Fabrication of High Aspect Ratio Silicon Nanostructure with Sphere Lithography and Metal-Assisted Chemical Etching and its Wettability

Metal-assisted chemical etching (MACE) is a site-selective etching process produced by a catalyst reaction at the interface between noble metal and silicon. This paper aims to make clear the applicability of sphere lithography and MACE to the fabrication of high aspect ratio Si nanostructures. The capacity to control the etched profiles and the scale extension are investigated. First, silica particles (e.g. φ1 μm) were self-assembled on a Si substrate. After the reduction of particle size via argon ion bombardment, a gold layer was deposited using the particles as a mask. The substrate was then etched with a mixture of hydrofluoric acid and hydrogen peroxide. It was found that an array of nanopillars with a regular pitch, good separation, and an aspect ratio of about 52 was produced. The effects of MACE conditions on final profiles were clarified. A limitation of this approach is the small (several millimeters) area fabricated due to the dependence on the vacuum technique (ion bombardment, Au deposition), and the size of the area limits its practical applications. Thus, Ag nanoparticles (e.g. φ150 nm) were applied. The relationship between the concentration of the Ag suspension, the Ag assembled layer, and the morphology of MACE structures was made clear. A spray method was applied to extend the deposited area of Ag particles up to φ100 mm. Finally, the effects of the cross-sectional profile on the contact angle of a water droplet were examined. By applying a high aspect ratio nanostructure on the substrate, the water contact angle increased up to 153 degrees while that without the structure is 58 degrees

Advancing nanofabrication processes for the generation of multifunctional surfaces

Ubiquitous in the natural world, micro- and/or nano-structured surfaces can afford simultaneous control over a range of interfacial properties; providing an attractive solution for where the accumulation of fluids (fog/rain/oil) and bacteria, and the mismanaged interaction of photons, can impede the safety or efficiency of the surface. Although surfaces found in nature provide a wealth of inspiration, replicating the structures synthetically persists to be a challenge, particularly so when striving for scalability and simplicity to encourage industrial/commercial uptake. Furthermore, the fabrication challenges become amplified when aiming for sub-wavelength structures; often necessary to unlock or enhance additional functionality. In this thesis, I present novel fabrication routes based on lithography and reactive ion etching (RIE) to achieve a range of ordered structures at the nano-scale in glass and silicon, and further replicate the resultant structures into polymers. I explore scalable masking techniques including block copolymer (BCP) lithography, laser interference lithography (LIL) and nanoimprint lithography (NIL), to achieve a series of pitches from 50 – 600 nm. By coupling the masking with novel combinations of etching chemistries, and taking advantage of the etch resistivity of different materials, I fabricate high aspect ratio nanostructures through simplified processes and demonstrate their ability to target applications in wettability, photonics and anti-bacterial action. Specifically, for silicon and glass nanocones, I focus on their anti-fogging, superhydrophobic, anti-reflective and anti-bacterial properties. I also investigate the impact of the nanostructure morphology on a sub-class of water-repellent surfaces, namely, slippery liquid infused porous surfaces, and their ability to retain lubricant under dynamic conditions; continuing on the theme of smart nanostructure design and simplified fabrication to pave a route to multifunctional surfaces. It is anticipated that the surfaces and their properties will find use as car windscreens, coatings for solar panels, high-rise glass facades, and high-touch surfaces to name a few

Functional Texture Design and Texturing Processes

Various functions can be obtained by applying regular patterns or textures to surfaces. Depending on the function, the required dimensions of the texture, such as the pitch, vary over a wide range: from nanometers for optical function to millimeters for friction. In addition, the high aspect ratio of the cross sectional profile or the hierarchical structure of a micro- or nano-structure is required to control the wettability, for example. This paper reviews various texturing processes as well as the functionalities thus attained and their application

Fabrication of high aspect ratio silicon micro-/nano-pore arrays and surface modification aiming at long lifetime liquid-infused-type self-cleaning function

This paper discusses a fabrication process of high aspect ratio (AR) silicon micro-/nano-pore structures and modification of their surfaces to improve the function of liquid-infused-type self-cleaning surfaces. The structure and its hydrophobic surface play an important role to hold a special liquid (a lubricant) on the surface tight to produce an intermediate lubricant layer and any liquid drops, including low surface tension liquids such as oil, can slide easily on it. The nanopore structure with an AR as high as 30 was fabricated by etching in a solution of hydrofluoric acid and hydrogen peroxide. This process based on a catalyst reaction of an array of Au islands that was deposited on a silicon substrate through a particle mask. This original hydrophilic surface was changed to hydrophobic one by depositing self-assembled monolayer of octadecyltrichlorosilane to modify the energy balance at the interface of the solid structure, the lubricant, another liquid, and air. Then the lubricant could be well retained. The functional lifetime was evaluated by measuring the liquid residue on the surface after number of liquid dash. It was confirmed that longer lifetime was obtained with higher AR nanopore structure

SYNTHESIS OF SILICON BASED NANOSTRUCTURES FOR BIOMIMICKING AND BIOMEDICAL APPLICATIONS

Ph.DDOCTOR OF PHILOSOPH

Advances in Unconventional Lithography

The term Lithography encompasses a range of contemporary technologies for micro and nano scale fabrication. Originally driven by the evolution of the semiconductor industry, lithography has grown from its optical origins to demonstrate increasingly fine resolution and to permeate fields as diverse as photonics and biology. Today, greater flexibility and affordability are demanded from lithography more than ever before. Diverse needs across many disciplines have produced a multitude of innovative new lithography techniques. This book, which is the final instalment in a series of three, provides a compelling overview of some of the recent advances in lithography, as recounted by the researchers themselves. Topics discussed include nanoimprinting for plasmonic biosensing, soft lithography for neurobiology and stem cell differentiation, colloidal substrates for two-tier self-assembled nanostructures, tuneable diffractive elements using photochromic polymers, and extreme-UV lithography

Nanopatterning with Photonic Nanojets: Review and Perspectives in Biomedical Research

: Nanostructured surfaces and devices offer astounding possibilities for biomedical research, including cellular and molecular biology, diagnostics, and therapeutics. However, the wide implementation of these systems is currently limited by the lack of cost-effective and easy-to-use nanopatterning tools. A promising solution is to use optical methods based on photonic nanojets, namely, needle-like beams featuring a nanometric width. In this review, we survey the physics, engineering strategies, and recent implementations of photonic nanojets for high-throughput generation of arbitrary nanopatterns, along with applications in optics, electronics, mechanics, and biosensing. An outlook of the potential impact of nanopatterning technologies based on photonic nanojets in several relevant biomedical areas is also provide

Nanostructured glass covers for photovoltaic applications

Ph.DDOCTOR OF PHILOSOPH

Characterisation and Modelling of Wicking on Ordered Silicon Nanostructured Surfaces fabricated by Interference Lithography and Metal-Assisted Chemical Etching

Ph.DDOCTOR OF PHILOSOPH