Copper and platinum dual-single-atoms supported on crystalline graphitic carbon nitride for enhanced photocatalytic CO_(2) reduction

Single-atom Pt catalysts are designed to promote efficient atom utilization,whereas effective decrease of Pt loading and improvement of photocatalytic activity in monoatomic Pt-deposited systems is still ongoing.Atomically dispersed metal species in crystalline carbon nitride are still challenging owing to their high crystallization and structural stability.In this study,we developed a novel single-atomic Pt-Cu catalyst for reducing noble metal loading by combining Pt with earth-abundant Cu atoms and enhancing photocatalytic CO_(2)reduction.N-vacancy-rich crystalline carbon nitride was used as a fine-tuning ligand for isolated Pt-Cu atom dispersion based on its accessible functional N vacancies as the seeded centers.The synthesized dimetal Pt-Cu atoms on crystalline carbon nitride(Pt Cu-cr CN)exhibited high selectivity and activity for CO_(2)conversion without the addition of any cocatalyst or sacrificial agent.In particular,we demonstrated that the diatomic Pt-Cu exhibited high mass activity with only 0.32 wt% Pt loading and showed excellent photocatalytic selectivity toward CH_(4)generation.The mechanism of CO_(2)photoreduction for Pt Cu-cr CN was proposed based on the observations and analysis of aberration-corrected high-angle annular dark-field scanning transmission electron microscopy images,in situ irradiated X-ray photoelectron spectroscopy,and in situ diffuse reflectance infrared Fourier transform spectroscopy.The findings of this work provide insights for abrogating specific bifunctional atomic metal sites in noble metal-based photocatalysts by reducing noble metal loading and maximizing their effective mass activity.

Towards Intelligent Reflecting Surface Empowered 6G Terahertz Communications: A Survey

Terahertz(THz)communications have been widely envisioned as a promising enabler to provide adequate bandwidth and achieve ultra-high data rates for sixth generation(6G)wireless networks.In order to mitigate blockage vulnerability caused by serious propagation attenuation and poor diffraction of THz waves,an intelligent reflecting surface(IRS),which manipulates the propagation of incident electromagnetic waves in a programmable manner by adjusting the phase shifts of passive reflecting elements,is proposed to create smart radio environments,improve spectrum efficiency and enhance coverage capability.Firstly,some prospective application scenarios driven by the IRS empowered THz communications are introduced,including wireless mobile communications,secure communications,unmanned aerial vehicle(UAV)scenario,mobile edge computing(MEC)scenario and THz localization scenario.Then,we discuss the enabling technologies employed by the IRS empowered THz system,involving hardware design,channel estimation,capacity optimization,beam control,resource allocation and robustness design.Moreover,the arising challenges and open problems encountered in the future IRS empowered THz communications are also highlighted.Concretely,these emerging problems possibly originate from channel modeling,new material exploration,experimental IRS testbeds and intensive deployment.Ultimately,the combination of THz communications and IRS is capable of accelerating the development of 6G wireless networks.

Effect of Al_2O_3 Buffer Layers on the Properties of Sputtered VO_2 Thin Films

VO_2 thin films were grown on silicon substrates using Al_2O_3 thin films as the buffer layers. Compared with direct deposition on silicon, VO_2 thin films deposited on Al_2O_3 buffer layers experience a significant improvement in their microstructures and physical properties. By optimizing the growth conditions, the resistance of VO_2 thin films can change by four orders of magnitude with a reduced thermal hysteresis of 4 °C at the phase transition temperature. The electrically driven phase transformation was measured in Pt/Si/Al_2O_3/VO_2/Au heterostructures. The introduction of a buffer layer reduces the leakage current and Joule heating during electrically driven phase transitions. The C–V measurement result indicates that the phase transformation of VO_2 thin films can be induced by an electrical field.

Wafer-level substrate-free YIG single crystal film for a broadband tunable terahertz isolator

Yttrium iron garnet(YIG)is a promising material for various terahertz applications due to its special optical properties.At present,a high-quality YIG wafer is the desire of terahertz communities and it is still challenging to prepare substrate-free YIG single crystal films.In this work,we prepared wafer-level substrate-free La:YIG single crystal films,for the first time,to our knowledge.Terahertz optical and magneto-optical properties of La:YIG films were characterized by terahertz time domain spectroscopy(THz-TDS).Results show that the as-prepared La:YIG film has an insertion loss of less than 3 dB and a low absorption coefficient of less than10 cm-1below 1.6 THz.Benefitting from the thickness of the substrate-free YIG films and low insertion loss,their terahertz properties could be further manipulated by simply using a wafer-stacking technique.When four La:YIG films were stacked,there was an insertion loss of less than 10 dB in the range of 0.1-1.2 THz.The Faraday rotation angle of the four-layer-stacked La:YIG films reached 19°,and the isolation could reach17 dB.By further increasing the stacking number to eight pieces,a remarkable Faraday rotation angle of45°was achieved with an isolation of 23 dB,which is important for practical application in the THz band.This material may provide a milestone opportunity to make various non-reciprocal devices,such as isolators and phase shifters.

All-dielectric terahertz metasurface for linearly-polarized multichannel transmission and superposition states of spherical and vortex waves

Compared to pure vortex waves,the superposition state of spherical waves and vortex waves has enough degrees of freedom to upgrade applications in particle manipulation,information encryption,and large-capacity communications.Here,we propose a new scheme to achieve superposition states and multichannel transmission of vortex and spherical waves.Two transmissive all-silicon metasurfaces that enable mutual interference between linearly polarized(LP)waves in the terahertz region are demonstrated.Type A can achieve interference between x and y polarized waves,while type B can achieve interference between x(or y)and x(or y)polarized waves.The multichannel transmission and superposition states of topological charges of+3,+2,and+4 are designed and demonstrated from theoretical,simulative,and experimental perspectives at 1.1 THz.In addition,the objective fact that the focused superposition state must be observed close to the focal plane is also revealed.The measured results are in good agreement with the theoretical and simulative results.This work provides an idea for the design of ultrathin terahertz devices and could be applied in the fields of information encryption and highfrequency communications.

In-situ growth of MAX phase coatings on carbonised wood and their terahertz shielding properties

Electromagnetic interference(EMI)shielding materials have received considerable attention in recent years.The EMI shielding effectiveness(SE)of materials depends on not only their composition but also their microstructures.Among various microstructure prototypes,porous structures provide the advantages of low density and high terahertz wave absorption.In this study,by using carbonised wood(CW)as a template,1-mm-thick MAX@CW composites(Ti2AlC@CW,V2A1C@CW,and Cr2AlC@CW)with a porous structure were fabricated through the molten salt method.The MAX@CW composites led to the formation of a conductive network and multilayer interface,which resulted in improved EMI SE.The average EMI SE values of the three MAX@CW composites were>45 dB in the frequency of 0.6-1.6 THz.Among the composites,V2A1C@CW exhibited the highest average EMI SE of 55 dB.

Enhanced performance of a fast GaAs-based terahertz modulator via surface passivation

Surface-modified semiconductors show enormous potential for opto-terahertz(THz)spatial modulation due to their enhanced modulation depth(MD)along with their inherent broad bandwidth.Taking full advantage of the surface modification,a performance-enhanced,all-optical,fast switchable THz modulator was achieved here based on the surface-passivated Ga As wafer.With a decreased surface recombination rate and prolonged carrier lifetime induced by passivation,S-passivated Ga As was demonstrated as a viable candidate to enhance THz modulation performance in MD,especially at low photodoping levels.Despite a degraded modulation rate owing to the longer carrier lifetime,this passivated Ga As modulator simultaneously realizes a fast modulation at a 69-MHz speed and as high an MD as ~94% in a spectral wideband of 0.2-1.2 THz.The results demonstrated a new strategy to alleviate the tradeoff between high MD and speed in contrast to bare surfaces or heterogeneous films/unusual geometry on semiconductors including Si,Ge,and GaAs.