Junke Jiang

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.

An AlAs/germanene heterostructure with tunable electronic and optical properties via external electric field and strain

By means of comprehensive first-principles calculations, we investigate the stability, electronic and optical properties of an AlAs/germanene heterostructure. In particular, electric field and strain are used to tailor its electronic band gap and dielectric function. The binding energy and interlayer distance indicate that germanene and AlAs monolayers in the AAI pattern are bound together via van der Waals interaction with a maximum indirect-gap of 0.494 eV, which is expected to have potential application in the field of field-effect transistors. Under a negative E-field and compressive strain, the bandgaps of the AAI-stacking show a near-linear and linear decrease behavior, respectively, whereas the response of the bandgaps to a positive E-field and tensile strain displays a dramatic and monotonous decrease relationship. The work function of the AAI-stacking is calculated to be 4.35 eV smaller than that of individual monolayers. Besides, the optical properties are also calculated. The imaginary parts of the dielectric function of the germanene/AlAs heterobilayer exhibit a significant enhancement in comparison with the considered monolayers, indicating the improvement of the capability of absorbing photons. In particular, the imaginary part of the dielectric function of the heterostructure is enhanced with the increase of E-field and mechanical strain, which suggests that the optical properties of the heterostructure can be improved by E-field and mechanical strain. Simultaneously, a red-shift or blue-shift can be observed with the changes in E-field and mechanical strain. All these nontrivial and tunable properties endow the AlAs/germanene nanocomposite with great potential for FETs, strain sensors, photocatalysis, field emission, energy harvesting, and photonic devices.

Design of graphene-like gallium nitride and WS2/WSe2 nanocomposites for photocatalyst applications

The geometric, electronic and optical properties of the graphene-like gallium nitride (GaN) monolayer paired with WS2 or WSe2 were studied systematically using the first-principles calculations. GaN interacts with WS2 or WSe2 via van der Waals interaction and all the most stable configurations of these two nanocomposites exhibit direct band gap characteristics. Meanwhile, the type-II heterojunctions are formed because the conduction band minimums and valence band maximums are respectively contributed by WS2 (or WSe2) and GaN. The imaginary parts of the dielectric function and the absorption spectra of the heterostructures were also calculated and the relatively improved optical properties were observed because of the new interband transitions. In addition, the band offsets as well as the intrinsic electric fields resulting from the interlayer charge transfer indicate that the electron-hole pairs recombination can be effectively inhibited, which is conducive for the photocatalysis process. Moreover, the band gaps of the heterostructures can be modulated by applying biaxial strains and even shift away the conduction band edge potential from the H+/H2 potential in a certain range, which further enhances the photocatalyst performance. The results indicate that GaN/WS2 or GaN/WSe2 nanocomposites are good candidate materials for photocatalyst or photoelectronic applications.

Tunable electronic structure and enhanced optical properties in quasi-metallic hydrogenated/fluorinated SiC heterobilayer

Graphene-like silicon carbide (SiC) has emerged as a rapidly rising star on the horizon of two-dimensional (2D) layered materials. In this work, we execute a systematic theoretical investigation of the atomic and electronic structure of a fully hydrogenated/fluorinated SiC (H/F-SiC) heterobilayer, which has a quasi-metallic character in its most stable stacking pattern, to predict its electronic and optical properties. We demonstrate that a direct band gap at the Γ point can be opened in the quasi-metallic H/F-SiC heterobilayer by applying an external electric field (E-field). Especially, when altering the strength of the E-field, this system undergoes a transition from quasi-metallic state to semiconductor. We predict that the mobilities are rather high due to the low carrier effective mass and high Fermi velocity. Light absorption spectra indicate that the H/F-SiC heterobilayer has evident infrared light absorption, and complete electron–hole separation can enhance the photocatalytic efficiency. Our findings pave the way for experimental research on the development of 2D material science using weak interlayer interactions and indicate the great application potential of the H/F-SiC heterobilayer in future nanoelectronics and optoelectronics.

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.

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.