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Black phosphorus (BP) has recently attracted considerable attention due to its unique structure and fascinating optical and electronic properties as well as possible applications in photothermal agents. However, its main drawback is rapid degradation in ambient environments of H2O and O2, which has led to much research on the improvement of its stability. Unfortunately, this research has not shown great improvement in carrier mobilities. Here, we perform scanning tunneling microscopy observations of few-layer BP (FLBP) sheets exfoliated in ultrahigh vacuum and reveal, for the first time, the existence of lattice oxygen introduced during crystal growth. As a proof-of-concept application, hydrogenation is conducted to remove the lattice oxygen atoms followed by phosphorization, which repairs the phosphorous vacancies caused by mechanical exfoliation and hydrogenation. The resulting FLBP sheets show high ambipolar field-effect mobilities of 1374 cm2 V–1 s–1 for holes and 607 cm2 V–1 s–1 for electrons at 2 K....

Atomically thin two-dimensional (2D) crystals have gained tremendous attentions owing to their potential impacts to the future electronics technologies, as well as the exotic phenomena emerging in these materials. Monolayer of {\alpha} phase Sb ({\alpha}-antimonene) that shares the same puckered structure as black phosphorous, has been predicted to be stable with precious properties. However, the experimental realization still remains challenging. Here, we successfully grow high-quality monolayer {\alpha}-antimonene, with the thickness finely controlled. The {\alpha}-antimonene exhibits great stability upon exposure to air. Combining scanning tunneling microscope, density functional theory calculations and transport measurement, it is found that the electron band crossing the Fermi level exhibits a linear dispersion with a fairly small effective mass, and thus a good electrical conductivity. All of these properties make the {\alpha}-antimonene promising in the future electronic applications., Comment: 14 pages, 5 figures

We demonstrate an efficient way of tuning the atomic buckling in stanene to open a topologically nontrivial energy gap. By tuning the growth kinetics, we obtain an unexpected high-buckled 3 × 3 stanene on the Bi(111) substrate. Scanning tunneling microscopy study combined with density functional theory calculation confirms that the 3 × 3 stanene is a distorted 1 × 1 structure with a high-buckled Sn in every three 1 × 1 unit cells. The high-buckled 3 × 3 stanene favors a large band inversion at the Γ point, and the spin–orbit coupling opens a topologically nontrivial energy gap. This study provides an alternate way to tune the topology of monolayer topological materials.

We have grown nearly freestanding single-layer $1{T}^{\ensuremath{'}}\ensuremath{-}\mathrm{WT}{\mathrm{e}}_{2}$ on graphitized $6H$-SiC(0001) by using molecular beam epitaxy (MBE), and characterized its electronic structure with scanning tunneling microscopy/spectroscopy (STM/STS). The existence of topological edge states at the periphery of single-layer $\mathrm{WT}{\mathrm{e}}_{2}$ islands was confirmed. Surprisingly, a bulk band gap at the Fermi level and insulating behaviors were also found in single-layer $\mathrm{WT}{\mathrm{e}}_{2}$ at low temperature, which are likely associated with an incommensurate charge order transition. The realization of two-dimensional topological insulators (2D TIs) in single-layer transition-metal dichalcogenide provides a promising platform for further exploration of the 2D TIs' physics and related applications.

Surface reactivity is important in modifying the physical and chemical properties of surface-sensitive materials, such as the topological insulators. Even though many studies addressing the reactivity of topological insulators towards external gases have been reported, it is still under heavy debate whether and how the topological insulators react with ${\mathrm{H}}_{2}\mathrm{O}$. Here, we employ scanning tunneling microscopy to directly probe the surface reaction of $\mathrm{B}{\mathrm{i}}_{2}\mathrm{T}{\mathrm{e}}_{3}$ towards ${\mathrm{H}}_{2}\mathrm{O}$. Surprisingly, it is found that only the top quintuple layer is reactive to ${\mathrm{H}}_{2}\mathrm{O}$, resulting in a hydrated Bi bilayer as well as some Bi islands, which passivate the surface and prevent subsequent reaction. A reaction mechanism is proposed with ${\mathrm{H}}_{2}\mathrm{Te}$ and hydrated Bi as the products. Unexpectedly, our study indicates that the reaction with water is intrinsic and not dependent on any surface defects. Since water inevitably exists, these findings provide key information when considering the reactions of $\mathrm{B}{\mathrm{i}}_{2}\mathrm{T}{\mathrm{e}}_{3}$ with residual gases or atmosphere.

By using scanning tunneling microscopy (STM) / spectroscopy (STS), we systematically characterize the electronic structure of lightly doped 1T-TiSe2, and demonstrate the existence of the electronic inhomogeneity and the pseudogap state. It is found that the intercalation induced lattice distortion impacts the local band structure and reduce the size of the charge density wave (CDW) gap with the persisted 2x2 spatial modulation. On the other hand, the delocalized doping electrons promote the formation of pseudogap. Domination by either of the two effects results in the separation of two characteristic regions in real space, exhibiting rather different electronic structures. Further doping electrons to the surface confirms that the pseudogap may be the precursor for the superconducting gap. This study suggests that the competition of local lattice distortion and the delocalized doping effect contribute to the complicated relationship between charge density wave and superconductivity for intercalated 1T-TiSe2., Comment: 12 pages, 5 figures