Search results for "Nolay"
showing 10 items of 588 documents
Incommensurate phases in adsorbed monolayers: structure and energy of domain walls
2002
Abstract The properties of incommensurate films of domain-wall structure formed on the (1 0 0) plane of face centered cubic crystals are studied by Monte Carlo simulation. The wall energies, wall structure and the wall–wall interaction are determined for different types of domain walls occurring in films which form the c(2×2) registered structure. The systems characterized by different strength and corrugation of the surface potential and of different misfit between adsorbate and adsorbent are discussed. It is demonstrated that heavy as well as light walls are rather strongly localized. Moreover, it is shown that the incommensurate structure with crossing heavy walls has higher stability th…
First principles simulations of 2D Cu superlattices on the MgO(0 0 1) surface
2004
AbstractFirst principles slab simulations of copper 2D superlattices of different densities on the perfect MgO(001) surface are performed using the DFT method as implemented into the CRYSTAL98 computer code. In order to clarify the nature of interfacial bonding, we consider regular 1/4, 1/2 and 1 monolayer (ML) coverages and compare results of our calculations with various experimental and theoretical data. Our general conclusion is that the physical adhesion associated with a Cu polarization and charge redistribution gives the predominant contribution to the bonding of the regular Cu 2D layer on the MgO(001) surface.
Monte Carlo Study of Dense Monolayer and Bilayer Films on the (100) Plane of Face-Centered Cubic Crystals
1999
A Monte Carlo simulation method in the canonical and in the grand canonical ensembles is used to study the behavior and properties of dense monolayer and bilayer films formed on the (100) plane of model face-centered cubic crystals. Systems with different effects due to the periodicity of the gas−solid potential are considered, and the mechanism of melting in the first and the second adsorbed layer is discussed. It is demonstrated that the film structure is very sensitive to the gas−solid potential corrugation, as well as to the temperature and the surface coverage. In particular, it is shown that monolayer films formed on weakly corrugated surfaces exhibit the incommensurate (dense) phase …
In-situ monitoring by Raman spectroscopy of the thermal doping of graphene and MoS2 in O-2-controlled atmosphere
2017
The effects of temperature and atmosphere (air and O2) on the doping of monolayers of graphene (Gr) on SiO2 and Si substrates, and on the doping of MoS2 multilayer flakes transferred on the same substrates have been investigated. The investigations were carried out by in situ micro-Raman spectroscopy during thermal treatments up to 430 °C, and by atomic force microscopy (AFM). The spectral positions of the G and 2D Raman bands of Gr undergo only minor changes during treatment, while their amplitude and full width at half maximum (FWHM) vary as a function of the temperature and the used atmosphere. The thermal treatments in oxygen atmosphere show, in addition to a thermal effect, an effect a…
Graphene p-Type Doping and Stability by Thermal Treatments in Molecular Oxygen Controlled Atmosphere
2015
Doping and stability of monolayer low defect content graphene transferred on a silicon dioxide substrate on silicon are investigated by micro-Raman spectroscopy and atomic force microscopy (AFM) during thermal treatments in oxygen and vacuum controlled atmosphere. The exposure to molecular oxygen induces graphene changes as evidenced by a blue-shift of the G and 2D Raman bands, together with the decrease of I2D/IG intensity ratio, which are consistent with a high p-type doping (∼1013 cm-2) of graphene. The successive thermal treatment in vacuum does not affect the induced doping showing this latter stability. By investigating the temperature range 140-350 °C and the process time evolution, …
Observation of instability of faceted crystals in lipid monolayers
1998
Abstract The morphological instabilities of two-dimensional hexagonal crystals in lipid monolayers are studied. Fluorescence microscopy indicates that beyond a critical size the faceted crystal develops into dendrites with unusual tip growth behavior, which is not consistent with the current theory of dendritic growth. The morphological transitions in relation to the driving force for two-dimensional crystal growth are also studied.
On melting of two-dimensional monolayer films
1996
The melting of two-dimensional films formed on the (100) fcc crystal is studied by Monte Carlo simulation. The results obtained suggest that in systems with only weakly corrugated surface potential, exhibiting the hexagonal close packed solid structure, the melting transition is followed by the lsing-like transition as predicted by the theory of Nelson and Halperin. In the case of highly corrugated surface potential, the film forms registered structure which disorders gradually as the temperature is raised.
Grazing-Incidence X-ray Diffraction Study of Octadecanoic Acid Monolayers
1998
We report the observation of X-ray scattering profiles from monolayers of octadecanoic acid in the vicinity of room temperature and evidence for the existence near room temperature of all four hexatic rotator phases L2d, Ov, L‘1, and LS, which differ in the details of their molecular tilt. While the incontrovertible triple-reflection signature of the chiral L‘1 phase was not observed, we propose that the previously reported rapid annealing behavior in this phase can lead to the disappearance of one, and in some cases two, of the three peaks.
Quadratic Nonlinear Behaviour of Various Langmuir-Blodgett Molecules
1989
The Langmuir-Blodgett (L-B) technique is well known as a method of building-up ordered arrays of organic molecules, and especially as a means of imposing a noncentrosymmetric structure from molecules that crystallize in a centrosymmetric space group(1–3). L-B films for use in quadratic nonlinear optics can be ordered in a statistically noncentrosymmetric lattice. The method involves the compression of a mono-layer of the organic molecule, spread on top of a water surface, into a two-dimensional solid, followed by the repeated dipping of the substrate to be coated into and out of the subphase. Monolayers may be deposited onto the substrate both on immersion and withdrawal, resulting in a cen…
Structural properties of phosphatidylcholine in a monolayer at the air/water interface
1991
Neutron reflectivities of phosphatidylcholine monolayers in the liquid condensed (LC) phase on ultrapure H 2 O and D 2 O subphases have been measured on a Langmuir film balance. Using a dedicated liquid surface reflectometer, reflectivities down to R = 10 -6 in the momentum transfer range Q z = 0–0.4A -1 were accessed. In a new approach, by refining neutron reflectivity data from chain-perdeuterated DPPC-d 62 in combination with x-ray measurements on the same monolayer under similar conditions it is shown that the two techniques mutually complement one another. This analysis leads to a detailed conception of the interface structure. It is found that in the LC phase (which is analogous to th…