Electron bombardment, decomposition

Chain reactions such as those described above, in which atomic species or radicals play a rate-determining part in a series of sequential reactions, are nearly always present in processes for the preparation of thin films by die decomposition of gaseous molecules. This may be achieved by thermal dissociation, by radiation decomposition (photochemical decomposition), or by electron bombardment, either by beams of elecuons or in plasmas. The molecules involved cover a wide range from simple diatomic molecules which dissociate to atoms, to organometallic species with complex dissociation patterns. The... 

F.C. Tompkins, The Decomposition of Solid Azides by Electron Bombardment , PrRoySoc A223, 267—82 (1954) 39) J. Sawkill, Nu-... 

It thus appears that a possible and fast mechanism for the production of ozone is by way of oxygen atoms which act as catalysts for the conversion of 02 O3. Because oxygen atoms are essentially slow in destruction of ozone, the limiting stationary process must be the destruction of ozone via the same type of process which is responsible for oxygen destruction—e.g., electron bombardment—or else the increase in temperature of the discharge which would finally provoke the thermal decomposition of ozone and make Reaction 3 a limiting process. 

The electron bombardment of explosives has been undertaken by various investigators in an effort to initiate or decompose the material under study. One of the early investigations was undertaken by Kallmann and Schrankler [30], who bombarded TNT, mercury fulminate, nitrocellulose, and to some extent, picrates and azides with 10-kV, 1-mA electrons in vacuo but were unable to produce explosions. However, when heavy ions of argon and mercury were used, initiations were achieved with several substances with each of the ions. Muraour [31 ] subjected lead azide and silver acetylide to 90 kV at 3 mA for 3 min and only achieved explosion with silver acetylide. Both explosives blackened upon electron irradiation. Muraour believed that the explosion was either a thermal effect or that, by chance, a sufficiently large number of molecules decomposed at one point to bring about complete decomposition. 

The decomposition of various azides by electron bombardment has been studied. Muller and Brous [98, 99] studied sodium azide, Groocock and Tompkins [100] investigated barium and sodium azides, and Groocock [101] investigated a-lead azide. In each case only gas evolution was studied and detected [102]. 

The information contained in the mass spectra of isothiazolium salts strongly depends on the ionisation methods. The electron bombardment (El) of non-volatile salts afforded thermal reaction in the ion source. The thermal reactions included the formation of anhydrobases [(M-H)+ -HX] dimerization and decomposition... 

There are several interesting features shown by the results which bear discussion. From an examination of Figures 2 to 4 it is evident that the hydrazine yield decreases with increasing discharge power intensity despite a corresponding increase in the decomposition of ammonia. The only reasonable explanation for these results which has been advanced is that hydrazine is formed in the discharge by a complex reaction mechanism and is subsequently decomposed by electron bombardment or other collision phenomena (4, II, 12,13,14). 

The technique is restricted to materials which have a high decomposition temperature and can tolerate electron bombardment some complex materials (including many carbides and oxides) can survive the process with their stoichiometry relatively intact, but others decompose. 

Decomposition of Sodium Azide by ControUed Electron Bombardment and by Ultraviolet Light , JChemPhys 1,482-91 (1933) 9) H. Kallmann... 

Physically, the PI source resembles the electron bombardment source, with a light source and monochromator replacing the heated filament and electron trap. Since there is no heated filament, the PI source has the further advantage that decompositions promoted by heat are eliminated. 

The electron bombardment ionization of a molecule as described above produces an excited molecular ion, which, in attempting to gain stability, may decompose in a number of different ways by unimo-lecular reaction to fragment ions or neutrals. The relative abundance of the molecular ion is determined by its ability to resist decomposition, but the stability of fragment ions is dependent on the relative rates of reaction that form and destroy the ion. 

The metal-metal bond energies may be calculated from calorimetric, kinetic, electron bombardment data, etc. If, in the gas phase, the molecular structure of the compound is the same as in the solid state, then its enthalpy of decomposition may be represented by the sum of enthalpies of particular bonds, neglecting the distances of these bonds. For iron carbonyls Fe(CO)5, Fe2(CO)9, and Fe3(CO)i2, as well as for cobalt complexes Co(CO)4, Co2(CO)g, and Co4(CO)i2, the following relationships are obeyed ... 

Studies on positive and negative ion formation as a result of the electron bombardment of hexafluoroacetone have provided the value <4.16 eV for the bond dissociation energy D[CF,—CO-CF,) this expm mental value is larger than the estimated value, and the difference, < 0.46 eV, may represent the maximum activation energy for the decomposition CF -CO- CFs- CX>. ... 

Production of a cation of allylleneimine by electron bombarding is well known in studies of mass spectrometry on pyrrole [32]. A polymer, from a vinyl pyrrole, which is produced from uncleavaged pyrrole and acetylene consists of monosubstituted pyrrole rings. This is made evident by the discrepancy in IR spectra between polypyrrole and poly(pyrrole-2,5-diyl)-like polypyrrole [33], and by the thermal decomposition... 

An external magnetic field has also been used to confine the plasma [143]. An arrangement where electromagnets are located under the cathode is known as the controlled plasma magnetron method [144]. The diffusion of electrons to the walls is prevented by the magnetic field between cathode and anode. This results in an increase in electron density, and consequently in a faster decomposition of silane and a higher deposition rate. At a deposition rate of 1 nm/s, device quality material is obtained [144]. In addition, a mesh is located near the anode, and the anode can by biased externally, both in order to confine the plasma and in order to control ion bombardment. 

Electron impact (El) ionization is one of the most classic ionization techniques used in mass spectrometry. A glowing filament produces electrons, which are then accelerated to an energy of 70 eV. The sample is vaporized into the vacuum where gas phase molecules are bombarded with electrons. One or more electrons are removed from the molecules to form odd electron ions (M+ ) or multiply charged ions. Solids, liquids and gases can be analyzed by El, if they endure vaporization without decomposition. Therefore the range of compounds which can be analyzed by El is somewhat limited to thermally stable and volatile compounds. The coupling with gas chromatography has been well established for... 

UV exposure (at k < 300 nm) of the AZ resist prior to plasma etching causes polymer cross-linking (167, 168) or decomposition (169) of the resist photosensitizer near the surface. Thus, a hardened shell or case is formed that permits a higher bake temperature without resist flow and also reduces the etch rate due to plasma exposure. Exposure to inert plasma (e.g., N2) causes similar effects (170), possibly because of ion and electron, as well as UV, bombardment of the resist surface. When F-containing discharges are used, fluorination of the resist surface occurs that strengthens the resist (because of the formation of C-F bonds) and minimizes reactivity (171). 

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