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arXiv2018

Selective intracellular delivery and intracellular recordings combined on MEA biosensors

Biological studies on in vitro cell cultures are of fundamental importance to investigate cells response to external stimuli, such as new drugs for treatment of specific pathologies, or to study communication between electrogenic cells. Although three-dimensional (3D) nanostructures brought tremendous improvements on biosensors used for various biological in vitro studies, including drug delivery and electrical recording, there is still a lack of multifunctional capabilities that could help gaining deeper insights in several bio-related research fields. In this work, the electrical recording of large cell ensembles and the intracellular delivery of few selected cells are combined on the same device by integrating microfluidics channels on the bottom of a multi-electrode array decorated with 3D hollow nanostructures. The novel platform allows to record intracellular-like action potentials from large ensembles of cardiomyocytes derived from human Induced Pluripotent Stem Cells (hiPSC) and from the HL-1 line, while different molecules are selectively delivered into single/few targeted cells. The proposed approach shows high potential for enabling new comprehensive studies that can relate drug effects to network level cell communication processes.

physics.app-ph↗
arXiv2018

Tunable Eight-Element MIMO Antenna Based on the Antenna Cluster Concept

Realizing capacity demands of future wireless communications requires improved spectral efficiency in the sub-6-GHz frequency bands. This paper proposes a novel eight-element multiple-input multiple-output (MIMO) antenna that can be tuned from 1.7 to 6 GHz. The design is based on the antenna cluster concept, where weighted feeding of multiple antenna elements is used to modify the operating frequency. This paper extends the theory of the concept to account for multiple separate clusters, thus enabling it to be used for MIMO. The proposed antenna achieves over 60% efficiency at frequencies above 3 GHz, and the system exceeds the ergodic capacity of the ideal 7x7 MIMO in that band.

eess.SP↗
arXiv2018

Asymptotic modelling of phononic box crystals

We introduce phononic box crystals, namely arrays of adjoined perforated boxes, as a three-dimensional prototype for an unusual class of subwavelength metamaterials based on directly coupling resonating elements. In this case, when the holes coupling the boxes are small, we create networks of Helmholtz resonators with nearest-neighbour interactions. We use matched asymptotic expansions, in the small hole limit, to derive simple, yet asymptotically accurate, discrete wave equations governing the pressure field. These network equations readily furnish analytical dispersion relations for box arrays, slabs and crystals, that agree favourably with finite-element simulations of the physical problem. Our results reveal that the entire acoustic branch is uniformly squeezed into a subwavelength regime; consequently, phononic box crystals exhibit nonlinear-dispersion effects (such as dynamic anisotropy) in a relatively wide band, as well as a high effective refractive index in the long-wavelength limit. We also study the sound field produced by sources placed within one of the boxes by comparing and contrasting monopole- with dipole-type forcing; for the former the pressure field is asymptotically enhanced whilst for the latter there is no asymptotic enhancement and the translation from the microscale to the discrete description entails evaluating singular limits, using a regularized and efficient scheme, of the Neumann's Green's function for a cube. We conclude with an example of using our asymptotic framework to calculate localized modes trapped within a defected box array.

physics.app-ph↗
arXiv2018

Thermally Oxidized Two-dimensional TaS2 as a High-\k{appa} Gate Dielectric for MoS2 Field-Effect Transistors

We report a new approach to integrating high-\k{appa} dielectrics in both bottom- and top-gated MoS2 field-effect transistors (FETs) through thermal oxidation and mechanical assembly of layered twodimensional (2D) TaS2. Combined X-ray photoelectron spectroscopy (XPS), optical microscopy, atomic force microscopy (AFM), and capacitance-voltage (C-V) measurements confirm that multilayer TaS2 flakes can be uniformly transformed to Ta2O5 with a high dielectric constant of ~ 15.5 via thermal oxidation, while preserving the geometry and ultra-smooth surfaces of 2D TMDs. Top-gated MoS2 FETs fabricated using the thermally oxidized Ta2O5 as gate dielectric demonstrate a high current on/off ratio approaching 106, a subthreshold swing (SS) down to 61 mV/dec, and a field-effect mobility exceeding 60 cm2V-1 s-1 at room temperature, indicating high dielectric quality and low interface trap density.

physics.app-ph↗
arXiv2018

Synthesizing Cu-Sn nanowires alloy in highly-ordered Aluminum Oxide templates by using electrodeposition method

In this research a novel and simple electrochemical method is developed in order to facilitate the large-scale production of nanowires. The proposed electrochemical technique shows versatile controllability over chemical composition and crystalline structure of Cu-Sn nanowires. Another important factor, which could be controlled by using this method, is the order structure of nanowires more accurately in comparison to conventional synthesizing procedures. As a result, the Cu-Sn nanowires as well as Aluminum Oxide templates synthesized by using the proposed electrochemical method are examined due to their morphology and chemical structure to find a relation between electrodeposition's solution chemistry and materials properties of Cu-Sn nanowires. The results show that the proposed electrochemical method maintains a highly-ordered morphology as well as versatile controllability over chemical composition of nanowires, which could be used to optimize the procedure for industrial applications due to low cost and simple experimental setup.

physics.app-ph↗
arXiv2018

An electrically pumped phonon-polariton laser

We report a device that provides coherent emission of phonon polaritons, a mixed state between photons and optical phonons in an ionic crystal. An electrically pumped GaInAs/AlInAs quantum cascade structure provides intersubband gain into the polariton mode at = 26.3 μm, allowing self-oscillations close to the longitudinal optical phonon energy of AlAs. Because of the large computed phonon fraction of the polariton of 65%, the emission appears directly on a Raman spectrum measurement exhibiting a Stokes and anti-Stokes component with the expected shift of 48 meV.

physics.app-ph↗
arXiv2018

Tunable interferometers on a flexible polymer chip

To facilitate the implementation of large scale photonic quantum walks, we have developed a polymer waveguide platform capable of robust, polarization insensitive single mode guiding over a broad range of visible and near- infrared wavelengths. These devices have considerable elasticity, which we exploit to enable tuning of optical behaviour by precise mechanical deformations. In this work, we investigate pairs of beamsplitters arranged as interferometers. These systems demonstrate stable operation over a wide range of phases and reflectivities. We discuss device performance, and present an outlook on flexible polymer chips supporting large, reconfigurable optical circuits.

physics.app-ph↗
arXiv2018

Swept-Frequency Drumhead Mechanical Resonators

We demonstrate a high-Q ($>5 \times 10^{6}$) swept-frequency membrane mechanical resonator achieving octave resonance tuning via an integrated heater and an unprecedented acceleration noise floor below 1 $μ$g Hz$^{-1/2}$ for frequencies above 50 kHz. This device is compatible with established batch fabrication techniques, and its optical readout is compatible with low-coherence light sources (e.g., a monochromatic light-emitting diode). The device can also be mechanically stabilized (or driven) with the same light source via bolometric optomechanics, and we demonstrate laser cooling from room temperature to 10 K. Finally, this method of frequency tuning is well-suited to fundamental studies of mechanical dissipation; in particular, we recover the dissipation spectra of many modes, identifying material damping and coupling to substrate resonances as the dominant loss mechanisms.

physics.app-ph↗
arXiv2018

Tuning of envelope in high overtone bulk acoustic wave resonator

This report presents a robust composite resonator known as the high overtone bulk acoustic wave resonator (HBAR) for demonstrating experimentally the ability of the resonator to tune the envelope of the spectrum by applying dc bias. The reported HBAR exhibits exceptionally high-quality factor in the frequency range of 700 MHz to 3 GHz and high effective coupling coefficient over the broad range of microwave frequencies. The HBAR is based on thin Ba0.5Sr0.5TiO3 film sandwiched between two electrodes forming a transducer, supported by a thick sapphire substrate which is a low acoustic loss material. The resonator works on the principle of induced piezoelectricity due to the applied dc bias. The minima of the envelope changes from 1.16 GHz with S11 of -3.51 dB at 100 kV/cm bias to 1.90 GHz with S11 of -42.23 dB at 700 kV/cm bias, giving a relative tunability of the envelope to be around 64%. The spacing of the parallel resonance frequency (SPRF) for different bias voltages are also presented in this report. The quality factor of the resonator is over 22,000 at around 2GHz.

physics.app-ph↗
arXiv2018

A random laser based on diamond nanoneedles

Random lasers use radiative gain and multiple scatterers in disordered media to generate light amplification. In this study, we demonstrate a random laser based on diamond nanoneedles that act as scatterers in combination with fluorescent dye molecules that serve as a gain medium. Random lasers realized using diamond possess high spectral radiance with angle-free emission and thresholds of 0.16 mJ. The emission dependence on the pillar diameter and density is investigated, and optimum lasing conditions are measured for pillars with spacing and density of 336 nm and ~ 2.9x10^10 cm-2. Our results expand the application space of diamond as a material platform for practical, compact photonic devices and sensing applications.

physics.optics↗
arXiv2018

Effect of Polarization Field on the Photocurrent Characteristics of GaN/AlN Multi-Quantum-Well Avalanche Photodiode

Polarization is an important property of GaN/AlN multi-quantum-well (MQW) avalanche diode (MAPD) but has been ignored in recent analyses of MAPD to simplify the Monte Carlo simulation. Here, the photocurrent characteristics of GaN/AlN MAPD are investigated to understand the role of polarization field in the MQW structure. Carrier multiplication in AlN/GaN MAPD is found as a result of interfacial impact ionization not much helped from external field but instead considerably contributed by the polarization field. In addition, the movement of ionized electrons out of quantum well is proved as Fowler-Nordheim tunneling process helped by the polarization field in AlN barrier. Furthermore, the transport of ionized electrons through MQW structure is found influenced by the reverse polarization field in GaN layer, which could be suppressed by the external electric field. With all the three effects, the quick photocurrent increase of GaN/AlN MAPD is ascribed to the efficient transport of interfacial-ionized electrons step by step out of MQW at high voltages, which is in big difference from conventional APD due to avalanche breakdown.

physics.app-ph↗
arXiv2018

Semi-Classical Analysis and Design of Quantum dot Based Electrically Pumped plasmonic nanolaser

Recently there is an increasing attention to electrically pumped room temperature sub-wavelength plasmon sources because of their various potential applications mainly in the integrated plasmonic field. In this paper, a GaAs/AlGaAs quantum dot based waveguide integrated plasmonic nanolaser is introduced and theoretically investigated. Using a semi-classical rate equation model, performance of our nanolaser is studied and its characteristics are presented in details. The proposed nanolaser has a tiny footprint of 0.25 um2, room temperature operating condition and CMOS friendly process while having remarkable output performance. The new structure generates 1uW output power with 3.5mA injection current ( the threshold pump current is calculated to be about 2.5uA ) in 850 nm and has wide modulation frequency of 10 THz in threshold pumping rate, large Purcell factor about 3460 and high output coupling ratio to the host plasmonic waveguide.

physics.optics↗
arXiv2018

Kirigami Metamaterials for Reconfigurable Toroidal Circular Dichroism

The ancient paper craft of kirigami has recently emerged as a potential tool for the design of functional materials. Inspired by the kirigami concept, we propose a class of kirigami-based metamaterials whose electromagnetic functionalities can be switched between nonchiral and chiral states by stretching the predesigned split-ring resonator array. Single-band, dual-band and broadband circular polarizers with reconfigurable performance are experimentally demonstrated with maximum circular dichroisms of 0.88, 0.94 and 0.92, respectively. The underlying mechanism is explained and calculated via detailed analysis of the excited multipoles, including the electric, magnetic, and toroidal dipoles and quadrupole. Our approach enables tailoring the electromagnetic functionalities in kirigami patterns and provides an alternate avenue for reconfigurable optical metadevices with exceptional mechanical properties.

physics.class-ph↗
arXiv2018

3D-Printed Optics for Wafer-Scale Probing

Mass production of photonic integrated circuits requires high-throughput wafer-level testing. We demonstrate that optical probes equipped with 3D-printed elements allow for efficient coupling of light to etched facets of nanophotonic waveguides. The technique is widely applicable to different integration platforms.

physics.app-ph↗
arXiv2018

Geometric Influence of High Curvature on the Performance of Thin Film Transistors

The development of thin film transistor (TFTs) based integrated circuits on flexible substrates promise interesting approaches to human interface systems. Recently TFTs have been fabricated on textured surfaces such as textiles, paper, artificially corrugated or dimpled substrates, threads and fibers. This can result in the TFTs metal-insulator-semiconductor (MIS) stack being significantly distorted from a planar zero-curvature geometry to having non zero and potentially high curvature. Although the direct deposition on textured surfaces do not result in mechanical stress (as for example in bending, buckling or wrinkling), the geometry of high curvature can significantly influence the current voltage characteristics of the TFT. Here we present a closed form analytical model describing the geometrical impact of high curvature on the electrical performance of the TFT. Models are obtained from the solution to the Poisson-Boltzmann equation in polar co-ordinates and are verified using TCAD simulations. The techniques to generalize the results to adapt to any texture and semiconducting material are also discussed with experimental verification. This work forms an analytical basis to understand the impact of curvature on the electrostatics of the MIS stack and the current voltage characteristics of the TFT.

physics.app-ph↗
arXiv2018

When supporting electrolyte matters - tuning capacitive response of graphene oxide via electrochemical reduction in alkali and alkaline earth metal chlorides

The ability to tune charge storage properties of graphene oxide (GO) is of utmost importance for energy conversion applications. Here we show that electrochemical reduction of GO is highly sensitive to the cations present in the solution. GO is reduced at lower potential in alkali metal chloride solutions than in alkaline earth metal chlorides. During the reduction, capacitance of GO increases from 10 to 70 times. Maximum capacitances of reduced GO are between 65 and 130 F g-1, depending on the electrolyte and the presence of conductive additive. We propose that different interactions of cations with oxygen functional groups of GO during the reduction are responsible for the observed effect.

cond-mat.mtrl-sci↗
arXiv2018

Manipulation of magnetizations by spin-orbit torques

The control of magnetization by electric current is a rapidly developing area motivated by a strong synergy between breakthrough basic research discoveries and industrial applications in the fields of magnetic recording, magnetic field sensors, spintronics and nonvolatile memories. In recent years, the discovery of the spin-orbit torque has opened a spectrum of opportunities to manipulate the magnetization efficiently. This article presents a review of the historical background and recent literature focusing on spin-orbit torques (SOTs), highlighting the most exciting new scientific results and suggesting promising future research directions. It starts with an introduction and overview of the underlying physics of spin-orbit coupling effects in bulk and at interfaces, then describes the use of SOTs to control ferromagnets and antiferromagnets. Finally, we summarize the prospects for the future developments of spintronics devices based on SOTs.

physics.app-ph↗