J. J. DeCorpo

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.

ArF excimer laser multiphoton-ionization mass spectrometry of organic molecules

Abstract Mass spectra are obtained for 27 organic molecules following irradiation with focussed 193-nm (6.42-eV) photons from an ArF excimer laser. The molecules chosen represent several classes of organic compound. Comparisons between the multiphoton-ionization mass spectra and low-energy electron-impact mass spectra indicate that the dominant ionization pathway is non-resonant two-photon absorption. Data for benzaldehyde and CS 2 provide clear exceptions to this mechanism. These two molecules exhibit enhanced fragmentation owing to the presence of one-photon resonances.

Ion implantation studies of (SN)x and (CH)x

Abstract We report the results of the initial investigation of the application of ion implantation for the “doping” of the electroactive polymers, (SN) x and (CH) x . Increases in conductivity have been measured for some (CH) x samples after being implanted. Evidence for the formation of a discrete chemical species has been observed in the case of (CH) x implanted with Br + ions. Advantages and drawbacks associated with this technique are discussed.

Characterization of polymeric thin films by low-damage secondary ion mass spectrometry

Abstract Static or low-damage secondary ion mass spectrometry (SIMS) is used to characterize thin films of a series of poly(alkyl)-methacrylates consisting of the methyl, ethyl, isobutyl, n-butyl and lauryl substituents. Relative ion intensities at four m/z values are used to distinguish between the various homologs. Ion intensities at m/z values characteristic of the substituent group appear to be significant relative to the backbone (hydrocarbon type) ion intensities. Low-damage SIMS offers a means of direct and “apparent” nondestructive analysis of polymeric thin films.

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.

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.

Identification of the vapor phase species of (SN)x

Abstract A mass spectrometric study of the vapor phase species obtained by heating (SN) x (polythiazyl), polymeric sulfur nitride, at 140°C utilizing direct (collision free) and indirect (multiple wall collisions) sampling is reported. The experiments show that depolymerization occurs and that the major neutral species in the vapor of (SN) x is (SN) 4 , possibly of bent chain structure. Evidence for a hydride impurity in the (SN) x polymer has been obtained.

Simple method for adiabatically sampling reactive gaseous systems for mass spectrometric analysis

An understanding of the nature of the chemical processes occuring in dynamic, reactive, gaseous systems, such as hydrocarbon flames and chemical lasers, requires knowledge of the chemical species that actually exist in these systems. This paper reports the design and use of a flow‐type reactor tube which is passed through the ion source of a mass spectrometer permitting the components of a reacting gas phase system to be extracted adiabatically through a 10 μ orifice into the ion source for analysis. The procedure for drilling this orifice with a focused CO2 laser is presented, together with data which indicate that the reactive species extracted from a flame zone are representative of those existing within the reactive system.

Field ionization and field desorption mass spectra of polymeric sulfur nitride

Abstract Field ionization and field desorption mass spectra of polymeric sulfur nitride, (SN) x , are reported. The results show that (SN) x vaporizes as a (SN) 4 species isomeric in structure to cyclic S 4 N 4 . Field desorption spectra, obtained by subliming a sample of (SN) x on to the field emitter, contain only the (SN) 4 + ion. In this communication we report the field ionization and field desorption mass spectra obtained for polymeric sulfur nitride, (SN) x . The polymer (SN) x has a number of unusual properties [1–4]. It is highly anisotropic; it is a conductor and becomes a superconductor at 0.3°K; and it may be sublimed to form (SN) x films of structure identical to the crystals from which it is sublimed. This unique set of properties has made (SN) x the subject of intensive study [1–5]. The vapor-phase species are of particular interest because of their role in the production of (SN) x films. While the chemical and physical properties of the (SN) x crystals and films have been documented [1–4], the vapor phase species, which repolymerize as (SN) x films on cool surfaces, have been a subject of speculation. Recently, however, we used phase-angle mass spectrometry [5] to determine that an (SN) 4 species is the major gas-phase component of (SN) x vapors. Analysis of electron-impact mass spectra and appearance potential measurements of (SN) x vapors, cyclic S 4 N 4 , and S 2 N 2 suggested that the (SN) 4 species sublimed from (SN) x is a structural isomer of cyclic S 4 N 4 .

Mass-spectral investigation of AsF5-doped (CH)x

Abstract Polyacetylene, (CH)x, doped with arsenic pentafluoride has been the subject of considerable study since the discovery of its high electrical conductivity, but controversy has surrounded the form of the dopant in the polymer. We report the results of a mass-spectral study aimed at identifying the arsenic fluoride species present after doping. The results demonstrate that AsF6− is present, and models are proposed to explain the possible source of the controversy concerning previous anlytical results. A method of synthesis is suggested for reproducible production of a pure AsF6−-doped material.