2D Layers of Group VA Semiconductors: Fundamental Properties and Potential Applications

Evidence of Higher Order Phonon Anharmonicity in Gray Arsenic Crystal

Phonons play a key role in the heat transport process of quantum materials. The understanding of thermal behaviors of phonons will be beneficial for designing modern electronic devices. In this study, we utilize specific heat, Raman spectroscopy, and first-principles calculations combined with the phonon Boltzmann transport equation to explore the thermal transport of gray arsenic. Our specific heat data indicate the presence of the phonon anharmonicity at high temperature. This is further supported by temperature-dependent Raman data showing evident phonon softening and line width broadening. More interestingly, from the analysis of temperature-dependent Raman modes, we found that the four-phonon scattering process is indispensable for interpreting the line width broadening at high temperatures. Moreover, we evaluate the importance of the four-phonon scattering process in the heat transport of gray arsenic using the moment tensor potential method. Our work sheds light on the importance of a higher order phonon scattering process in heat transport of the materials with moderate thermal conductivity.

Toxic gas sensing performance of arsenene functionalized by single atoms (Ag, Au): a DFT study

The detection and removal of toxic gases from the air are imminent tasks owing to their hazards to the environment and human health. Based on DFT calculations with VdW correction, adsorption configurations, adsorption energies, and electronic properties were compared for the adsorption of toxic gas molecules (CO, NO, NO2, SO2, NH3 and H2S) on pure arsenene (p-arsenene) and Ag/Au-doped arsenene (Ag/Au-arsenene). Our calculations show that all molecules considered to chemisorb on Ag/Au-arsenene and the substitution of noble metal, particularly Ag, could remarkably enhance the interactions and charge transfer between the gas molecules and Ag/Au-arsenene. Thus, Ag/Au-arsenene is expected to show higher sensitivity in detecting CO, NO, NO2, SO2, NH3 and H2S molecules than p-arsenene. Furthermore, the changes in the vibrational frequencies of gas molecules and the work functions of Ag/Au-arsenene substrates upon adsorption are shown to be closely related to the adsorption energies and charge transfer between the molecules and Ag/Au-arsenene, which is dependent on the molecules. Therefore, Ag/Au-arsenene-based gas sensors are expected to show good selectivity of molecules. The analysis of theoretical recovery time suggested that Ag-arsenene shows high reusability while detecting H2S, CO, and NO, whereas Au-arsenene has high selectivity to sensing NO at room temperature. With the increase in work temperature and decrease in recovery times, Ag/Au-arsenene could be used to detect NH3 and NO2 from factory emission and automobile exhaust with quite good reusability. The above results indicated that Ag/Au-arsenene shows good performance in toxic gas sensing with high sensitivity, selectivity, and reusability at different temperatures.

Electronic, mechanical and gas sensing properties of two-dimensional γ-SnSe

Two-dimensional (2D) materials are excellent candidates for advanced flexible electronics and gas sensors. Herein, we systematically investigate the layer-dependent electronic structures, mechanical properties and gas sensing characteristics of the newly synthesized γ-SnSe based on first-principles calculations. Bulk γ-SnSe is a typical van der Waals layered material with an indirect narrow band gap, while monolayer and multilayer γ-SnSe can be obtained through mechanical exfoliation due to its low cleavage energy. The band gap of γ-SnSe gradually increases with decreasing layers, reaching a value of 2.25 eV for the monolayer due to weakened interlayer coupling. Mechanical analysis reveals strong anisotropy in multilayer γ-SnSe, whereas the monolayer exhibits a negative Poisson's ratio (-0.023/-0.025). Additionally, based on the analysis of electronic structures, adsorption energies and charge transfer of the host materials after adsorption of various gases, it is found that the γ-SnSe monolayer demonstrates enhanced sensitivity and selectivity towards NO, NO2, and SO2 compared to CO, CO2, H2S and NH3. These findings highlight the potential of γ-SnSe as an excellent gas-sensitive material for the detection of nitrogen oxides and sulfur dioxide.

Emerging 2D pnictogens: a novel multifunctional photonic nanoplatform for cutting-edge precision treatment

The elements of the pnictogen group, known as the 15th (VA) family in the periodic table, including phosphorus (P), arsenic (As), antimony (Sb) and bismuth (Bi), have been widely used by alchemists to treat various diseases since ancient times and hold a pivotal position in the history of medicine, owing to their diverse pharmacological activities. Recently, with the development of modern nanotechnology, pnictogen group elements appear in a more innovative form, namely two-dimensional (2D) pnictogens (i.e. phosphorene, arsenene, and bismuthene) with a unique layered crystal structure and extraordinary optoelectronic characteristics, which endow them with significant superiority as a novel multifunctional photonic nanoplatform for cutting-edge precision treatment of various diseases. The puckered layer structure with ultralarge surface area make them ideal drug and gene delivery vectors that can avoid degradation and reduce target effects. The anisotropic morphology allows their easier internalization by cells and may improve gene transfection efficiency. Tunable optoelectronic characteristics endow them with excellent phototherapy performance as well as the ability to act as an optical switch to initiate subsequent therapeutic events. This review provides a brief overview of the properties, preparation and surface modifications of 2D pnictogens, and then focuses on its applications in cutting-edge precision treatment as a novel multifunctional photonic nanoplatform, such as phototherapy, photonic medicine, photo-adjuvant immunotherapy and photo-assisted gene therapy. Finally, the challenges and future development trends for 2D pnictogens are provided. With a focus on 2D pnictogen-based multifunctional photonic nanoplatforms, this review may also provide profound insights for the next generation innovative precision therapy.

Electrical Contacts With 2D Materials: Current Developments and Future Prospects

Current electrical contact models are occasionally insufficient at the nanoscale owing to the wide variations in outcomes between 2D mono and multi-layered and bulk materials that result from their distinctive electrostatics and geometries. Contrarily, devices based on 2D semiconductors present a significant challenge due to the requirement for electrical contact with resistances close to the quantum limit. The next generation of low-power devices is already hindered by the lack of high-quality and low-contact-resistance contacts on 2D materials. The physics and materials science of electrical contact resistance in 2D materials-based nanoelectronics, interface configurations, charge injection mechanisms, and numerical modeling of electrical contacts, as well as the most pressing issues that need to be resolved in the field of research and development, will all be covered in this review.

Potential and Progress of 2D Materials in Photomedicine for Cancer Treatment

Over the last decades, photomedicine has made a significant impact and progress in treating superficial cancer. With tremendous efforts many of the technologies have entered clinical trials. Photothermal agents (PTAs) have been considered as emerging candidates for accelerating the outcome from photomedicine based cancer treatment. Besides various inorganic and organic candidates, 2D materials such as graphene, boron nitride, and molybdenum disulfide have shown significant potential for photothermal therapy (PTT). The properties such as high surface area to volume, biocompatibility, stability in physiological media, ease of synthesis and functionalization, and high photothermal conversion efficiency have made 2D nanomaterials wonderful candidates for PTT to treat cancer. The targeting or localized activation could be achieved when PTT is combined with chemotherapies, immunotherapies, or photodynamic therapy (PDT) to provide better outcomes with fewer side effects. Though significant development has been made in the field of phototherapeutic drugs, several challenges have restricted the use of PTT in clinical use and hence they have not yet been tested in large clinical trials. In this review, we attempted to discuss the progress, properties, applications, and challenges of 2D materials in the field of PTT and their application in photomedicine.

Recent Advances in Surface Modifications of Elemental Two-Dimensional Materials: Structures, Properties, and Applications

The advent of graphene opens up the research into two-dimensional (2D) materials, which are considered revolutionary materials. Due to its unique geometric structure, graphene exhibits a series of exotic physical and chemical properties. In addition, single-element-based 2D materials (Xenes) have garnered tremendous interest. At present, 16 kinds of Xenes (silicene, borophene, germanene, phosphorene, tellurene, etc.) have been explored, mainly distributed in the third, fourth, fifth, and sixth main groups. The current methods to prepare monolayers or few-layer 2D materials include epitaxy growth, mechanical exfoliation, and liquid phase exfoliation. Although two Xenes (aluminene and indiene) have not been synthesized due to the limitations of synthetic methods and the stability of Xenes, other Xenes have been successfully created via elaborate artificial design and synthesis. Focusing on elemental 2D materials, this review mainly summarizes the recently reported work about tuning the electronic, optical, mechanical, and chemical properties of Xenes via surface modifications, achieved using controllable approaches (doping, adsorption, strain, intercalation, phase transition, etc.) to broaden their applications in various fields, including spintronics, electronics, optoelectronics, superconducting, photovoltaics, sensors, catalysis, and biomedicines. These advances in the surface modification of Xenes have laid a theoretical and experimental foundation for the development of 2D materials and their practical applications in diverse fields.