Field anode/emitter

Note The field anode is usually referred to as field emitter, FI emitter, or FD emitter. The properties of the field emitter are of key importance for FI- and FD-MS. The electrode on the opposite side is called field cathode or simply counter electrode. 

Field ionization emitters are mounted 0 5 to 2 mm from the cathode, which often also serves as a slit. The gaseous sample from a batch inlet system is allowed to diffuse into the high-field area around the microtips of the anode. The electric field is concentrated at the emitter tips, and ionization occurs via a quantum mechanical tunneling mechanism in which electrons from the analyte are extracted by the microtips of the anode. Little vibrational or rotational energy is imparted to the analyte, and little fragmentation occurs. 

Molecules can lose an electron when subjected to a high electric potential resulting in field ionization (FI) [366,534,535]. High fields can be created in an ion source by applying a high voltage between a cathode and an anode called a field emitter. A field emitter consists of a wire covered with microscopic carbon dendrites, which greatly amplify the effective field at the carbon points. 

There are two geometries for a ballast resistor, a thin film under the CNT (vertical resistor), or a thin film at the side of the CNT (horizontal resistor). Now, the local field for field emission from carbon is extremely high, 109 V/m, which may be 10 times larger than the breakdown field of many insulators. Given the dimensions of an emission system, it is likely that the thickness of any ballast resistor thin film will be smaller than that of the net cathode-anode distance. Thus, the applied field is likely to cause breakdown in any vertical ballast resistor design. Thus, horizontal ballast resistors are a safer option. However, they are more difficult to implement because they must be placed between each emitter and the current feed. 

Fig. 2. Schematic drawing of one form of the field emission microscope. E, glass envelope S phosphorescent screen M, metal backing A, anode lead-in T, emitter tip C, tip support structure V, vacuum lead.

Fio. 9. Sketch of field emission microscope assembly for mobility studies. D, inner Dewar <8, screen A, anode T, tip, TA, tip assembly M, platinum foil mortar, filled with copper wires, oxidized in ssiln electric heating of M produces a controllable flux of oxygen MA, gas emitter assembly V, vacuum lead, sealed off. Outer Dewar and electrical leads are not shown. 

LMI sources with needle emitters operate in essentially the same way as field ionization or field desorption sources. The filament is resistively heated to melt the metal film and/or promote its flow to the tip of the emitter. Typically, the emitter or anode is positively biased 3-5 kV with respect to its counter electrode, the cathode the actual operating voltage is determined... 

Govyadinov, A. N., and Zakhvitcevich, S. A., Field emitter arrays based on natural self-organized porous anodic alumina. J. Vac. Sci. Technol. B 16,1222 (1998). 

Microstructured surfaces, as well as micromachined substrates and devices discussed in Sects. II, III, and iy are suitable for a number of applications. They include reflective and absorbing surfaces, wavelength-sensitive filters, multiaperture lens arrays and Fresnel microoptics, field emitter arrays, precision apertures, or molds for microstructured surfaces of other materials. Microstructured alumina ceramics can also be used for tuned broadband infrared emitters. In addition, due to the robustness at high temperatures and well-developed and controlled porosity, the freestanding, heat-treated micromachined anodic alumina substrates can be used for the fabrication of sensors that incorporate a high temperature microheater with low power consumption. 

The potential applications of CNTs due to their small dimension and excellent physicochemical properties make them useful in wide ranges from multifunctional composites, electrochemical electrode, and/or additives, field emitters, to nanosized semiconductor devices. Up to now, commercialized fields of CNTs are the filler in anode materials of lithium-ion secondary battery. ... 

The surface of the sp -carbon film was examined as a cold emitter of electrons in a normal applied electric field. Figure 11.18 shows the volt-current characteristic of a vacuum diode with a flat sp -carbon cathode at room temperature. The figure is plotted in the Schottky coordinates log(7) — where U is the applied voltage. The distance between the anode and cathode was about 0.3 mm. As can be seen in Figure 11.18, the electron emission from the cathode can be described by the Schottky law ... 

Fig. 32. Field emission microscope for adsorption studies. A—gas bottle B—break off seal C—inverted ionization gauge (also serves as selective getter) D—Granville-Phillips valve E—ionization gauge F—grounding rings G—double Dewar H—emitter assembly (tip mounted on hairpin support wire, equipped with potential leads for measuring resistance) I—anode terminal J—willemite screen settled onto tin-oxide conductive coating K—ground glass port L—trap.

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