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We combine ultrafast electron diffraction and time-resolved terahertz spectroscopy measurements to link structure and electronic transport properties during the photoinduced insulator-metal transitions in vanadium dioxide. We determine the structure of the metastable monoclinic metal phase, which exhibits antiferroelectric charge order arising from a thermally activated, orbital-selective phase transition in the electron system. The relative contribution of the photoinduced monoclinic and rutile metals to the time-dependent and pump-fluence-dependent multiphase character of the film is established, as is the respective impact of these two distinct phase transitions on the observed changes in terahertz conductivity. Our results represent an important example of how light can control the properties of strongly correlated materials and demonstrate that multimodal experiments are essential when seeking a detailed connection between ultrafast changes in optical-electronic properties and lattice structure., Competing Interests: The authors declare no conflict of interest.

This work reports on the fabrication and characterization of a graphene based variable optical attenuator integrated on a photonic Si 3 N 4 waveguide and operating at 855 nm wavelength. The variable optical attenuator utilizes the gate voltage dependent optical absorption of a graphene layer, located in the evanescent field of the waveguide. A maximum attenuation of 17 dB is obtained at -3 V gate voltages for a device length of 700 µm. The measured voltage dependent absorption was found to be in good agreement with theoretical simulations, taking into account inter- and intra-band optical conductivity of graphene. An outlook is given on possible margins for increasing the operation speed and reducing the insertion loss of the device, using an optimized layout and improved fabrication processes.

Vertical metal-insulator-graphene (MIG) diodes for radio frequency (RF) power detection are realized using a scalable approach based on graphene grown by chemical vapor deposition and TiO 2 as barrier material. The temperature dependent current flow through the diode can be described by thermionic emission theory taking into account a bias induced barrier lowering at the graphene TiO 2 interface. The diodes show excellent figures of merit for static operation, including high on-current density of up to 28 A cm -2 , high asymmetry of up to 520, strong maximum nonlinearity of up to 15, and large maximum responsivity of up to 26 V -1 , outperforming state-of-the-art metal-insulator-metal and MIG diodes. RF power detection based on MIG diodes is demonstrated, showing a responsivity of 2.8 V W -1 at 2.4 GHz and 1.1 V W -1 at 49.4 GHz.

Thermo-optical tuning of the refractive index is one of the pivotal operations performed in integrated silicon photonic circuits for thermal stabilization, compensation of fabrication tolerances, and implementation of photonic operations. Currently, heaters based on metal wires provide the temperature control in the silicon waveguide. The strong interaction of metal and light, however, necessitates a certain gap between the heater and the photonic structure to avoid significant transmission loss. Here we present a graphene heater that overcomes this constraint and enables an energy efficient tuning of the refractive index. We achieve a tuning power as low as 22 mW per free spectral range and fast response time of 3 µs, outperforming metal based waveguide heaters. Simulations support the experimental results and suggest that for graphene heaters the spacing to the silicon can be further reduced yielding the best possible energy efficiency and operation speed.

The excellent electronic and mechanical properties of graphene provide a perfect basis for high performance flexible electronic and sensor devices. Here, we present the fabrication and characterization of flexible graphene based Hall sensors. The Hall sensors are fabricated on 50 μm thick flexible Kapton foil using large scale graphene grown by chemical vapor deposition technique on copper foil. Voltage and current normalized sensitivities of up to 0.096 V VT(-1) and 79 V AT(-1) were measured, respectively. These values are comparable to the sensitivity of rigid silicon based Hall sensors and are the highest values reported so far for any flexible Hall sensor devices. The sensitivity of the Hall sensor shows no degradation after being bent to a minimum radius of 4 mm, which corresponds to a tensile strain of 0.6%, and after 1000 bending cycles to a radius of 5 mm.

The sensitivity of graphene based devices to surface adsorbates and charge traps at the graphene/dielectric interface requires proper device passivation in order to operate them reproducibly under ambient conditions. Here we report on the use of atomic layer deposited aluminum oxide as passivation layer on graphene field effect devices (GFETs). We show that successful passivation produce hysteresis free DC characteristics, low doping level GFETs stable over weeks though operated and stored in ambient atmosphere. This is achieved by selecting proper seed layer prior to deposition of encapsulation layer. The passivated devices are also demonstrated to be robust towards the exposure to chemicals and heat treatments, typically used during device fabrication. Additionally, the passivation of high stability and reproducible characteristics is also shown for functional devices like integrated graphene based inverters.

We report on a method for the fabrication of graphene on a silicon dioxide substrate by solid-state dissolution of an overlying stack of a silicon carbide and a nickel thin film. The carbon dissolves in the nickel by rapid thermal annealing. Upon cooling, the carbon segregates to the nickel surface forming a graphene layer over the entire nickel surface. By wet etching of the nickel layer, the graphene layer was allowed to settle on the original substrate. Scanning tunneling microscopy (STM) as well as Raman spectroscopy has been performed for characterization of the layers. Further insight into the morphology of the layers has been gained by Raman mapping indicating micrometer-size graphene grains. Devices for electrical measurement have been manufactured exhibiting a modulation of the transfer current by backgate electric fields. The presented approach allows for mass fabrication of polycrystalline graphene without transfer steps while using only CMOS compatible process steps.

Objectives: In Switzerland there is a shortage of population-based information on heart failure (HF) incidence and case fatalities (CF). The aim of this study was to estimate HF event rates and both in- and out-of-hospital CF rates., Methods: Data on HF diagnoses coded according to I 50 (ICD 10) were taken from the Federal Hospital Statistics Database and the Cause of Death Database for the year 2005., Results: Although the total estimated number of HF events was higher for women (n = 4,201) than for men (n = 3,819), men showed higher numbers up to age group 65-74. Looking at age-specific HF cases per 100,000 population, men had higher rates in all age groups. The latter is also true of the age-standardised HF event rate (82.9/100,000 versus 51.4/100,000 population). Overall, CF was 26.3% and higher for women (32.2%) than for men (19.8%). The same is true of out-of-hospital CF but not of in-hospital CF., Conclusion: The HF event rate was 20% higher than the HF hospital discharge rate. Out-of-hospital death from HF accounted for the largest proportion of total HF deaths. Sex differences in both the number of HF events and HF event rates can be explained by the larger number of women than men aged 55+ in the Swiss population.

Enkephalin-deficient knockout mice, a genetic model of enhanced anxiety responses, and wild-type controls were housed in two separate facilities on the same campus using different caging systems. Stress reactivity was evaluated in these animals using a zero-maze test followed by c-Fos expression analysis in limbic brain regions. Animals with genetically or pharmacologically enhanced anxiety reared and tested in the same facility displayed similar behavioral reactivity and c-Fos induction. However, we found much stronger anxiety-related behavioral responses and higher c-Fos levels when animals were house in individually ventilated cages, independent of their genetic background.