Jiraroj T-Thienprasert

Hydrogen impurities are known to significantly influence the electronic properties of delafossite oxides CuMO2 (M = Al, Ga, In) by passivating acceptor defects, thereby impacting the p-type conductivity of these materials. Identifying H and its configurations is, therefore, important to understand the properties of these materials. In this study, we employ hybrid density-functional theory calculations to investigate the vibrational properties of various hydrogen-related defects, including interstitial hydrogen (Hi), the hydrogen-copper antisite complex (Hi–CuM), and hydrogen-copper vacancy complexes (Hi–VCu, 2Hi–VCu). Our calculations provide the first theoretical predictions of local vibrational modes associated with these defects, revealing frequencies ranging from approximately 2800 to 3800 cm−1. These results offer valuable insights into the behavior of hydrogen in CuMO2 and serve as a reference for future experimental investigations using techniques such as infrared spectroscopy. By identifying distinct vibrational signatures for different hydrogen configurations, this study lays the groundwork for defect characterization and passivation mechanisms in delafossite oxides, which are critical for optimizing their electronic and optical properties.

The pesticide contamination in the environment has become a global concern. So far, pesticide adsorption from waste solution is one of the most economic strategies for pesticide removal. Carbon-based nanomaterials were reported to be potential pesticide sorbents. To date, nanosized graphene oxide (GO) has been discovered. Its nanosize, which is comparable to pesticide sizes, is attractive enough to explore its performance to be the pesticide sorbent. Thus, herein, the adsorption mechanisms of a single pesticide on GO were studied by comparing 6-pesticide systems. Three types of common pesticides (cyfluthrin (CFT) (pyrethroid), ivermectin (IVM) (avermectin), and diazinon (DZ) (organophosphate)) were used as pesticide models. All pesticides rapidly adhere to GO at the graphene-like region. The π-π and π-alkyl interactions contribute most to pesticide adhesion. The adsorption of CFT and DZ is led by the π-π stacking, whereas bulky IVM uses the π-alkyl forces. Having more pesticides results in self-clustering. Pesticides pile up and avoid lying on the oxygenated area. IVM is the most favorable for GO and shows tight self-packing via dispersion force and hydrogen bonding. Overall, this work displays the encouraging ability of nanosized GO to effectively absorb all pesticides which will benefit future applications in pest control.

Transparent conducting oxides with p-type conductivity hold immense potential for various electronic applications. The role of native point defects in delafossite CuMO2 (M = Al, Ga, In) as the source of p-type conductivity has been widely acknowledged. However, understanding the primary defects governing the electrical properties and devising strategies for improvement remains a critical challenge. In this study, we employ range-separated hybrid density functional calculations to elucidate the impact of acceptor defects and their interactions with hydrogen on electrical conductivity. Our findings demonstrate that hydrogen plays a pivotal role in controlling p-type conductivity in these oxides. Our investigation reveals that the interactions between hydrogen interstitial Hi and copper vacancy VCu lead to the formation of stable complexes that are electrically inactive. Considerable binding energies are observed for Hi–VCu complexes, indicating that they are highly bound complexes with low formation energy and, thus, high concentrations under both O-rich and O-poor conditions. A second hydrogen can be bound to VCu to form 2Hi–VCu complexes, which are thermodynamically stable and function as a single donor. Furthermore, hydrogen can bind with the antisite acceptor defects, CuM, forming Hi–CuM complexes. However, the lower binding energies associated with these complexes suggest likely dissociation into isolated Hi and CuM at relatively low temperatures. By shedding light on the strong influence of hydrogen passivation of acceptor defects, this study offers valuable insights into p-type conductivity in delafossite CuMO2.

Gallium is the most viable donor dopant. However, the pinned Fermi level remains far from the conduction band edge, resulting in a semi-insulating material. It is not easy to dope n-type ZnSb₂O₄.

The discovery of new and stable two-dimensional pentagonal materials with piezoelectric properties is essential for technological advancement. Inspired by recently reported piezoelectric materials penta-BCN and penta-BSiN, we proposed penta-BGeN and penta-BSnN as new members of the penta-family based on first-principles calculations. Comprehensive analyses indicated that both penta-BGeN and penta-BSnN are thermodynamically, dynamically, mechanically, and thermally stable. In terms of mechanical stability, the elastic constant decreased as lower elements in group 4A of the periodic table were used. Therefore, penta-BGeN and penta-BSnN are softer than penta-BCN and penta-BSiN. In terms of piezoelectric properties, piezoelectric stress and strain tensors increase following the same pattern. In group 4A, penta-BSnN had the highest intrinsic piezoelectricity, especially the e₂₂ piezoelectric stress. Typically, the piezoelectric strain d_ij coefficient increases with material softness; penta-BSnN possessed the highest d_ij. Thus, due to its inherent piezoelectricity, penta-BSnN has tremendous potential as a nanoscale piezoelectric material.

Density-functional calculations reveal thermodynamic stability and equilibrium crystal shape of β-PbO₂ under various growth conditions.

Recently, the C₂N monolayer with an optical bandgap of 1.96 eV has emerged as a novel two-dimensional material for modern optoelectronic devices. Herein, we report its bandgap modulation by using a simple bilayer formation that includes the application of an electric field and strain. We identify four energetically favorable bilayer configurations (AA-, AB-, AB′-, and Min-stacking) by using a hybrid functional, obtaining a calculated bandgap of 1.3–1.6 eV. When subjected to a perpendicular electric field up to 4 V/nm, the bandgap decreases by as much as 0.5 eV, which correlates with the increasing energy of the valence-band maximum, where the N-p_x and N-p_y states shift closer to the N-p_z state. Without the electric field, the bandgap decreases when the interlayer distance is contracted by a compressive strain. We express the strain (or interlayer distance) and the physical applied pressure via the stabilized jellium equation of state. For the Min-stacking configuration, the bandgap decreases from 1.75 to 0.9 eV upon applying a pressure of 35 GPa. The strain-induced reduction in the bandgap is similarly monitored under an applied electric field. Our theoretical work suggests that the electric field and strain (or applied pressure) can be used to tune the electronic properties of the bilayer C₂N.

Li atoms adsorbed on penta-BCN via different packing patterns are investigated.