Effect of Temperature on Recovery of Surface Segregation of Ti on Nb Film

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  • Nb膜上に偏析したTi層の再生速度の温度依存性
  • Nb マク ジョウ ニ ヘンセキシタ Tiソウ ノ サイセイ ソクド ノ オンド イソンセイ

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Abstract

The kinetics of the surface composition recovery was studied in the case of Ti segregation on a Nb film which works as a getter material. The surface concentration of Ti is kept constant at 80 at% with Auger electron spectroscopy, and 60 at% with X-ray photoelectron spectroscopy on the Nb film, when Ti segregates on the surface by diffusing through the Nb film from the substrate. The getter function of this material is estimated to be due to both the high sticking coefficient of residual gases to Ti and the high diffusion coefficients of oxygen and carbon in Nb. Therefore, the coexistence of Ti and Nb on the surface seems to be important. The saturation concentration is independent of the heating temperature and film thickness. Even if the Ti segregation layer is sputtered away, Ti is supplied from underneath and the surface composition can be kept constant when the supply rate is equivalent to the removal rate of Ti. Therefore, the surface composition is maintained automatically in this material. The saturation phenomenon is useful for the conventional fabrication of such functional materials. By observing the dynamic equilibrium between the supply rate and the removal rate, the temperature dependence of the supply rate was estimated. To vary the supply rate, the specimen temperature was changed. The sputtering rate was precisely calibrated before the experiment and was varied to control the removal rate. From the behavior of the surface concentration increase upon segregation and of the dynamic equilibrium, a model to analyze the kinetics of diffusion, segregation and dynamic equilibrium is proposed.

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