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Palladium (Pd) nanostructures have been actively adapted for various applications and their properties and applicability closely depend on their shape, size, and density. In this paper, the evolution of self-assembled Pd nanostructures on the hexagonal c-plane GaN is presented by the systematical control of Pd deposition amount (DA) at distinctive temperatures. Pd nanostructures of various configurations, sizes, and densities are demonstrated based on the solid-state dewetting of Pd thin films and a clear distinction in the growth regimes is observed. Three growth regimes are clearly observed depending on the variation of DA, i.e., (i) the agglomeration of Pd nanoparticles, (ii) the coalescence of wiggly Pd nanostructures, and finally (iii) the growth of nanovoids and layers. Owing to the temperature-dependent dewetting process, the growth regimes are markedly shifted, resulting in the distinctive Pd nanostructures within the identical DA range. The results are discussed in conjunction with the surface diffusion, Volmer–Weber and coalescence growth model, and surface/interface energy minimization mechanism. In addition, the evolution of optical properties, emission band, and lattice properties are probed by reflectance, photoluminescence, and Raman spectroscopy, which exhibit varying spectral intensity and peak positions according to the surface morphology of Pd nanostructures. [ABSTRACT FROM AUTHOR]

Silver (Ag) nanostructures have demonstrated the feasibility of being utilized in various optoelectronic, catalytic, biomedical, and sensor devices due to their excellent surface plasmon resonance characteristics. The geometrical structure, spacing, and spatial arrangement of nanostructures are crucial for controlling the properties and device performance. Herein, we demonstrate the fabrication of various configurations of self-assembled Ag nanostructures on GaN (0001) by the systematic control of deposition thickness and annealing duration. The surface morphology evolution is thoroughly investigated, and the corresponding influence on optical properties is probed. The evolution of Ag nanostructures in response to thermal annealing is described based on the dewetting of thin films, Volmer-Weber growth model, coalescence growth, and surface energy minimization mechanism. For the deposition amount variation between 1 and 100 nm, the Ag nanostructures show gradual morphological transitions such as small nanoparticles (NPs) to enlarged NPs between 1 and 7 nm, elongated nanostructures to cluster networks between 10 and 30 nm, and void evolution with layered nanostructures between 40 and 100 nm. In addition, the annealing duration effect has been studied between 0 and 3600 s, where the Ag nanostructures exhibit the evolution of network-like, elongated and isolated irregular shapes, ascribed to Ostwald's ripening along with Ag sublimation. Furthermore, corresponding Raman, photoluminescence, and reflectance spectra reveal the morphology-dependent behaviors and are discussed based on the phonon, emission band, scattering, absorption, and surface plasmon effect. [ABSTRACT FROM AUTHOR]

Porous GaN exhibits unique optoelectronic, chemical, and physical properties such as shift of band gap, increased surface area ratio, excellent chemical, mechanical, and thermal stability as well as efficient luminescence as compared to its bulk counterpart. Herein, we demonstrate a precise, efficient, and still cost-effective method of the fabrication of porous GaN through the enhanced GaN decomposition by using Au nanoparticles (NPs) as a catalyst, in which the size, density, and shape of the pores (nanoholes, NHs) can be precisely controlled. By the thermal annealing assisted with the Au NPs, the NHs are successfully fabricated, and the existence of Au NPs significantly accelerate the GaN decomposition at the interface between the NPs and GaN due to the Ga absorption by the Au NPs. We systematically study the formation mechanism of NHs assisted by the Au NPs by means of annealing temperature, duration, and Au deposition amount, and the results are systematically analyzed and discussed. [ABSTRACT FROM AUTHOR]