Broadband and Tunable Light Harvesting in Nanorippled MoS2 Ultrathin Films

Photoluminescence of MoS2 on Plasmonic Gold Nanoparticles Depending on the Aggregate Size

Transition metal dichalcogenides (TMDs) are promising candidates for ultrathin functional semiconductor devices. In particular, incorporating plasmonic nanoparticles into TMD-based devices enhances the light-matter interaction for increased absorption efficiency and enables control of device performance such as electronic, electrical, and optical properties. In this heterohybrid structure, manipulating the number of TMD layers and the aggregate size of plasmonic nanoparticles is a straightforward approach to tailoring device performance. In this study, we use photoluminescence (PL) spectroscopy, which is a commonly employed technique for monitoring device performance, to analyze the changes in electronic and optical properties depending on the number of MoS2 layers and the size of the gold nanoparticle (AuNP) aggregate under nonresonant and resonant excitation conditions. The PL intensity in monolayer MoS2/AuNPs increases as the size of aggregates increases irrespective of the excitation conditions. The strain induced by AuNPs causes a red shift, but as the aggregates grow larger, the effect of p-doping increases and the blue shift becomes prominent. In multilayer MoS2/AuNPs, quenched PL intensity is observed under nonresonant excitation, while enhancement is noted under resonant excitation, which is mainly contributed by p-doping and LSPR, respectively. Remarkably, the alteration in the spectral shape due to resonant excitation is evident solely in small aggregates of AuNPs across all layers.

Locally Strained 2D Materials: Preparation, Properties, and Applications

2D materials are promising for strain engineering due to their atomic thickness and exceptional mechanical properties. In particular, non-uniform and localized strain can be induced in 2D materials by generating out-of-plane deformations, resulting in novel phenomena and properties, as witnessed in recent years. Therefore, the locally strained 2D materials are of great value for both fundamental studies and practical applications. This review discusses techniques for introducing local strains to 2D materials, and their feasibility, advantages, and challenges. Then, the unique effects and properties that arise from local strain are explored. The representative applications based on locally strained 2D materials are illustrated, including memristor, single photon emitter, and photodetector. Finally, concluding remarks on the challenges and opportunities in the emerging field of locally strained 2D materials are provided.

Broadband Photon Harvesting in Organic Photovoltaic Devices Induced by Large-Area Nanogrooved Templates

Thin-film organic photovoltaic (OPV) devices represent an attractive alternative to conventional silicon solar cells due to their lightweight, flexibility, and low cost. However, the relatively low optical absorption of the OPV active layers still represents an open issue in view of efficient devices that cannot be addressed by adopting conventional light coupling strategies derived from thick PV absorbers. The light coupling to thin-film solar cells can be boosted by nanostructuring the device interfaces at the subwavelength scale. Here, we demonstrate broadband and omnidirectional photon harvesting in thin-film OPV devices enabled by highly ordered one-dimensional (1D) arrays of nanogrooves. Laser interference lithography, in combination with reactive ion etching (RIE), provides the controlled tailoring of the height and periodicity of the silica grooves, enabling effective tuning of the anti-reflection properties in the active organic layer (PTB7:PCBM). With this strategy, we demonstrate a strong enhancement of the optical absorption, as high as 19% with respect to a flat device, over a broadband visible and near-infrared spectrum. The OPV device supported on these optimized nanogrooved substrates yields a 14% increase in short-circuit current over the corresponding flat device, highlighting the potential of this large-scale light-harvesting strategy in the broader context of thin-film technologies.

Durable Rapid Self-Disinfection, Reusable Protective Clothing Based on the Ag-Pd@MoS2 Nanozyme with Enhanced Triple-Mode Synergistic Antibacterial Effect

Personal protective clothing plays an important role in isolating microorganisms and harmful ultrafine dust, but it cannot quickly inactivate bacteria intercepted on the surface, making it a potential source of infection. However, spontaneous and durable rapid sterilization is a major challenge for commercial protective clothing. Herein, we exquisitely engineered a visible light-enhanced Ag-Pd@MoS₂ nanozyme-based fabric, named PVDF/Ag-Pd@MoS₂/PAN fabric (PAPMP fabric), with prominent triple-mode synergistic antibacterial effect through the replacement reaction, electrospinning technique, and vacuum filtration method. The modification of Ag-Pd greatly strengthened the absorption of MoS₂ nanosheets to the visible light spectrum (390-780 nm) and its corresponding catalytic performance. Meanwhile, the combination of MoS₂ nanosheets significantly enhanced the oxidase-like characteristics of Ag-Pd under sunlight irradiation, increasing the yield of surface-bound ¹O₂ ∼4.54 times in 5 min. In addition, the obtained Ag-Pd@MoS₂ nanozyme showed an excellent photo-to-thermal conversion property (36.12%), which enabled the sharp increase in the surface temperature of the PAPMP fabric to 62.8 °C in 1 min under a solar simulator (1 W/cm²). Correspondingly, the obtained PAPMP fabric exhibited excellent intrinsic antibacterial effect and greatly shortened the sterilization time from 4 h to only 5 min under sunlight stimulation. The rapid antibacterial effect of the fabric was attributable to the enhanced production rate of surface-bound reactive oxygen species and the increased temperature by solar irradiation. Notably, the fabric still maintained the efficient germicidal effect even after 30 washing cycles. In addition to high reusability, the fabric also had outstanding biological compatibility and water resistance. Our work provides a novel strategy to improve the inherent timely sterilization and heat preservation efficiency of protective clothing.

Flat-optics hybrid MoS2/polymer films for photochemical conversion

Novel light harvesting platforms and strategies are crucial to develop renewable photon to energy conversion technologies that overcome the current global energy and environmental challenges. Two-dimensional (2D) transition metal dichalcogenide (TMD) semiconductor layers are particularly attractive for photoconversion applications but new ultra-compact photon harvesting schemes are urgently required to mitigate their poor photon absorption properties. Here, we propose a flat-optics scheme based on nanogrooved ultra-thin MoS₂ layers conformally grown onto large area (cm² scale) nanopatterned templates. The subwavelength re-shaping of the 2D-TMD layers promotes the excitation of photonic Rayleigh anomaly (RA) modes, uniquely boosting a strong in-plane electromagnetic confinement. By tailoring the illumination conditions, we demonstrate effective tuning of the photonic anomalies over a broadband visible spectrum across the absorption band of relevant polluting dye molecules. Thanks to the strong photonic in-plane confinement, we achieve a resonant enhancement of the photodissociation rate of methylene blue (MB) molecules, well above a factor of 2. These results highlight the potential of flat-optics photon harvesting schemes for boosting photoconversion efficiency in large-scale hybrid 2D-TMD/polymer layers, with a strong impact in various applications ranging from new-generation photonics to waste water remediation and renewable energy storage.

1D/2D Hybrid Te/Graphene and Te/MoS2: Multifaceted Broadband Photonics and Green-Energy Applications

We highlight the enhanced electronic and optical functionalization in the hybrid heterojunction of one-dimensional (1D) tellurene with a two-dimensional (2D) monolayer of graphene and MoS₂ in both lateral and vertical geometries. The structural configurations of these assemblies are optimized with a comparative analysis of the energetics for different positional placements of the 1D system with respect to the hexagonal 2D substrate. The 1D/2D coupling of the electronic structure in this unique assembly enables the realization of the three different types of heterojunctions, viz. type I, type II, and Z-scheme. The interaction with 1D tellurene enables the opening of a band gap of the order of hundreds of meV in 2D graphene for both lateral and vertical geometries. With both static and time-dependent first-principles analysis, we indicate their potential applications in broadband photodetection and absorption, covering a wide range of visible to infrared (near-IR to mid-IR) spectrum from 380 to 10 000 nm. We indicate that this 1D/2D assembly also has bright prospects in green-energy harvesting.

Temperature induced modulation of resonant Raman scattering in bilayer 2H-MoS2

The temperature evolution of the resonant Raman scattering from high-quality bilayer 2H-MoS[Formula: see text] encapsulated in hexagonal BN flakes is presented. The observed resonant Raman scattering spectrum as initiated by the laser energy of 1.96 eV, close to the A excitonic resonance, shows rich and distinct vibrational features that are otherwise not observed in non-resonant scattering. The appearance of 1st and 2nd order phonon modes is unambiguously observed in a broad range of temperatures from 5 to 320 K. The spectrum includes the Raman-active modes, i.e. E[Formula: see text]([Formula: see text]) and A[Formula: see text]([Formula: see text]) along with their Davydov-split counterparts, i.e. E[Formula: see text]([Formula: see text]) and B[Formula: see text]([Formula: see text]). The temperature evolution of the Raman scattering spectrum brings forward key observations, as the integrated intensity profiles of different phonon modes show diverse trends. The Raman-active A[Formula: see text]([Formula: see text]) mode, which dominates the Raman scattering spectrum at T = 5 K quenches with increasing temperature. Surprisingly, at room temperature the B[Formula: see text]([Formula: see text]) mode, which is infrared-active in the bilayer, is substantially stronger than its nominally Raman-active A[Formula: see text]([Formula: see text]) counterpart.

Experimental Realization and Computational Investigations of B2S2 as a New 2D Material with Potential Applications

A new two-dimensional material B₂S₂ has been successfully synthesized for the first time and validated using first-principles calculations, with fundamental properties analyzed in detail. B₂S₂ has a similar structure as transition-metal dichalcogenides (TMDs) such as MoS₂, and the experimentally prepared free-standing B₂S₂ nanosheets show a uniform height profile lower than 1 nm. A thickness-modulated and unique oxidation-level dependent band gap of B₂S₂ is revealed by theoretical calculations, and vibration signatures are determined to offer a practical scheme for the characterization of B₂S₂. It is shown that the functionalized B₂S₂ is able to provide favorable sites for lithium adsorption with low diffusion barriers, and the prepared B₂S₂ shows a wide band photoluminescence response. These findings offer a feasible new and lighter member for the TMD-like 2D material family with potential for various aspects of applications, such as an anode material for Li-ion batteries and electronic and optoelectronic devices.

Engineering van der Waals Materials for Advanced Metaphotonics

The outstanding chemical and physical properties of 2D materials, together with their atomically thin nature, make them ideal candidates for metaphotonic device integration and construction, which requires deep subwavelength light-matter interaction to achieve optical functionalities beyond conventional optical phenomena observed in naturally available materials. In addition to their intrinsic properties, the possibility to further manipulate the properties of 2D materials via chemical or physical engineering dramatically enhances their capability, evoking new science on light-matter interaction, leading to leaped performance of existing functional devices and giving birth to new metaphotonic devices that were unattainable previously. Comprehensive understanding of the intrinsic properties of 2D materials, approaches and capabilities for chemical and physical engineering methods, the resulting property modifications and novel functionalities, and applications of metaphotonic devices are provided in this review. Through reviewing the detailed progress in each aspect and the state-of-the-art achievement, insightful analyses of the outstanding challenges and future directions are elucidated in this cross-disciplinary comprehensive review with the aim to provide an overall development picture in the field of 2D material metaphotonics and promote rapid progress in this fast emerging and prosperous field.

Enhanced Catalytic Activity of a New Nanobiocatalytic System Formed by the Adsorption of Cytochrome c on Pluronic Triblock Copolymer Stabilized MoS2 Nanosheets

The formation of nanobiohybrids through the immobilization of enzymes on functional nanomaterials has opened up exciting research opportunities at the nanobiointerfaces. These systems hold great promise for a wide range of applications in biosensing, biocatalytic, and biomedical fields. Here, we report the formation of a hybrid nanobiocatalytic system through the adsorption of cytochrome c (Cyt c) on pluronic triblock copolymer, P123 (PEO-b-PPO-b-PEO), stabilized MoS2 nanosheets. The use of pluronic polymer has helped not only to greatly stabilize the exfoliated MoS2 nanosheets but also to allow easy adsorption of Cyt c on the nanosheets without major structural changes due to its excellent biocompatibility and soft protein-binding property. By comparing the catalytic activity of the Cyt c-MoS2 nanobiohybrid with that of the free Cyt c and as-prepared MoS2 nanosheets, we have demonstrated the active role of the nanobiointeractions in enhancing the catalytic activity of the hybrid. Slight structural perturbation at the active site of the Cyt c upon adsorption on MoS2 has primarily facilitated the peroxidase activity of the Cyt c. As the MoS2 nanosheets and the native Cyt c individually exhibit weaker intrinsic peroxidase activities, their mutual modulation at the nanobiointerface has made the Cyt c-MoS2 a novel nanobiocatalyst with superior activity.

Free-standing plasmonic nanoarrays for leaky optical waveguiding and sensing

Flat optics nanogratings supported on thin free-standing membranes offer the opportunity to combine narrowband waveguided modes and Rayleigh anomalies for sensitive and tunable biosensing. At the surface of high-refractive index Si₃N₄ membranes we engineered lithographic nanogratings based on plasmonic nanostripes, demonstrating the excitation of sharp waveguided modes and lattice resonances. We achieved fine tuning of these optical modes over a broadband Visible and Near-Infrared spectrum, in full agreement with numerical calculations. This possibility allowed us to select sharp waveguided modes supporting strong near-field amplification, extending for hundreds of nanometres out of the grating and enabling versatile biosensing applications. We demonstrate the potential of this flat-optics platform by devising a proof-of-concept nanofluidic refractive index sensor exploiting the long-range waveguided mode operating at the sub-picoliter scale. This free-standing device configuration, that could be further engineered at the nanoscale, highlights the strong potential of flat-optics nanoarrays in optofluidics and nanofluidic biosensing.

Omnidirectional and broadband photon harvesting in self-organized Ge columnar nanovoids

Highly porous Germanium surfaces with uniformly distributed columnar nanovoid structures are fabricated over a large area (wafer scale) by large fluence Sn⁺irradiation through a thin silicon nitride layer. The latter represents a one-step highly reproducible approach with no material loss to strongly increase photon harvesting into a semiconductor active layer by exploiting the moth-eye antireflection effect. The ion implantation through the nitride cap layer allows fabricating porous nanostructures with high aspect ratio, which can be tailored by varying ion fluence. By comparing the reflectivity of nanoporous Ge films with a flat reference we demonstrate a strong and omnidirectional reduction in the optical reflectivity by a factor of 96% in the selected spectral regions around 960 nm and by a factor of 67.1% averaged over the broad spectral range from 350 to 1800 nm. Such highly anti-reflective nanostructured Ge films prepared over large-areas with a self-organized maskless approach have the potential to impact real world applications aiming at energy harvesting.

Ambient Pressure Chemical Vapor Deposition of Flat and Vertically Aligned MoS2 Nanosheets

Molybdenum disulfide (MoS₂) got tremendous attention due to its atomically thin body, rich physics, and high carrier mobility. The controlled synthesis of large area and high crystalline monolayer MoS₂ nanosheets on diverse substrates remains a challenge for potential practical applications. Synthesizing different structured MoS₂ nanosheets with horizontal and vertical orientations with respect to the substrate surface would bring a configurational versatility with benefit for numerous applications, including nanoelectronics, optoelectronics, and energy technologies. Among the proposed methods, ambient pressure chemical vapor deposition (AP-CVD) is a promising way for developing large-scale MoS₂ nanosheets because of its high flexibility and facile approach. Here, we show an effective way for synthesizing large-scale horizontally and vertically aligned MoS₂ on different substrates such as flat SiO₂/Si, pre-patterned SiO₂ and conductive substrates (TaN) benefit various direct TMDs production. In particular, we show precise control of CVD optimization for yielding high-quality MoS₂ layers by changing growth zone configuration and the process steps. We demonstrated that the influence of configuration variability by local changes of the S to MoO₃ precursor positions in the growth zones inside the CVD reactor is a key factor that results in differently oriented MoS₂ formation. Finally, we show the layer quality and physical properties of as-grown MoS₂ by means of different characterizations: Raman spectroscopy, scanning electron microscopy (SEM), photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS). These experimental findings provide a strong pathway for conformally recasting AP-CVD grown MoS₂ in many different configurations (i.e., substrate variability) or motifs (i.e., vertical or planar alignment) with potential for flexible electronics, optoelectronics, memories to energy storage devices.

Smart Textiles Based on MoS2 Hollow Nanospheres for Personal Thermal Management

Two-dimensional transition metal dichalcogenides are of particular interest in high-performance photothermal conversion, yet there remains a huge challenge in their practical application in smart textiles for healthcare, energy, and personal protection. Herein, we controllably prepared MoS₂ hollow nanospheres with a high photothermal conversion efficiency of 36% via a microemulsion-hydrothermal method, which was further applied to construct photothermal fibers for personal thermal management after a hot-blast dip-drying process. Because of the prominent photothermal effect, the temperature of the photothermal fibers sharply increases from the room temperature value of 25.0 to 55.5 °C in 60 s under near-infrared illumination with a power density of 500 W/cm². Furthermore, the photothermal fiber pad demonstrated an obvious temperature enhancement of 38.0 °C from a skin temperature of 22.0 °C after it was irradiated by natural sunlight for 60 s. Significantly, the antibacterial elimination rates of the photothermal fibers for Escherichia coli and Staphylococcus aureus are ∼99.9 and ∼99.8%, respectively. This strategy affords an avenue toward the practical application of photothermal materials in smart fibers for personal thermoregulation.