90 research outputs found
Crystalline and electronic structure of single-layer TaS
Single-layer TaS is epitaxially grown on Au(111) substrates. The
resulting two-dimensional crystals adopt the 1H polymorph. The electronic
structure is determined by angle-resolved photoemission spectroscopy and found
to be in excellent agreement with density functional theory calculations. The
single layer TaS is found to be strongly n-doped, with a carrier
concentration of 0.3(1) extra electrons per unit cell. No superconducting or
charge density wave state is observed by scanning tunneling microscopy at
temperatures down to 4.7 K.Comment: 6 pages, 4 figure
Quasi-free-standing single-layer WS2 achieved by intercalation
Large-area and high-quality single-layer transition metal dichalcogenides can
be synthesized by epitaxial growth on single-crystal substrates. An important
advantage of this approach is that the interaction between the single-layer and
the substrate can be strong enough to enforce a single crystalline orientation
of the layer. On the other hand, the same interaction can lead to hybridization
effects, resulting in the deterioration of the single-layer's native
properties. This dilemma can potentially be solved by decoupling the
single-layer from the substrate surface after the growth via intercalation of
atoms or molecules. Here we show that such a decoupling can indeed be achieved
for single-layer WS2 epitaxially grown on Ag(111) by intercalation of Bi atoms.
This process leads to a suppression of the single-layer WS2-Ag substrate
interaction, yielding an electronic band structure reminiscent of free-standing
single-layer WS2
Pnictogens Allotropy and Phase Transformation during van der Waals Growth
Pnictogens have multiple allotropic forms resulting from their ns2 np3
valence electronic configuration, making them the only elemental materials to
crystallize in layered van der Waals (vdW) and quasi-vdW structures throughout
the group. Light group VA elements are found in the layered orthorhombic A17
phase such as black phosphorus, and can transition to the layered rhombohedral
A7 phase at high pressure. On the other hand, bulk heavier elements are only
stable in the A7 phase. Herein, we demonstrate that these two phases not only
co-exist during the vdW growth of antimony on weakly interacting surfaces, but
also undertake a spontaneous transformation from the A17 phase to the
thermodynamically stable A7 phase. This metastability of the A17 phase is
revealed by real-time studies unraveling its thickness-driven transition to the
A7 phase and the concomitant evolution of its electronic properties. At a
critical thickness of ~4 nm, A17 antimony undergoes a diffusionless shuffle
transition from AB to AA stacked alpha-antimonene followed by a gradual
relaxation to the A7 bulk-like phase. Furthermore, the electronic structure of
this intermediate phase is found to be determined by surface self-passivation
and the associated competition between A7- and A17-like bonding in the bulk.
These results highlight the critical role of the atomic structure and
interfacial interactions in shaping the stability and electronic
characteristics of vdW layered materials, thus enabling a new degree of freedom
to engineer their properties using scalable processes
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