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Register a new userMultichannel remote polarization control enabled by nanostructured Liquid Crystalline Networks
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Added by
Fabrizio Sgrignuoli
Publication date
2019
fields
Physics
and research's language is
English
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In this article we demonstrate that a grating fabricated through nanoscale volumetric crosslinking of a liquid crystalline polymer enables remote polarization control over the diffracted channels. This functionality is a consequence of the responsivity of liquid crystal networks upon light stimuli. Tuning the photonic response of the device is obtained thanks to both a refractive index and a shape change of the grating elements induced by a molecular rearrangement under irradiation. In particular, the material anisotropy allows for nontrivial polarization state management over multiple beams. Absence of any liquid component and a time response down to 0.2 milliseconds make our device appealing in the fields of polarimetry and optical communications.
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Accurate extraction of liquid is the first step towards low-volume liquid delivery and nanocharacterization, which plays a significant role in biomedical research. In this study, a tip-shaped graphene nanopipette (GNP) is proposed by encapsulating the biomolecule solution on the prefabricated metal tip with graphene. The volume of the encapsulated liquid is highly controllable at zeptoliter precision by tuning the encapsulating speed and the number of graphene encapsulation rounds. Using protein (ferritin) solution as an example, it has been confirmed by finite element analysis and the controlled experiments that the GNP allows the delivery of ferritin solution at the zeptoliter-scale. Furthermore, GNP is demonstrated as a new type of tip-shaped liquid cell, which is suitable for multiple nanocharacterization techniques. In particular, due to the ultra-sharp tip shape, isotope (13C)-labelled glucose solution encapsulated in GNP has been characterized by atom probe tomography (APT) in the laser-pulsed mode. Analysis of the mass spectrum and the reconstructed three-dimensional chemical maps reveals the quantitative distribution and the compositions of individual glucose molecules. The GNP is expected to be introduced to deliver liquid in the range of zeptoliters to attoliters, and brings a new capability for characterization of biological specimens in their near-native state.
Unlike conventional optics, plasmonics enables unrivalled concentration of optical energy well beyond the diffraction limit of light. However, a significant part of this energy is dissipated as heat. Plasmonic losses present a major hurdle in the development of plasmonic devices and circuits that can compete with other mature technologies. Until recently, they have largely kept the use of plasmonics to a few niche areas where loss is not a key factor, such as surface enhanced Raman scattering and biochemical sensing. Here, we discuss the origin of plasmonic losses and various approaches to either minimize or mitigate them based on understanding of fundamental processes underlying surface plasmon modes excitation and decay. Along with the ongoing effort to find and synthesize better plasmonic materials, optical designs that modify the optical powerflow through plasmonic nanostructures can help in reducing both radiative damping and dissipative losses of surface plasmons. Another strategy relies on the development of hybrid photonic-plasmonic devices by coupling plasmonic nanostructures to resonant optical elements. Hybrid integration not only helps to reduce dissipative losses and radiative damping of surface plasmons, but also makes possible passive radiative cooling of nano-devices. Finally, we review emerging applications of thermoplasmonics that leverage Ohmic losses to achieve new enhanced functionalities. The most successful commercialized example of a loss-enabled novel application of plasmonics is heat-assisted magnetic recording. Other promising technological directions include thermal emission manipulation, cancer therapy, nanofabrication, nano-manipulation, plasmon-enabled material spectroscopy and thermo-catalysis, and solar water treatment.
Electron correlations amplify quantum fluctuations and, as such, they have been recognized as the origin of a rich landscape of quantum phases. Whether and how they lead to gapless topological states is an outstanding question, and a framework that allows for determining novel phases and identifying new materials is in pressing need. Here we advance a general approach, in which strong correlations cooperate with crystalline symmetry to drive gapless topological states. We test this design principle by exploring Kondo lattice models and materials whose space group symmetries may promote different kinds of electronic degeneracies, with a particular focus on square-net systems. Weyl-Kondo nodal-line semimetals -- with nodes pinned to the Fermi energy -- are identified in both two and three dimensions. We apply the approach to identify materials for the realization of these correlation-driven topological semimetal phases. Our findings illustrate the potential of the proposed design principle to guide the search for new topological phases and materials in a broad range of strongly correlated systems.
The coupling of laser light to matter can exert sub-cycle coherent control over material properties, with optically induced currents and magnetism shown to be controllable on ultrafast femtosecond time scales. Here, by employing laser light consisting of both linear and circular pulses, we show that charge of specified spin and crystal momentum can be created with precision throughout the first Brillouin zone. Our hybrid pulses induce in a controlled way both adiabatic intraband motion as well as vertical interband excitation between valence and conduction bands, and require only a gapped spin split valley structure for their implementation. This scenario is commonly found in the 2d semi-conductors, and we demonstrate our approach with monolayer WSe$_2$. We thus establish a route from laser light to local control over excitations in reciprocal space, opening the way to the preparation of momenta specified excited states at ultrafast time scales.
We propose a concentrated thermionic emission solar cell design, which demonstrates a high solar-to-electricity energy conversion efficiency larger than 10% under 600 sun, by harnessing the exceptional electrical, thermal and radiative properties of the graphene as a collector electrode. By constructing an analytical model that explicitly takes into account the non-Richardson behavior of the thermionic emission current from graphene, space charge effect in vacuum gap, and the various irreversible energy losses within the subcomponents, we perform a detailed characterization on the conversion efficiency limit and electrical power output characteristics of the proposed system. We systematically model and compare the energy conversion efficiency of various configurations of graphene-graphene and graphene-diamond and diamond-diamond thermionic emitter, and show that utilizing diamond films as an emitter and graphene as a collector offers the highest maximum efficiency, thus revealing the important role of graphene in achieving high-performance thermionic emission solar cell. A maximum efficiency of 12.8% under 800 sun has been revealed, which is significantly higher than several existing solid-state solar cell designs, such as the solar-driven thermoelectric and thermophotovoltaic converters. Our work thus opens up new avenues to advance the efficiency limit of thermionic solar energy conversion and the development of next-generation novel-nanomaterial-based solar energy harvesting technology.
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