Thermionic emitters

Also increasingly common, as CVD precursors, are many halogen-acetylacetonate complexes, such as trifluoro-acetylacetonate thorium, Th(C5H4F302)4, used in the deposition of thoriated tungsten for thermionic emitters, the trifluoro-acetylacetonates of hafnium and zirconium and the hexafluoro-acetylacetonates of calcium, copper, magnesium, palladium, strontium, and yttrium. 

The TID design proposed Patterson consists of an alkali metal doped cerwlc cylinder, containing an embedded heater surrounded by a cylindrical collector electrode [100]. The ceramic thermionic emitter is biased at a negative potential with respect to the collector electrode, and it is heated to a surface temperature of 400-800 C, depending on the mode of detection. The response of the detector to different elements depends on the electronic work function of the thermionic surface (i.e., the... 

The colloidal particles are often deposited on metallic electrodes in the form of adsorbed coatings. Rubber and graphite coatings can be formed in this way, using solvent mixtures (water-acetone) as the dispersion media. The advantage of this method is that additives can firmly be codeposited with, for example, rubber latex. Thermionic emitters for radio valves are produced in a similar manner. The colloidal suspensions of alkaline earth carbonates are deposited electrophoretically on the electrode and are later converted to oxides by using an ignition process. 

Thermionic emitter in spacecrafts (W, CVD-W, W—Re). The important properties are high-temperature resistance and stability against cesium vapor. 

The vaporization of barium tungstates (Sect. 4.2) is of interest for thermionic emitters used in certain types of arc lamps, that of ZrOj-based solid solutions for high-refractory ceramics (Sect. 4.3), and that of glasses for their production (Sect. 

Fro. 74. Bayard-Alpert inverted ionization gauge 5966, modified for 1 in. OD straight through pumping leads (C). 1—Thermionic emitter 2—Electron eolleotor 3—Jgn collector. 

Another approach to this problem is to allow dissociation to occur, but to provide a mechanism for recombination. With hydrogen this can be accomplished by surrounding the emitter with a clean metal surface. A gauge of the type built by Klopfer (112) should avert such difficulties. This remedy is likely to be less successful with oxygen and other gases for which recombination is not as efficient as for hydrogen. In some circumstances the chemical effects of the thermionic emitter can be minimized by operating in a flow system. A rapid flow of gas... 

A patent describing a thermionic emitter for generating positive ions that incorporated a mixtnre of beta-alumina and inert material snch as charcoal positioned on a filament for heating the mixture has been issued. Two decades later, an alkali cation emitter, based on intercalated alkali ions in a graphite matrix, was proposed. When heated on a red hot filament, this source emits ions from alkali salts, which snbseqnently can be used to form product ions. 

Apart from transistors, several other solid state devices have been discussed [78], like junctions, photon and electron beam switches and various kinds of sensors. One property of diamond which has stimulated considerable interest in the recent years is the negative electron affinity (NEA) of suitably prepared surfaces [78,80]. The electron affinity, of a material is defined as the difference between the energy of a free electron in vacuum and the bottom of the conduction band Fyac - E. In Fig. 8 the electronic bands of p-doped clean and H-terminated (111) diamond surfaces near the surface are depicted, based on the results of UV-photoemission measurements. For the H-terminated surface, the electron affinity becomes negative once an electron is injected into the conduction band from a suitable contact or by UV excitation, it will easily leave the crystal and be emitted into vacuum. This effect, which is also observed on monohydride terminated (100) surfaces, is not unique to diamond but was also observed in a few other semieonductors with high band gaps [80]. Apart from a scientific interest, the NEA of diamond makes it an attractive eandidate for the replacement of thermionic emitters as electron beam sourees and as a miniature electron emitter for field emission displays. 

Only a very limited number of standard methods are reported in which sublimation is an important aspect. These comprise an ASTM standard for measurement of sublimation from thermionic emitters, and two standards from Germany and Japan testing the stability of dyes and printing inks to sublimation. The first covers the determination of the quantity, rate, and identity of sublimed, evaporated, or sputtered materials, whilst the latter two are concerned with textile materials and semimanufactured products. 

Figure 39. Ion source using a thermionic emitter in a collision chamber for ionization...

Bombick et al. [3] presented a simple, low cost method for producing thermal potassium metal ions for use as Cl reagents. All studies were performed on a commercial gas chromatography-mass spectrometiy (GC-MS) system. Thermionic emitters of a mixture of silica gel and potassium salts were mounted on a fabricated probe assembly and inserted into the Cl volume of the ion source through the direct insertion probe inlet. Since adduct ions (also referred to as cationized molecular ions or pseudomolecular ion ) of the type (M + K)+ have been observed, molecular weight information is easily obtained. The method is adaptable to any mass spectrometer with a Cl source and direct inlet probe (DIP). In addition, the technique is compatible with chromatographic inlet systems, i.e., GC-MS modes, which will provide additional dimensions of mass spectral information. 

Bombiok D, Pinkston JD, Allison J. Potassium ion chemical ionization and other uses of an alkali thermionic emitter in mass spectrometry. Anal Chem. 1984 56 396-402. Schmelzeisen-Redeker G, Giessmam U, Rollgen FW. In-beam ionization by alkali ion attachment applying a two-filament ion source. Org Mass Spectrom. 1985 20 305-309. Anderson WR Jr, Frick W, Daves CD Jr A direct technique for obtaining electron-impact mass spectra of polar, involatile compounds. Application to underivatized disacchaiides. J Am Chem Soc. 1978 100 1974-75. 

Bombick D, Pinkston JD, Allison J. Potassium ion chemical ionization and other uses of an alkali thermionic emitter in mass spectrometry. Anal Chem. 1984 56 396 02. 

Haq FU. Construction of thermionic alkali-ion sources. J Phys E Sci Instrum. 1986 19 275-6. Tan TL, Ong PP, Fong TM, Soo KA. Studies of rubidium aluminosilicates Rb ions as thermionic emitters. Int J Mass Spectrom Ion Process. 1994 34 221-8. 

Conventional SEM (developed originally with thermionic emitters) operates typically in high-vacuum conditions and at high accelerating voltage e.g. 10- 0 keV), offers an image resolution of some... 

Similarly, the field emitter can be adapted by reducing the work function. The practical device is called the Schottky field emission gun, but it is really a field-enhanced thermionic emitter. The sharp tip is coated with zirconium oxide. The field is reduced by flattening the tip and acts to reduce the potential barrier, but the electrons are thermally excited over the low barrier, not sucked through it. 

Yada, K., Masaoka, H., Shoji, Y., Tanji, T. (1989). Studies of refractory carbides, nitrides, and borides as the thermionic emitters for electron-microscopy. Journal of Electron Microscopy Technique, 12, 252-261. doi 10.1002/jemt. 1060120308 PMID 2795231. 

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