Two-Dimensional Pnictogen for Field-Effect Transistors

Unveiling excitons in two-dimensional β -pnictogens

In this paper, we investigate the optical, electronic, vibrational, and excitonic properties of four two-dimensional β -pnictogen materials-nitrogenene, phosphorene, arsenene, and antimonene-via density functional theory calculations and the Bethe-Salpeter equation. These materials possess indirect gaps with significant exciton binding energies, demonstrating isotropic behavior under circular light polarization and anisotropic behavior under linear polarization by absorbing light within the visible solar spectrum (except for nitrogenene). Furthermore, we observed that Raman frequencies red-shift in heavier pnictogen atoms aligning with experimental observations; simultaneously, quasi-particle effects notably influence the linear optical response intensively. These monolayers' excitonic effects lead to optical band gaps optimized for solar energy harvesting, positioning them as promising candidates for advanced optoelectronic device applications.

Identifying, Resolving, and Quantifying Anisotropy in ReS2 Nanomechanical Resonators

As an emerging two-dimensional semiconductor, rhenium disulfide (ReS₂ ) is renowned for its strong in-plane anisotropy in electrical, optical, and thermal properties. In contrast to the electrical, optical, optoelectrical, and thermal anisotropies that are extensively studied in ReS₂ , experimental characterization of mechanical properties has largely remained elusive. Here, it is demonstrated that the dynamic response in ReS₂ nanomechanical resonators can be leveraged to unambiguously resolve such disputes. Using anisotropic modal analysis, the parameter space for ReS₂ resonators in which mechanical anisotropy is best manifested in resonant responses is determined. By measuring their dynamic response in both spectral and spatial domains using resonant nanomechanical spectromicroscopy, it is clearly shown that ReS₂ crystal is mechanically anisotropic. Through fitting numerical models to experimental results, it is quantitatively determined that the in-plane Young's moduli are 127 and 201 GPa along the two orthogonal mechanical axes. In combination with polarized reflectance measurements, it is shown that the mechanical soft axis aligns with the Re-Re chain in the ReS₂ crystal. These results demonstrate that dynamic responses in nanomechanical devices can offer important insights into intrinsic properties in 2D crystals and provide design guidelines for future nanodevices with anisotropic resonant responses.

Size-tunable bismuth quantum dots for self-powered photodetectors under ambient conditions

Although black phosphorus analogue, bismuthene, has been extensively investigated in recent years, yet the investigation into the photoelectronic devices is still in its infancy. In this contribution, uniform zero-dimensional (0D) bismuth (Bi) quantum dots (QDs) with different sizes were successfully synthesized by a simple solvothermal method. The as-synthesized 0D Bi QDs serve as working electrode materials by a direct deposition for photoelectrochemical (PEC)-type photodetection. The PEC results demonstrate that the as-fabricated 0D Bi QD-based electrode not only possess suitable self-powered broadband photoresponse, but also displays excellent photodetection performance. Under simulated light, the photocurrent density and photoresponsivity of the as-fabricated 0D Bi QD-based electrode can reach 2690 nA cm^-2, and 22.0μA W^-1, respectively. In addition, the as-prepared Bi QDs with the average diameter of 17 nm exhibit the best PEC photoresponse behavior in the studied size range of Bi QDs, mainly ascribed to the synergistic effect of suitable band gap and accessible active sites. It is anticipated that the uniform Bi QDs can be served as building blocks for a variety of photoelectronic devices, further expanding the application prospects of bismuthene, and can provide in-depth acknowledge on the performance optimization of monoelement Bi-based optical devices.

2D Arsenene and Arsenic Materials: Fundamental Properties, Preparation, and Applications

As emerging 2D materials, arsenene and arsenic materials have attracted rising interest in the past few years. The diverse crystalline phases, exotic electrical characteristics, and widespread applications of 2D arsenene and arsenic bring them great research value and utilization potential. Herein, the recent progress of 2D arsenene and arsenic is reviewed in terms of fundamental properties, preparation, and applications. The fundamental properties of 2D arsenene and arsenic, including the crystal phases, environmental stability, and electrical structure, from theoretical to experimental reports are first summarized. Then, the experimental processes for preparing 2D arsenene and arsenic, along with their respective advantages and disadvantages, are introduced including epitaxial growth, mechanical exfoliation, and liquid-phase exfoliation. Moreover, applications of 2D arsenene and arsenic are discussed, suggesting a wide range of applications of 2D arsenene and arsenic in field-effect transistors, sensors, catalysts, biological applications, and so on. Finally, some perspectives about the challenges and opportunities of promising 2D arsenene and arsenic are provided. This review provides a helpful guidance and stimulates more focus on future explorations and developments of 2D arsenene and arsenic.

Pressure Effect on Electronic and Excitonic Properties of Purely J-Aggregated Monolayer Organic Semiconductor

Different from monolayer inorganic semiconductors, such as transition metal dichalcogenides, monolayer organic semiconductors derived from perylene have attracted much attention because of their strong absorption and bright photoluminescence (PL). Pressure has proved to be an effective tool in probing the exciton behavior in monolayer semiconductors. Here, by studying the high-pressure behavior of purely J-aggregated monolayer organic semiconductors experimentally and theoretically, we find a red shift of PL spectra due to a decrease of band gap, which is consistent with fluorescent images taken under pressure. The PL center dominates the perylene group and the band edges are flat, indicating Frenkel exciton in the monolayer organic semiconductor under ambient conditions. With increasing pressure, the band edges become more dispersive, suggesting the exciton transform to Wannier-Mott exciton, which is commonly observed in inorganic semiconductors.

Responsive principles and applications of smart materials in biosensing

Biosensing is a rising analytical field for detection of biological indicators using transducing systems. Smart materials can response to external stimuli, and translate the stimuli from biological domains into signals that are readable and quantifiable. Smart materials, such as nanomaterials, photonic crystals and hydrogels have been widely used for biosensing purpose. In this review, we illustrate the incorporation of smart materials in biosensing systems, including the design of responsive materials, their responsive mechanism of biosensing, and their applications in detection of four types of common biomolecules (including glucose, nucleic acids, proteins, and enzymes). In the end, we also illustrate the current challenges and prospective of using smart materials in biosensing research fields.