2 research outputs found
Bimetallic NickelāCobalt Nanosized Layers Supported on Polar ZnO Surfaces: MetalāSupport Interaction and Alloy Effects Studied by Synchrotron Radiation X-ray Photoelectron Spectroscopy
The interaction of ultrathin bimetallic NiāCo
layers (0.25
and 1.5 nm) supported on polar (0001)ĀZnāZnO and (0001Ģ
)ĀOāZnO
substrates was investigated by synchrotron-based photoelectron spectroscopy
(PES) under ultrahigh vacuum (UHV) and O<sub>2</sub> environments.
Monometallic Ni and Co layers were also characterized to highlight
the influence of NiāCo synergetic effects on the metalāsupport
interaction. At room temperature, cobalt is partially oxidized, while
nickel is metallic. The effect of ZnO surface termination is minor,
while the influence of surface hydroxyl groups is discussed. Annealing
at 773 K in UHV promotes oxidation of monometallic Ni and Co layers
but has little influence on bimetallic NiāCo. In addition,
significant agglomeration of the NiāCo overlayer is observed,
with a parallel increase in the surface Co concentration. Agglomeration
of NiāCo is more pronounced on O-terminated ZnO. Upon annealing
in 1 Ć 10<sup>ā6</sup> mbar of O<sub>2</sub>, both Ni
and Co readily oxidize and redisperse over the ZnO substrate. Moreover,
cobalt tends to segregate over nickel, creating a concentration gradient
between the two alloy constituents (probably a coreāshell-like
structure). Overall, our results indicate that the interaction at
the NiāCo/ZnO interface is influenced by the synergetic effects
between the two metals and to a lesser extent by the substrate termination.
Taking into account the substantial progress made in the synthesis
of ZnO nanostructures and surfaces, this study can assist in the effort
toward improved ZnO-based catalysts with tailored properties
Study of Ferrocene Dicarboxylic Acid on Substrates of Varying Chemical Activity
Ferrocene-based
molecules are extremely appealing as they offer
a prospect of having built-in spin or charge functionality. However,
there are only limited number of studies of structural and electronic
properties on surfaces so far. We investigated the self-assembly processes
of 1,1ā²-ferrocene dicarboxylic acid molecules (C<sub>12</sub>H<sub>10</sub>FeO<sub>4</sub>) on both metallic (Ag(111), Au(111),
and Cu(110)) and insulating (Cu<sub>3</sub>N/CuĀ(110)) surfaces with
high-resolution ncAFM/STM, XPS, and NEXAFS. The experimental evidence
is corroborated with total energy DFT calculations and ncAFM simulations.
The combined experimental and theoretical analysis allows detailed
understanding of the unique arrangement and adsorption geometries
of the molecules on different substrates, as well as the different
chemical stability of the carboxylic (COOH) groups. The molecules
on noble (Ag, Au) surfaces show only a weak interaction with the substrate
forming a complex self-assembled pattern, driven by weak intermolecular
interactions. In contrast, the analysis reveals the carboxylic groups
undergo dehydrogenation on the Cu(110) and Cu<sub>3</sub>N/CuĀ(110).
As a result, the oxygen atoms form strong chemical bonds to the substrate
Cu atoms and impose an orientation on the ferrocene cyclopentadienyl
rings perpendicular to the substrate