6 research outputs found
Topological Dirac Semimetal Na3Bi Films in the Ultrathin Limit via Alternating Layer Molecular Beam Epitaxy
Ultrathin films of Na3Bi on insulating substrates are desired for opening a
bulk band gap and generating the quantum spin Hall effect from a topological
Dirac semimetal, though continuous films in the few nanometer regime have been
difficult to realize. Here, we utilize alternating layer molecular beam epitaxy
(MBE) to achieve uniform and continuous single crystal films of Na3Bi(0001) on
insulating Al2O3(0001) substrates and demonstrate electrical transport on films
with 3.8 nm thickness (4 unit cells). The high material quality is confirmed
through in situ reflection high-energy electron diffraction (RHEED), scanning
tunneling microscopy (STM), x-ray diffraction (XRD), and x-ray photoelectron
spectroscopy (XPS). In addition, these films are employed as seed layers for
subsequent growth by codeposition, leading to atomic layer-by-layer growth as
indicated by RHEED intensity oscillations. These material advances facilitate
the pursuit of quantum phenomena in thin films of Dirac semimetals.Comment: 11 pages, 5 figure
Supplement Number 1
Supplemental Information document containing additional implant details, a furnace schematic, a discussion of the importance of purge times, results of annealing Ga2O3 in forming gas, contact resistance analysis, additional XRD plots, and additional STEM images
Tailoring the Electronic Structure of Covalently Functionalized Germanane via the Interplay of Ligand Strain and Electronegativity
The
covalent functionalization of 2D crystals is an emerging route
for tailoring the electronic structure and generating novel phenomena.
Understanding the influence of ligand chemistry will enable the rational
tailoring of their properties. Through the synthesis of numerous ligand-functionalized
germanane crystals, we establish the role of ligand size and electronegativity
on functionalization density, framework structure, and electronic
structure. Nearly uniform termination only occurs with small ligands.
Ligands that are too sterically bulky will lead to partial hydrogen
termination of the framework. With a homogeneous distribution of different
ligands, the band gaps and Raman shifts are dictated by their relative
stoichiometry in a pseudolinear fashion similar to Vegard’s
law. Larger and more electronegative ligands expand the germanane
framework, thereby lowering the band gap and Raman shift. Simply by
changing the identity of the organic ligand, the band gap can be tuned
by ∼15%, highlighting the power of functionalization chemistry
to manipulate the properties of single-atom thick materials