A deceleration lens system for hybrid mass spectrometers

Abstract

A simple and efficient deceleration system for the coupling of magnetic and electric sector instruments to quadrupole analyzers is described. The transmission efficiency of the system appears to be at least 80% or better as the ions are decelerated from 3 keV to 30 eV (a deceleration factor of 1 : 100). No mass discrimination was observed in the range up to mass 1OOO.The technique of mass spectrometry has, in tQe last few years, grown enormously. Much of this new growth has been in the development of multisector and hybrid instruments, and in the techniques made possible by these new instruments. Combination of a quadrupole mass analyzer with electric and magnetic sectors produces several advantages. For example, artifact peaks can be eliminated and resolution can be improved.' Hybrid instruments, with various combinations of magnetic and electric sectors linked to quadrupole analyzers have been described and advantages have been However, quadrupolar analyzers work best with low energy (10-15 eV) ions, while electric and magnetic sectors are usually used with high energy ions, typically with energies of several keV. Thus, in order to mass-analyze ions with a quadrupole after magnetic-or electric-sector analysis, the ions must first be decelerated.A simple deceleration system which has been used to slow ions from 3 keV to 5 eV energy while maintaining, high transmission of ions through the system is described in this paper. This deceleration system has been used with a type CH5 double-focusing mass spectrometer (Varian MAT, Bremen, FRG). This instrument is of reversed geometry and uses an acceleration voltage of 3 kV. Following deceleration, ions can either be analyzed with a quadrupole mass analyzer, or injected into a quadrupole ion trap (Quistor), as recently described. DESCRIPTIONThe deceleration system is located after the electrostatic analyzer (ESA) of our hybrid instrument A schematic diagram of the instrument is given in Fig, 1, showing the location of the deceleration system. A collision cell is located in the second field-free region, between the magnet and the electric sector. As with most hybrid machines, the quadrupole is operated at a floating ground potential slightly below (10-15 V) the acceleration potential, depending on the desired final ion kinetic energy. A schematic representation of the lens system is shown in Fig. 2. The first element of the deceleration system consists of four steering electrodes that allow beam shaping and focusing, shown as lens A in Fig. 2 (y electrodes not shown). The focusing electrodes are 30 mm long, and a potential of 0-30 V can be applied independently to each of the four electrodes.Author to whom correspondence should be addressed. The deceleration system is constructed of stainless steel. The electrodes are of two sizes. The shorter electrodes are 6.3mm long, with a 6.3mm diameter centre hole. The long electrodes are 25.4 mm long with a 11 mm diameter centre hole. The electrodes are spaced 3.2 mm apart by ceramic insulators. The entire deceleration system is 10...

Interface for a four-sector mass spectrometer with a dual-purpose collision cell: High transmission at low to intermediate energies

“…Deceleration of ions that move with kilovolt energies is not trivial and has been a goal of instrumentalists for many years [8][9][10][11][12][13][14][15][16][17][18][19]. Many studies have been carried out in hybrid configuration instruments (typically BEqQ), where the high energy ions generated from a sector mass spectrometer are decelerated, refocused, and injected into devices like a quadrupole [9,12,13,16], hexapole [11], octapole [15], or drift cell [14]. A few groups have addressed the problem of deceleration for collisions in four-sector instruments, experimentally [10,17,19] or theoretically [18].…”

A low‐pressure penning ion source for volatile organic compounds

“…Ions leaving the Penning ion source are decelerated and focused by a modified deceleration lens system, according to Ref. 6. Mass analysis is done by a quadrupole mass analyzer (QMA 150, ro= 3.45 mm, d = 8 mm, 1 = 200 mm, Balzers) which is floated relative to the formation potential of the ions.…”

Mass and energy selected ion beam for deposition and ion induced surface modifications

“…Different methods to decelerate ions down to 10 eV and even lower energies were reported in the literature. [15][16][17] This article describes the construction of a low energy ͑5-500 eV͒, mass selected ͑1-2048 amu͒ ion beam source for the investigation of ion induced surface modifications and for the deposition of very thin films. As this instrument will be operated in an ultrahigh vacuum ͑UHV͒ chamber equipped with low-energy electron diffraction ͑LEED͒, XPS, and XPD to study substrate-film interactions and film growth mechanisms, no attempt was made to reach high ion currents.…”