Background Gas Composition Research Articles

Chemically assisted ion beam etching of GaAs, Ti, and Mo

Investigations with argon and chlorinated ion beams have shown that the etch rates of GaAs and Ti are strongly dependent on the flux of molecular and atomic chlorine. Etch rate increases were observed with an increase in the chlorine flux from the background gas composition or from the impinging ion beam. At increased chlorine concentrations in the presence of ion bombardment, wall profiles were altered from an overcut slope to nearly vertical. In the etching of Mo, etch rates were limited by the removal of low volatility chlorides by ion-assisted mechanisms.

Accuracy of Chemiluminescent Analyzers Measuring Nitric Oxide in Stack Gases

The measurement of nitric oxide (NO) concentrations in combustion products by chemiluminescence has several advantages over alternative methods. As a result, the chemiluminescent analyzer (CLA) has become a standard instrument for most laboratory and field emission tests involving NO. Several investigators have found that background gas composition can measurably affect the NO concentration indicated by a CLA. The potential significance of these conclusions prompted this investigation. The objective was to assess the accuracy of commercial CLAs measuring NO in combustion products. The results of this investigation are summarized, focusing on the measurement of NO in combustion products from fuels burned in air. The experimental results discussed show that the commercial CLAs tested generally indicate NO concentrations lower than actual when operated according to the manufacturers' recommendations measuring NO in combustion products. The errors introduced by neglecting the effects of sample background gas composition variations can be as high as 11% for the A-CLA and 5% for the S-CLA. These errors are significantly greater than the inaccuracy usually associated with CLAs (approximately 1%). Examination of quenching data, gas viscosities, and the results of binary background gas tests, as part of this investigation, indicated that CO/sub 2/, O/sub 2/, and H/sub 2/Omore » are responsible for most of the errors. Each of these gases decreases a CLA's sensitivity to NO. CO/sub 2/ is often present at high concentrations in combustion products and accounts for most of the errors at near stoichiometric conditions. Oxygen is present in high concentrations in fuel-lean combustion products and accounts for most of the errors under these conditions. The concentrations of H/sub 2/O in combustion products dried to dew points less than ambient temperatures are small.« less