RESUMEN
Focused ion beam (FIB) technology has become a promising technique in micro- and nano-prototyping due to several advantages over its counterparts such as direct (maskless) processing, sub-10 nm feature size, and high reproducibility. Moreover, FIB machining can be effectively implemented on both conventional planar substrates and unconventional curved surfaces such as optical fibers, which are popular as an effective medium for telecommunications. Optical fibers have also been widely used as intrinsically light-coupled substrates to create a wide variety of compact fiber-optic devices by FIB milling diverse micro- and nanostructures onto the fiber surface (endfacet or outer cladding). In this paper, the broad applications of the FIB technology in optical fibers are reviewed. After an introduction to the technology, incorporating the FIB system and its basic operating modes, a brief overview of the lab-on-fiber technology is presented. Furthermore, the typical and most recent applications of the FIB machining in optical fibers for various applications are summarized. Finally, the reviewed work is concluded by suggesting the possible future directions for improving the micro- and nanomachining capabilities of the FIB technology in optical fibers.
RESUMEN
Vertical stacking of monolayers via van der Waals (vdW) assembly is an emerging field that opens promising routes toward engineering physical properties of two-dimensional materials. Industrial exploitation of these engineering heterostructures as robust functional materials still requires bounding their measured properties so as to enhance theoretical tractability and assist in experimental designs. Specifically, the short-range attractive vdW forces are responsible for the adhesion of chemically inert components and are recognized to play a dominant role in the functionality of these structures. Here, we reliably quantify the strength of ambient vdW forces in terms of an effective Hamaker coefficient for chemical vapor deposition-grown graphene and show how it scales by a factor of two or three from single to multiple layers on standard supporting surfaces such as copper or silicon oxide. Furthermore, direct measurements on freestanding graphene provide the means to discern the interplay between the vdW potential of graphene and its supporting substrate. Our results demonstrated that the underlying substrates could be controllably exploited to enhance or reduce the vdW force of graphene surfaces. We interpret the physical phenomena in terms of a Lifshitz theory-based analytical model.
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Spectrum splitting represents a valid alternative to multi-junction solar cells for broadband light-to-electricity conversion. While this concept has existed for decades, its adoption at the industrial scale is still stifled by high manufacturing costs and inability to scale to large areas. Here we report the experimental validation of a novel design that could allow the widespread adoption of spectrum splitting as a low-cost approach to high efficiency photovoltaic conversion. Our system consists of a prismatic lens that can be manufactured using the same methods employed for conventional CPV optic production, and two inexpensive CuInGaSe(2) (CIGS) solar cells having different composition and, thus, band gaps. We demonstrate a large improvement in cell efficiency under the splitter and show how this can lead to substantial increases in system output at competitive cost using existing technologies.
RESUMEN
Despite the current interest in the scientific community in exploiting divergent surface properties of graphitic carbon allotropes, conclusive differentiation remains elusive even when dealing with parameters as fundamental as adhesion. Here, we set out to provide conclusive experimental evidence on the time evolution of the surface properties of highly oriented pyrolytic graphite (HOPG), graphene monolayer (GML) and multiwalled carbon nanotubes (MWCNTs) as we expose these materials to airborne contaminants, by providing (1) statistically significant results based on large datasets consisting of thousands of force measurements, and (2) errors sufficiently self-consistent to treat the comparison between datasets in atomic force microscopy (AFM) measurements. We first consider HOPG as a model system and then employ our results to draw conclusions from the GML and MWCNT samples. We find that the surface properties of aged HOPG are indistinguishable from those of aged GML and MWCNT, while being distinct from those of cleaved HOPG. Herein, we provide a sufficient body of evidence to disregard any divergence in surface properties for multidimensional sp (2) carbon allotropes that undergo similar aging processes.
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We present a proof of concept demonstration of a novel optical element: a light-responsive aperture that can track a moving light beam. The element is created using a thermally-activated transparency-switching material composed of paraffin wax and polydimethylsiloxane (PDMS). Illumination of the material with a focused beam causes the formation of a localized transparency at the focal spot location, due to local heating caused by absorption of a portion of the incident light. An application is proposed in a new design for a self-tracking solar collector.
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Maintaining reliable energy supplies with resilience to extreme weather, water shortage and rising electricity and cooling demand is crucial to successfully implementing the clean energy transition. The integrated power and water systems found in several hyper-arid countries, featuring cooling-driven electrical demand and near-total dependence on seawater desalination, offer case studies illustrating energy system robustness to these conditions. We use linear optimization to minimize costs in a model system based on the resiliency-oriented energy system of the United Arab Emirates (UAE) while progressively decarbonizing the energy mix. We demonstrate that high levels of renewable energy adoption are economically favorable under conservative future technology cost assumptions, even including strict resiliency requirements, and draw conclusions for other energy systems making the transition to renewable energy under challenging climatic conditions, especially regarding the role of water desalination, demand flexibility, energy storage, and suitability of conventional design rules for ensuring resilience in renewable-dominated systems.
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In this work, we study the surface energy of monolayer, bilayer and multilayer graphene coatings, produced through exfoliation of natural graphite flakes and chemical vapor deposition. We employ bimodal atomic force microscopy and micro-Raman spectroscopy for high spatial resolution and large area scanning of force of adhesion on the regions of the graphene/SiO2 surface with different graphene layers. Our measurements show that the interface conditions between graphene and SiO2 dominate the experimentally observed graphene surface energy. This finding sheds new light on the controversy surrounding graphene transparency studies. By separating the surface energy into polar and non-polar interactions, our findings suggest that monolayer graphene is nearly van der Waals opaque but partially transparent (near 60%) to polar interactions, which is further supported by characterizing graphene on the copper surface and two levels of density functional theory simulation. In addition to providing quantitative insight into the surface interactions of complicated graphene coatings, this work demonstrates a new route to nondestructively monitor the interface between graphene and coated substrates.