Various Silver Nanostructures on Sapphire Using Plasmon Self-Assembly and Dewetting of Thin Films

Abstract

Silver (Ag) nanostructures demonstrate outstanding optical, electrical, magnetic, and catalytic properties and are utilized in photonic, energy, sensors, and biomedical devices. The target application and the performance can be inherently tuned by control of configuration, shape, and size of Ag nanostructures. In this work, we demonstrate the systematical fabrication of various configurations of Ag nanostructures on sapphire (0001) by controlling the Ag deposition thickness at different annealing environments in a plasma ion coater. In particular, the evolution of Ag particles (between 2 and 20 nm), irregular nanoclusters (between 30 and 60 nm), and nanocluster networks (between 80 and 200 nm) are found be depended on the thickness of Ag thin film. The results were systematically analyzed and explained based on the solid-state dewetting, surface diffusion, Volmer–Weber growth model, coalescence, and surface energy minimization mechanism. The growth behavior of Ag nanostructures is remarkably differentiated at higher annealing temperature (750 °C) due to the sublimation and temperature-dependent characteristic of dewetting process. In addition, Raman and reflectance spectra analyses reveal that optical properties of Ag nanostructures depend on their morphology. Electronic supplementary materialThe online version of this article (doi:10.1007/s40820-016-0120-6) contains supplementary material, which is available to authorized users.

Evolution of Ternary AuAgPd Nanoparticles by the Control of Temperature, Thickness, and Tri-Layer

“…Therefore, the evolution of alloy NPs at high temperature can also be affected by the Ag sublimation, such that we see size reduction and shape transformation. The sublimation loss of Ag in this case was much lower compared to the pure Ag nanoparticles due to the inter-mixing with Au and Pd [29]. Furthermore, the atomic homogeneity of metal elements can improve with increased temperature, exceeding the melting point, as observed in previous results [36]; however, Ag can be extensively sublimated.…”

“…On the other hand, the reflectance was significantly attenuated in the visible region, i.e., 420-600 nm making a wide dip centered ay~460 nm, which might be the absorption enhancement due to the surface plasmon resonance of alloy NPs [37][38][39]. The peak observed in the UV region and NIR region can be due to the quadrupolar and dipolar resonance mode of alloy NPs, respectively, which has been previously observed in the case of pure Ag and Pd NPs [27,29]. The formation of peaks and dips in a similar manner with pure metal NPs indicates that the alloy NPs are composed of well-mixed Au, Ag, and Pd and the optical response collectively contributed by each element.…”

“…Generally, Ag Lα1 peak counts are higher in comparison with Ag Lα1 and Pd Lα1 peak counts due to the higher atomic number of Au. From the EDS counts of elements, Au and Pd were found to vary slightly within the error range throughout the temperature; however, Ag gradually decreased above 600 • C. This indicates that Ag sublimation occurred significantly above 600 • C and the sublimation rate escalates along with the temperature [28,29]. Therefore, the evolution of alloy NPs at high temperature can also be affected by the Ag sublimation, such that we see size reduction and shape transformation.…”

“…Previous results clearly showed the distinct dewetting behavior of Au, Ag, and Pd metal layers on various substrates. Generally, Ag layers have shown significant dewetting around 400 • C, whereas Au and Pd demonstrated visible dewetting above 500 and 600 • C, respectively [27][28][29]. On the other hand, the interaction force between metal film and substrate will also play an important role in the dewetting process, such that the interaction force of Pd-sapphire is higher than Au-sapphire, which will be discussed in the later section on altered tri-layer deposition.…”

Self-assembled antireflection coatings for light trapping based on SiGe random metasurfaces

“…One viable and promising route is solid-state dewetting of ultra-thin films of metals 18,[34][35][36][37][38][39][40][41] and semiconductors, [42][43][44][45][46] a natural phenomenon exploited for the self-assembly of high-quality photonic structures. The instability giving rise to the dewetting phenomenon in thin films is mediated by the surface diffusion of atoms and occurs upon annealing at high temperature (even well below the melting point of the material) [47][48][49][50][51][52][53][54][55][56][57][58] .…”