2 research outputs found
Van der Waals Epitaxy of Weyl-Semimetal T<b><sub>d</sub></b>āWTe<sub><b>2</b></sub>
Epitaxial
growth of WTe2 offers significant advantages,
including the production of high-quality films, possible long-range
in-plane ordering, and precise control over layer thicknesses. However,
the mean island size of WTe2 grown by molecular beam epitaxy
(MBE) in the literature is only a few tens of nanometers, which is
not suitable for the implementation of devices at large lateral scales.
Here we report the growth of Td -WTe2 ultrathin
films by MBE on monolayer (ML) graphene, reaching a mean flake size
of ā110 nm, which is, on overage, more than three times larger
than previous results. WTe2 films thicker than 5 nm have
been successfully synthesized and exhibit the expected Td phase atomic
structure. We rationalize the epitaxial growth of Td-WTe2 and propose a simple model to estimate the mean flake size
as a function of growth parameters that can be applied to other transition
metal dichalcogenides (TMDCs). Based on nucleation theory and the
KolmogorovāJohnsonāMehāAvrami (KJMA) equation,
our analytical model supports experimental data showing a critical
coverage of 0.13 ML above which WTe2 nucleation becomes
negligible. The quality of monolayer WTe2 films is demonstrated
by electronic band structure analysis using angle-resolved photoemission
spectroscopy (ARPES), which is in agreement with first-principles
calculations performed on free-standing WTe2 and previous
reports. We found electron pockets at the Fermi level, indicating
a n-type doping of WTe2 with an electron
density of n = 2.0 Ā± 0.5 Ć 1012 cmā2 for each electron pocket
High Spin Polarization at Ferromagnetic MetalāOrganic Interfaces: A Generic Property
A high
spin polarization of states around the Fermi level, <i>E</i><sub>F</sub>, at room temperature has been measured in
the past at the interface between a few molecular candidates and the
ferromagnetic metal Co. Is this promising property for spintronics
limited to these candidates? Previous reports suggested that certain
conditions, such as strong ferromagnetism, i.e., a fully occupied
spin-up d band of the ferromagnet, or the presence of Ļ bonds
on the molecule, i.e., molecular conjugation, needed to be met. What
rules govern the presence of this property? We have performed spin-resolved
photoemission spectroscopy measurements on a variety of such interfaces.
We find that this property is robust against changes to the molecule
and ferromagnetic metalās electronic properties, including
the aforementioned conditions. This affirms the generality of highly
spin-polarized states at the interface between a ferromagnetic metal
and a molecule and augurs bright prospects toward integrating these
interfaces within organic spintronic devices