2 research outputs found
Ferromagnetic Layers in a Topological Insulator (Bi,Sb)<sub>2</sub>Te<sub>3</sub> Crystal Doped with Mn
Magnetic topological insulators (MTIs) have recently
become a subject
of poignant interest; among them, Z2 topological insulators
with magnetic moment ordering caused by embedded magnetic atoms attract
special attention. In such systems, the case of magnetic anisotropy
perpendicular to the surface that holds a topologically nontrivial
surface state is the most intriguing one. Such materials demonstrate
the quantum anomalous Hall effect, which manifests itself as chiral
edge conduction channels that can be manipulated by switching the
polarization of magnetic domains. In the present paper, we uncover
the atomic structure of the bulk and the surface of Mn0.06Sb1.22Bi0.78Te3.06 in conjunction
with its electronic and magnetic properties; this material is characterized
by naturally formed ferromagnetic layers inside the insulating matrix,
where the Fermi level is tuned to the bulk band gap. We found that
in such mixed crystals septuple layers (SLs) of Mn(Bi,Sb)2Te4 form structures that feature three SLs, each of which
is separated by two or three (Bi,Sb)2Te3 quintuple
layers (QLs); such a structure possesses ferromagnetic properties.
The surface obtained by cleavage includes terraces with different
terminations. Manganese atoms preferentially occupy the central positions
in the SLs and in a very small proportion can appear in the QLs, as
indirectly indicated by a reshaped Dirac cone
Laterally Selective Oxidation of Large-Scale Graphene with Atomic Oxygen
Using
X-ray photoemission microscopy, we discovered that oxidation
of commercial large-scale graphene on Cu foil, which typically has
bilayer islands, by atomic oxygen proceeds with the formation of the
specific structures: though relatively mobile epoxy groups are generated
uniformly across the surface of single-layer graphene, their concentration
is significantly lower for bilayer islands. More oxidized species
like carbonyl and lactones are preferably located at the centers of
these bilayer islands. Such structures are randomly distributed over
the surface with a mean density of about 3× 10<sup>6</sup> cm<sup>–2</sup> in our case. Using a set of advanced spectromicroscopy
instruments including Raman microscopy, X-ray photoelectron spectroscopy
(μ-XPS), Auger electron spectroscopy (nano-AES), and angle-resolved
photoelectron spectroscopy (μ-ARPES), we found that the centers
of the bilayer islands where the second layer nucleates have a high
defect concentration and serve as the active sites for deep oxidation.
This information can be potentially useful in developing lateral heterostructures
for electronics and optoelectronics based on graphene/graphene oxide
heterojunction