5 research outputs found
Room Temperature Metalation of 2H-TPP Monolayer on Iron and Nickel Surfaces by Picking up Substrate Metal Atoms
Here, it is demonstrated, using high-resolution X-ray spectroscopy and density functional theory calculations, that 2<i>H</i>-tetraphenyl porphyrins metalate at room temperature by incorporating a surface metal atom when a (sub)monolayer is deposited on 3d magnetic substrates, such as Fe(110) and Ni(111). The calculations demonstrate that the redox metalation reaction would be exothermic when occurring on a Ni(111) substrate with an energy gain of 0.89 eV upon embedding a Ni adatom in the macrocycle. This is a novel way to form, <i>via</i> chemical modification and supramolecular engineering, 3d-metal–organic networks on magnetic substrates with an intimate bond between the macrocycle molecular metal ion and the substrate atoms. The achievement of a complete metalation by Fe and Ni can be regarded as a test case for successful preparation of spintronic devices by means of molecular-based magnets and inorganic magnetic substrates
Silicon Monomer Formation and Surface Patterning of Si(001)‑2 × 1 Following Tetraethoxysilane Dissociative Adsorption at Room Temperature
The
adsorption of tetraethoxysilane (TEOS, Si[OC<sub>2</sub>H<sub>5</sub>]<sub>4</sub>) on the Si(001)-2 × 1 surface at 300 K
is studied through a joint experimental and theoretical approach,
combining scanning tunneling microscopy (STM) and synchrotron radiation
X-ray photoelectron spectroscopy (XPS) with first-principles simulations
within the density functional theory (DFT). XPS shows that all Si–O
bonds within the TEOS molecules are broken upon adsorption, releasing
one Si atom per dissociated molecule, while the ethoxy (−OC<sub>2</sub>H<sub>5</sub>) groups form new Si–O bonds with surface
Si dimers. A comparison between experimental STM images and DFT adsorption
configurations shows that the four ethoxy groups bind to two second-neighbor
silicon dimers within the same row, while the released silicon atom
is captured as a monomer on an adjacent silicon dimer row. Additionally,
the surface displays alternate ethoxy- and Si adatom-covered rows
as TEOS coverage increases. This patterning, which spontaneously forms
upon TEOS adsorption, can be used as a template for the nanofabrication
of one-dimensional self-organized structures on Si(001)-2 × 1
Self-Assembled Multilayer Graphene Oxide Membrane and Carbon Nanotubes Synthesized Using a Rare Form of Natural Graphite
The
fabrication of flexible multilayer graphene oxide (GO) membrane
and carbon nanotubes (CNTs) using a rare form of high-purity natural
graphite, vein graphite, is reported for the first time. Graphite
oxide is synthesized using vein graphite following Hummer’s
method. By facilitating functionalized graphene sheets in graphite
oxide to self-assemble, a multilayer GO membrane is fabricated. Electric
arc discharge is used to synthesis CNTs from vein graphite. Both multilayer
GO membrane and CNTs are investigated using microscopy and spectroscopy
experiments, i.e., scanning electron microscopy (SEM), atomic force
microscopy (AFM), high-resolution transmission electron microscopy
(HRTEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction
(XRD), thermogravimetric analysis (TGA), core level photoelectron
spectroscopy, and C <i>K</i>-edge X-ray absorption spectroscopy
(NEXAFS), to characterize their structural and topographical properties.
Characterization of vein graphite using different techniques reveals
that it has a large number of crystallites, hence the large number
of graphene sheets per crystallite, preferentially oriented along
the (002) plane. NEXAFS and core level spectra confirm that vein graphite
is highly crystalline and pure. Fourier transform infrared (FT-IR)
and C 1s core level spectra show that oxygen functionalities (−C–OH,
−CO,–C–O–C−) are introduced
into the basal plane of graphite following chemical oxidation. Carbon
nanotubes are produced from vein graphite through arc discharge without
the use of any catalyst. HRTEM confirm that multiwalled carbon nanotube
(MWNTs) are produced with the presence of some structure in the central
pipe. A small percentage of single-walled nanotubes (SWNTs) are also
produced simultaneously with MWNTs. Spectroscopic and microscopic
data are further discussed here with a view to using vein graphite
as the source material for the synthesis of carbon nanomaterials
Chemical Bonds and Charge-Transfer Dynamics of a Dye–Hierarchical-TiO<sub>2</sub> Hybrid Interface
The
adsorption of Zn-tetraphenylporphyrin (ZnTPP) on nanoporous
hierarchically organized anatase TiO<sub>2</sub> structures and the
properties of the corresponding hybrid interface were studied by synchrotron
radiation experiments. The molecular structure, electronic properties,
and bonding with nanostructured TiO<sub>2</sub> surfaces were analyzed
by photoemission (XPS and UPS) and X-ray absorption spectroscopy (XAS).
The charge transfer at the interface was investigated by means of
valence band resonant photoemission experiments (ResPES) at the C
K-edge. We show that the charge-transfer dynamics between the photoexcited
ZnTPP and TiO<sub>2</sub> is strongly influenced by the presence of
defects on the TiO<sub>2</sub> surface. On a stoichiometric anatase
nanostructure, ZnTPP bonding occurs primarily via carbon atoms belonging
to the molecular phenyl rings, and this creates a preferential channel
for the charge transfer. This phenomenon is reduced in the case of
defective TiO<sub>2</sub> surface, where ZnTPP interacts mainly through
the molecule macrocycle. Our results represent a surface science study
of the dye molecule behavior on a nanoporous TiO<sub>2</sub> photoanode
relevant to dye-sensitized or hybrid solar cell applications, and
they show the importance of the surface oxidation state for the charge-transfer
process
Physical Delithiation of Epitaxial LiCoO<sub>2</sub> Battery Cathodes as a Platform for Surface Electronic Structure Investigation
We report a novel delithiation process for epitaxial
thin films
of LiCoO2(001) cathodes using only physical methods, based
on ion sputtering and annealing cycles. Preferential Li sputtering
followed by annealing produces a surface layer with a Li molar fraction
in the range 0.5 x < 1, characterized by
good crystalline quality. This delithiation procedure allows the unambiguous
identification of the effects of Li extraction without chemical byproducts
and experimental complications caused by electrolyte interaction with
the LiCoO2 surface. An analysis by X-ray photoelectron
spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) provides
a detailed description of the delithiation process and the role of
O and Co atoms in charge compensation. We observe the simultaneous
formation of Co4+ ions and of holes localized near O atoms
upon Li removal, while the surface shows a (2 × 1) reconstruction.
The delithiation method described here can be applied to other crystalline
battery elements and provide information on their properties that
is otherwise difficult to obtain