... BOMBARDED METAL SURFACES DURING CHEMISORPTION USING LOW DOSE SIMS AND MULTIPHOTON RESONANCE I... more ... BOMBARDED METAL SURFACES DURING CHEMISORPTION USING LOW DOSE SIMS AND MULTIPHOTON RESONANCE IONIZATION FM KIMOCK, JP BAXTER and N ... tenths of a microsecond after the ion pulse, the volume of neutrals is irradiated with a laser pulse whose ...
Multiphoton resonance ionization spectroscopy has been used to determine the polar-angle and the ... more Multiphoton resonance ionization spectroscopy has been used to determine the polar-angle and the kinetic-energy distributions of rhodium atoms desorbed from ion-bombarded Rh{100} surface in the fine-structure components of the a 4Fj (J=9/2 and 7/2) ground-state multiplet. The peak in the energy distribution of the metastable level (4F7/2 with excitation energy of 0.2 eV) is found to occur roughly at the same value as the ground-state (4F9/2) distribution but decays more gradually at higher energies. The measured spectra have been used to investigate the dependence of the excitation probability on the takeoff angle (θ) as well as the emission velocity (v). It is shown that the excitation probability depends strongly on these parameters, approaching an exponential dependence on l/[v cos(θ)] at higher velocities (> 5×l05cm/sec).
ABSTRACT The thermal decomposition of methanol on a clean Pd[lcub]111[rcub] surface has been inve... more ABSTRACT The thermal decomposition of methanol on a clean Pd[lcub]111[rcub] surface has been investigated using X-ray photoelectron spectrometry (XPS), secondary ion mass spectrometry (SIMS) and thermal desorption spectrometry (TDS). In this work, we observe that the methanolic C–O bond activation on Pd[lcub]111[rcub] is a strongly coverage dependent process. At lower and higher coverages, XPS data suggest that CH3Oads is the principle product. At near monolayer coverage the methanolic C–O bond dissociates at 175 K to produce CH3,ads, which is characterized by a C 1s binding energy of 283.8 eV, and is stable up to 400 K. A stepwise dehydrogenation of CH3,ads to form CH2,ads (methylene) and CHads (methylidyne) is observed above 400 K. Surface methyl and its dehydrogenated forms are characterized both by the chemical shift of the XPS C 1s peak from 283.8 to 284.8 eV and by positive ion SIMS peaks with . The gaseous products detected by TDS are methanol, CO, hydrogen, methane and water. This observation implies that the methanolic C–O bond cleavage is contingent upon a special molecular arrangement of precursors before reaction and that the CH3,ads product is stabilized by ancillary reaction products, such as CO.
We report the photoionization of ion beam desorbed amino acids using femtosecond laser pulses at ... more We report the photoionization of ion beam desorbed amino acids using femtosecond laser pulses at 195 and 260 nm. Ionization of ion-desorbed glycine, alanine, valine, leucine, isoleucine, and phenylalanine using 195 nm laser pulses is found to produce almost exclusively a decarboxylated ion fragment, while tyrosine and tryptophan produce a functional group cation. The adiabatic ionization potentials for the former amino acids correspond to the removal of an electron from the amine nitrogen atom, while for tyrosine and tryptophan it corresponds to the removal of an electron from the aromatic functional group. We find that fragmentation is initiated by the formation of a radical site which leads to an α-cleavage reaction and, depending upon which electron is removed, results in the formation of a decarboxylated ion or a functional group ion. These results indicate that a significant fraction of the amino acids are desorbed intact, but are fragmented when ionized. Except for leucine, isoleucine, and phenylala...
The design and application of a detector is described, which is capable of simultaneously measuri... more The design and application of a detector is described, which is capable of simultaneously measuring energy and angular distributions of neutral particles desorbed from surfaces. Specific applications to ion bombardment studies are presented. The detector utilizes the state selectivity, sensitivity, and pulsed characteristics of multiphoton resonance ionization as a time-of-flight sensitive postionization technique. A microchannel-plate element allows position-sensitive detection of the laser-ionized particles. Sample data are presented for ground-state Rh atoms desorbed from clean, ion-bombarded Rh foil and Rh(111) surfaces.
We report the use of femtosecond laser photoionization of sputtered neutral molecules to enhance ... more We report the use of femtosecond laser photoionization of sputtered neutral molecules to enhance the sensitivity of detection and to improve the prospects for molecule-specific imaging experiments. Results are presented for patterned metal oxides, polycyclic aromatic hydrocarbons and several amino acids. In addition to increased signal levels, we find that is photoionization generally yields simpler mass spectra than the corresponding SIMS spectra, although considerable fragmentation is observed in both cases.
A chemical imaging time-of-flight secondary ion mass spectrometer is described. It consists of a ... more A chemical imaging time-of-flight secondary ion mass spectrometer is described. It consists of a liquid metal ion gun, medium energy resolution reflectron mass analyzer, liquid nitrogen cooled sample stage, preparation chamber and dual stage entry port. Unique features include compatibility with laser postionization experiments, large field of view, cryogenic sample handling capability and high incident ion beam current. Instrument performance is illustrated by the characterization of scanning electron microscopy grids, silver and functionalized polystyrene beads and the postionization of an organic overlayer on a gold substrate.
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 1991
A comparison of a polyethylene additive extract sample, deposited from solution as a submonolayer... more A comparison of a polyethylene additive extract sample, deposited from solution as a submonolayer on Ag, was made to an in situ surface analysis of a bulk polyethylene sample using time-of-flight static secondary ion mass spectrometry (TOF-SIMS). The in situ analysis was able to confirm most of the additives detected in the extract. The additive mass range of 200–1200 Daltons was relatively free of spectral interferences due to the polyethylene matrix. High mass resolution studies were used to assist in the assignment of molecular identities to the additives. Molecular ions for the additives were predominantly Ag cationized adducts for the extract sample, and [M+H]+ or [M+Na]+ species for the bulk polyethylene. Deposition of standard additive solutions on Ag demonstrated the detection sensitivity of TOF-SIMS, illustrating the potential for molecular imaging of polymer domains as small as a few μm2 . The relative extent of oxidation of Naugard 524, an antioxidant additive, also was c...
Journal of Electron Spectroscopy and Related Phenomena, 1972
... of Electron Spectroscopy and Related Phenomena Elsevier Publishing Company, Amsterdam Printed... more ... of Electron Spectroscopy and Related Phenomena Elsevier Publishing Company, Amsterdam Printed in The Netherlands ELECTRON SPECTROSCOPY OF THE NICKELOXYGEN SYSTEM KS KIM and RE DAVIS Department of Chemistry, Purdue University, Lafayette, md. ...
The factors which influence chemical shifts are examined in order to elucidate the cause of the a... more The factors which influence chemical shifts are examined in order to elucidate the cause of the anomalous chemical shifts for Cd and Ag oxides. The effects of extra-atomic relaxation are accounted for using a procedure employing experimental Auger and binding energies. Atomic partial ionic charges for some simple Cd, Ag, and Zn compounds are calculated from experimental binding energies using a model which includes the effects of lattice potentials and extra-atomic relaxation. Inclusion of extra-atomic relaxation effects did not have a drastic effect on the relative ionicities computed for these selected compounds. However, for CdO, a large extra-atomic relaxation energy contribution reduces the binding energy by 0.5 eV more than is predicted from nearest neighbor electronegativity arguments.
... BOMBARDED METAL SURFACES DURING CHEMISORPTION USING LOW DOSE SIMS AND MULTIPHOTON RESONANCE I... more ... BOMBARDED METAL SURFACES DURING CHEMISORPTION USING LOW DOSE SIMS AND MULTIPHOTON RESONANCE IONIZATION FM KIMOCK, JP BAXTER and N ... tenths of a microsecond after the ion pulse, the volume of neutrals is irradiated with a laser pulse whose ...
Multiphoton resonance ionization spectroscopy has been used to determine the polar-angle and the ... more Multiphoton resonance ionization spectroscopy has been used to determine the polar-angle and the kinetic-energy distributions of rhodium atoms desorbed from ion-bombarded Rh{100} surface in the fine-structure components of the a 4Fj (J=9/2 and 7/2) ground-state multiplet. The peak in the energy distribution of the metastable level (4F7/2 with excitation energy of 0.2 eV) is found to occur roughly at the same value as the ground-state (4F9/2) distribution but decays more gradually at higher energies. The measured spectra have been used to investigate the dependence of the excitation probability on the takeoff angle (θ) as well as the emission velocity (v). It is shown that the excitation probability depends strongly on these parameters, approaching an exponential dependence on l/[v cos(θ)] at higher velocities (> 5×l05cm/sec).
ABSTRACT The thermal decomposition of methanol on a clean Pd[lcub]111[rcub] surface has been inve... more ABSTRACT The thermal decomposition of methanol on a clean Pd[lcub]111[rcub] surface has been investigated using X-ray photoelectron spectrometry (XPS), secondary ion mass spectrometry (SIMS) and thermal desorption spectrometry (TDS). In this work, we observe that the methanolic C–O bond activation on Pd[lcub]111[rcub] is a strongly coverage dependent process. At lower and higher coverages, XPS data suggest that CH3Oads is the principle product. At near monolayer coverage the methanolic C–O bond dissociates at 175 K to produce CH3,ads, which is characterized by a C 1s binding energy of 283.8 eV, and is stable up to 400 K. A stepwise dehydrogenation of CH3,ads to form CH2,ads (methylene) and CHads (methylidyne) is observed above 400 K. Surface methyl and its dehydrogenated forms are characterized both by the chemical shift of the XPS C 1s peak from 283.8 to 284.8 eV and by positive ion SIMS peaks with . The gaseous products detected by TDS are methanol, CO, hydrogen, methane and water. This observation implies that the methanolic C–O bond cleavage is contingent upon a special molecular arrangement of precursors before reaction and that the CH3,ads product is stabilized by ancillary reaction products, such as CO.
We report the photoionization of ion beam desorbed amino acids using femtosecond laser pulses at ... more We report the photoionization of ion beam desorbed amino acids using femtosecond laser pulses at 195 and 260 nm. Ionization of ion-desorbed glycine, alanine, valine, leucine, isoleucine, and phenylalanine using 195 nm laser pulses is found to produce almost exclusively a decarboxylated ion fragment, while tyrosine and tryptophan produce a functional group cation. The adiabatic ionization potentials for the former amino acids correspond to the removal of an electron from the amine nitrogen atom, while for tyrosine and tryptophan it corresponds to the removal of an electron from the aromatic functional group. We find that fragmentation is initiated by the formation of a radical site which leads to an α-cleavage reaction and, depending upon which electron is removed, results in the formation of a decarboxylated ion or a functional group ion. These results indicate that a significant fraction of the amino acids are desorbed intact, but are fragmented when ionized. Except for leucine, isoleucine, and phenylala...
The design and application of a detector is described, which is capable of simultaneously measuri... more The design and application of a detector is described, which is capable of simultaneously measuring energy and angular distributions of neutral particles desorbed from surfaces. Specific applications to ion bombardment studies are presented. The detector utilizes the state selectivity, sensitivity, and pulsed characteristics of multiphoton resonance ionization as a time-of-flight sensitive postionization technique. A microchannel-plate element allows position-sensitive detection of the laser-ionized particles. Sample data are presented for ground-state Rh atoms desorbed from clean, ion-bombarded Rh foil and Rh(111) surfaces.
We report the use of femtosecond laser photoionization of sputtered neutral molecules to enhance ... more We report the use of femtosecond laser photoionization of sputtered neutral molecules to enhance the sensitivity of detection and to improve the prospects for molecule-specific imaging experiments. Results are presented for patterned metal oxides, polycyclic aromatic hydrocarbons and several amino acids. In addition to increased signal levels, we find that is photoionization generally yields simpler mass spectra than the corresponding SIMS spectra, although considerable fragmentation is observed in both cases.
A chemical imaging time-of-flight secondary ion mass spectrometer is described. It consists of a ... more A chemical imaging time-of-flight secondary ion mass spectrometer is described. It consists of a liquid metal ion gun, medium energy resolution reflectron mass analyzer, liquid nitrogen cooled sample stage, preparation chamber and dual stage entry port. Unique features include compatibility with laser postionization experiments, large field of view, cryogenic sample handling capability and high incident ion beam current. Instrument performance is illustrated by the characterization of scanning electron microscopy grids, silver and functionalized polystyrene beads and the postionization of an organic overlayer on a gold substrate.
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 1991
A comparison of a polyethylene additive extract sample, deposited from solution as a submonolayer... more A comparison of a polyethylene additive extract sample, deposited from solution as a submonolayer on Ag, was made to an in situ surface analysis of a bulk polyethylene sample using time-of-flight static secondary ion mass spectrometry (TOF-SIMS). The in situ analysis was able to confirm most of the additives detected in the extract. The additive mass range of 200–1200 Daltons was relatively free of spectral interferences due to the polyethylene matrix. High mass resolution studies were used to assist in the assignment of molecular identities to the additives. Molecular ions for the additives were predominantly Ag cationized adducts for the extract sample, and [M+H]+ or [M+Na]+ species for the bulk polyethylene. Deposition of standard additive solutions on Ag demonstrated the detection sensitivity of TOF-SIMS, illustrating the potential for molecular imaging of polymer domains as small as a few μm2 . The relative extent of oxidation of Naugard 524, an antioxidant additive, also was c...
Journal of Electron Spectroscopy and Related Phenomena, 1972
... of Electron Spectroscopy and Related Phenomena Elsevier Publishing Company, Amsterdam Printed... more ... of Electron Spectroscopy and Related Phenomena Elsevier Publishing Company, Amsterdam Printed in The Netherlands ELECTRON SPECTROSCOPY OF THE NICKELOXYGEN SYSTEM KS KIM and RE DAVIS Department of Chemistry, Purdue University, Lafayette, md. ...
The factors which influence chemical shifts are examined in order to elucidate the cause of the a... more The factors which influence chemical shifts are examined in order to elucidate the cause of the anomalous chemical shifts for Cd and Ag oxides. The effects of extra-atomic relaxation are accounted for using a procedure employing experimental Auger and binding energies. Atomic partial ionic charges for some simple Cd, Ag, and Zn compounds are calculated from experimental binding energies using a model which includes the effects of lattice potentials and extra-atomic relaxation. Inclusion of extra-atomic relaxation effects did not have a drastic effect on the relative ionicities computed for these selected compounds. However, for CdO, a large extra-atomic relaxation energy contribution reduces the binding energy by 0.5 eV more than is predicted from nearest neighbor electronegativity arguments.
Uploads
Papers by Nicholas Winograd