Applications of metal surfaces nanostructured by ion beam sputtering

Ordering Enhancement of Ion Bombardment-Induced Nanoripple Patterns: A Review

Low-energy ion bombardment (IB) has emerged as a promising, maskless nanofabrication tool for quasi-periodic nanoripples, marked by a high throughput and low cost. As templates, these IB-induced, self-organized surface nanoripples have shown potential for applications in diverse fields. However, the challenge of tailoring the ordering of these ripple patterns is preventing the widespread application of IB. Moreover, the enhancement of the ordering of these self-organized nanostructures involves the fundamental academic questions of nanoripple coupling (or superimposition) and guided self-organization. This review first focuses on the experimental progress made in developing representative strategies for the ordering enhancement of IB-induced nanoripples in terms of ion beams and targets. Second, we present our understanding of these developments from the perspectives of ripple superposition and guided self-organization. In particular, the basic conditions for ripple superposition under the non-conservation of mass are deduced based on the common features of the results from rocking bombardments of a single material and the bombardment of bilayer systems, providing insight into the mechanisms at play and deepening our understanding of these experimental observations. Finally, areas for future research are given, with the aim of improving ripple ordering from the viewpoints of ripple superimposition and guided self-organization. All this may re-stimulate interest in this field and will be of importance in advancing the academic research and practical applications of IB-induced nanopatterns.

Ion Beam Nanopatterning of Biomaterial Surfaces

Ion beam irradiation of solid surfaces may result in the self-organized formation of well-defined topographic nanopatterns. Depending on the irradiation conditions and the material properties, isotropic or anisotropic patterns of differently shaped features may be obtained. Most intriguingly, the periodicities of these patterns can be adjusted in the range between less than twenty and several hundred nanometers, which covers the dimensions of many cellular and extracellular features. However, even though ion beam nanopatterning has been studied for several decades and is nowadays widely employed in the fabrication of functional surfaces, it has found its way into the biomaterials field only recently. This review provides a brief overview of the basics of ion beam nanopatterning, emphasizes aspects of particular relevance for biomaterials applications, and summarizes a number of recent studies that investigated the effects of such nanopatterned surfaces on the adsorption of biomolecules and the response of adhering cells. Finally, promising future directions and potential translational challenges are identified.

Role of Hierarchical Protrusions in Water Repellent Superhydrophobic PTFE Surface Produced by Low Energy Ion Beam Irradiation

The surface wettability of polytetrafluoroethylene (PTFE) was investigated with low energy Ar⁺ ion beam irradiation varied from 300 eV to 800 eV both at normal and oblique angle of incidence (0°–70°) and at a low irradiation time of few 10 s of seconds. A remarkable change in surface wettability was observed, surface became hydrophobic to superhydrophobic just at 800 eV energy and in 30 s time. A systematic increase in the contact angle was observed with increase in beam energy and irradiation time. For a given ion energy and a threshold irradiation time, the hierarchical protrusions developed that leads to the rolling and bouncing of water droplet even on the horizontal PTFE surface. For the above energy range, the rolling speed was found to be in the range of ~19–31 mm/s. This induced wetting behaviour due to ion irradiation leads to the Cassie-Baxter state as confirmed by the calculation of sliding angle, contact angle hysteresis (CAH) and surface free energy (S_E). The CAH values were found to be reduced from 18° for untreated surface (S_E ~ 20 mN/m) to 2° for 800 eV, 180 s irradiated surface (S_E ~ 0.35 mN/m) at normal incidence.

Light scattering properties of self-organized nanostructured substrates for thin-film solar cells

We investigate the scattering properties of novel kinds of nano-textured substrates, fabricated in a self-organized fashion by defocused ion beam sputtering. These substrates provide strong and broadband scattering of light and can be useful for applications in thin-film solar cells. In particular, we characterize the transmitted light in terms of haze and angle-resolved scattering, and we compare our results with those obtained for the commonly employed Asahi-U texture. The results indicate that the novel substrate has better scattering properties compared to reference Asahi-U substrates. We observe super-Lambertian light scattering behavior in selected spectral and angular regions due to the peculiar morphology of the nano-textured interface, which combines high aspect ratio pseudo random structures with a one-dimensional periodic pattern. The enhancement of light absorption observed in a prototype thin film semiconductor absorber grown on nano-textured glass with respect to an Asahi-U substrate further confirms the superior light trapping properties of the novel substrate.

Plasmon resonance of silver micro-sphere in fiber taper

We have experimentally studied the plasmon resonance phenomenon of a silver micro-sphere with a diameter of 2.3 μm in cone-shaped air cavity of a hollow fiber taper. To take insight into the plasmon resonance phenomenon, we move the micro-sphere along the fiber and observe the significant shift of the resonance peak. We also explore the light response in both infrared and visible wavelength band by finite difference time domain method. The significant variations of the magnetic and power field distribution are observed. The interesting results imply that the configuration has great potential in optical sensors and color filters.