Radiant energy – Ionic separation or analysis – Ion beam pulsing means with detector synchronizing means
Patent
1999-03-08
2000-06-20
Anderson, Bruce C.
Radiant energy
Ionic separation or analysis
Ion beam pulsing means with detector synchronizing means
250282, 250288, B01D 5944, H01J 4900
Patent
active
060780436
DESCRIPTION:
BRIEF SUMMARY
This invention relates to mass selectors for separating particles according to their mass. The term "mass selector" as used herein is intended to include not only apparatus in which separation (or filtration) of particles having a particular mass or range of masses is effected for the purpose of studying and/or using such particles, but also separation of particles according to their mass for determining the chemical composition of a sample by mass spectrometry. However, the present invention is mainly concerned with a mass selector operated as a filter to enable particles of a selected mass or range of masses to be separated for further study and/or use.
The present invention is particularly suitable in the growing field of cluster physics which involves studying particles of nanometre dimensions. Improvement of existing mass selection techniques in this field is urgently needed.
In existing time-of-flight mass spectrometers currently used for the investigation of free clusters, a beam of ionized particles to be studied is accelerated by a high voltage pulse across a pulse region and subsequent static acceleration fields and, in most cases, is detected at the end of a field-free region. Sometimes, an exit gate is used instead of the detector to filter out one particle size. In such cases, the acceleration of the particles is such that particles of the same mass reach the exit gate at the same time. By opening the exit gate momentarily, particles of the same size can pass through the gate whilst particles of other sizes reach the gate when closed and so do not pass through. The mass of the particles selected for passage through the gate is chosen by opening the gate an appropriate time after the voltage pulse has been applied across the plates.
However, a disadvantage of this standard type of mass selector is that it has a very low total transmission (<10.sup.-1). Thus, it is not suitable for use if a large number of mass-selected particles are required (eg for surface or matrix deposition of mass-selected clusters). The standard techniques for the production of continuous mass-selected ion beams involving magnetic sector field or quadrupole mass selectors, which combine higher resolution with a high transmission, only have limited mass ranges and can typically only be used for particles with masses less than about 5000 amu (atomic mass units).
It is an object of the present invention to provide an improved mass selector which can enable the problem of low total transmission to be obviated or mitigated whilst at the same time being suitable for use with particles having a wider range of masses than has been possible with conventional magnetic sector field or quadrupole mass selectors.
According to one aspect of the present invention, there is provided a mass selector for separating particles in a particle beam according to mass, said selector including a pair of first electrodes between which is defined an elongate first path for the passage of the particle beam, means for focusing the particle beam so that, in use, a focused particle beam passes along the elongate first path, a pair of second electrodes spaced from the pair of first electrodes in a direction transversely of the direction of extent of the first path, said pair of second electrodes defining therebetween an elongate second path for separated particles, said second path being parallel to said first path, first voltage-applying means for applying a first voltage pulse across said first electrodes so that, in use, the particles in a portion of the beam which is in said elongate first path are accelerated transversely of their direction of movement along said first path towards said second path, second voltage-applying means for applying a second voltage pulse across said second electrodes so that, in use, particles which have been accelerated by said first voltage pulse and which have entered said second path are decelerated transversely of their direction of movement along said second path, and means for controlling the first and second vol
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Palmer Richard E
Von Issendorff Bernd
Anderson Bruce C.
University of Birmingham
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