Antenna-assisted picosecond control of nanoscale phase transition in vanadium dioxide

Nanoscale devices in which the interaction with light can be configured using external control signals hold great interest for next-generation optoelectronic circuits. Materials exhibiting a structural or electronic phase transition offer a large modulation contrast with multi-level optical switching and memory functionalities. In addition, plasmonic nanoantennas can provide an efficient enhancement mechanism for both the optically induced excitation and the readout of materials strategically positioned in their local environment. Here, we demonstrate picosecond all-optical switching of the local phase transition in plasmonic antenna-vanadium dioxide (VO2) hybrids, exploiting strong resonant field enhancement and selective optical pumping in plasmonic hotspots. Polarization- and wavelength-dependent pump-probe spectroscopy of multifrequency crossed antenna arrays shows that nanoscale optical switching in plasmonic hotspots does not affect neighboring antennas placed within 100 nm of the excited antennas. The antenna-assisted pumping mechanism is confirmed by numerical model calculations of the resonant, antenna-mediated local heating on a picosecond time scale. The hybrid, nanoscale excitation mechanism results in 20 times reduced switching energies and 5 times faster recovery times than a VO2 film without antennas, enabling fully reversible switching at over two million cycles per second and at local switching energies in the picojoule range. The hybrid solution of antennas and VO2 provides a conceptual framework to merge the field localization and phase-transition response, enabling precise, nanoscale optical memory functionalities

Hybrid Photonics: Integration, Design and Devices: feature issue introduction

We introduce the Optical Materials Express feature issue on Hybrid Photonics: Integration, Design and Devices. This issue comprises a collection of ten papers including six invited and four contributed papers from well-established research groups and prominent scientists in the field. These papers cover the development, characterization, control, technologies and applications of hybrid devices for photonics

Resistive switching in silicon suboxide films

We report a study of resistive switching in a silicon-based memristor/resistive RAM (RRAM) device in which the active layer is silicon-rich silica. The resistive switching phenomenon is an intrinsic property of the silicon-rich oxide layer and does not depend on the diffusion of metallic ions to form conductive paths. In contrast to other work in the literature, switching occurs in ambient conditions, and is not limited to the surface of the active material. We propose a switching mechanism driven by competing field-driven formation and current-driven destruction of filamentary conductive pathways. We demonstrate that conduction is dominated by trap assisted tunneling through noncontinuous conduction paths consisting of silicon nanoinclusions in a highly nonstoichiometric suboxide phase. We hypothesize that such nanoinclusions nucleate preferentially at internal grain boundaries in nanostructured films. Switching exhibits the pinched hysteresis I/V loop characteristic of memristive systems, and on/off resistance ratios of 104:1 or higher can be easily achieved. Scanning tunneling microscopy suggests that switchable conductive pathways are 10 nm in diameter or smaller. Programming currents can be as low as 2 μA, and transition times are on the nanosecond scale

Single artificial atoms in silicon emitting at telecom wavelengths

Given its unrivaled potential of integration and scalability, silicon is likely to become a key platform for large-scale quantum technologies. Individual electron-encoded artificial atoms either formed by impurities or quantum dots have emerged as a promising solution for silicon-based integrated quantum circuits. However, single qubits featuring an optical interface needed for large-distance exchange of information have not yet been isolated in such a prevailing semiconductor. Here we show the isolation of single optically-active point defects in a commercial silicon-on-insulator wafer implanted with carbon atoms. These artificial atoms exhibit a bright, linearly polarized single-photon emission at telecom wavelengths suitable for long-distance propagation in optical fibers. Our results demonstrate that despite its small bandgap (~ 1.1 eV) a priori unfavorable towards such observation, silicon can accommodate point defects optically isolable at single scale, like in wide-bandgap semiconductors. This work opens numerous perspectives for silicon-based quantum technologies, from integrated quantum photonics to quantum communications and metrology

TSPO ligands stimulate ZnPPIX transport and ROS accumulation leading to the inhibition of P. falciparum growth in human blood

After invading red blood cells (RBCs), Plasmodium falciparum (Pf) can export its own proteins to the host membrane and activate endogenous channels that are present in the membrane of RBCs. This transport pathway involves the Voltage Dependent Anion Channel (VDAC). Moreover, ligands of the VDAC partner TranSlocator PrOtein (TSPO) were demonstrated to inhibit the growth of the parasite. We studied the expression of TSPO and VDAC isoforms in late erythroid precursors, examined the presence of these proteins in membranes of non-infected and infected human RBCs, and evaluated the efficiency of TSPO ligands in inhibiting plasmodium growth, transporting the haem analogue Zn-protoporphyrin-IX (ZnPPIX) and enhancing the accumulation of reactive oxygen species (ROS). TSPO and VDAC isoforms are differentially expressed on erythroid cells in late differentiation states. TSPO2 and VDAC are present in the membranes of mature RBCs in a unique protein complex that changes the affinity of TSPO ligands after Pf infection. TSPO ligands dose-dependently inhibited parasite growth, and this inhibition was correlated to ZnPPIX uptake and ROS accumulation in the infected RBCs. Our results demonstrate that TSPO ligands can induce Pf death by increasing the uptake of porphyrins through a TSPO2-VDAC complex, which leads to an accumulation of ROS

Yttrium implantation and addition element effects on high temperature oxidation behaviour of reference steels

Yttrium implanted and unimplanted various reference steels were oxidized at 700 °C, under controlled atmosphere (oxygen partial pressure: 0.04 Pa), for 24 h to observe the yttrium implantation and the addition element effects on steel high temperature oxidation behaviours. Yttrium implantation effects on reference steels were characterized using analytical and structural techniques such as Rutherford Backscattering Spectrometry (RBS), Reflection High Energy Electron Diffraction (RHEED), X-ray Diffraction (XRD) and Glancing Angle X-ray Diffraction (GAXRD). Yttrium implanted and unimplanted reference steel oxidation behaviours were observed by thermogravimetry and in situ high temperature X-ray diffraction. Our results clearly show that yttrium implantation and high temperature oxidation induced the formation of several yttrium mixed oxides which closely depend on the reference steel addition elements. Moreover, these yttrium mixed oxides seem to be responsible for the improved reference steel oxidation resistance at high temperature

Are volatile unsaturated aldehydes from diatoms the main line of chemical defence against copepods?

New experiments comparing the effects of 3 species of phytoplankton Prorocentrum minimum Schiller 1933 (PM), Thalassiosira rotula Meunier 1910 strains (TR1) and (TR2), and Skeletonema pseudocostatum (SPC) on the fecundity and egg- hatching rates of Cal