ABSTRACT
The Au partially embedded nanostructure (PEN) is synthesized by ion irradiation on an Au thin film deposited on a glass substrate using a 50 keV Ar ion. Scanning electron microscopy results show ion beam-induced restructuring from irregularly shaped nanostructures (NSs) to spherical Au NSs, and further ion irradiation leads to the formation of well-separated spherical nanoparticles. Higuchi's algorithm of surface analysis is utilized to find the evolution of surface morphology with ion irradiation in terms of the Hurst exponent and fractal dimension. The Au PEN is evidenced by Rutherford backscattering spectrometry and optical studies. Also, the depth of the mechanism behind synthesized PEN is explained on the basis of theoretical simulations, namely, a unified thermal spike and a Monte Carlo simulation consisting of dynamic compositional changes (TRIDYN). Another set of plasmonic NSs was formed on the surface by thermal annealing of the Au film on the substrate. Glucose sensing has been studied on the two types of plasmonic layers: nanoparticles on the surface and PEN. The results reveal the sensing responses of both types of plasmonic layers. However, PEN retains its plasmonic behavior as the NSs are still present after washing with water, which demonstrates the potential for reusability. RESEARCH HIGHLIGHTS: Synthesis of PENs by ion irradiation Utilization of Higuchi's algorithm to explore the surface morphology. Unified thermal spike and TRIDYN simulations being used to explain the results. Glucose is only used as a test case for reusability of substrate.
ABSTRACT
We present the morphological evolution and fractal characterizations of CaF2 thin-film surfaces modified by bombardment with 100 MeV Au+8 ions at various fluences. Atomic force microscopy (AFM) combined with line profile and two-dimensional power spectral density (2D-PSD) analysis was utilized to investigate the evolution of surface morphology as a function of fluence. The AFM images were utilized to investigate the relationship between fractal dimension, roughness exponent, lateral correlation length, and ion fluence. The surface erosion owing to sputtering was depicted using Rutherford backscattering spectrometry. The structural characteristics' dependency on fluence was explored with the help of glancing angle x-ray diffraction measurements on virgin and irradiated samples. Tensile stress calculated using a peak shift in the glancing angle x-ray diffractogram showed an increase in tensile stress with fluence that caused the surface to crack after the fracture strength of the surface was crossed. 2D-PSD analysis signified the role of sputtering over surface diffusion for the observed surface modifications. Fractal dimensions first increased and then decreased with ion fluence. The lateral correlation length decreased, while the roughness exponent increased with fluence after the threshold value.
ABSTRACT
Surface re-organization in nanodimensional fluoride (LiF and BaF2) thin films is observed under dense electronic excitation produced by swift heavy ion (SHI) irradiation. The irradiation was performed at an angle of less than 15° with respect to the film surface while keeping the sample at liquid nitrogen temperature. The surface of the irradiated samples was characterized by atomic force microscopy (AFM) and scanning electron microscopy (SEM) complemented by energy dispersive X-ray spectroscopy (EDX). Detailed analyses indicate that the surface starts cracking at lower fluence. With an increase in the ion fluence, the materials shrinking and surface re-structuring lead to lamellae periodic structures. The average width of the wall decreases, while the separation and the height of the structures increase with the fluence. The composition of the lamellae walls and the gap in between were analyzed by EDX. At the highest fluence of irradiation, a strong signal of the substrate and negligible signals of F and Ba are observed between the walls of the lamellae structures, which shows that the entire deposited material is removed and the Si substrate is completely exposed to the ion beam. It is also observed that the substrate remains unaffected by SHI irradiation and does not undergo any structural transformation as evident by cross-sectional SEM micrographs. Such surface re-organization is not expected in fluoride thin films due to their non-amorphizable nature even at very high fluence SHI irradiation. The concept of grain rotation under SHI irradiation is used to explain the re-organization phenomena in such non-amorphizable materials.
