Cold cathodes

Fig. 15. Cold-cathode ionisation gauge, where A = anode, C = cathode, M = horseshoe magnet, and = microammeter (15).

Gauges. Because there is no way to measure and/or distinguish molecular vacuum environment except in terms of its use, readings related to gas-phase concentration ate provided by diaphragm, McCleod, thermocouple, Pitani gauges, and hot and cold cathode ionization gauges (manometers). 

C. A. Spindt, Development Program on a Cold Cathode Electron Gun, NASA CR 159570, Stanford Research Institute, Menlo Park, Calif., 1979, pp. 37-38. 

With such properties, it could be the ideal material for many semiconductor applications, such as high-power and high-frequency transistors and cold cathodes, or in the harsh environment found in internal-combustion and jet engines. With the advent of CVD diamond, it is now possible to take advantage of these properties. 

The sample was analysed with a primary ion beam of extracted from an oxygen cold cathode discharge type source. A well-focussed 200 nA spot was attained at 4keV per molecular ion. The beam was scanned over a square of side 400 pm to produce a uniform primary beam current density and thus a flat-bottomed crater. In order to eliminate crater-edge effects, the counting system was only enabled when the centre of deflection of the beam was in a central area 125 x 125 pm. 

The IEF gel is prefocused for 1 h using reverse polarity with the following buffer (kept cold) cathode (lower tank) 0.05 M histidine anode (upper tank) 0.01 M glutamic acid. Prefocusing is for 20 min at 200 V, then 20 min at 300 V, and finally 20 min at 400 V. The current... 

Fig. 1.33. Cold cathode of Philips vacuum gauge. The microammeter A gives an indication of the pressure.

Ionization and condensation nuclei detectors alarm at the presence of invisible combustion products. Most industrial ionization smoke detectors are of the dual chamber type. One chamber is a sample chamber the other is a reference chamber. Combustion products enter an outer chamber of an ionization detector and disturb the balance between the ionization chambers and trigger a highly sensitive cold cathode tube that causes the alarm. The ionization of the air in the chambers is caused by a radioactive source. Smoke particles impede the ionization process and trigger the alarm. Condensation nuclei detectors operate on the cloud chamber principle, which allows invisible particles to be detected by optical techniques. They are most effective on Class A fires (ordinary combustibles) and Class C fires (electrical). 

Coking steam coal grade (U.K.), 6 713t Coking tests, coal, 6 727, 755 Cola beverages, 6 366 Colchicine, 2 72, 74, 91 13 302 Cold-cathode ionization gauges,... 

Penniman-Zoph process, 19 400 Penning cold-cathode ionization gauges,... 

A precision aneroid manometer is used for measurements in the 760— 1 torr range. Thermocouple gauges are used in the 1 — 1 x 10 3 range. A cold cathode ionization gauge is used in the high vacuum range down to 10-6 torr. 

The material properties of PS offer new ways of making electronic devices. For the manufacture of cold cathodes, for example, oxidized microporous polysilicon has been found to be a promising material. The application of basic semiconductor processing steps such as doping, oxidation and CVD to a macroporous material enable us to fabricate silicon-based capacitors of high specific capacitance. Both devices will be discussed below. 

A schematic view of the cold cathode fabrication process is shown in Fig. 10.18. The cold cathode is fabricated by low pressure chemical vapor deposition (LPCVD) of 1.5 pm of non-doped polysilicon on a silicon wafer or a metallized glass substrate. The topmost micrometer of polysilicon is then anodized (10 mA cnT2, 30 s) in ethanoic HF under illumination. This results in a porous layer with inclusions of larger silicon crystallites, due to faster pore formation along grain boundaries. After anodization the porous layer is oxidized (700 °C, 60 min) and a semi-transparent (10 nm) gold film is deposited as a top electrode. 

Fig. 10.18 Schematic view of the fabrication process of a porous polysilicon-based cold cathode. Note that metallized glass may also serve as a substrate. Redrawn from [Ko21].

Fig. 10.19 (a) Current-voltage characteristic of the cold cathode according to the circuit shown in Fig. 10.18. (b) A Fowler-Nordheim... 

This type of traveling wave tube with cold cathode has been developed and met reasonable performance. However, a good system pumping around the cathode was difficult to achieve in the small enclosed spaces. 

Octachlorodibenzothiophene (88) has been formed by irradiation of a solution of pentachlorobenzenesulfenyl chloride in CCI4 in a low-pressure, cold cathode mercury arc (62%). A similar photolysis of bis-(pentachlorophenyl) sulfide, prepared by the action of sulfur monochloride and sulfuryl chloride on benzene in the presence of aluminum chloride, also yielded 88 (42%). Both routes are shown in Scheme 4. 

The formation of ions is a consequence of either a discharge at a high electric field strength (so-called cold-cathode or Penning discharge, see... 

Cold-cathode ionization vacuum gauges (Penning vacuum gauges)... 

In all those measurement instruments which use the ionization of gas molecules as the measurement principle (cold-cathode and hot-cathode ionization vacuum gauges), strong magnetic leakage fields or electrical potentials can have a major influence on the pressure indication. At low pressures it is also possible for wall potentials which deviate from the cathode potential to influence the ion trap current. 

Thermocouple vxuum gauge Bimetallic vacuum gauge Thermistor vacuum gauge Cold-cathode ionization vacuum gauge... 

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