This paper presents a methodology for designing a compact wideband dual stop-band filter by cascading transmission zeros using Electric-LC (ELC) resonators in coplanar waveguide (CPW) technology on a silicon substrate. Traditional filter design often relies on full-wave simulations and optimization processes, which are computationally intensive. Instead, the proposed approach simplifies the design process by numerically characterizing individual ELC resonator pairs and constructing a database of scattering parameters ($S$ matrices) corresponding to different geometrical configurations. By selecting and cascading appropriate $S$ matrix blocks, both the lower and upper stopbands of the filter can be synthesized with significantly reduced simulation time. Experimental validation was performed on a fabricated filter (with a $61-70 \text{GHz}$ passband), showing good agreement with numerical predictions, despite minor discrepancies attributed to loss effects not fully reproduced in the simulation environment.

The discovery of graphene has opened novel exciting opportunities in terms of functionalities and performances for spintronics devices. To date, it is mainly graphene properties for efficient in-plane spin transport which have been put forward. [1] We will present here experimental results concerning integration of graphene and other 2D Materials in vertical Magnetic Tunnel Junctions (MTJ), with strong technological potential. [2]We will show that a thin graphene passivation layer, directly integrated by low temperature catalyzed chemical vapor deposition (CVD), [3] allows to preserve a highly surface sensitive spin current polarizer/analyzer behavior. Characterizations of complete spin valves making use of graphene grown by CVD will be presented. The graphene layer prevents the oxidation of ferromagnets, unlocking in turn the exploration of spin filtering phenomena at graphene/ferromagnet interfaces, [4] as well as the introduction of novel ambient/wet processes for spintronics such as atomic layer deposition (ALD) and electro-grafting. [5] We will discuss the measured experimental spin signals in light of bulk band structure spin filtering effect as usually observed with MgO, but also highlight the role of interfacial hybridization (a.k.a. spinterface) for spin selection with ab-initio calculations in support. [6] The interfacial hybridization potential for spintronics will be underlined by the discussion of graphene/insulating FM based MTJ devices towards gated 2D spin sources. [7] We will further discuss the various observed spin filtering effects by analyzing results with other 2D materials (such as h-BN and ${\mathrm {WS}}_{2}$) integrated in MTJ devices. [8] Finally, we will expand the discussion to a novel pulsed laser deposition (PLD) approach for the definition of complex van der Waals heterostructures of 2D materials in MTJs. [9] This PLD growth approach unlocks the association in heterostructure of wide families of multifunctional 2D materials, including the most delicate ones. The different presented experiments unveil promising approaches for the quantum engineering of multifunctional 2D materials heterostructures for spintronics

In this paper, we introduce a novel concept of tunable and miniaturized filtersthat embed, as voltage-controlled elements, state-of-the-art variable capacitors, based on vertically aligned carbon nanotubes (VACNTs). Starting from a theoretical estimation of the voltage-dependent capacitance between two adjacent CNTs, we extended this physics principle to a large matrix of CNTs, suitably placed on the molybdenum electrodes of an interdigitatedcapacitor (IDC), since molybdenum can withstand the high temperature necessary in the plasma process for the growth of the VACNTs. The IDC is the tunable element of a microwave filter, which must fulfill the need for both reconfigurability (being either a low-pass, a high-pass, or a band-pass filter, at discretion) and low-voltage frequency tuning of reflection/transmission coefficients. For all these reasons, a very compact layout made of T-type cells (comprising VACNT-based variable capacitors and distributed inductors) was designed, simulated, fabricated, and tested, targeting the C, X, and Ku bands (4–16 GHz) for wireless and radar applications. Taking as a reference the free-space wavelength λ0 at 10 GHz, the band-pass filter has overall dimensions of just 3.19 mm × 3.47 mm (i.e., 0.11λ0 × 0.12λ0), with the minimum of the reflection coefficient shifting of 1.16 GHz (within the X band) for an applied dc bias voltage of just 4 V and spanning between −24.81 dB and −36.13 dB. Furthermore, the maximum rejection is 31.65 dB, and the 3-dB fractional bandwidth is 12.44%. The proposed filters are the proof that nanomaterials can be profitably integrated into microwave components for next-generation transceivers.

Atomically thin 2D materials have drawn considerable attention in the past years with potential ranging from transistors to optoelectronics. As such, they are now foreseen as strong candidates for epitaxy‐free technologies and the tetrad of size‐weight‐power‐and‐cost (SWAP‐C) reduction. Targeting radiofrequency (RF) applications, the 2D semiconducting transition metal dichalcogenides (TMDC) family can offer the opportunity of wide tunability of their electronic properties, providing a large variety of band gaps. However, evaluation and integration of those materials into discrete components requires a stabilization of their properties. This work focuses on the evaluation of a large‐scale compatible fabrication/passivation process on large area (>1000 µm 2 ) monolayers of the prototypical 2D semiconductor MoS 2 . The process is developed including pre‐ and post‐patterning protection/passivation layers. It is shown to reduce the initial natural p‐doping of the sample, leading to lower transistor threshold voltages, a 10 6 I ON / I OFF ratio, and an effective averaged field‐effect mobility under ambient conditions of 20 cm 2 V −1 s −1 (up to 35 cm 2 V −1 s −1 for some devices), which represents an increase by a 40‐fold factor compared to a conventional process carried on the large scale platform. This work represents an important step toward the integration of 2D TMDCs in discrete RF circuits and components.

Magnonics rely on the wave nature of the magnetic excitations to process information, an approach that is common to many fields such as photonics, phononics, and plasmonics. Nevertheless, magnons, the quanta of spin-wave excitations, have the unique advantage to be at frequencies that are lying between a few GHz to tens of GHz, that is, in the technologically relevant radio-frequency bands for 4G and 5G telecommunications. Furthermore, their typical wavelengths are compatible with onchip integration. Here, we demonstrate radio-frequency signal filtering by a micron-scale magnonic crystal (MC) based on a nanopatterned 20 nm-thick film of yttrium iron garnet with a minimum feature size of 100 nm where the Bragg vector is set to be k(B) = 2.1 mu m(-1). We map the intensity and the phase of spin waves (SWs) propagating in the periodic magnetic structure using phase-resolved microfocus Brillouin light-scattering spectroscopy. Based on these maps, we obtain the SW dispersion and the attenuation characteristics. Efficient filtering is obtained with a frequency selectivity of 20 MHz at an operating frequency of 4.9 GHz. The results are analyzed by performing time- and frequency-resolved full-scale micromagnetic simulations of the MC that reproduce quantitatively the complexity of the harmonic response across the magnonic band gap and allow the identification of the relevant SW-quantized modes, thereby providing an in-depth insight into the physics of SW propagation in periodically modulated nanoscale structures.

The paper investigates electrical characterizations of CNTs (carbon nanotubes) within a SEM chamber. The originality of the proposed approach relies in its high versatility that is made possible thanks to nanoprobes moved by 6-DoF nanopositioning robots. Using this configuration, the influence of several factors are evaluated to know the electrical behavior of the measurement system. The paper presents several experimental characterizations of CNTs. The measured values of electrical resistance are in complete agreement with known results from the literature but were obtained in a much more versatile way.

This paper reports the extraction of electrical impedance at microwave frequencies of vertically aligned multi-wall carbon nanotubes (VA MWCNT) bundles/forests grown on a silicon substrate. Dedicated resonating devices were designed for antenna application, operating around 10 GHz and benefiting from natural inductive/capacitive behavior or complex conductivity in the microwave domain. As obtained from S-parameters measurements, the capacitive and inductive behaviors of VA MWCNT bundles were deduced from device frequency resonance shift.

We report on the integration of atomically thin 2D insulating hexagonal boron nitride (h-BN) tunnel barriers into magnetic tunnel junctions (2D-MTJs) by fabricating two illustrative systems (Co/h-BN/Co and Co/h-BN/Fe) and by discussing h-BN potential for metallic spin filtering. The h-BN is directly grown by chemical vapor deposition on prepatterned Co and Fe stripes. Spin-transport measurements reveal tunnel magneto-resistances in these h-BN-based MTJs as high as 12% for Co/h-BN/h-BN/Co and 50% for Co/h-BN/Fe. We analyze the spin polarizations of h-BN/Co and h-BN/Fe interfaces extracted from experimental spin signals in light of spin filtering at hybrid chemisorbed/physisorbed h-BN, with support of ab initio calculations. These experiments illustrate the strong potential of h-BN for MTJs and are expected to ignite further investigations of 2D materials for large signal spin devices.

A reflective diffraction grating with a periodic square-wave profile will combine the effects of thin-film interference with conventional grating behavior when composed, of features having a different refractive index than that of the substrate. A grating period of 700-1300 nm was modeled and compared for both silicon (Si) and silicon dioxide (SiO2) to determine the behavior of light interaction with the structures. Finite element analysis was used to study nanostructures having a multirefractive index grating and a conventional single material grating. A multimaterial grating has the same diffraction efficiency as that of a grating formed in a single material, but had the advantage of having an ordered relationship between the grating dimensions (thickness and period) and the intensity of reflected and diffracted optical wavelengths. We demonstrate a color-selective feature of the modeled SiO2 grating by fabricating samples with grating periods of 800 and 1000 nm, respectively. A high diffraction efficiency was measured for the green wavelength region as compared to other colors in the spectrum for 800 nm grating periodicity; whereas wavelengths within the red region of spectrum interfered constructively for the grating with 1000 nm periodicity resulting a higher efficiency for red color bandwidth. The results show that diffraction effects can be enhanced by the thin-film interference phenomenon to produce color selective optical devices.

A new way to improve the current stability of an in-plane gated CNT emitters cathode with a closed loop control has been investigated. Ageing has been performed with a variation of external conditions by introducing hydrogen into the vacuum chamber and resulting in a low impact on the stability due to the feedbacked adjustment of the local electric field at the apex of CNTs given by the closed loop control. This structure also shows strong stability over time in normal conditions.

Nanometre-scale features with special shapes impart a broad spectrum of unique properties to the surface of insects. These properties are essential for the animal’s survival, and include the low light reflectance of moth eyes, the oil repellency of springtail carapaces and the ultra-adhesive nature of palmtree bugs. Antireflective mosquito eyes and cicada wings are also known to exhibit some antifogging and self-cleaning properties. In all cases, the combination of small feature size and optimal shape provides exceptional surface properties. In this work, we investigate the underlying antifogging mechanism in model materials designed to mimic natural systems, and explain the importance of the texture’s feature size and shape. While exposure to fog strongly compromises the water-repellency of hydrophobic structures, this failure can be minimized by scaling the texture down to nanosize. This undesired effect even becomes non-measurable if the hydrophobic surface consists of nanocones, which generate antifogging efficiency close to unity and water departure of droplets smaller than 2 μm. The antifogging properties of a structured surface can be considerably enhanced if the feature size is small enough and if the feature shapes are cones rather than cylinders.

We demonstrate an enhanced, bidirectional, in-plane magnetic field tuning of the gyrotropic resonance frequency of a magnetic vortex within a disk by introducing a flat edge. When the core is in its vicinity, the flat edge locally reduces the core's directional dynamic stiffness for movement parallel to the edge. This strongly reduces the net dynamic core stiffness, leading to the gyrotropic frequency being significantly less than when the core is centered (or located near the round edge). This leads to the measurable range of gyrotropic frequencies being more than doubled and also results in a clear chirality-mediated bistability of the gyrotropic resonance frequency due to what is effectively a chirality-dependence of the core's confining potential.

In the brain, learning is achieved through the ability of synapses to reconfigure the strength by which they connect neurons (synaptic plasticity). In promising solid-state synapses called memristors, conductance can be finely tuned by voltage pulses and set to evolve according to a biological learning rule called spike-timing-dependent plasticity (STDP). Future neuromorphic architectures will comprise billions of such nanosynapses, which require a clear understanding of the physical mechanisms responsible for plasticity. Here we report on synapses based on ferroelectric tunnel junctions and show that STDP can be harnessed from inhomogeneous polarization switching. Through combined scanning probe imaging, electrical transport and atomic-scale molecular dynamics, we demonstrate that conductance variations can be modelled by the nucleation-dominated reversal of domains. Based on this physical model, our simulations show that arrays of ferroelectric nanosynapses can autonomously learn to recognize patterns in a predictable way, opening the path towards unsupervised learning in spiking neural networks.

A graphene-based metamaterial lens is theoretically proposed by combining plasmonic nanoribbons with Fresnel Zone Plate (FZP) architecture to realize wavelength-selective and tunable lensing. The plasmonic FZP lens shows higher focal intensity and efficiency compared to conventional FZP. As compared with normal graphene FZP, the lensing effect of the plasmonic FZP can be enhanced by 83 times. When compared with Au thin film based FZP lenses, the graphene plasmonic lenses can achieve comparable lensing effects, but with a thinner geometry and with an additional advantage of being wavelength selective and tuneable. The analyses of selectivity and tunability of the plasmonic lens show that the plasmonic lens functions as a filter with broadband incident light or as a switch which can be turned on and off via changing the Fermi levels. The diffraction between neighboring graphene nanoribbons and the effect of the substrate on the lensing effect is also discussed. The plasmonic effect of the nanoribbons only contributes to the focal intensity without affecting the diffraction properties of Fresnel zone plate lenses such as focal lengths. This plasmonic FZP lens is an ideal combination of near and far field optics. However, the complex interaction of diffractions within and between the FZP rings could lead to a significant change of the lensing effect, which opens the possibility of creating innovative graphene metamaterial devices. The findings in this work can be used for developing wavelength-selective electro-optical applications operating in the infrared and terahertz ranges.

Tunable plasmonic enhancements in graphene based Fresnel zone plate lenses Sunan Deng1, Haider Butt1,*, Kyle Jiang1, Bruno Dlubak2, Piran R. Kidambi, 3 Pierre Seneor2, and Stephane Xavier4, Ali K. Yetisen5 1School of Mechanical Engineering, University of Birmingham, Birmingham B15 2TT, UK 2Unité Mixte de Physique CNRS/Thales, 91767 Palaiseau, France, and Université Paris Sud, 91405 Orsay, France 3Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA 4Thales Research and Technology, 9 Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA 1767 Palaiseau, France 5Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA *Email: h.butt@bham.ac.uk

The electrical properties of gold nanorods nanostructured silicon nitride films are comprehensively investigated with the aid of metal-insulator-metal capacitors and RF MEMS capacitive switches. Different nanorod diameters and densities were grown on the bottom electrode and with orientation normal to dielectric film surface. A simple physical model, which does not take the effect of electric field fringing into account, was developed to describe both the DC and low frequency electrical properties. It has been shown that the nanorods distribution and dimensions determine the electrical properties as well as the dielectric charging phenomena of the nanostructured films. Finally, in MEMS switches it has been shown that the nanorods presence does not affect the capacitance variance nor the RF characteristics of the device.

Flat lenses when compared to curved surface lenses have the advantages of being aberration free and they offer a compact design necessary for a myriad of electro-optical applications. In this paper we present flat and ultra-thin lenses based on graphene, the world’s thinnest known material. Monolayers and low number multilayers of graphene were fabricated into Fresnel zones to produce Fresnel zone plates which utilize the absorption properties of graphene for their operation. The working of the lens and their performance in the visible and terahertz regimes was analyzed computationally. Experimental measurements were also performed to characterize the lens in the visible regime and a good agreement was obtained with the simulations. The work demonstrates the principle of atom thick graphene-based lenses, with perspectives for ultra-compact integration.

Vortex core polarity switching in NiFe disks has been evidenced using an all-electrical magnetoresistive rectification scheme. Simulation and experiments yield a consistent rectified signal loss when driving core gyration at high powers. With increasing power, the frequency range over which the loss occurs grows and the resonance downshifts in frequency, consistent with nonlinear core dynamics and periodic core polarity switching induced by the core reaching its critical velocity. Core-polarity-dependent rectification signals enable an independent verification of the switched core polarity. We also demonstrate the ability to impede core polarity switching by displacing the core towards the disk's edge where an increased core stiffness reduces the core velocity.

We report on statistical analysis and consistency of electrical performances of devices based on a large scale passivated graphene platform. More than 500 graphene field effect transistors (GFETs) based on graphene grown by chemical vapor deposition and transferred on 4 in. SiO2/Si substrates were fabricated and tested. We characterized the potential of a two-step encapsulation process including an Al2O3 protection layer to avoid graphene contamination during the lithographic process followed by a final Al2O3 passivation layer subsequent to the GFET fabrication. Devices were investigated for occurrence and reproducibility of conductance minimum related to the Dirac point. While no conductance minimum was observed in unpassivated devices, 75% of the passivated transistors exhibited a clear conductance minimum and low hysteresis. The maximum of the device number distribution corresponds to a residual doping below 5 × 1011 cm−2 (0.023 V/nm). This yield shows that GFETs integrating low-doped graphene and exhibiting small hysteresis in the transfer characteristics can be envisaged for discrete components, with even further potential for low power driven electronics.