DIRECT DETECTION OF PICOSECOND PULSES EMITTED BY AN INJECTION LASER WITH ACTIVE MODE LOCKING.

An Agat-SF linear-scan streak image-converter camera was used to record output pulses of 2. 7 psec duration generated by an injection laser with an external dispersive resonator operated in the active mode-locking regime. The duration of the pulses was determined by the reciprocal of the spectral width and the product of the duration and the spectral width was 0. 30.

Electron-beam-induced direct etching of graphene

We present electron-beam-induced oxidation of single- and bilayer graphene devices in a low-voltage scanning electron microscope. We show that the injection of oxygen leads to targeted etching at the focal point, enabling us to pattern graphene with a resolution of better than 20 nm. Voltage-contrast imaging, in conjunction with finite-element simulations, explain the secondary-electron intensities and correlate them to the etch profile. © 2013 Elsevier Ltd. All rights reserved.

Direct temperature mapping of nanoscale plasmonic devices.

Side by side with the great advantages of plasmonics in nanoscale light confinement, the inevitable ohmic loss results in significant joule heating in plasmonic devices. Therefore, understanding optical-induced heat generation and heat transport in integrated on-chip plasmonic devices is of major importance. Specifically, there is a need for in situ visualization of electromagnetic induced thermal energy distribution with high spatial resolution. This paper studies the heat distribution in silicon plasmonic nanotips. Light is coupled to the plasmonic nanotips from a silicon nanowaveguide that is integrated with the tip on chip. Heat is generated by light absorption in the metal surrounding the silicon nanotip. The steady-state thermal distribution is studied numerically and measured experimentally using the approach of scanning thermal microscopy. It is shown that following the nanoscale heat generation by a 10 mW light source within a silicon photonic waveguide the temperature in the region of the nanotip is increased by ∼ 15 °C compared with the ambient temperature. Furthermore, we also perform a numerical study of the dynamics of the heat transport. Given the nanoscale dimensions of the structure, significant heating is expected to occur within the time frame of picoseconds. The capability of measuring temperature distribution of plasmonic structures at the nanoscale is shown to be a powerful tool and may be used in future applications related to thermal plasmonic applications such as control heating of liquids, thermal photovoltaic, nanochemistry, medicine, heat-assisted magnetic memories, and nanolithography.

Direct detection of molecular biorecognition by dipole sensing mechanism.

This work investigates the feasibility of transducing molecular-recognition events into a measurable potentiometric signal. It is shown for the first time that biorecognition of acetylcholine (ACh) can be translated to conformational changes in the enzyme, acetylcholine-esterase (AChE), which in turn induces a measurable change in surface potential. Our results show that a highly sensitive detector for ACh can be obtained by the dilute assembly of AChE on a floating gate derived field effect transistor (FG-FET). A wide concentration range response is observed for ACh (10(-2)-10(-9)M) and for the inhibitor carbamylcholine CCh (10(-6)-10(-11)M). These enhanced sensitivities are modeled theoretically and explained by the combined response of the device to local pH changes and molecular dipole variations due to the enzyme-substrate recognition event.

High resolution direct measurement of temperature distribution in silicon nanophotonics devices.

Following the miniaturization of photonic devices and the increase in data rates, the issues of self heating and heat removal in active nanophotonic devices should be considered and studied in more details. In this paper we use the approach of Scanning Thermal Microscopy (SThM) to obtain an image of the temperature field of a silicon micro ring resonator with sub-micron spatial resolution. The temperature rise in the device is a result of self heating which is caused by free carrier absorption in the doped silicon. The temperature is measured locally and directly using a temperature sensitive AFM probe. We show that this local temperature measurement is feasible in the photonic device despite the perturbation that is introduced by the probe. Using the above method we observed a significant self heating of about 10 degrees within the device.

A parametrically excited vibration energy harvester

In the arena of vibration energy harvesting, the key technical challenges continue to be low power density and narrow operational frequency bandwidth. While the convention has relied upon the activation of the fundamental mode of resonance through direct excitation, this article explores a new paradigm through the employment of parametric resonance. Unlike the former, oscillatory amplitude growth is not limited due to linear damping. Therefore, the power output can potentially build up to higher levels. Additionally, it is the onset of non-linearity that eventually limits parametric resonance; hence, this approach can also potentially broaden the operating frequency range. Theoretical prediction and numerical modelling have suggested an order higher in oscillatory amplitude growth. An experimental macro-sized electromagnetic prototype (practical volume of ∼1800 cm3) when driven into parametric resonance, has demonstrated around 50% increase in half power band and an order of magnitude higher peak power density normalised against input acceleration squared (293 μW cm-3 m-2 s4 with 171.5 mW at 0.57 m s-2) in contrast to the same prototype directly driven at fundamental resonance (36.5 μW cm-3 m-2 s4 with 27.75 mW at 0.65 m s-2). This figure suggests promising potentials while comparing with current state-of-the-art macro-sized counterparts, such as Perpetuum's PMG-17 (119 μW cm-3 m-2 s4). © The Author(s) 2013.

Direct measurement of the vortex migration caused by traveling magnetic wave

We studied the magnetisation of a 2 in. diameter YBCO thin film in the presence of traveling magnetic waves with six hall sensors. Simulation based on finite element method was conducted to reproduce the process of magnetisation. We discovered that the magnetisation of YBCO thin film based on traveling waves does not follow the constant current density assumption as used in the standing wave condition. We have shown that the traveling wave is more efficient in transporting the flux into the YBCO thin film, which suggests the potential of a flux injection device for high temperature superconducting coils. © 2014 AIP Publishing LLC.

Chirp-enhanced direct modulation of a monolithic sub-Terahertz dual laser transmitter

A technique enabling 10 Gbps data to be directly modulated onto a monolithic sub-THz dual laser transmitter is proposed. As a result of the laser chirp, the logical zeros of the resultant sub-THz signal have a different peak frequency from that of the logical ones. The signal extinction ratio is therefore enhanced by suppressing the logical zeros with a filter stage at the receiver. With the aid of the chirp-enhanced filtering, an improved extinction ratio can be achieved at moderate modulation current. Hence, 10 GHz modulation bandwidth of the transmitter is predicted without the need for external modulators. In this paper, we demonstrate the operational principle by generating an error-free (bit error rate less than 10-9) 100 Mbps Manchester encoded signal with a centre frequency of 12 GHz within the bandwidth of an envelope detector, whilst direct modulation of a 100 GHz signal at data rates of up to 10 Gbps is simulated by using a transmission line model. This work could be a key technique for enabling monolithic sub-THz transmitters to be readily used in high speed wireless links. © 2013 IEEE.

Local strain rate and curvature dependences of scalar dissipation rate transport in turbulent premixed flames: A direct numerical simulation analysis

The statistical behaviours of the instantaneous scalar dissipation rate Nc of reaction progress variable c in turbulent premixed flames have been analysed based on three-dimensional direct numerical simulation data of freely propagating statistically planar flame and V-flame configurations with different turbulent Reynolds number Ret. The statistical behaviours of N c and different terms of its transport equation for planar and V-flames are found to be qualitatively similar. The mean contribution of the density-variation term T1 is positive, whereas the molecular dissipation term (-D2) acts as a leading order sink. The mean contribution of the strain rate term T2 is predominantly negative for the cases considered here. The mean reaction rate contribution T3 is positive (negative) towards the unburned (burned) gas side of the flame, whereas the mean contribution of the diffusivity gradient term (D) assumes negative (positive) values towards the unburned (burned) gas side. The local statistical behaviours of Nc, T1, T2, T 3, (-D2), and f(D) have been analysed in terms of their marginal probability density functions (pdfs) and their joint pdfs with local tangential strain rate aT and curvature km. Detailed physical explanations have been provided for the observed behaviour. © 2014 Y. Gao et al.

Parametric resonance for vibration energy harvesting with design techniques to passively reduce the initiation threshold amplitude

A vibration energy harvester designed to access parametric resonance can potentially outperform the conventional direct resonant approach in terms of power output achievable given the same drive acceleration. Although linear damping does not limit the resonant growth of parametric resonance, a damping dependent initiation threshold amplitude exists and limits its onset. Design approaches have been explored in this paper to passively overcome this limitation in order to practically realize and exploit the potential advantages. Two distinct design routes have been explored, namely an intrinsically lower threshold through a pendulum-lever configuration and amplification of base excitation fed into the parametric resonator through a cantilever-initial-spring configuration. Experimental results of the parametric resonant harvesters with these additional enabling designs demonstrated an initiation threshold up to an order of magnitude lower than otherwise, while attaining a much higher power peak than direct resonance. © 2014 IOP Publishing Ltd.

Direct epitaxial growth of θ-Ni2Si by reaction of a thin Ni(10 at.% Pt) film with Si(1 0 0) substrate

The reaction between an 11 nm Ni(10 at.% Pt) film on a Si substrate has been examined by in situ X-ray diffraction (XRD), atom probe tomography (APT) and transmission electron microscopy (TEM). In situ XRD experiments show the unusual formation of a phase without an XRD peak through consumption of the metal. According to APT, this phase has an Si concentration gradient in accordance with the θ-Ni2Si metastable phase. TEM analysis confirms the direct formation of θ-Ni2Si in epitaxy on Si(1 0 0) with two variants of the epitaxial relationship. © 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.