IonCCD Detector for Miniature Sector-Field Mass Spectrometer: Investigation of Peak Shape and Detector Surface Artifacts Induced by keV Ion Detection

Abstract

A recently described ion charge coupled device detector IonCCD (Sinha and Wadsworth, Rev. Sci. Instrum. 76(2), 2005; Hadjar, J. Am. Soc. Mass Spectrom. 22(4), [612][613][614][615][616][617][618][619][620][621][622][623][624] 2011) is implemented in a miniature mass spectrometer of sector-field instrument type and MattauchHerzog (MH)-geometry (Rev. Sci. Instrum. 62(11), 2618-2620, 1991; Burgoyne, Hieftje and Hites J. Am. Soc. Mass Spectrom. 8(4), 307-318, 1997; Nishiguchi, Eur. J. Mass Spectrom. 14 (1), 7-15, 2008) for simultaneous ion detection. In this article, we present first experimental evidence for the signature of energy loss the detected ion experiences in the detector material. The two energy loss processes involved at keV ion kinetic energies are electronic and nuclear stopping. Nuclear stopping is related to surface modification and thus damage of the IonCCD detector material. By application of the surface characterization techniques atomic force microscopy (AFM) and X-ray photoelectrons spectroscopy (XPS), we could show that the detector performance remains unaffected by ion impact for the parameter range observed in this study. Secondary electron emission from the (detector) surface is a feature typically related to electronic stopping. We show experimentally that the properties of the MH-mass spectrometer used in the experiments, in combination with the IonCCD, are ideally suited for observation of these stopping related secondary electrons, which manifest in reproducible artifacts in the mass spectra. The magnitude of the artifacts is found to increase linearly as a function of detected ion velocity. The experimental findings are in agreement with detailed modeling of the ion trajectories in the mass spectrometer. By comparison of experiment and simulation, we show that a detector bias retarding the ions or an increase of the B-field of the IonCCD can efficiently suppress the artifact, which is necessary for quantitative mass spectrometry.

Preliminary Demonstration of an IonCCD as an Alternative Pixelated Anode for Direct MCP Readout in a Compact MS-Based Detector

“…The short MCPIonCCD spacing allowed us to use a relatively low voltage gradient while ensuring high electric fields for the outgoing electrons. In early work [3], we demonstrated that the IonCCD can be floated at high voltages (±3 kV) which would facilitate its use as an MCP anode in different configurations, especially when ion sources and/or analyzers cannot be biased at high voltage. Thus, the floating capability of the IonCCD provides an extra degree of freedom for instrument design.…”

“…The PEEK holder ensured an MCP-IonCCD air gap of about 250 μm, assuming the IonCCD chip was flush with the printed circuit board surface (i.e., the CCD board). The assembly was mounted on the focal plane of the MH-MS, which was described in detail in an earlier work [3].…”

“…Although instrument resolution was less than expected, improvements in resolution will be pursued in future work. The detector described in this paper is mounted in the focal plane of a miniature sector-field Mattauch-Herzog geometry mass spectrometer (MH-MS), described elsewhere [3]. The signal used in this work is that from the challenging Xe 2+ ion with an effective one-half mass unit separation between the isotope peaks.…”

High-efficiency cross-beam magnetic electron-impact source for improved miniature Mattauch-Herzog mass spectrometer performance

“…In earlier work, 18 we showed how a new sectorfield magnet, referred to as a high dynamic mass range magnet, increased the instrument's mass range while retaining the ability to detect all masses from the maximum designed value down to unit mass (i.e., the proton). The new magnet design was later implemented in the commercial IonCam TM system 11 for evaluation by Kennedy Space Center -National Aeronautics and Space Administration for possible use in their Regolith and Environmental Science and Oxygen and Lunar Volatile Extraction project.…”

Distance-of-Flight Mass Spectrometry with IonCCD Detection and an Inductively Coupled Plasma Source

“…The IonCCD camera technology is based on that of lightsensitive charge-coupled devices, but the photo-sensitive semiconductive layer has been replaced by a metal-oxide semiconductor layer for direct charge detection [18]. Previous work with the IonCCD camera has focused on its applicability to Mattauch-Herzog mass spectrograph instruments [17,[19][20][21], ion mobility mass spectrometry [22,23], and the measurement of ion-beam spatial distributions [24]-all of which necessitate the detection of a spatially disperse ion cloud. The IonCCD detector array is nominally 27.5% longer than the previously employed MCP/phosphor screen detector, with a total length of 5.1 cm, but the reduced active area around the edges of the MCP/phosphor detector makes the IonCCD effectively > 27.5% longer.…”