The design, construction, and characterization of a miniature array of 16 rods forming nine quadrupole mass analyzers for residual gas analysis are presented. The novel design takes advantage of the reduction of the dimensions and hence the mean free path to broaden the dynamic range by extending the operating pressure range up to 10 mTorr at the high end while maintaining the low-end sensitivity and mass resolution. The small size, low weight, low power consumption, and low cost of this mass analyzer enable many new applications such as in situ process control in high pressure processes. Applications which take advantage of the capability of operating the source pressure two orders of magnitude higher than conventional devices such as high-pressure contaminant monitoring are discussed. Data on high-pressure effects on the ionizer lifetime in various atmospheres and nonlinearities of the signal are presented and correlated with theoretical analysis. Ray tracing simulations and Monte Carlo statistical calculations are used to provide an understanding of the sensitivity reduction at pressures substantially higher than 10 mTorr. These calculations take into account the ion charge density in the source and the dissociation, charge exchange, and energy loss by the ions when colliding with residual molecules along the length of the rods.
First results of a beam-beam, single-collision study of negative-ion mass spectra produced by attachment of zero-energy electrons to the molecules of the explosives RDX, PETN, and TNT are presented. The technique used is reversal electron attachment detection (READ) wherein the zero-energy electrons are produced by focusing an intense electron beam into a shaped electrostatic field which reverses the trajectory of electrons. The target beam is introduced at the reversal point, and attachment occurs because the electrons have essentially zero longitudinal and radial velocity. The READ technique is used to obtain the "signature" of molecular ion formation and/or fragmentation for each explosive. Present data are compared with results from atmospheric-pressure ionization and negative-ion chemical ionization methods.
Pressing needs for miniature mass spectrometers became apparent during the last decade in process monitoring and control, space exploration, and environmental screening. Besides the small footprint, common requirements include low cost, low power consumption, field portability, reliability, autonomy, and ease-of-use. Design concepts and construction technologies of miniaturized quadrupole sensors were guided by cost reduction requirements without sacrifice of performance. The first miniature and complete quadrupole mass spectrometer system was introduced as the Micropole sensor. The concept featured a novel technique to assemble and operate multiple miniature quadrupoles in parallel. The short analyzer length offers a significant advantage by enabling direct mass filtering at pressures up in the 10(-2) torr range. High voltages at higher frequencies (10-20 MHz) are required for acceptable mass resolving powers. Additional trade-offs were uncovered in miniature sensors leading to designs optimized for each class of applications. Real time ray tracing of ions injected and filtered in the quadrupole field is used early in the design stage to predict the performance and reliability of the device.
Articles you may be interested inCusp type electrostatic analyzer for measurements of medium energy charged particles Rev. Sci. Instrum. 77, 123303 (2006); 10.1063/1.2405358New type of compact electrostatic energy analyzer adequate to measurement of charge exchange neutral particles with a low counting yield Rev.The design, fabrication techniques, and first test results of a new type of micromachined energy analyzer for charged particles are presented. The novel design is based on a Bessel Box straight-line geometry with focusing in one dimension. The problem of small acceptance area due to the (kastically reduced overall dimensions is accounted for by the use of a parallel array of small analyzers simultaneously. We describe the fabrication of a proof-of-concept micromachined Bessel Box array by means of anisotropic wet etching of (110) silicon, and we present ray-tracing simulations for a simple geometry. Finally, we show some test results of Auger electrons and discuss possible applications of generic small charged particle analyzers.
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