Shinku

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An omegatron mass spectrometer was employed to detect some extremely small amount of impurities in solids. The gases evolved during a vacuum heat treatment of extra pure samples of oxides, sulfides, and selenides, were analyzed by means of the omegatron mass spectrometer. The detected gases have been NH₃, NO, H₂S, CO, CO₂, CS₂, HCl, H₂O, and hydrocarbons. The origin of these gases are discussed as follows ; (1) the gases produced by thermal decomposition of reactants which were remained after the sample was made by dry process and/ or the evolution of gaseous imprities which were included during wet process. (2) the gaseous products produced by chemical reaction of impurities with the sample. (3) the evolution of adsorbed gases. (4) the evolution of reagent which was used to store the sample, (5) residual gases in the vacuum system.
The amount of gas evolved (QQ) from these samples was estimated as follows ; in the case of flow method, Q = S∫Pdt and in the case of static method, Q= PV. The consideration on ideal cases shows that smaller amount of impurities less than 1 ppb of the material is detectable. The sensitivity of this method has been.shown to be high and the method has been found to be useful in detection of traces of gaseous impurities less than 1 ppm.
Possible sources of error in quantitative analysis are disct ssed as follows; (1) the gaseous imp, rities remain after the evolution of first heating cycle. (2) the absolute meas Irements of partial pressure and of pumping.speed are difficult for active gases.

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The performance and pumping characteristics are described on an evaporator utilizing a getter-ion pump and a titanium sublimation pump. The titanium film which is discontinuously deposited from a stranded wire of titanium and tungsten onto the inner wall of the sump can evacuate the volume of about 401 from 10^-4Torr to 10^-8 Torr within 75 min. with the co-operation of an 8 l/sec ion pump. Mass spectrometric analyses during the evacuation show that the titanium sublimation pump can evacuate active gases exclusively and the appendage of small getter ion pump is very effective to eliminate methane and inert.gas such as argon.
The major components of the residual gas at 8×10^-8 Torr are M/e =2, 16, 18, 28, 29, 40, 44 and the heavy hydrocarbon peaks are negligiblly low.
The temperature-dependency of the pumping characteristics is also investigated. The pump-down rate is promoted by use of a liquid nitrogen cryo-panel arranged around the sublimation pump cartridge. The variations of mass peaks with the panel temperature in the unbaked system are due to the desorption of loosely adsorbed gases, and the pumping speed by the evaporated film itself seems to be nearly constant in the temperature range of -50° to 100°C.
The gas burst during evaporation of aluminum is depressed to 10^-7 Torr order at room temperature and to 10^-8 Torr order with the co-operation of cryopumping.

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