Annealing-Driven Optical and Structural Modulation in Ag-C60 Nanocomposites for Surface Plasmon Enhancement
摘要
The innovation of efficient photonic devices benefits every area of life on Earth. Therefore, the optics field is emerging extensively. In this work, the thermal co-deposition technique is used to fabricate the Ag-C60 nanocomposite thin films. The silver particles are embedded in a fullerene C60 matrix on a quartz window. The obtained nanocomposites are annealed at different temperatures. Rutherford backscattering spectroscopy (RBS) analysis is used to determine Ag metal concentration and film thickness which are found to be ~ 2.5% and ~ 80 nm respectively. Here, the thin films of Ag-C60 exhibit a remarkably strong surface plasmon resonance (SPR) signal at 432 nm as a consequence of annealing temperature, which is investigated using UV–visible absorption spectroscopy. The SPR signals demonstrated first redshift and then blue shift at ascending temperature. This occurs on account of compaction and transformation of the C60 matrix at low and high annealing temperatures respectively as conferred in the text. The energy band gap for Ag-C60 nanocomposite is estimated at different annealing temperatures. A significant increase in the band gap, from 1.74 to 2.51 eV, was observed through the classical Tauc plot analysis. Transmission electron microscopy is executed to investigate the particle–particle interaction behavior responsible for switching SPR signals. The as-deposited film has a silver particle size of 4.3 nm, which increases to 5.6 nm after annealing. Higher annealing temperatures promote silver nanoparticle ripening due to increased diffusivity, resulting in larger Ag particles. The thermal-induced transformation of the C60 host matrix is examined using Raman spectroscopy, revealing a shift in the G-band position from 1574 cm-1 (as-deposited) to 1598 cm-1 at 400 °C, indicative of structural reorganization and thermal degradation at elevated temperatures. Concurrently, the D-band intensity weakens with increasing temperature, suggesting a loss of crystallinity in the C60 framework. The transformation leads to the formation of amorphous carbon, characterized by disordered sp2 and sp3 bonds, as evidenced by the broad D band and changes in the G band. This behavior lies in demonstrating a controlled thermal-induced transition of a molecular solid (C60) into an amorphous carbon phase, which significantly influences the material’s optical and plasmonic properties. This compaction and phase transition are crucial for tailoring thin films for advanced optical, electronic, and sensing applications. The AFM result reveals an increase in grain size with respect to the increase in surface energy at high temperatures. The surface roughness increasing and randomly decreasing with an increase in annealing temperature up to 400 °C can be attributed to the irregular distribution and phase changes which influence the surface morphology as well as atomic arrangement. X-ray photoelectron spectroscopy investigates the elemental composition and chemical bonding and states in nanocomposite thin films subjected to thermal annealing confirming the presence of silver (Ag), carbon (C), and oxygen (O).