Light formation mechanisms induced by well-aligned sub-20-nm Ag quantum dots produced alongside patterned porous Si walls and bottoms

Sub-20-nm Ag nanoparticles created via sputtering were freely moved into preformed Si pores and were arranged along both wall and lower surfaces in etched Si layers via a post-thermal annealing treatment. The variously sized Ag quantum dots on the porous Si facilitate broadband visible emission via photo-generated enhanced luminescent effects, i.e., plasmonic effects of Ag nanoparticles by electron transfer from the Si-based matrix to the metallic Ag. The emission wavelengths and intensities, depending on the sizes of the Ag quantum dots, were determined by the degree of oxidation of the Si-based substrate such as Si, SiO_x, and SiO₂, according to different post-thermal annealing conditions. The morphological, microstructural, and optical evolution of Ag nanoparticles and Si pores were simply observed via side-cross-sectional scanning electron microscopy, X-ray diffraction, transmission electron microscopy, and crystalline-controlled photoluminescence analyses, respectively. The origin of a new systematic luminescence mechanism based on energy-equilibria is also presented.