Silicon whiskers

Alternatives to activated tungsten wire emitters are also known, but less widespread in use. Cobalt and nickel [44,47] as well as silver [48] can be electrochemi-cally deposited on wires to produce activated FD emitters. Mechanically strong and efficient emitters can be made by growing fine silicon whiskers from silane gas on gold-coated tungsten or tantalum wires of 60 pm diameter. [45] Finally, on the fracture-surface of graphite rods fine microcrystallites are exposed, the sharpness of which provides field strengths sufficient for ionization. [49]... 

Fig. 3.14 A ToF spectrum of a high purity silicon whisker in hydrogen image gas, obtained with a pulsed-laser imaging atom-probe. Below 80 K, silicon is an excellent insulator. However, the tip surface can be easily field evaporated with the stimulation of laser pulses.

Except for Si02, all other nanowires are well crystalline, mostly oriented along [111] direction. The VLS crystal growth mechanism was first proposed by Wagner et al. [200] for silicon whisker growth. Essentially, they reduced SiCLj using hydrogen... 

This book serves as an introduction to advanced inorganic fibers and aims to support fundamental research, assist applied scientists and designers in industry, and facilitate materials science instruction in universities and colleges. Its three main sections deal with fibers which are derived from the vapor phase such as single crystal silicon whiskers or carbon nanotubes, from the liquid phase such as advanced glass and single crystal oxide fibers, and from solid precursor fibers such as carbon and ceramic fibers. 

Almost all short fibers, which are derived from the vapor phase, grow by a vapor-liquid-solid (VLS) phase transformation, including single crystal silicon whiskers and carbon nanotubes. Only rarely does the growth of short fibers or whiskers occur by a vapor-solid (VS) phase transformation, and the evidence for this type of phase transformations is often difficult to obtain experimentally. 

Figure 3. Growth of irregular arrays of silicon whiskers. Courtesy of Dr. E. I. Givargizov, Russian Academy of Sciences, Moscow.

Regular growth (Figure 5) of silicon whiskers occurs when gold droplets of equal size are deposited on the growth substrate before the reaction is initiated. This result is obtained when the gold droplets are deposited by lithography or similar means. In this case the catalyst particles have will equal diameters and activities and, as a result, forests of individual... 

The most important products, which can be synthesized from the vapor phase, are silicon whiskers and nanowhiskers, silicon carbide whiskers and nanowhiskers, short carbon and graphite fibers, and carbon nanotubes. 

Figure 11. Sharpening of a single-crystal silicon whisker tip (schematic drawing). This illustration shows, from left to right, the effect of progressive etching in HF.

Figure 13 Sharpened, diamond-coated silicon whisker. Product bulletin, Containerless Research Inc., Evanston, IL., with permission from Dr. P. C. Nordine, President.

Table VII. Potential uses of single crystal silicon whiskers...

The effect of particle shape on particle size distribution was investigated by Naito et al. (1998) with commercial particle size analyzers based on five different measuring principles electrical sensing zone, laser diffraction and scattering, x-ray sedimentation, photosedimentation, and light attenuation. The particles used are blocky aluminum oxide and barium titanate particles, flaky boron nitride particles, and rodlike silicon whisker ceramic powders. Altogether, four commer-... 

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