Ramachandran Tholkappiyan, Ali Ashraf, Deader Firdous Ahmad, Shafeekali Hibah, Zheng Lianxi, Butt Haider, Rezeq Moh'd
Department of Physics, Khalifa University of Science and Technology, Abu Dhabi 127788, United Arab Emirates.
Department of Mechanical and Nuclear Engineering, Khalifa University of Science and Technology, Abu Dhabi 127788, United Arab Emirates.
Langmuir. 2025 Jan 21;41(2):1271-1280. doi: 10.1021/acs.langmuir.4c03580. Epub 2025 Jan 7.
Self-assembled gold nanoparticles (Au-NPs) possess distinctive properties that are highly desirable in diverse nanotechnological applications. This study meticulously explores the size-dependent behavior of Au-NPs under an electric field, specifically focusing on sizes ranging from 5 to 40 nm, and their subsequent assembly into 2D monolayers on an n-type silicon substrate. The primary objective is to refine the assembly process and augment the functional characteristics of the resultant nanostructures. Utilizing a multifaceted analytical approach encompassing X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDXS), atomic force microscopy (AFM), and COMSOL multiphysics simulation, this work yields comprehensive insights. Results reveal that the electric field and nanoparticle size critically influence assembly dynamics due to variations in surface energy and electrostatic interactions. Larger Au-NPs (20, 30, and 40 nm) experience enhanced dipolar interactions and more substantial polarizability, enabling more efficient alignment and organization under an applied electric field. This leads to the formation of structured, uniform monolayers with minimal vacancies and smoother surfaces. In contrast, smaller Au-NPs (5, 10, and 15 nm) exhibit lower polarizability, which hampers alignment and promotes clustering and voids. XRD analysis delineates notable disparities in peak intensities and positions: smaller Au-NPs exhibit diminished (111) peak intensities, indicative of uneven distribution and crystallinity, whereas larger particles manifest higher intensities and well-defined peaks across multiple crystallographic planes. SEM images portray diverse surface coverages with AFM corroborating that larger Au-NPs achieve uniform and continuous monolayers with minimal height variations. COMSOL simulations substantiate these findings by illustrating the efficient alignment and settling of larger Au-NPs under the electric field. This study bridges critical gaps in understanding how nanoparticle size modulates assembly dynamics and the resultant properties of 2D Au-NP monolayers, offering pivotal insights into engineering advanced nanostructured materials tailored to specific applications in electronics, coatings, photonics, and catalysis.
自组装金纳米颗粒（Au-NPs）具有独特的性质，这些性质在各种纳米技术应用中非常受欢迎。本研究精心探索了电场作用下Au-NPs的尺寸依赖性行为，特别关注5至40纳米范围内的尺寸，以及它们随后在n型硅衬底上组装成二维单层的情况。主要目标是优化组装过程并增强所得纳米结构的功能特性。利用包括X射线衍射（XRD）、扫描电子显微镜（SEM）与能量色散X射线光谱（EDXS）、原子力显微镜（AFM）以及COMSOL多物理场模拟在内的多方面分析方法，这项工作获得了全面的见解。结果表明，由于表面能和静电相互作用的变化，电场和纳米颗粒尺寸对组装动力学有至关重要的影响。较大的Au-NPs（20、30和40纳米）经历增强的偶极相互作用和更大的极化率，从而在施加电场时能够更有效地排列和组织。这导致形成具有最小空位和更光滑表面的结构化、均匀单层。相比之下，较小的Au-NPs（5、10和15纳米）表现出较低的极化率，这阻碍了排列并促进了聚集和空隙的形成。XRD分析描绘了峰强度和位置的显著差异：较小的Au-NPs表现出减弱的（111）峰强度，表明分布不均匀和结晶度低，而较大的颗粒在多个晶面上表现出更高的强度和明确的峰。SEM图像描绘了不同程度的表面覆盖率，AFM证实较大的Au-NPs实现了具有最小高度变化的均匀连续单层。COMSOL模拟通过说明较大的Au-NPs在电场下的有效排列和沉降来证实这些发现。这项研究填补了理解纳米颗粒尺寸如何调节组装动力学以及二维Au-NP单层的所得性质方面的关键空白，为工程设计适用于电子、涂层、光子学和催化等特定应用的先进纳米结构材料提供了关键见解。
