Top Metal Research Articles

Triple-frequency terahertz modulator based on electronically controllable metamaterial from the coupling effect

This paper proposes a triple-frequency terahertz amplitude modulator that utilizes an I-shaped strip and four U-shaped metal patches within a common metal-substrate configuration. The top metal layer consists of an I-shaped strip and four U-shaped metal patches, while the bottom substrate layer is made of polyimide. Amplitude modulation is achieved through adjusting the plasma frequency of the high-electron-mobility transistors, resulting in a modulation depth of nearly 93% at resonance frequencies of 0.26 and 0.49 THz. At 0.6 THz, the modulation depth reaches 65%, demonstrating excellent performance. Resonance frequencies are determined by electric field and surface current distribution. The triple-frequency terahertz amplitude modulator is applicable in various fields, including terahertz communications and imaging.

New correlations for focusing effect evaluation of the light metal layer in the lower head of a nuclear reactor in case of severe accident

In case of a severe accident (SA) in a nuclear reactor, the core heats up and materials melt and relocate to the lower head of the vessel. In such configuration, stratification occurs between the oxide and metal phases present in the melt. When the metal phase is lighter than the oxide phase, the maximum heat flux applied to the vessel wall is concentrated at the location of this top metal layer, creating the so-called “focusing effect”. The modelling of the focusing effect is essential for SA codes to properly evaluate the vessel failure time or to demonstrate the vessel integrity, when In Vessel Retention (IVR) strategy is implemented. However, existing correlations used in SA codes for focusing effect modelling have some limitations: if the thickness of the metal layer becomes very small, they predict an extremely high heat flux. Moreover, they were validated with tests using water, whereas the Prandtl number was found to play a significant role in this heat transfer.In this paper, the focusing effect is studied based on 3D Direct Numerical Simulations (DNS) of a cylindrical metal layer, covering all possible metal layer characteristics in terms of geometry and boundary conditions, especially for its top surface where the intensity of radiative heat transfer may vary. The analysis of the fluid behavior and the quantitative results obtained allow to derive new correlations and a new model based on the radial profile of the mean temperature of the system and on the radial profile at the top surface. Results at reactor scale confirm the overestimation of existing 0D model used in SA codes for a thin metal layer and highlight the relevance of the proposed model for focusing effect evaluation during transient situations.

Dual-frequency terahertz amplitude modulator based on the coupling effect of cross-shaped structure and U-shaped metal patches

This letter presents a dual-frequency terahertz amplitude modulator based on a cross-shaped structure and U-shaped metal patches. Its structural unit is a typical metal-substrate structure. The top metal consists of a cross-shaped structure and U-shaped metal patches, and the bottom substrate layer is made of quartz. Amplitude modulation is achieved by adjusting the temperature of the vanadium dioxide (VO2) patches. The modulation depth can be approximately 75 %. The mechanism of the resonance frequency is explained by the equivalent circuit model. The proposed structure shows good amplitude modulation capability at different incidence and azimuth angles by changing the location of the VO2 patches. The dual-frequency terahertz amplitude modulator can be used in terahertz communication, imaging, etc.

Si3N4 Dielectric Hemi-sphere Arrayed Plasmonic Metasurface With Top Metal Coating for Multiresonant Absorption in NIR Regime

Si3N4 Dielectric Hemi-sphere Arrayed Plasmonic Metasurface With Top Metal Coating for Multiresonant Absorption in NIR Regime

A coating design to rule them all: asymmetric Fabry-Perot resonators with diverse optical response based on Au films with high-temperature sensitivity.

Thermal annealing of thin metal films induces morphology changes that have a dramatic effect in the optical properties. Here we propose an asymmetric Fabry-Perot resonator consisting of a top metal film, a dielectric spacer, and a bottom metal mirror that can display a diverse infrared response. Thermally induced morphology changes result in large reflectivity variations within a limited temperature range following the top film transition between conductive, highly lossy, and transparent regimes. This behavior arises from the combination of the top film properties with interference effects in the multilayer. Furthermore, the proposed structure holds promise for potential sensing applications, as its optical response displays four times larger temperature sensitivity than a single film.

Tunable nonreciprocal thermal emitter based on graphene/indium arsenide/silver microstructure

Nonreciprocal thermal radiation has been studied by people. However, previous research has mainly focused on TM waves. Therefore, this article investigates a nonreciprocal transmitter based on TE transverse waves. Nonreciprocal emitters completely violate Kirchhoff's law and can be applied to various thermal radiation devices. However, there is little research on tunable nonreciprocal thermal emitters. In this article, we innovatively replace the previous top metal grating structure with a graphene grating. The gate voltage of graphene can regulate the nonreciprocal radiation intensity of the device in this article, without the need to resimulate the structure, and can achieve tunable strong nonreciprocal radiation effects. When the incident angle is 30°, the azimuth angle is 72° and the external magnetic field is 3 T, the thermal emitter can obtain strong nonreciprocal thermal radiation at a wavelength of about 16.6 μm. The difference between emissivity and absorptivity is greater than 0.91, indicating the presence of significant strong nonreciprocal radiation. We explained the physical background of this effect by studying the electromagnetic field distribution at the resonance peak.

P/N-Type Conversion of 2D MoTe2 Controlled by Top Gate Engineering for Logic Circuits.

Two-dimensional (2D) transition-metal dichalcogenides (TMDCs) are regarded as promising materials for next-generation logic circuits. Top gate field-effect transistors (FETs) have independent gate control ability and can be fabricated directly on TMDC materials without a transfer process. Therefore, it has the merits of device reliability and complementary metal-oxide semiconductor (CMOS) process compatibility, which are demanded in practical circuit-level integration. However, the fabrication of the top gate FET involves depositing an insulating dielectric layer and a gate electrode in sequence on the TMDC channel material, which may affect the device performance. Insightfully investigating the influences of different top-gate-deposition methods on the electrical properties of the TMDC channel and further harnessing these influences to realize a homogeneous CMOS device on an identical 2D TMDC platform are with practice significance. In this work, p/n-type controllable top gate FET arrays based on 2H-MoTe2 are fabricated by using different top-gate-deposition methods. The electron-beam evaporation (EBE) of top metal gate exhibits an obvious n-doping effect on the 2H-MoTe2 channel and converts it from p-type to n-type, whereas the thermal evaporation of top gate affects little to the channel. High-resolution transmission electron microscopy (HR-TEM) analysis reveals that the high-energy metal atoms from the EBE process can penetrate through the 30 nm gate dielectric layers (including 10 nm Al2O3 seeding layer), leading to multiple atomic defects in both MoTe2 and the interface between MoTe2 and Al2O3. Furthermore, by utilizing the top gate engineering, a large-scale double-top-gate MoTe2 homogeneous CMOS inverter array is fabricated. The CMOS inverters exhibit clear logic swing, negligible hysteresis, and high device yield (∼93%), indicating high device reliability and stability. Notably, the fabrication process is facile, free from transfer procedure, and compatible with traditional silicon technology. This work promotes the application of 2D TMDCs in nanoelectronics integration.

Sol-Gel Derived ZnO Thin Films with Nonvolatile Resistive Switching Behavior for Future Memory Applications

Herein we report on a facile sol-gel spin-coating technique to fabricate ZnO thin films that grow preferentially along the (002) plane on FTO substrates. By employing the magnetron sputtering technique to deposit a tungsten (W) top metal electrode onto these ZnO thin films, we successfully realize a W/ZnO/FTO memory device that exhibits self-rectifying and forming-free resistive switching characteristics. Notably, the as-prepared device demonstrates impressive nonvolatile and bipolar resistive switching behavior, with a high resistance ratio (RHRS/RLRS) exceeding two orders of magnitude at a reading voltage of 0.1 V. Moreover, it exhibits ultralow set and reset voltages of approximately +0.5 V and −1 V, respectively, along with exceptional durability. In terms of carrier transport properties, the low resistance state of the device is dominated by ohmic conduction, whereas the high resistance state is characterized by trap-controlled space-charge-limited current conduction. This work highlights the potential of the ZnO-based W/ZnO/FTO memory device as a promising candidate for future high-density nonvolatile memory applications.

The micro-resistive groove detector: a new compact single amplification-stage MPGD

In this paper, we introduce a novel single amplification-stage Micro-Pattern Gaseous Detector (MPGD) that incorporates a Diamond-Like Carbon (DLC)-based resistive electrode at the bottom of micro-groove structures, the micro-Resistive Groove (μRGroove) detector. The μRGroove shares a similar compact stack geometry with the micro-Resistive WELL (μRWELL) detector, but it distinguishes itself by employing a groove structure for charge amplification instead of a well. The top metal layer of the grooves naturally forms an array of strips. By incorporating additional 1-dimensional (1D) readout strips beneath the DLC electrode, a 2-dimensional (2D) strip-readout scheme can be easily implemented. Two prototypes of the μRGroove (10 cm× 10 cm) were manufactured in 2022 at CERN, and their performance was evaluated through X-ray and beam tests. The results indicate a gas gain > 104, an energy resolution of ~ 25%, and negligible charging-up effects for 8 keV Cu X-rays. Additionally, the detection efficiency was found to be ~ 95%, with a position resolution of ∼ 75 μm for 150-GeV/c muons. The μRGroove boasts a compact design and robustness against discharges. Furthermore, compared to the μRWELL, it offers cost savings in detector fabrication and yields significantly higher signal amplitude (approximately double) at the same gas gain. These attributes position the μRGroove as a promising candidate for large-area and low-material-budget tracking applications.

Terahertz angle sensor based on the asymmetry coupling of the square and L-shaped structure

This letter presents a terahertz angle sensor using a rectangular and double L-shaped structure. The structure unit of the sensor consists of a typical metal-medium structure, with the top metal pattern comprising a rectangle and a double L-shaped structure. At the same time, the bottom layer is made of polyimide, a dielectric material. By varying the position and number of L-shaped structures, a terahertz angle sensor based on a spring-shaped structure is created. The terahertz angle sensor achieves a Q value of 120.6 with a sensitivity of 3.45 GHz per degree. The terahertz angle sensor offers high-angle resolution and may find applications in terahertz communication, imaging, sensing, and other related fields.

Strain-induced polarization modulation at GaN/Ti interface for flexible thin-film sensor

We have demonstrated an effective piezoelectric polarized interface modulation in a GaN/Ti Schottky structure and fabricated a flexible GaN-based sensor using a double-transfer method. Chemical etching of the Ni sacrificial layer successfully removes the temporary substrate without damaging the metal electrodes. The fabricated flexible GaN-based sensor, with top and bottom Ti metal Schottky contacts, exhibits a current on/off characteristic under external strain. Specifically, the current shows a 53.9% reduction under 2.3% tensile strain and a 67.8% enhancement under −2.3% compressive strain at a 5 V bias voltage. It was found that the light/dark current ratio in the GaN/Ti Schottky junction significantly increases near zero-bias voltage under 2.3% tensile strain, likely indicating an enhanced built-in piezoelectric polarized field at the interface. This work advances the study of flexible sensors based on wurtzite III–V nitrides for wearable electronics and optoelectronics.

A mid-infrared ultra-wideband polarization-independent tunable perfect absorber based on Dirac metal materials

A mid-infrared ultra-wideband tunable terahertz absorber based on bulk Dirac semimetal (BDS) is presented. It has a simple three-layer structure: a top BDS metal layer, a middle dielectric layer, and a bottom reflective metal layer. The BDS layer was designed by creating a square cavity and a long rectangular cavity in the center of the BDS rectangle. The long rectangle was then rotated by 90° to form a centrosymmetric cavity. Using CST Studio Suite software, we numerically simulate the absorption characteristics. The simulation results indicate that the absorber achieves a high absorption (>90 %) of about 47.59 THz in the range of 37.5–90 THz when the Fermi energy level is 70 meV. The average absorption exceeds 95 %. In addition, adjusting the Fermi energy level of the BDS alters the absorption bandwidth. The centrosymmetric design of the structure ensures the absorber exhibits insensitivity to different polarization modes and angles of incidence, as well as excellent absorption stability. The designed shock absorber also exhibits excellent tolerance in manufacturing, reducing fabrication challenges and enabling practical applications. In addition, our design possesses the unique ability to modulate light in the mid-infrared band. These remarkable properties position our findings with significant potential in fields such as spectral analysis, optical biosensing technology, infrared sensing, and related applications.

A broadband second-order bandpass frequency selective surface for microwave and millimeter wave application.

This paper presents a frequency selective surface (FSS) with a wideband second-order bandpass response in the dual-band of microwave and millimeter wave. The overall structure consists of three layers of metal pattern and two layers of thin dielectric substrate. The top and bottom metal layers have capacitive patches with integrated curled Jerusalem cross slot resonators, while the intermediate metal layer has an inductive grid structure with cross-shaped slot resonators. The incorporated slot resonators play a pivotal role in achieving the desired transmission poles or zeros, which enable a wideband second-order filtering response in the dual-band and a quick roll-off at the passband edges, increasing the efficacy of electromagnetic shielding. To fully investigate the structure's frequency response, an equivalent circuit model of the structure is created, spanning the complete frequency range of 5-50 GHz. Physical samples are created and measured to confirm the suggested approach's efficacy. The passband center frequencies of the FSS are found at f1 = 19.42 GHz and f2 = 42.78 GHz, and the - 3dB bandwidth is 4.34 GHz (17.25-21.59 GHz) and 8.54 GHz (38.51-47.05 GHz), respectively. The simulation results align well with the experimental data. The transmission response rapidly transitions from the passband to the stopband at the passband boundaries.

Design and analysis of K and Ku-band wide-angle polarization-insensitive dual-band perfect metamaterial absorber

This paper presents a polarization-insensitive dual-band metamaterial perfect absorber applied to the Ku and K bands. The proposed dual-band metamaterial absorber (MMA) is a three-layer structure of metal-dielectric-metal. The top metal layer consists of a split circle ring, two intersecting square rings, and a circle ring, the bottom metal layer is made of copper, and the middle dielectric layer is made of FR-4. The simulation results show that the MMA has two absorption peaks at frequencies of 12.06 GHz and 19.07 GHz, with absorption rates of 99.95% and 99.73%, respectively. The MMA exhibits good polarization insensitivity in TE and TM modes. In TE mode, the increase in incident angle significantly broadens the absorption bandwidth. The experimental results verified the dual-band perfect absorption of MMA and the incident angle gain characteristic of TE mode. The proposed dual-band MMA can be applied in related fields such as radar antennas, satellite communication, and sensing.

Supported tetra-atom clusters on g-CN as catalysts for electrochemical reduction of carbon dioxide to formate: A computational study

Single-cluster catalysts (SCCs) have emerged as highly efficient catalysts for the CO2 reduction reaction (CO2RR), providing a promising avenue to solve the carbon dilemma. Based on density functional theory calculations, we systematically investigated the capability of 12 tetra-atom transitional-metal clusters anchored on g-CN (TM4@g-CN) for CO2RR and found that all clusters have good stability on the substrate. Notably, the charge variation of the top metal atom (TM4) of six SCCs is close to zero which makes them readily donate electrons to the adsorbate CO2 and subsequent reaction intermediates. Our results demonstrate that CO2 can be efficiently reduced to HCOOH on Ni4, Cu4, and Au4@g-CN with low limiting potentials of −0.21, −0.22, and −0.19 V, respectively, outperforming the corresponding single-atom counterparts. Both ΔG(∗CO2) and ΔG(∗OCHO/∗COOH) exhibit a volcano relationship with the reaction activity, and the TM4 serves as electron reservoirs throughout the entire reaction process. This work offers valuable insights for the advancement of cost-effective supported single cluster catalysts.

Plasmonic metamaterial absorber for MWIR and LWIR bispectral microbolometers

Plasmonic metamaterial absorbers (PMAs) designed for multispectral imaging in the infrared (IR) with uncooled microbolometers are investigated. The study presents Fourier transform infrared spectroscopy (FTIR) measurements of PMAs consisting of metal-insulator-metal-stacks (MIM) with square-shaped micropatches as top metal layers. The measurements reveal high absorptances of 82% to 99% for distinct wavelengths within a range from 2 μm to 9.2 μm. The spectra are evaluated with respect to the lateral dimensions of the patches and to the refractive indices of the used dielectrics SiO2, Al2O3 and Ta2O5. Numerical simulations and analytical calculations of the TM010-mode using the transmission line model (TLM) for microstrip antennas show good qualitative agreement with the measurement results. Additionally, bispectral PMAs were fabricated consisting of fields of PMAs with two different patch sizes arranged in a chessboard pattern. The individual fields of this pattern correspond to microbolometers with 12 μm pitch in shape and size. Two distinct absorption maxima can be seen in the spectra measured by FTIR. The choice of materials, deposition methods and patterning processes is suitable for the integration into the existing Fraunhofer IMS's nanotube microbolometer technology to realize multispectral infrared imaging. The fabrication process is CMOS-compatible and carried out on 8-in. wafers.

Microcavity enhancement vs Auger recombination in variable thickness type-II superlattices in resonant cavity mid-infrared light emitting diodes

In this study, we investigate the tradespace between the improvement of mid-infrared light-emitting diode efficiency through microcavity enhancement vs reduction of Auger recombination for different W-superlattice thicknesses. Several sample designs are modeled and then grown and fabricated to test the tradespace at different W-superlattice thicknesses down to the quantum well limit. In a half-cavity, with a single reflector from the top metal contact, intermediate thickness W-superlattices gave the highest efficiencies, outperforming those in the W-quantum well limit across the entire measured current range. Experimentally, we report wallplug efficiencies of 0.4% for a room temperature 3.2 μm device. W-superlattices of intermediate thickness were also found to be optimal for a full-cavity device with a bottom distributed Bragg reflector added. The resonant full cavity did strongly improve the peak spectral radiance, with a measured increase of four to five times for a 3.6 μm device, and a value that is >250 times larger than previously reported.

Wideband terahertz absorber based on the coupling of the double ellipse de-overlapping and I-shaped structure

In this letter, a wideband terahertz absorber based on a double ellipse de-overlapping and an I-shaped structure is presented. Its structure unit is a typical metal-medium-metal structure, the top metal is composed of a double ellipse de-overlapping and the central layer of an I-shaped structure, and the bottom layer is also a double ellipse de-overlapping. Broadband absorption is achieved by adjusting the structural parameters of the unit, equivalent circuit model is used to evaluate the resonant frequencies of different absorption peaks. The operation frequencies of the absorber can be extended from 5.5 THz to about 1.2 THz. The operation bandwidth of terahertz waves decreases from close to 2 THz to about 0.5 THz by adjusting the structural parameters of the unit. The device demonstrates excellent broadband absorption ability at various incidence angles, exhibiting strong angular stability. The wideband terahertz absorber can be used in terahertz communication, terahertz imaging, terahertz sensing, and other fields.

Thermally-stable solar energy absorber structure with machine learning optimization

Major problems that the world is currently confronting include global warming and the energy crisis, and the optimal absorption of solar spectrum radiation is a pivotal stage for a green future for the effective usage of solar thermal energy. The available solar absorbers are temperature sensitive and do not provide perfect absorption for a wide operation range. The major objectives of the proposed paper are to overcome these limitations and present an ultrawideband thermally stable solar absorber. The developed absorber utilizes a high melting point material comprising a Ti reflector element, a Si3N4 dielectric layer, and a pi-shaped top TiN metal layer. Within the spectral range spanning from 200 to 2500 nm, a notable average absorption rate of 97.69 % is attained. This structure has also demonstrated exceptionally under the AM1.5 conditions with a spectral absorption efficiency of 96 %. This work presents a novel optimization approach for solar absorbers, employing K-nearest neighbor (KNN) regression models to enhance design optimization by simulation time reduction with an R2 score of 0.999. The novelty resides in the absorber surface shape, utilization of cost efficient, sustainable, and thermally stable materials, as well as the KNN regression model for optimization of proposed solar absorber structure. Due to the angle and polarization insensitive characteristics, this structure can be potentially utilized for solar energy harvesting and shielding.

PICMIC-0: a 5 μm pitch hexagonal pixel sensor with an original tri-axis readout

We present in this paper a new sensor called PICMIC-0 that is intended to exploit the intrinsic spatial resolution of the MicroChannel Plate (MCP) detectors. Manufactured using 6-metal TowerJazz 180 nm wafer technology, the sensor features hexagonal charge collection pixels on the top metal layer with a pitch of 5 μm and covering an area of 7.4 × 6.4 mm2. The 2 million of the pixels of this sensor are not read out individually.Each pixel is connected to a straight-line in either 0°, 120° or -120° orientation, in which a current is produced in case of a hit. Each of these readout strip-lines is connected to a readout cell which receives this current, amplifies it using a current mirror and converts it into a digital signal by means of a current comparator. The data is collected from the digital outputs of the readout cells using a priority encoder readout scheme and transmitted in frames of 400 ns. This projective readout system reduces the number of channels to be read out from 2 million pixels to 2556 readout cells integrated within the pixel matrix. Using three projections reduces the ambiguity in case of multiple hits.