275 research outputs found
Pressure induced Raman and fluorescence singularities in
The pressure effect on the fluoride scheelite laser host is studied
at room temperature up to 26 GPa by Raman scattering and up to 40 GPa by
fluorescence of doped sample. The Raman spectra exhibit three
singularities at the vicinity of 6 GPa, 10-12 GPa and 16-17 GPa. The samples
pressurized to 21 GPa or higher do not recover the original phase after being
released, giving more Raman lines than original samples. The luminescence
spectra of are collected in the energy range corresponding to
following transitions , and
. Singularities are observed in the vicinity of 6 GPa, 10 GPa, 16
GPa, 23 GPa in agreement with the Raman study. Moreover, an irreversible
transition occurs at 23 GPa. The samples pressurized to above 26 GPa become
amorphous when released and all the sharp lines disappear. Above 31 GPa, the
spectra at high pressures show only some broad bands corresponding to
transitions between two multiplets of the configuration of .
These singularities suggest possible phase transformations leading to lowering
of the lattice symmetry.Comment: 12 pages, 13 figures, 2 table, LaTe
Imaging isodensity contours of molecular states with STM
We present an improved way for imaging the local density of states with a
scanning tunneling microscope, which consists in mapping the surface topography
while keeping the differential conductance (d/d) constant. When
archetypical C molecules on Cu(111) are imaged with this method, these
so-called iso-d/d maps are in excellent agreement with theoretical
simulations of the isodensity contours of the molecular orbitals. A direct
visualization and unambiguous identification of superatomic C orbitals
and their hybridization is then possible
Lunar regolith as a feedstock for selective laser melting
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Atomistic mechanisms for the ordered growth of Co nano-dots on Au(788): comparison of VT-STM experiments and multi-scaled calculations
Hetero-epitaxial growth on a strain-relief vicinal patterned substrate has
revealed unprecedented 2D long range ordered growth of uniform cobalt
nanostructures. The morphology of a Co sub-monolayer deposit on a Au(111)
reconstructed vicinal surface is analyzed by Variable Temperature Scanning
Tunneling Microscopy (VT-STM) experiments. A rectangular array of nano-dots
(3.8 nm x 7.2 nm) is found for a particularly large deposit temperature range
lying from 60 K to 300 K. Although the nanodot lattice is stable at room
temperature, this paper focus on the early stage of ordered nucleation and
growth at temperatures between 35 K and 480 K. The atomistic mechanisms leading
to the nanodots array are elucidated by comparing statistical analysis of
VT-STM images with multi-scaled numerical calculations combining both Molecular
Dynamics for the quantitative determination of the activation energies for the
atomic motion and the Kinetic Monte Carlo method for the simulations of the
mesoscopic time and scale evolution of the Co submonolayer
Pressure effects on the Raman spectrum of
The pressure influence on the lattice vibration of has been studied
by Raman diffusion up to 17 GPa. Most Raman frequencies increase with
increasing pressure. Three singularities in the pressure induced frequency
evolution are observed around 1.5 GPa, 10 GPa and 17 GPa. The samples
pressurized to 17 GPa or higher do not revert to the ambient pressure phase
after being released, the new phase showing different Raman spectra from the
ordinary one. It is suggested that undergoes probably sudden lattice
deformations at about 1.5 GPa and 10 GPa, and an irreversible phase
transformation above 17 GPa.Comment: LaTeX file, 3 ps figures, 8 page
Revealing sub-{\mu}m inhomogeneities and {\mu}m-scale texture in H2O ice at Megabar pressures via sound velocity measurements by time-domain Brillouin scattering
Time-domain Brillouin scattering technique, also known as picosecond
ultrasonic interferometry, which provides opportunity to monitor propagation of
nanometers to sub-micrometers length coherent acoustic pulses in the samples of
sub-micrometers to tens of micrometers dimensions, was applied to
depth-profiling of polycrystalline aggregate of ice compressed in a diamond
anvil cell to Megabar pressures. The technique allowed examination of
characteristic dimensions of elastic inhomogeneities and texturing of
polycrystalline ice in the direction normal to the diamond anvil surfaces with
sub-micrometer spatial resolution via time-resolved measurements of variations
in the propagation velocity of the acoustic pulse traveling in the compressed
sample. The achieved two-dimensional imaging of the polycrystalline ice
aggregate in-depth and in one of the lateral directions indicates the
feasibility of three-dimensional imaging and quantitative characterization of
acoustical, optical and acousto-optical properties of transparent
polycrystalline aggregates in diamond anvil cell with tens of nanometers
in-depth resolution and lateral spatial resolution controlled by pump laser
pulses focusing.Comment: 32 pages, 5 figure
Functionalizing surfaces of 3D printed objects with an integrated low-cost atmospheric pressure micro plasma torch
Polymer 3D printing via the Fused Filament Fabrication (FFF) technology is a now well-known process designed to build three-dimensional objects from computer-aided-design (CAD) models in a layer-by-layer method. First dedicated for prototyping, this technology is now widely spread on the additive manufacturing (AM) and production market. With the decreasing costs of the equipment and materials needed as well as the growing simplicity of use and reliability of the technique, one can now have a 3D printer for the same cost and as user-friendly as a regular desktop inkjet printer. Among the commercially distributed thermoplastics, polylactic acid (PLA) and acrylonitrile butadiene styrene (ABS) are the two most outspread but one can also find acrylonitrile styrene acrylate (ASA), polyethylene terephthalate (PET) polycarbonate (PA) and much more. When assuming that single material 3D printed objects are obtained from growing layers in the (xy) plane stacked along the z axis, they are known to show really good tensile strength in the x and y direction but much less in the z direction due to insufficient interlayer bounding. Bigger problems arise when trying to print a multi-material object. Indeed, the chemical incompatibility of the different printed materials as well as their different thermal expansion coefficients are from the materials properties that can cause a very weak diffusion bonding at the interface. Authors started recently to focus on this problematic and very few studies can be found on the subject. To overcome the problem, we consider here improving the wettability of the printed polymer at the interface layer as it cause the extruded material to better spread over this layer, hence increasing the diffusion bonding. This work aims to investigate the effect of an atmospheric cold plasma treatment on the wettability and bonding of 3D printed objects. For this task, we designed an atmospheric pressure dielectric barrier discharge (DBD) plasma torch integrated on a commercial 3D printer. Thus, the device can be controlled to apply a plasma treatment while printing an object. As the deposition process will need to be done on complex surfaces and on thermal sensitive materials, a new type of high voltage nano-pulse generator had to be developed for this device. It gives the possibility to generate a homogeneous plasma (with less filament discharge) in a very small volume and a relatively extended plasma plume with a limitation of the gas temperature. Wettability measurements and tensile tests were carried out on 3D printed + plasma treated objects, obtained with our newly designed device. The material bonding is evaluated either within a single-material specimen by applying the treatment at the interlayers or within a multi-material one by treating only the interface layer of the two different materials.
Pulling and Stretching a Molecular Wire to Tune its Conductance
A scanning tunnelling microscope is used to pull a polythiophene wire from a
Au(111) surface while measuring the current traversing the junction. Abrupt
current increases measured during the lifting procedure are associated to the
detachment of molecular sub-units, in apparent contradiction with the expected
exponential decrease of the conductance with wire length. \textit{Ab initio}
simulations reproduce the experimental data and demonstrate that this
unexpected behavior is due to release of mechanical stress in the wire, paving
the way to mechanically gated single-molecule electronic devices
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