Pradhan Gobinda, Dey Partha P, Sharma Ashwini K
Department of Physics, Indian Institute of Technology Guwahati Guwahati - 781039 Assam India
RSC Adv. 2019 Apr 26;9(23):12895-12905. doi: 10.1039/c9ra01867k. eCollection 2019 Apr 25.
Growth dynamics of thin films expressed by scaling theory is a useful tool to quantify the statistical properties of the surface morphology of the thin films. To date, the growth mechanism for 2D van der Waals materials has been rarely investigated. In this work, an experimental investigation was carried out to identify the scaling behavior as well as the growth mechanism of 2D MoS thin films, grown on glass substrates by pulsed laser deposition for different deposition time durations, using atomic force microscopy images. The growth of MoS films evolved from layer-by-layer to layer plus island with the increase in deposition time from 20 s to 15 min. The film surface exhibited anisotropic growth dynamics in the vertical and lateral directions where RMS roughness varied with deposition time as ∼ with the growth exponent = 0.85 ± 0.11, while the lateral correlation length was = with 1/ = 0.49 ± 0.09. The films showed a local roughness exponent = 0.89 ± 0.01, global roughness exponent = 1.72 ± 0.14 and spectral roughness exponent = 0.85 ± 0.03, suggesting that the growth of MoS thin films followed intrinsic anomalous scaling behavior ( < 1, = ≠ ). Shadowing owing to conical incoming particle flux distribution towards the substrate during deposition has been attributed to the anomalous growth mode. The optical properties of the films, extracted from ellipsometric analysis, were also correlated with RMS roughness and cluster size variation which unveiled the important role played by surface roughness and film density.
用标度理论表示的薄膜生长动力学是量化薄膜表面形貌统计特性的有用工具。迄今为止，二维范德华材料的生长机制鲜有研究。在这项工作中，进行了一项实验研究，以确定通过脉冲激光沉积在玻璃基板上不同沉积时间生长的二维MoS薄膜的标度行为以及生长机制，使用原子力显微镜图像。随着沉积时间从20秒增加到15分钟，MoS薄膜的生长从逐层生长演变为层加岛状生长。薄膜表面在垂直和横向方向上表现出各向异性生长动力学，其中均方根粗糙度随沉积时间变化，生长指数β = 0.85±0.11，而横向相关长度ξ随沉积时间变化，1/ξ = 0.49±0.09。薄膜显示出局部粗糙度指数α = 0.89±0.01，全局粗糙度指数β = 1.72±0.14，光谱粗糙度指数γ = 0.85±0.03，表明MoS薄膜的生长遵循内在的反常标度行为（α < 1，β = γ ≠ α）。沉积过程中朝向基板的锥形入射粒子通量分布导致的阴影效应被认为是反常生长模式的原因。从椭偏分析中提取的薄膜光学性质也与均方根粗糙度和团簇尺寸变化相关，这揭示了表面粗糙度和薄膜密度所起的重要作用。
