Surface-Mediated Thin Terbium Hydride Film Formation

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• 作者：Marek Knor ; Robert Nowakowski ; Ewa Nowicka ; Ryszard Du
• 刊名：Langmuir
• 出版年：2010
• 出版时间：March 2, 2010
• 年：2010
• 卷：26
• 期：5
• 页码：3302-3307
• 全文大小：869K
• 年卷期：v.26,no.5(March 2, 2010)
• ISSN：1520-5827

文摘

This work was performed to study the correlation between the surface and bulk phenomena that occur during H₂ interaction with terbium, leading to three-hydride TbH_x (x ≈ 3) formation. This reaction is accompanied by the transition of the original metal into a semiconductor. It was found that thin films are particularly useful for such studies. Measurements of work function changes ΔΦ(H/Tb) were chosen to illustrate the surface phenomena, and the relative electrical resistance R(H/Tb)/R₀ and light transparency T(H/Tb)/T₀ correspond to the bulk properties. Additionally, BET experiments were performed to determine the influence of three-hydride formation on the area of a thin Tb film. It was observed at 298 K that a precursor state of the adsorbate arose at the beginning of the reaction, when (H/Tb < 0.1), decreasing the work function by ΔΦ = 12 mV. A higher uptake of hydrogen caused an increased work function, followed by ΔΦ transients. This has been interpreted as local hydride formation on the surface and its expansion into the bulk, until a concentration of H/Tb ≈ 3 was reached. TbH_x (x ≈ 3) formation resulted in ΔΦ = 200 mV and an increase in the thin film area by a factor of 3. These phenomena were accompanied by characteristic changes in the bulk properties. The light-reflecting thin Tb film was transformed into a transparent hydride, with an 23-fold increase in R/R₀. At 78 K, only a small amount of hydrogen (H/Tb = 0.13) was consumed, leading to ΔΦ = −23 mV. This uptake is stable up to 100 K. Increasing the temperature above this value resulted in the additional large absorption of hydrogen. This could suggest the formation of a low-temperature surface phase of the hydride.