Sputtering insertion materials

Another possibility is the sputter ion source. Here inside the source gaseous ions are accelerated to the reflector electrode containing an insert made of the element to be vaporized. Due to the sputtering effect, the material evaporates and is converted into ions. This technique is universal and applicable for all elements. Fig. 17 shows a sketch of a sputter source ... 

In this ion source the cesium atoms used to cause sputtering, are ionized in an inert-gas discharge. The cathode containing a small amount of the material whose beam is to be produced, is inserted in the chamber through the air lock. The ionized cesium then sputters the solid cathode material to produce negative ions. This ion-source is used to produce the negative ions of almost all the solid materials. 

The ion source produces a beam of ions from a few milligrams of solid material. The element is first chemically extracted from the sample (e.g., a rock, rain water, a meteorite) and then loaded into a sample holder and inserted into the ion source through a vacuum lock. Atoms are sputtered from the sample by cesium ions (using multicathode SNICS ion source), which are produced on a hot spherical ionizer and focused to a small spot on the sample. Negative ions produced on the surface of the sample are extracted from the ion source and sent down the evacuated beam-line toward the first magnet. At this point the beam current is about 10 pA (mostly due to the stable isotopes), which corresponds to 10 ions per second. 

In the case of ex situ application of an elemental catalyst, a number of physical vapor deposition techniques can be utilized, including sputtering and molecular beam epitaxy. In this way, a few to tens of monolayers of the catalyst metal are deposited onto the substrate, which is then inserted into the CVD reactor. For both of these choices the rationale for depositing a few monolayers of the catalyst is twofold. First, an extremely low coverage of the catalyst material will facilitate islanding, which is critical to nanowire formation. Second, the amount of catalyst on the substrate will dictate the size of the metal islands, which in turn will dictate the diameter of the nanowires. The primary drawback to these two approaches is that the size distribution of the islands caimot be readily controlled. 

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