Position-sensitive detector of electrons
Spectrometric Position-Sensitive Detector of Electrons with Base Energy Shift
Tech Area / Field
- INS-DET/Detection Devices/Instrumentation
8 Project completed
Senior Project Manager
Tyurin I A
Russian Academy of Sciences / Physical Technical Institute, Russia, St Petersburg
- VNIIEF, Russia, N. Novgorod reg., Sarov
- University of Saskatchewan / Department of Electrical and Computer Engineering, Canada, SK, Saskatoon
Development of micro- and nanoelectronics, new material fabrication technologies, research in the fields of biology and biotechnology, medicine, criminology etc. is considerably based on the development of analytical molecular and atomic level characterization methods. These methods provide an information on crystalline structure of solids, molecular structure, crystal growth conformities and on the properties of surfaces. At some modern brunches of technology the analytical nondestructive characterization techniques are the parts of technological equipment and support the process control in the on-line regime. One of set of the most widely spread methods, that follows the basic demands of modern technology of solids is the one based on the detection of so-called secondary electron emission from a sample induced by a different primary radiation (x-rays, ion and electron beams, laser etc.). Spectrum of emitted electrons and its angular distribution allows to define composition, molecular and atomic structure, defects and other important parameters.
Conventional energy dispersive electron detectors are based on electrostatic and magnet analyzers, channeltrons (or microchannel plates) and in the case of fine spatial distribution registration the precise mechanical goniometers are mostly used. Electrostatic and magnet analyzers have the largest possible resolution but they have small relative aperture and large overall dimensions that in some cases makes their application problematic or even impossible. Channeltrons and microchannel plates are very compact but they are not sensitive to electron energy.
Another opportunity is the use of the semiconductor detectors mostly Si based, but their direct application does not solve the task completely: together with the possibility of the spatial resolution by the use of matrix that consists from such small detection elements one meets the problem of sensitivity to the small energy electrons due to their lower detection limit. The nature of this limit is the fact that small energy electrons are not able to reach the active zone of a detector because they have not enough energy to penetrate through near surface cap layer of detector (entrance window). Also the noise spectrum dominates in the small signal region and suppresses the signal from electrons. As the result the total lower-limit registration value the room-temperature semiconductor detectors appears to be at the level of several keV that makes their application not effective for the registration of typical secondary electron emission 70% of which have the energy lower than some keV.
The goal of this project is the development of the principle of registration of the typical secondary electron emission spectrum with its preliminary acceleration and development on this base the detector for new generation of secondary electron emission analytical equipment for material characterization. The principal under development provides to reach sensitivity from the zero energy of emitted electrons and liner transforming of electron energy to the output signal through the whole spectrum. It consists of preliminary acceleration of emitted electrons in electrostatic field that is equivalent to the shift of the spectrum as the whole on the value of accelerating voltage. Together with that the optimization of configuration of electrical field for each analytical technique (e.g. cylindrical, flat, focusing) allow to obtain the spatial distribution of the emitted electrons and to reconstruct their initial spectrum.
It is evident that the value of accelerating potential should equal or grater of semiconductor detector low limit, that should be minimized for the most appropriate level for real application. For the existing detectors this value is about 10-15 kV but after the optimization of detector structure design may be decreased down to several kV.
Several variants of such detector geometry are possible:
· Detector matrix – electrical field – point electron source.
· Detector matrix – electrical field – plane electron source.
· Point detector – electrical field - 2 electron source.
In accordance with this such detectors may be used in:
· analytical equipment:
- EXAFS- synchrotron beamlines and EXAFS laboratory devices
- electron microscopes;
- XPS spectrometers;
- AES spectrometers;
- Other equipment that uses secondary emission as the signal.
· as the wide aperture tritium detectors for:
- control of environment pollution;
- nuclear fusion.
Applications are wider than the part of some laboratory devices. Namely, modernization of the existing devices and development of new generation of analytical equipment is possible on the base of such detectors. Together with this, independent manufacturing of detecting systems of such a type as the parts for analytical equipment and for pollution monitoring is of commercial value. Enterprises of microelectronics (silicon detectors, their matrixes with small dark currents and super shallow p-n junctions) together with the ones from Ministry of Defense (acceleration systems, radiation detectors and electrovacuum systems) will take parts in production that is in complete coincidence with ISTC programs conditions.
The Project is supposed to be performed by A.F.Ioffe PTI of RAS and RINP-VNIIF teams that have necessary background for fulfilling the works under the Project and large experience in this field.
PTI Team has the experience in development, manufacturing and maintenance of analytical devices based on the phenomenon of electron emission. Thus, the Head of the Team is the leading specialist in modern characterization techniques, USSR State Prize winner, Dr. Sci., Professor, member-correspondent of Academy of Natural Sciences, member of Academy of Engineering Sciences, leader of Scientific School. The Team is involved in development of semiconductor detectors for more than 30 years and has more than 100 publications in this field.
Researchers from RINP-VNIIF have large experience in the field of x-fluorescence analysis, development of methods of registration of different radiation and detectors and devices for these methods. Their experience is necessary for development of technology of manufacturing of such detectors (control of impurities in silicon and their effective hettering), determining of characteristics of detectors and in methodological problems in their applications.
Both organizations have sufficient background in as experimental equipment and technology for starting the works over the Project. During the works it will be upgraded and the additional special devices will be purchased.
Development of a number of new devices and units is supposed in the frames of the Project. Microelectronics fabrication technologies, isotope sources and devices for generation of different radiation will be used.
Project duration is three years. The results will be delivered as technical reports, presentations, experimental unit of detector system and protocols of its testing.
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