Electric lamp and discharge devices – Photosensitive – Secondary emitter type
Reexamination Certificate
1998-11-13
2001-07-17
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
Photosensitive
Secondary emitter type
C313S1030CM, C313S1050CM, C313S104000
Reexamination Certificate
active
06262521
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a particle detector for the direct or indirect detection of beam-carried particles, such as ions, electrons, energetically neutral particles and photons. The detector is of the kind that includes a body that has a beam-incident surface which is able to release secondary electrons in numbers proportional to the number of particles incident on said surface, and a secondary electron multiplier channel whose inlet opening is located adjacent the beam-incident surface and functions to amplify the number of secondary electrons. The invention also relates to a method of detecting charged particles, such as ions and electrons, in a beam that contains charged and charge-free particles.
2. Description of the Related Art
Secondary electron multipliers are well-known detectors to those skilled in the art, and are used, for instance, in the detection of ions and other particles, such as electrons and energetically neutral particles. In one application, in addition to containing sought-after ions, a gas beam also includes neutral, charge-free particles that are able to interfere with the detection of ions. It is therefore desirable that solely ions strike the detector.
One known method involves generating an electromagnetic field that causes the charged ion-particles to deviate in a direction that differs from the direction of the original gas beam, therewith forming a separate ion beam. This ion beam is then caused to impinge on a detector. Although some ion losses occur when breaking-up the gas beam, the accuracy of the detection process is markedly improved in relation to a measuring or analyzing process that is carried out directly on the original gas beam.
Channel-type secondary electron multipliers are commercially available. These multipliers include a typical flared or funnel-like inlet opening which is intended to receive a particle-carrying beam for detection, wherewith the particles carried by the beam release secondary electrons in numbers proportional to the number of particles present. Released secondary electrons are attracted into an electron multiplier channel and there trigger an electron avalanche which falls onto an anode or collector at the end of the channel, in which the electron charge that has been torn down is measured. The principles of this type of detection are well known to the person skilled in this art and will not therefore be described in more detail in this document.
EP 0 401 879 A2 teaches a secondary electron multiplier in the form of a monolithic, ceramic body that includes a funnel shaped entry port to an electron multiplier channel. The body is provided internally with a semiconductive secondary electron emitting layer along the channel walls. The channel preferably extends three-dimensionally in a spiral path through the body and exits contiguous to an anode. This device is intended to be used for measuring or analyzing a purely ion beam that contains no disturbing or interfering particles.
Important criteria that separate different types of detectors are sensitivity, accuracy, efficiency and response time.
The response time, i.e. the time between two measuring processes, is dependent on the time taken to recharge the channel layer with electrons subsequent to triggering an electron avalanche.
Sensitivity and accuracy are contingent on detector temperature and the electrical conductivity of the detector, among other things. It is essential to cool the detector effectively, which also lengthens the useful life span of the detector.
Efficiency relates to the relative proportion of incident particles that are detected. The object of the present invention is to provide a detector and a method that are more efficient than present-day detectors and methods.
SUMMARY OF THE INVENTION
The detector of the present invention includes a body having a beam-incident surface which is able to release secondary electrons in numbers proportional to the number of particles incident on said surface, and a secondary electron multiplier channel having an inlet opening located in the beam-incident surface and functioning to amplify the number of secondary electrons, wherein the detector is characterized in that the detector includes a plurality of secondary electron multiplier channels whose respective inlet openings are disposed in one and the same beam-incident surface and take-up secondary electrons emitted therefrom.
The present invention also relates to a method of detecting particles in a beam that includes charged and non-charged particles in gas phase, e.g. downstream of a mass filter, said method comprising the steps of applying an electric field such as to cause the charged particles to collect and form a tubular surface layer around the remaining beam of charge-free particles therewith generating two coaxially layered beams, wherein the tubular outer layer of charged particles can be captured by at least one secondary electron multiplier and/or the charge-free particles in the residual beam can be captured by another secondary electron multiplier, and wherein signals can be read from the electron multipliers. The tubular outer layer of charged particles may conveniently be spaced from the residual, center beam of neutral particles. This enables the inlet openings of a plurality of electron multipliers to be disposed in a ring around the center beam, or core beam, therewith providing a detector of greatly improved efficiency with respect to known detectors. These electron multiplier channels may have a common, first beam-incident surface from which the first array of secondary electrons are released.
The signal from each individual electron multiplier can be read separately, thereby providing a multi-channel analysis facility.
According to the invention, the detector, e.g. for detecting a beam of charged particles and neutral particles in gas phase, may include a) means for generating an electric field which acts on the charged particles and changes their direction of movement in relation to the direction of movement of the neutral or charge-free particles, b) a secondary electron multiplier that includes a particle-incident means that functions to release secondary electrons in numbers proportional to the number of incident particles, and means for amplifying the number of secondary electrons. The detector is characterized in that the means for generating the electric field acting on the charged particles includes a charge which is opposite to the charge of the charged particles and is disposed in a ring, e.g. around the gas beam, such as to attract the charged particles and therewith form a particle beam of hollow cross-section, e.g. externally of a central core beam of charge-free particles, and in that a plurality of secondary electron multipliers are provided for receiving the hollow beam.
The detector may also include a beam-incident surface that is comprised solely of a ring segment or a linear surface having a plurality of inputs to secondary electron multiplier channels extending through the body.
For the sake of simplicity, and by way of example only, the following description will be made solely with reference to charged particles in the form of ions, although it will be understood that the invention is not restricted to ion detection.
The respective input openings of the secondary electron multipliers may be disposed in a ring, for instance around the central core of charge-free particles, for receiving the hollow ion beam. The input openings may be disposed in one plane or mutually displaced in different planes along the beam. They may also be disposed in some other way, for instance with incident planes or dynodes extending into the tubular beam, said ions impinging on the incident planes and releasing the secondary electrons which are then guided into electron multipliers.
The detector may have a generally basin-shaped or funnel-shaped surface, and an opening may be provided in the bottom of the basin shape. The funnel-shaped or basin-shaped surface may be coated with a
Lauche Hans
Lundin Richard
Guharay Karabi
Patel Ashok
Ware Fressola Van der Sluys & Adolphson LLP
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