3 research outputs found
Self-Assembled Monolayer-Functionalized Half-Metallic Manganite for Molecular Spintronics
(La,Sr)MnO<sub>3</sub> manganite (LSMO) has emerged as the standard ferromagnetic electrode in organic spintronic devices due to its highly spin-polarized character and air stability. Whereas organic semiconductors and polymers have been mainly envisaged to propagate spin information, self-assembled monolayers (SAMs) have been overlooked and should be considered as promising materials for molecular engineering of spintronic devices. Surprisingly, up to now the first key step of SAM grafting protocols over LSMO surface thin films is still missing. We report the grafting of dodecyl (C12P) and octadecyl (C18P) phosphonic acids over the LSMO half-metallic oxide. Alkylphosphonic acids form ordered self-assembled monolayers, with the phosphonic group coordinated to the surface and alkyl chains tilted from the surface vertical by 43° (C12P) and 27° (C18P). We have electrically characterized these SAMs in nanodevices and found that they act as tunnel barriers, opening the door toward the integration of alkylphosphonic acid//LSMO SAMs into future molecular/organic spintronic devices such as spin OLEDs
Interdependency of Subsurface Carbon Distribution and Graphene–Catalyst Interaction
The
dynamics of the graphene–catalyst interaction during
chemical vapor deposition are investigated using in situ, time- and
depth-resolved X-ray photoelectron spectroscopy, and complementary
grand canonical Monte Carlo simulations coupled to a tight-binding
model. We thereby reveal the interdependency of the distribution of
carbon close to the catalyst surface and the strength of the graphene–catalyst
interaction. The strong interaction of epitaxial graphene with Ni(111)
causes a depletion of dissolved carbon close to the catalyst surface,
which prevents additional layer formation leading to a self-limiting
graphene growth behavior for low exposure pressures (10<sup>–6</sup>–10<sup>–3</sup> mbar). A further hydrocarbon pressure
increase (to ∼10<sup>–1</sup> mbar) leads to weakening
of the graphene–Ni(111) interaction accompanied by additional
graphene layer formation, mediated by an increased concentration of
near-surface dissolved carbon. We show that growth of more weakly
adhered, rotated graphene on Ni(111) is linked to an initially higher
level of near-surface carbon compared to the case of epitaxial graphene
growth. The key implications of these results for graphene growth
control and their relevance to carbon nanotube growth are highlighted
in the context of existing literature
Atomic and Electronic Structure of the BaTiO<sub>3</sub>/Fe Interface in Multiferroic Tunnel Junctions
Artificial multiferroic tunnel junctions combining a
ferroelectric
tunnel barrier of BaTiO<sub>3</sub> with magnetic electrodes display
a tunnel magnetoresistance whose intensity can be controlled by the
ferroelectric polarization of the barrier. This effect, called tunnel
electromagnetoresistance (TEMR), and the corollary magnetoelectric
coupling mechanisms at the BaTiO<sub>3</sub>/Fe interface were recently
reported through macroscopic techniques. Here, we use advanced spectromicroscopy
techniques by means of aberration-corrected scanning transmission
electron microscopy (STEM) and electron energy-loss spectroscopy (EELS)
to probe locally the nanoscale structural and electronic modifications
at the ferroelectric/ferromagnetic interface. Atomically resolved
real-space spectroscopic techniques reveal the presence of a single
FeO layer between BaTiO<sub>3</sub> and Fe. Based on this accurate
description of the studied interface, we propose an atomistic model
of the ferroelectric/ferromagnetic interface further validated by
comparing experimental and simulated STEM images with atomic resolution.
Density functional theory calculations allow us to interpret the electronic
and magnetic properties of these interfaces and to understand better
their key role in the physics of multiferroics nanostructures