Oxidant additives, plasma

Depending upon the particular precursors generated in the gas phase, etching, recombination, or film formation (i.e., polymerization) can occur. Also, gas-phase oxidant additives (O2, F2, CI2, etc.) can dissociate and react with unsaturate species. As an example, O2 can undergo the following reactions in a CF4 plasma ... 

Mass spectrometer studies of oxidant additions to fluoro- and chlorocarbon gases have demonstrated that the relative reactivity of atoms with unsaturate species in a glow discharge follows the sequence F -- O > Cl > Br (41), Of course, the most reactive species present will preferentially undergo saturation reactions that reduce polymer formation and that may increase halogen atom concentration. Ultimately, determination of the relative reactivity of the plasma species allows prediction of the primary atomic etchants in a plasma of specific composition. 

CO oxidation experiments were performed on Pt/alumina and Pt/ceria model catalysts, prepared by colloidal lithography. The samples were prepared without any of the additional plasma or UV-ozone pretreatments steps described in Preparation Procedures. Figure 4.38 shows T50 (the temperature at which 50% of reactant conversion is reached) and E (the apparent activation energy) as a function of CO oxidation cycle (ramping up and down in temperature). It is seen that both T50 and E initially shifts up during... 

Tercero, J.E., Namin, S., Lahiri, D., Balani, K., Tsoukias, N., and Agarwal, A. (2009) Effect of carbon nanotube and aluminum oxide addition to plasma-sprayed hydroxyapatite coating s mechanical properties and biocompatibility. Mater. Sci. Eng. C, 29 (7), 2195-2202. 

Figures 1 and 2 shows the principles of thermal and electron beam evaporation. Materials with a low melting point (many metals) are evaporated from graphite boats by resistive heating. For materials with a higher melting point (e.g., metal oxides), electron beam evaporation is commonly used. Evaporation is a fast process with deposition rates of 500-5,000 nm/s for metals and 100-1,000 nm/s for oxides. Film quality and adhesion to the substrate may suffer from the low energy of evaporated particles (0.2-0.5 eV). Modem evaporatiOTi processes therefore make use of an additional plasma. The evaporated particles crossing the plasma zone are activated and ionized and consequently can form a much denser film.

Plasma treatment of microchannels can be useful for improving the functionality of microdevices. For example, previous studies have shown that PDMS microchannels can be made hydrophilic by the addition of silane molecules with polar head groups [6]. In this process (3-mercaptopropyl)trimethoxysilane (3-MPS) was absorbed to PDMS to increase the hydrophilic properties of microchannels. Additionally, plasma polymerization has been used to induce in the long-term hydrophilic surface modification by covalently bonding a polymer layer to the surface. Barbier et al. [7] describe a method based on plasma polymerization modification with acrylic acid coatings. First, argon plasma pretreatment was used to activate trace oxygen molecules in the chamber, which partially oxidize the top layer of the substrate. This step cross-linked the surface to reduce ablation of silicon... 

In films generated in oxygen plasma, the contribution of arsenic oxides exceeds that of indium oxides. Addition of NF3 gas to oxygen plasma results in a strong shift in synthesis towards formation of indium and arsenic fluorides. All indium in the film is combined with fluorine, and the arsenic peak is a superposition of several components -arsenic oxyfluorides. Composition of the generated film also includes nitrogen. 

Quantitative aluminum deterrninations in aluminum and aluminum base alloys is rarely done. The aluminum content is generally inferred as the balance after determining alloying additions and tramp elements. When aluminum is present as an alloying component in alternative alloy systems it is commonly deterrnined by some form of spectroscopy (qv) spark source emission, x-ray fluorescence, plasma emission (both inductively coupled and d-c plasmas), or atomic absorption using a nitrous oxide acetylene flame. 

Addition of nitric oxide, NO, to the plasma during Si02 deposition gives siUcon oxynitride films. 

Two colorimetric methods are recommended for boron analysis. One is the curcumin method, where the sample is acidified and evaporated after addition of curcumin reagent. A red product called rosocyanine remains it is dissolved in 95 wt % ethanol and measured photometrically. Nitrate concentrations >20 mg/L interfere with this method. Another colorimetric method is based upon the reaction between boron and carminic acid in concentrated sulfuric acid to form a bluish-red or blue product. Boron concentrations can also be deterrnined by atomic absorption spectroscopy with a nitrous oxide—acetjiene flame or graphite furnace. Atomic emission with an argon plasma source can also be used for boron measurement. 

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