NH3 and PH3 adsorption through single walled ZnS nanotube: First principle insight

Janus HfSSe monolayer: a promising candidate for SO2and COCl2gas sensing

Janus monolayers based on transition metal dichalcogenides have garnered significant interest as potential materials for nano electronic device applications due to their exceptional physical and electronic properties. In this study, we investigate the stability of the Janus HfSSe monolayer usingab initiomolecular dynamics simulations and analyze the electronic properties in its pristine state. We then examine the impact of adsorbing toxic gas molecules (AsH3, COCl2, NH3, NO2, and SO2) on the monolayer's structure and electronic properties, testing their adsorption on different active sites on top of hafnium, selenium, and sulfur. The sensitivity of the gas molecules is quantified in terms of their adsorption energy, with the highest and lowest energies being observed for SO2(-0.278 eV) and NO2(-0.095 eV), respectively. Additionally, we calculate other properties such as recovery time, adsorption height, Bader charge, and charge difference density to determine the sensitivity and selectivity of the toxic gas molecules. Our findings suggest that the Janus HfSSe monolayer has the potential to function as SO2and COCl2gas sensor due to its high sensitivity for these two gases.

Ultrahigh sensitivity with excellent recovery time for NH3 and NO2 in pristine and defect mediated Janus WSSe monolayers

We demonstrated ultrahigh sensitivity with excellent recovery time for H2S, NH3, NO2, and NO molecules on the sulfur and selenium surfaces of Janus WSSe monolayers using density functional theory. The selenium surface of the WSSe monolayer showed strong adsorption in comparison to the sulfur surface. The respective adsorption energies for H2S, NH3, NO2 and NO molecules are -0.193 eV, -0.220 eV, -0.276 eV, and -0.189 eV. These values are higher than the experimentally reported values for ultrahigh sensitivity gas sensors based on MoS2, MoSe2, WS2, and WSe2 monolayers. The computed adsorption energy and recovery time suggest that the desorption of gas molecules can be achieved easily in the WSSe monolayer. Further, the probable vacancy defects SV, SeV, and (S/Se)V and antisite defects SSe, and SeS are considered to understand their impact on the adsorption properties with respect to the pristine WSSe monolayer. We observed that the defect-including WSSe monolayers showed enhanced adsorption energy with fast recovery, which makes the Janus WSSe monolayer an excellent material for nanoscale gas sensors with ultrahigh sensitivity and excellent recovery time.

Planar graphitic ZnS, buckling ZnS monolayers and rolled-up nanotubes as nonlinear optical materials: first-principles simulation

Nonlinear optical (NLO) materials have an ability to generate new coherent light. At the present stage, three dimensional (3D) mid-infrared NLO materials suffer from various deficiencies such as low laser damage thresholds (LDTs) for AgGaQ₂ (Q = S, Se); the band gaps of most intensively studied two-dimensional (2D) NLO materials are not wide enough to avoid two-photon absorption (TPA); a steady NLO property regardless of diameter and chirality is absent in one-dimensional (1D) single-walled nanotubes (SWNTs). In this research, the electronic and second harmonic generation (SHG) properties of planar graphitic ZnS (g-ZnS) monolayer, buckling reconstructed ZnS (R-ZnS) monolayer which is synthesized in a recent experiment, and rolled-up SWNTs are investigated with first-principles simulations. Theoretical results suggest the SHG coefficients of planar g-ZnS, buckling R-ZnS and rolled-up SWNTs are comparable with that of AgGaS₂ crystals. The band gaps of planar g-ZnS and ZnS SWNTs are ∼3.8 eV, and that of buckling R-ZnS is as wide as ∼4.0 eV, indicating high LDTs and reduced TPA as NLO materials. The TPA edges can be further blue shifted by using incident light beams with a polarized electric field perpendicular to buckling R-ZnS. On the other hand, the TPA edges of ZnS SWNTs are nearly not affected by diameter and chirality. The SHG coefficients of ZnS SWNTs are much less influenced by chirality and diameter than those of SiC, GeC and BN SWNTs. Therefore, they are superior ultrathin NLO materials, and especially have a potential application in the mid-infrared regime where high-quality NLO crystals are emergently needed.

Contradictory large SHG coefficients and wide bandgaps are simultaneously discovered in planar graphitic ZnS, buckling ZnS monolayers and rolled-up nanotubes.

XH3 (X=P or N) Adsorption on Pristine, Pt-Doped and Vacancy-Defective (8,8) Boron Nitride Nanotubes: DFT Calculations

The adsorption energies (E ad), interaction distances, changes of geometric and electronic structures of XH3 (X=P or N) gas molecule adsorption on pristine, platinum (Pt) doped and vacancy-defected single-walled (8,8) boron nitride nanotubes (BNNTs) have been calculated using the density functional theory (DFT). The effect of the Pt doping on B and N sites (PtB,N-doped) and the B and N vacancy defects (VB,N-defected BNNT) on the sensing behavior of pristine (8,8) BNNTs toward PH3 and NH3 gases have been examined. According to the obtained results, PH3 and NH3 molecules were more likely to be absorbed on the PtB,N-doped and VN-defected BNNT with relatively higher E ad compared with the pristine and VB-defected BNNTs. Therefore the order of the obtained E ad were PtB-doped BNNT/NH3>PtB-doped BNNT/PH3>PtN-doped BNNT/NH3>PtN-doped BNNT/PH3 for the PtB,N-doped BNNTs, and VN-defected BNNT/NH3>VN-defected BNNT/PH3>VB-defected BNNT/NH3>VB-defected BNNT/PH3 for the VB , N-defected BNNTs systems. The partial density of states (PDOS) of the adsorption systems indicated the strong interaction between the adsorbed PH3 and NH3 molecules and the substrates, i.e. PtB,N-doped BNNT and VN-defected BNNT. Therefore, it can concluded that the PtB,N-doped and VN-defected BNNTs have potential applicability in the gas-sensing detection of PH3 and NH3 with good sensitivity.

Electronic properties of a pristine and NH3/NO2 adsorbed buckled arsenene monolayer

The electronic charge density associated with the inter-frontier orbitals of (a) NH₃ arsenene and (b) NO₂-arsenene.

Study on adsorption and desorption of ammonia on graphene

The gas sensor based on pristine graphene with conductance type was studied theoretically and experimentally. The time response of conductance measurements showed a quickly and largely increased conductivity when the sensor was exposed to ammonia gas produced by a bubble system of ammonia water. However, the desorption process in vacuum took more than 1 h which indicated that there was a larger number of transferred carriers and a strong adsorption force between ammonia and graphene. The desorption time could be greatly shortened down to about 2 min by adding the flow of water-vapor-enriched air at the beginning of the recovery stage which had been confirmed as a rapid and high-efficiency desorption process. Moreover, the optimum geometries, adsorption energies, and the charge transfer number of the composite systems were studied with first-principle calculations. However, the theoretical results showed that the adsorption energy between NH3 and graphene was too small to fit for the experimental phenomenon, and there were few charges transferred between graphene and NH3 molecules, which was completely different from the experiment measurement. The adsorption energy between NH4 and graphene increased stage by stage which showed NH4 was a strong donor. The calculation suggested that H2O molecule could help a quick desorption of NH4 from graphene by converting NH4 to NH3 or (NH3)n(H2O)m groups, which was consistent with the experimental results. This study demonstrates that the ammonia gas produced by a bubble system of ammonia water is mainly ammonium groups of NH3 and NH4, and the NH4 moleculars are ideal candidates for the molecular doping of graphene while the interaction between graphene and the NH3 moleculars is weak.