Distorted colloidal arrays as designed template

Playing with sizes and shapes of colloidal particles via dry etching methods

Monolayers of self-assembled quasi-spherical colloidal particles are essential building blocks in the field of materials science and engineering. More typically, they are used as a template for the fabrication of nanostructures if they serve, for instance, as a mask for deposition of new material on the surface on which particles are assembled or for etching of the material underneath; in this case, they are removed afterwards. This is what occurs in colloidal or nanosphere lithography. In some other cases, they are not used as a sacrificial material but they are incorporated in the final structure because they are inherently interesting for their properties. Independently of their specific use and application, different strategies have been devised in order to modify size and shape of colloidal particles, so as to enrich the variety of attainable patterns and to tailor the properties of the final structures and materials. In this review, we will focus on one of the most widespread methods to shape spherical colloidal particles, i.e. dry etching techniques. We will follow the development of such approaches until recent days, so as to trace an extensive panorama of the diverse parameters that can be harnessed to achieve specific morphological changes and highlight the characteristic features of the variants of this method. We will finally discuss how particles modified via dry etching can be used for patterning or can be resuspended in solvents for very diverse applications.

Manipulation and Applications of Hotspots in Nanostructured Surfaces and Thin Films

The synthesis of nanostructured surfaces and thin films has potential applications in the field of plasmonics, including plasmon sensors, plasmon-enhanced molecular spectroscopy (PEMS), plasmon-mediated chemical reactions (PMCRs), and so on. In this article, we review various nanostructured surfaces and thin films obtained by the combination of nanosphere lithography (NSL) and physical vapor deposition. Plasmonic nanostructured surfaces and thin films can be fabricated by controlling the deposition process, etching time, transfer, fabrication routes, and their combination steps, which manipulate the formation, distribution, and evolution of hotspots. Based on these hotspots, PEMS and PMCRs can be achieved. This is especially significant for the early diagnosis of hepatocellular carcinoma (HCC) based on surface-enhanced Raman scattering (SERS) and controlling the growth locations of Ag nanoparticles (AgNPs) in nanostructured surfaces and thin films, which is expected to enhance the optical and sensing performance.

Nanoring Arrays on Fe Coated Substrate: Formation and Guidance for the Growth of Hierarchical CNTs

In this article, we report the formation of nanoring structures on Fe coated substrate and their application in guiding the growth of carbon nanotube (CNT) patterns with hierarchical structures. The formation of nanorings involves the etching of polystyrene (PS) monolayer colloidal crystals (MCCs) under reactive ion etching (RIE), and the redeposition and cross-linkage of the active degradation products at the contact line between the MCCs and the substrate. After washing out the MCCs, insoluble nanorings with hexagonal order on the substrate are developed. The RIE process can control the morphology of the nanorings, as well as the distribution of the Fe element on the substrate; thus, a continuous Fe layer and separated Fe discs on the substrate are created on substrate after washing, depending on the etching time and the shield of MCCs. The surviving Fe element can work as the catalyst to initiate the in situ growth of aligned CNTs in the following chemical vapor deposition (CVD) process, while the Fe element underneath the nanorings keep its inactivity. Eventually, CNT patterns with hierarchical structures are formed. One level originates from the surviving Fe layer; the other level is templated from the nanoring structures, which cause the blank area in the CNT bundles.