Bombardment with positive ions

In the first investigation 20), ethylene in the collision chamber was bombarded with positive ions, and the intensities of the fragment ions, obtained after the charge exchange, were recorded. The mass spectra were thus not normalized. At low pressure only primary ions were observed that were formed from ethylene in the charge exchange, but at higher pressures also secondary and tertiary ions were obtained as a result of ion-molecule reactions between the primary ions and the ethylene molecules in the collision chamber. 

Sputtering is the process of covering a metallic or nonmetallic workpiece with thin films of metal. The surface to be coated is bombarded with positive ions in a gas discharge tube, which is evacuated to a low pressure. 

Plasma sheaths are thin regions present in every gaseous discharge perpendicular to the surface of a solid in contact with a plasma and have a net electrical charge, usually positive, surrounding the body. Plasma sheaths are important from the viewpoint of materials treatment since they control the transport process of the chemically activated species generated in the plasma towards the surface of the substrate, as well as the bombardment with positive ions of that surface and the chemical reactivity of surface induced by it. 

Charging can be a significant problem when the sample is an insulator. Bombarding the sample with positive ions can lead to implantation of positive ions as well as the emission of electrons. One way that this problem can be overcome is by flooding the sample surface with a beam of low-energy electrons [50]. 

The mechanism we believe is responsible for the large SiOj-to-Si etch-rate ratios which have been obtained in fluorine-deficient discharges is based on several experimental observations. First of all, it has been shown that there are several ways in which carbon can be deposited on surfaces exposed to CF, plasmas. One way is to subject the surface to bombardment with CF ions which are the dominant positive ionic species in a CF plasma. The extent to which this can occur is shown by the Auger spectra in Fig. 3.3. Curve (a) is the Auger spectrum of a clean silicon surface and curve (b) is the Auger spectrum of the same surface after bombardment with 500 eV CFj" ions. Note that the silicon peak at 92 eV is no longer visible after the CFj bombardment indicating the presence of at least two or three monolayers of carbon. Another way in which carbon can be deposited on surfaces is by dissociative chemisorption of CFj or other fluorocarbon radicals. 

Secondary-ion mass spectrometry (SIMS) of a thin layer of nucleic acid bases deposited on a silver foil under bombardment with Ar ions at 3 kV gives intense pseudomolecular ions [M H] but practically no simple bond cleavage fragments. Another new technique is that of (pulsed) laser induced desorption (LD). When applied to nucleotide bases such as cytosine or adenine (266 nm, quadruplet neodymium laser or 347 nm, ruby laser) the technique has good detection limits, particularly for ions with a short lifetime (up to 100 nsec). The technique makes use of a time-of-flight instrument and is utilized in both modes, positive (PI) and negative ions (NI). Both bases exhibit an intense [BH]" ion. These results are similar to those obtained by Cf plasma desorption (PD). 

This paper is primarily concerned with the direct method of glow discharge polymerization. The bombardment of positive ions plays an important role in film formation by the direct method as mentioned above, but the bombarding ion itself and the reactive species in the gas phase may contribute to film formation. The relative importance of these factors depends on the discharge conditions. A theoretical equation for the growth rate of film will be presented from a phenomenological point of view and compared with experimental results. The theory takes into account bombardment by ions and transport of ions. 

Typical spatiotemporal profiles of potential are shown in Fig. 8 [26]. The left electrode is driven by a sinusoidal radio frequency voltage Frf = Fosin(a)t). The case shown is for an argon discharge with Fq = 100 V and u>/2n — 13.56 MHz. The potential distribution is such that the electrodes are bombarded by positive ions during the whole period of the RF cycle, while most electrons are trapped in the plasma. Only electrons with kinetic energy greater than the sheath potential can reach the walls. Electrons leak to the walls during a short time in the cycle when... 

A new trend emerged. The production of intentionally diverse composite carbon films, rich in a variety of graphitic nanostructures, became commonplace. These films contained wide assortments of naturally occurring carbonaceous nanostructures, including but certainly not limited to carbon particles, onions, clusters, fullerenes, nanotubes, and nanofibers. These nanostructured carbon films performed significantly better than both the planar carbon and Spindt metallic emitters with tum-on fields as low as l-5V/pm. Moreover, it was determined that carbon has one of the lowest sputter coefficients [287], making its allotropes extremely stable when bombarded by positive ions associated with local liberated ionized gas species. 

Figure 14.37 The SIMS process. Positive and negative ions are ejected from the surface by bombardment with inert ions (He+).

Laboratory. The isotope produced was the 20-hour Fm. During 1953 and early 1954, while discovery of elements 99 and 100 was withheld from publication for security reasons, a group from the Nobel Institute of Physics in Stockholm bombarded with O ions, and isolated a 30-min a-emitter, which they ascribed to 100, without claiming discovery of the element. This isotope has since been identified positively, and the 30-min half-life confirmed. The chemical properties of fermium have been studied solely with tracer amounts, and in normal aqueous media only the (III) oxidation state appears to exist. The isotope and heavier isotopes can be produced by intense neutron irradiation of lower elements such as plutonium by a process of successive neutron capture interspersed with beta decays until these mass numbers and atomic numbers are reached. Twenty isotopes and isomers of fermium are known to exist. Fm, with a half-life of about 100.5 days, is the longest lived. °Fm, with a half-life of 30 min, has been shown to be a product of decay of Element 102. It was by chemical identification of Fm that production of Element 102 (nobelium) was confirmed. Fermium would probably have chemical properties resembling erbium. 

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