RESUMEN
The interaction of corresponding molecular building blocks of the complexes A···BX3 would provide valuable information to quickly estimate the properties of the solar cell. In this work, the H···X hydrogen bond between the organic cations A+ (CH3NH3+, NH2CHNH2+, NH2CHOH+) and the inorganic anions BX3- (B = Sn2+, Pb2+, X = F-, Cl-, Br-, I-) were studied by theoretical calculation at the B3LYP-D3/ma-def2-TZVP level to investigate the stability of the complexes A···BX3. The strength of H···X hydrogen bond is enhanced in the order of NH2CHNH2+ < CH3NH3+ < NH2CHOH+, Sn2+ < Pb2+, and weakened in the order of F- > Cl- > Br- > I-, indicating that the complexes A···BX3 enhances with the increase of electron donating ability of B and the decrease of electron donating ability of X, and application of the substituent A = NH2CHOH+ may be effective to enhance the stability of perovskite and replace the toxic metal Pb by Sn. Graphical abstract.
RESUMEN
Alloying/doping in two-dimensional (2D) materials is emerging as an increasingly important strategy due to the wide-range bandgap tunability and versatility of these materials. Monolayer 2D transition metal dichalcogenide (TMD) alloy has been investigated both theoretically and experimentally in recent years. Here, we synthesized a bilayer MoS2(1-x)Se2x semiconductor alloy via the chemical-vapor deposition technique. The as-grown triangular MoS2(1-x)Se2x flakes with size of roughly 10 µm were observed by optical microscope and scanning electron microscope (SEM). The 1.4-1.9 nm thickness of the samples, as measured by AFM, means that bilayer MoS2(1-x)Se2x alloys were grown. The characteristic Raman modes related to Mo-S and Mo-Se vibrations were observed in the Raman spectrum. Two emission peaks were respectively found, corresponding to the A and B excitons in the photoluminescence (PL) spectrum. XPS measurements confirmed the Se doping of the alloy. The first-principles calculation results show a contraction of the band gap value with the increase of Se doping in the MoS2 lattice. Compared with monolayer MoS2(1-x)Se2x alloy, the band bending effect is more obvious, and the bilayer MoS2(1-x)Se2x alloy still shows the direct band gap luminescence characteristic, which has certain guiding significance for the growth of two-dimensional materials and for device preparation.
RESUMEN
Magnetic transport spectroscopy is investigated in quantum point contacts (QPCs) fabricated in Al0.25Ga0.75N/GaN heterostructures. The magnetic field perpendicular to the two-dimensional electron gas (2DEG) is shown to depopulate the quasi-one-dimensional energy levels in the first two-dimensional (2D) subband faster than those in the second one. In GaN based heterostructures, the energy levels in the second 2D subband is generally concealed in the fast course of depletion and hence rarely detected. The perpendicular magnetic field facilitates the observation of the second 2D subband, and provides a method to study the properties of these energy levels. A careful analysis on the rate of the magnetic depletion with respect to the level index and confinement is carried out, from which the profile of the lateral confinement in GaN based QPCs is found to be triangular. The stability diagram at T shows the energy separation between the first and second 2D subband to be in the range of 32 to 42 meV.
RESUMEN
Gate-defined quantum point contacts (QPCs) were fabricated with Al0.25Ga0.75N/GaN heterostructures grown by metal-organic chemical vapor deposition (MOCVD). In the transport study of the Zeeman effect, greatly enhanced effective g factors (g*) were obtained. The in-plane g* is found to be 5.5 ± 0.6, 4.8 ± 0.4, and 4.2 ± 0.4 for the first to the third subband, respectively. Similarly, the out-of-plane g* is 8.3 ± 0.6, 6.7 ± 0.7, and 5.1 ± 0.7. Increasing g* with the population of odd-numbered spin-splitted subbands are obtained at 14 T. This portion of increase is assumed to arise from the exchange interaction in one-dimensional systems. A careful analysis shows that not only the exchange interaction but the spin-orbit interaction (SOI) in the strongly confined QPC contributes to the enhancement and anisotropy of g* in different subbands. An approach to distinguish the respective contributions from the SOI and exchange interaction is therefore proposed.
