Secondary Electron Conduction Research Articles

Modeling of complex interfaces: Gadolinium‐doped ceria in contact with yttria‐stabilized zirconia

AbstractGadolinium‐doped ceria (GDC) and yttria‐stabilized zirconia (YSZ) are well‐known electrolyte materials in solid oxide fuel cells (SOFCs). Although they can be used independently, it is common to find them in combination in SOFCs, where they are used as protective layers against the formation of secondary phases or electron conduction blockers. Despite their different optimum operating temperatures, it appears that oxygen conduction is not affected by their interface. However, the intrinsic mechanisms of oxygen diffusion at these interfaces still remain unclear. One of the main difficulties when modeling the contact between different materials, or indeed different particles of the same material, is caused by the structural complexity of these systems. If we wish to evaluate the properties of the materials, we first need to obtain a model that includes the main features of the GDC/YSZ interface, such as large‐scale defects or cation interdiffusion in the contiguous phase. Since the generation of such a mixed system is complicated, we show here how the “amorphization and recrystallization” strategy can help us to obtain realistic systems. In this, the first of our papers on the structure and properties of layered GDC/YSZ materials, we discuss the structural features of the grain boundary between GDC and YSZ obtained by molecular dynamics simulations.

Point light source detection characteristics of a SEC vidicon digital TV camera

Optimization of the point source detection properties of a Secondary Electron Conduction (SEC) vidicon TV camera tube as a detector of point light sources such as star fields or certain optical spectra requires the accurate determination of peak height, half-peak width, background, and location of the point image. Two perpendicular Gaussian curves have been used to define a point image, allowing changes in the parameters of these Gaussian curves to be used in the study of SEC vidicon point source properties as a function of electrical and optical parameters. Peak height was shown to depend on priming time and a method was developed to reduce the priming time by almost an order of magnitude by momentarily raising the target voltage during priming. Power supply specifications needed for 0.1 pixel (picture element) addressing accuracy were found to be +/-0.03 V. Focus current was optimized to obtain the best sensitivity and resolution over the entire target. Peak height, background, and half-peak width were found to be strongly dependent on readout beam current. Target voltage, over the limited range examined, was found to affect only the gain without compromising other image parameters, so that any value could be used, consistent with gain and sensitivity required.

Secondary electron conduction camera tube for space applications

A camera tube based on the SEC (secondary electron conduction) effect has been developed for space applications. The background to the initiation of this development is briefly mentioned and anticipated applications are reviewed. These comprise the use as a detector in astronomical instruments (cameras and spectrographs), in a star field camera, and in special instruments for earth observation. The tube construction is described where it concerns the modifications made to the original standard tube produced by the firm Heimann GmbH. Finally, a first assessment of the tube performance is summarized as measured in a standard test facility operating in the standard European scan format.

Television studies of faint meteors

Low-light-level television systems have shown considerable promise in the optical extension of meteor flux measurements to faint magnitudes. In particular, the secondary electron conduction vidicon has demonstrated its ability to detect fast, faint meteors. Such a system has been calibrated and used to obtain the cumulative flux of meteors above threshold masses of .1 to .001 gram. The results indicate a basic continuity with photographic and satellite measurements. The observed data were further analyzed for diurnal and directional effects.-

Video Display of X‐Ray Images: I . X‐Ray Topographs

This paper discusses in detail the direct viewing of x‐ray topographs via a secondary electron conduction (SEC) vidicon system. The various geometries used to record large area topographs, the theoretical and experimentally obtainable resolutions, and the applications of the different geometries for obtaining information about the defects within crystals are illustrated. Finally, some qualitative comparisons of a practical nature are made with other video systems used for recording x‐ray topographs.

Evaluation of X-Ray Image Intensifiers as Detectors for X-Ray Astronomy

Proposed experiments in X-ray astronomy require a detector capable of forming a high resolution image of a weak source. An X-ray image intensifier incorporating a microchannel plate (MCP) has been studied as a candidate for this application. Experiments have shown that the device is sensitive to single X-ray photons and has adequate quantum efficiency. Consideration has been given to the possibility of improving the quantum efficiency by deposition on the input surface of the MCP of a material with high photoelectric yield in the wavelength region of interest. Photographs of the output light from the image intensifier show than an X-ray photon detected at the MCP results in a spot on the film of about 60μ M diameter. Since the position of the centroid of the spot could be determined to better accuracy, the device h as sufficient resolution for the contemplated experiment. Detector noise is found to be so low that it would no limitation on the experiment's sensitivity. The image can be retrieved and transmitted to the ground by focussing a television camera on the face of the fiber optic output of the X-ray image intensifier; the data show that a Secondary Electron Conduction vidicon is sensitive enough to se e the output resulting from a single X-ray photon. An alternative technique would sense charge pulses from the MCP on a fine wire grid, avoiding the need for a phosphor and providing superior time resolution and simpler data compression. Since the detector is to be used in a satellite-borne experiment, its space qualification must be established. Two launches on sounding rockets have failed to impair the usefulness of one unit that has been studied over a period of more than a year. A long term test of continuous performance in high vacuum has so far shown encouraging results. A count life test has shown that an MCP can last through detection of orders of magnitude more counts than could be expected in the course of a mission. X-ray image intensifiers appear entirely suitable for high resolution X-ray astronomy.

A Comparison of Camera Tubes in Underwater Television Cameras

A vidicon camera and a secondary electron conduction camera were compared on the basis of noise, modulation transfer function at high and low contrasts, sensitivity, response to scene motion and response to bright sources within the field of view. The tests were conducted with underwater resolution charts of 90% and 40% contrast. Since the cameras had different fields of view and video bandwidths, all measurements were made with a 5-MHz cutoff filter with the camera located to give the proper geometrical relationship with the special underwater resolution charts used. The results of these tests led to the conclusion that the vidicon is superior at high scene contrast and brightness, while the SEC camera tube is better at low scene contrast and brightness levels.

Limiting resolution of low-light-level imaging sensors.

Through the aid of electronic light amplifiers, observers can view terrain on moonless nights with near-daylight acuity. This improvement in vision is obtained by using imaging sensors with larger lenses, greater quantum efficiencies, wider spectral responses, and larger photosensitive areas than those of the unaided eye. The observer’s improved resolving power using these sensors can be calculated in terms of a limiting resolution vs light level and an elemental signal-to-noise ratio at any operating point. The analysis facilitates the comparison of sensors on an equal basis and provides the system designer with more detailed sensor operating data. As examples, the limiting performance is calculated for the image orthicon and the secondary-electron conduction camera tube with and without cascaded image intensifiers. The calculated results are compared to those measured and are found to be in good agreement.

A low light level slow scan TV camera for satellite application

A short description of the Owl satellite TV camera system and of several unique design features used with the secondary electron conduction (SEC) camera tube is presented. The dependence of the SNR on the scanning speed is analyzed, and the SNR is maximized for an amplifier employing a low noise field-effect transistor. The optimum scanning speed corresponds to an amplifier using a bandwidth of 8 kHz and a gate biasing resistor of a value in excess of 250 MΩ. To satisfy the requirements of optimum scan rate and low data telemetry bandwidth, an intermittent scanning procedure is employed in which the scanning beam touches the unscanned area of the target in a fraction of the scanning time only. This procedure combines the advantages of low noise level and high efficiency charge removal in a single scan. The single exposure scan feature reduces the efficiency of the TV system unless a small bias illumination is applied on the photosensitive surface to avoid the ineffiencies caused by the velocity distribution of the scanning beam.

A High Sensitivity Satellite-Borne Television Camera for the Detection of Auroras

A high sensitivity satellite-borne television camera has been developed to measure such faint light sources as auroras. A secondary electron conduction (SEC) television camera tube is used as the image sensor. In the present application for the Rice/NASA satellites code-named Owls, the tube is exposed by the application of a high voltage pulse of 0.1 sec or 0.2 sec duration. The picture is scanned for about 19 sec, and the video is digitized in synchronism with the satellite PCM system. The television data are then telemetered to the ground either real time or stored in one of the tape recorders. The optical system super-imposes star images on the picture for azimuthal aspect reference. The sensitivity of the slow scan camera was measured; it agrees with the sensitivity of a camera scanning at normal scan rate. Comparison was made of the relative sensitivity of the camera at the wavelength of the three most important auroral components. The camera has sensitivity comparable with the dark-adapted human eye. The weight of the system is 3.9 kg, and the power dissipation is 3.9 W.

A television scan converter tube using a silicon diode array target

A new type 7 scan converter tube is discussed which utilizes the silicon diode array target described in the preceding paper. The target in the camera tube integrates the hole diffusion current generated by an optical image. Since it is also possible to generate hole-electron pairs by energetic electron beam bombardment, video signals can be written onto the target by a second scanning beam incident from the side opposite the reading beam (the side the light is incident on in the camera tube). Current gain results from the fact that many hole-electron pairs may be created by a single energetic electron. The gain process is a form of electron bombardment induced conductivity (IEBIC) which appropriately may be called Secondary Hole Diffusion (SHD) in contrast to Secondary Electron Conduction (SEC). Memory may be built into the target by the use of appropriate traps for the holes. Thus a two-gun device of this sort may be used for scan conversion, scan compression and repeat, random access memories as well as provide a tool for the study of physical processes in silicon. Such devices have been constructed and tested and experimental results will be presented.

Secondary electron conduction (SEC) for signal amplification and storage in camera tubes

Previous studies <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1,2</sup> of the electrical properties of thin-film low-density deposits of insulators have led us to investigate their application as electrostatic storage targets. It was found that the charge image on the target is not only established by transmitted secondary electrons but that the backward conduction of secondary electrons through the layer also contributes to the amplifying mechanism. Free electrons created by the incident primary electron which are normally not observed as emitted secondary electrons can be conducted through the voids of the low-density layer to the target signal plate under the action of an electric field. This mechanism leads to an efficient conversion of photoelectrons with several kev energy into a large number of positive charge centers on the surface of the layer which are accessible to a low-energy reading beam. The secondary electron conduction (SEC) effect provides, therefore, high target gain while solid-state time lag does not occur. The high resistivity of such layers, many orders of magnitude greater than that of insulators in bulk form, is advantageous for long-time integration and storage. The target has a large storage capacity useful not only to provide a wide dynamic range, but also to accommodate the more intense signals required for low contrast image detection. The capacity is small enough, however, to eliminate discharge lag. Compatibility of the SEC target with standard photosurfaces, such as S-11, S-20, and various ultraviolet sensitive types, has been demonstrated in sealed-off tubes. The performance of SEC vidicon tubes is reported, and it is concluded that the SEC target offers the potential of overcoming several limitations found in present day camera tubes.