Abnormal Near-Infrared Absorption in 2D Black Phosphorus Induced by Ag Nanoclusters Surface Functionalization

2D Amino-Functionalized Black Phosphorus: A New Approach to Improve Hydrogen Gas Detection Performance

In recent years, hydrogen has gained attention as a potential solution to replace fossil fuels, thus reducing greenhouse gas emissions. The development of ever improving hydrogen sensors is a topic that is constantly under study due to concerns about the inherent risk of leaks of this gas and potential explosions. In this work, a new, long-term, stable phosphorene-based sensor was developed for hydrogen detection. A simple functionalization of phosphorene using urea was employed to synthesize an air-stable material, subsequently used to prepare films for gas sensing applications, via the drop casting method. The material was deeply characterized by different techniques (scanning electron microscopy, X-ray diffraction, X-ray photoelectron, and Raman spectroscopy), and the stability of the material in a noninert atmosphere was evaluated. The phosphorene-based sensor exhibited high sensitivity (up to 700 ppm) and selectivity toward hydrogen at room temperature, as well as long-term stability over five months under ambient conditions. To gain further insight into the gas sensing mechanism over the surface, we employed a dedicated apparatus, namely operando diffuse reflectance infrared Fourier transform, by exposing the chemoresistive sensor to hydrogen gas under dry air conditions.

Thermoelectrically Driven Dual-Mechanism Regulation on SERS and Application Potential for Rapid Detection of SARS-CoV-2 Viruses and Microplastics

Electric-induced surface-enhanced Raman scattering (E-SERS) has been widely studied for its flexible regulation of SERS after the substrate is prepared. However, the enhancement effect is not sufficiently high in the E-SERS technology reported thus far, and no suitable field of application exists. In this study, a highly sensitive thermoelectrically induced SERS substrate, Ag/graphene/ZnO (AGZ), was fabricated using ZnO nanoarrays (NRs), graphene, and Ag nanoparticles (NPs). Applying a temperature gradient to the ZnO NRs enhanced the SERS signals of the probe molecules by a factor of approximately 20. Theoretical and experimental results showed that the thermoelectric potential enables the simultaneous modulation of the Fermi energy level of graphene and the plasma resonance peak of Ag NPs, resulting in a double enhancement in terms of physical and chemical mechanisms. The AGZ substrate was then combined with a mask to create a wearable thermoelectrically enhanced SERS mask for collecting SARS-CoV-2 viruses and microplastics. Its SERS signal can be enhanced by the temperature gradient created between a body heat source (∼37 °C) and a cold environment. The suitability of this method for virus detection was also examined using a reverse transcription-polymerase chain reaction and SARS-CoV-2 virus antigen detection. This work offers new horizons for research of E-SERS, and its application potential for rapid detection of the SARS-CoV-2 virus and microplastics was also studied.

Photodetection and Infrared Imaging Based on Cd3As2 Epitaxial Vertical Heterostructures

Due to the nontrivial electronic structure, Cd₃As₂ is predicted to possess various transport properties and outstanding photoresponses. Photodetectors based on topological materials are mostly made up of nanoplates, yet monolithic in situ heteroepitaxial Cd₃As₂ photodetectors are rarely reported to date owing to the crystal mismatch between Cd₃As₂ and semiconductors. Here, we demonstrate Cd₃As₂/Zn_xCd_1-xTe/GaSb vertical heteroepitaxial photodetectors via molecule beam epitaxy. By constructing dual-Schottky junctions, these photodetectors show high responsivity and external quantum efficiency in a broadband spectrum. Based on the strong and fast photoresponse, we achieved visible light to near-infrared imaging using a one-pixel imaging system with a galvo. Our results illustrate that the integration of three-dimensional Dirac semimetal Cd₃As₂ with semiconductors has potential applications in broadband photodetection and infrared cameras.

Sandwiching Phosphorene with Iron Porphyrin Monolayer for High Stability and Its Biomimetic Sensor to Sensitively Detect Living Cell Released NO

Instability of 2D phosphorene material is the major obstacle for its broad applications. Herein phosphorene is sandwiched with self-assembled iron porphyrin monolayers on both sides (I-Phene) to significantly enhance stability. Iron porphyrin has strong interaction with phosphorene through formation of PFe bonds. The sandwich structure offers excellent stability of phosphorene by both-sided monolayer protections for an intact phosphorene structure more than 40 days under ambient conditions. Meanwhile, the electron transfer between iron porphyrin and phosphorene result in a high oxidation state of Fe, making I-Phene biomimetic sensitivity toward oxidation of nitric oxide (NO) for 2.5 and 4.0 times higher than phosphorene and iron-porphyrin alone, respectively. Moreover, I-Phene exhibits excellent selectivity, a wide detection range, and a low detection limit at a low oxidation potential of 0.82 V, which is comparable with the reported noble metal based biomimetic sensors while ranking the best among all non-noble biomimetic ones. I-Phene is further used for real-time monitoring NO released from cells. This work provides effective approach against phosphorene degrading for outstanding stability, which has universal significance for its various important applications, and holds a great promise for a highly sensitive biomimetic sensor in live-cell assays.

P=O Functionalized Black Phosphorus/1T-WS2 Nanocomposite High Efficiency Hybrid Photocatalyst for Air/Water Pollutant Degradation

Research on layered two-dimensional (2D) materials is at the forefront of material science. Because 2D materialshave variousplate shapes, there is a great deal of research on the layer-by-layer-type junction structure. In this study, we designed a composite catalyst with a dimension lower than two dimensions and with catalysts that canbe combined so that the band structures can be designed to suit various applications and cover for each other’s disadvantages. Among transition metal dichalcogenides, 1T-WS₂ can be a promising catalytic material because of its unique electrical properties. Black phosphorus with properly controlled surface oxidation can act as a redox functional group. We synthesized black phosphorus that was properly surface oxidized by oxygen plasma treatment and made a catalyst for water quality improvement through composite with 1T-WS₂. This photocatalytic activity was highly efficient such that the reaction rate constant k was 10.31 × 10⁻² min⁻¹. In addition, a high-concentration methylene blue solution (20 ppm) was rapidly decomposed after more than 10 cycles and showed photo stability. Designing and fabricating bandgap energy-matching nanocomposite photocatalysts could provide a fundamental direction in solving the future’s clean energy problem.

Ag+ -Coupled Black Phosphorus Vesicles with Emerging NIR-II Photoacoustic Imaging Performance for Cancer Immune-Dynamic Therapy and Fast Wound Healing

A silver-ion-coupled black phosphorus (BP) vesicle (BP Ve-Ag⁺ ) with a second near infrared (NIR-II) window photoacoustic (PA) imaging capability was firstly constructed to maximize the potential of BP quantum dot (QD) in deeper bioimaging and diversified therapy. The embedded Ag⁺ could improve the relatively large band gap of BP QD via intense charge coupling based on theoretical simulation results, subsequently leading to the enhanced optical absorption capability, accompanied with the occurrence of the strong NIR-II PA signal. Guiding by NIR-II PA bioimaging, the hidden Ag⁺ could be precisely released with the disassembly of Ve during photodynamic therapy process and captured by macrophages located in lesion region for arousing synergistic cancer photodynamic/Ag⁺ immunotherapy. BP Ve-Ag⁺ can contrapuntally kill pathogenic bacteria and accelerate wound healing monitored by NIR-II PA imaging.

Silver-Laden Black Phosphorus Nanosheets for an Efficient In Vivo Antimicrobial Application

Nanobactericides represent one of the most efficient and promising strategies for eliminating bacterial infection considering the increasing resistance threats of conventional antibiotics. Black phosphorus (BP) is the most exciting postgraphene layered 2D nanomaterial with convincing physiochemical properties, yet the study of BP-based antibiotics is still in its infancy. Here, a compact silver nanoparticle (AgNP)-doped black phosphorus nanosheet (BPN) is constructed to synergistically enhance solar disinfection through the promoted reactive oxygen species (ROS) photogeneration, which is attributed to the improved electron-hole separation and recombination of BPNs as revealed from the systematic experimental studies. An in-depth density functional theory (DFT) calculation confirms that the integrated AgNPs provide a preferred site for facilitating the adsorption and activation of O₂ , thus promoting the more efficient and robust ROS generation on BPN-AgNP nanohybrids. Besides the enhanced photoinduced ROS, the anchored AgNPs simultaneously lead to a dramatically increased affinity toward bacteria, which facilitates a synergetic pathogen inactivation. Significantly, the convincing antimicrobial BPN-AgNP contributes to the prominent wound healing and antimicrobial ability in vivo with minimized biological burden. This sophisticated design of new 2D nanohybrids opens a new avenue for further exploiting BP-based nanohybrids in portable bandage and broad-spectrum disinfection applications.

Recent progress in black phosphorus and black-phosphorus-analogue materials: properties, synthesis and applications

Black phosphorus (BP), a novel two-dimensional (2D) layered semiconductor material, has attracted tremendous attention since 2014 due to its prominent carrier mobility, thickness-dependent direct bandgap and in-plane anisotropic physical properties. BP has been considered as a promising material for many applications, such as in transistors, photonics, optoelectronics, sensors, batteries and catalysis. However, the development of BP was hampered by its instability under ambient conditions, as well as by the lack of methods to synthesize large-area and high quality 2D nanofilms. Recently, some BP-analogue materials such as binary phosphides (MPx), transition metal phosphorus trichalcogenides (MPX3), and 2D group V (pnictogens) and 2D group VI materials have attracted increasing interest for their unique and stable structures, and excellent physical and chemical properties. This article, which focuses on BP and BP-analogue materials, will present their crystal structure, properties, synthesis methods and applications. Also the similarity and difference between BP and BP-analogue materials will be discussed, and the presentation of the future opportunities and challenges of the materials are included at the end.

Perpendicular Optical Reversal of the Linear Dichroism and Polarized Photodetection in 2D GeAs

The ability to detect linearly polarized light is central to practical applications in polarized optical and optoelectronic fields and has been successfully demonstrated with polarized photodetection of in-plane anisotropic two-dimensional (2D) materials. Here, we report the anisotropic optical characterization of a group IV-V compound-2D germanium arsenic (GeAs) with anisotropic monoclinic structures. High-quality 2D GeAs crystals show the representative angle-resolved Raman property. The in-plane anisotropic optical nature of the GeAs crystal is further investigated by polarization-resolved absorption spectra (400-2000 nm) and polarization-sensitive photodetectors. From the visible to the near-infrared range, 2D GeAs nanoflakes demonstrate the distinct perpendicular optical reversal with a 75-80° angle on both the linear dichroism and polarization-sensitive photodetection. Obvious anisotropic features and the high dichroic ratio of I_pmax /I_pmin ∼ 1.49 at 520 nm and I_pmax /I_pmin ∼ 4.4 at 830 nm are achieved by the polarization-sensitive photodetection. The polarization-dependent photocurrent mapping implied that the polarized photocurrent mainly occurred at the Schottky photodiodes between electrode/GeAs interface. These experimental results are consistent with the theoretical calculation of band structure and band realignment. Besides the excellent polarization-sensitive photoresponse properties, GeAs-based photodetectors also exhibit rapid on/off response. These results demonstrate that the 2D GeAs crystals have promising potential for polarization optical applications.

Two-dimensional black phosphorus: its fabrication, functionalization and applications

Phosphorus, one of the most abundant elements in the Earth (∼0.1%), has attracted much attention in the last five years since the rediscovery of two-dimensional (2D) black phosphorus (BP) in 2014. The successful scaling down of BP endows this 'old material' with new vitality, resulting from the intriguing semiconducting properties in the atomic scale limit, i.e. layer-dependent bandgap that covers from the visible light to mid-infrared light spectrum as well as hole-dominated ambipolar transport characteristics. Intensive research effort has been devoted to the fabrication, characterization, functionalization and application of BP and other phosphorus allotropes. In this review article, we summarize the fundamental properties and fabrication techniques of BP, with particular emphasis on the recent progress in molecular beam epitaxy growth of 2D phosphorus. Subsequently, we highlight recent progress in BP (opto)electronic device applications achieved via customized manipulation methods, such as interface, defect and bandgap engineering as well as forming Lego-like stacked heterostructures.

High-Performance Wafer-Scale MoS2 Transistors toward Practical Application

Atomic thin transition-metal dichalcogenides (TMDs) are considered as an emerging platform to build next-generation semiconductor devices. However, to date most devices are still based on exfoliated TMD sheets on a micrometer scale. Here, a novel chemical vapor deposition synthesis strategy by introducing multilayer (ML) MoS₂ islands to improve device performance is proposed. A four-probe method is applied to confirm that the contact resistance decreases by one order of magnitude, which can be attributed to a conformal contact by the extra amount of exposed edges from the ML-MoS₂ islands. Based on such continuous MoS₂ films synthesized on a 2 in. insulating substrate, a top-gated field effect transistor (FET) array is fabricated to explore key metrics such as threshold voltage (V _T ) and field effect mobility (μ_FE ) for hundreds of MoS₂ FETs. The statistical results exhibit a surprisingly low variability of these parameters. An average effective μ_FE of 70 cm² V^-1 s^-1 and subthreshold swing of about 150 mV dec^-1 are extracted from these MoS₂ FETs, which are comparable to the best top-gated MoS₂ FETs achieved by mechanical exfoliation. The result is a key step toward scaling 2D-TMDs into functional systems and paves the way for the future development of 2D-TMDs integrated circuits.