Singh Jitendra Pal, Kim So Hee, Won Sung Ok, Lee Ik-Jae, Chae Keun Hwa
Advanced Analysis Center, Korea Institute of Science and Technology Seoul 02792 Republic of Korea
Beamline Division, Pohang Accelerator Lab Pohang 37673 Republic of Korea.
RSC Adv. 2018 Sep 5;8(55):31275-31286. doi: 10.1039/c8ra02873g.
The phenomena related to thin film growth have always been interesting to the scientific community. Experiments related to these phenomena not only provide an understanding but also suggest a path for the controlled growth of these films. For the present work, MgO thin film growth on fused quartz was investigated using angle-dependent near-edge X-ray absorption fine structure (NEXAFS) measurements. To understand the growth of MgO, sputtering was allowed for 5, 10, 25, 36, 49, 81, 144, 256, and 400 min in a vacuum better than 5.0 × 10 torr. NEXAFS measurements revealed the evolution of MgO at the surface of fused quartz for sputtering durations of 144, 256, and 400 min. Below these sputtering durations, no MgO was observed. NEXAFS measurements further envisaged a systematic improvement of Mg ion coordination in the MgO lattice with the sputtering duration. The onset of non-interacting molecular oxygen on the surface of the sputtered species on fused quartz was also observed for sputtering duration up to 81 min. Angle-dependent measurements exhibited the onset of an anisotropic nature of the formed chemical bonds with sputtering, which dominated for higher sputtering duration. X-ray diffraction (XRD) studies carried out for sputtering durations of 144, 256, and 400 min exhibited the presence of the rocksalt phase of MgO. Annealing at 700 °C led to the dominant local electronic structure and improved the crystallinity of MgO. Rutherford backscattering spectrometry (RBS) and cross-sectional scanning electron microscopy (SEM) revealed a layer of almost 80 nm was obtained for a sputtering duration of 400 min. Thus, these angle-dependent NEXAFS measurements along with XRD, RBS, and SEM analyses were able to give a complete account for the growth of the thin films. Moreover, information specific to the coordination of the ions, which is important in case of ultrathin films, could be obtained successfully using this technique.
与薄膜生长相关的现象一直是科学界感兴趣的。与这些现象相关的实验不仅能增进理解，还为这些薄膜的可控生长指明了方向。在本研究中，利用角分辨近边X射线吸收精细结构（NEXAFS）测量法研究了熔融石英上MgO薄膜的生长情况。为了了解MgO的生长过程，在真空度优于5.0×10托的环境下进行了5、10、25、36、49、81、144、256和400分钟的溅射。NEXAFS测量揭示了在144、256和400分钟溅射时间下，熔融石英表面MgO的演变情况。在这些溅射时间以下，未观察到MgO。NEXAFS测量进一步设想，随着溅射时间的延长，MgO晶格中Mg离子的配位会有系统的改善。对于长达81分钟的溅射时间，还观察到了熔融石英上溅射物种表面非相互作用分子氧的出现。角分辨测量表明，随着溅射的进行，形成的化学键呈现出各向异性，且在较长溅射时间下占主导地位。对144、256和400分钟溅射时间进行的X射线衍射（XRD）研究表明存在MgO的岩盐相。在700℃退火导致了占主导地位的局部电子结构，并提高了MgO的结晶度。卢瑟福背散射光谱（RBS）和横截面扫描电子显微镜（SEM）显示，在400分钟的溅射时间下获得了一层近80纳米厚的薄膜。因此，这些角分辨NEXAFS测量以及XRD、RBS和SEM分析能够全面描述薄膜的生长情况。此外，使用该技术可以成功获得与离子配位相关的特定信息，这在超薄薄膜的情况下非常重要。
