Search results for " clusters"
showing 10 items of 1091 documents
Atomistic Theory of the Growth Mode for a Thin Metallic Film on an Isulating Substrate
2002
We have developed a novel theory for predicting the growth mode of a thin metallic film on an insulating substrate. Our theory combines ab initio electronic structure calculations for several ordered metal/insulator interfaces with varying metal coverage, with a thermodynamic method known in the theory of alloys. We illustrate this approach for an Ag film deposited on a MgO(001) substrate. Ab initio Hartree-Fock calculations predict a high mobility of adsorbed silver atoms on the perfect magnesia surface even at low temperatures. Our theoretical analysis clearly demonstrates that the growth of metal islands is predominant at the initial stage of silver deposition on MgO, which agrees with t…
A stable path to ferromagnetic hydrogenated graphene growth
2014
In this paper, we propose a practical way to stabilize half-hydrogenated graphene (graphone). We show that the dipole moments induced by an hexagonal-boron nitride (h-BN) substrate on graphene stabilize the hydrogen atoms on one sublattice of the graphene layer and suppress the migration of the absorbed hydrogen atoms. Based upon first principle spin polarized density of states (DOS) calculations, we show that the half hydrogenated graphene (graphone) obtained in different graphene-h-BN heterostructures exhibits a half metallic state. We propose to use this new exotic material for spin valve and other spintronics devices and applications.
Molecular-mediated assembly of silver nanoparticles with controlled interparticle spacing and chain length
2012
In the present work, we report on a one-pot method for the assembly of noble metal nanoparticles with tunable optical properties, assembly length and interparticle spacing. The synthetic colloidal route is based on the covalent binding among OH-terminated silver nanoparticles by means of dicarboxylic acids with a defined molecular length. As a result, the initially symmetric plasmon band of silver nanoparticles splits into two plasmonic modes when nanoparticles are assembled due to the strong near-field plasmon coupling. We noticed a very good correlation between the plasmon wavelength shift and the interparticle spacing that is represented by the universal scaling law of the surface plasmo…
Unraveling the Formation of Core−Shell Structures in Nanoparticles by S-XPS
2010
The combination of the surface sensitivity of X-ray photoelectron spectroscopy (XPS) with the high flux and variable photon energy excitation of Synchrotron radiation (S-XPS) is used to probe the atomic distribution of bimetallic nanoparticles. Based on the energy dependence of the photoemission differential cross section of core level photoelectrons, we propose a methodology to monitor the formation and to evaluate sizes of the core−shell structure. We have successfully applied it to unveil the mechanism involved in the atomic rearrangement of thermally treated Pt0.7Pd0.3 nanoparticles.
Chip-to-chip plasmonic interconnects and the activities of EU project NAVOLCHI
2012
In this paper, the chip-to-chip interconnection architecture adopted by the EU-project NAVOLCHI are discussed. The plasmonic physical layer consisting of a plasmonic nanoscale laser, a modulator, an amplifier and a detector is introduced. Current statuses of the plasmonic devices are reviewed.
Femtosecond exciton dynamics in WSe2 optical waveguides
2020
Van-der Waals (vdW) atomically layered crystals can act as optical waveguides over a broad range of the electromagnetic spectrum ranging from Terahertz to visible. Unlike common Si-based waveguides, vdW semiconductors host strong excitonic resonances that may be controlled using non-thermal stimuli including electrostatic gating and photoexcitation. Here, we utilize waveguide modes to examine photo-induced changes of excitons in the prototypical vdW semiconductor, WSe2, prompted by femtosecond light pulses. Using time-resolved scanning near-field optical microscopy we visualize the electric field profiles of waveguide modes in real space and time and extract the temporal evolution of the op…
Tuning the Ultrafast Response of Fano Resonances in Halide Perovskite Nanoparticles
2020
International audience; The full control of the fundamental photophysics of nanosystems at frequencies as high as few THz is key for tunable and ultrafast nanophotonic devices and metamaterials. Here we combine geometrical and ultrafast control of the optical properties of halide perovskite nanoparticles, which constitute a prominent platform for nanophotonics. The pulsed photoinjection of free carriers across the semiconducting gap leads to a subpicosecond modification of the far-field electromagnetic properties that is fully controlled by the geometry of the system. When the nanoparticle size is tuned so as to achieve the overlap between the narrowband excitons and the geometry-controlled…
On the determination of the intramolecular potential energy surface of polyatomic molecules: Hydrogen sulfide and formaldehyde as an illustration
2009
International audience; We present here an approach for determining the Hamiltonian of polyatomic molecules that allows one to successfully solve the problem of potential energy surface (PES) determination via construction and diagonalization of a Hamiltonian matrix of large dimension. In the suggested approach, the Hamiltonian is very simple and can be used both for any "normal" polyatomic molecule and for any isotopic species of a molecule. Molecules with two to four equivalent X-Y bonds are considered, and for illustration of the efficiency of the suggested approach, numerical calculations are made for the three-atomic (hydrogen sulfide) and four-atomic (formaldehyde) molecules.
Luminescence of ferroelectric crystals: LiNbO3and KNbO3
2000
Abstract The thermostimulated luminescence and time-resolved luminescence of LiNbO3 (congruent, stoichiometric, Eu−, Mn−, or Cr−doped) and KNbO3 crystals (undoped, Fe−, or Mn− doped) excited by X-ray, pulsed nitrogen laser or pulsed electron beam were studied. The luminescence decay times of niobium-oxygen groups (regular or perturbed by defect or impurity) were obtained. It is shown that the energy transfer from bulk to the activator in LiNbO3 is not effective during the electron-hole recombination process.
Highly Sensitive plasmonic silver nanorods
2011
We compare the single-particle plasmonic sensitivity of silver and gold nanorods with similar resonance wavelengths by monitoring the plasmon resonance shift upon changing the environment from water to 12.5% sucrose solution. We find that silver nanoparticles have 1.2 to 2 times higher sensitivity than gold, in good agreement with simulations based on the boundary-elements-method (BEM). To exclude the effect of particle volume on sensitivity, we test gold rods with increasing particle width at a given resonance wavelength. Using the Drude-model of optical properties of metals together with the quasi-static approximation (QSA) for localized surface plasmons, we show that the dominant contrib…