Suppression of Phase Transformation in Nb-H Thin Films below Switchover Thickness
Suppression of Phase Transformation in Nb-H Thin Films below Switchover Thickness
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DOI：
10.1021/acs.nanolett.6b02467
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发表时间：
2016-10-01
期刊：
影响因子：
10.8
通讯作者：
Pundt, Astrid
中科院分区：
文献类型：
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作者：
Burlaka, Vladimir;Wagner, Stefan;Pundt, Astrid
金属氢（M-H）纳米尺寸系统中的氢吸收（例如，薄膜、团簇）是一个基本的和技术相关的主题，由于氢传感器、纯化膜和氢存储解决方案的最新发展，其变得更加重要。最近的研究表明，附着在刚性基底上的纳米系统中的氢（H）吸收可导致GPa范围内的机械应力。报道了载氢铌（Nb）薄膜的约-10GPa（压缩）应力。当传统的应力释放通道关闭时，例如，通过减小系统尺寸。在本文中，我们证明了高应力可以用来强烈修改系统的热力学。特别地，通过将膜厚度减小到低于λ值d（so）来实现相变的完全抑制。结合原位扫描隧道显微镜（STM）和原位X射线衍射（XRD）测量，用于确定外延Nb/Al_2 O_3薄膜的厚度范围从55到5 μ m。在T = 294 K时，薄膜厚度d（so）= 9 ± 1 nm.这一结果得到了补充方法的支持，如电动势（EMF），电阻和机械应力测量结合理论建模。
Hydrogen uptake in metal hydrogen (M-H) nanosized systems (e.g., thin films, clusters) is both a fundamental and a technologically relevant topic, which is becoming more important due to the recent developments of hydrogen sensors, purification membranes, and hydrogen storage solutions. It was recently shown that hydrogen (H) absorption in nanosized systems adhered to rigid substrates can lead to ultrahigh mechanical stress in the GPa range. About -10 GPa (compressive) stress were reported for hydrogen loaded niobium (Nb) thin films. Such high stresses can be achieved when conventional stress-release channels are closed, e.g., by reducing the system size. In this paper, we demonstrate that the high stress can be used to strongly modify the system's thermodynamics. In particular, a complete suppression of the phase transformation is achieved by reducing the film thickness below a switchover value d(so). Combined in situ scanning tunneling microscopy (STM) and in situ X-ray diffraction (XRD) measurements serve to determine the switchover thickness of epitaxial Nb/Al2O3 films in the thickness range from 55 to 5 rim. A switchover thickness d(so) = 9 +/- 1 nm is found at T = 294 K. This result is supported by complementary methods such as electromotive force (EMF), electrical resistance, and mechanical stress measurements in combination with theoretical modeling.