Field-emitting structures

Figure 12. Field emitting structures and point sources for electron microscope guns. Regular array of sharpened silicon whisker. Courtesy of Dr. E. I. Givargizov, Russian Academy of Sciences, Moscow.

Thus, ultrasharp tips with nanometer-scale radii of curvature (10 to 20 nm) are used as field-emitting structures, i.e., cold cathodes" in vacuum microelectronics. They also used as a point source of electrons for electron microscope guns. An ultrasharp tip (Figure 14) is one to several atoms wide at its apex, and is used as a source of coherently emitted electrons for holographic studies [35] [37]. Cells with extracting electrodes ("Spindt triodes") are also made by this technique [36]. 

FEM Field emission microscopy [62, 101, 102] Electrons are emitted from a tip in a high field Surface structure... 

On the other hand they do have a high aspect ratio, and are quite suitable for field emission applications. Their structure means that the field emitting sites have more redundancy than simple CNTs, so the emitting site could pass along a wall, giving a higher stability. 

Extension of the tunnelling problem to three dimensions was first attempted by Itskovich who showed that the band structure of the emitter would affect both the FN plot and TED. Gadzuk and Politzer and Cutler have argued that the spatial extent of the wave-function is important in determining the yield of field emitted electrons, and the latter authors conclude that the Fowler-Nordheim model succeeds for 2>d metals only because the contribution from the 3d band to the total field emitted current is small so that the current reflects the nearly-free-electron character of the 4s-p bands. 

Organic polymers that emit light on the imposition of an electric field have commanded increasing attention in the last decade both for their scientific interest and as potential materials for electrooptical and optoelectronic applications. A number of reviews on electroluminescent polymers focusing the basic physics [1-5], synthesis and properties [6,7], device operation and materials [8-11], design and synthesis [12] blue emitting structures [13] have been published. Some books are also out on the subject [14—18]. 

Over the last decade, the chemistry of the carbon-carbon triple bond has experienced a vigorous resurgence [1]. Whereas construction of alkyne-con-taining systems had previously been a laborious process, the advent of new synthetic methodology based on organotransition metal complexes has revolutionized the field [2]. Specifically, palladium-catalyzed cross-coupling reactions between alkyne sp-carbon atoms and sp -carbon atoms of arenes and alkenes have allowed for rapid assembly of relatively complex structures [3]. In particular, the preparation of alkyne-rich macrocycles, the subject of this report, has benefited enormously from these recent advances. For the purpose of this review, we Emit the discussion to cychc systems which contain benzene and acetylene moieties only, henceforth referred to as phenylacetylene and phenyldiacetylene macrocycles (PAMs and PDMs, respectively). Not only have a wide... 

The field of science that studies the interaction of electromagnetic radiation with matter is known as spectroscopy. Spectroscopic studies on the wavelength, the intensity of the radiation absorbed, emitted, or scattered by a sample, or how the intensity of the radiation changes as a function of its energy and wavelength, provide accurate tools for studying the composition and structure of many materials (Davies and Creaser 1991 Creaser and Davies 1988). 

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