Twisted Nano-optics: Manipulating Light at the Nanoscale with Twisted Phonon Polaritonic Slabs

Recent discoveries have shown that when two layers of van der Waals (vdW) materials are superimposed with a relative twist angle between their respective in-plane principal axes, the electronic properties of the coupled system can be dramatically altered. Here, we demonstrate that a similar concept can be extended to the optics realm, particularly to propagating polaritons, hybrid light-matter interactions. To do this, we fabricate stacks composed of two twisted slabs of a polar vdW crystal (MoO3) supporting low-loss anisotropic phonon polaritons (PhPs), and image the propagation of the latter when launched by localized sources (metal antennas). Our images reveal that under a critical angle the PhPs isofrequency curve (determining the PhPs momentum at a fixed frequency) undergoes a topological transition. Remarkably, at this angle, the propagation of PhPs is strongly guided along predetermined directions (canalization regime) with no geometrical spreading (diffraction-less). These results demonstrate a new degree of freedom (twist angle) for controlling the propagation of polaritons at the nanoscale with potential for nano-imaging, (bio)-sensing, quantum applications and heat management

The influence of the method of an arc discharge initiation on the product of plasma dynamic synthesis in the W-C system

Cubic tungsten carbide WC1-x is distinguished by the difficulty of obtaining in a dispersed and bulk form. The article attempts to plasma dynamic synthesis of cubic tungsten carbide in powder form. The method is based on the use of a coaxial magnetoplasma accelerator for the generating a supersonic plasma jet, which is then rapidly cooled. The possibility of obtaining a powder with a predominant content of WC1-x (up to 95%) is shown. Studying the influence of the method of an arc discharge initiation allowed to reveal the efficiency of using graphitization in comparison with carbon fibers

Femtomolar detection of the heart failure biomarker NT-proBNP in artificial saliva using an immersible liquid-gated aptasensor with reduced graphene oxide

Measuring NT-proBNP biomarker is recommended for preliminary diagnostics of the heart failure. Recent studies suggest a possibility of early screening of biomarkers in saliva for non-invasive identification of cardiac diseases at the point-of-care. However, NT-proBNP concentrations in saliva can be thousand time lower than in blood plasma, going down to pg/mL level. To reach this level, we developed a label-free aptasensor based on a liquid-gated field effect transistor using a film of reduced graphene oxide monolayer (rGO-FET) with immobilized NT-proBNP specific aptamer. We found that, depending on ionic strength of tested solutions, there were different levels of correlation in responses of electrical parameters of the rGO-FET aptasensor, namely, the Dirac point shift and transconductance change. The correlation in response to NT-proBNP was high for 1.6 mM phosphate-buffered saline (PBS) and zero for 16 mM PBS in a wide range of analyte concentrations, varied from 1 fg/mL to 10 ng/mL. The effects of transconductance and Dirac point shift in PBS solutions of different concentrations are discussed. The biosensor exhibited a high sensitivity for both transconductance (2 uS/decade) and Dirac point shift (2.3 mV/decade) in diluted PBS with the linear range from 10 fg/mL to 1 pg/mL. The aptasensor performance has been also demonstrated in undiluted artificial saliva with the achieved limit of detection down to 41 fg/mL (~4.6 fM)

Session Types for the Transport Layer: Towards an Implementation of TCP

Session types are a typing discipline used to formally describe communication-driven applications with the aim of fewer errors and easier debugging later into the life cycle of the software. Protocols at the transport layer such as TCP, UDP, and QUIC underpin most of the communication on the modern Internet and affect billions of end-users. The transport layer has different requirements and constraints compared to the application layer resulting in different requirements for verification. Despite this, to our best knowledge, no work shows the application of session types at the transport layer. In this work, we discuss how multiparty session types (MPST) can be applied to implement the TCP protocol. We develop an MPST-based implementation of a subset of a TCP server in Rust and test its interoperability against the Linux TCP stack. Our results highlight the differences in assumptions between session type theory and the way transport layer protocols are usually implemented. This work is the first step towards bringing session types into the transport layer

Deposition of cubic tungsten carbide coating on metal substrates at sputtering of electric discharge plasma

Hexagonal modifications of tungsten carbide are widely used in various metalworking products and tools. However, the cubic tungsten carbide phase is still poorly understood due to significant difficulties in its synthesis, both in the form of powdered products, and in bulk form. This leads to the impossibility of conducting direct studies of its physical and mechanical properties. This paper shows the opportunity to obtain bulk coatings with a thickness of up to 70 µm, mainly consisting of cubic tungsten carbide using the plasma-dynamic method. The coating formation occurs when spraying the electric discharge tungsten-carbon containing plasma on a metal substrate made of a titanium and aluminum alloy due to the high rate of sputtering and crystallization. This allows synthesizing a stable coating adherent to the substrate based on cubic tungsten carbide with a purity of its yield of at least 85 wt.%

Deposition of cubic tungsten carbide coating on metal substrates at sputtering of electric discharge plasma

Hexagonal modifications of tungsten carbide are widely used in various metalworking products and tools. However, the cubic tungsten carbide phase is still poorly understood due to significant difficulties in its synthesis, both in the form of powdered products, and in bulk form. This leads to the impossibility of conducting direct studies of its physical and mechanical properties. This paper shows the opportunity to obtain bulk coatings with a thickness of up to 70 µm, mainly consisting of cubic tungsten carbide using the plasma-dynamic method. The coating formation occurs when spraying the electric discharge tungsten-carbon containing plasma on a metal substrate made of a titanium and aluminum alloy due to the high rate of sputtering and crystallization. This allows synthesizing a stable coating adherent to the substrate based on cubic tungsten carbide with a purity of its yield of at least 85 wt.%

Enabling propagation of anisotropic polaritons along forbidden directions via a topological transition

Polaritons with directional in-plane propagation and ultralow losses in van der Waals (vdW) crystals promise unprecedented manipulation of light at the nanoscale. However, these polaritons present a crucial limitation: their directional propagation is intrinsically determined by the crystal structure of the host material, imposing forbidden directions of propagation. Here, we demonstrate that directional polaritons (in-plane hyperbolic phonon polaritons) in a vdW crystal (α-phase molybdenum trioxide) can be directed along forbidden directions by inducing an optical topological transition, which emerges when the slab is placed on a substrate with a given negative permittivity (4H–silicon carbide). By visualizing the transition in real space, we observe exotic polaritonic states between mutually orthogonal hyperbolic regimes, which unveil the topological origin of the transition: a gap opening in the dispersion. This work provides insights into optical topological transitions in vdW crystals, which introduce a route to direct light at the nanoscale