Efficient Solar-Driven Interfacial Water Evaporator using Hydrogel Modified Carbon-Based Biomass with Abundant Microchannels.

The conventional sea water desalination technologies are not yet adopted worldwide, especially in the third world countries due to their high capital cost as well as large energy requirement. To solve this issue in a sustainable way an interfacial solar water evaporation device is designed and proposed in this article using the branches of Prunus serrulata (PB). The PB has abundant microchannels and shows excellent photothermal conversion capability after carbonization. Moreover, the easy access to raw materials and the facile fabrication process makes the solar water evaporating device very cost effective for seawater desalination application. Experiments show that in the presence of the fabricated evaporator the evaporation rate of water can reach 3.5 kg m-2  h-1 under 1 sun, which is superior to many similar experimental devices. In addition, its advantages, such as effective sewage purification capability, low cost, and environmental friendliness, make this evaporator highly competitive in the extensive promotion of this technology and can be considered as a new sustainable solution for seawater desalination with great application potential and prospects.

Uncooled Mid-Infrared Sensing Enabled by Chip-Integrated Low-Temperature-Grown 2D PdTe2 Dirac Semimetal.

Next-generation mid-infrared (MIR) imaging chips demand free-cooling capability and high-level integration. The rising two-dimensional (2D) semimetals with excellent infrared (IR) photoresponses are compliant with these requirements. However, challenges remain in scalable growth and substrate-dependence for on-chip integration. Here, we demonstrate the inch-level 2D palladium ditelluride (PdTe2) Dirac semimetal using a low-temperature self-stitched epitaxy (SSE) approach. The low formation energy between two precursors facilitates low-temperature multiple-point nucleation (∼300 °C), growing up, and merging, resulting in self-stitching of PdTe2 domains into a continuous film, which is highly compatible with back-end-of-line (BEOL) technology. The uncooled on-chip PdTe2/Si Schottky junction-based photodetector exhibits an ultrabroadband photoresponse of up to 10.6 µm with a large specific detectivity. Furthermore, the highly integrated device array demonstrates high-resolution room-temperature imaging capability, and the device can serve as an optical data receiver for IR optical communication. This study paves the way toward low-temperature growth of 2D semimetals for uncooled MIR sensing.

Oxygen Vacancies Trigger Rapid Charge Transport Channels at the Engineered Interface of S-Scheme Heterojunction for Boosting Photocatalytic Performance.

Although oxygen vacancies (Ovs) have been intensively studied in single semiconductor photocatalysts, exploration of intrinsic mechanisms and in-depth understanding of Ovs in S-scheme heterojunction photocatalysts are still limited. Herein, a novel S-scheme photocatalyst made from WO3-Ov/In2S3 with Ovs at the heterointerface is rationally designed. The microscopic environment and local electronic structure of the S-scheme heterointerface are well optimized by Ovs. Femtosecond transient absorption spectroscopy (fs-TAS) reveals that Ovs trigger additional charge movement routes and therefore increase charge separation efficiency. In addition, Ovs have a synergistic effect on the thermodynamic and kinetic parameters of S-scheme photocatalysts. As a result, the optimal photocatalytic performance is significantly improved, surpassing that of single component WO3-Ov and In2S3 (by 35.5 and 3.9 times, respectively), as well as WO3/In2S3 heterojunction. This work provides new insight into regulating the photogenerated carrier dynamics at the heterointerface and also helps design highly efficient S-scheme photocatalysts.

Bio-Derived Photothermal Materials and Evaporators for Sustainable Solar Energy-Driven Water Process.

Interfacial solar steam generation (ISSG) is considered as an excellent seawater desalination technology because of its electricity-independent nature, low cost, and portability. However, improving the water evaporation efficiency, simplifying the fabrication process, and reducing the overall cost of the evaporator are still challenging. Here, an efficient and sustainable solar water evaporator is fabricated with carbonized ginkgo biloba leaves as the structural basis of photothermal materials. The combination of the abundant capillary channels in ginkgo leaves paired with polyacrylamide (PAM) hydrogel accelerates water transportation and solar-driven evaporation. The fabricated evaporator shows excellent photothermal conversion capability and evaporates water at 2.39 kg m-2 h-1 under 1 sun irradiation. In addition, the device exhibits remarkable stability in simulated seawater and can effectively realize seawater desalination or sewage treatment. As a result, the system is promising for future highly efficient solar evaporation due to its environmental protection and low cost.

Utilization of group 10 2D TMDs-PdSe2 as a nonlinear optical material for obtaining switchable laser pulse generation modes.

In-plane anisotropic two-dimensional (2D) materials have gained considerable interest in the field of research, due to having the potential of being used in different device applications. Recently, among these 2D materials, group 10 transition metal dichalcogenides (TMDs) pentagonal Palladium diselenide (PdSe2) is utilized in various sections of researches like nanoelectronics, thermoelectric, spintronics, optoelectronics, and ultrafast photonics, owing to its high air stability and broad absorption spectrum properties. In this paper, it is demonstrated that by utilizing this novel 2D layered PdSe2 material as a saturable absorber (SA) in an EDF laser system, it is possible to obtain switchable laser pulse generation modes. At first, the Q-switching operation mode is attained at a threshold pump power of 56.8 mW at 1564 nm, where the modulation range of pulse duration and repetition rate is 18.5 µs-2.0 µs and 16.4 kHz-57.0 kHz, respectively. Afterward, the laser pulse generation mode is switched to the mode-locked state at a pump power of 63.1 mW (threshold value) by changing the polarization condition inside the laser cavity, and this phenomenon persists until the maximum pump power of 230.4 mW. For this mode-locking operation, the achieved pulse duration is 766 fs, corresponding to the central wavelength and 3 dB bandwidth of 1566 nm and 4.16 nm, respectively. Finally, it is illustrated that PdSe2 exhibits a modulation depth of 7.01%, which substantiates the high nonlinearity of the material. To the best of the authors' knowledge, this is the first time of switchable modes for laser pulse generation are achieved by using this PdSe2 SA. Therefore, this work will encourage the research community to carry out further studies with this PdSe2 material in the future.

Direct Evidence of Void-Induced Structural Relaxations in Colloidal Glass Formers.

Particle dynamics in supercooled liquids are often dominated by stringlike motions in which lines of particles perform activated hops cooperatively. The structural features triggering these motions, crucial in understanding glassy dynamics, remain highly controversial. We experimentally study microscopic particle dynamics in colloidal glass formers at high packing fractions. With a small polydispersity leading to glass-crystal coexistence, a void in the form of a vacancy in the crystal can diffuse reversibly into the glass and further induces stringlike motions. In the glass, a void takes the form of a quasivoid consisting of a few neighboring free volumes and is transported by the stringlike motions it induces. In fully glassy systems with a large polydispersity, similar quasivoid actions are observed. The mobile particles cluster into stringlike or compact geometries, but the compact ones can be further broken down into connected sequences of strings, establishing their general importance.

Phosphorus Incorporation into Co9 S8 Nanocages for Highly Efficient Oxygen Evolution Catalysis.

The improvement of activity of electrocatalysts lies in the increment of the density of active sites or the enhancement of intrinsic activity of each active site. A common strategy to realize dual active sites is the use of bimetal compound catalysts, where each metal atom contributes one active site. In this work, a new concept is presented to realize dual active sites with tunable electron densities in monometal compound catalysts. Dual Co2+ tetrahedral (Co2+ (Td )) and Co3+ octahedral (Co3+ (Oh )) coordination active sites are developed and adjustable electron densities on the Co2+ (Td ) and Co3+ (Oh ) are further achieved by phosphorus incorporation (P-Co9 S8 ). The experimental results and density functional theory calculations show that the nonmetal P doping can systematically modulate charge density of Co2+ (Td ) and Co3+ (Oh ) in P-Co9 S8 and simultaneously improve the electrical conductivity of Co9 S8 , which substantially enhances oxygen evolution reaction performance of P-Co9 S8 .

In2Se3 nanosheets with broadband saturable absorption used for near-infrared femtosecond laser mode locking.

Indium selenide (In2Se3) has attracted tremendous attention due to its favorable electronic features, broad tunable bandgap, high stability and other attractive properties. However, its further applications for nonlinear optics have not yet been fully explored. In this work, we demonstrate that few-layer α-In2Se3 nanosheets exhibit strong saturable absorption properties over a wide wavelength range covering 800, 1064 and 1550 nm. The few-layer α-In2Se3 nanosheets used for this experiment are fabricated via a simple ultrasonic exfoliation in liquid. Stable ultrafast mode-locking laser pulses are obtained from both ytterbium-doped and erbium-doped fiber laser systems operating at 1064 and 1550 nm, respectively. A pulse duration as short as 215 fs was achieved in the Er-doped fiber laser system. Stable output pulses over 6 h of operation were obtained in both laser systems. The pulse energy and peak power of the laser output pulses were increased by reducing the In2Se3 thickness. These results indicate that α-In2Se3 nanosheets with low layer numbers are promising candidates for broad ultrafast photonics devices, such as optical switchers, Q-switchers and mode lockers.

Laser Q-switching with PtS2 microflakes saturable absorber.

Numerous studies have been conducted to explore the performance of two-dimensional (2D) layered nano-materials based saturable absorber (SA) for pulsed laser applications. However, fabricating materials in nanoscale requires complicated preparation processes, high energy consumption, and high expertise. Hence, the study of pulsed laser performance based on the saturable absorber prepared by layered materials with bulk-micro size have gained a great attention. Platinum disulfide (PtS2), which is newly developed group 10 2D layered materials, offers great potential for the laser photonic applications owing to its high carrier mobility, broadly tunable natural bandgap energy, and stability. In this work, the first passively Q-switched Erbium (Er) doped fiber laser is demonstrated with an operational wavelength of 1568.8 nm by using PtS2 microflakes saturable absorber, fabricated by a simple liquid exfoliation in N-Methyl-2-pyrrolidone (NMP) and then incorporated into polyvinyl alcohol (PVA) polymer thin film. A stable Q-switched laser operation is achieved by using this PtS2-SA within a fiber laser ring cavity. The maximum average output power is obtained as 1.1 mW, corresponding to the repetition rate of 24.6 kHz, the pulse duration of 4.2 µs, and single pulse energy of 45.6 nJ. These results open up new applications of this novel PtS2 layered material.

High-performance MoS2/Si heterojunction broadband photodetectors from deep ultraviolet to near infrared.

Polycrystalline 2D layered molybdenum disulfide (MoS2) films were synthesized via a thermal decomposition method. The MoS2/Si heterostructures were constructed in situ by synthesis MoS2 on plane Si substrates. Such MoS2/Si heterostructures exhibited high sensitivity to light illumination with wavelengths ranging from the deep ultraviolet to the near infrared. Photoresponse analysis reveals that a high responsivity of 23.1 A/W, a specific detectivity of 1.63×1012 Jones, and a fast response speed of 21.6/65.5 µs were achieved. Notably, the MoS2/Si heterojunction photodetector could operate with excellent stability and repeatability over a wide frequency range up to 150 kHz. The high performance could be attributed to the high-quality heterojunction between MoS2 and Si obtained by the in situ fabrication process. Such high performance with broadband response suggests that MoS2/Si heterostructures could have great potential in optoelectronic applications.

The WS2 quantum dot: preparation, characterization and its optical limiting effect in polymethylmethacrylate.

Due to the matching surface energy, WS2 quantum dots (QDs) can be obtained through direct liquid exfoliation in N-methyl-2-pyrrolidone rather than an ethanol and water mixture. Ultra-small WS2 QDs with a diameter of 2.4 nm are fabricated by an ultrasound method followed by high speed centrifugation up to 10 000 rpm. An excellent nonlinear optical (NLO) property of the WS2 QD/ polymethylmethacrylate (PMMA) composite for the nanosecond pulsed laser at both 532 and 1064 nm has been measured. Results illustrate the lower onset thresholds (F ON ), lower optical limiting thresholds (F OL ), and higher two-photon absorption coefficient (ß) with respect to a higher concentration of embedded WS2 QDs into the PMMA solid state matrix for both 532 and 1064 nm.

Constructing Interfacial Energy Transfer for Photon Up- and Down-Conversion from Lanthanides in a Core-Shell Nanostructure.

We report a new mechanistic strategy for controlling and modifying the photon emission of lanthanides in a core-shell nanostructure by using interfacial energy transfer. By taking advantage of this mechanism with Gd(3+) as the energy donor, we have realized efficient up- and down-converted emissions from a series of lanthanide emitters (Eu(3+) , Tb(3+) , Dy(3+) , and Sm(3+) ) in these core-shell nanoparticles, which do not need a migratory host sublattice. Moreover, we have demonstrated that the Gd(3+) -mediated interfacial energy transfer, in contrast to energy migration, is the leading process contributing to the photon emission of lanthanide dopants for the NaGdF4 @NaGdF4 core-shell system. Our finding suggests a new direction for research into better control of energy transfer at the nanometer length scale, which would help to stimulate new concepts for designing and improving photon emission of the lanthanide-based luminescent materials.

High-power passively mode-locked Nd:YVO(4) laser using SWCNT saturable absorber fabricated by dip coating method.

Passive mode locked laser is typically achieved by the Semiconductor Saturable absorber Mirror, SESAM, saturable absorber, which is produced by expensive and complicated metal organic chemical vapor deposition method. Carbon based single wall carbon nanotube (SWCNT), saturable absorber, is a promising material which is capable to produce stable passive mode-locking in the high power laser cavity over a wide operational wavelength range. This study has successfully demonstrated the high power mode locking laser system operating at 1 micron by using SWCNT based absorbers fabricated by dip coating method. The proposed fabrication method is practical, simple and cost effective for fabricating SWCNT saturable absorber. The demonstrated high power Nd:YVO(4) mode-locked laser operating at 1064nm have maximum output power up to 2.7W,with the 167MHz repetition rate and 3.1 ps pulse duration, respectively. The calculated output pulse energy and peak power are 16.1nJ and 5.2kW, respectively.

2D Semi-Metallic Hafnium Ditelluride: A Novel Nonlinear Optical Material for Ultrafast and Ultranarrow Photonics Applications.

2D semi-metallic hafnium ditelluride material is used in several applications such as solar steam generation, gas sensing, and catalysis owing to its strong near-infrared absorbance, high sensitivity, and distinctive electronic structure. The zero-bandgap characteristics, along with the thermal and dynamic stability of 2D-HfTe2, make it a desirable choice for developing long-wavelength-range photonics devices. Herein, the HfTe2 -nanosheets are prepared using the liquid-phase exfoliation method, and their superior nonlinear optical properties are demonstrated by the obtained modulation depth of 11.9% (800 nm) and 6.35% (1560 nm), respectively. In addition, the observed transition from saturable to reverse saturable absorption indicates adaptability of the prepared material in nonlinear optics. By utilizing a side polished fiber-based HfTe2 -saturable absorber (SA) inside an Er-doped fiber laser cavity, a mode-locked laser with 724 fs pulse width and 56.63 dB signal-to-noise ratio (SNR) is realized for the first time. The generated laser with this SA has the second lowest mode-locking pump threshold (18.35 mW), among the other 2D material based-SAs, thus paving the way for future laser development with improved efficiency and reduced thermal impact. Finally, employing this HfTe2 -SA, a highly stable single-frequency fiber laser (SNR ≈ 74.56 dB; linewidth ≈ 1.268 kHz) is generated for the first time, indicating its promising ultranarrow photonic application.

Multiwalled Carbon Nanotube-Based On-Body Patch Antenna for Detecting COVID-19-Affected Lungs.

A novel rectangular patch antenna based on multiwall carbon nanotubes has been designed and developed for assisting the initial detection of COVID-19-affected lungs. Due to their highly conductive nature, each nanotube echoes electromagnetic waves in a unique manner, influencing the increase in bandwidth. The proposed antenna operates at 6.63, 7.291, 7.29, and 7.22 GHz with a higher bandwidth classified as an ultrawide band and can be used on a human body phantom model because of its flexibility and decreased radiation qualities. Flame retardant 4 is chosen as a substrate with a uniform thickness of 1.62 mm due to its inexpensive cost and excellent electrical properties. The maximum specific absorption rate of the proposed antenna is obtained as 1.77 W/kg for 10 g of tissues. For testing purposes, a model including all the known features of COVID-19-affected lungs is developed. The designed antenna exhibits excellent performance in free space, normal lungs, and affected lung environments. It might be utilized as a first screening device for COVID-19 patients, especially in resource-constrained areas where traditional medical equipment such as X-ray and computerized tomography scans are scarce.

Waste Egg Tray and Toner-Derived Highly Efficient 3D Solar Evaporator for Freshwater Generation.

With the advancement of civilization, water purification, as well as management and disposal of ever-increasing municipal solid waste (MSW), and e-waste, have become global concerns. To address these issues in a sustainable way, a 3D solar evaporator has been proposed in this paper by repurposing recycled paper from MSW in the form of egg trays and waste dry toner (e-waste) using a facile fabrication method. The unique 3D porous structure, fibrous surface, superior water absorbing capability as well as low thermal conductivity of wastepaper-derived egg trays make them an excellent candidate for an efficient solar evaporator, while the waste toner powder coating significantly enhances the optical absorbance capacity. Under 1 sun illumination, the proposed solar evaporator demonstrates an excellent evaporation rate and efficiency of 1.3 kg/m2 h and 78.5%, respectively. Moreover, the competitive advantage of the 3D structure in collecting solar irradiance at various light incident angles in comparison to a 2D structure, excellent cycle stability, low processing temperature, and the use of low-cost waste materials enable its use for large-scale water purification systems.

Beyond Tristimulus Color Vision with Perovskite-Based Multispectral Sensors.

In this study, optical multispectral sensors based on perovskite semiconductors have been proposed, simulated, and characterized. The perovskite material system combined with the 3D vertical integration of the sensor channels allow for realizing sensors with high sensitivities and a high spectral resolution. The sensors can be applied in several emerging areas, including biomedical imaging, surveillance, complex motion planning of autonomous robots or vehicles, artificial intelligence, and agricultural applications. The sensor elements can be vertically integrated on a readout electronic to realize sensor arrays and multispectral digital cameras. In this study, three- and six-channel vertically stacked perovskite sensors are optically designed, electromagnetically simulated, and colorimetrically characterized to evaluate the color reproduction. The proposed sensors allow for the implementation of snapshot cameras with high sensitivity. The proposed sensor is compared to other sensor technologies in terms of sensitivity and selectivity.

Nonlinear Optical Activities in Two-Dimensional Gallium Sulfide: A Comprehensive Study.

The nonlinear optical (NLO) properties of two-dimensional (2D) materials are fascinating for fundamental physics and optoelectronic device development. However, relatively few investigations have been conducted to establish the combined NLO activities of a 2D material. Herein, a study of numerous NLO properties of 2D gallium sulfide (GaS), including second-harmonic generation (SHG), two-photon excited fluorescence (TPEF), and NLO absorption are presented. The layer-dependent SHG response of 2D GaS identifies the noncentrosymmetric nature of the odd layers, and the second-order susceptibility (χ2) value of 47.98 pm/V (three-layers of GaS) indicates the superior efficiency of the SHG signal. In addition, structural deformation induces the symmetry breaking and facilitates the SHG in the bulk samples, whereas a possible efficient symmetry breaking in the liquid-phase exfoliated samples results in an enhancement of the SHG signal, providing prospective fields of investigation for researchers. The generation of TPEF from 800 to 860 nm depicts the two-photon absorption characteristics of 2D GaS material. Moreover, the saturable absorption characteristics of 2D GaS are realized from the largest nonlinear absorption coefficient (ß) of -9.3 × 103, -91.0 × 103, and -6.05 × 103 cm/GW and giant modulation depths (Ts) of 24.4%, 35.3%, and 29.1% at three different wavelengths of 800, 1066, and 1560 nm, respectively. Hence, such NLO activities indicate that 2D GaS material can facilitate in the technical advancements of future nonlinear optoelectronic devices.

Fabrication of 2D PdSe2/3D CdTe Mixed-Dimensional van der Waals Heterojunction for Broadband Infrared Detection.

Room-temperature infrared photodetectors are in great demand because of their vitally important applications in the military and civilian fields, which has inspired intensive studies in recent decades. Here, we present the fabrication of a large-size PdSe2/CdTe mixed-dimensional van der Waals (vdW) heterojunction for room-temperature infrared detection. Taking advantage of the wide light absorption of the multilayer PdSe2, high-quality vdW interface, and unique mixed-dimensional device geometry, the present device is capable of detecting an ultrawide light up to long-wave infrared (LWIR) of 10.6 µm at room temperature. In addition, our photodetector exhibits a good capability to follow short pulse infrared signals with a quick response rate of 70 ns, a large responsivity of 324.7 mA/W, and a reasonable specific detectivity of 3.3 × 1012 Jones. Significantly, the assembled photodetector is highly sensitive to a polarized infrared light signal with a decent polarization sensitivity of 4.4. More importantly, an outstanding LWIR imaging capability based on the PdSe2/CdTe vdW heterojunction at nonrefrigeration condition is demonstrated. Our work paves a novel route for the design of highly polarization-sensitive, room-temperature infrared photodetectors.

Two-Dimensional Gallium Sulfide as a Novel Saturable Absorber for Broadband Ultrafast Photonics Applications.

Two-dimensional (2D) gallium sulfide (GaS) offers a plethora of exceptional electrical and optical properties, allowing it to be used in a wide range of applications, including photodetectors, hydrogen generation, and nonlinear optical devices. In this paper, ultrathin 2D GaS nanosheets are synthesized using the liquid-phase exfoliation method, and the structure, morphology, and chemical composition of the as-prepared nanosheets are extensively investigated. After depositing 2D GaS nanosheets on side polished fibers, successful saturable absorbers (SAs) are fabricated for the first time. The realized modulation depths are 10 and 5.3% at 1 and 1.5 µm, respectively, indicating the wideband saturable absorption performance of the prepared SAs. By integrating GaS-SAs into three different wavelength-based fiber laser cavities, stable mode-locked pulses are achieved, having pulse durations of 46.22 ps (1 µm), 614 fs (1.5 µm), and 1.02 ps (2 µm), respectively. Additionally, different orders of harmonic mode-locked pulses with the highest repetition rate of 0.55 GHz (45th order) and Q-switched pulses with the shortest pulse duration of 2.2 µs are obtained in the telecommunication waveband. These findings suggest that 2D GaS has a lot of potential for broadband ultrafast photonics in nonlinear photonics devices.