Unfortunately, poor empirical data during early-stage oxidation has left our current understanding of oxidation incomplete and woefully inadequate. Measurement techniques previously used for oxidation kinetics characterization include microbalance, x-ray diffraction, Fourier-transform infrared spectroscopy, and spectroscopic ellipsometry. However, these techniques lack the necessary time-resolution or vertical resolution in addition to not providing any spatial data, which is essential to early-stage oxidation studies to understand both oxidation kinetics and mechanisms. A novel rapid and surface-sensitive data collection technique that provides three-dimensional spatial data of a growing oxide layer with sub-nanometer thickness resolution using white-light interferometry has been developed here. This technique will be the first technique capable of providing real-time spatial results of early-stage oxidation growth. The effectiveness of this characterization tool is shown by observing the early-stage oxidation kinetics and film cracking of uranium heated to 90 °C under 500 torr of pure O2. Initially a parabolic oxidation growth is observed. Once the oxide layer reaches ≈30 nm, the epitaxial stresses between the uranium substrate and oxide film layer causes localized cracking in addition to the observed transition of the parabolic growth rate to a linear growth rate. The results of the white-light interferometry are verified by glancing incidence x-ray diffraction.

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Research paper thumbnail of Spectroscopic Ellipsometry and White-Light Interferometry Investigation into Time-Dependent Oxidation Rates of Uranium in Pure Oxygen

Microscopy and Microanalysis

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Research paper thumbnail of Comparative Experimental Study of X-Ray Absorption Spectroscopy and Electron Energy Loss Spectroscopy on Passivated U Surfaces

MRS Proceedings

X-ray absorption spectroscopy and electron energy loss spectroscopy are complementary analytical ... more X-ray absorption spectroscopy and electron energy loss spectroscopy are complementary analytical techniques on energy and spatial resolution. These techniques are based on the same fundamental physical process of core excitation with either an incident photon or incident electron. In the proper experimental configuration the electron and photon inelastic scattering amplitudes are comparable and thus the x-ray and electron absorption edges look identical. We have applied these two complementary analytical techniques to investigate the electronic structure of C ion implanted U. Implantation of C+ ions into U238 has been shown to produce a physically and chemically modified surface layer that passivates the surface preventing further air oxidation and corrosion. Comparison of the resultant spectra reveal that transitions between the initial state and a series of final states yield numerous strong features at the absorption edge that can provide structural information and information on...

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Research paper thumbnail of Effects of Plume Hydrodynamics and Oxidation on the Composition of a Condensing Laser-Induced Plasma

The journal of physical chemistry. A, Jan 15, 2018

High-temperature chemistry in laser ablation plumes leads to vapor-phase speciation, which can in... more High-temperature chemistry in laser ablation plumes leads to vapor-phase speciation, which can induce chemical fractionation during condensation. Using emission spectroscopy acquired after ablation of a SrZrO target, we have experimentally observed the formation of multiple molecular species (ZrO and SrO) as a function of time as the laser ablation plume evolves. Although the stable oxides SrO and ZrO are both refractory, we observed emission from the ZrO intermediate at earlier times than SrO. We deduced the time-scale of oxygen entrainment into the laser ablation plume using an O environment by observing the in-growth of ZrO in the emission spectra relative to ZrO, which was formed by reaction of Zr with O from the target itself. Using temporally resolved plume-imaging, we determined that ZrO formed more readily at early times, volumetrically in the plume, while SrO formed later in time, around the periphery. Using a simple temperature-dependent reaction model, we have illustrated...

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Research paper thumbnail of A modulated molecular beam study of the energy of simple gases scattered from pyrolytic graphite

Surface Science

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Research paper thumbnail of EXAFS investigation of UF4

Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films

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Research paper thumbnail of The surface topography of pyrolitic carbons and of gold thin films by scanning tunneling microscopy: Grain boundaries and surface defects

Thin Solid Films

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Research paper thumbnail of Surface site specificity on the basal plane of graphite: 1.06 μm laser damage threshold and reactivity with oxygen between 350 and 2300 K

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures

This paper reports on the use of scanning tunneling microscopy (STM) to document changes in the n... more This paper reports on the use of scanning tunneling microscopy (STM) to document changes in the nanometer-scale morphology of the basal plane of highly oriented pyrolytic graphite after in situ exposure to 7 ns, 1064 nm Nd:YAG, and to ms Nd:Glass laser pulses producing surface temperatures up to 2300 K, and after ex situ exposure to temperatures as low as

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Research paper thumbnail of Cluster Formation in Laser-Induced Ablation and Evaporation of Solids Observed by Laser Ionization Time-Offlight Mass-Spectrometry and Scanning Tunneling Microscopy

MRS Proceedings

ABSTRACTLaser ionization time-of-flight mass analysis (LIMA) used pulses (5ns) of a frequency- qu... more ABSTRACTLaser ionization time-of-flight mass analysis (LIMA) used pulses (5ns) of a frequency- quadrupled Nd-YAG laser (266 nm) focused onto spots of 4–100 μm diameter to ablate material, and a reflectron time of flight tube to mass-analyze the plume. The observed mass spectra for Si, Pt, SiC, and UO2 varied in the distribution of ablation products among atoms, molecules and clusters, depending on laser power density and target material.Cleaved surfaces of highly oriented pyrolytic graphite (HOPG) positioned at room temperature either 10 cm away from materials ablated at 10−5 Torr by 1–3 excimer laser (308 nm) pulses of 20 ns duration or 1 m away from materials vaporized at 10−8 Torr by 10 Nd-Glass laser pulses of 1 ms duration were analyzed by Scanning Tunneling Microscopy (STM) in air with Ångstrom resolution. Clusters up to 30 Å in diameter were observed.

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Research paper thumbnail of Design of a molecular beam surface scattering apparatus for velocity and angular distribution measurements

Journal of Vacuum Science and Technology

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Research paper thumbnail of Clusters formed in laser-induced ablation of Si, SiC, Pt, UO2 and evaporation of UO2 observed by laser ionization time-of-flight mass spectrometry and scanning tunneling microscopy

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures

Cluster formation is traditionally observed by mass spectrometry, which has the disadvantage that... more Cluster formation is traditionally observed by mass spectrometry, which has the disadvantage that the detection sensitivity often decreases with increasing mass. Alternatively, one may collect the clusters onto an atomically flat substrate and identify them by scanning tunneling microscopy (STM). Both techniques were used here. For the first technique, a Nd:YAG laser (frequency quadrupled to 266 nm, 5 ns pulse

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Research paper thumbnail of Modulated molecular-beam studies of the surface chemistry of silicon reaction with reactive gases

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures

The method of studying the kinetics of gas--solid surface reactions using modulated molecular bea... more The method of studying the kinetics of gas--solid surface reactions using modulated molecular beams and mass-spectrometric detection is described. Results obtained for Si(111) etching by H(g) and deposition from SiHâ are presented.

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Research paper thumbnail of Atomic arrangement of sulfur adatoms on Mo(001) at atmospheric pressure: A scanning tunneling microscopy study

Physical Review Letters, 1988

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Research paper thumbnail of Predicting threshold and location of laser damage on optical surfaces

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Reactions of modulated molecular beams with pyrolytic graphite. III. Hydrogen

The Journal of Chemical Physics, 1975

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Experimental study to validate a model of hillock’s formation in aluminum thin films

Journal of Applied Physics, 1996

The growth of holes and hillocks in thin films has been reported extensively and for a multitude ... more The growth of holes and hillocks in thin films has been reported extensively and for a multitude of film–substrate systems. A recently developed model [F. Y. Genin, J. Appl. Phys. 77, 5130 (1995)] which analyzes the formation of a ridge at a traveling grain boundary due to stress and capillarity driving forces provides a quantitative description of the growth of the hillocks. In order to test the model, the surface morphology of aluminum thin films deposited on oxidized silicon substrates and annealed at 450 °C in argon is investigated; the profiles of thermal hillocks are measured by atomic force microscopy. The comparison shows excellent agreement between modeled and experimental profiles.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Computational Modeling of Uranium and Plutonium Hydriding- the role of Surface Oxide Layers, Oxycarbides, Carbides & Impurities

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Couches surfaciques a faible energie d'extraction produites par ablation au laser a photons a faible longueur d'onde

L'invention se rapporte a des photons a faible longueur d'onde utilises pour produire l&#... more L'invention se rapporte a des photons a faible longueur d'onde utilises pour produire l'ablation de matiere a partir d'une cible a faible energie d'extraction disposee sur un substrat adapte. Les photons a faible longueur d'onde ont une longueur d'onde inferieure ou egale a la longueur d'onde du visible. La composition elementaire du depot est regie par la composition de la cible et de l'environnement gazeux dans lequel se deroule le processus d'ablation. Ledit processus se deroule dans une chambre de depot sur laquelle est monte un laser a faible longueur d'onde et qui inclut un porte-substrat qu'il est possible de faire tourner, d'incliner, de chauffer et de refroidir. La matiere cible est placee sur un support qui fait tourner la cible pendant l'ablation au laser. En outre, la chambre de depot comporte une pompe a vide, un dispositif externe d'alimentation en gaz dote d'un atomiseur et d'un generateur de radicaux...

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Research paper thumbnail of Reactions of Modulated Molecular Beams with Fyrolytic Graphite I. Experimental Apparatus and Data Interpretation

An apparatus for the study of gas·-solid reactions which produce a gaseous reaction product is de... more An apparatus for the study of gas·-solid reactions which produce a gaseous reaction product is described. The reactant gas contacts the solid as a molecular beam travelli:ng in vacuum. Gaseous reaction products are monitored by a mass spectrometer as they are emitted from the surface. ~~he technique relies heavily upon the modulation of the molecular beam, which impr~ves sensitivity by shifting the information from the very noisy zero frequency (de) band to a narrow band ac mode which has considerably less noise. In addition, modulation of the reactant beam induces modulation at the same frequency in the reaction products and the phase difference between these two signals contains important kinetic information. The method of comparing theoretical models of the surface processes with the phase and amplitude information provided by the experiment is described.

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Research paper thumbnail of Advances in the Development of White-Light Interferometry for In-Situ Uranium Hydride Kinetic Data Collection

Microscopy and Microanalysis

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Research paper thumbnail of White-light interferometry for early-stage metal oxide growth characterization

Measurement Science and Technology

Oxidation of metals can provide a functional oxide film or an oxide layer that can lead to materi... more Oxidation of metals can provide a functional oxide film or an oxide layer that can lead to material degradation causing performance limiting concerns. Because of the technological and economic impacts of oxidation, understanding early-stage oxidation growth and its mechanisms is of high importance. Unfortunately, poor empirical data during early-stage oxidation has left our current understanding of oxidation incomplete and woefully inadequate. Measurement techniques previously used for oxidation kinetics characterization include microbalance, x-ray diffraction, Fourier-transform infrared spectroscopy, and spectroscopic ellipsometry. However, these techniques lack the necessary time-resolution or vertical resolution in addition to not providing any spatial data, which is essential to early-stage oxidation studies to understand both oxidation kinetics and mechanisms. A novel rapid and surface-sensitive data collection technique that provides three-dimensional spatial data of a growing oxide layer with sub-nanometer thickness resolution using white-light interferometry has been developed here. This technique will be the first technique capable of providing real-time spatial results of early-stage oxidation growth. The effectiveness of this characterization tool is shown by observing the early-stage oxidation kinetics and film cracking of uranium heated to 90 °C under 500 torr of pure O2. Initially a parabolic oxidation growth is observed. Once the oxide layer reaches ≈30 nm, the epitaxial stresses between the uranium substrate and oxide film layer causes localized cracking in addition to the observed transition of the parabolic growth rate to a linear growth rate. The results of the white-light interferometry are verified by glancing incidence x-ray diffraction.

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Research paper thumbnail of Spectroscopic Ellipsometry and White-Light Interferometry Investigation into Time-Dependent Oxidation Rates of Uranium in Pure Oxygen

Microscopy and Microanalysis

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Research paper thumbnail of Comparative Experimental Study of X-Ray Absorption Spectroscopy and Electron Energy Loss Spectroscopy on Passivated U Surfaces

MRS Proceedings

X-ray absorption spectroscopy and electron energy loss spectroscopy are complementary analytical ... more X-ray absorption spectroscopy and electron energy loss spectroscopy are complementary analytical techniques on energy and spatial resolution. These techniques are based on the same fundamental physical process of core excitation with either an incident photon or incident electron. In the proper experimental configuration the electron and photon inelastic scattering amplitudes are comparable and thus the x-ray and electron absorption edges look identical. We have applied these two complementary analytical techniques to investigate the electronic structure of C ion implanted U. Implantation of C+ ions into U238 has been shown to produce a physically and chemically modified surface layer that passivates the surface preventing further air oxidation and corrosion. Comparison of the resultant spectra reveal that transitions between the initial state and a series of final states yield numerous strong features at the absorption edge that can provide structural information and information on...

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Effects of Plume Hydrodynamics and Oxidation on the Composition of a Condensing Laser-Induced Plasma

The journal of physical chemistry. A, Jan 15, 2018

High-temperature chemistry in laser ablation plumes leads to vapor-phase speciation, which can in... more High-temperature chemistry in laser ablation plumes leads to vapor-phase speciation, which can induce chemical fractionation during condensation. Using emission spectroscopy acquired after ablation of a SrZrO target, we have experimentally observed the formation of multiple molecular species (ZrO and SrO) as a function of time as the laser ablation plume evolves. Although the stable oxides SrO and ZrO are both refractory, we observed emission from the ZrO intermediate at earlier times than SrO. We deduced the time-scale of oxygen entrainment into the laser ablation plume using an O environment by observing the in-growth of ZrO in the emission spectra relative to ZrO, which was formed by reaction of Zr with O from the target itself. Using temporally resolved plume-imaging, we determined that ZrO formed more readily at early times, volumetrically in the plume, while SrO formed later in time, around the periphery. Using a simple temperature-dependent reaction model, we have illustrated...

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Research paper thumbnail of A modulated molecular beam study of the energy of simple gases scattered from pyrolytic graphite

Surface Science

Bookmarks Related papers MentionsView impact

Research paper thumbnail of EXAFS investigation of UF4

Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films

Bookmarks Related papers MentionsView impact

Research paper thumbnail of The surface topography of pyrolitic carbons and of gold thin films by scanning tunneling microscopy: Grain boundaries and surface defects

Thin Solid Films

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Surface site specificity on the basal plane of graphite: 1.06 μm laser damage threshold and reactivity with oxygen between 350 and 2300 K

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures

This paper reports on the use of scanning tunneling microscopy (STM) to document changes in the n... more This paper reports on the use of scanning tunneling microscopy (STM) to document changes in the nanometer-scale morphology of the basal plane of highly oriented pyrolytic graphite after in situ exposure to 7 ns, 1064 nm Nd:YAG, and to ms Nd:Glass laser pulses producing surface temperatures up to 2300 K, and after ex situ exposure to temperatures as low as

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Cluster Formation in Laser-Induced Ablation and Evaporation of Solids Observed by Laser Ionization Time-Offlight Mass-Spectrometry and Scanning Tunneling Microscopy

MRS Proceedings

ABSTRACTLaser ionization time-of-flight mass analysis (LIMA) used pulses (5ns) of a frequency- qu... more ABSTRACTLaser ionization time-of-flight mass analysis (LIMA) used pulses (5ns) of a frequency- quadrupled Nd-YAG laser (266 nm) focused onto spots of 4–100 μm diameter to ablate material, and a reflectron time of flight tube to mass-analyze the plume. The observed mass spectra for Si, Pt, SiC, and UO2 varied in the distribution of ablation products among atoms, molecules and clusters, depending on laser power density and target material.Cleaved surfaces of highly oriented pyrolytic graphite (HOPG) positioned at room temperature either 10 cm away from materials ablated at 10−5 Torr by 1–3 excimer laser (308 nm) pulses of 20 ns duration or 1 m away from materials vaporized at 10−8 Torr by 10 Nd-Glass laser pulses of 1 ms duration were analyzed by Scanning Tunneling Microscopy (STM) in air with Ångstrom resolution. Clusters up to 30 Å in diameter were observed.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Design of a molecular beam surface scattering apparatus for velocity and angular distribution measurements

Journal of Vacuum Science and Technology

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Research paper thumbnail of Clusters formed in laser-induced ablation of Si, SiC, Pt, UO2 and evaporation of UO2 observed by laser ionization time-of-flight mass spectrometry and scanning tunneling microscopy

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures

Cluster formation is traditionally observed by mass spectrometry, which has the disadvantage that... more Cluster formation is traditionally observed by mass spectrometry, which has the disadvantage that the detection sensitivity often decreases with increasing mass. Alternatively, one may collect the clusters onto an atomically flat substrate and identify them by scanning tunneling microscopy (STM). Both techniques were used here. For the first technique, a Nd:YAG laser (frequency quadrupled to 266 nm, 5 ns pulse

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Modulated molecular-beam studies of the surface chemistry of silicon reaction with reactive gases

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures

The method of studying the kinetics of gas--solid surface reactions using modulated molecular bea... more The method of studying the kinetics of gas--solid surface reactions using modulated molecular beams and mass-spectrometric detection is described. Results obtained for Si(111) etching by H(g) and deposition from SiHâ are presented.

Bookmarks Related papers MentionsView impact