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外延Pd(111)/Al2O3(0001)薄膜的超高真空直流磁控溅射沉积

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发表于 2018-3-27 15:00:28 | 显示全部楼层 |阅读模式
外延Pd(111)/Al2O3(0001)薄膜的超高真空直流磁控溅射沉积
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films 36, 030602 (2018);

https://doi.org/10.1116/1.5021609
Angel Aleman, Chao Li, and Hicham Zaid
  Department of Materials Science and Engineering, University of California Los Angeles, Los Angeles, California 90095Hanna Kindlund

ABSTRACT
摘要

Pd(111) thin films, ∼245 nm thick, are deposited on Al2O3(0001) substrates at ≈0.5Tm, where Tm is the Pd melting point, by ultrahigh vacuum dc magnetron sputtering of Pd target in pure Ar discharges. Auger electron spectra and low-energy electron diffraction patterns acquired in situ from the as-deposited samples reveal that the surfaces are compositionally pure 111-oriented Pd. Double-axis x-ray diffraction (XRD) ω-2θ scans show only the set of Pd 111 peaks from the film.
In triple-axis high-resolution XRD, the full width at half maximum intensity Γω of the Pd 111 ω-rocking curve is 630 arc sec. XRD 111 pole figure obtained from the sample revealed six peaks 60°-apart at a tilt angles corresponding to Pd 111 reflections. XRD ϕ scans show six 60°-rotated 111 peaks of Pd at the same ϕ angles for 112⎯⎯2¯3 of Al2O3 based on which the epitaxial crystallographic relationships between the film and the substrate are determined as (111)Pd(111)Pdǁ(0001)Al2O3(0001)Al2O3 with two in-plane orientations of[112⎯⎯]Pd[112¯]Pdǁ[112⎯⎯0]Al2O3[112¯0]Al2O3 and [21⎯⎯1⎯⎯]Pd[21¯1¯]Pdǁ[112⎯⎯0]Al2O3[112¯0]Al2O3. Using triple axis symmetric and asymmetric reciprocal space maps, interplanar spacings of out-of-plane (111) and in-plane (112⎯⎯2¯) are found to be 0.2242 ± 0.0003 and 0.1591 ± 0.0003 nm, respectively. These values are 0.18% lower than 0.2246 nm for (111) and the same, within the measurement uncertainties, as 0.1588 nm for (112⎯⎯2¯) calculated from the bulk Pd lattice parameter, suggesting a small out-of-plane compressive strain and an in-plane tensile strain related to the thermal strain upon cooling the sample from the deposition temperature to room temperature. High-resolution cross-sectional transmission electron microscopy coupled with energy dispersive x-ray spectra obtained from the Pd(111)/Al2O3(0001) samples indicate that the Pd-Al2O3 interfaces are essentially atomically abrupt and dislocation-free.
These results demonstrate the growth of epitaxial Pd thin films with (111) out-of-plane orientation with low mosaicity on Al2O3(0001).


        通过真空直流磁控溅射Pd靶在纯Ar气氛放电中,在Al2O3(0001)衬底上以约0.5Tm(其中Tm为Pd熔点)沉积厚约245nm的Pd(111)薄膜。从所沉积的原样中获取的俄歇电子谱和低能电子衍射图像显示,表面组成上是纯111-取向的Pd。双轴-X射线衍射(XRD) ω-2θ扫描仅显示膜的一组Pd 111峰。在三轴-高分辨率XRD中,Pd 111 Γω-摇摆曲线的半峰高宽度Γω为630弧秒。从样品获得的XRD 111极图显示在对应于Pd 111反射的倾斜角处有60°-相隔的6个峰。XRD ϕ扫描显示,在对于Al2O3的112⎯⎯2¯3相同的φ角度下有6个Pd 的60°-旋转的111峰。基于此,薄膜和基底之间的外延结晶关系被确定为(111)Pd(111)Pdǁ(0001)Al2O3(0001)Al2O3,具有两个面内取向[112⎯⎯]Pd[112¯]Pdǁ[112⎯⎯0]Al2O3[112¯0]Al2O3和[21⎯⎯1⎯⎯]Pd[21¯1¯]Pdǁ[112⎯⎯0]Al2O3[112¯0]Al2O3。使用三轴对称和不对称倒易空间图,发现面外(111)和面内(112⎯⎯2¯)的晶面间距分别为0.2242±0.0003和0.1591±0.0003nm。这些数值比(111)的0.2246nm低0.18%,在测量的不确定性范围内,对(112⎯⎯2¯)其值是相同的,为0.1588nm,该值是由块体Pd晶格参数计算得出的;这表明,相对于将样品从沉积温度冷却至室温时的热应变,存在一个小的平面外压缩应变和面内拉伸应变。高分辨率-横截面透射电子显微镜图结合从Pd(111)/Al2O3(0001)样品获得的能量色散x射线谱图显示Pd-Al2O3界面基本上是原子级突变,且无位错。这些结果表明外延Pd薄膜的生长的(111)面外取向,在Al2O3(0001)处具有低镶嵌度。


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