Janus 2D materials exhibit many excellent properties for their broken symmetry, and are widely applied in piezoelectricity and optoelectronics. The mechanical, piezoelectric and vibrational properties of 2D Janus MSiGeN4 (M=Cr, Hf, Mo, Nb, Ta, Ti, V, W, and Zr) are explored by density functional theory (DFT). Janus MSiGeN4 are more flexible than MSi2N4, but stiffer than MGe2N4. HfSiGeN4 has the largest me* and mh* among all systems. Janus WSiGeN4 have larger e11 and d11 than WSi2N4 and WGeN4. The piezoelectric polarization in-plane strain is much stronger than vertical piezoelectric polarization. NbSiGeN4 possesses the maximum electromechanical coupling constants of 0.310, indicating superior electromechanical energy-conversion. Born-effective charge and Bader charge are analyzed to elucidate the strength of piezoelectric properties. The infrared spectrum and dielectric constants are also explored.
Two-dimensional (2D) materials have attracted extensive attention in optoelectronics owing to their tunable electronic and optical properties. Among them, 2D cubic boron nitride (c-BN) and diamond-like carbon (C) exhibit outstanding semiconductor properties. Herein, we systematically investigate how the intercalation components, surface functionalization by fluorination/hydrogenation, and interlayer stacking synergistically regulate the electronic structures of BN/C intercalated heterostructures. Our calculations reveal that carbon intercalation induces sequential B-to-C-to-N charge transfer, enabling continuous bandgap modulation from 1.200 to 4.660 eV. Carbon-rich structures exhibit pronounced strain sensitivity and undergo a semiconductor-to-metal transition under 6% compressive strain. The optimized heterostructures show favorable optical absorption and reflection characteristics, indicating potential for broadband photodetectors and photocatalytic water splitting. This work provides theoretical insights into the rational design of F/H-functionalized BN/C intercalated 2D materials for high-performance optoelectronic, catalytic, and sensing applications.
We investigate the packing and backbone-orientation distributions in self-assembled monolayers of hydrogen-terminated, monobrominated, and dibrominated regioregular quater(3-hexylthiophene) derivatives on graphite by scanning tunneling microscopy (STM). The hydrogen-terminated derivative, examined at the neat-liquid/graphite interface, forms a herringbone arrangement with discrete Fourier spots and two preferred backbone orientations. The brominated derivatives, examined at trichlorobenzene/graphite interfaces, form lamellar structures: the monobrominated derivative shows streak-like Fourier features and two preferred backbone orientations, whereas the dibrominated derivative exhibits approximately parallel backbones, discrete Fourier spots, and a narrower distribution around one preferred orientation within the analyzed domain. AMBER calculations for individual molecules on graphene show an increase in adsorption-energy magnitude of approximately 3 kcal mol⁻¹ per terminal H-to-Br substitution. This trend suggests that molecule–substrate interactions contribute to the observed packing together with intermolecular interactions. These results highlight terminal bromination as a molecular design variable for tuning oligothiophene packing and orientational organization on graphite.
In this study, we present a DFT analysis examining the interaction between H2 and Ca/g-C3N4. Using the hybrid exchange–correlation functional PBE0/def2-TZVP with dispersion corrections D3BJ, we examined the optimized geometries, adsorption energies, charge transfer, and electronic structure changes induced by successive H2 adsorption. The analysis included frontier molecular orbital energies, natural bond orbitals, AIMALL analysis, IGMPlot, PDOS and steric effect localization function analysis. We found that the Ca and N dual atoms in Ca/g-C3N4 acts as adsorption centers that polarizes incoming H2 molecules and mediate weak interactions through a combination of electrostatic polarization and orbital hybridization between the d orbitals of Ca, the lone pair of N, and σ/σ∗ orbitals of H2. The HOMO–LUMO gap exhibited a non-monotonic variation with increasing H2 coverage. Charge analyses confirmed dual atom role, with electron transfer occurring from H2 to Ca and from N to H2.
We have used k-resolved inverse photoemission spectroscopy to measure the temperature-dependent intensity of radiative transitions into unoccupied electronic states of Ni(110) along its ΓY¯ high-symmetry line in the surface Brillouin zone. Our measurements yield a strong temperature dependence of a transition into an unoccupied crystal-derived surface state. This temperature dependence weakens as the position of the state moves away from the Y¯ high-symmetry point. We use a Debye–Waller model to interpret the intensity attenuation of the direct transitions with increasing temperature. From our results of a transition into the sp-derived bulk state observed at ∼ 1 eV above the Fermi level, we estimate the effective surface Debye temperature of Ni(110) to be 240 ± 20 K.
