Detection of H2S, HF and H2 pollutant gases on the surface of penta-PdAs2 monolayer using DFT approach.

In this research, the adsorption of targeted noxious gases like H2S, HF and H2 on penta-PdAs2 monolayer are deeply studied by means of the density functional theory (DFT). After the capturing of three kind of pollutant gases (H2S, HF and H2), it is observed that, the electronic properties are slightly affected from the pristine one. In all cases, the physisorption interaction found with adsorption energy of - 0.49, - 0.39 and - 0.16 eV for H2S, HF and H2 gases, respectively. Which is exposed that H2S gas strongly absorbed on penta-PdAs2 nanosheet. In case of HF (H2) gas adsorbed systems, the obtained charge transfer is + 0.111 e (+ 0.037 e), revealed that the electrons are going to PdAs2 nanosheet from the HF (H2) molecules. Further, under the non-equilibrium Green's function (NEGF) theory, the IV response and sensitivity of absorbed H2S, HF and H2 have been discussed. The results demonstrate that the H2S molecules on PdAs2 has suitable adsorption strength and explicit charge transfer compared with other targeted molecules. Hence, our novel findings of H2S, HF and H2 targeted gas sensing on penta-PdAs2 nanosheet might provide reference-line to design modern gas sensor device at the nano-scale.

Selective and sensitive toxic gas-sensing mechanism in a 2D Janus MoSSe monolayer.

With an inspiration of sensing toxic gases, this study is aimed at exploring the potential of a Janus MoSSe monolayer as a gas sensor. Here, we focused on the adsorption mechanism after the exposure to NH3, NO2, NO, HCN, CO2, CO, H2, H2S and SO2 on both the S and Se sites of MoSSe. We investigated the structural geometries and electronic, sensing and electron-transport properties before and after adsorption of the aforementioned gases by applying DFT calculations. The results revealed the higher binding strength of NO2/SO2 and NO on Se and S sites, respectively, among all the gas adsorptions on the MoSSe monolayer. Moreover, DOS revealed strong orbital contributions at EF, which confirmed the n/p-type semiconducting character for the NO/NO2 adsorbed MoSSe monolayer. Further, the specific work function alteration after the adsorption of NO2, SO2 and NO indicated that the MoSSe monolayer could be a potential candidate for Φ-type gas sensor at 300 K. Additionally, the higher electron transmission and prominent electrical response values of 76.4/56 µA and 82 µA suggested a maximum sensitivity of 98%/89% and 93% at a particular voltage for NO2/SO2 and NO on Se and S sites, respectively. Thus, our results promote surface selectivity, i.e. S or Se site, and better sensitivity with recycling potential could enable sensing application of the Janus MoSSe monolayer for toxic gases detection.

Strain modulating electronic band gaps and SQ efficiencies of semiconductor 2D PdQ2 (Q = S, Se) monolayer.

We studied the physical, electronic transport and optical properties of a unique pentagonal PdQ2 (Q = S, Se) monolayers. The dynamic stability of 2Dwrinkle like-PdQ2 is proven by positive phonon frequencies in the phonon dispersion curve. The optimized structural parameters of wrinkled pentagonal PdQ2 are in good agreement with the available experimental results. The ultimate tensile strength (UTHS) was calculated and found that, penta-PdS2 monolayer can withstand up to 16% (18%) strain along x (y) direction with 3.44 GPa (3.43 GPa). While, penta-PdSe2 monolayer can withstand up to 17% (19%) strain along x (y) dirrection with 3.46 GPa (3.40 GPa). It is found that, the penta-PdQ2 monolayers has the semiconducting behavior with indirect band gap of 0.94 and 1.26 eV for 2D-PdS2 and 2D-PdSe2, respectively. More interestingly, at room temperacture, the hole mobilty (electron mobility) obtained for 2D-PdS2 and PdSe2 are 67.43 (258.06) cm2 V-1 s-1 and 1518.81 (442.49) cm2 V-1 s-1, respectively. In addition, I-V characteristics of PdSe2 monolayer show strong negative differential conductance (NDC) region near the 3.57 V. The Shockly-Queisser (SQ) effeciency prameters of PdQ2 monolayers are also explored and the highest SQ efficeinciy obtained for PdS2 is 33.93% at -5% strain and for PdSe2 is 33.94% at -2% strain. The penta-PdQ2 exhibits high optical absorption intensity in the UV region, up to 4.04 × 105 (for PdS2) and 5.28 × 105 (for PdSe2), which is suitable for applications in optoelectronic devices. Thus, the ultrathin PdQ2 monolayers could be potential material for next-generation solar-cell applications and high performance nanodevices.

First-Principles Study of Mn-Doped and Nb-Doped CsPbCl3 Monolayers as an Absorber Layer in Solar Cells.

The density functional theory (DFT) based analysis of cubic phase cesium lead chloride (CsPbCl3) perovskite is reported. Here the absence of imaginary frequencies in the phonon dispersion curves of unit cell of bulk and monolayer CsPbCl3 showed that both the structures are dynamically stable. The pristine CsPbCl3 monolayer is a wide bandgap semiconductor with an energy gap of 3.24 eV; therefore, an approach to alter its properties was adopted by doping Mn at the Pb-site and Nb at the Cs-site, respectively. In these Mn- and Nb-doped CsPbCl3 monolayers, intermediate states were generated in both the cases due to Mn-3d and Nb-4d orbitals, respectively, which makes the transfer of excited photoelectrons easier from the valence band to the conduction band. The absorption coefficient plots of Mn-doped and Nb-doped CsPbCl3 monolayers indicated that their absorption edges get shifted toward low photon energy, i.e. red shifted compared to the pristine CsPbCl3 monolayer. As both the impurity atoms considered are transition metals, we have also taken into account the effect of spin polarization on electronic and optical properties of doped monolayers. Solar cell parameters of all of these monolayers have been calculated using the Shockley-Queisser (SQ) limit. The short-circuit current density (Jsc) of the Nb-doped CsPbCl3 monolayer was obtained around 655.45 A/m2, and the efficiency of this material came out to be around 15.68%. For the Mn-doped CsPbCl3 monolayer the value of Jsc came to be around 525.68 A/m2 and showed strikingly high efficiency of 26.88% thus being a suitable candidate for its application as an absorber layer in solar cells.