Beam profile analysis for a 252Cf plasma-desorption time-of-flight mass spectrometer

Secondary ions sputtered in individual MeV ion impacts are analyzed in a high resolution time-of-flight mass spectrometer. The initial radial velocity distributions of low mass ͑up to m/zϷ300 u͒ positive and negative secondary ions, sputtered from carbon-containing molecular solids ͑polymers, bioorganic molecules, and fullerene targets͒ are investigated. The first (͗v͒͘ and second ͑͗v 2 ͒͘ moments of the velocity distributions vary systematically with the atomic composition of secondary ions of the typePositive ions formed from extensive fragmentation-rearrangement of the original molecular structure ͑e.g., C n ϩ ͒ tend to be ejected towards the MeV ion trajectory ͑positive mean radial velocity͒ and to have the largest ͗v 2 ͘. Saturated species ͑e.g., C n X 2n , XϭF, H͒ tend to have smaller ͗v 2 ͘ and negative ͗v͘. These effects are weaker as the stopping power of the primary ions is decreased and are not observed for negative ions. The observed effects demonstrate a correlation between chemical composition of an ion and its formation and ejection processes. The chemical transformations and the processes leading to ion formation and ejection are functions of both the density and the gradient of the deposited energy at a particular position from the track center. This interconnection results in a regular dependence of the properties of ejected ions ͑e.g., momentum received͒ on their chemical composition. The correlation of the momentum imparted to the fragment ions with the geometry of impact indicates that such species are predominantly ejected in a nonevaporative process.

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“…Other instrumental effects such as divergency due to the acceleration grids 22 and finite size of the irradiated spot on FIG. 1.…”

Section: Effect Of the Stop Detector Collimatormentioning

confidence: 99%

Low-mass secondary-ion ejection from molecular solids by MeV heavy ions: Radial velocity distributions

et al. 1996

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“…It also results in a divergence of the secondary ion away from the expected path. The divergence of a secondary ion depends on the grid size and the wire diameter of the grid 4 . Furthermore, it has been shown that a smaller grid size and a smaller wire diameter reduce the beam divergence.…”

Section: Introductionmentioning

confidence: 99%

Electric field penetration effects in time-of-flight measurements

Abeywarna

Ariyaratne

2003

Sri Lankan J Phys

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The field imperfections in the mass spectrometers were studied by means of two Plasma desorption time-of-flight mass spectrometers. The experiment was performed by investigating the influence of the field leakage due to the post acceleration on the measured values of the initial axial energy of secondary ions, in the presence of the grounded grids, which are usually employed to separate the fields inside the mass spectrometers. It has been found that the changes of 0.4% in the effective lengths of the acceleration gap and the field free region respectively are possible due to the field penetration into those regions from the post acceleration gap of the mass spectrometer. The analyses also show clearly the significance of the influence of the field penetration of the post acceleration on the measured values of the initial axial energy. The initial axial energies of H + , H 2 + , 6 Li + , 7 Li + , Na + and Cs + measured under the minimum field penetration condition were found to be 4.7 eV, 4.7 eV, 0.6 eV, 0.7 eV, 0.7 eV and 1.3 eV respectively, and they had been reduced to 4.4 eV, 4.4 eV, 0.3 eV, 0.4 eV, 0.4 eV and 1.0 eV once the values were corrected separately for field penetration. These results indicate that the field penetration through a grid is a secondary effect and it is hardly unavoidable in the mass spectrometers.

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Applications of high‐performance mass spectrometry to the surface analysis of materials

Schuetzle¹,

Riley²,

Vries³

et al. 1984

Mass Spectrometry Reviews

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Beam profile analysis for a 252Cf plasma-desorption time-of-flight mass spectrometer

Cited by 12 publications

References 4 publications

Low-mass secondary-ion ejection from molecular solids by MeV heavy ions: Radial velocity distributions

Low-mass secondary-ion ejection from molecular solids by MeV heavy ions: Radial velocity distributions

Electric field penetration effects in time-of-flight measurements

Applications of high‐performance mass spectrometry to the surface analysis of materials

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