Jeffrey R. Wyatt

Combined XPS and SIMS study of amino acid overlayers

Abstract Factors influencing the SIMS fragmentation patterns are studied for three simple amino acids-glycine, α-alanine, and serine-deposited onto Ag substrates from aqueous solution. Secondary ion emissions are measured for 1 keV Ar + ions incident at 70° from sample normal as a function of substrate preparation and solution concentration. Studies by XPS and X-ray induced AES prior to SIMS analysis show that the amino acids adsorb in a film on the Ag surface and that the film thickness increases with solution concentration. In addition, considerable amounts of amino acid can be deposited on the surface from a water film retained during extraction from a concentrated solution. On acid etched samples, positive ion fragments of mass AgM, Ag(M − 45), Ag, M + 1, and M − 45 are observed, where M is the molecular, weight of the parent amino acid. With the exception of the (M + 1) + fragment, these peak intensities behaved similarly for the different surface concentrations. When the adsorbed film grows too thick, the positive molecular ion emissions drop considerably; this substantiates the need for proximity between the Ag substrate and the amino acid molecule.

High-performance secondary ion mass spectrometer

A high‐performance research‐oriented secondary ion mass spectrometer (SIMS), based on a double‐focusing mass spectrometer, has been designed, constructed, and evaluated. This instrument is relatively free of some of the instrumental limitations associated with conventional molecular SIMS instrumentation such as energy and mass discrimination. Theoretical design considerations and its construction are discussed. Its performance has been evaluated in various operational modes using a variety of samples and some important instrumental parameters are reported. Finally, the novel and outstanding high‐mass capability of this SIMS instrument is demonstrated.

Secondary ion mass spectrometry of metal salts: Polyatomic ion emission

The mass and intensity distribution of cluster ions emitted from several alkali halide (MX) salts bombarded with Ar+ and Xe+ ions are reported. Cluster ions of the type [M(MX)n]+ and [X(MX)n]− are seen where 1≤ n < 100. We present evidence supporting the formation of cluster ions with specific geometric structures. In addition, we find that the stability of the cluster ions is dependent on the surface energy of the cluster, on the size of the constituent atoms, and on the effective lifetimes of the ions.

Ultra-High Mass Spectrometry

Massive cluster ions of CsI (mass-to-charge ratio > 25,000) have been produced, mass analyzed, and detected with a conventional double-focusing mass spectrometer. Variations in the ion intensity distributions depend on the relative lifetime of the ions. These results are of fundamental interest, but they also impact the practical limits of mass spectrometry.

Separation and indirect detection by capillary zone electrophoresis of ppb (w/w) levels of aluminum ions in solutions of multiple cations

Abstract Solutions of multiple cations in aqueous solutions at concentrations as low as 200 ppb were analyzed by capillary zone electrophoresis. Aluminum ions were cleanly separated from Li + , K + , Ca 2+ , Cr 3+ , Zn 2+ , CU 2+ , and other ions less than 6 min after injection of the solution on a 50 cm × 50 μm I.D. uncoated fused-silica capillary column at 15 kV. Indirect detection at 204 nm was carried out using a pH 2.8 background electrolyte containing 5.2 m M ephedrine as a UV-absorbing co-ion and 4.7 m M α-hydroxyisobutyric acid as a completing counter ion. Mobilities for Al 3+ and 14 other complexed cations were determined for this electrolyte.

Fast-atom molecular secondary-ion mass spectrometry

Abstract A commercial ion gun has been modified to generate a diffuse fast-atom beam for molecular secondary-ion mass spectrometry (SIMS). Ion-to-neutral conversion mechanisms have been investigated to determine the nature of the ion neutralization process. When the ion beam passes through a narrow selected-metal aperture, so that ion/surface interactions are increased, the fast-atom component of the beam is enhanced. The potential and kinetic emission of electrons from the metal surface can account for an ion and electron recombination mechanism. Residual charge-exchange reactions between the primary ions and neutral species in the ion gun assembly are a contributing ion neutralization process. The diffuse fast-atom component of the ion/atom beam is obtained by electrostatic deflection of the ions out of the beam following ion neutralization. The fast-atom beam provides several analytical advantages over an ion beam. These advantages and applications of the fast-atom molecular SIMS approach to the analysis of polymers and insulators are discussed.

COULOMETRIC METHOD FOR THE QUANTIFICATION OF LOW-LEVEL CONCENTRATIONS OF HYDRAZINE AND MONOMETHYLHYDRAZINE

A sensitive and simple coulometric method has been developed for the determination of hydrazine and monomethylhydrazine (MMH) in solution. This coulometric method can readily be used in conjunction with impingers to measure the amount of hydrazine and MMH in air. The method has a limit of detection of less than 25 ng of hydrazine or MMH in 40 mL of solution, which corresponds to less than 2 ppb in 10 L of air. External standards are not necessary as calibration can be performed electronically. The dynamic range of the coulometric method extends from 25 ng to greater than 2500 ng in 40 mL of solution. At the higher concentrations the relative standard deviation was about 2%. The method gave excellent agreement with the two current National Institute for Occupational Safety and Health approved methods at the higher end of this concentration range.

Application of dynamic emittance matching to secondary ion mass spectrometry

The implementation of the dynamic emittance matching (DEM) concept into our secondary ion mass spectrometer is described. The importance of this feature is presented in terms of increased ion transmission when operating at low primary ion beam fluxes, that is, the static secondary ion mass spectrometry (SIMS) or molecular SIMS mode. A discussion of the principle and the design of the DEM electronics in the system is given. Experimental comparisons are presented and discussed which contrast DEM and conventional results with respect to viewing area, ion transmission, and imaging capability.

Determination of hydrogen in perfluorinated polyalkylethers using time-of-flight secondary ion mass spectrometry, infrared spectroscopy, and nuclear magnetic resonance spectrometry

Abstract A series of perfluorinated polyalkylethers were analyzed for hydrogen using time-of-flight secondary ion mass spectrometry (TOF-SIMS), Fourier transform infrared spectroscopy (FTIR), and nuclear magnetic resonance spectrometry (NMR). A high degree of correlation between the integrated TOF-SIMS signal for H - secondary ions and the FTIR and NMR results was found. From FTIR and NMR analysis of standard samples a calibration plot of H - secondary ion abundance versus hydrogen content was prepared.

Mass spectrometric characterization of halogen doped polyacetylene

Abstract Mass spectrometry was used to investigate the volatile species given off when polyacetylene, which had been exposed to I 2 , Br 2 , Cl 2 , or F 2 , was heated in vacuo . A correlation of the conductivity of the samples with the amount of molecular halogen ions (X 2 + ) evolved was observed. These results are consistent with the present concept for the form of the dopant in the polymer. In the I 2 case, two sources of iodine in the (CH) x were found and these were related to the presence of I 3 − and I 5 − in the polymer films.