This paper investigates the potential of Limoges porcelain as a substrate for advanced high-frequency electronic applications through a comprehensive dielectric characterization from 10 kHz to 20 GHz. Preliminary impedance spectroscopy (10 kHz - 1 MHz) reveals a stable relative permittivity (epsilon r) between 6.3 and 6.6 for both glazed and unglazed samples, with a slight negative dispersion attributed to interfacial polarization mechanisms. Characterization at microwave frequencies using a cylindrical cavity perturbation method at 4.5 GHz demonstrates a decrease in epsilon r to values of 5.2 and 5.3 for glazed and unglazed plates, respectively, with a loss tangent (tan delta) of approximately 1.2 & times; 10- 2. To assess the performance of the porcelain substrates in integrated configurations, Ti/ Cu coplanar waveguide (CPW) resonators were fabricated using standard photolithography and lift-off processes. Broadband electromagnetic modeling up to 20 GHz using Momentum software yields results that are consistent with the experimental resonance frequencies for epsilon r values between 5.2 and 5.7. While the extraction of intrinsic losses at these frequencies is challenged by a strong interplay between metallic conductivity and dielectric dissipation, the results confirm that Limoges porcelain maintains stable dielectric properties well into the Kuband. These results support the relevance of porcelain as a chemically and thermally stable substrate, offering robust dielectric performance for RF and microwave packaging applications.

Upon illumination, photocatalysts generate charge carriers for redox reactions, but their efficiency is often limited by carrier recombination and poor minority-carrier diffusion, despite many existing junction engineering strategies. Here we exploit the insulator-metal transition in VO2 to produce a material that promotes efficient charge separation and enhances the photocatalytic conversion of methane through the spontaneous formation of junctions. We find that the photocatalytic activity peaks at the critical temperature of the transition, which we attribute to coexisting insulating and metallic domains with non-integer dimensional boundaries and sizes smaller than the minority-carrier diffusion length. Increasing the charge-separating interface length by decreasing the film thickness improves the photocatalytic activity and C-C coupling between alkoxy intermediates, leading to a propane selectivity of 100%. Moreover, electrically triggering the phase transition at lower temperatures further boosts methane conversion via field-assisted carrier activation. Overall, the metal-insulator transition provides an effective alternative to complex nanoscale junction engineering in photocatalysis.

Owing to their metal-insulator transition properties, Niobium oxide(NbOx) thin films have emerged as promising candidates for neuromorphic devices. We present the electrical behavior of NbOxlayers in out-of-plane metal-insulator-metal structures under current-controlled operation. The devices exhibit relaxation oscillations with frequencies up to 2 MHz, while the burst envelopes of these oscillations evolve over millisecond timescales. Beyond steady-state regimes, we observe continuous spiking, transient oscillations, and discrete oscillation packets, demonstrating rich, multi-timescale dynamics. These behaviors, combining high-frequency spiking with slower burst modulation, are relevant for neuromorphic systems emulating biological neuronal activity and for applications such as central pattern generators (CPGs). Our findings highlight the importance of long-timescale characterization for evaluating the neuromorphic potential of oxide-based oscillators.

High-order harmonic generation (HHG) in semiconductor thin films from ultrashort mid-infrared laser drivers holds the potential for the realization of integrated sources of extreme ultraviolet light. Here, we demonstrate solid-state HHG in zinc oxide thin films synthesized by the radiofrequency reactive magnetron sputtering process directly on the cleaved facets of optical fibers. Harmonics 3 to 13 of the radiation from a fiber-based laser system delivering 500 kW, 96 fs pulses at 3130 nm are produced in the thin film and guided along the fiber. A proper choice of the laser wavelength and fiber material allows for filtering out the mid-IR pump laser and achieving the HHG mode selection. The possibility to nanostructure the fiber exit by, e.g., focused ion beam milling paves the way to an increased control over the HHG spatial mode.

We present the design, realization and performance of a millimeter-wave patch antenna with frequency reconfiguration capabilities generated by integrating ferroelectric interdigitated tunable capacitors (FIDC). The tunable capacitors are based on Ba0.8Sr0.2TiO3 (BST) ferroelectric layers and exhibit very good and stable performances over the microwave and millimeter-wave bands, with a maximum tunability of 40% for a bias voltage of 100 V. The ferroelectric layers have been integrated in the slot-loop excitation circuit of the antenna and their Direct Current (DC) polarization allows a continuous frequency reconfiguration of the antenna around 30 GHz. An electrical model of the whole radiating device has been developed allowing extracting the range of capacitance values to be integrated into the excitation slot for an optimum frequency tuning. The fabricated antenna shows a variation of the operation frequency from 28.5 GHz to 34.95 GHz, corresponding to a frequency tuning of 22.6%. The antenna is very well matched all over the operating frequency band, with total efficiencies between 20% (0 V bias on FIDCs) and 65%(100 V bias).

Terahertz (THz) wireless technology offers unprecedented capabilities in sensing, imaging, and communication for 6G perceptive networks. Recent reconfigurable THz metasurfaces enable adaptive beam manipulation, supporting diverse functionalities like frequency, polarization, spatial, and temporal adjustments for rapid communications and object tracking. However, these are hindered by multilayer complexity, insertion losses, and scalability challenges. Here, it is overcome these constraints by realizing a pioneering single-layer, optically activated tunable metasurface incorporating Germanium Telluride (GeTe) material, acquiring multifunctional THz sensing, imaging, and communication within a unified platform for the first time. GeTe's low-power, non-volatile switching facilitates dynamic reconfiguration, eliminating bulky bias networks of traditional THz metasurfaces. This measured metasurface delivers an adaptive sub-THz communication channel with extensive coverage and enhanced passive object detection via wide frequency-dispersive scanning. Leveraging phase-change material-driven tunability, this antenna technique enables efficient, adaptive 6G connectivity and high-precision localization, with transformative potential for low Earth orbit networks, smart cities, and advanced Internet of Things (IoT).

THz amplitude modulators and switches are considered to be the main building blocks of future THz communication systems. Despite rapid progress, modulation and switching devices in this electromagnetic spectrum lag far behind other frequency ranges. Currently, THz modulators face major challenges in consistently producing high modulation depths over large frequency bands. Moreover, a convenient integration for practical applications requires that the modulation/switching properties can be electrically controlled. Devices fulfilling all these conditions remain to be demonstrated. In this work, we show that W-doped VO2 films grown by direct-current magnetron sputtering can be efficiently used for the development of reliable, large-area, broadband THz wave modulators. We demonstrate that W doping permits not only to tune the insulator-to-metal transition (IMT) temperature of VO2 but also, most importantly, to control the topology of the electrically activated transition. In situ/operando X-ray diffraction and Raman spectroscopy characterizations of the devices, coupled with standard resistivity measurements and time-domain THz spectroscopy, unambiguously demonstrate that the changes in the spatial distribution of the IMT are due to structural distortions induced by W doping. These findings are exploited to validate VO2-based devices whose IMT can be triggered either thermally or electrically over areas as large as 3.8 × 10 mm2, hence permitting the development of efficient THz modulators operating over a large spectral range (0.2-2 THz) with MDs reaching 96%.

We present the design and performances of a transmitting antenna array (Transmit-array) operating at 100 GHz, enabling radiation pattern reconfiguration by integration of GeTe phase-change materials (PCMs). The overall device is proposed as a simple single-layer structure in which the elementary cells are spaced by lambda/2 in both planar directions and are consisting of a metal split-ring resonator printed on a dielectric substrate and integrating patterns of the GeTe material. The radiation pattern reconfiguration is achieved by specific distributions of dissimilar unit cells having 180 degrees phase shift between them. This phase shift is achieved by alternating between the amorphous and crystalline states of the GeTe patterns within the split rings using laser optical activation.

We introduce an innovative method for imaging the spectral profile of a terahertz (THz) waveguide's output beam. Our proposed approach is based on the synthetic aperture (SA) imaging technique integrated into a time domain spectroscopy (TDS) system in transmission configuration. Using this approach, we demonstrate the reconstruction of space-frequency maps, and two-dimensional transverse images at different frequencies of the guided beam at the output of the THz waveguide under test. These outcomes mark a significant step forward in the development of characterization methods of THz waveguides.

Surface plasmon resonance detections based on phase changes have demonstrated superior sensitivities over the intensity, spectral and angular methods due to the singularity effect (abrupt change of phase value) observed at resonance. The Goos–Hänchen effect, a higher first order derivative of the phase, can be observable as a lateral displacement of the reflected wave at total internal reflection and magnified by the surface plasmons. The GH sensitivity can be further improved through the addition of a phase change material nanolayer beneath the gold. Vanadium dioxide (VO2) belongs to the family of phase change materials that exhibit reversible insulator-metal behavior when heated above 68℃. Adding a thin layer of VO2 below the metal proved to theoretically enhance the sensitivity of a conventional gold-based surface plasmon biosensor (up to 28 times of improvement in comparison with the bare gold configuration).

We demonstrate the integration of vanadium dioxide single-crystal nanobeams fabricated by modified vapor–liquid–solid method as electrical switching elements into a radio-frequency transmission line and evaluate the performances of the overall device in modulating the transmission of the conveyed RF electromagnetic waves. The switching capability of the RF device is based on the metal–insulator transition of VO2 nanobeams, with an on/off electrical switching ratio of 104, i.e., resistance modulation from more than 106Ω when the wires are in the insulating state to only ≈20Ω when they are in the metal-like state. The thermal and electrical activation of the VO2 wires between the two dissimilar states is resulting in RF switching performances characterized by more than 15 dB change in the transmission coefficient of the device over the 100 MHz–24 GHz frequency domain.

On behalf of the Organizing Committee, it is our great pleasure to invite you to the 27th European Microwave Week (EuMW), which will take place between 22 and 27 September 2024 at Paris Expo Porte de Versailles in Paris, France.

AbstractRapid plasmonic biosensing has attracted wide attention in early disease diagnosis and molecular biology research. However, it was still challenging for conventional angle-interrogating plasmonic sensors to obtain higher sensitivity without secondary amplifying labels such as plasmonic nanoparticles. To address this issue, we developed a plasmonic biosensor based on the enhanced lateral position shift by phase singularity. Such singularity presents as a sudden phase retardation at the dark point of reflection from resonating plasmonic substrate, leading to a giant position shift on reflected beam. Herein, for the first time, the atomically thin layer of Ge2Sb2Te5 (GST) on silver nanofilm was demonstrated as a novel phase-response-enhancing plasmonic material. The GST layer was not only precisely engineered to singularize phase change but also served as a protective layer for active silver nanofilm. This new configuration has achieved a record-breaking largest position shift of 439.3 μm measured in calibration experiments with an ultra-high sensitivity of 1.72 × 108 nm RIU−1 (refractive index unit). The detection limit was determined to be 6.97 × 10−7 RIU with a 0.12 μm position resolution. Besides, a large figure of merit (FOM) of 4.54 × 1011 μm (RIU∙°)−1 was evaluated for such position shift interrogation, enabling the labelfree detection of trace amounts of biomolecules. In targeted biosensing experiments, the optimized sensor has successfully detected small cytokine biomarkers (TNF-α and IL-6) with the lowest concentration of 1 × 10−16 M. These two molecules are the key proinflammatory cancer markers in clinical diagnosis, which cannot be directly screened by current clinical techniques. To further validate the selectivity of our sensing systems, we also measured the affinity of integrin binding to arginylglycylaspartic acid (RGD) peptide (a key protein interaction in cell adhesion) with different Mn2+ ion concentrations, ranging from 1 nM to 1 mM.

Exosomes have shown great potential in serving as a cancer biomarker over these years since they carry crucial information of their parent cells. Therefore, detection of exosomes is of vital importance to the early-stage diagnostics of multiple major diseases. In this paper, we have proposed a real-time and label-free sensing technique based on 2D Ge2Sb2Te5 (GST) nanomaterial enhanced plasmonic substrate. We have achieved a detection limit down to 104 exosomes/mL based on Goos–Hänchen (GH) shift measurement, which is more than two orders of magnitude superior to conventional SPR sensing techniques. Moreover, the detection of unpurified exosomes directly in cell culture supernatant (CCS) has been successfully demonstrated with a significant experimental GH shift signal of more than 120 μm been detected. Multiple control experiments using exosome-free solutions and control antibody coated substrates have also been performed, which validates the specificity of our device. The proposed plasmonic sensing scheme with enhanced sensing performance has the capability of detecting exosomes at low concentration levels. It also possesses the ability of direct detection of exosomes in CCS, which offers a convenient and efficient platform for exosome detection and analysis. We envision that this technique can serve as a promising tool in early-stage clinical diagnostics and treatment.

In this paper, we have designed and fabricated an atomically thin plasmonic sensing substrate based on two-dimensional phase change material Ge2Sb2Te5 and silver (Ag-GST). This substrate offers an ultra-low reflection in the SPR curves and a strong optical phase singularity. A custom-built SPR setup was developed here to directly measure the phase-singularity-induced lateral position shift. We have obtained a SPR sensitivity regarding the lateral position shift of 9.9577 x 10^7 μm/RIU, which is 3 orders of magnitudes higher than current position shift sensing scheme based on hyperbolic metamaterial. Due to the ultra-high SPR sensitivity, the binding processes between peptide and integrins directly from un-purified liposomes were real-time monitored. The concentrations of Mn2+ ions ranging from 1 fM to 1 mM on the binding dynamics have been systematically monitored with our developed phase-sensitive surface plasmon resonance biosensors.

We propose a terahertz (THz) 3D imaging and spectroscopy approach using planar synthetic arrays. In order to improve the acquisition time, the number of antenna elements needed in the synthetic array is reduced by employing a sparse synthetic array. The performances of the full synthetic array and the sparse array are compared experimentally in both imaging and material characterizations.