586 research outputs found
Self-assembled metallic nanoparticle template --- a new approach of surface nanostructuring at nanometer scale
In the present work, the formation of silver and copper nanostructures on
highly oriented pyrolytic graphite (HOPG) modified with self-assembled gold
nanoparticles (Au NPs) is demonstrated. Surface patterning with nanometer
resolution was achieved. Different methods such as field emission scanning
electron microscopy (FEGSEM), energy dispersive spectrometry (EDS) and X-ray
photoelectron spectroscopy (XPS) were used to illustrate a selective deposition
of silver and copper on Au NPs. The mechanism of silver and copper ions
reduction on Au NP with -dodecanethiol coating is discussed.Comment: 6 pages, 3 figure
Ultrafast filling of an electronic pseudogap in an incommensurate crystal
We investigate the quasiperiodic crystal (LaS)1.196(VS2) by angle and time
resolved photoemission spectroscopy. The dispersion of electronic states is in
qualitative agreement with band structure calculated for the VS2 slab without
the incommensurate distortion. Nonetheless, the spectra display a temperature
dependent pseudogap instead of quasiparticles crossing. The sudden
photoexcitation at 50 K induces a partial filling of the electronic pseudogap
within less than 80 fs. The electronic energy flows into the lattice modes on a
comparable timescale. We attribute this surprisingly short timescale to a very
strong electron-phonon coupling to the incommensurate distortion. This result
sheds light on the electronic localization arising in aperiodic structures and
quasicrystals
Significant reduction of electronic correlations upon isovalent Ru substitution of BaFe2As2
We present a detailed investigation of Ba(Fe0.65Ru0.35)2As2 by transport
measurements and Angle Resolved photoemission spectroscopy. We observe that Fe
and Ru orbitals hybridize to form a coherent electronic structure and that Ru
does not induce doping. The number of holes and electrons, deduced from the
area of the Fermi Surface pockets, are both about twice larger than in
BaFe2As2. The contribution of both carriers to the transport is evidenced by a
change of sign of the Hall coefficient with decreasing temperature. Fermi
velocities increase significantly with respect to BaFe2As2, suggesting a
significant reduction of correlation effects. This may be a key to understand
the appearance of superconductivity at the expense of magnetism in undoped iron
pnictides
Cs-induced charge transfer on (2x4)-GaAs(001) studied by photoemission
Cesium adsorption on 2x4 GaAs (001) was studied by photoemission and low
energy electron diffraction. The different Cs induced changes of the As 3d and
Ga 3d core level spectra show that charge transfer is almost complete for Ga
surface sites, but is negligible to surface As at a coverage smaller than 0.3
ML. The situation is opposite for a coverage larger than 0.3ML, at which
transfer occurs to As but no longer to Ga. Charge transfer to As atoms leads to
disordering and destabilization and induces surface conversion from the As-rich
surface to the Ga-rich 4x2 one after annealing at a reduced temperature of 450
C
Simulating high-pressure surface reactions with molecular beams
Using a reactive molecular beam with high kinetic energy () it is
possible to speed gas-surface reactions involving high activation barriers
(), which would require elevated pressures () if a random gas
with a Maxwell-Boltzmann distribution is used. By simply computing the number
of molecules that overcome the activation barrier in a random gas at and
in a molecular beam at =, we establish an -
equivalence curve, through which we postulate that molecular beams are ideal
tools to investigate gas-surface reactions that involve high activation
energies. In particular, we foresee the use of molecular beams to simulate gas
surface reactions within the industrial-range ( 10 bar) using
surface-sensitive Ultra-High Vacuum (UHV) techniques, such as X-ray
photoemission spectroscopy (XPS). To test this idea, we revisit the oxidation
of the Cu(111) surface combining O molecular beams and XPS experiments. By
tuning the kinetic energy of the O beam in the range 0.24-1 eV we achieve
the same sequence of surface oxides obtained in Ambient Pressure Photoemission
(AP-XPS) experiments, in which the Cu(111) surface was exposed to a random
O gas up to 1 mbar. We observe the same surface oxidation kinetics as in
the random gas, but with a much lower dose, close to the expected value derived
from the equivalence curve
Structural and Mechanical Properties of DLC/TiN Coatings on Carbide for Wood-Cutting Applications
In this work, the diamond-like carbon and
titanium nitride (DLC/TiN) multilayer
coatings were prepared on a cemented
tungsten carbide substrate (WC—3 wt.%
Co) using the cathodic vacuum arc physical
vapor deposition (Arc-PVD) method and
pulsed Arc-PVD method with a graphite
cathode for the deposition of TiN and
carbon layers, respectively. The structural
and mechanical properties of the prepared
coatings were studied, and different
techniques, such as scanning electron
microscope (SEM), energy-dispersive X-ray
spectroscopy (EDX), X-ray diffraction
(XRD), Raman spectroscopy, and
microindentation techniques investigated
their microstructure, composition, and
phases. The prepared coatings had a
multilayer structure with distinct phases of
DLC, TiN, and carbide substrate. The
potentiodynamic polarization method
(PDP) was performed for the DLC/TiN
multilayer coatings in 3% NaCl solution to
evaluate the corrosion resistance of the
prepared coatings. It has been shown that
the DLC layer provided the coating with a
polarization resistance of 564.46 kΩ.
Moreover, it has been demonstrated that
the DLC/TiN coatings had a high hardness
of 38.7–40.4 GPa, which can help to
extend the wood-cutting tools’ life
Simulating high-pressure surface reactions with molecular beams
Using a reactive molecular beam with high kinetic energy (Ekin), it is possible to speed gas-surface reactions involving high activation barriers (Eact), which would require elevated pressures (P0) if a random gas with a Maxwell-Boltzmann distribution is used. By simply computing the number of molecules that overcome the activation barrier in a random gas at P0 and in a molecular beam at Ekin = Eact, we establish an Ekin-P0 equivalence curve, through which we postulate that molecular beams are ideal tools to investigate gas-surface reactions that involve high activation energies. In particular, we foresee the use of molecular beams to simulate gas surface reactions within the industrial-range (>10 bar) using surface-sensitive ultra-high vacuum (UHV) techniques, such as X-ray photoemission spectroscopy (XPS). To test this idea, we revisit the oxidation of the Cu(111) surface combining O2 molecular beams and XPS experiments. By tuning the kinetic energy of the O2 beam in the range of 0.24-1 eV, we achieve the same sequence of surface oxides obtained in ambient pressure photoemission (AP-XPS) experiments, in which the Cu(111) surface was exposed to a random O2 gas up to 1 mbar. We observe the same surface oxidation kinetics as in the random gas, but with a much lower dose, close to the expected value derived from the equivalence curveTED2021-130446B-I00, PID2020-116093RBC4
- …