Growth of Ni and Ni-Cr Alloy Thin Films on MgO(001): Effect of Alloy Composition on Surface Morphology
Growth of Ni and Ni-Cr Alloy Thin Films on MgO(001): Effect of Alloy Composition on Surface Morphology
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MgO(001) 上 Ni 和 Ni-Cr 合金薄膜的生长：合金成分对表面形貌的影响
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发表时间：
2016
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影响因子：
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通讯作者：
P. Reinke
中科院分区：
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作者：
Gopalakrishnan Ramalingam;P. Reinke
利用扫描隧道显微镜（STM）和原子力显微镜（AFM）研究了衬底处理、温度和成分对MgO（001）衬底上生长的Ni-Cr薄膜表面形貌的影响。酸蚀刻和高温沉积（400 ℃）的组合将产生光滑的薄膜和平台（宽达30 nm），适用于研究表面上的化学反应的进展。使用两种不同的处理来制备用于沉积的MgO衬底，并且它们引入膜表面形态的特征差异。在磷酸处理的衬底上生长的薄膜在薄膜生长的初始阶段呈现降低的成核密度，这导致长而宽的台阶。由于Ni（001）/MgO（001）系统中约16%的晶格失配，在400 ℃下的膜生长产生不连续的膜，并且需要两步生长过程来获得连续的层。在100 ℃下沉积Ni膜，并在300 ℃下进行2小时的生长后退火，以获得更光滑的表面。仅添加5 wt. % Cr改变了生长过程，并在400 ℃下产生连续的膜，而不去湿，与纯Ni膜相反。随着Cr含量的增加，膜变得逐渐平滑，具有更宽的平台。Ni 5Cr合金薄膜的均方根表面粗糙度为3.63+/-0.75 nm，而Ni 33 Cr薄膜更光滑，均方根粗糙度仅为0.29 +/-0.13 nm。与Cr合金化引发的膜生长的变化是由于界面化学的变化，这有利于改变MgO表面上的金属原子的初始吸附，并建议减少的Ehrlich-Schwoebel势垒。具有良好表面结构的光滑Ni-Cr薄膜的生长为与合金性能相关的广泛表面科学研究开辟了新途径。
The effects of substrate treatment, temperature and composition on the surface morphology of Ni-Cr thin films grown on MgO(001) are studied by scanning tunneling microscopy (STM) and atomic force microscopy (AFM). A combination of acid-etching and high temperature deposition (400C) will result in smooth films and terraces (up to 30 nm wide) suitable for the study of progression of chemical reactions on the surface. Two different treatments are used to prepare the MgO substrates for deposition and they introduce characteristic differences in film surface morphology. Thin films that are grown on the phosphoric acid-treated substrates present reduced nucleation density during the initial stages of film growth which results in long and wide terraces. Due to the about 16 percent lattice mismatch in the Ni(001)/MgO(001) system, film growth at 400C yields discontinuous films and a two-step growth process is necessary to obtain a continuous layer. Ni films are deposited at 100C and subjected to a post-growth anneal at 300C for 2 hours to obtain a smoother surface. The addition of just 5 wt. percent Crchanges the growth processes and yields continuous films at 400C without de-wetting in contrast to pure Ni films. With increasing Cr content, the films become progressively smoother with wider terraces. Ni5Cr alloy thin films have an rms surface roughness of 3.63+/-0.75 nm while Ni33Cr thin film is smoother with an rms roughness of only 0.29 +/-0.13 nm. The changes in film growth initiated by alloying with Cr are due to changes in the interfacial chemistry which favorably alters the initial adsorption of the metal atoms on MgO surface and suggests a reduction of the Ehrlich-Schwoebel barrier. The growth of smooth Ni-Cr thin films with well-defined surface structure opens up a new pathway for a wide range of surface science studies related to alloy performance.