Radiant energy – With charged particle beam deflection or focussing – With detector
Patent
1998-02-11
1999-10-19
Westin, Edward P.
Radiant energy
With charged particle beam deflection or focussing
With detector
313103R, 313532, H01J 4300, H01J 4304
Patent
active
059693614
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
This invention relates to a particle detector sensitive to the position.
"Particles" refers particularly to charged particles such as ions and electrons, and photons.
The invention is applicable particularly to atom probes and more particularly to any domain in which a correlation between space and time is to be found.
For example, the invention is thus applicable in particle Physics to Time of Flight Secondary Ion Microscopy, mass spectrometry and Time of Flight Charge Coupled Devices.
The invention can precisely identify particle impacts on a detector fitted with electron multiplication means (usually microchannel plates), in space and time.
These particles may reach the detector at very close instants, or simultaneously.
Therefore, the invention relates to a two-dimensional spatial detector with high spatial resolution and high time resolution.
2. State of Prior Art
Several spatial particle detectors that use Microchannel Plates are already known.
During the last twenty years, it has been necessary to develop this type of detector in a wide variety of domains, such as spatial imagery or elementary particle physics.
However, very few detectors are capable of localizing multiple impacts in both space and time.
The fields of application for which these detectors have been developed explain the limitations of typical spatial detectors to a large extent.
Thus, detectors developed for imagery give a very good spatial resolution but are incapable of precisely measuring impact instants.
In the elementary particles domain, a large number of systems have been developed capable of precisely measuring the instant of impact and the position of particles.
These systems, which have been developed for detection of rare events, are frequently incapable of resolving simultaneous events, or events very close in time.
Thus a distinction is made between two major families of spatial detectors.
The first family includes detectors sensitive to simultaneous events but with a mediocre time resolution.
For example, this is the case of CCD camera detectors.
These detectors have a good spatial resolution and are sensitive to multiple events.
However, the information "read" time for a CCD camera is long (several milliseconds) and thus determines the "dead time" in the time of flight measurement system associated with the camera.
When events are separated by a time less than his dead time (which is always the case in an atom robe), it is impossible to unambiguously assign a time of flight to a displayed impact.
In this respect, refer to document (1) which, like the other documents mentioned below, is mentioned at the end of this description.
Therefore, this limitation prevents its use for this application.
The second family includes "fast" detectors.
These detectors are capable of discriminating impacts very close together in time, separated only by a few tens to a few hundreds of nanoseconds.
The best known among them are the Resistive Anode Encoder and the Wedge And Strip Anode.
Refer to document (2) for further information about this subject.
The principle of these detectors is based on a spatial or time division of the charge generated by the impact at the exit from the microchannel plates.
These detectors all have the same disadvantage: when more than two events strike this type of detector simultaneously, the calculated position is the center of gravity of the positions of each impact.
Therefore, these detectors are sensitive to only one event at a time.
In fact, there are only two known detectors capable of precisely identifying multiple impacts in time and in space.
These two detectors have been developed for time of flight mass spectrometry systems, for example such as three-dimensional atom probes.
The first of these two detectors is described in documents (3) to (7).
The principle of this first detector is as follows.
An assembly of microchannel plates is placed in front of a square grid of 10.times.10 anodes which is laid out in a plane.
Therefore, it may be said that it is a checker board
REFERENCES:
M.K. Miller, "Implementation of the optical atom probe", pp. 494-500, Surface Science 266 (1992).
A. Cerezo, T.J. Godfrey, and G.D.W. Smith, "Application of a position-sensitive detector to atom probe microanalysis", pp. 862-866, Rev. Sci. Instrum. 59(6), Jun. 1988.
D. Blavette, A. Bostel, J.M. Sarrau, B. Deconihout, A. Menand, "An atom probe for three-dimensional tomography", pp. 432-434, Nature vol. 363, Jun. 3, 1993.
D. Blavette, B. Deconihout, A. Bostel, J.M. Sarray, M. Bouet, A. Menand, "Review of Scientific Instruments", pp. 2911-2919, vol. 64, No. 10, Oct. 1993, American Institute of Physicis.
B. Deconihout, A. Bostel, P. Bas, S. Chambreland, L. Letellier, F. Danoix D. Blavette, "Investigation of some selected metallurgical probelms with the tomographic atom probe", pp. 145-154, Applied Surface Science 76/77 (1994).
B. Blavette and A. Menand, "New Developments in Atom Probe Techniques and Potential Applications to Materials Science", pp. 21-26, Materials Research Society, vol. XIX, No. 7, Jul. 1994.
B. Deconihout, A. Bostel, M. Bouet, J.M. Sarrau, P. Bas, D. Blavette, "Performance of the multiple events position sensitive detector used in the tomographic atom probe", pp. 428-437, Applied Surface Science 87/88 (1995).
A. Cerezo, T.J. Godfrey, J.M. Hyde, S.J. Sijbrandij, G.D.W. Smith, "Improvements in three-dimensional atom probe design", pp. 374-381, Applied Surface Science 76/77 (1994).
Tohru Kinugawa and Tatsuo Arikawa, "Position-sensitive time-of-flight mass spectrometer using a fast optical imaging technique", pp. 3599-3607, Rev. Sci. Instrum. 63 (7), Jul. 1992.
Blavette Didier
Bostel Alain
Deconihout Bernard
Centre National de la Recherche Scientifique
Wells Nikita
Westin Edward P.
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