Ruishen Meng

The electronic and optical properties of novel germanene and antimonene heterostructures

In this work, the structural, electronic and optical properties of novel atomically thin systems based on germanene and antimonene nanocomposites have been investigated by means of density functional theory. We find that the germanene and antimonene monolayers are bound to each other via orbital hybridization with enhanced binding strength. Most importantly, the band gap opening can be achieved. Our results demonstrate that the AAII pattern has a direct band gap characteristic with a moderate value of up to 391 meV, while the other three patterns have indirect band gaps tunable from 37 to 171 meV. In particular, changing the direction and strength of the external electric field (E-field) can effectively tune the energy gap of the germanene/antimonene bilayer over a wide range even with a semiconductor–metal transition. The work function of the heterobilayer in the AAII pattern which possesses a direct band gap can be tinkered up from −3.21 to 12.33 eV by applying different E-field intensities. In addition, the germanene/antimonene bilayer exhibits more pronounced optical conductivity. The tunable bandgaps and work function together with a superior visible light response capability make the germanene/antimonene bilayer a viable candidate for optoelectronic applications.

First-Principles Study of Sulfur Dioxide Sensor Based on Phosphorenes

The adsorption behaviors of sulfur dioxide (SO2) gas molecule over pristine, boron-, silicon-, sulfur-, and nitrogen-doped phosphorenes are theoretically studied using first-principles approach based on density-functional theory. The adsorption energy (Ea), adsorption distance (d), and Mulliken charge (Q) of SO2 molecules adsorbed on the different phosphorenes are calculated. The simulation results demonstrate that pristine phosphorene is sensitive to SO2 gas molecule with a moderate adsorption energy and an excellent charge transfer, while evidence of negative effect is observed during doping with S and N. We also observe that B- or Si-doped phosphorene exhibits extremely high reactivity toward SO2 with a stronger adsorption energy, indicating that they are not suitable for use as SO2 sensors, but have potential applications in the development of metal-free catalysts for SO2. Therefore, we suggest that pristine phosphorene could be an excellent candidate as sensor for the polluting gas SO2.

First Principles Investigation of Small Molecules Adsorption on Antimonene

The gas-adsorption behaviors of the pristine antimonene are investigated by first principles calculations to exploit its potential for high-performance gas sensing. The results show that the atmospheric gas molecules (N2, CO2, O2, and H2O) presented ubiquitously in the sensing environments weakly bind to antimonene, while the polluted gas adsorbates (NH3, SO2, NO, and NO2) show stronger affinity toward antimonene with considerable adsorption energies and elevated charge transfers. Considering the susceptibility of the electronic properties of antimonene induced by the adsorbed molecules, we suggest that single-layered antimonene could be an eligible sensing material for polluted gases detection.

Tuning the electronic and optical properties of graphane/silicane and fhBN/silicane nanosheets via interfacial dihydrogen bonding and electrical field control

In this work, using density functional theory (DFT) with van der Waals (vdW) corrections, the effects of dihydrogen bonding on the stability, electronic and optical properties of a graphane/silicane heterobilayer and a fully hydrogenated hexagonal boron nitride (fhBN)/silicane heterobilayer were investigated. Our results reveal that dihydrogen bonding at the interface (C–H⋯H–Si, N–H⋯H–Si or B–H⋯H–Si) would induce interface polarizations, which greatly modulate the electronic and optical properties of the heterobilayers. Moreover, the stability and electronic properties of the graphane/silicane heterobilayer and the fhBN/silicane heterobilayer can be tuned with electric fields (E-fields), yielding not only the band gap of the heterobilayers in a semiconductor–metal transition but also widely tunable binding strengths. More importantly, the mobilities of the graphane/silicane heterobilayer and the fhBN/silicane heterobilayer we predicted are electron-dominated, reasonably high (improvable up to 170 cm2 V−1 s−1 for the graphane/silicane heterobilayer and ∼550 cm2 V−1 s−1 for the fhBN/silicane heterobilayer along the Γ–M direction) and extremely anisotropic. Furthermore, we analysed the dielectric function and the absorption coefficient, and it is evident that the optical properties of the heterobilayers show a much larger spectral range compared with the isolated graphane, fhBN and silicane, especially the fhBN/silicane heterobilayer showing enhanced visible light absorption. These results offer new opportunities for developing electronic and opto-electronic devices based on the graphane/silicane heterobilayer and the fhBN/silicane heterobilayer. More importantly, our findings pave the way for investigating the effect of dihydrogen bondings not only on the electronic properties but also on the opto-electronic properties of the composite hydrogenated materials.

First-Principles Study of Nitric Oxide Sensor Based on Blue Phosphorus Monolayer

The sensing properties of pristine, B-, Al-, Si-, and S-doped blue phosphorus (BP) monolayer to nitric oxide (NO) are theoretically investigated using density functional theory and non-equilibrium Green’s function method. We systematically discuss the concentration effect, sensing mechanism, and current–voltage (I–V) response of BP adsorbing NO molecule. Our results show that the pristine BP exhibits a weak sensitivity for NO molecule, while B-, Al-, and Si-doped BP strongly adsorb NO via robust chemical bonds, meaning a good potential in metal-free catalysts, but unsuitable as NO sensors. Interestingly, S-doped BP is recommended as a desirable material for NO detection due to moderate adsorption energy and large charge transfer. Besides, the flowing current in S-doped BP can be significantly improved after NO adsorption under the same bias voltage. Therefore, S-doped BP could be a good candidate as an NO sensor.

Monolayer ZnS as a Promising Candidate for NH 3 Sensor: A First-Principle Study

In this paper, the interaction of atmospheric gas molecules (NH₃, NO₂, SO₂, CO, CO₂, CH₄, O₂, and NO) with monolayer graphene-like hexagonal ZnS (g-ZnS) is studied with the first-principle calculations to explore its potential application as gas sensor. Among all the gas molecules, NH₃, and SO₂, NO₂ act as a strong donor and acceptor with apparent charge transfer of 0.200, −0.121, and −0.115 e. We further calculated the current-voltage (I−V) relation using the nonequilibrium Greens function formalism. It can be indicated from the results that a mark change of the I−V relation before and after the adsorption of NH₃, which makes monolayer g-ZnS a prospective gas sensor for NH₃. In addition, under the mechanical strain the adsorption is substantially enhanced with significant impact on the properties of adsorbates and g-ZnS layer, especially for the NH₃, NO₂, and NO-monolayer g-ZnS configurations. The results presented herein demonstrate that monolayer g-ZnS can be the potential gas sensor of NH₃ with high sensitivity and selectivity.

The Influence of Tensile Stress on Polyaniline as Strain Sensor

In this letter, we report a first-principles study to investigate the influence of tensile stress on HCl-doped emeraldine-base polyaniline (PANI-Cl) as strain sensors by means of dispersion-corrected density functional theory computations. Our results show that up to a strain of ~17%, the strain increases linearly with the tensile stress. The analysis of the band gap changes and the density of states variations at Fermi level with tensile stress provide insight into the role that the tensile stress plays in affecting the conductivity of PANI-Cl. The sensitivity of PANI-Cl as strain sensors is also calculated, which show a stress dependence. We hope that our findings may open new opportunities in fabricating conducting polymer-based strain sensors.

Enhancement of H 2 S detection in impurity-doped graphene

After the discovery of graphene, considerable researches have been studied to search its superior performance. In this work, the adsorption behaviors of sulfureted hydrogen (H2S) on pristine, tungsten (W), chromium (Cr) and copper (Cu)-doped graphene has been explored in this paper by the means of first-principles calculations based on density-functional theory (DFT). We have calculated the shortest distance between the gas molecule and doped atoms, transfer charge, adsorption energy, and density of states of systems. We get the conclusion that graphene dopes with transition metal will significantly modify the structure of pristine graphene. After the adsorption of H2S gas molecule, the doped transition metal atoms will remarkable protrude out of from plane layer which indicating the doped atoms have a substantial impact on the graphene. More surprisingly, tungsten and copper doped graphene exhibit a significantly high sensitive to the H2S gas molecule with a larger adsorption along with a evident charge transfer while the insensitive adsorption behaviors of H2S on graphene is observed in our calculation. To get a further insight into the interaction between H2S gas molecule and substrate, we also calculate the density of states; our simulation results demonstrate the presence of orbital hybridization between metal atoms and gas molecule, which further confirms the improvement of adsorption capability of graphene. Therefore, Graphene doped with tungsten and copper elements have a promising application prospect in the field of H2S gas sensor.

Modelling for electric devices: Adsorption of polluted gases on g-ZnO monolayer

The gas sensing adsorption performance of the graphene-like two dimensional material, Zinc oxide monolayer (g-ZnO), was studied using first principle calculation to exploit its potential as polluted gas sensing materials. The common polluted gas molecules, CO, H<inf>2</inf>S, NH<inf>3</inf>, SO<inf>2</inf>, NO and NO<inf>2</inf> were selected to examine their affinity with g-ZnO monolayer according to binding energy, charge transfer, adsorption distance and variation of the bond length and angle. The calculation results show that CO is weakly physically adsorbed on g-ZnO, while H<inf>2</inf>S, NH<inf>3</inf> and NO exhibit relatively stronger interaction with g-ZnO with moderate adsorption energies in the range of − 0.375 to −0.618 eV. Likewise, SO<inf>2</inf> and NO<inf>2</inf> show the highest reactivity towards g-ZnO with the highest adsorption energies of −0.754 and −0.769 eV, respectively and the largest charge transfers and shortest adsorption distances. The results indicate that g-ZnO can be a suitable materials for the detection of H<inf>2</inf>S, NH<inf>3</inf> and NO gases and also a promising candidates as a catalyst for SO<inf>2</inf> and NO<inf>2</inf>.

First-principles study of gas adsorptin on indium nitride monolayer as gas sensor applications

Using first-principles calculation within density functional theory, we study the gas (H₂O, H₂, H₂S, and CO₂) adsorption properties of single-layer indium nitride (InN). The four different adsorption sites (Bridge, In, N, Hollow) are chosen to investigate and the most sensitive adsorption site is found (N site for H₂ and H₂O gases; In site for H₂S; center site for CO₂) based on the adsorption energy, band gap and charge transfer. Through our research, the results indicate that InN is sensitive to NH₃ and H₂O. It is shown that H₂ gas molecules act as charge acceptors for the monolayer, except H₂S, H₂O adsorption which are found to be a charge donor. We perform a perpendicular electric field to the system and find its enhancement effect for adsorption energy of gas adsorption. Our theoretical results indicates that monolayer InN is a promising candidate for gas sensing applications.