Germanene, a single-atom-thick germanium nanosheet in a honeycomb lattice, was proposed to be a Dirac fermion material beyond graphene. We performed scanning tunneling microscopy and in situ Raman spectroscopy studies combined with first-principles calculations on the atomic structures and the electronic and phonon properties of germanene on Au(111). The low-buckled 1 × 1 germanene honeycomb lattice was determined to exist in an unexpected rectangular √7 × √7 superstructure. Through in situ Raman measurements, distinctive vibrational phonon modes were discovered in √7 × √7 germanene, revealing the special coupling between the Dirac fermion and lattice vibrations, namely, electron-phonon coupling (EPC). The significant enhancement of EPC is correlated with the tensile strain, which is evoked by the singular buckled structure of √7 × √7 germanene on the Au(111) substrate. Our results present clear evidence for the existence of epitaxial germanene and elucidate the exotic properties of germanene on Au(111).

Using a genetic algorithm combined with density functional theory calculations, we perform a global search for the lowest-energy structures of B clusters with n = 46, 48, 50. Competition among different structural motifs including a hollow cage, core-shell, bilayer, and quasi-planar, is investigated. For B, a core-shell B@B structure resembling the larger B clusters with n ≥ 68 is found to compete with a quasi-planar structure with a central hexagonal hole. A quasi-planar configuration with two connected hexagonal holes is most favorable for B. More interestingly, an unprecedented bilayer structure is unveiled at B, which can be extended to a two-dimensional bilayer phase exhibiting appreciable stability. Our results suggest alternatives to the cage motif as lower-energy B cluster structures with n > 50.

Vacancy engineering plays vital role in the design of high‐performance electrocatalysts. Here, we introduced coupled cation‐vacancy pairs in Ni‐doped CoSe to achieve boosted hydrogen evolution reaction (HER) activity through a facile topochemical intercalation approach. Adjacent Co vacancy pairs and heteroatom Ni doping contribute together for the upshift of the Se 4pz orbital, which induces larger overlap between the Se 4p and H 1s orbitals. As a result, the free energy of H adsorption can be lowered significantly. With an advanced HER activity of 185.7 mV at 10 mA cm−2, this work provides new direction and guidance for the design of novel electrocatalysts.

No abstract