Single crystal diamond membranes for nanoelectronics.

Single crystal, nanoscale diamond membranes are highly sought after for a variety of applications including nanophotonics, nanoelectronics and quantum information science. However, so far, the availability of conductive diamond membranes has remained an unreachable goal. In this work we present a complete nanofabrication methodology for engineering high aspect ratio, electrically active single crystal diamond membranes. The membranes have large lateral directions, exceeding ∼500 × 500 µm2 and are only several hundreds of nanometers thick. We further realize vertical single crystal p-n junctions made from the diamond membranes that exhibit onset voltages of ∼10 V and a current of several mA. Moreover, we deterministically introduce optically active color centers into the membranes, and demonstrate for the first time a single crystal nanoscale diamond LED. The robust and scalable approach to engineer the electrically active single crystal diamond membranes offers new pathways for advanced nanophotonic, nanoelectronic and optomechanical devices employing diamond.

A Sub-millimeter, Inductively Powered Neural Stimulator.

Wireless neural stimulators are being developed to address problems associated with traditional lead-based implants. However, designing wireless stimulators on the sub-millimeter scale (<1 mm3) is challenging. As device size shrinks, it becomes difficult to deliver sufficient wireless power to operate the device. Here, we present a sub-millimeter, inductively powered neural stimulator consisting only of a coil to receive power, a capacitor to tune the resonant frequency of the receiver, and a diode to rectify the radio-frequency signal to produce neural excitation. By replacing any complex receiver circuitry with a simple rectifier, we have reduced the required voltage levels that are needed to operate the device from 0.5 to 1 V (e.g., for CMOS) to ~0.25-0.5 V. This reduced voltage allows the use of smaller receive antennas for power, resulting in a device volume of 0.3-0.5 mm3. The device was encapsulated in epoxy, and successfully passed accelerated lifetime tests in 80°C saline for 2 weeks. We demonstrate a basic proof-of-concept using stimulation with tens of microamps of current delivered to the sciatic nerve in rat to produce a motor response.

Quantum-confined single photon emission at room temperature from SiC tetrapods.

Controlled engineering of isolated solid state quantum systems is one of the most prominent goals in modern nanotechnology. In this letter we demonstrate a previously unknown quantum system namely silicon carbide tetrapods. The tetrapods have a cubic polytype core (3C) and hexagonal polytype legs (4H)--a geometry that creates spontaneous polarization within a single tetrapod. Modeling of the tetrapod structures predicts that a bound exciton should exist at the 3C-4H interface. The simulations are confirmed by the observation of fully polarized and narrowband single photon emission from the tetrapods at room temperature. The single photon emission provides important insights into understanding the quantum confinement effects in non-spherical nanostructures. Our results pave the way to a new class of crystal phase nanomaterials that exhibit single photon emission at room temperature and therefore are suitable for sensing, quantum information and nanophotonics.

The structure-function relationships of a natural nanoscale photonic device in cuttlefish chromatophores.

Cuttlefish, Sepia officinalis, possess neurally controlled, pigmented chromatophore organs that allow rapid changes in skin patterning and coloration in response to visual cues. This process of adaptive coloration is enabled by the 500% change in chromatophore surface area during actuation. We report two adaptations that help to explain how colour intensity is maintained in a fully expanded chromatophore when the pigment granules are distributed maximally: (i) pigment layers as thin as three granules that maintain optical effectiveness and (ii) the presence of high-refractive-index proteins-reflectin and crystallin-in granules. The latter discovery, combined with our finding that isolated chromatophore pigment granules fluoresce between 650 and 720 nm, refutes the prevailing hypothesis that cephalopod chromatophores are exclusively pigmentary organs composed solely of ommochromes. Perturbations to granular architecture alter optical properties, illustrating a role for nanostructure in the agile, optical responses of chromatophores. Our results suggest that cephalopod chromatophore pigment granules are more complex than homogeneous clusters of chromogenic pigments. They are luminescent protein nanostructures that facilitate the rapid and sophisticated changes exhibited in dermal pigmentation.

Photoluminescent SiC tetrapods.

Recently, significant research efforts have been made to develop complex nanostructures to provide more sophisticated control over the optical and electronic properties of nanomaterials. However, there are only a handful of semiconductors that allow control over their geometry via simple chemical processes. Herein, we present a molecularly seeded synthesis of a complex nanostructure, SiC tetrapods, and report on their structural and optical properties. The SiC tetrapods exhibit narrow line width photoluminescence at wavelengths spanning the visible to near-infrared spectral range. Synthesized from low-toxicity, earth abundant elements, these tetrapods are a compelling replacement for technologically important quantum optical materials that frequently require toxic metals such as Cd and Se. This previously unknown geometry of SiC nanostructures is a compelling platform for biolabeling, sensing, spintronics, and optoelectronics.

Virus-templated iridium oxide-gold hybrid nanowires for electrochromic application.

A highly porous electrode comprised of biologically templated iridium oxide-gold (IrO(2)-Au) hybrid nanowires is introduced for electrochromic applications. A filamentous M13 virus is genetically engineered to display IrO(2)-binding peptides on the viral surface and used as a template for the self-assembly of IrO(2) nanoclusters into a nanowire. The open porous morphology of the prepared nanowire film facilitates ion transport. Subsequently, the redox kinetics of the IrO(2) nanowires seems to be limited by the electric resistance of the nanowire film. To increase the electron mobility in the nanowires, gold nanoparticles are chemically linked to the virus prior to the IrO(2) mineralization, forming a gold nanostring structure along the long axis of the virus. The resulting IrO(2)-Au hybrid nanowires exhibit a switching time of 35 ms for coloration and 25 ms for bleaching with a transmission change of about 30.5% at 425 nm. These values represent almost an order of magnitude faster switching responses than those of an IrO(2) nanowire film having the similar optical contrast. This work shows that genetically engineered viruses can serve as versatile templates to co-assemble multiple functional molecules, enabling control of the electrochemical properties of nanomaterials.

Coupling of silicon-vacancy centers to a single crystal diamond cavity.

Optical coupling of an ensemble of silicon-vacancy (SiV) centers to single-crystal diamond microdisk cavities is demonstrated. The cavities are fabricated from a single-crystal diamond membrane generated by ion implantation and electrochemical liftoff followed by homo-epitaxial overgrowth. Whispering gallery modes spectrally overlap with the zero-phonon line (ZPL) of the SiV centers and exhibit quality factors ∼ 2200. Lifetime reduction from 1.8 ns to 1.48 ns is observed from SiV centers in the cavity compared to those in the membrane outside the cavity. These results are pivotal in developing diamond integrated photonics networks.

Homoepitaxial growth of single crystal diamond membranes for quantum information processing.

Homoepitaxial growth of single crystal diamond membranes is demonstrated employing a microwave plasma chemical vapor deposition technique. The membranes possess excellent structural, optical, and spin properties, which make them suitable for fabrication of optical microcavities for applications in quantum information processing, photonics, spintronics, and sensing.

Biologically templated photocatalytic nanostructures for sustained light-driven water oxidation.

Over several billion years, cyanobacteria and plants have evolved highly organized photosynthetic systems to shuttle both electronic and chemical species for the efficient oxidation of water. In a similar manner to reaction centres in natural photosystems, molecular and metal oxide catalysts have been used to photochemically oxidize water. However, the various approaches involving the molecular design of ligands, surface modification and immobilization still have limitations in terms of catalytic efficiency and sustainability. Here, we demonstrate a biologically templated nanostructure for visible light-driven water oxidation that uses a genetically engineered M13 virus scaffold to mediate the co-assembly of zinc porphyrins (photosensitizer) and iridium oxide hydrosol clusters (catalyst). Porous polymer microgels are used as an immobilization matrix to improve the structural durability of the assembled nanostructures and to allow the materials to be recycled. Our results suggest that the biotemplated nanoscale assembly of functional components is a promising route to significantly improved photocatalytic water-splitting systems.

Virus-templated assembly of porphyrins into light-harvesting nanoantennae.

Biological molecules can be used as versatile templates for assembling nanoscale materials because of their unique structures and chemical diversities. Supramolecular organization of molecular pigments, as is found in the natural light-harvesting antenna, has drawn attention for its potential applications to sensors, photocatalytic systems, and photonic devices. Here we show the arrangement of molecular pigments into a one-dimensional light-harvesting antenna using M13 viruses as scaffolds. Chemical grafting of zinc porphyrins to M13 viruses induces distinctive spectroscopic changes, including fluorescence quenching, the extensive band broadening and small red shift of their absorption spectrum, and the shortened lifetime of the excited states. Based on these optical signatures we suggest a hypothetical model to explain the energy transfer occurring in the supramolecular porphyrin structures templated with the virus. We expect that further genetic engineering of M13 viruses can allow us to coassemble other functional materials (e.g., catalysts and electron transfer mediators) with pigments, implying potential applications to photochemical devices.