Tolstova Yulia, Omelchenko Stefan T, Shing Amanda M, Atwater Harry A
Department of Applied Physics and Materials Science, California Institute of Technology, Pasadena, CA 91125, USA.
Sci Rep. 2016 Mar 17;6:23232. doi: 10.1038/srep23232.
The crystallographic orientation of a metal affects its surface energy and structure, and has profound implications for surface chemical reactions and interface engineering, which are important in areas ranging from optoelectronic device fabrication to catalysis. However, it can be very difficult and expensive to manufacture, orient, and cut single crystal metals along different crystallographic orientations, especially in the case of precious metals. One approach is to grow thin metal films epitaxially on dielectric substrates. In this work, we report on growth of Pt and Au films on MgO single crystal substrates of (100) and (110) surface orientation for use as epitaxial templates for thin film photovoltaic devices. We develop bias-assisted sputtering for deposition of oriented Pt and Au films with sub-nanometer roughness. We show that biasing the substrate decreases the substrate temperature necessary to achieve epitaxial orientation, with temperature reduction from 600 to 350 °C for Au, and from 750 to 550 °C for Pt, without use of transition metal seed layers. In addition, this temperature can be further reduced by reducing the growth rate. Biased deposition with varying substrate bias power and working pressure also enables control of the film morphology and surface roughness.
金属的晶体取向会影响其表面能和结构，对表面化学反应和界面工程有着深远影响，而这些在从光电器件制造到催化等诸多领域都很重要。然而，制造、定向和切割沿不同晶体取向的单晶金属可能非常困难且成本高昂，尤其是对于贵金属而言。一种方法是在介电衬底上外延生长金属薄膜。在这项工作中，我们报道了在具有（100）和（110）表面取向的MgO单晶衬底上生长Pt和Au薄膜，用作薄膜光伏器件的外延模板。我们开发了偏压辅助溅射技术来沉积粗糙度低于纳米级的定向Pt和Au薄膜。我们表明，对衬底施加偏压可降低实现外延取向所需的衬底温度，对于Au，温度从600℃降至350℃，对于Pt，温度从750℃降至550℃，且无需使用过渡金属籽晶层。此外，通过降低生长速率，该温度还可进一步降低。改变衬底偏压功率和工作压力进行偏压沉积，还能够控制薄膜的形貌和表面粗糙度。
