Alan Slavin - Academia.edu (original) (raw)
Papers by Alan Slavin
Journal of Vacuum Science and Technology a Vacuum Surfaces and Films, 1989
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 2005
J. Phys. Chem.;(United …, 1988
... However, the CC stretching force constant in adsorbed ethylene can be estimated from the deut... more ... However, the CC stretching force constant in adsorbed ethylene can be estimated from the deuteriated ethylene vibrational frequencies, and a general correlation between deuteriated vibrational frequency and adsorbed CC force constant is proposed. ...
Physical Review B, 2000
The thermal desorption of atoms from two-dimensional deposit islands on a substrate may be limite... more The thermal desorption of atoms from two-dimensional deposit islands on a substrate may be limited by the rate of desorption from island edges. In earlier work, Slavin and Young developed a theory for the form of the desorption curves for such systems, as a function of the average island size, that agreed well with experimental data until just beyond the peak maximum. The fitting procedure provided values for the desorption energy, the average island radius, the standard deviation of the island-size distribution function, and the frequency of vibration of an atom at an island edge. The current study extends this work by incorporating a theoretical expression for the initial distribution of island sizes, due to Ardell, into the previous theory. The Ardell function provides a value for the average initial island radius and the standard deviation of the distribution without any curve fitting, if the surface coverage and the number of islands are known. It also enables the experimental thermal desorption data to be fitted over the entire desorption curve, which provides an independent check on the experimental value for surface coverage. The results using the Ardell distribution are in good agreement with all the parameters obtainable from the experimental data.
Surface Science, Jul 1, 1991
ABSTRACT
Surface Science, 2005
Ultrathin oxide films grown in vacuum are important in many industrial areas, including microelec... more Ultrathin oxide films grown in vacuum are important in many industrial areas, including microelectronics and heterogeneous catalysis. In this paper, the dependence of oxide stoichiometry, growth kinetics, thickness and stability on O2 pressure and annealing temperature are explored using a high-stability quartz-crystal microbalance and Auger spectroscopy, for the oxidation of lead on gold as a model system. The oxide thickness
Surface Science, 1986
ABSTRACT
Progress in Surface Science, 1995
This paper outlines some of the outstanding problems associated with the experimental determinati... more This paper outlines some of the outstanding problems associated with the experimental determination of the growth modes of thin metal fihns on dissimilar metal substrates, and suggests approaches for overcoming them. SpeciIicaUy, it discusses ways to differentiate between Stranski-Krastanov and alloy growth, the quantitative fitting of "Auger signaltime" plots, and the determination of the stoichiometry of surface alloys. A comparison of the observed growth modes with those predicted by the Macroscopic Atom Method shows that the results predicted by this method must be treated with extreme caution. Acronyms AS-t CEM EELS FM imfp LEED ML SK VW Auger signal-time Corrected effective medium Electron energy loss spectroscopy Frank-van der Merwe Inelastic mean free path Low energy electron diffraction Macroscopic atom model Monolayer: The quantity of deposited metal required to complete the surface layer.
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 1992
The growth of oxide on bulk tin has been modeled in a layer-by-layer fashion by using successivel... more The growth of oxide on bulk tin has been modeled in a layer-by-layer fashion by using successively greater deposits of Sn on a Au(111) surface. The Au does not oxidize and merely acts as a support. Auger electron spectroscopy, electron energy-loss spectroscopy, and work function measurements have been made. The initial fast-growth stage of the oxide is complete by about 3×104 L. SnO2 forms either for oxygen exposures up to 1900 L or with oxide films limited to about 1 monolayer in thickness. For films up to nine atomic layers thick, a thin layer of SnO, probably one monolayer in thickness, forms on the surface with SnO2 underneath. It appears that for a Sn deposit up to the equivalent of one atomic layer in thickness, the oxygen bonds above the surface, while for larger deposits the oxygen moves below the surface. A comparison is made with earlier results for lead and bismuth.
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 1986
In various spectroscopies composite curves are often encountered which are linear superpositions ... more In various spectroscopies composite curves are often encountered which are linear superpositions of overlapping, chemically shifted spectral peaks. Separation of such a composite into its individual components allows the identification of the chemical complex by its chemical shift, and the determination of the amount of the element in the complex from the strength of the spectral component. This paper describes a Fourier transform method for the decomposition of such a composite spectrum which is applicable under two conditions which are often satisfied in practice: all the chemically shifted peaks of the element of interest must have very similar line shapes, and one of these peaks must be observable in isolation to provide a reference line shape. Even in the event of line broadening this technique should give good starting parameters for the number and positions of the components. Applications to XPS and Auger spectroscopy are discussed.
International Journal of Heat and Mass Transfer, 2004
ABSTRACT
International Journal of Heat and Mass Transfer, 2002
Many analytical models exist for the thermal conductivity of packed pebble beds in a static gas, ... more Many analytical models exist for the thermal conductivity of packed pebble beds in a static gas, but all require adjustable parameters to give good fits to experimental data. The present paper differs from earlier ones in including a measurable parameter for the particle roughness. With this, the conductivity for an uncompressed bed can be calculated with no adjustable parameters, provided
Fusion Engineering and Design, 2001
This paper tests a recently developed theory for the thermal conductivity of a packed pebble bed ... more This paper tests a recently developed theory for the thermal conductivity of a packed pebble bed in the presence of a gas, at substantially higher temperatures than previously used to test the theory, by fitting previous measurements on lithium zirconate in helium. The ultimate goal of the theory is the prediction of the thermal conductivity of a packed bed using only parameters that can be measured directly from the particles. The main innovations in the theory are its description of the conduction across the narrow gaps between irregularly shaped particles having several points of contact, in terms of the average gap width and area, and the introduction of a new expression for bridging the change in gas conductivity between the low and high pressure limits. In the case of the lithium zirconate beds, the theoretical fits require a third fitting parameter to take account of the oblateness of these pebbles. The fitted curves then describe very well both the temperature and pressure dependence of the experimental data, and provide reasonable values for all the fitting parameters. The model shows that conduction through the points of contact can be ignored, at least for the small test beds modeled.
American Journal of Physics, 2008
A metal film that is only a few atomic layers thick, on an appropriate substrate, creates a quant... more A metal film that is only a few atomic layers thick, on an appropriate substrate, creates a quantum well that confines the conduction electrons in the direction perpendicular to the film. As a result, components of the wavevector in the plane of the film are quasicontinuous, but the perpendicular component is discrete. The result is a strong oscillatory dependence of the film properties on film thickness, including the Fermi energy and the density of states. We show that these quantum effects associated with the film thickness can be understood within the free electron theory of metals. Because of its simplicity, the thin-film quantum well is appropriate as a problem for senior undergraduate and graduate students and provides an introduction to quantum size effects.
Physical Review B, 1990
Auger-electron spectroscopy, electron-energy-loss spectroscopy, and work-function measurements ha... more Auger-electron spectroscopy, electron-energy-loss spectroscopy, and work-function measurements have been used to make a comparison between the oxidation of bulk polycrystalline bismuth and thin bismuth films (of the order of one-monolayer thickness) on the Au(111) surface. Because the gold acts as an inert support, the thin films may be used to model bulk oxidation kinetics in a layer-by-layer fashion. The results indicate that a two-monolayer-thick oxide, BiO, grows laterally across the surface of bulk bismuth and reaches completion at an oxygen exposure of about 12000 langmuirs [1 langmuir (L)-:1 0 6 Torr s]; no precursor stage of chemisorbed oxygen has been observed. This is followed by the continued growth of the oxide at a much slower rate. The same oxide occurs for Bi on Au(111), even for submonolayer quantities of Bi for which the oxide is only one layer thick. Chemical reactivity measurements of thicker films of Bi on Au(111) suggest that a cooperative two-layer reconstruction of the surface occurs upon oxidation, which probably takes place during the oxidation of bulk Bi, as well. The common bulk oxide of bismuth, Bi203, was never observed on either surface. There is evidence to suggest that the surface oxide lattice parameter relaxes to that of the bulk oxide when the oxide achieves a thickness of about seven monolayers. Most of the conclusions reported here are similar to those of an earlier study involving the oxidation of lead.
Review of Scientific Instruments, 1983
This note describes an overflow sensor used as the level controller for automatic filling systems... more This note describes an overflow sensor used as the level controller for automatic filling systems for liquid nitrogen. It serves as an inexpensive and reliable alternative to level-sensing devices in applications where the container is to be refilled to the top at regular intervals.
Surface Science, 1987
The oxidation of thin lead overlayers on a predominantly (111) polycrystalline gold surface at ro... more The oxidation of thin lead overlayers on a predominantly (111) polycrystalline gold surface at room temperature and oxygen pressure of 8 • 10-6 Tort was investigated using Auger electron spectroscopy (AES). Oxidation was monitored using the oxide lead peak obtained by spectral decomposition. This peak experiences a shift from pure lead of 2.3 + 0.1 eV for deposits up to 3 monolayer-equivalents (ME) and 2.7 +0.1 eV for deposits greater than about 4 ME. The oxygen signal for a I ME deposit at saturation exposure is about 20% of the value expected for a complete oxygen monolayer. This is explained in terms of clusters of about 5 Pb atoms for each oxygen atom. This differs from the PbO stoichiometry which has been observed under similar conditions on bulk lead and also claimed for the oxidation of thin lead deposits on Ag and Cu. Also contrary to results on Ag and Cu is the rate of oxygen uptake on Au which increases with lead coverage in the submonolayer region; this is explained by the absence of adsorption and surface diffusion of oxygen on gold, and the need for clusters of about 5 lead atoms for oxidation to occur. Deposition of more than 1 ME of lead results in lead-gold compound formation as observed by previous authors. Exposure of this compound to oxygen causes oxidation of the surface lead with inward migration of gold from the surface. The oxide layer is about 2 monolayers thick and greatly reduces the rate of further oxidation. The large decrease in the gold substrate signal on oxidation is a sensitive method for differentiating between compound formation a'ad alternative growth modes for the bimetallic surface.
Review of Scientific Instruments, 2003
This article describes a high-stability quartz-crystal microbalance (QCM) and the methodology for... more This article describes a high-stability quartz-crystal microbalance (QCM) and the methodology for measuring the change in mass during thin-film growth in deposition and sputter processes. Much lower noise and higher-frequency stability have been achieved than with conventional QCMs. A stability of ±0.1 Hz at 6 MHz has been obtained over 4 h, with a rms stability of 0.03 Hz. The adsorption of one atomic monolayer of oxygen produces a frequency shift of about 5 Hz, so this stability enables the QCM to be used to determine the stoichiometry of submonolayer oxide films, as well as for high-accuracy measurements of adsorbate sticking probability and ion-milling rate.
Journal of Vacuum Science and Technology a Vacuum Surfaces and Films, 1989
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 2005
J. Phys. Chem.;(United …, 1988
... However, the CC stretching force constant in adsorbed ethylene can be estimated from the deut... more ... However, the CC stretching force constant in adsorbed ethylene can be estimated from the deuteriated ethylene vibrational frequencies, and a general correlation between deuteriated vibrational frequency and adsorbed CC force constant is proposed. ...
Physical Review B, 2000
The thermal desorption of atoms from two-dimensional deposit islands on a substrate may be limite... more The thermal desorption of atoms from two-dimensional deposit islands on a substrate may be limited by the rate of desorption from island edges. In earlier work, Slavin and Young developed a theory for the form of the desorption curves for such systems, as a function of the average island size, that agreed well with experimental data until just beyond the peak maximum. The fitting procedure provided values for the desorption energy, the average island radius, the standard deviation of the island-size distribution function, and the frequency of vibration of an atom at an island edge. The current study extends this work by incorporating a theoretical expression for the initial distribution of island sizes, due to Ardell, into the previous theory. The Ardell function provides a value for the average initial island radius and the standard deviation of the distribution without any curve fitting, if the surface coverage and the number of islands are known. It also enables the experimental thermal desorption data to be fitted over the entire desorption curve, which provides an independent check on the experimental value for surface coverage. The results using the Ardell distribution are in good agreement with all the parameters obtainable from the experimental data.
Surface Science, Jul 1, 1991
ABSTRACT
Surface Science, 2005
Ultrathin oxide films grown in vacuum are important in many industrial areas, including microelec... more Ultrathin oxide films grown in vacuum are important in many industrial areas, including microelectronics and heterogeneous catalysis. In this paper, the dependence of oxide stoichiometry, growth kinetics, thickness and stability on O2 pressure and annealing temperature are explored using a high-stability quartz-crystal microbalance and Auger spectroscopy, for the oxidation of lead on gold as a model system. The oxide thickness
Surface Science, 1986
ABSTRACT
Progress in Surface Science, 1995
This paper outlines some of the outstanding problems associated with the experimental determinati... more This paper outlines some of the outstanding problems associated with the experimental determination of the growth modes of thin metal fihns on dissimilar metal substrates, and suggests approaches for overcoming them. SpeciIicaUy, it discusses ways to differentiate between Stranski-Krastanov and alloy growth, the quantitative fitting of "Auger signaltime" plots, and the determination of the stoichiometry of surface alloys. A comparison of the observed growth modes with those predicted by the Macroscopic Atom Method shows that the results predicted by this method must be treated with extreme caution. Acronyms AS-t CEM EELS FM imfp LEED ML SK VW Auger signal-time Corrected effective medium Electron energy loss spectroscopy Frank-van der Merwe Inelastic mean free path Low energy electron diffraction Macroscopic atom model Monolayer: The quantity of deposited metal required to complete the surface layer.
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 1992
The growth of oxide on bulk tin has been modeled in a layer-by-layer fashion by using successivel... more The growth of oxide on bulk tin has been modeled in a layer-by-layer fashion by using successively greater deposits of Sn on a Au(111) surface. The Au does not oxidize and merely acts as a support. Auger electron spectroscopy, electron energy-loss spectroscopy, and work function measurements have been made. The initial fast-growth stage of the oxide is complete by about 3×104 L. SnO2 forms either for oxygen exposures up to 1900 L or with oxide films limited to about 1 monolayer in thickness. For films up to nine atomic layers thick, a thin layer of SnO, probably one monolayer in thickness, forms on the surface with SnO2 underneath. It appears that for a Sn deposit up to the equivalent of one atomic layer in thickness, the oxygen bonds above the surface, while for larger deposits the oxygen moves below the surface. A comparison is made with earlier results for lead and bismuth.
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 1986
In various spectroscopies composite curves are often encountered which are linear superpositions ... more In various spectroscopies composite curves are often encountered which are linear superpositions of overlapping, chemically shifted spectral peaks. Separation of such a composite into its individual components allows the identification of the chemical complex by its chemical shift, and the determination of the amount of the element in the complex from the strength of the spectral component. This paper describes a Fourier transform method for the decomposition of such a composite spectrum which is applicable under two conditions which are often satisfied in practice: all the chemically shifted peaks of the element of interest must have very similar line shapes, and one of these peaks must be observable in isolation to provide a reference line shape. Even in the event of line broadening this technique should give good starting parameters for the number and positions of the components. Applications to XPS and Auger spectroscopy are discussed.
International Journal of Heat and Mass Transfer, 2004
ABSTRACT
International Journal of Heat and Mass Transfer, 2002
Many analytical models exist for the thermal conductivity of packed pebble beds in a static gas, ... more Many analytical models exist for the thermal conductivity of packed pebble beds in a static gas, but all require adjustable parameters to give good fits to experimental data. The present paper differs from earlier ones in including a measurable parameter for the particle roughness. With this, the conductivity for an uncompressed bed can be calculated with no adjustable parameters, provided
Fusion Engineering and Design, 2001
This paper tests a recently developed theory for the thermal conductivity of a packed pebble bed ... more This paper tests a recently developed theory for the thermal conductivity of a packed pebble bed in the presence of a gas, at substantially higher temperatures than previously used to test the theory, by fitting previous measurements on lithium zirconate in helium. The ultimate goal of the theory is the prediction of the thermal conductivity of a packed bed using only parameters that can be measured directly from the particles. The main innovations in the theory are its description of the conduction across the narrow gaps between irregularly shaped particles having several points of contact, in terms of the average gap width and area, and the introduction of a new expression for bridging the change in gas conductivity between the low and high pressure limits. In the case of the lithium zirconate beds, the theoretical fits require a third fitting parameter to take account of the oblateness of these pebbles. The fitted curves then describe very well both the temperature and pressure dependence of the experimental data, and provide reasonable values for all the fitting parameters. The model shows that conduction through the points of contact can be ignored, at least for the small test beds modeled.
American Journal of Physics, 2008
A metal film that is only a few atomic layers thick, on an appropriate substrate, creates a quant... more A metal film that is only a few atomic layers thick, on an appropriate substrate, creates a quantum well that confines the conduction electrons in the direction perpendicular to the film. As a result, components of the wavevector in the plane of the film are quasicontinuous, but the perpendicular component is discrete. The result is a strong oscillatory dependence of the film properties on film thickness, including the Fermi energy and the density of states. We show that these quantum effects associated with the film thickness can be understood within the free electron theory of metals. Because of its simplicity, the thin-film quantum well is appropriate as a problem for senior undergraduate and graduate students and provides an introduction to quantum size effects.
Physical Review B, 1990
Auger-electron spectroscopy, electron-energy-loss spectroscopy, and work-function measurements ha... more Auger-electron spectroscopy, electron-energy-loss spectroscopy, and work-function measurements have been used to make a comparison between the oxidation of bulk polycrystalline bismuth and thin bismuth films (of the order of one-monolayer thickness) on the Au(111) surface. Because the gold acts as an inert support, the thin films may be used to model bulk oxidation kinetics in a layer-by-layer fashion. The results indicate that a two-monolayer-thick oxide, BiO, grows laterally across the surface of bulk bismuth and reaches completion at an oxygen exposure of about 12000 langmuirs [1 langmuir (L)-:1 0 6 Torr s]; no precursor stage of chemisorbed oxygen has been observed. This is followed by the continued growth of the oxide at a much slower rate. The same oxide occurs for Bi on Au(111), even for submonolayer quantities of Bi for which the oxide is only one layer thick. Chemical reactivity measurements of thicker films of Bi on Au(111) suggest that a cooperative two-layer reconstruction of the surface occurs upon oxidation, which probably takes place during the oxidation of bulk Bi, as well. The common bulk oxide of bismuth, Bi203, was never observed on either surface. There is evidence to suggest that the surface oxide lattice parameter relaxes to that of the bulk oxide when the oxide achieves a thickness of about seven monolayers. Most of the conclusions reported here are similar to those of an earlier study involving the oxidation of lead.
Review of Scientific Instruments, 1983
This note describes an overflow sensor used as the level controller for automatic filling systems... more This note describes an overflow sensor used as the level controller for automatic filling systems for liquid nitrogen. It serves as an inexpensive and reliable alternative to level-sensing devices in applications where the container is to be refilled to the top at regular intervals.
Surface Science, 1987
The oxidation of thin lead overlayers on a predominantly (111) polycrystalline gold surface at ro... more The oxidation of thin lead overlayers on a predominantly (111) polycrystalline gold surface at room temperature and oxygen pressure of 8 • 10-6 Tort was investigated using Auger electron spectroscopy (AES). Oxidation was monitored using the oxide lead peak obtained by spectral decomposition. This peak experiences a shift from pure lead of 2.3 + 0.1 eV for deposits up to 3 monolayer-equivalents (ME) and 2.7 +0.1 eV for deposits greater than about 4 ME. The oxygen signal for a I ME deposit at saturation exposure is about 20% of the value expected for a complete oxygen monolayer. This is explained in terms of clusters of about 5 Pb atoms for each oxygen atom. This differs from the PbO stoichiometry which has been observed under similar conditions on bulk lead and also claimed for the oxidation of thin lead deposits on Ag and Cu. Also contrary to results on Ag and Cu is the rate of oxygen uptake on Au which increases with lead coverage in the submonolayer region; this is explained by the absence of adsorption and surface diffusion of oxygen on gold, and the need for clusters of about 5 lead atoms for oxidation to occur. Deposition of more than 1 ME of lead results in lead-gold compound formation as observed by previous authors. Exposure of this compound to oxygen causes oxidation of the surface lead with inward migration of gold from the surface. The oxide layer is about 2 monolayers thick and greatly reduces the rate of further oxidation. The large decrease in the gold substrate signal on oxidation is a sensitive method for differentiating between compound formation a'ad alternative growth modes for the bimetallic surface.
Review of Scientific Instruments, 2003
This article describes a high-stability quartz-crystal microbalance (QCM) and the methodology for... more This article describes a high-stability quartz-crystal microbalance (QCM) and the methodology for measuring the change in mass during thin-film growth in deposition and sputter processes. Much lower noise and higher-frequency stability have been achieved than with conventional QCMs. A stability of ±0.1 Hz at 6 MHz has been obtained over 4 h, with a rms stability of 0.03 Hz. The adsorption of one atomic monolayer of oxygen produces a frequency shift of about 5 Hz, so this stability enables the QCM to be used to determine the stoichiometry of submonolayer oxide films, as well as for high-accuracy measurements of adsorbate sticking probability and ion-milling rate.