Contact evaluation of the penta-PdPSe/graphene vdW heterojunction: tuning the Schottky barrier and optical properties.

In this work, we design a van der Waals heterojunction composed of semiconducting penta-PdPSe and semi-metallic graphene (G) monolayers based on state-of-the-art theoretical calculations. Our results show that both monolayers well preserve their intrinsic features and possess an n-type near Ohmic Schottky contact with a low Schottky barrier height of 0.085 eV for the electrons at the vertical interface. The electronic band alignment suggests a negative band bending of -1.47 eV at the lateral interface, implying electrons as the major transport carriers. Moreover, the transmission gap closely mirrors the heterojunction's band gap, indicating a subtle yet profound interaction between graphene and penta-PdPSe monolayers, which leads to enhanced optical absorption coefficient reaching 106 cm-1 and strong conductivity spanning the visible to ultraviolet region. In addition, our study demonstrates the ability to modify the penta-PdPSe/G heterojunction interface, switching between p-type as well as Ohmic contacts by applying external electric fields. These properties render the penta-PdPSe/G heterojunction promising for optoelectronic applications.

Enhanced As-COF nanochannels as a high-capacity anode for K and Ca-ion batteries.

Covalent organic frameworks can be used for next-generation rechargeable metal-ion batteries due to their controllable spatial and chemical architectures and plentiful elemental reserves. In this study, the arsenic-based covalent organic framework (As-COF) is designed by employing the geometrical symmetry of a semiconducting phosphazene-based covalent organic framework that uses p-phenylenediamine as a linker and hexachorocyclotriphosphazene as an As-containing monomer in a C3-like spatial configuration. The As-COF with engineered nanochannels demonstrates exceptional anodic behavior for potassium (K) and calcium (Ca) ion batteries. It exhibits a high storage capacity of about 914(2039) mA h g-1, low diffusion barriers of 0.12(0.26) eV, low open circuit voltage of 0.23(0.18) V, and a minimal volume expansion of 2.41(2.32)% for K (Ca) ions. These attributes collectively suggest that As-COF could significantly advance high-capacity rechargeable batteries.

Overview of radon gas in groundwater around the world: Health effects and treatment technologies.

The natural radioactive decay of uranium in rocks and soils gives rise to the presence of radon in groundwater. The existence of radon in groundwater at activity levels way higher than the reference limits set by US-EPA and WHO was widely covered in literature. The exposure to elevated levels of radon in ground and drinking water have been reported in literature to cause adverse health impacts. The aim of the present paper is to give an overview of radon gas in groundwater followed by the safe limits suggested by international organizations and agencies such as US-EPA and WHO. The paper also discusses the health effects associated with the exposure to radon levels and the estimation of the annual effective dose through ingestion and inhalation. This is followed by the radon levels around the world as well as the corresponding annual effective doses reported in literature. The determination techniques of radon levels in water covered in literature such as liquid scintillation counting, gamma-ray spectrometry and emanometry were also discussed and reviewed in the present work. Next, the paper sheds light on the most frequently used treatment techniques such as aeration, adsorption, filtration as well as biological techniques and evaluates their efficiency in mitigating radon levels in water. The paper also highlights the main precautions and future mitigation plans for radon in groundwater as well as delved onto future research perspectives of radon. It was found out that the type of rock played a key role in determining the radon levels. For instance, granitic rock types were reported to contribute to the elevation in the groundwater radon levels due to their characteristic permeability as a result of the formed fractures as well as their natural incorporation of high levels of uranium. Some of the reported radon levels in groundwater in literature were way higher than the guidelines set by the World Health Organization (WHO) for drinking water and US-EPA alternative higher maximum contaminant level. This review paper could be of importance to researchers working on the evaluation as well as the treatment of radon gas in water as it will provide a critical and state of the art review on radon gas in groundwater.

Mechanistic Study on Steric Activity Interplay of Olefin/Polar Monomers for Industrially Selective Late Transition Metal Catalytic Reactions.

A significant issue in developing metal-catalyzed plastic polymer materials is obtaining distinctive catalytic characteristics to compete with current plastics in industrial commodities. We performed first-principle DFT calculations on the key insertion steps for industrially important monomers, vinyl fluoride (VF) and 3,3,3-trifluoropropene (TFP), to explain how the ligand substitution patterns affect the complex's polymerization behaviors. Our results indicate that the favorable 2,1-insertion of TFP is caused by less deformation in the catalyst moiety of the complexes in contrast to the 1,2-insertion mode. In contrast to the VF monomer, the additional interaction between the fluorine atoms of 3,3,3-trifluoropropene and the carbons of the catalyst ligands also contributed to favor the 2,1-insertion. It was found that the regioselectivity of the monomer was predominated by the progressive alteration of the catalytic geometry caused by small dihedral angles that were developed after the ligand-monomer interaction. Based on the distribution of the 1,2- and 2,1-insertion products, the activity and selectivity were influenced by the steric environment surrounding the palladium center; thus, an increased steric bulk visibly improved the selectivity of the bulkier polar monomer (TFP) during the copolymerization mechanism. In contrast, better activity was maintained through a sterically less hindered Pd metal center; the calculated moderate energy barriers showed that a catalyst with less steric hindrance might provide an opportunity for a wide range of prospective industrial applications.

Exploring the Structural Stability of 1T-PdO2 and the Interface Properties of the 1T-PdO2/Graphene Heterojunction.

Motivated by a recent study on the air stability of PdSe2, which also reports the metastability of the PdO2 monolayer [Hoffman A. N.. npj 2D Mater. Appl.2019, 3( (1), ), 50.], in this work, we use density functional theory (DFT) to further explore the thermal, dynamic, and mechanical stability of monolayer PdO2 and study its structural and electronic properties. We further studied its vertical heterojunction composed of 1T-PdO2 and graphene monolayers. We show that both the monolayer and the heterojunction are energetically and dynamically stable with no negative frequencies in the phonon spectrum and belong to the vdW-type. 1T-PdO2 is an indirect-band-gap semiconductor with band-gap values of 0.5 eV (GGA) and 1.54 eV (HSE06). The interface properties of the heterojunction show that the n-type Schottky barrier height (SBH) becomes negative at the vertical interface in the PdO2/graphene contact, forming an Ohmic contact and mainly suggesting the potential of graphene for efficient electrical contact with the PdO2 monolayer. However, at the same time, a negative band bending occurs at the lateral interface based on the current-in-plane model. Moreover, the optical absorption of the PdO2/graphene heterojunction under visible-light irradiation is significantly enhanced compared to the situation in their free-standing monolayers.

First-Principles Study of the Structural, Electronic, and Enhanced Optical Properties of SnS/TaS2 Heterojunction.

Although the electronics and optoelectronics based on two-dimensional (2D) SnS have attracted great interest, their development is hindered by the large contact resistance at the interface of the metal-semiconductor junction. In this work, using first-principles calculations, we evaluate the contact performance in a van der Waals heterostructure composed of 2D SnS and TaS2. We demonstrate that holes can freely transfer from the electrode to the channel as a consequence of the Schottky-barrier-free interface as well as an upward band bending. Moreover, we show that the intrinsic properties of the SnS monolayer are well-preserved in the heterojunction, which is different from those of contact with metal surfaces. An enhanced optical response is also observed as compared with the freestanding sheet. Given the recent experimental synthesis of the SnS-TaS2 superlattice, this study enhances the understanding of the interface properties of SnS-based metal contact, which is essential for future device applications.